System and adding hydraulic fluid to the balancing line of a jib of a level luffing crane

#The present invention relates to devices for automatic balancing of the jib of a crane with articulated or telescopic arms as a function of the variation in the span of this jib, and more particularly such as an automatic balancing device with hydraulic control.

#French Patent No. 82.19842 (2 536 733) describes an automatic hydraulic balancing device for the jib of a crane in which a hydraulic jack chamber controlling the movement of the auxiliary arm of the jib and a chamber of the hydraulic jack controlling the counterweight balancing beam are connected together in series, while the other chamber of each of the two jacks is selectively connected using a hydraulic distributor either to a hydraulic fluid supply source, or to a hydraulic fluid reservoir. The result is that fluid is transferred into the balancing line between the two jacks, causing automatic balancing of the jib by proportional displacements of the centres of gravity of the auxiliary arm and the counterweight.

#This known device enjoys deserved success, however, it does have the disadvantage that due to leaks that occur in hydraulic circuits, particularly at seals, there may be a lack of synchronisation in the movements of the auxiliary arm and the counterweight balancing beam which can disturb operation of the device.

#Two preferred embodiments are described below as examples that are in no way limitative in order to facilitate understanding of the invention, with reference to the attached diagrammatic drawings in which:

#FIG. 1 is a side view of the jib of a crane with articulated arms and a hydraulic balancing device equipped with a system according to the invention for the automatic addition of fluid, the auxiliary arm being shown in the horizontal position;

#FIG. 2 is a view similar to FIG. 1, but with the auxiliary arm in the pendular position; and

#FIGS. 1 and 2 show the jib of a crane with articulated arms equipped with a hydraulic automatic balancing system as described in French patent published as number 2 536 733. The crane jib comprises a main arm 1 articulated to a turret 2 around a horizontal axis and which is tilted under the control of a jack 3. An auxiliary arm 4 is articulated at the front end of arm 1, and a balancing beam 5 fitted with a counterweight 6 is articulated at its rear end. A double acting hydraulic jack 7 is installed at the front end of the main arm 1 and its rod is attached to the auxiliary arm 4. Similarly, a double acting hydraulic jack 8 is installed at the rear end of the main arm 1, and its rod is attached to the balancing beam 5. The chamber of the jack 7 with an annular section is connected through a pipe 9, called the balancing pipe, to the chamber with an annular section of hydraulic jack 8, while the full section chambers of these two jacks are selectively connected through a hydraulic distributor 10 to a hydraulic fluid supply pump 11 and to a hydraulic fluid reservoir 12.

#As explained in patent No. 2 536 733 mentioned above, if the operator would like to extend the span of the jib starting from the position shown in FIG. 2, he puts the distributor 10 into its right position in the view shown on this figure, such that the full section chamber of the jack 8 is supplied with fluid and, by displacement of the rod of this jack, simultaneously swings the balancing beam 5 with its counterweight 6, and due to the connection between the jacks 7 and 8, lifts the auxiliary arm 4. Since the value of the counterweight is calculated as a function of the self-weight of the elements of the jib and the lever arms, the jib is thus balanced at all times.

#According to the invention, a hydraulic line 13 connects the pump 11 to the balancing pipe 9 through a solenoid valve 14 and a non-return valve 15. The solenoid valve 14 is controlled through a logic controller 16 by mechanical, hydraulic, electric or electronic type detectors 17, 18 installed on the auxiliary arm 4 and on the main arm 1 respectively.