EXTENDIBLE BOOM, PARTICULARLY FOR CRANES

Abstract: A double-acting hydraulic unit (1) for telescopic booms comprises a cylinder (2) and a hollow piston rod (4) with a piston (3) that divides the cylinder into a piston side chamber (5) and a piston rod chamber (7). Two main conduits (10, 11) lead to the cylinder and two main conduits (10', 11') lead away from the piston rod to a co-operating hydraulic unit. Within the piston rod (4), there is a displaceable transmission element (16) that is arranged to actuate a locking device which in an active state engages into a seat (19) in a gable portion (8) to the cylinder (2). When the transmission element (16) is in an inner end position, the locking device (17) is inactive, whereby the piston (3) is freely movable relative to the cylinder. When the piston (3) reaches an outer end position at the same time as the actuation of the transmission element (16) by a carrier of an adjacent hydraulic unit terminates, then the transmission element is displaced axially, a wedge body (21) actuating the locking device (17) so that it engages into the seat (19). In this way the piston rod is locked mechanically and automatically in its outer end position.

Description: EXTE DIBLE BOOM, PARTICULARLY FOR CRANES Technical Field of the Invention The present invention relates to an extendible boom comprising a plurality of telescopical boom sections which are displaceable into and out of each other by means of double- acting hydraulic units, of which each one separately comprises a cylinder and a hollow piston rod with a piston that divides the interior of the cylinder into two chambers, namely a piston side chamber between the piston and a first gable portion of the cylinder and a piston rod chamber between the piston and a second gable portion with a hole through which the piston rod is reciprocally displaceable, two main conduits being arranged between co-operating, adjacent hydraulic units, of which conduits a first one has the purpose of feeding oil or a hydrau¬ lic medium from an inner hydraulic unit to the piston side chamber in the outwardly next unit in order to push the piston rod out of the cylinder of the latter unit, while the other conduit has the purpose of feeding oil to the piston rod chamber in the same cylinder from the inwardly located unit in order to push the piston rod into it. Background of the Invention and Prior Art Extendible booms of the type generally defined above are often included as jib levers in cranes. In this application it is desirable to be able to control the interrelated motions of the separate telescopic boom sections in a predetermined and distinct way, more specifically so that, when the boom should be extended, the innermost movable telescopic boom section is displaced to a fully pushed-out end position, before the pushing-out of the following, outwardly located boom section is initiated, besides which the second innermost boom section is fully pushed out before the pushing-out of the next boom section is initiated, and so forth, till all boom sections in question have been pushed out. Inversely, at a contraction of the boom the individual boom section shall be completely pushed in into each inwardly located boom section before the pushing-in of this one into the next inwardly located boom section is initiated. Among professionals in the field, such an adjustment of the telescopic boom sections is called sequential adjustment. Another strong desire in the crane industry is that the hydrau- lie units that are used for the displacement of the telescopic boom sections into and out of each other shall be able to be hydraulically connected with each other in another way than by means of external hoses, since this type of hydraulic conduits is sensitive to damages by external influence. In order to attain the above-mentioned desires various problem solutions have been suggested, of which two are disc¬ losed in WO 93/08116 and WO 93/10034. In the former publication, a hydraulic unit is described with a non-return valve arranged in the bottom of the cylinder, which valve is opened by the actuation of a stop of an outwardly located cylinder only after the unit having been extended to maximal length. The latter publication describes an arrangement according to which an internal central tube that is fastened in the bottom of the individual cylinder, has the purpose of engaging into the hollo piston rod during most - but not all - of the piston stroke in order to permit the oilflow from an inwardly located hydraulic unit to the next, outwardly located hydraulic unit