Abstract:
A hydraulically actuatable jib for a loading crane includes at least two jib extensions, the first jib extension being designed as an outer jib extension and the second jib extension being designed as an inner jib extension. At least two feed cylinders extend and react the at least two jib extensions. A hydraulic circuit for a working fluid includes a retraction line for retracting the feed cylinders in a pressurized manner, and the retraction line opens into the feed cylinder of the outer jib extension. A tank is provided for releasing the working fluid, and a control valve can be switched into an open position when the outer jib extension reaches a defined retraction position, particularly when the outer jib extension is substantially fully retracted. The valve thereby supplies the feed cylinder of the inner jib extension with pressurized working fluid.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The object of the invention is to provide an improved hydraulically actuable jib for a loading crane. 
     2. Description of Related Art 
     Hydraulically actuable jibs for loading cranes are already known in large numbers from the state of the art. Thus, for example, EP 0 566 720 B1 of Nov. 10, 1992, discloses a multi-stage telescopic jib, in particular for a loading crane on a truck, wherein a respective hydraulic unit having a piston and a cylinder is arranged between successive telescopic arms arranged one within the other, wherein, at least in regard to the cylinder of the innermost arm, a tube projects from the cylinder end axially into the cylinder chamber, the tube, when the piston is at least partially retracted, extending into the hollow piston rod in sealed relationship with the piston, and thus sealing off the cylinder chamber with respect to the internal chamber in the hollow piston rod, wherein the internal chamber in each hollow piston rod is connected to the cylinder chamber of the next inner hydraulic unit by way of a preferably rigid line, and the internal chamber in each hollow piston rod communicates with the cylinder chamber of the same hydraulic unit when the piston is fully extended. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention concerns a hydraulically actuable jib for a loading crane, comprising:
         at least two jib extensions, wherein a first one of the one jib extensions is in the form of an outer jib extension and a second one of the jib extensions is in the form of an inner jib extension, and   at least two thrust cylinders for extension and retraction of the at least two jib extensions,   a hydraulic circuit for a working medium—in particular oil—comprising a retraction line for pressure-actuated retraction of the thrust cylinders, wherein the retraction line opens into the thrust cylinder of the outer jib extension, and   a tank for delivery of the working medium, and   a switching valve which is switchable into an open position by the attainment of a defined retraction position of the outer jib extension—in particular when the outer jib extension is substantially fully retracted—and thereby feeds the thrust cylinder of the inner jib extension with pressurized working medium.       

     The invention further concerns a loading crane comprising a hydraulically actuable jib and in addition a vehicle comprising such a loading crane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Details and advantages of the present invention are described more fully hereinafter by means of a specific description with reference to the embodiments by way of example illustrated in the drawings in which: 
         FIG. 1  shows a side view of a loading crane with hydraulically actuable jibs and jib extensions; 
         FIG. 2  shows a diagrammatic view of two thrust cylinders wherein one thrust cylinder is provided for an outer jib extension and one for an inner jib extension, both thrust cylinders being in the retracted condition; 
         FIG. 3  shows a diagrammatic view of two thrust cylinders, wherein one thrust cylinder is completely extended and one thrust cylinder is retracted; 
         FIG. 4  shows a diagrammatic view of four thrust cylinders with a thrust cylinder for an outermost jib extension and three thrust cylinders for three inner jib extensions; 
         FIG. 5  shows a section through a detail view of a thrust cylinder; and 
         FIG. 6  shows a vehicle with a loading crane having a jib with jib extensions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention concerns a loading crane comprising a hydraulically actuable jib. Such a hydraulically actuable jib can be advantageously used specifically in relation to loading cranes. 
     A vehicle may comprise such a loading crane. Such loading cranes with hydraulically actuable jibs can advantageously be used specifically on vehicles. 
     In the invention, the fact that the working medium of the retraction line between the tank and the inlet opening at the thrust cylinder of the outer jib extension does not communicate with the thrust cylinder of the inner jib extension in any position of the thrust cylinder of the inner jib extension as long as the outer jib extension has not reached its retraction position provides a retraction line which is independent of the thrust cylinder of the inner jib extension, whereby the thrust cylinder of the outer jib extension can be pressurized directly with the working medium—even when the thrust cylinder of the inner jib extension is fully extended. 
