JP3792372B2

JP3792372B2 - Reach forklift

Info

Publication number: JP3792372B2
Application number: JP27541797A
Authority: JP
Inventors: 義人林
Original assignee: 住友ナコマテリアルハンドリング株式会社
Priority date: 1997-10-08
Filing date: 1997-10-08
Publication date: 2006-07-05
Anticipated expiration: 2017-10-08
Also published as: JPH11122721A

Description

【０００１】
【発明の属する技術分野】
本発明は、本来の後輪駆動に加えて前輪を補助的に駆動するリーチフォークリフトに関する。
【０００２】
【従来の技術】
この種のリーチフォークフト１の外形が図４に示される。図４（ａ）は側面図、図４（ｂ）は上面図である。図において、車両本体２の前方側には左右一対のレグ３，４が延在して形成され、そのレグ３，４の間に前後方向に移動可能なマスト５が配置されている。そして、マトス５にフォーク６が上下動可能に配設されている。
【０００３】
左右一対のレグ２，３の先端には、左前輪１１と右前輪１２とが配設されている。車両本体２の下部左側には後輪１３が配設され、車両本体２の下部右側にはキャスタ輪１４が配設されている。後輪１３は、ハンドル７で操舵可能であるともに、アクセルレバー８の操作量に応じた駆動力を発生させる駆動モータに減速機を介して連結されている。
【０００４】
このようなリーチフォークリフト１において、リフト５を前に進出させ、フォーク６に荷物を載せた状態にすると、重心が車両本体２からレグ２，３の側に移動し、駆動輪である後輪１３に作用する荷重が減少する。このような状態で、摩擦係数の低い路面、例えば冷凍庫内の滑りやすい路面でリーチフォークフト１を走行又は発進させようとしても、後輪１３がスリップすることがある。
【０００５】
そこで、車両本体２の下部の後輪１３だけではなく、各々のレグ３，４の先端に設けられた前輪１１，１２を補助的に駆動することが行われている。しかし、前輪１１，１２を常時駆動すると、前輪１１，１２が２輪速度差ステア制御系のように形態になり、かじ取り用の後輪１３との間で競合が生じ、小回りの出来るリーチフォークリフト１の操作性が損なわれる。そのため、リーチフォークリフト１の発進時のスリップを後輪の速度と前輪の速度との差により検出し、スリップを検出したときに限り、前輪１１，１２を補助的に駆動してスリップからの脱出を容易にすることが行われている。
【０００６】
【発明が解決しようとする課題】
しかしながら、駆動輪である後輪１３がスリップしたことを検出したときしか、前輪１１，１２を駆動しないので、前輪１１，１２の駆動機構が有効に活用されていないという問題点があった。
【０００７】
そこで、本発明は、駆動輪である後輪がスリップしたときに前輪を補助的に駆動してスリップからの脱出を容易にするとともに、車両の運転状況に応じて後輪及び前輪の２輪駆動を有効に活用することができるリーチフォークリフトを提供することを目的とする。
【０００８】
【課題を解決するための手段】
前記課題を解決する本発明のうち請求項１記載の発明は、車両本体の下部に設けられ、車両を走行させる主モータに連結される後輪と、車両前方に延在して形成された左右一対のレグの各々に設けられ、車両の走行を補助する補助モータに連結される前輪と、前記後輪の回転方向と回転数を制御する第１コントローラと、前記第１コントローラにおける前記後輪の回転方向と回転数に関する後輪速度指令信号と、前記前輪の回転方向と速度の検出に基づく帰還信号との偏差信号の正負と大きさに基づいて、前記補助モータの回転方向と回転数を制御する第２コントローラと、を備えるリーチフォークリフトである。
【０００９】
請求項２記載の発明は、請求項１において、前記第２コントローラは、前記後輪速度指令信号に応じた車両速度が得られており、前記偏差信号が所定範囲のゼロ近くである場合には、前記補助モータを駆動せず、前記前輪をフリーにするものである。
【００１０】
請求項３記載の発明は、請求項１又は２において、前記補助モータは、車輪に内蔵され、直接車輪を駆動するホイールインモータである。
【００１１】
請求項４記載の発明は、車両本体の下部に設けられ、車両を走行させる主モータに連結される後輪と、車両前方に延在して形成された左右一対のレグの各々に設けられ、車両の走行を補助する補助モータに連結される前輪と、前記後輪の回転方向と回転数を制御する第１コントローラと、前記第１コントローラにおける前記後輪の回転方向と回転数に関する後輪速度指令信号と、前記前輪の回転方向と速度の検出に基づく帰還信号との偏差信号の正負と大きさに基づいて、前記補助モータの回転方向と回転数を制御する第２コントローラと、を備えるリーチフォークリフトであって、
前記第２コントローラは、
（１）前進又は後進の発進時に前記後輪がスリップし、前記後輪速度指令信号に応じた車両速度が得られず、前記偏差信号が正又は負のいずれかの方向に大きくなり、前記前輪を前記後輪と同じ方向に駆動してスリップ脱出を補助し、
（２）前進又は後進の停止時に前記後輪がスリップし、前記後輪速度指令信号がゼロであるのに車両が走行し、前記偏差信号が負又は正のいずれかの方向に出力され、前記前輪を車両停止方向に駆動し、
（３）坂道上昇時に前記後輪が減速又は逆転しはじめると、前記後輪速度指令信号に応じた車両速度が得られず、前記偏差信号が正の方向に大きくなり、前記前輪を坂道上昇方向に駆動して坂道上昇を補助し、
（４）坂道下降時に前記後輪のアクセルを緩めるか又はブレーキをかけると、前記後輪速度指令信号が小さいか又はゼロであるのに車両が早く走行し、前記偏差信号が負の方向に大きくなり、前記前輪を前記後輪と逆方向に駆動するものである。
【００１２】
請求項５記載の発明は、車両本体の下部に設けられ、車両を走行させる主モータに連結される後輪と、車両前方に延在して形成された左右一対のレグの各々に設けられ、車両の走行を補助する補助モータに連結される前輪と、前記後輪の回転方向と回転数を制御する第１コントローラと、前記第１コントローラにおける前記後輪の回転方向と回転数に関する後輪速度指令信号と、前記前輪の回転方向と速度の検出に基づく帰還信号との偏差信号の正負と大きさに基づいて、前記補助モータの回転方向と回転数を制御する第２コントローラと、を備えるリーチフォークリフトであって、
前記第２コントローラは、前記後輪速度指令信号に応じた車両速度が得られており、前記偏差信号が所定範囲のゼロ近くである場合には、前記補助モータを駆動せず、前記前輪をフリーにするとともに、
前記第２コントローラは、
（１）前進又は後進の発進時に前記後輪がスリップし、前記後輪速度指令信号に応じた車両速度が得られず、前記偏差信号が正又は負のいずれかの方向に大きくなり、前記前輪を前記後輪と同じ方向に駆動してスリップ脱出を補助し、
