JP3709255B2

JP3709255B2 - Hydraulic drive device for traveling vehicle equipped with work implement

Info

Publication number: JP3709255B2
Application number: JP11695697A
Authority: JP
Inventors: 幸次兵藤
Original assignee: Hitachi Construction Machinery Co Ltd
Current assignee: Hitachi Construction Machinery Co Ltd
Priority date: 1997-05-07
Filing date: 1997-05-07
Publication date: 2005-10-26
Anticipated expiration: 2017-05-07
Also published as: JPH10311420A

Description

【０００１】
【発明の属する技術分野】
本発明はバケットを搭載し、原動機の回転数に応じて可変容量油圧ポンプの押退け容積を変えることにより走行速度を変えるようにしたホイールローダー、フォークリフト等の作業機搭載走行車両の油圧駆動装置の技術分野に属する。
【０００２】
【従来の技術】
ホイールローダー等のような作業車両の走行用駆動回路には可変容量油圧ポンプと、それに駆動される油圧モーターを含む油圧閉回路から成る静油圧無段変速装置（ＨＳＴ）が用いられる場合が多い。図７は静油圧無段変速装置として構成された従来例に係る作業走行車両の油圧走行駆動回路図の一例を示したものである。
【０００３】
原動機１に連結された可変容量油圧ポンプ２から吐出した作動油は主管路１７Ａ，１７Ｂを介して油圧モーター３に供給され、油圧モーター３をその流量に応じた速さで回転させる。油圧モーター３は差動歯車等の駆動力伝達機構９を介してタイヤ１０ａ，１０ｂに連結されていて、油圧モーター３の正逆回転に応じて作業車両が前後進するようになっている。可変容量油圧ポンプ２は、固定容量油圧ポンプとしてのチャージポンプ４および搭載した作業機を駆動するための作業機用ポンプ２４と共に原動機１に連結され、原動機操作手段としての加速踏板２３の運転者による踏込み操作に応じて可変速回転駆動される。作業機用ポンプ２４の吐出油は作業機制御弁２５を介して進路切替弁２６と作業機用制御弁２７に分流して供給されていて、作業機用制御弁２７を切替え制御することによりバケット等を駆動する作業機用アクチュエーター２８への油供給が制御され、これにより作業機用アクチュエーター２８が伸縮動作する。
【０００４】
一方、チャージポンプ４の吐出油は絞り５を介してチャージリリーフ弁６に導かれることにより、絞り５の下流側にチャージポンプ４の吐出圧より低圧のチャージリリーフ圧ｐI が生じるようになっている。このチャージリリーフ圧ｐI は減圧弁１１に一次圧として導かれ、下流側に絞り５の前後差圧Δｐに応じた二次圧ｐIIを発生させる。減圧弁１１の二次圧ｐIIは絞り１２を介して前後進切替弁１３に導かれ、さらに、この前後進切替弁１３を介して傾転シリンダー１４の左右のシリンダー室１４ａ，１４ｂに導かれている。絞り１２と前後進切替弁１３を繋ぐ管路１５の途中に分岐管路１８が接続されていて、この分岐管路１８中に可変絞り弁１９が介装されている。そして、前後進切替弁１３は前後進切替スイッチ２１の切替えにより電磁的に左右の切替え位置に切り替わる。
【０００５】
即ち、前後進切替スイッチ２１が中立位置Ｎの状態にある時は前後進切替弁１３の左右の電磁部には電力が供給されないから、左右のバネ力の拮抗する押圧力により前後進切替弁１３も中央の中立位置に保持される。この時は傾転シリンダー１４の左右のシリンダー室１４ａ，１４ｂは共に油タンク６０に連通しているので同圧になり、傾転シリンダー１４のピストン１４ｃは左右のバネから受ける拮抗する押圧力により中央の中立位置に保持される。このピストン１４ｃに可変容量油圧ポンプ２の傾転制御腕２ａが連結されていて、ピストン１４ｃが中立位置にある時は可変容量油圧ポンプ２の傾転量が０になるように設定されている。従って、この時は可変容量油圧ポンプ２からの吐出流量は０になるから、作業車両は停止状態に保たれる。
【０００６】
次に、運転者が前後進切替スイッチ２１を前進位置Ｆに切り替えると、前後進切替弁１３の左の電磁部が励磁されることにより、前後進切替弁１３は左の切替位置ｌに切り替わる。これにより、減圧弁１１の二次圧ｐIIは管路１６ａを経て傾転シリンダー１４の右のシリンダー室１４ａに導かれ、左のシリンダー室１４ｂは油タンク６０に連通する。右のシリンダー室１４ａに導かれた減圧弁１１の二次圧ｐIIは左のシリンダー室１４ｂ内のバネの弾撥力に抗してピストン１４ｃを左方向に移動させる。ピストン１４ｃは減圧弁１１の二次圧ｐIIと左のシリンダー室１４ｂ内のバネの弾撥力が拮抗する位置で停止する。このピストン１４ｃの移動量に応じて可変容量油圧ポンプ２の傾転制御腕２ａが回動するから、可変容量油圧ポンプ２の押退け容積ｑ、従って吐出流量Ｑは減圧弁１１の二次圧ｐIIの増減に応じて増減し、油圧モーター３の回転数もそれに応じて増減する。
【０００７】
前後進切替スイッチ２１が後進位置Ｒに切り替えられた時も全く同様であって、減圧弁１１の二次圧ｐIIの増減に応じてピストン１４ｃが右方向に移動し、傾転制御腕２ａが逆方向に回動するから、可変容量油圧ポンプ２の押退け容積ｑも減圧弁１１の二次圧ｐIIの増減に応じて増減する。減圧弁１１の制御圧はチャージポンプ４の吐出圧と、これに対向する減圧弁１１の一次圧ｐI および二次圧ｐIIであるから、減圧弁１１の二次圧ｐIIは絞り５の前後差圧Δｐに比例して増減し、その最大値はチャージリリーフ圧ｐI になる。絞り５の前後差圧Δｐはチャージポンプ４の吐出流量、従って、原動機１の回転数Ｎに比例（正確には２次比例）して増減する。つまり、可変容量油圧ポンプ２の押退け容積ｑは原動機１の回転数Ｎに比例して増減する。
【０００８】
【発明が解決しようとする課題】
いま、上述の作業走行車両がバケットに砂利を積載してダンプトラックに向かって移動し、その高い位置にある荷台上に放土する作業を行う場合について考慮する。図６はかかる砂利荷搭載作業を示す模式図であり、（ａ）および（ｂ）はこの作業工程の前期および後期の状態を示す。始めに、作業走行車両４０はダンプトラック５０から離れた位置にあり、地面を掘削する等した土砂をバケット４１に積載し、（ａ）に示すように、バケット４１の支持腕４２を持ち上げながら比較的速い速度でダンプトラック５０に向かって走行する。そして、作業走行車両４０がダンプトラック５０に近付いた時は、（ｂ）に示すように、バケット４１や車両の一部がダンプトラック５０に衝突しないように低速乃至微速走行に切り替えながら、支持腕４２を上側に回動させてバケット４１をダンプトラック５０の荷台５１上に掲げるようにした後バケット４１を回動させ、その中の土砂を荷台５１上に放土する。