     That retraction line makes it possible to feed oil at the retraction side to the outer thrust cylinder—that is to say the thrust cylinder which is furthest away from the crane mast—when it is not yet fully retracted, until it is entirely retracted. In that condition the switching valve is actuated—that is to say opened—to the inner thrust cylinder—this therefore being the thrust cylinder which is next rearwardly and which is disposed closer to the crane mast, whereby oil is no longer fed to the outer thrust cylinder as it is already fully retracted. The oil flows by way of the control valve into the inner thrust cylinder and causes it to retract. 
     This therefore provides a sequential control whereby one thrust cylinder after the other is retracted and in that situation the retraction line opens directly into the outer thrust cylinder. In this respect, it should be pointed out that “inner thrust cylinder” means the thrust cylinder of the inner jib extension and “outer thrust cylinder” means the thrust cylinder of the outer jib extension, those expressions being known to one skilled in the art as customary abbreviations. 
     In the normal case, in that respect, the outer jib extension is that of a smaller diameter and the inner jib extension is that of a larger diameter, but naturally this could also be reversed—with respect to the outer and inner jib extension and/or the smaller and larger diameter. 
     Further advantageous configurations of the invention are defined in the appendant claims. 
     It has proven to be particularly advantageous if the retraction line passes through at least the thrust cylinder of the inner jib extension without the working medium in the retraction line communicating with the thrust cylinder during the passage therethrough. It is possible to achieve an extremely compact structure by virtue of passing the retraction line through the thrust cylinder of the inner jib extension. 
     In a preferred embodiment it can be provided that the retraction line is adapted to be telescopic in the interior of the thrust cylinder of the inner jib extension. A telescopic configuration for the retraction line makes it possible to adapt the length of the retraction line to the effective length of the thrust cylinder, that is to say the telescopic retraction line can move together with the thrust cylinder. 
     It can further preferably be provided that the retraction line has at least two internested tubes which are adapted to be telescopically moveable relative to each other. A telescopic configuration can particularly preferably be produced by two internested tubes. 
     It has proven to be particularly advantageous if a seal is provided between the two internested tubes. The provision of a seal means that it is possible to provide that the working medium which passes within the internested tubes cannot escape therefrom and flow into the internal space in the thrust cylinder. 
     It can particularly preferably be provided that the thrust cylinder of the inner jib extension has at least one cylinder, at least one piston and at least one piston rod wherein one of the two tubes is provided stationarily in the cylinder of the thrust cylinder and the second tube is provided stationarily in the piston rod of the thrust cylinder. The stationary provision of the two tubes in the thrust cylinder can ensure that both tubes are moved uniformly together with the thrust cylinder. 
     In that respect, it has proven to be particularly advantageous if the outer one of the two tubes has an opening in a peripheral surface of the tube, the opening being provided at an end region of the tube. The provision of an opening at an end region of the tube can provide that, when the tubes are substantially fully retracted, the working medium can pass from the cylinder into the piston rod by way of the opening. It will be appreciated that it could equally also be envisaged that this functionality can be implemented in a different way, for example by a check valve opening in the one of the substantially fully extended tubes, whereby the working medium could pass from the cylinder into the piston rod. 
     In a preferred embodiment, it can be provided that the piston has at least one extension passage, the extension passage extending from a cylinder chamber into a piston rod chamber. The working medium can flow from the cylinder chamber into the piston rod chamber by way of an extension passage in the piston. 
     It has further proven to be advantageous if the piston has at least one retraction passage, the retraction passage extending from the cylinder chamber into the piston rod chamber, a check valve being provided in the retraction passage. A retraction passage in the piston can provide that the working medium can flow from the piston rod chamber into the cylinder chamber during retraction. 
     It has been found to be advantageous if the piston rod has at least one piston rod passage, the piston rod passage extending from an end region of the piston rod towards the other end region of the piston rod, the switching valve being arranged at the one end region and a chamber surrounding the piston rod being provided at the other end region, the chamber which surrounds the piston rod being provided in the cylinder of the thrust cylinder. The implementation of a piston rod passage can provide that the pressurized working medium can flow into the chamber surrounding the piston rod and thereby retract the thrust cylinder. 
     Preferably, it can further be provided that at least one check valve is provided on the piston rod passage. The provision of a check valve on the piston rod passage means that, upon extension of the thrust cylinder, the working medium which is in the chamber surrounding the piston rod can escape therefrom and can flow away by way of the check valve—by means of passing through the piston rod passage. 
     In a possible embodiment, it can be provided that the switching valve is in the form of a directional control valve—preferably a 2/2-way valve. 
     In a preferred embodiment, it can be provided that the switching valve is adapted to be mechanically actuable. That can contribute to an inexpensive variant of a switching valve. 
