| 摘要 |
Device for maintaining a tool attachment in a knuckle boom crane, preferably for forest machines, on a constant level above the ground. The knuckle boom comprises a main boom which can be raised and lowered by means of a double-acting hydraulic cylinder (4), and an outer boom pivotal relative to the main boom by means of a likewise double-acting hydraulic cylinder (6). To ensure the vertical adjustment of the tool attachment, the lift cylinder (4) is connectible to the outer boom cylinder (6) via a compensator (21) in such a manner that an amount of hydraulic fluid which is proportional to the amount of hydraulic fluid which upon activation of the outer boom is pressed out from the lifting or the lowering side, respectively, of one of the cylinders (4, 6), is pressed into the lowering or the lifting side, respectively, of the other cylinder. The compensator comprises at least one hydraulic cylinder (22) having two chambers (23, 26) which are separated by a piston (31) movable in the cylinder and having two different working areas or displacements (24, 25) in the two chambers (23, 26). The lift cylinder (4) is connectible to one chamber (26) and the outer boom cylinder to the other chamber (23). |