【０００９】
作業走行車両４０にこのような動きをさせるためには、運転者は加速踏板２３や制動踏板２０を微妙に踏み操作して原動機１の回転数Ｎを変化させたり、管路１５中のパイロット圧油を可変絞り１９を介して油タンク６０に還流させて制動状態にしたりしなければならない。即ち、運転者が加速踏板２３を踏み込むと、原動機１の回転数Ｎが増加して減圧弁１１の二次圧ｐIIが高くなり、ピストン１４ｃの左方向の移動により傾転制御腕２ａが反時計回り方向に回動し、可変容量油圧ポンプ２の作動油の吐出流量が増加することにより作業走行車両４０が加速走行し、運転者が制動踏板２０を踏み込むと、可変絞り１９の絞り量が減少して管路１５内の減圧弁１１の二次圧ｐIIが低下し、ピストン１４ｃの右方向の移動により傾転制御腕２ａが時計回り方向に回動し、可変容量油圧ポンプ２の作動油の吐出流量が減少することにより作業走行車両４０が減速走行する。
【００１０】
このように、作業走行車両４０がダンプトラック５０に近付いた時、バケット４１を上方に持ち上げる操作を行いながら、加速踏板２３や制動踏板２０を踏み操作して作業走行車両４０の走行速度を微調整するのは運転者にとって煩わしく精神的に負担の大きいものであった。本発明は従来技術におけるかかる課題を解決して、バケット４１によるダンプトラック５０の荷台５１への土砂の積込作業のように、作業走行車両４０をゆっくり前進させながらバケット４１を持ち上げ操作する作業の操作性を向上させることができる作業機搭載走行車両の油圧駆動装置を提供することを目的とする。
【００１１】
【課題を解決するための手段】
本発明は上記課題を解決するために、
土砂等の荷を載せて持ち上げるバケットを搭載した作業機搭載走行車両に使用される作業機搭載走行車両の油圧駆動装置であって、原動機に連結された可変容量油圧ポンプと、この可変容量油圧ポンプの吐出油により駆動される走行用油圧モーターと、前記可変容量油圧ポンプと共に前記原動機に連結された固定容量油圧ポンプ及び作業機用ポンプと、この作業機用ポンプの吐出油により駆動される作業機用アクチュエーターと、前記固定容量油圧ポンプの吐出油が導かれその吐出油の圧力に基づいて前記可変容量油圧ポンプの押退け容積を変更する押退け容積変更手段と、前記可変容量油圧ポンプから前記走行用油圧モーターに供給される作動油の供給方向を変えることにより走行車両の前後の進行方向を切り替える進行方向切替手段と、運転者により操作されその操作に応じて前記原動機の回転数を変更する原動機操作手段とを備え、積載作業時にこの原動機操作手段を操作することにより、前記固定容量油圧ポンプの回転数を変更して前記押退け容積変更手段を通じて前記可変容量油圧ポンプの押退け容積を変更し、かつ、前記可変容量油圧ポンプの回転数を変更して、前記走行用油圧モーターの回転速度を調整できるようにするとともに、前記作業機用ポンプの回転数を変更して前記作業機用アクチュエーターの駆動速度を調整できるようにした作業機搭載走行車両の油圧駆動装置において、前記バケットの高さ位置を検出する高さ検出手段と、前記走行用油圧モーターの回転速度を制限するように前記押退け容積変更手段に導かれる固定容量油圧ポンプの吐出油の流路の圧油を逃がしてその圧油の圧力を設定値以上に上昇させないようにすることができるリリーフ弁と、前記高さ検出手段が所定の高さ以上の前記バケットの高さ位置を検出し、かつ、前記進行方向切替手段が前進方向に切り替えられたときに、前記リリーフ弁を機能させ得るように制御する制御回路とを設けて構成した。
【００１３】
【発明の実施の形態】
進行方向切替手段は周知のパイロット油圧式または電磁式の方向切替弁で構成することができる。押退け容積変更手段はピストンの移動量に応じて可変容量油圧ポンプの押退け容積が変わる傾転シリンダーで構成することができる。後述する速度制限手段としてのリリーフ弁による速度制限動作を現場の状況に応じて弾力的に行わせるために、そのリリーフ弁による速度制限動作を行わせるか否かを選択するための選択手段を設けると良い。また、前記リリーフ弁により走行用油圧モーターの回転速度が制限される所定速度を現場の状況に応じて調整できるような構成としても良い。
【００１４】
以下、図面を参照して本発明を具体化した一具体例を詳細に説明する。図１は本具体例に係る作業走行車両の油圧走行駆動回路図である。同図において、従来例と同一または同一と見做せる個所には同一の符号を付し、その重複する説明を省略する。７ａ，７ｂは主管路１７Ａ，１７Ｂ間に設けられ、絞り５の下流側への作動油の逆流を防止すると共に主管路１７Ａ，１７Ｂへのチャージポンプ４の吐出油の供給を可能にする逆止弁、８ａ，８ｂは主管路１７Ａ，１７Ｂ間にそれぞれ設けられ、主管路１７Ａ，１７Ｂ内の最大許容圧を規定するリリーフ弁、２２は前後進切替弁１３の電磁部を励磁させるための直流電源、２９は常時は閉位置ロにあり、電磁部に電流が流れると開位置イに切り替わる電磁開閉弁、３０はチャージポンプ４の吐出油の流路における減圧弁１１の下流側の圧油を逃がすように電磁開閉弁２９の下流に配設されたリリーフ弁、３１は管路１５の途中から分岐して電磁切替弁２９およびリリーフ弁３０を介して油タンク６０に到る側管路、３２は作業走行車両４０本体に設けられ、バケット４１の支持腕４２が所定の高さに達すると、内部接点が閉成して同図で矢印ｉで示す電流路が形成される近接スイッチ、３３は自動減速動作を行わせるか否かを選択するための選択スイッチ、３４ａ，３４ｂはそれぞれの接点が直列接続され、さらに、直流電源２２と電磁開閉弁２９とで閉回路を形成する電磁リレー、３７は前後進切替弁１３の流出室から油タンク６０に到る管路中に介装された絞りである。
【００１５】
次に、本具体例の動作を説明する。前後進切替スイッチ２１が中立位置Ｎの状態にある時の動作は従来例と全く変わらない。運転者が前後進切替スイッチ２１を前進位置Ｆに切り替えると共に選択スイッチ３３を投入した時は、前後進切替弁１３の左の電磁部が励磁されると共に電磁リレー３４ａ，３４ｂのコイルの一端にそれぞれ直流電源２２の電圧が印加される。これにより、作業走行車両４０は前述のように前進走行し、やがてダンプトラック５０に近付くと、運転者は作業機用制御弁２７を切り替えてバケット４１の支持腕４２を上向きに回動させる作業機用アクチュエーター２８を伸長させる。
【００１６】
これによりバケット４１が上昇して所定の高さに達すると、近接スイッチ３２の内部接点が閉成し、直流電源２２から選択スイッチ３３、電磁リレー３４ａのコイルおよび近接スイッチ３２の内部接点を経て同図で矢印ｉで示す電流が流れ、電磁リレー３４ａ内部の常開接点が閉成する。一方、電磁リレー３４ｂのコイルの他端は接地されているので、このコイルに直流電源２２から電流が流れ、電磁リレー３４ｂの内部の常開接点は閉成している。従って、直流電源２２から電磁リレー３４ａ，３４ｂの内部のそれぞれの常開接点を経て電磁開閉弁２９の電磁部に電流が流れ、電磁開閉弁２９は閉位置ロから開位置イに切り替えられる。