     In that respect, it is particularly preferably provided that the jib has at least one—preferably at least two—further inner jib extension(s) with a thrust cylinder or cylinders, wherein the working medium of the retraction line between the tank and the inlet opening at the thrust cylinder of the outermost jib extension does not communicate with the thrust cylinders of the inner jib extensions in any position of the thrust cylinders of the inner jib extensions as long as the outermost jib extension has not reached its retraction position. The use of a plurality of inner jib extensions and associated thrust cylinders can contribute to enhancing the reach of the jib. 
       FIG. 1  shows a loading crane  101  with a crane mast  102 , a first jib  103  and a second jib  100 . The hydraulically actuable jib  100  has a plurality of jib extensions  1 ,  2 ,  3  and  4 . The jib extensions  1 ,  2 ,  3  and  4  are extended and retracted with associated thrust cylinders  11 ,  21 ,  31  and  41 , respectively. 
     In this preferred embodiment, the loading crane  101  has a further third jib  104  which has jib extensions which are also telescopic and hydraulically actuable. 
     Preferably, such loading cranes  101  are mounted on vehicles. However, they are also used in stationary situations. 
       FIG. 2  shows a diagrammatic view of two thrust cylinders  21  and  11  for two jib extensions (not shown), an outer jib extension  1  and an inner jib extension  2 . In this respect, the thrust cylinder  11  is arranged at the outer jib extension  1  and the thrust cylinder  21  is arranged at the inner jib extension  2 . Both thrust cylinders  11  and  21  are completely retracted in  FIG. 2 . 
     Extension Process: 
     For extension purposes, the extension line  7  or the working medium  5  (not shown) therein is subjected to pressure. The extension line  7  opens into the cylinder chamber  261  of the cylinder  26 . By virtue of pressurization, the working medium  5  is propagated in the cylinder  26  or its cylinder chamber  21  and, in that case, displaces the piston  27  and therewith also the piston rod  28 , so the piston rod  28  extends. Hitherto, the working medium  5  was only able to propagate in the cylinder chamber  261 , whereby it is exclusively the thrust cylinder  21  that is extended, and not the thrust cylinder  11 . 
     In this preferred embodiment, the piston rod  28  has at least one piston rod passage  282 , the piston rod passage  282  extending from one end region of the piston rod  28  towards the other end region of the piston rod  28 , the switching valve  22  being arranged at the one end region and a chamber  262  which surrounds the piston rod  28  being provided at the other end region, wherein the chamber  262  which surrounds the piston rod  28  is provided in the cylinder  26  of the thrust cylinder  21 . 
     So that the piston rod  28  can extend, the working medium  5  (not shown) which is in the chamber  262  surrounding the piston rod  28  must escape. For that purpose, the working medium  5  can flow out of the thrust cylinder  21  from the chamber  262  surrounding the piston rod  28  by way of the piston rod passage  282  and the check valve  283 . The working medium  5  can then flow back into a tank  50  by way of the two telescopic tubes  23  and  24 . 
     In this preferred embodiment, the telescopic tubes  23  and  24  are provided in the interior of the thrust cylinder  21 , whereby it is possible to achieve a very compact thrust cylinder  21 . 
     After the piston rod  28  is substantially completely extended there is an opening between the cylinder chamber  261  and the piston rod chamber  281 . Those two chambers  261  and  281  are connected together by way of the extension passage  271  which is now open. Opening of the extension passage  271  was made possible by an opening  29  provided in the peripheral surface of the tube  23 , the opening  29  being at an end region of the tube  23 . With this preferred embodiment, the opening  29  is in the form of a through aperture in the peripheral surface of the tube  23 . Working medium  5  can now flow through the opening  29  and the extension passage  27  from the cylinder chamber  261  into the piston rod chamber  281  and from there further by way of the extension line  7  to the cylinder chamber  161  of the cylinder  16  of the thrust cylinder  11 . The pressurized working medium  5  is now propagated in the cylinder chamber  161  of the thrust cylinder  11  whereby the piston  17  and the piston rod  18  are extended. 
     The working medium  5  in the chamber  162  surrounding the piston rod  18  can flow away by way of the retraction line  6  in this extension process. In addition, as is usual, the working  1  medium  5  flows back into the tank  50  by way of the two tubes  24  and  23 . As already mentioned, that is in turn preferably effected through the thrust cylinder  21 , without the working medium  5  communicating with the thrust cylinder  21  while passing therethrough. 
