PROBLEM TO BE SOLVED: To simplify an interlocking structure for automatic vehicle speed control, in a working vehicle which can execute automatic vehicle speed control of constantly holding the driving of a working part by reducing the speed at the time of an overload on an engine 6.SOLUTION: An electric motor 170 as a gear shift actuator is linked with the straight-ahead rotatable shaft 105 of the straight-ahead HST type transmission machine 35 through a linkage mechanism 171 in another system from the operating system which heads for the straight-ahead rotatable shaft 105 from a main shift lever 77. When the present engine load factor LF is more than the setting load factor LFa, namely, at the time of the overload of the engine, the electric motor 170 is so driven in accordance with the instruction from the controller 190 that the straight-ahead rotatable shaft 105 of the straight-ahead HST type transmission machine 35 moves rotationally to a head slowing down direction through the linkage mechanism 171.COPYRIGHT: (C)2008,JPO&INPIT【課題】エンジン6の過負荷時に車速を減速して作業部の駆動を一定に保持する自動車速制御を実行可能な作業車両において、自動車速制御のための連動構造を簡素化する。【解決手段】直進用HST式変速機構35の直進用回動軸105に、変速アクチュエータとしての電動モータ170を、主変速レバー77から直進用回動軸105に向かう操作系統とは別系統の連係機構171を介して関連付ける。現在のエンジン負荷率LFが設定負荷率LFa以上である過負荷時には、直進用HST式変速機構35の直進用回動軸105を連係機構171を介して前進減速方向に回動させるべく、コントローラ190からの指令にて電動モータ170を駆動させるように構成する。【選択図】図8