【００１７】
これにより、リリーフ弁３０が管路１５に連通するから、管路１５内の減圧弁１１の二次圧ｐIIがリリーフ弁３０のバネ弾性力により規定される比較的低い設定圧ｐ₂に達すると、リリーフ弁３０が開いて管路１５内のパイロット圧油を油タンク６０に還流させるから、管路１５内のパイロット圧はリリーフ弁３０の設定圧ｐ₂に制限される。なお、前後進切替スイッチ２１が後進位置Ｒに切り替えられた時、あるいは、選択スイッチ３３を投入しなかった時は電磁リレー３４ｂのコイルまたは電磁リレー３４ａのコイルに直流電源２２から電流が供給されないので、電磁開閉弁２９は閉位置ロの侭となり、この場合の動作は従来例と全く変わらない。
【００１８】
図２、図３および図４は運転者が選択スイッチ３３を投入して前後進切替スイッチ２１を前進位置Ｆに切り替えた時の原動機１の回転数Ｎとそれぞれ減圧弁１１の二次圧ｐII、可変容量油圧ポンプ２の押退け容積ｑおよび可変容量油圧ポンプ２の吐出流量Ｑの関係を示す特性図である。図２に示すように、原動機１の回転数Ｎが０から起動回転数Ｎ₀に達するまでは減圧弁１１の制御圧であるチャージポンプ４の吐出圧は減圧弁１１のバネに打ち勝つ程強くないので、減圧弁１１は閉じている。原動機１の回転数Ｎが起動回転数Ｎ₀を越えると減圧弁１１が開き、管路１５内の減圧弁１１の二次圧ｐIIが原動機１の回転数Ｎの増加量に比例して上昇し、発進回転数Ｎ₁に達すると、傾転シリンダー１４のピストン１４ｃが左方向に移動し、図３および図４に示すように、可変容量油圧ポンプ２の押退け容積ｑおよび吐出流量Ｑが０から立ち上がることにより油圧モーター３が回転して作業走行車両４０が前方に発進する。原動機１の回転数Ｎが発進回転数Ｎ₁を越えて増加すると、押退け容積ｑはその増加量に比例して増加し、吐出流量Ｑはその増加量に対して２次関数的に増加する。
【００１９】
バケット４１が所定の高さまで上昇して近接スイッチ３２の内部接点が閉成した時は、前述のように、電磁開閉弁２９は閉位置ロから開位置イに切り替わり、リリーフ弁３０を管路１５に連通させる。運転者の加速踏板２３の踏み込みにより原動機１の回転数Ｎが増加して第１抑制回転数Ｎ₂に達すると、減圧弁１１の二次圧ｐIIはリリーフ弁３０の設定圧ｐ₂になり、リリーフ弁３０が開いて管路１５内のパイロット圧油を油タンク６０に還流させる。このため、原動機１の回転数Ｎが抑制回転数Ｎ₂を越えて増加しても減圧弁１１の二次圧ｐIIはリリーフ弁３０の設定圧ｐ₂以上には上昇せず、従って、可変容量油圧ポンプ２の押退け容積ｑも抑制押退け容積ｑ₂以上に増加することはない。可変容量油圧ポンプ２の吐出流量Ｑは押退け容積ｑが変わらなくても原動機１の回転数Ｎの増大に連れて可変容量油圧ポンプ２の回転数も増加するから、回転数Ｎの増加分に対して比例して増加し、最大回転数Ｎ₄で第１最大流量Ｑ_maxになる。
【００２０】
一方、バケット４１が所定の高さまで上昇しなかった時は近接スイッチ３２の内部接点が開いた侭なので、電磁開閉弁２９は閉位置ロにあり、リリーフ弁３０は管路１５から分離されているため、原動機１の回転数Ｎが増加して抑制回転数Ｎ₂に達しても減圧弁１１の二次圧ｐIIは上昇し続け、リリーフ弁６のリリーフ圧ｐ₄に達した後は一定となる。可変容量油圧ポンプ２の押退け容積ｑは減圧弁１１の二次圧ｐIIがリリーフ弁６のリリーフ圧ｐ₄に達するまでに到らない原動機１の回転数Ｎ₃で最大押退け容積ｑ₃に達し、その後は一定となる。可変容量油圧ポンプ２の吐出流量Ｑは原動機１の回転数Ｎが回転数Ｎ₃に達するまでは２次関数的に増加し、回転数Ｎ₃に達した後は回転数Ｎの増加分に対して比例して増加し、最大回転数Ｎ₄で第２最大流量Ｑ_max′になる。
【００２１】
このように、本具体例では管路１５の途中から分岐して油タンク６０に到る側管路３１に電磁切替弁２９およびリリーフ弁３０を介装し、バケット４１が所定の高さまで上昇して近接スイッチ３２の内部接点が閉成した時、電磁開閉弁２９は閉位置ロから開位置イに切り替わるようにしたので、作業走行車両４０がバケット４１によるダンプトラック５０の荷台５１への土砂の積込作業を行うような場合に、選択スイッチ３３を投入しておくことにより、原動機１の回転数Ｎを増大させてダンプトラック５０に向かって速い速度で近付いても、バケット４１が所定の高さまで上昇した後は減圧弁１１の二次圧ｐIIは最大でもリリーフ弁３０の設定圧ｐ₂に抑制されるから、可変容量油圧ポンプ２の吐出流量Ｑも最大でもリリーフ弁３０が動作しない場合の第２最大流量Ｑ_max′よりかなり低い第１最大流量Ｑ_maxに抑制される。従って、作業走行車両４０がバケット４１を持ち上げて土砂の積込動作に入った後は走行速度が低速に抑えられるから、煩わしい加速踏板２３や制動踏板２０の頻繁な踏み操作を行わなくても、バケット４１や車両の一部がダンプトラック５０に衝突するのを防止することができる。
【００２２】
本具体例では絞り５の下流側のチャージリリーフ圧ｐI を一次圧とする減圧弁１１の二次圧ｐIIにより可変容量油圧ポンプ２の押退け容積ｑを制御する構成となっているが、減圧弁１１を設けずに単に絞り５の前後差圧Δｐにより制御するようにしても良く、その場合、リリーフ弁３０は、チャージポンプ４の吐出油の流路における絞り５の下流側の圧油を逃がすように配設する。図５はかかる構成を有した本発明の他の具体例に係る作業走行車両の油圧走行駆動回路図である。同図において、３５はチャージポンプ４の吐出油を前後進切替弁１３の流入室に導く高圧側管路、３６は前後進切替弁１３の流出室と絞り５の下流側管路とを結ぶ低圧側管路である。この具体例では電磁切替弁２９およびリリーフ弁３０が介装される側管路３１は高圧側管路３５と低圧側管路３６との間に接続される。その他の構成および動作は先の具体例のものと変わらない。
【００２３】
上述のように、作業走行車両４０が前進走行する時のみ電磁開閉弁２９が閉位置ロから開位置イに切り替えられるようにしたのは、バケット４１に土砂を積載した状態でバケット４１を上昇させながら、またはバケット４１を上昇させた侭、後進するような作業は実際には殆ど無く、運転者はバケット４１に積載した土砂をダンプトラック５０の荷台５１上に放土した後は速やかに後進走行（後退）する操作を行う場合が多いからである。もしも、作業走行車両４０の後進走行時にも電磁開閉弁２９が開位置イに切り替えられるようにすると、バケット４１に積載した土砂をダンプトラック５０の荷台５１上に放土した後、バケット４１を下降させながら後進走行している時に、ある時点で急に作業走行車両４０の走行速度が速まると、後方の安全確認がし辛いので危険性が高まる。
【００２４】
なお、上述の具体例では、バケット４１が所定の高さまで上昇したことを近接スイッチ３２により検出するようにしたが、バケット４１の支持腕４２の回動角を検知する角度センサー等により検知するようにしても良い。