only after the inwardly located unit having been substantially completely extended to maximal length. However, none of these problem solutions guarantees an absolutely reliable fastening of the piston rods in their fully pushed-out, outer end positions; something that causes an unstable adjustment of the motions of the telescopic boom sections. Objects and Features of the Invention The present invention aims to overcome the above- mentioned disadvantages of the previously known constructions and provide an extendible boom the hydraulic units of which ma be adjusted in a better way than previously. Thus, a primary object of the invention is to create a boom whose hydraulic units for a sequential adjustment of the different telescopic boom sections are of such a nature that they are capable of reliably holding their piston rod in the pushed-out end position as long as the piston rod in each outwardly located hydraulic unit is not pushed into its inner end position. A further object is to achieve this sequential adjustment automatically and in a mechanical way, i.e., without necessitating for instance an electric regulation of valves. A further object of the invention is to realize the problem solution by means of hydraulic units which are hydraulically connected to each other via stationary or stiff conduits. According to the invention, at least the primary object is attained by the features as defined in the characterizing clause of claim 1. Preferred embodiments of the invention are further defined in the dependent claims. Brief Description of the Appended Drawings In the drawings Fig 1 is a schematic longitudinal section through a hydraulic unit included in an extendible boom according to the invention, Fig 2 also shows schematic longitudinal sections through four hydraulic units included in an extendible boom for the adjustment of equally many telescopic boom sections, three units being made in the way shown in figure 1, while an outer unit being of a simpler construction, and the piston rods of all units being shown in a pushed-in, inner end position, Fig 3 shows analogous longitudinal sections of the same hydraulic units as in figure 2, but showing the piston rod of the innermost unit pushed out to an outer end position, Fig 4 is an illustration corresponding to figure 3 showing how the pushing-out of the piston rod of the second innermost hydraulic unit has been started, Fig 5 is an enlarged longitudinal section through a useful, constructive embodiment of the hydraulic unit according to figure 1, only the outer portion of the cylinder being shown and the piston rod and the associated piston being illustrated in the proximity of, although at some distance from an outer end position, ig 6 is a longitudinal section corresponding to figure 5 showing the piston rod fully pushed-out to the outer end position, and Fig 7-9 are enlarged cross-sections A, B and C, respectively, in figure 6. Detailed Description of a Preferred Embodiment of the Invention The description of the invention that follows below is mainly made with reference to figures 1 to 4 which illustrate the invention schematically. The concrete construction example illustrated in figures 5 to 9 will only be dealt with briefly. However, it should be pointed out that analogous components in the two examples have the same reference numerals. In figure 1 reference numeral 1 generally designates a hydraulic unit or a so called hydraulic cylinder which comprise a cylinder 2 as such, a piston 3 and a piston rod 4. The piston 3 divides the interior of cylinder 2 into two chambers, namely piston side chamber 5 between the piston and a first gable portion or bottom 6, and a piston rod chamber 7 between the piston and a second gable portion 8 in which there is a hole 9 through which the piston rod 4 is reciprocally movable. To the piston side chamber 5 leads a first main conduit 10. A second main conduit 11 is connected to the piston rod chamber 7. The piston rod 4 is hollow by comprising a tubular portion 12 that confines a cavity 13. At its free end, piston rod 4 has a head 14. In the area of this head, two further hydraulic conduits designated 10' and 11', respectively, are connected to the piston rod. Reference is now made to figure 2 which illustrates h an extendible boom according to the invention comprises severa further hydraulic units 1', 1" and 1"' beside the unit 1. Although the individual telescopic boom sections, that togethe form an extendible boom, are not shown in the drawings, in practice the first hydraulic unit 1 is mounted on an inner boo section, the