| 摘要 |
A hydraulic crane with increased maximum lifting power in the high-position range, i.e. when the first boom section of the crane is located above the horizontal plane, comprises a position-detecting means (8) for detecting the position of the first boom section (2), and a load-sensing means (25) for sensing the load on the crane. Further, the crane has a relief valve (21) which is arranged on the lifting side of a piston and cylinder unit (5) for operating the first boom section (2) and which opens when the load on the crane exceeds a predetermined value. When the position-detecting means (8) detects that the crane is located within the high-position range and the load on the crane sensed by the load-sensing means (25) exceeds a predetermined value, the function of the relief valve is disconnected, e.g. by means of a valve (24). This makes it possible to guarantee the load carrying performance in the high-position range and permit an increased load resulting in an increased maximum lifting power. To avoid overload of the crane when the relief valve is disconnected, the maximum permissible speed for operating the first boom section is reduced, so that the dynamic forces become insignificant. |