（２）前進又は後進の停止時に前記後輪がスリップし、前記後輪速度指令信号がゼロであるのに車両が走行し、前記偏差信号が負又は正のいずれかの方向に出力され、前記前輪を車両停止方向に駆動し、
（３）坂道上昇時に前記後輪が減速又は逆転しはじめると、前記後輪速度指令信号に応じた車両速度が得られず、前記偏差信号が正の方向に大きくなり、前記前輪を坂道上昇方向に駆動して坂道上昇を補助し、
（４）坂道下降時に前記後輪のアクセルを緩めるか又はブレーキをかけると、前記後輪速度指令信号が小さいか又はゼロであるのに車両が早く走行し、前記偏差信号が負の方向に大きくなり、前記前輪を前記後輪と逆方向に駆動するものである。
【００１３】
請求項６記載の発明は、請求項４又は５において、前記補助モータは、車輪に内蔵され、直接車輪を駆動するホイールインモータである。
【００１４】
【発明の実施の形態】
本発明の実施形態を図面を用いて説明する。本発明にかかるリーチフォークリフトの全体構造は図４で説明したものと同様であるので、前述した図４の説明で代用する。
【００１５】
図４に付加して説明すべき部分は、図２に示される前輪とそのモータの連結形態と、図３に示される後輪の駆動機構である。
【００１６】
図２において、レグ側の固定軸２１に嵌入される内輪２２と、内輪２２に対して軸受２３を介して回転可能な外輪２４と、外輪２４の外周に焼き付けられたゴム製のホイール２５とから前輪１１，１２が構成されている。この前輪１１，１２に対する補助モータ１５，１６は、内輪２２側のステータコア２６と、外輪２４側の鉄心中に永久磁石２７を挿入してなるロータコア２８とからなる高力密度（ハイデンシティ）モータである。
【００１７】
補助モータ１５，１６は前輪１１，１２に内蔵されたホイールインモータであり、前輪１１，１２は減速機を介することなく補助モータ１５，１６で直接駆動（ダイレクトドライブ）される。補助モータ１５，１６は、永久磁石を常に和動的に作用させる磁気回路により構成され、コンパクトで低速大トルクを発生させることができるので、ダイレクトドライブにすることができる。
【００１８】
このような前輪１１，１２と補助モータ１５，１６のホイールインモータで且つダイレクトドライブの連結形態により、減速機を介する駆動に比較すると回転に伴う機械的ロスが殆どなく、レグへの取付けも自在であって、メンテナンスもフリーとなる。特に補助的に駆動しない場合、通常の従動輪のようにフリーに回転するという利点がある。すなわち、通常は従動輪として使い、必要な場合だけ補助的に駆動するということができる。
【００１９】
図３において、後輪１３は、主モータ１７の出力軸に同軸配置されたギアボックス３１の横向き出力軸３２に嵌入される構成となっている。主モータの反出力軸側にはモータシャフト３３が突設されており、このモータシャフト３３に嵌入されたブレーキディスク３４の外周にブレーキパッド３５が配設されている。後述するブレーキ開放スイッチからの指令がオフになると、ブレーキパッド３５が閉じてブレーキディスク３４を挟むデッドマンブレーキのブレーキ装置となっている。なお、ブレーキ装置には、後輪１３に対する機械式ブレーキに限らず、プラッギングブレーキや回生ブレーキの如き電気制動式ブレーキを付加することができる。
【００２０】
図１は、前述した優れた特性を有する前輪１１，１２及び補助モータ１５，１６を含む駆動制御の回路構成図である。
【００２１】
図において、車両駆動制御の回路は、第１コントローラ５１、主モータ駆動回路部５２、第２コントローラ５３、補助モータ駆動回路部５４を主要部分として構成されている。
【００２２】
主モータ駆動回路部５２において、主モータ１７は力行用コンタクタ６１を介してバッテリ電源５５に接続されている。主モータ１７は電機子１７ａと界磁巻線１７ｂから構成される直巻直流モータである。界磁巻線１７ｂには前進用コンタクタ６２及び後進用コンタクタ６３が接続されている。両コンタクタ６２，６３の相補的な切り換え動作により、界磁巻線１７ｂに流れる界磁電流の方向が変わると、主モータ１７が正逆回転される。
【００２３】
メイントランジスタ６４はそのアノードが界磁巻線１７ｂの前進用コンタクタ６２及び後進用コンタクタ６３の側に接続され、エミッタが接地側に接続されることで、主モータ１７に対して直列に接続されている。そして、そのベース端子には第１コントローラ５１からの公知のチョッパ（断続）信号が入力される。なお、６５ａは転流用ダイオード、６５ｂはアンチブレーキダイオード、６５ｃは回生用ダイオード、８５は後輪１３の回転数を検出する回転計である。
【００２４】
第１コントローラ５１には、アクセル８から操作量に応じた指令値が入力され、更に前進スイッチ６７及び後進スイッチ６８も接続されている。アクセル８の指令値が第１コントローラ５１に入力されると、力行用コンタクタ６１を作動させるためのトランジスタスイッチ６９が閉じる。また前進スイッチ６７又は後進スイッチ６８がオンになると、前進用コンタクタ６２を作動させるトランジスタスイッチ７０や後進用コンタクタ６３を作動させるトランジスタスイッチ７１が相補的に切り換わる。また図示されないブレーキペダルを放すと、ブレーキ開放スイッチ７２がオフになり、図３のブレーキパッド３５が閉じてブレーキが作用するが、そのブレーキ開放スイッチ７２のオフ信号は第１コントローラ５１に出力される。主モータ１７の電機子１７ａの回転数は回転計７３で検出され、第１コントローラ５１に出力される。なお、前述した前進スイッチ６７及び後進スイッチ６８等が前後進指令手段を構成し、前述したブレーキ開放スイッチ７２がブレーキ指令手段を構成する。
【００２５】
補助モータ駆動回路部５４において、補助モータ１５，１６は図２で説明したように高力密度モータであり、第２コントローラ５３からの指令値で作動するドライバ７５，７６で駆動される。
【００２６】
第２コントローラ５３は、第１コントローラ５１からの後輪速度指令５６を指令信号とし、前輪の回転方向と速度の検出に基づく前輪回転計速度信号を帰還信号５７とするとする速度制御系である。
【００２７】
後輪速度指令５６は、アクセル８を倒す方向で決まる前進又は後進の後輪１３の回転方向と、アクセル８を倒す程度で決まる回転数で決まる指令であり、前進で回転数が大きくなると、正の方向に大きな指令値を比例的に出力し、後進で回転数が大きくなると、負の方向に大きな指令値を比例的に出力する。
【００２８】
前輪回転計速度信号の帰還信号５７は、前輪１１，１２の各々に対する回転計７３，７４と、回転計７３，７４の出力の和を得る加算器７８と、加算器７８からの出力を１／２する演算器７９とからなる機器の出力で得られ、前輪１１，１２の実際の走行速度が前進方向で大きいと、正の方向に大きな信号値を比例的に出力し、前輪１１，１２の実際の走行速度が後進方向で大きくなると、負の方向に大きな信号値を比例的に出力する。
【００２９】