【００２５】
【発明の効果】
以上説明したように請求項１記載の発明によれば、前記「課題を解決するための手段」の項に示した手段を採用しているので、土砂を積載したバケットを持ち上げながらダンプトラックに近づき、荷台上に放土するような作業を行う時に、煩わしい加速踏板や制動踏板の頻繁な踏み操作を行わなくても、速やかにダンプトラックに近付きながら、バケットや車両の一部がダンプトラックに衝突するのを防止でき、上記作業を安全かつ効率的に行うことができる。
【図面の簡単な説明】
【図１】本発明の具体例に係る作業走行車両の油圧走行駆動回路図
【図２】原動機の回転数と減圧弁の二次圧との関係を示す特性図
【図３】原動機の回転数と可変容量油圧ポンプの押退け容積との関係を示す特性図
【図４】原動機の回転数と可変容量油圧ポンプの吐出流量との関係を示す特性図
【図５】本発明の他の具体例に係る作業走行車両の油圧走行駆動回路図
【図６】従来例に係る砂利荷搭載作業を示す模式図
【図７】同じく、作業走行車両の油圧走行駆動回路図
【符号の説明】
１原動機
２可変容量油圧ポンプ
２ａ傾転制御腕
３油圧モーター
４チャージポンプ
５，１２，３７絞り
６チャージリリーフ弁
８ａ，８ｂ，３０リリーフ弁
１１減圧弁
１３前後進切替弁
１４傾転シリンダー
１４ａ，１４ｂシリンダー室
１４ｃピストン
２０制動踏板
２１前後進切替スイッチ
２３加速踏板
２４作業機用ポンプ
２５作業機制御弁
２６進路切替弁
２７作業機用制御弁
２９電磁開閉弁
３２近接スイッチ
３３選択スイッチ
３４ａ，３４ｂ電磁リレー
４０作業走行車両[0001]
BACKGROUND OF THE INVENTION
The present invention provides a hydraulic drive device for a traveling vehicle equipped with a work machine such as a wheel loader, a forklift, etc., which is equipped with a bucket and changes the traveling speed by changing the displacement volume of the variable displacement hydraulic pump according to the rotational speed of the prime mover. It belongs to the technical field.
[0002]
[Prior art]
A hydrostatic continuously variable transmission (HST) including a variable displacement hydraulic pump and a hydraulic closed circuit including a hydraulic motor driven by the variable displacement hydraulic pump is often used as a driving circuit for a work vehicle such as a wheel loader. FIG. 7 shows an example of a hydraulic traveling drive circuit diagram of a working traveling vehicle according to a conventional example configured as a hydrostatic continuously variable transmission.
[0003]
The hydraulic fluid discharged from the variable displacement hydraulic pump 2 connected to the prime mover 1 is supplied to the hydraulic motor 3 via the main pipelines 17A and 17B, and the hydraulic motor 3 is rotated at a speed corresponding to the flow rate. The hydraulic motor 3 is connected to the tires 10a and 10b via a driving force transmission mechanism 9 such as a differential gear, so that the work vehicle moves forward and backward according to the forward and reverse rotation of the hydraulic motor 3. The variable displacement hydraulic pump 2 is connected to the prime mover 1 together with a charge pump 4 as a fixed displacement hydraulic pump and a work implement pump 24 for driving the mounted work implement, and is driven by a driver of an acceleration tread 23 as a prime mover operating means. It is driven to rotate at a variable speed according to the stepping operation. The oil discharged from the work machine pump 24 is supplied to the course switching valve 26 and the work machine control valve 27 through the work machine control valve 25 in a divided manner, and the bucket is controlled by switching the work machine control valve 27. The oil supply to the working machine actuator 28 for driving the working machine is controlled, and the working machine actuator 28 is expanded and contracted.