     Retraction Process: 
     For the retraction process, the retraction line  6  is put under pressure. The working medium  5  (not shown) in the retraction line  6  occurs directly at the inlet opening  12  of the thrust cylinder  11  of the outer jib extension  1  (not shown). In that case, the retraction line  6  passes transversely through the thrust cylinder  21 , through two telescopic tubes  23  and  24 . The two tubes  23  and  24  are connected together by way of a seal  25 , whereby no working medium can issue from the two tubes  23  and  24  towards the chambers  261  and  281  of the thrust cylinder  21 , that surround those tubes  23  and  24 . Due to pressurization in the retraction line  6 , the working medium  5  is propagated in the chamber  262  surrounding the piston rod  18 , whereby the piston rod  18  and the piston  17  are retracted (as shown in  FIG. 3 ). 
     As soon as the thrust cylinder  11  is completely retracted, the switching valve  22  at the thrust cylinder  21  is preferably mechanically actuated by way of a lever  51 , whereby the feed flow to the piston rod passage  282  is switched into the enabled condition for the working medium  5  of the retraction line  6 . Opening of the switching valve could equally also be effected in any other conceivable fashion like, for example, electrically. 
     Now the working medium  5  in the retraction line  6  can flow by way of the control valve  22  and the piston rod passage  282  into the chamber surrounding the piston rod  28  and can be propagated therein, whereby the piston  27  and the piston rod  28  are retracted. 
     Because the two tubes  23  and  24  are telescopic, they are retracted at the same time with the piston  27  and the piston rod  28  (and likewise also extended in the extension process). 
     The working medium  5 , which is not under pressure in the cylinder chamber  261 , is urged out of the cylinder  26  in that retraction movement and can flow away by way of the extension line  7 . 
     If a plurality of thrust cylinders  21  of that kind are connected in succession (see  FIG. 4 ), then the working medium  5 , which is flowing away in the extension line  7 , can respectively flow away through the successively connected thrust cylinders  21 , through the piston rod chamber  281 , then through the extension passage  271  and then through the opening  29  in the tube  23  and through the cylinder chamber  261 . 
     If the opening  29  of the tube  23  should already be closed again, as, for example, the piston  27  and the piston rod  28  are already retracted a distance and thus close the opening  29 , the working medium  5  can nonetheless escape through that thrust cylinder  21  as the piston  27  has the retraction passage  272  which has a check valve  273 . Thus, when the piston  27  or the piston rod  28  is partially or entirely retracted, oil  5  can flow out of the retraction line  7  by way of the piston rod  281 , the check valve  273  of the retraction passage  272 , and further by way of the cylinder chamber  261  through the thrust cylinder  21 . 
     Such a configuration for a sequential control makes it possible to achieve both sequential extension of the thrust cylinders  21  and  11  and also sequential retraction of the thrust cylinders  11  and  21 . 
     It is only when the thrust cylinder  21  is substantially completely extended that the working medium  5  is enabled for the thrust cylinder  11 , and it is only then that the thrust cylinder  11  can be extended. 
     Equally, the thrust cylinder  21  can only be retracted when the thrust cylinder  11  is substantially completely retracted and in that case, the control valve  22  of the thrust cylinder  21  switches open, whereby it is only the thrust cylinder  21  that can retract. 
       FIG. 4  shows a diagrammatic view of a hydraulically actuable jib  100  (see  FIG. 1 ) for a load crane  101  (see  FIG. 1 ). In this preferred embodiment, the hydraulically actuable jib  100  has four jib extensions  1 ,  2 ,  3  and  4  (see  FIG. 1 ), wherein one jib extension is in the form of an outermost jib extension  1  and the other three jib extensions  2 ,  3  and  4  are in the form of inner jib extensions  2 ,  3  and  4 . The jib extensions  1 ,  2 ,  3  and  4  each have at least one thrust cylinder  11 ,  21 ,  31  and  41  with which the jib extensions  1 ,  2 ,  3  and  4  can be retracted and extended. In this arrangement, the hydraulically actuable jib  100  has a hydraulic circuit for a working medium  5 —in this preferred embodiment, the working medium being oil—with a retraction line  6  for pressurized retraction of the thrust cylinders  11 ,  21 ,  31  and  41 , the retraction line  6  opening into the thrust cylinder  11  of the outermost jib extension  1 . The jib  100  further has an extension line  7  for pressurized extension of the thrust cylinders  11 ,  21 ,  31  and  41 . The thrust cylinders  21 ,  31  and  41  each have a switching valve  22 ,  32  and  42  which, by the attainment of a defined retraction position of the next outwardly disposed jib extension or its thrust cylinder  11 ,  21  and  31 —in particular when the outer jib extension  1 ,  2  and  3  or the thrust cylinders  11 ,  21  and  31  thereof are substantially completely retracted—can be switched into the open position and thereby can feed pressurized working medium  5  to the next inner thrust cylinders  21 ,  31  and  41 , respectively, of the inner jib extensions  2 ,  3  and  4 . In that case, the working medium  5  of the retraction line  6  between a tank (not shown) and the inlet opening  12  at the thrust cylinder  11  of the outermost jib extension  1  does not communicate with the thrust cylinders  21 ,  31  and  41  of the inner jib extensions  2 ,  3  and  4  in any position of the thrust cylinders  21 ,  31  and  41  of the inner jib extensions  2 ,  3  and  4 , as long as the outermost jib extension  1  or the thrust cylinder  11  has not reached its retraction position. 