第２コントローラ５３は、後輪速度指令５６から帰還信号５７を引き算して偏差信号ｅを得る演算器７９と、偏差信号ｅに対する比較器８０及び調整器８１とからなる。比較器８０は、偏差信号ｅがゼロを挟む所定範囲内に小さいと、断続器５７にオフ信号を出力し、偏差信号が前記所定範囲を越えると、断続器５７にオン信号を出力するものである。断続器５７がオフになると、補助モータ１５，１６に対するバッテリ電源５５の接続が断たれ、前輪１１，１２はフリーに回転する。断続器５７がオンになると、補助モータ１５，１６にバッテリ電源５５の電力が供給され、前輪１１，１２は調節器８１からの出力に基づき制御されて駆動される。調節器８１は、偏差信号ｅが正の方向に大きいと、前輪１１，１２を後輪１３と同じ方向に比例的な回転数で駆動し、偏差信号ｅが負の方向に大きいと、前輪１１，１２を後輪１３と逆方向に比例的な回転数で駆動する。
【００３０】
つぎに、図１の車両駆動制御回路の作動例を、（１）前進又は後進の発進時、（２）前進又は後進の停止時、（３）坂道上昇時、（４）坂道下降時に分けて説明する。
【００３１】
まず、（１）の前進又は後進の急発進時を説明する。例えば、前進スイッチ６７をオンにし、アクセル８の操作量に応じた指令値を第１コントローラ５１に入力すると、トランジスタスイッチ６９により力行コンタクタ６１が閉じ、トランジスタスイッチ７０，７１により先後進コンタクタ６２，６３が相補的に切り換わって前進用になるとともに、メイントランジスタ６４に対するチョッパ信号によりアクセル操作量に応じた電流が主モータに流れ、後輪がアクセル操作量に応じた力行力で前進方向に駆動される。そして、第１コントローラ５１は第２コントローラ５３に対して、アクセル操作量に応じた前進方向即ちプラスの後輪速度指令５６を出力している。
【００３２】
このとき、前輪１１，１２はダイレクトドライブであるため通常はフリーな従動輪として機能し、スリップすることなく回転する。しかし、後輪１３は駆動輪でありしかも重心が前方に移動した場合にはスリップしやすい。後輪１３がスリップすると、車両は発進せず、前輪回転計速度信号に基づく帰還信号５７がゼロのままである。すると、演算器７９からアクセル操作量に応じた大きさの正の偏差信号ｅが調節器８１に出力され、前輪１１，１２は偏差信号ｅの大きさに応じてドライバ７５，７６及び補助モータ１５，１６を介して前進方向に駆動され、後輪１３のスリップ状態からの脱出を補助する。後輪１３のスリップが解消されると、後輪速度指令５６に応じて車両が走行するため、前輪回転計速度信号に基づく帰還信号５７と一致することになり、偏差信号ｅはゼロ近傍になって、前輪１１，１２は元の従動輪に戻る。
【００３３】
なお、比較器８０は、系全体の遅れを考慮したものである。アクセルと車両速度との間には遅れがあり、前輪１１，１２で検出される車両速度即ち前輪速度信号５７が第１コントローラ５１の後輪速度指令５７に一致しないからといって直ちに前輪１１，１２をフリーから駆動に変えることは好ましくないからである。また、後進の発進時に後輪にスリップが生じた場合は、後輪速度指令５６、帰還信号５７及び偏差信号ｅの正負の関係が逆になり、前進が後進になるだけで同様の作動になる。
【００３４】
つぎに、（２）の前進又は後進の急停止時を説明する。例えば、前進時にブレーキペダルを踏み込む急停止操作をすると、ブレーキ開放スイッチ７２がオンになり、図３のブレーキパッド３５が閉じて後輪１３がロックされ、アクセル８の操作量に関係なく、後輪速度指令５６がゼロになる。しかし、重心が前輪１１，１２側に移動していると、後輪１３がロックされたままスリップし、慣性で車両が走行することがある。前輪１１，１２が前進方向に回転するため、前輪回転計速度信号に基づく帰還信号５７が負の出力となり、後輪速度指令５６がゼロであるため、偏差信号ｅは負の出力となる。調節器８１は負の偏差信号ｅの大きさに基づき、前輪１１，１２はドライバ７５，７６及び補助モータ１５，１６を介して後進方向に駆動され、車両が慣性で走行するのを阻止して急停止を補助する。
【００３５】
なお、後進の急停止時に車両が慣性で走行する場合は、後輪速度指令５６はゼロのまま、帰還信号５７及び偏差信号ｅの正負の関係が逆になり、前輪１１，１２が前進方向に駆動され、車両の後進方向への急停止を補助する。
【００３６】
つぎに、（３）の坂道上昇時を説明する。坂道の程度が少なく、後輪速度指令５６に応じた車両速度が得られていると、後輪速度指令５６と前輪回転計速度信号に基づく帰還信号５７との偏差信号ｅがゼロ近傍であって、前輪１１，１２はフリーな従動輪のままである。
【００３７】
坂道の上り勾配が急になり、車両への負荷が増大すると、後輪速度指令５６に応じた車両速度が得られず、車両は減速しはじめる。車両の運転者はアクセル８を前進方向に操作して車両の速度を保とうとする。すると、後輪速度指令５６は更に大きくなるのに、帰還信号５７が小さくなって、正の偏差信号ｅが出力される。この正の偏差信号ｅが比較器８０の所定値より大きくなると、調節器８１は正の偏差信号ｅに基づき、前輪１１，１２はドライバ７５，７６及び補助モータ１５，１６を介して前進方向に駆動され、車両の坂道登攀を補助する。
【００３８】
坂道の上り勾配が更に急になり、アクセル８を前進方向の最大まで操作しても車両が止まって後戻りしはじるめると、後輪速度指令５６は最大のままであるが、帰還信号５７の正負が逆転し正の出力となる。すると、偏差信号ｅは輪速度指令５６＋帰還信号５７となって正の方向に多くなり、大きくなった偏差信号ｅに基づき、前輪１１，１２はドライバ７５，７６及び補助モータ１５，１６を介して更に強力に前進方向に駆動され、車両の坂道逆行を阻止する。
【００３９】
つぎに、（４）の坂道下降時を説明する。坂道の程度が少なく、後輪速度指令５６に応じた車両速度が得られていると、後輪速度指令５６と前輪回転計速度信号に基づく帰還信号５７との偏差信号ｅがゼロ近傍であって、前輪１１，１２はフリーな従動輪のままであるのは坂道上昇時と同じである。
【００４０】
坂道の下り勾配が急になると、後輪速度指令５６に応じた車両速度が得られず、車両は加速しはじめる。車両の速度に応じて運転者はアクセル８を中立位置に向かって戻していき、ブレーキをかける。しかし、下り勾配が急であると、アクセル８を中立位置に戻しても車両が加速しはじめ、後輪速度指令５６はゼロであるのに、前輪回転計速度信号に基づく帰還信号５７が負の値を出力し、偏差信号ｅは負の値となる。すると、負の偏差信号ｅに基づき、前輪１１，１２はドライバ７５，７６及び補助モータ１５，１６を介して坂道を上昇する方向に駆動され、車両の坂道下降時の加速を阻止する。もちろん、車両の坂道下降時の加速が、前輪１１，１２の補助的駆動で止められない場合、運転者はブレーキペダルを操作、後輪１３の機械式ブレーキ力も付加される。
【００４１】
【発明の効果】
本発明にかかる請求項１記載の発明によると、後輪の回転方向と回転数に関する後輪速度指令信号と、前輪の回転方向と速度の検出に基づく帰還信号とによる速度制御系とすることにより、車両の通常走行時は前輪をフリーとして車両の小回りを確保し、スリップ時等のように車両の通常走行時以外は前輪を補助駆動として使用することを自動的に行うことができる。
【００４２】