[0004]
On the other hand, the discharge oil of the charge pump 4 is guided to the charge relief valve 6 through the throttle 5 so that a charge relief pressure pI lower than the discharge pressure of the charge pump 4 is generated downstream of the throttle 5. . This charge relief pressure pI is guided to the pressure reducing valve 11 as a primary pressure, and a secondary pressure pII corresponding to the differential pressure Δp across the throttle 5 is generated downstream. The secondary pressure pII of the pressure reducing valve 11 is guided to the forward / reverse switching valve 13 through the throttle 12, and is further guided to the left and right cylinder chambers 14a, 14b of the tilting cylinder 14 through the forward / backward switching valve 13. Yes. A branch pipe 18 is connected in the middle of a pipe 15 connecting the throttle 12 and the forward / reverse switching valve 13, and a variable throttle valve 19 is interposed in the branch pipe 18. The forward / reverse switching valve 13 is electromagnetically switched to the left / right switching position by switching the forward / reverse switching switch 21.
[0005]
That is, when the forward / reverse selector switch 21 is in the neutral position N, power is not supplied to the left and right electromagnetic parts of the forward / reverse selector valve 13, and therefore the forward / reverse selector valve 13 is driven by a pressing force that antagonizes the left and right spring forces. Is also held in the neutral position. At this time, the left and right cylinder chambers 14a and 14b of the tilting cylinder 14 are both in communication with the oil tank 60 so that they have the same pressure, and the piston 14c of the tilting cylinder 14 is centered by the antagonistic pressing force received from the left and right springs. Is held in the neutral position. The tilt control arm 2a of the variable displacement hydraulic pump 2 is connected to the piston 14c, and the tilt amount of the variable displacement hydraulic pump 2 is set to 0 when the piston 14c is in the neutral position. Accordingly, at this time, the discharge flow rate from the variable displacement hydraulic pump 2 becomes 0, so that the work vehicle is kept stopped.
[0006]
Next, when the driver switches the forward / reverse switching switch 21 to the forward position F, the left electromagnetic part of the forward / reverse switching valve 13 is excited, so that the forward / reverse switching valve 13 is switched to the left switching position l. As a result, the secondary pressure pII of the pressure reducing valve 11 is guided to the right cylinder chamber 14a of the tilting cylinder 14 via the pipe line 16a, and the left cylinder chamber 14b communicates with the oil tank 60. The secondary pressure pII of the pressure reducing valve 11 guided to the right cylinder chamber 14a moves the piston 14c in the left direction against the elastic force of the spring in the left cylinder chamber 14b. The piston 14c stops at a position where the secondary pressure pII of the pressure reducing valve 11 and the elastic force of the spring in the left cylinder chamber 14b antagonize. Since the tilt control arm 2a of the variable displacement hydraulic pump 2 rotates according to the movement amount of the piston 14c, the displacement volume q of the variable displacement hydraulic pump 2, and hence the discharge flow rate Q, is the secondary pressure pII of the pressure reducing valve 11. The number of rotations of the hydraulic motor 3 is also increased or decreased accordingly.
[0007]
The same applies when the forward / reverse selector switch 21 is switched to the reverse position R. The piston 14c moves to the right according to the increase or decrease of the secondary pressure pII of the pressure reducing valve 11, and the tilt control arm 2a is reversed. Since it rotates in the direction, the displacement volume q of the variable displacement hydraulic pump 2 also increases or decreases according to the increase or decrease of the secondary pressure pII of the pressure reducing valve 11. Since the control pressure of the pressure reducing valve 11 is the discharge pressure of the charge pump 4 and the primary pressure pI and the secondary pressure pII of the pressure reducing valve 11 opposed thereto, the secondary pressure pII of the pressure reducing valve 11 is the differential pressure across the throttle 5. It increases or decreases in proportion to Δp, and its maximum value becomes the charge relief pressure pI. The front-rear differential pressure Δp of the throttle 5 increases or decreases in proportion to the discharge flow rate of the charge pump 4 and, therefore, the rotational speed N of the prime mover 1 (more precisely, it is secondary proportional). That is, the displacement volume q of the variable displacement hydraulic pump 2 increases or decreases in proportion to the rotational speed N of the prime mover 1.
[0008]
[Problems to be solved by the invention]
Now, consider the case where the above-mentioned work traveling vehicle is loaded with gravel in a bucket, moves toward a dump truck, and performs the work of discharging on a loading platform at a high position. FIG. 6 is a schematic diagram showing such a gravel loading operation, and (a) and (b) show the states of the first and second stages of this work process. First, the work traveling vehicle 40 is located away from the dump truck 50, and earth and sand excavated from the ground is loaded on the bucket 41, and comparison is made while lifting the support arms 42 of the bucket 41 as shown in FIG. Drive toward the dump truck 50 at a relatively fast speed. When the work traveling vehicle 40 approaches the dump truck 50, as shown in (b), the support arm is switched while switching from low speed to low speed so that the bucket 41 and a part of the vehicle do not collide with the dump truck 50. 42 is turned upward so that the bucket 41 is lifted on the loading platform 51 of the dump truck 50, and then the bucket 41 is rotated, and the earth and sand in the bucket 41 is discharged onto the loading platform 51.
[0009]
In order to cause the work traveling vehicle 40 to make such a movement, the driver slightly depresses the acceleration tread plate 23 or the brake tread plate 20 to change the rotational speed N of the prime mover 1 or the pilot pressure in the pipe 15. The oil must be recirculated to the oil tank 60 through the variable throttle 19 to be in a braking state. That is, when the driver steps on the acceleration tread 23, the rotational speed N of the prime mover 1 increases, the secondary pressure pII of the pressure reducing valve 11 increases, and the tilt control arm 2a moves counterclockwise due to the leftward movement of the piston 14c. When the work traveling vehicle 40 accelerates by rotating in the turning direction and the hydraulic oil discharge flow rate of the variable displacement hydraulic pump 2 increases, the throttle amount of the variable throttle 19 decreases when the driver steps on the brake tread plate 20. As a result, the secondary pressure pII of the pressure reducing valve 11 in the pipe line 15 decreases, and the tilt control arm 2a rotates in the clockwise direction by the rightward movement of the piston 14c, and the hydraulic oil of the variable displacement hydraulic pump 2 flows. As the discharge flow rate decreases, the work traveling vehicle 40 travels at a reduced speed.
