| 摘要 |
<p>PROBLEM TO BE SOLVED: To dispense with selective change of setting of a control mode selector valve mechanism 14 for each of boom extending/retracting hydraulic cylinder 7-1, 7-2 when a hook suspension length holding device, which maintains a fixed suspension length of a hook 4 in an extending/retracting action of a multistage boom 3 by synchronously operating extending/retracting of the boom extending/ retracting hydraulic cylinders 7-1, 7-2 and lowering/hoisting of a winch hydraulic motor 8 with control oil in a boom extending/retracting selector valve 9, is used for a crane sequentially extended/retracted by means of a plurality of boom extending/retracting hydraulic cylinders 7-1, 7-2 varied in an extension/ retraction amount of the multistage boom 3 to a unit supply oil amount. SOLUTION: The winch hydraulic motor 8 hoisting/lowering a winch 5 is constructed of a variable displacement hydraulic motor, and for each of the boom extending/retracting hydraulic cylinders 7-1, 7-2, displacement of the winch driving hydraulic motor 8 is changed, so that necessity for selective change of setting of the control mode control valve mechanism 14 is dispensable.</p> |