請求項２記載の発明によると、通常走行時とそれ以外の区別を明瞭にし、スリップ時のような特別の場合にだけ、前輪を補助駆動として使用することを自動的に行うことができる。
【００４３】
請求項３記載の発明によると、前輪はダイレクトドライブのホイールインモータで駆動されるため、通常走行時は従動輪として機能するものの、通常走行時以外には補助駆動輪として機能するという使い分けがし易い機構である。
【００４４】
請求項４及び５記載の発明によると、前後進時の急発進又は急停車時の駆動補助、坂道上昇時又は坂道下降時の駆動補助など、通常走行以外のあらゆる場合に、前輪を補助駆動として使用するができる。
【００４５】
請求項６記載の発明によると、前輪はダイレクトドライブのホイールインモータで駆動されるため、通常走行時は従動輪として機能するものの、通常走行時以外には補助駆動輪として機能するという使い分けがし易い機構である。
【図面の簡単な説明】
【図１】本発明のリーチフォークリフトの制御ブロック図である。
【図２】ホイールインタイプモータによる前輪の断面図である。
【図３】後輪の駆動部を示す上面図である。
【図４】リーチフォークリフトの外形図である。
【符号の説明】
１リーチフォークリフト
１１左側前輪
１２右側前輪
１３後輪
１５左側前輪用補助モータ
１６右側前輪用補助モータ
１７主モータ
５１第１コントローラ
５２主モータ駆動回路部
５３第２コントローラ
５４補助モータ駆動回路部
５６後輪速度指令
５７帰還信号（前輪速度信号）
ｅ偏差信号
６７前進スイッチ
６８後進スイッチ
７２ブレーキ開放スイッチ
７３回転計
７４回転計
２６ステータコア（ホイールインモータ）
２７永久磁石（ホイールインモータ）
２８ロータコア（ホイールインモータ）
３４ブレーキディスク（ブレーキ装置）
３５ブレーキパッド（ブレーキ装置）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reach forklift that auxiliaryly drives a front wheel in addition to the original rear wheel drive.
[0002]
[Prior art]
The outline of this type of reach folkft 1 is shown in FIG. 4A is a side view and FIG. 4B is a top view. In the figure, a pair of left and right legs 3, 4 are formed on the front side of the vehicle body 2, and a mast 5 movable in the front-rear direction is disposed between the legs 3, 4. A fork 6 is arranged on the matos 5 so as to be movable up and down.
[0003]
A left front wheel 11 and a right front wheel 12 are disposed at the ends of the pair of left and right legs 2 and 3. A rear wheel 13 is disposed on the lower left side of the vehicle body 2, and a caster wheel 14 is disposed on the lower right side of the vehicle body 2. The rear wheel 13 can be steered by the handle 7 and is connected to a drive motor that generates a driving force corresponding to the operation amount of the accelerator lever 8 via a speed reducer.
[0004]
In such a reach forklift 1, when the lift 5 is advanced forward and a load is placed on the fork 6, the center of gravity moves from the vehicle main body 2 to the legs 2 and 3, and the rear wheel 13 serving as a drive wheel. The load acting on is reduced. In such a state, the rear wheel 13 may slip even if the reach folkft 1 is driven or started on a road surface having a low friction coefficient, for example, a slippery road surface in the freezer.
[0005]
Therefore, not only the rear wheel 13 at the lower part of the vehicle body 2 but also the front wheels 11 and 12 provided at the tips of the legs 3 and 4 are driven in an auxiliary manner. However, when the front wheels 11 and 12 are always driven, the front wheels 11 and 12 are configured like a two-wheel speed difference steering control system, and a competition occurs with the rear wheel 13 for steering, and the reach forklift 1 that can make a small turn. The operability of is impaired. Therefore, the slip at the start of the reach forklift 1 is detected by the difference between the speed of the rear wheel and the speed of the front wheel, and only when the slip is detected, the front wheels 11 and 12 are driven auxiliary to escape from the slip. It has been made easy.