[0010]
As described above, when the work traveling vehicle 40 approaches the dump truck 50, the operation speed of the work traveling vehicle 40 is finely adjusted by stepping on the acceleration tread plate 23 or the brake tread plate 20 while performing the operation of lifting the bucket 41 upward. It was bothersome and mentally burdensome for the driver. The present invention solves such a problem in the prior art, and performs an operation of lifting the bucket 41 while slowly moving the work traveling vehicle 40 forward, such as loading of earth and sand onto the loading platform 51 of the dump truck 50 by the bucket 41. An object of the present invention is to provide a hydraulic drive device for a traveling vehicle equipped with a work machine that can improve operability.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention
A hydraulic drive device for a working machine-equipped traveling vehicle used in a working machine-equipped traveling vehicle equipped with a bucket for loading and lifting a load such as earth and sand, a variable displacement hydraulic pump coupled to a prime mover, and the variable displacement hydraulic pump Traveling hydraulic motor driven by the discharge oil of the engine, a fixed displacement hydraulic pump and a work machine pump coupled to the prime mover together with the variable displacement hydraulic pump, and a work machine driven by the discharge oil of the work machine pump Actuator, a displacement displacement change means for guiding displacement oil of the fixed displacement hydraulic pump and changing displacement volume of the variable displacement hydraulic pump based on the pressure of the discharge oil, and the travel from the variable displacement hydraulic pump A traveling direction switching means for switching the traveling direction of the traveling vehicle by changing the supply direction of the hydraulic oil supplied to the hydraulic motor, A motor operating means that is operated by a driver and changes the rotational speed of the prime mover according to the operation, and by operating the prime mover operating means during a loading operation, the rotational speed of the fixed displacement hydraulic pump is changed. While changing the displacement volume of the variable displacement hydraulic pump through the displacement displacement changing means and changing the rotation speed of the variable displacement hydraulic pump, the rotational speed of the traveling hydraulic motor can be adjusted. In the hydraulic drive device for a working vehicle-equipped traveling vehicle, the height detection for detecting the height position of the bucket is made possible by adjusting the rotational speed of the working machine pump to adjust the driving speed of the working machine actuator. means and, in the flow path of the oil discharged from the fixed displacement hydraulic pump is guided to the押退only capacity changing means to limit the rotational speed of the travel hydraulic motor To discharge oil detected and relief valve can be prevented to increase the pressure of the pressurized oil above the set value, the height position of said height detecting means above a predetermined height the bucket, and, And a control circuit that controls the relief valve to function when the traveling direction switching means is switched to the forward direction.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The traveling direction switching means can be constituted by a well-known pilot hydraulic type or electromagnetic direction switching valve. The displacement volume changing means can be constituted by a tilt cylinder whose displacement volume of the variable displacement hydraulic pump changes according to the movement amount of the piston . In order to perform a speed limiting operation by a relief valve as a speed limiting unit, which will be described later, in a flexible manner according to the situation at the site, a selection unit is provided for selecting whether or not to perform a speed limiting operation by the relief valve. And good. The predetermined speed at which the rotational speed of the traveling hydraulic motor is limited by the relief valve may be adjusted according to the situation at the site.
[0014]
Hereinafter, a specific example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a hydraulic traveling drive circuit diagram of a working traveling vehicle according to this example. In the figure, parts that are considered to be the same as or the same as those of the conventional example are denoted by the same reference numerals, and redundant description thereof is omitted. Reference numerals 7a and 7b are provided between the main pipe lines 17A and 17B , and prevent the backflow of the hydraulic oil to the downstream side of the throttle 5, and enable the supply of the discharge oil of the charge pump 4 to the main pipe lines 17A and 17B . Valves 8a and 8b are provided between the main pipelines 17A and 17B , respectively, a relief valve for defining the maximum allowable pressure in the main pipelines 17A and 17B , and 22 a DC power source for exciting the electromagnetic part of the forward / reverse switching valve 13 , 29 is normally in the closed position b, and is an electromagnetic on-off valve that switches to the open position a when current flows in the electromagnetic part, and 30 releases the pressure oil downstream of the pressure reducing valve 11 in the discharge oil flow path of the charge pump 4. In this way, a relief valve 31 arranged downstream of the electromagnetic on-off valve 29 is branched from the middle of the pipe line 15 to reach the oil tank 60 via the electromagnetic switching valve 29 and the relief valve 30. Working vehicle When the support arm 42 of the bucket 41 reaches a predetermined height, the internal contact is closed to form a current path indicated by an arrow i in FIG. Selection switches 34a and 34b for selecting whether or not to perform the operation are connected in series with each other, an electromagnetic relay in which a closed circuit is formed by the DC power supply 22 and the electromagnetic switching valve 29, and 37 is a forward / reverse switching It is a throttle interposed in a pipe line from the outflow chamber of the valve 13 to the oil tank 60.
[0015]
Next, the operation of this example will be described. The operation when the forward / reverse selector switch 21 is in the neutral position N is not different from the conventional example. When the driver switches the forward / reverse selector switch 21 to the forward position F and turns on the selector switch 33, the left electromagnetic part of the forward / reverse selector valve 13 is excited and one end of each coil of the electromagnetic relays 34a and 34b is excited. The voltage of the DC power supply 22 is applied. As a result, when the work traveling vehicle 40 travels forward as described above and eventually approaches the dump truck 50, the driver switches the work implement control valve 27 to rotate the support arm 42 of the bucket 41 upward. The actuator 28 is extended.
[0016]
As a result, when the bucket 41 rises and reaches a predetermined height, the internal contact of the proximity switch 32 is closed, and the same connection is made from the DC power supply 22 via the selection switch 33, the coil of the electromagnetic relay 34a, and the internal contact of the proximity switch 32. In the figure, a current indicated by an arrow i flows, and the normally open contact inside the electromagnetic relay 34a is closed. On the other hand, since the other end of the coil of the electromagnetic relay 34b is grounded, a current flows from the DC power source 22 to this coil, and the normally open contact inside the electromagnetic relay 34b is closed. Therefore, the electromagnetic relay 34a from the DC power supply 22, a current flows through the solenoid of the solenoid valve 29 via respective normally open contacts of the internal 34b, the electromagnetic valve 29 is switched from the closed position B to the open position i.
