| 摘要 |
PURPOSE:To prevent accidents such as coming-off of a track and breakage of a sprocket shaft from occurring by a method wherein the difference of the tension of track during forward movement and that during backward movement is suitably selected. CONSTITUTION:When the tendency is produced that an idler 4 is pushed back by means of the driving torque of a sprocket 3 against the force of a spring 14 at the changing-over of a forward/backward movement change-over operating lever 9 to backward movement, a directional change-over valve 34, which is shifted rightward for changing-over by means of a lever 9, leads pressure oil discharged by a hydraulic pressure pump 35 to a large cylindrical chamber 33 in order to push a piston 31 so that grease in a small cylindrical chamber 32 is forcibly supplied to a chamber 12a of a cylinder 12, resulting in shifting the cylinder 12 and a spring retainer 13 rightward against a spring 14. Accordingly, the deflection of the spring 14 is increased and the force of the spring 14 to push the idler 4 is also increased, resulting in increasing the tension of the track 6 and eliminating the slacking of the track. |