[0006]
[Problems to be solved by the invention]
However, since the front wheels 11 and 12 are driven only when it is detected that the rear wheel 13 that is the drive wheel slips, the drive mechanism of the front wheels 11 and 12 is not effectively utilized.
[0007]
Accordingly, the present invention facilitates escape from slip by driving the front wheel auxiliary when the rear wheel, which is the drive wheel, slips, and driving the two wheels of the rear wheel and the front wheel according to the driving situation of the vehicle. An object of the present invention is to provide a reach forklift that can effectively utilize the above.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 of the present invention that solves the above-mentioned problems is provided in a lower part of the vehicle main body, connected to a main motor for running the vehicle, and left and right formed to extend forward of the vehicle. A front wheel provided on each of the pair of legs and connected to an auxiliary motor that assists in running of the vehicle, a first controller that controls the rotation direction and the rotation speed of the rear wheel, and the rear wheel of the first controller Control the rotation direction and rotation speed of the auxiliary motor based on the sign and magnitude of the deviation signal between the rear wheel speed command signal related to the rotation direction and rotation speed and the feedback signal based on the detection of the rotation direction and speed of the front wheel. A reach forklift comprising a second controller.
[0009]
According to a second aspect of the present invention, in the first aspect, the second controller obtains a vehicle speed corresponding to the rear wheel speed command signal, and the deviation signal is close to zero within a predetermined range. The auxiliary motor is not driven and the front wheels are freed.
[0010]
The invention according to claim 3 is the wheel-in motor according to claim 1 or 2, wherein the auxiliary motor is built in a wheel and directly drives the wheel.
[0011]
The invention according to claim 4 is provided at each of a rear wheel provided at a lower portion of the vehicle main body and connected to a main motor for running the vehicle, and a pair of left and right legs formed to extend forward of the vehicle, A front wheel connected to an auxiliary motor for assisting in running of the vehicle, a first controller for controlling the rotation direction and the rotation speed of the rear wheel, and a rear wheel speed relating to the rotation direction and rotation speed of the rear wheel in the first controller. And a second controller for controlling the rotational direction and the rotational speed of the auxiliary motor based on the sign and magnitude of the deviation signal between the command signal and the feedback signal based on detection of the rotational direction and speed of the front wheel. A forklift,
The second controller is
(1) the rear wheel slips during forward or reverse of the start, the vehicle speed corresponding to the rear wheel velocity command signal is obtained, et al are not, the deviation signal increases in the positive or negative either direction, the Drive the front wheel in the same direction as the rear wheel to assist slip escape,
(2) The rear wheel slips when stopping forward or reverse, the vehicle travels even when the rear wheel speed command signal is zero, and the deviation signal is output in either a negative or positive direction, Drive the front wheels in the direction of vehicle stop,
(3) When the rear wheel at the time of rising slope begins to decelerate or reverse, the vehicle speed corresponding to the rear wheel velocity command signal is not obtained, et al., The deviation signal increases in the positive direction, the slope increase the front wheel Driving in the direction to assist in climbing the hill,
(4) When the rear wheel accelerator is loosened or the brake is applied when descending on a slope, the vehicle travels faster even if the rear wheel speed command signal is small or zero, and the deviation signal increases in the negative direction. Thus, the front wheel is driven in the opposite direction to the rear wheel.
[0012]
The invention according to claim 5 is provided at each of a rear wheel provided at a lower portion of the vehicle main body and connected to a main motor for running the vehicle, and a pair of left and right legs formed to extend forward of the vehicle, A front wheel connected to an auxiliary motor for assisting in running of the vehicle, a first controller for controlling the rotation direction and the rotation speed of the rear wheel, and a rear wheel speed relating to the rotation direction and rotation speed of the rear wheel in the first controller. And a second controller for controlling the rotational direction and the rotational speed of the auxiliary motor based on the sign and magnitude of the deviation signal between the command signal and the feedback signal based on detection of the rotational direction and speed of the front wheel. A forklift,
When the vehicle speed corresponding to the rear wheel speed command signal is obtained and the deviation signal is close to zero within a predetermined range, the second controller does not drive the auxiliary motor and frees the front wheel. And
The second controller is
(1) When the vehicle starts moving forward or backward, the rear wheel slips, the vehicle speed corresponding to the rear wheel speed command signal cannot be obtained, and the deviation signal increases in either a positive or negative direction. Driving in the same direction as the rear wheel to assist slip escape,
(2) The rear wheel slips when stopping forward or reverse, the vehicle travels even when the rear wheel speed command signal is zero, and the deviation signal is output in either a negative or positive direction, Drive the front wheels in the direction of vehicle stop,
(3) When the rear wheel starts to decelerate or reverse when the hill rises, the vehicle speed corresponding to the rear wheel speed command signal cannot be obtained, the deviation signal increases in the positive direction, and the front wheel moves up the hill. To help climb the hill,
(4) When the rear wheel accelerator is loosened or the brake is applied when descending on a slope, the vehicle travels faster even if the rear wheel speed command signal is small or zero, and the deviation signal increases in the negative direction. Thus, the front wheel is driven in the opposite direction to the rear wheel.
[0013]
A sixth aspect of the present invention is the wheel-in motor according to the fourth or fifth aspect , wherein the auxiliary motor is built in a wheel and directly drives the wheel.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. Since the overall structure of the reach forklift according to the present invention is the same as that described with reference to FIG. 4, the description of FIG. 4 described above is used instead.
[0015]
The parts to be described in addition to FIG. 4 are the connection form of the front wheel and its motor shown in FIG. 2 and the drive mechanism of the rear wheel shown in FIG.
[0016]
In FIG. 2, an inner ring 22 fitted into the leg-side fixed shaft 21, an outer ring 24 rotatable with respect to the inner ring 22 via a bearing 23, and a rubber wheel 25 baked on the outer periphery of the outer ring 24. Front wheels 11 and 12 are configured. The auxiliary motors 15 and 16 for the front wheels 11 and 12 are high force density (high density) motors including a stator core 26 on the inner ring 22 side and a rotor core 28 in which a permanent magnet 27 is inserted into an iron core on the outer ring 24 side. is there.
[0017]
The auxiliary motors 15 and 16 are wheel-in motors built in the front wheels 11 and 12, and the front wheels 11 and 12 are directly driven (direct drive) by the auxiliary motors 15 and 16 without using a reduction gear. The auxiliary motors 15 and 16 are constituted by a magnetic circuit that always causes the permanent magnets to act in a harmonious manner, and can generate a low-speed large torque in a compact manner, so that it can be a direct drive.