[0017]
As a result, the relief valve 30 communicates with the conduit 15, and therefore when the secondary pressure pII of the pressure reducing valve 11 in the conduit 15 reaches a relatively low set pressure p ₂ defined by the spring elastic force of the relief valve 30. since the pilot pressure oil in the conduit 15 the relief valve 30 is opened is refluxed to the oil tank 60, the pilot pressure in the conduit 15 is limited to the set pressure p ₂ of the relief valve 30. When the forward / reverse selector switch 21 is switched to the reverse position R, or when the selector switch 33 is not turned on, no current is supplied from the DC power source 22 to the coil of the electromagnetic relay 34b or the coil of the electromagnetic relay 34a. The electromagnetic on-off valve 29 becomes a trap at the closed position B, and the operation in this case is not different from the conventional example.
[0018]
2, 3, and 4 show the rotational speed N of the prime mover 1 and the secondary pressure pII of the pressure reducing valve 11 when the driver turns on the selection switch 33 and switches the forward / reverse selector switch 21 to the forward position F, respectively. FIG. 6 is a characteristic diagram showing a relationship between a displacement volume q of the variable displacement hydraulic pump 2 and a discharge flow rate Q of the variable displacement hydraulic pump 2. As shown in FIG. 2, the discharge pressure of the charge pump 4, which is the control pressure of the pressure reducing valve 11, is not strong enough to overcome the spring of the pressure reducing valve 11 until the rotational speed N of the prime mover 1 reaches the starting rotational speed N _0. Therefore, the pressure reducing valve 11 is closed. Rotational speed N of the engine 1 exceeds the cranking speed N ₀ and the pressure reducing valve 11 is opened, secondary pressure pII of the pressure reducing valve 11 in the conduit 15 rises in proportion to the increase of the rotational speed N of the engine 1 When the starting rotational speed N ₁ is reached, the piston 14c of the tilting cylinder 14 moves to the left, and the displacement volume q and the discharge flow rate Q of the variable displacement hydraulic pump 2 are 0 as shown in FIGS. The hydraulic motor 3 rotates and the work traveling vehicle 40 starts forward. When the rotational speed N of the prime mover 1 exceeds the starting rotational speed N ₁ , the displacement volume q increases in proportion to the increase amount, and the discharge flow rate Q increases in a quadratic function with respect to the increase amount. .
[0019]
When the bucket 41 rises to a predetermined height and the internal contact of the proximity switch 32 is closed, as described above, the electromagnetic on-off valve 29 is switched from the closed position B to the open position A, and the relief valve 30 is connected to the pipe line 15. Communicate with. When the rotational speed N of the prime mover 1 is increased by the driver's depression of the acceleration tread 23 and reaches the first suppression rotational speed N ₂ , the secondary pressure pII of the pressure reducing valve 11 becomes the set pressure p ₂ of the relief valve 30, The relief valve 30 is opened and the pilot pressure oil in the pipe line 15 is returned to the oil tank 60. For this reason, even if the rotational speed N of the prime mover 1 exceeds the restraining rotational speed N ₂ , the secondary pressure pII of the pressure reducing valve 11 does not rise above the set pressure p ₂ of the relief valve 30, and therefore the variable capacity The displacement volume q of the hydraulic pump 2 does not increase more than the suppression displacement volume q ₂ . Even if the displacement volume q does not change, the discharge flow rate Q of the variable displacement hydraulic pump 2 increases with the increase in the rotational speed N of the prime mover 1, so that the rotational speed of the variable displacement hydraulic pump 2 increases. It increases proportionally, and reaches the first maximum flow rate Q _max at the maximum rotational speed N ₄ .
[0020]
On the other hand, when the bucket 41 does not rise to a predetermined height, the internal contact of the proximity switch 32 is open, so that the electromagnetic on-off valve 29 is in the closed position B and the relief valve 30 is separated from the pipe line 15. Therefore, even if the rotation speed N of the prime mover 1 increases and reaches the suppression rotation speed N ₂ , the secondary pressure pII of the pressure reducing valve 11 continues to rise and becomes constant after reaching the relief pressure p ₄ of the relief valve 6. . The displacement volume q of the variable displacement hydraulic pump 2 reaches the maximum displacement volume q ₃ at the rotational speed N ₃ of the prime mover 1 where the secondary pressure pII of the pressure reducing valve 11 does not reach the relief pressure p ₄ of the relief valve 6. And then it becomes constant. Discharge flow rate Q of the variable displacement hydraulic pump 2 until the rotational speed N of the engine 1 reaches a rotational speed N ₃ increases quadratically, after reaching the rotational speed N ₃ whereas the increase in the rotational speed N It increases in proportion to the second maximum flow rate Q _max ′ at the maximum rotational speed N ₄ .
[0021]
Thus, in this specific example, the electromagnetic switching valve 29 and the relief valve 30 are interposed in the side pipe 31 that branches from the middle of the pipe 15 and reaches the oil tank 60, and the bucket 41 rises to a predetermined height. Thus, when the internal contact of the proximity switch 32 is closed, the electromagnetic on-off valve 29 is switched from the closed position B to the open position A, so that the work traveling vehicle 40 can transfer the earth and sand to the loading platform 51 of the dump truck 50 by the bucket 41. When the loading operation is performed, the selector switch 33 is turned on so that the bucket 41 remains at a predetermined height even when the rotational speed N of the prime mover 1 is increased and approaches the dump truck 50 at a high speed. Since the secondary pressure pII of the pressure reducing valve 11 is suppressed to the set pressure p ₂ of the relief valve 30 at the maximum, the relief valve 30 operates even when the discharge flow rate Q of the variable displacement hydraulic pump 2 is also the maximum. The first maximum flow rate Q _max is considerably lower than the second maximum flow rate Q _max ′ when there is not. Accordingly, after the work traveling vehicle 40 lifts the bucket 41 and enters the earth and sand loading operation, the traveling speed is suppressed to a low speed, so that the frequent stepping operation of the troublesome acceleration tread plate 23 and the brake tread plate 20 is not performed. It is possible to prevent the bucket 41 and a part of the vehicle from colliding with the dump truck 50.