head 14 on the piston rod of the unit being connected to the second innermost boom section on which in turn the hydraulic unit 1' is mounted. In turn, the hydraulic unit 1' has the head 14 ' of the piston rod connected with the next tele¬ scopic boom section, and so forth. All the hydraulic units with the exception of the outer unit 1 '" are of the design shown in figure 1. The outer hydraulic unit 1'" is of a simpler construc¬ tion and comprises beside a cylinder merely a simple piston and a simple piston rod. The conduits 10', 11' hydraulically connect the unit 1 with the unit 1' . The conduits 10", 11" connect the unit 1' with the unit 1", and so forth. As may be further seen in figure 2, carriers designated 15 are connected to the free ends of the piston rods to all hydraulic units except the unit 1. Reference is now again made to figure 1. According to the invention, a transmission element 16 is arranged within the hollow piston rod 4, which element co-operates in the region of its inner end with a locking device designated by reference numeral 17 in its entirety, and which at its opposite end may at least indirectly be activated by a carrier 15 of an adjacent hydraulic unit. In the preferred embodiment according to figure 1, the transmission element 16 has the shape of a tube whose interior forms a duct or intermediate conduit 18. The locking device 17 comprises one or several radially movable taps arranged to, when in an active locking state, engage into a seat 19, which in the example is illustrated in the form of a circumscribing groove on the inside of a ring-shaped flange 20 that protrudes from the inside of the gable portion 8. At its inner end, the tube 16 has a wedge body 21 that has an oblique or conical surface arranged to cooperate with a correspondingly oblique surface on the locking tap or taps, more specifically in such a way that each locking tap is radially displaced outwardly when the wedge body 21 is distanced from the piston 3. The wedge body 21 is accommodated in a chamber 22 inside the piston portion. The chamber 22 is sealed relative to the cavity 13 in the piston rod 4 by a gasket 23. The chamber 22 communicates with the piston rod chamber 7 via a constantly open transverse ho] e 24. Further, chamber 22 commur. ' cates with the duct 18 within tube 16 via a second transverse hole 25 in the wall of the tube. In the piston 3 there is a gasket 26 which in a conven¬ tional manner keeps chambers 5 and 7 apart from each other. The piston 3 further comprises a non-return or clack valve which is schematically exemplified in the form of a sphere 27 that is loaded by a spring force, as illustrated in the form of a pressing coil spring 27'. In figure 1 the ball 27 is shown in a closing state in which it impedes communication between the piston side chamber 5 and a duct 28 extending through the piston, which duct leads to the cavity 13 of the piston rod. By means of a schematically shown carrier tap 29, the clack valve may be opened against the force of spring 27', permitting communication between chamber 5 and duct 28. This happens when the piston arrives to its outer end position and the free end of tap 29 gets in contact with the annular flange 20. It should be noted that conduit 10' is connected to an communicates with cavity 13 in the piston rod 4. At its outer end, the tube 16 has on one hand a trans- verse hole 30 in the tube wall, and on the other hand a first auxiliary piston 31. The transverse hole 30 is located in a chamber 32 which on one hand is sealed relative to the cavity 1 by a gasket 33, and on the other hand by a second gasket 34 relative to a space 35 in which the first auxiliary piston 31 i reciprocally movable. The auxiliary piston 31 divides the space 35 into two part-chambers 36, 37. Auxiliary piston 31 is actua¬ ted by a spring force that is schematically illustrated in the form of a pressing coil spring 38, which constantly strives to move the auxiliary piston in a direction outwards, towards the free end of the piston rod. Part-chamber 37 is also delimited b a second auxiliary piston 39 which is reciprocally movable in a course 40 in the piston rod head 14. Part-chamber 37 is filled with a hydraulic medium, preferably in the form of a grease th may be filled up via a nipple 41. As long as the auxiliary piston 39 is kept pressed-in in the position shown in figure 1, a pressure is upheld in the grease mass, which guarantees that the auxiliary piston 31 and the tube 16 are kept in an inner e position against the force of the spring 38. In this state, the locking device 17 is