[0018]
By such a wheel-in motor of the front wheels 11 and 12 and the auxiliary motors 15 and 16 and a direct drive connection form, there is almost no mechanical loss due to rotation compared to driving through a speed reducer, and attachment to the leg is also free. And maintenance is also free. In particular, when it is not driven supplementarily, there is an advantage that it rotates freely like a normal driven wheel. That is, it can be said that it is normally used as a driven wheel and is driven only when necessary.
[0019]
In FIG. 3, the rear wheel 13 is configured to be fitted into a lateral output shaft 32 of a gear box 31 that is coaxially disposed on the output shaft of the main motor 17. A motor shaft 33 protrudes on the side opposite to the output shaft of the main motor, and a brake pad 35 is disposed on the outer periphery of a brake disk 34 fitted into the motor shaft 33. When a command from a brake release switch, which will be described later, is turned off, the brake pad 35 is closed and the brake device of a deadman brake is sandwiched between the brake discs 34. Note that the brake device is not limited to a mechanical brake for the rear wheel 13, but an electric braking brake such as a plugging brake or a regenerative brake can be added.
[0020]
FIG. 1 is a circuit configuration diagram of drive control including front wheels 11 and 12 and auxiliary motors 15 and 16 having the above-described excellent characteristics.
[0021]
In the figure, the vehicle drive control circuit is composed mainly of a first controller 51, a main motor drive circuit section 52, a second controller 53, and an auxiliary motor drive circuit section 54.
[0022]
In the main motor drive circuit unit 52, the main motor 17 is connected to the battery power supply 55 via the powering contactor 61. The main motor 17 is a direct-winding DC motor composed of an armature 17a and a field winding 17b. A forward contactor 62 and a reverse contactor 63 are connected to the field winding 17b. When the direction of the field current flowing in the field winding 17b is changed by the complementary switching operation of both the contactors 62 and 63, the main motor 17 is rotated forward and backward.
[0023]
The main transistor 64 has an anode connected to the forward contactor 62 and the reverse contactor 63 side of the field winding 17b, and an emitter connected to the ground side, so that the main transistor 64 is connected in series to the main motor 17. Yes. A known chopper (intermittent) signal from the first controller 51 is input to the base terminal. In addition, 65a is a commutation diode, 65b is an anti-brake diode, 65c is a regeneration diode, and 85 is a tachometer that detects the number of revolutions of the rear wheel 13.
[0024]
A command value corresponding to an operation amount is input from the accelerator 8 to the first controller 51, and a forward switch 67 and a reverse switch 68 are also connected. When the command value of the accelerator 8 is input to the first controller 51, the transistor switch 69 for operating the power running contactor 61 is closed. When the forward switch 67 or the reverse switch 68 is turned on, the transistor switch 70 for operating the forward contactor 62 and the transistor switch 71 for operating the reverse contactor 63 are switched complementarily. When the brake pedal (not shown) is released, the brake release switch 72 is turned off and the brake pad 35 in FIG. 3 is closed and the brake is applied. The off signal of the brake release switch 72 is output to the first controller 51. . The rotation speed of the armature 17 a of the main motor 17 is detected by the tachometer 73 and output to the first controller 51. The forward switch 67 and the reverse switch 68 described above constitute forward / reverse command means, and the brake release switch 72 described above constitutes brake command means.
[0025]
In the auxiliary motor drive circuit unit 54, the auxiliary motors 15 and 16 are high-power density motors as described with reference to FIG. 2, and are driven by drivers 75 and 76 that operate according to a command value from the second controller 53.
[0026]
The second controller 53 is a speed control system in which the rear wheel speed command 56 from the first controller 51 is used as a command signal, and the front wheel tachometer speed signal based on the detection of the rotation direction and speed of the front wheels is used as a feedback signal 57.
[0027]
The rear wheel speed command 56 is a command determined by the rotational direction of the forward or reverse rear wheel 13 determined by the direction in which the accelerator 8 is tilted and the rotational speed determined by the degree to which the accelerator 8 is tilted. A large command value is proportionally output in the direction of, and when the rotational speed increases in the reverse direction, a large command value is proportionally output in the negative direction.
[0028]
The front wheel tachometer speed signal feedback signal 57 includes a tachometer 73, 74 for each of the front wheels 11, 12, an adder 78 for obtaining the sum of the outputs of the tachometers 73, 74, and an output from the adder 78 as 1 /. When the actual traveling speed of the front wheels 11 and 12 is large in the forward direction, a large signal value is proportionally output in the positive direction. When the actual traveling speed increases in the reverse direction, a large signal value is proportionally output in the negative direction.
[0029]
The second controller 53 includes a calculator 79 that obtains a deviation signal e by subtracting the feedback signal 57 from the rear wheel speed command 56, and a comparator 80 and an adjuster 81 for the deviation signal e. The comparator 80 outputs an off signal to the interrupter 57 when the deviation signal e is small within a predetermined range across zero, and outputs an on signal to the interrupter 57 when the deviation signal exceeds the predetermined range. is there. When the interrupter 57 is turned off, the battery power supply 55 is disconnected from the auxiliary motors 15 and 16, and the front wheels 11 and 12 rotate freely. When the interrupter 57 is turned on, the electric power of the battery power supply 55 is supplied to the auxiliary motors 15 and 16, and the front wheels 11 and 12 are controlled and driven based on the output from the regulator 81. When the deviation signal e is large in the positive direction, the adjuster 81 drives the front wheels 11 and 12 at a rotational speed proportional to the same direction as the rear wheel 13, and when the deviation signal e is large in the negative direction, the front wheel 11 , 12 are driven at a rotational speed proportional to the reverse direction of the rear wheel 13.
[0030]
Next, the operation example of the vehicle drive control circuit of FIG. 1 is divided into (1) When starting forward or backward, (2) When stopping forward or backward, (3) When climbing a slope, (4) When descending a slope explain.
[0031]
First, a description will be given of (1) sudden start of forward or reverse. For example, when the forward switch 67 is turned on and a command value corresponding to the operation amount of the accelerator 8 is input to the first controller 51, the power running contactor 61 is closed by the transistor switch 69, and the forward and backward contactors 62, 63 are closed by the transistor switches 70, 71. Are complementarily switched for forward movement, and a current corresponding to the accelerator operation amount flows to the main motor by the chopper signal to the main transistor 64, and the rear wheel is driven in the forward direction with a power running force corresponding to the accelerator operation amount. The The first controller 51 then outputs a forward direction corresponding to the accelerator operation amount, that is, a positive rear wheel speed command 56 to the second controller 53.
