PROBLEM TO BE SOLVED: To increase a control reaction speed so as to improve operation efficiency and prevent an engine failure, without decreasing the number of revolutions of an engine, by constantly sensing the movement of a rotary rear cover, and controlling the rear cover so that a trunnion shaft of a hydraulic infinite variable-speed drive for controlling a vehicle speed can be operated in a speed reduction direction when a position of the rear cover exceeds a set value by a fixed value or more, and so that the vehicle speed can be returned to the original speed when the rear cover is returned to an original position.SOLUTION: An ascendable/descendable rotary working machine is provided in the rear of a vehicle body. This tilling depth controller for a tractor is provided with a rear cover sensor for detecting the vertical rotation angle of the rear cover attached to the rotary working machine, and a speed reduction control means for controlling the trunnion shaft of the hydraulic infinite variable-speed drive for controlling the vehicle speed, in the speed reduction direction, on the basis of the detected result of the rear cover sensor, when the rotation angle of the rear cover exceeds a set value by a predetermined value or more.COPYRIGHT: (C)2008,JPO&INPIT【課題】本発明の課題は、ロータリのリヤカバーの動きを常にセンシングして、リヤカバーが設定値を一定以上越えると、車速を制御する油圧式無段変速装置のトラニオン軸を減速方向に作動させ、リヤカバーが元の位置に復帰すると車速を元に戻すように制御することで、エンジン回転を落すことなく、制御反応を速くして作業能率の向上、エンストの防止化を図る。【解決手段】本発明は、車体の後部に昇降可能なロータリ作業機を装着して設け、該ロータリ作業機に装着されたリヤカバーの上下回動角を検出するリヤカバーセンサを設け、前記リヤカバーの回動角が設定された設定値を所定値以上越えると、前記リヤカバーセンサの検出結果に基づき、車速を制御する油圧式無段変速装置のトラニオン軸を減速方向に制御する減速制御手段を設けてあることを特徴とするトラクタの耕深制御装置の構成とする。【選択図】図1