inactive. However, as soon as the second auxiliary piston 39 is allowed to dislocate a sufficient distance out of the appurtenant course, the pressure diminishes in the part-chamber 37 so that the spring 38 manages to move the auxiliary piston 31 and the tube 16 to an outer end position (see figure 4) . In this state, the locking device is actuated by the wedge body 21 being displaced to the right in figure 1 and forces the locking tap or taps to move radially outwardly. In figure 1 reference numeral 42 designates a hole in which suitable means may be placed, for instance bolts, for mechanical fastening of the free end of the piston rod to an adjacent telescopic boom section or its hydraulic unit. Although arbitrary hydraulic media are feasible to being used in the hydraulic system that is created by the different units, in practice usually oil is used. Therefore, only oil is referred to in the description of the function below. Function of the Invention In figure 2, the piston rods of all four hydraulic units 1, 1', 1" and 1"' are shown pushed-in into their inner end positions, which means that the extendible boom is contracted to its minimal length. The two main conduits 10, 11 which are connected to the innermost hydraulic unit 1, are in a non-shown way connected to a pump and a tank via at least a directional valve and preferably also via a load-holding valve. Thus, oil may flow in both directions through each one of the conduits 10, 11 in dependence upon how the associated directional valve is adjusted. When the boom is to be extended by a gradual pushing- out of the telescopic boom sections in question, the directional valve connects the conduit 10 with the pump, while the conduit 11 is kept open relative to the tank. Oil is fed into the piston side chamber 5 and sets the piston 3 into motion towards the outer end position. Thereby, any oil in the piston rod chamber 7 is evacuated to the tank via the conduit 11. The displacement of the piston the whole way from the inner end position to the outer end position is secured by means of the clack valve 27, which during the displacement prevents any communication between the piston side chamber and the duct 28. It should also be noted that the oil in the piston rod chamber 7 is forcibly pressed out into the conduit 11 in spite of the fact that the communication with the conduit 11' is open via the transverse hole 24, the chamber 22, the transverse hole 25, the tube conduit 18, the transverse hole 30 and the chamber 32, because of the fact that the piston rod chambers in all the other hydraulic units 1', 1" and 1'" are filled with oil. When the piston arrives to its oute end position according to figure 3, the locking device 17 is located opposite to the seat 19. At the same time the carrier tap 29 opens the clack valve 27; something that allows communication between the piston side chamber 5 and the duct 28. Therefore, oil may be fed from the chamber 5 into the ring- shaped cavity 13 inside the piston rod and further through the conduit 10' into the piston side chamber in the adjacent hydrau lic unit 1'. Thereby, a displacement is initiated of the piston 3 ' of the latter unit in the direction towards its outer end position, resulting in the piston rod 4' being pushed out of th associated cylinder 2' . This has the consequence that the carrier 15 is distanced from the free end or head 14 of the first piston rod 4 and liberates the auxiliary piston 39 so tha it may move outwardly, out of the appurtenant course. Thereby, the pressure in part-chamber 37 is reduced so that the spring 3 forces the auxiliary piston 31 and the tube 16 to move towards an outer end position. When this happens, wedge body 21 actuat the locking device 17 so that the locking taps of said device engage with the seat 19. In other words, the device 17 locks t piston 3 mechanically in its outer end position. The above described operations are repeated as soon a a piston rod in an outwardly located hydraulic unit reaches it outer end position. Also when the piston rod in the outermost, more simply designed unit 1"' reaches its outer end position, t carrier 15 is distanced from the free end of the piston rod in the adjacent hydraulic unit, involving that the latter piston rod is locked in its outer end position. When the telescopic boom sections are to be pushed into each other again in order to shorten the boom, the system works in the inverted way. The conduit 11 is connected to the pump by the directional valve, while the conduit 10 is connected to the tank. However, when oil is fed to the piston rod chamber 7 in