[0032]
At this time, since the front wheels 11 and 12 are direct drives, they normally function as free driven wheels and rotate without slipping. However, the rear wheel 13 is a driving wheel, and easily slips when the center of gravity moves forward. When the rear wheel 13 slips, the vehicle does not start, and the feedback signal 57 based on the front wheel tachometer speed signal remains zero. Then, a positive deviation signal e having a magnitude corresponding to the accelerator operation amount is output from the computing unit 79 to the adjuster 81, and the front wheels 11 and 12 are driven by the drivers 75 and 76 and the auxiliary motor 15 according to the magnitude of the deviation signal e. , 16 is driven in the forward direction to assist escape of the rear wheel 13 from the slip state. When the slip of the rear wheel 13 is eliminated, the vehicle travels in accordance with the rear wheel speed command 56, and therefore coincides with the feedback signal 57 based on the front wheel tachometer speed signal, and the deviation signal e becomes near zero. Thus, the front wheels 11 and 12 return to the original driven wheels.
[0033]
Note that the comparator 80 takes into account the delay of the entire system. There is a delay between the accelerator and the vehicle speed, and the vehicle speed detected by the front wheels 11, 12, that is, the front wheel speed signal 57 does not coincide with the rear wheel speed command 57 of the first controller 51. This is because it is not preferable to change 12 from free to drive. In addition, if slip occurs in the rear wheel when starting backward, the positive / negative relationship of the rear wheel speed command 56, the feedback signal 57, and the deviation signal e is reversed, and the same operation is performed only by moving forward. .
[0034]
Next, a description will be given of (2) when suddenly moving forward or reverse. For example, when a sudden stop operation is performed by depressing the brake pedal during forward travel, the brake release switch 72 is turned on, the brake pad 35 in FIG. 3 is closed, the rear wheel 13 is locked, and the rear wheel is independent of the operation amount of the accelerator 8. The speed command 56 becomes zero. However, if the center of gravity moves toward the front wheels 11 and 12, the rear wheel 13 may slip while being locked, and the vehicle may travel with inertia. Since the front wheels 11 and 12 rotate in the forward direction, the feedback signal 57 based on the front wheel tachometer speed signal is a negative output, and the rear wheel speed command 56 is zero, so the deviation signal e is a negative output. Based on the magnitude of the negative deviation signal e, the adjuster 81 drives the front wheels 11 and 12 in the reverse direction via the drivers 75 and 76 and the auxiliary motors 15 and 16 to prevent the vehicle from traveling with inertia. Assist sudden stop.
[0035]
When the vehicle travels with inertia during a sudden reverse stop, the rear wheel speed command 56 remains zero, the positive / negative relationship between the feedback signal 57 and the deviation signal e is reversed, and the front wheels 11 and 12 are moved in the forward direction. Driven to assist the sudden stop of the vehicle in the reverse direction.
[0036]
Next, (3) when the hill rises will be described. If the degree of slope is small and the vehicle speed corresponding to the rear wheel speed command 56 is obtained, the deviation signal e between the rear wheel speed command 56 and the feedback signal 57 based on the front wheel tachometer speed signal is near zero. The front wheels 11 and 12 remain free driven wheels.
[0037]
If the uphill slope becomes steep and the load on the vehicle increases, the vehicle speed according to the rear wheel speed command 56 cannot be obtained, and the vehicle begins to decelerate. The driver of the vehicle tries to keep the speed of the vehicle by operating the accelerator 8 in the forward direction. Then, although the rear wheel speed command 56 is further increased, the feedback signal 57 is decreased and a positive deviation signal e is output. When the positive deviation signal e becomes larger than a predetermined value of the comparator 80, the controller 81 is based on the positive deviation signal e, and the front wheels 11 and 12 are moved forward through the drivers 75 and 76 and the auxiliary motors 15 and 16. Driven to assist the climbing of the vehicle.
[0038]
If the uphill slope becomes steep and the vehicle stops and starts to move backward even if the accelerator 8 is operated to the maximum in the forward direction, the rear wheel speed command 56 remains at the maximum, but the feedback signal 57 Positive and negative are reversed to produce a positive output. Then, the deviation signal e becomes a wheel speed command 56 + a feedback signal 57 and increases in the positive direction. Based on the increased deviation signal e, the front wheels 11 and 12 pass through the drivers 75 and 76 and the auxiliary motors 15 and 16. It is further driven in the forward direction to prevent the vehicle from going backwards on the hill.
[0039]
Next, (4) when the slope descends will be described. If the degree of slope is small and the vehicle speed corresponding to the rear wheel speed command 56 is obtained, the deviation signal e between the rear wheel speed command 56 and the feedback signal 57 based on the front wheel tachometer speed signal is near zero. The front wheels 11 and 12 remain free driven wheels in the same manner as when the hill climbs.
[0040]
When the downhill slope becomes steep, the vehicle speed corresponding to the rear wheel speed command 56 cannot be obtained, and the vehicle starts to accelerate. The driver returns the accelerator 8 toward the neutral position according to the speed of the vehicle and applies the brake. However, if the downhill is steep, the vehicle begins to accelerate even when the accelerator 8 is returned to the neutral position, and the feedback signal 57 based on the front wheel tachometer speed signal is negative although the rear wheel speed command 56 is zero. Value is output, and the deviation signal e is a negative value. Then, based on the negative deviation signal e, the front wheels 11 and 12 are driven in the direction of ascending the hill via the drivers 75 and 76 and the auxiliary motors 15 and 16 to prevent acceleration of the vehicle when the hill is descending. Of course, when the acceleration when the vehicle is descending on the slope is not stopped by the auxiliary driving of the front wheels 11 and 12, the driver operates the brake pedal, and the mechanical braking force of the rear wheel 13 is also applied.
[0041]
【The invention's effect】
According to the first aspect of the present invention, a speed control system based on a rear wheel speed command signal relating to the rotation direction and the number of rotations of the rear wheel and a feedback signal based on the detection of the rotation direction and speed of the front wheel is provided. When the vehicle is traveling normally, the front wheels are free to ensure a small turning of the vehicle, and when the vehicle is not traveling normally, such as when slipping, the front wheels can be automatically used as auxiliary driving.