[0022]
In this specific example, the displacement volume q of the variable displacement hydraulic pump 2 is controlled by the secondary pressure pII of the pressure reducing valve 11 whose primary pressure is the charge relief pressure pI downstream of the throttle 5. 11 so as to control simply by the differential pressure Δp of the diaphragm 5 without a also provided rather good, in which case the relief valve 30, the hydraulic fluid downstream of the stop 5 in the flow path of the oil discharged from the charge pump 4 Arrange for escape. FIG. 5 is a hydraulic traveling drive circuit diagram of a working traveling vehicle according to another embodiment of the present invention having such a configuration. In the figure, 35 is a high-pressure side pipe that guides the discharge oil of the charge pump 4 to the inflow chamber of the forward / reverse switching valve 13, and 36 is a low pressure that connects the outflow chamber of the forward / backward switching valve 13 and the downstream line of the throttle 5. It is a side pipe line. In this specific example, the side pipe line 31 in which the electromagnetic switching valve 29 and the relief valve 30 are interposed is connected between the high pressure side pipe line 35 and the low pressure side pipe line 36. Other configurations and operations are the same as those in the previous specific example.
[0023]
As described above, the electromagnetic on-off valve 29 can be switched from the closed position B to the open position A only when the work vehicle 40 travels forward. The bucket 41 is lifted while the bucket 41 is loaded with earth and sand. On the other hand, when the bucket 41 is lifted, there is actually little work to go backwards, and after the driver releases the earth and sand loaded on the bucket 41 onto the loading platform 51 of the dump truck 50, the driver travels quickly. This is because there are many cases where an operation of moving backward is performed. If the electromagnetic on-off valve 29 can be switched to the open position a during reverse travel of the work vehicle 40, the soil loaded on the bucket 41 is discharged onto the loading platform 51 of the dump truck 50, and then the bucket 41 is lowered. If the traveling speed of the work traveling vehicle 40 suddenly increases at a certain point when the vehicle is traveling in reverse, the danger increases because it is difficult to confirm the safety behind the vehicle.
[0024]
In the embodiment described above, the bucket 41 is to be detected by a proximity switch 32 that has risen to a predetermined height, is detected by the angle sensor that detects the rotation angle of the support arm 42 of the bucket 41 You may do it.
[0025]
【The invention's effect】
As described above, according to the first aspect of the present invention, the means described in the above-mentioned section “Means for Solving the Problems” is adopted, so that the dump truck is approached while lifting the bucket loaded with earth and sand. When carrying out work such as unloading on the loading platform, buckets and parts of the vehicle collide with the dump truck while quickly approaching the dump truck without frequent troublesome stepping on the acceleration and brake treads. This can be prevented and the above work can be performed safely and efficiently.
[Brief description of the drawings]
FIG. 1 is a hydraulic travel drive circuit diagram of a work traveling vehicle according to a specific example of the present invention. FIG. 2 is a characteristic diagram showing a relationship between a rotational speed of a prime mover and a secondary pressure of a pressure reducing valve. Fig. 4 is a characteristic diagram showing the relationship between the displacement of the variable displacement hydraulic pump and the displacement of the variable displacement hydraulic pump. Fig. 4 is a characteristic diagram showing the relationship between the rotational speed of the prime mover and the discharge flow rate of the variable displacement hydraulic pump. FIG. 6 is a schematic diagram showing a gravel load mounting operation according to a conventional example. FIG. 7 is a hydraulic travel drive circuit diagram of the work traveling vehicle.
1 prime mover 2 variable displacement hydraulic pump 2a tilt control arm 3 hydraulic motor 4 charge pump 5, 12, 37 throttle 6 charge relief valve 8a, 8b, 30 relief valve 11 pressure reducing valve 13 forward / reverse switching valve 14 tilt cylinder 14a, 14b Cylinder chamber 14c Piston 20 Brake tread 21 Forward / reverse selector switch 23 Accelerating tread 24 Work machine pump 25 Work machine control valve 26 Path switch valve 27 Work machine control valve 29 Electromagnetic switching valve 32 Proximity switch 33 Select switch 34a, 34b Electromagnetic relay 40 Working vehicle

Claims

A hydraulic drive device for a working machine-equipped traveling vehicle mounted on a working machine-equipped traveling vehicle equipped with a bucket for loading and lifting a load such as earth and sand, the variable displacement hydraulic pump connected to a prime mover, and the variable displacement hydraulic pressure A traveling hydraulic motor driven by the pump discharge oil, a fixed displacement hydraulic pump and a work machine pump connected to the prime mover together with the variable displacement hydraulic pump, and an operation driven by the discharge oil of the work machine pump A displacement actuator for changing the displacement volume of the variable displacement hydraulic pump based on the pressure of the discharge oil guided by the discharge oil of the fixed displacement hydraulic pump; the traveling direction switching means for switching the traveling direction of the front and rear of the traveling vehicle by changing the feed direction of the hydraulic fluid supplied to the travel hydraulic motor, A motor operating means that is operated by a driver and changes the rotational speed of the prime mover according to the operation, and by operating the prime mover operating means during a loading operation, the rotational speed of the fixed displacement hydraulic pump is changed. While changing the displacement volume of the variable displacement hydraulic pump through the displacement displacement changing means and changing the rotation speed of the variable displacement hydraulic pump, the rotational speed of the traveling hydraulic motor can be adjusted. In the hydraulic drive device for a working vehicle-equipped traveling vehicle, the height detection for detecting the height position of the bucket is made possible by adjusting the rotational speed of the working machine pump to adjust the driving speed of the working machine actuator. means and, in the flow path of the oil discharged from the fixed displacement hydraulic pump is guided to the押退only capacity changing means to limit the rotational speed of the travel hydraulic motor To discharge oil detected and relief valve can be prevented to increase the pressure of the pressurized oil above the set value, the height position of said height detecting means above a predetermined height the bucket, and, A hydraulic drive device for a traveling vehicle equipped with a work machine , comprising: a control circuit that controls the relief valve to function when the traveling direction switching means is switched in the forward direction.

A displacement is provided in the flow path of the discharge oil of the fixed displacement hydraulic pump, and a pressure reducing valve that controls the secondary pressure in accordance with the differential pressure across the throttle is provided downstream of the restriction. The displacement volume of the variable displacement hydraulic pump is changed in accordance with the secondary pressure of the pressure reducing valve, and the relief valve releases pressure oil downstream of the pressure reducing valve in the discharge oil flow path. The hydraulic drive device for a traveling vehicle equipped with a work machine according to claim 1.

A throttle is provided in the flow path of the discharge oil of the fixed displacement hydraulic pump, the displacement volume changing means changes the displacement volume of the variable displacement hydraulic pump according to the differential pressure across the throttle, and the relief valve 2. The hydraulic drive device for a working vehicle-equipped traveling vehicle according to claim 1, wherein pressure oil on the downstream side of the throttle in the flow path is released .