the innermost hydraulic unit 1, not only the piston 3 in this unit is locked in its outer end position, but so are also the corresponding pistons 3' and 3" in the units 1' and 1". Only the piston 3'" in the outermost unit 1"' is freely movable. However, the oil from the conduit 11 may be fed via the previously men¬ tioned flow path (transverse hole 24, chamber 22, transverse hole 25, tube duct 18, transverse hole 30 and chamber 32) to the conduit 11' and further through the hydraulic units 1', 1" and the conduits 11" and 11"' to the piston rod chamber of the unit 1"'. In this way the piston 3'" is displaced from its outer end position to its inner end position. Since the clack valves in all mechanically locked pistons are open, the oil in the piston side chamber of the unit 1'" may be evacuated via the conduits 10'", 10" and 10 to the tank. As soon as the piston 3'" reaches its inner end position, the associated carrier 15 urges the auxiliary piston 39 into the associated course in the piston rod head of the adjacent hydraulic unit. This has the consequence that the tube serving as a transmission element brings the wedge body 21 to the left in the figure, whereby the locking device 17 is inactivated. Thus, the piston 3" becomes free to move in the direction towards its inner end position. These operations are repeated till all piston rods in the four hydraulic units have been pushed into their inner end positions, whereby the boom has been retracted to its minimal length. The advantages of the invention are many. By the fact that each controlled hydraulic unit mechanically locks the associated piston rod in a fully pushed-out state as soon as the pushing-out of the ; iston rod in the outwardly adjacent hydraulic unit is smarted, a distinct and reliable sequential adjustment of the different telescopic boom sections is attained independently of whether the boom is extended or contracted. By the fact that the piston rod head of the individual hydraulic unit slavishly follows the cylinder of the adjacent hydraulic unit, stiff or stationary hydraulic conduits may be arranged between co-operating units, for instance in the form of tubes. Here it should be particularly observed that the two conduits between adjacent units are connected to on one hand only one piston rod head and on the other hand to only one cylinder. Furthermore, the invention makes it possible to connect an unlimited number of cylinders with each other for the adjustment of an arbitrary number of telescopic boom sections. As to the practical embodiment shown in figures 5 to 9, it should be briefly mentioned that the clack valve 27 in this case is opened by an auxiliary piston 43 that is provided in a chamber filled with a hydraulic medium in the form of grease. When the main piston 3 arrives to its outer end position, the pressure in the grease is increased so that the piston 43 is se in motion and distances the valve ball from its associated seat As may be particularly seen in figure 7, the locking device 17 comprises three peripherically equidistantly separa¬ ted, radially movable locking taps. It should also be noted tha the auxiliary piston 39 which is actuatable by a carrier 15 of an adjacent hydraulic unit and has the purpose of setting in motion the tube 16 that serves as a transmission element, in this case is placed at a certain distance from the part-chamber 37 in which the auxiliary piston 31 is movable. In this context it should be pointed out that the positioning of the auxiliary piston 39 is not critical. On the contrary, it may be placed f distant from the piston rod head as such and be connected with the part-chamber 37 via a suitable conduit. It should also be noted that auxiliary piston 31 is not connected to any spring (cf. spring 38 in figure 1), but instead influenced by the internal oil pressure in the piston rod 11 which is always striving at pushing the auxiliary piston towards the outer end position. Feasible Modifications of the Invention The invention is not restricted only to the embodiments as described and shown in the drawings. Thus, it is feasible to provide a separate transmission element within the hollow piston rod, for adjusting the locking device, although the tube serving as an intermediate conduit advantageously is used as a trans¬ mission element. Opening and closing of the clack valve in the main piston of the cylinder may be effected in another way than by means of the schematically shown spring 27' and auxiliary piston 43. Moreover, the concrete design of the locking device 17 per se may be varied within wide limits.