[0042]
According to the second aspect of the invention, the distinction between normal driving and other than that can be made clear, and the front wheel can be automatically used as an auxiliary drive only in a special case such as a slip.
[0043]
According to the invention described in claim 3, since the front wheels are driven by a direct-drive wheel-in motor, the front wheels function as driven wheels during normal driving, but function as auxiliary driving wheels during normal driving. It is an easy mechanism.
[0044]
According to the inventions of claims 4 and 5 , the front wheels are used as auxiliary driving in all cases other than normal driving, such as driving assistance when suddenly moving forward or backward, driving assistance when suddenly stopping, driving assistance when climbing up or down a hill, etc. I can do it.
[0045]
According to the invention described in claim 6 , since the front wheels are driven by a direct drive wheel-in motor, they function as driven wheels during normal driving, but function as auxiliary driving wheels during normal driving. It is an easy mechanism.
[Brief description of the drawings]
FIG. 1 is a control block diagram of a reach forklift according to the present invention.
FIG. 2 is a sectional view of a front wheel by a wheel-in type motor.
FIG. 3 is a top view showing a drive unit of a rear wheel.
FIG. 4 is an external view of a reach forklift.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reach forklift 11 Left front wheel 12 Right front wheel 13 Rear wheel 15 Left front wheel auxiliary motor 16 Right front wheel auxiliary motor 17 Main motor 51 First controller 52 Main motor drive circuit unit 53 Second controller 54 Auxiliary motor drive circuit unit 56 Rear wheel Speed command 57 Feedback signal (front wheel speed signal)
e Deviation signal 67 Forward switch 68 Reverse switch 72 Brake release switch 73 Tachometer 74 Tachometer 26 Stator core (wheel-in motor)
27 Permanent magnet (wheel-in motor)
28 Rotor core (wheel-in motor)
34 Brake disc (brake device)
35 Brake pads (brake equipment)

Claims

A rear wheel provided at a lower portion of the vehicle body and connected to a main motor for running the vehicle;
Front wheels provided on each of a pair of left and right legs formed to extend in front of the vehicle and connected to an auxiliary motor that assists in running the vehicle;
A first controller for controlling the rotation direction and the rotation speed of the rear wheel;
Based on the sign and magnitude of a deviation signal between a rear wheel speed command signal relating to the rotation direction and rotation speed of the rear wheel and a feedback signal based on detection of the rotation direction and speed of the front wheel in the first controller. A reach forklift, comprising: a second controller that controls a rotation direction and a rotation speed of the motor.

When the vehicle speed corresponding to the rear wheel speed command signal is obtained and the deviation signal is close to zero within a predetermined range, the second controller does not drive the auxiliary motor and frees the front wheel. The reach forklift according to claim 1.

The reach forklift according to claim 1 or 2, wherein the auxiliary motor is a wheel-in motor built in a wheel and directly driving the wheel.

A rear wheel provided at a lower portion of the vehicle body and connected to a main motor for running the vehicle;
Front wheels provided on each of a pair of left and right legs formed to extend in front of the vehicle and connected to an auxiliary motor that assists in running the vehicle;
A first controller for controlling the rotation direction and the rotation speed of the rear wheel;
Based on the sign and magnitude of a deviation signal between a rear wheel speed command signal relating to the rotation direction and rotation speed of the rear wheel and a feedback signal based on detection of the rotation direction and speed of the front wheel in the first controller. A reach forklift comprising a second controller for controlling the rotational direction and the rotational speed of the motor,
The second controller is
(1) the rear wheel slips during forward or reverse of the start, the vehicle speed corresponding to the rear wheel velocity command signal is obtained, et al are not, the deviation signal increases in the positive or negative either direction, the Drive the front wheel in the same direction as the rear wheel to assist slip escape,
(2) The rear wheel slips when stopping forward or reverse, the vehicle travels even when the rear wheel speed command signal is zero, and the deviation signal is output in either a negative or positive direction, Drive the front wheels in the direction of vehicle stop,
(3) When the rear wheel at the time of rising slope begins to decelerate or reverse, the vehicle speed corresponding to the rear wheel velocity command signal is not obtained, et al., The deviation signal increases in the positive direction, the slope increase the front wheel Driving in the direction to assist in climbing the hill,
(4) When the rear wheel accelerator is loosened or the brake is applied when descending on a slope, the vehicle travels faster even if the rear wheel speed command signal is small or zero, and the deviation signal increases in the negative direction. becomes, lapis lazuli over Ji forklift to drive the front wheels to the rear wheels in the opposite direction.

A rear wheel provided at a lower portion of the vehicle body and connected to a main motor for running the vehicle;
Front wheels provided on each of a pair of left and right legs formed to extend in front of the vehicle and connected to an auxiliary motor that assists in running the vehicle;
A first controller for controlling the rotational direction and the rotational speed of the rear wheel;
Based on the sign and magnitude of a deviation signal between a rear wheel speed command signal relating to the rotation direction and rotation speed of the rear wheel and a feedback signal based on detection of the rotation direction and speed of the front wheel in the first controller. A reach forklift comprising a second controller for controlling the rotational direction and the rotational speed of the motor,
When the vehicle speed corresponding to the rear wheel speed command signal is obtained and the deviation signal is close to zero within a predetermined range, the second controller does not drive the auxiliary motor, and the front wheel And free
The second controller is
(1) When the vehicle starts moving forward or backward, the rear wheel slips, the vehicle speed corresponding to the rear wheel speed command signal cannot be obtained, and the deviation signal increases in either a positive or negative direction. To assist slip escape by driving in the same direction as the rear wheel,
(2) The rear wheel slips when stopping forward or reverse, the vehicle travels even when the rear wheel speed command signal is zero, and the deviation signal is output in either a negative or positive direction, Drive the front wheels in the direction of vehicle stop,
(3) When the rear wheel starts decelerating or reversing when the hill is rising, the vehicle speed corresponding to the rear wheel speed command signal cannot be obtained, the deviation signal increases in the positive direction, and the front wheel moves in the hill rising direction. To help climb the hill,
(4) When the rear wheel accelerator is loosened or the brake is applied when descending on a slope, the vehicle travels faster even if the rear wheel speed command signal is small or zero, and the deviation signal increases in the negative direction. A reach forklift that drives the front wheel in a direction opposite to the rear wheel.

The auxiliary motor is built in a wheel, Reach fork lift according to claim 4 or 5, wherein the wheel-in motor for driving the wheels directly.