Claims: CLAIMS. 1. Extendible boom, particularly for cranes, comprising a plurality of telescopical boom sections which are displaceable into and out of each other by means of double-acting hydraulic units (1) , of which each one separately comprises a cylinder (2) and a hollow piston rod (4) with a piston (3) that divides the interior of the cylinder into two chambers (5, 7) , namely a piston side chamber (5) between the piston and a first gable portion (6) of the cylinder and a piston rod chamber (7) betwee the piston and a second gable portion (8) with a hole (9) through which the piston rod (4) is reciprocally displaceable, two main conduits (10', 11'; 10", 11") being arranged between co-operating, adjacent hydraulic units (1, 1'; 1', 1"), of whic conduits a first one (10', 10") has the purpose of feeding oil or a hydraulic medium from an inner hydraulic unit (1, 1') to the piston side chamber (5) in the outwardly next unit in order to push the piston rod (4) out of the cylinder of the latter unit (2), while the other conduit (11', 11") has the purpose of feeding oil to the piston rod chamber (7) in the same cylinder from the inner unit (1, 1') in order to push the piston rod int it, c h a r a c t e r i z e d in that a displaceable trans¬ mission element (16) is placed within the hollow piston rod (4) which element is, in the region of one of its ends, arranged to actuate a locking device (17) which in an active state has the purpose of locking the piston (3) and the piston rod (4) in an axially stationary state relative to the cylinder (2) when the piston rod (4) is maximally pushed out of the cylinder, and which in an inactive state permits a displacement of the pisto rod relative to the cylinder, and which transmission element (16) is, in the region of its opposite end, at least indirectl actuatable by a carrier (15) which slavishly follows the move¬ ments of the piston rod (4) of the next outwardly located hydraulic unit (l 1 , 1"), more specifically in such a way that the carrier (15) keeps the locking device (17) in the inactive state via the transmission element (16) as long as the latter piston rod is in its fully pushed-in end position, but permits the locking device (17) to become actuated as soon as the piston rod leaves this pushed-in end position. 2 . Boom according to claim 1 , c h a r a c t e r i z e d in that the locking device comprises at least one tap (17) that is radially movable relative to the piston (3) and arranged to engage in a locking position into a seat (19) in the other gable portion (8) of the cylinder (2) , more specifically by axial displacement of the transmission element (16) in a direction away from the piston (3) , a wedge body (21) setting the tap in radial motion. 3. Boom according to claim 1 or 2, c h a r a c t e r i z e d in that the transmission element consists of a tube (16) that serves as a first intermediate conduit for the feeding of oil between the piston rod chambers (7) of the two co-operating hydraulic units, a ring-shaped cavity (13) between the outside of the tube (16) and a tubular portion (12) of the piston rod (4) serving as a second intermediate conduit for the feeding of oil between the piston side chambers (5) of the units. 4. Boom according to any one of the preceding claims, c h a r a c t e r i z e d in that, at its end that is distanced from the main piston (3) of the hydraulic unit, the transmission element (16) is connected to a first auxiliary piston (31) which confines one end of a chamber (37) filled with a hydraulic medium, for instance grease, which chamber is provided within a head (14) on the free end of the piston rod, and whose opposite end is confined by or is connected to a second auxiliary piston (39) that is movable into and out of a course (40) by direct or indirect actuation by said carrier, and in that the first auxi¬ liary piston (31) is actuated by a spring force that constantly strives to distance the transmission element (16) from the main piston (3) in order to actuate the locking device (17) and against the action of which the first auxiliary piston (31) is movable in the opposite directior when the second auxiliary piston (39) is pressed into the associated course for inactivation of the locking device (17) . 5. Boom according to any one of the preceding claims, c h a r a c t e r i z e d in that a clack valve (27) is arranged in the main piston (3) , which valve prevents communi¬ cation between the piston side chamber (5) and the other inter¬ mediate conduit (13) as long as the piston rod (4) is distanced from its outer, fully pushed-out end position, but which is opened mechanically and automatically as soon as the piston reaches said end position.

Inventors: ANDERSSON LARS, ANDERSSON, LARS
Applicants: ANDERSSON LARS, HIAB AB, ANDERSSON, LARS
Application year: 1996
Main classification: B66C23
IPC codes: B66C23, F15B11