     In this preferred embodiment, the retraction line  6  passes through all thrust cylinders  21 ,  31  and  41  of the inner jib extensions  2 ,  3  and  4  without the working medium  5  in the retraction line  6  communicating with the thrust cylinders  21 ,  31  and  41 , during the passage therethrough. 
     In that case, the retraction line  6  is of a telescopic configuration in the interior of the thrust cylinders  21 ,  31 ,  41 , by involving two internested tubes  23 ,  24  and  33 ,  34  and  43 ,  44 , respectively, which are telescopically moveable relative to each other. 
     In that arrangement, the tubes  23 ,  33  and  43  are respectively provided stationarily in the cylinders of the associated thrust cylinders  21 ,  31  and  41 , and the second tubes  24 ,  34  and  44  are respectively provided stationarily in the associated piston rods of the associated thrust cylinders  21 ,  31  and  41 . 
     In this preferred embodiment, the outer tubes  23 ,  33  and  43  respectively have openings  29 ,  39  and  49  in peripheral surfaces of the associated tubes, those openings  29 ,  39  and  49  being formed at end regions of the tubes  23 ,  33  and  43 , respectively. 
     In this preferred embodiment, the switching valves  22 ,  32  and  42  are in the form of 2/2-way valves and are actuated mechanically by way of the levers  51 ,  52  and  53 . 
     The extension and retraction movement of those four illustrated thrust cylinders  11 ,  21 ,  31  and  41  functions in substance in the same way as depicted in the specific description relating to  FIGS. 2 and 3 . 
     Both extension and also retraction are effected sequentially, that is to say there is only ever one thrust cylinder  11 ,  21 ,  31  or  41  that extends or retracts. For that purpose, the working medium  5  is only ever enabled for operation for the next outwardly disposed thrust cylinder  31 ,  21  and  11  or for the next inwardly disposed thrust cylinder  21 ,  31  and  41 , after substantially complete extension or retraction, respectively. 
       FIG. 5  shows a detail view of a section through a thrust cylinder  21  in a position as shown in  FIG. 3  when it is substantially fully extended. 
     The two telescopic tubes  23  and  24  extend in the interior of the thrust cylinder  21 . In that case, those two tubes  23  and  24  also extend transversely through the cylinder  26 , the piston  27  and the piston rod  28 . The telescopic line  6  which is arranged in the thrust cylinder  21  and which consists of the two tubes  23  and  24  makes it possible for the oil  5  required for retraction to be passed through the thrust cylinder  21  (and  31  and  41  as shown in  FIG. 4 ) forwardly to the thrust cylinder  11 , wherein, in this preferred embodiment, the rear larger tube  23  is connected to the cylinder  26  and the smaller tube  24  is connected to the piston rod  28 , the smaller tube  24  projecting into the larger tube  23  and being guided sealingly therein. The line  6  makes it possible to feed oil at the retraction side to the foremost thrust cylinder  11  which is not yet retracted (see  FIG. 3 ), until it is entirely retracted. In that condition, the control valve  22  (see  FIG. 3 ) is actuated (opened) to the next successive thrust cylinder  21 . Thereupon, the thrust cylinder  21  can retract. The process is implemented in succession until all thrust cylinders  21 ,  31 ,  41  (see  FIG. 4 ) are completely retracted. 
     This kind of control has the advantage over the previous kind that the control sequence is not at any moment determined by shutting off the return flow of oil, but always by controlled oil feed. The return oil flow is always free, both upon retraction and also upon extension. 
     The larger rearwardly disposed tube  23  is guided sealingly in the piston  27  and at the front end, after the seal or guide means, has an extension with radially arranged openings  29  which enable the flow of the piston-side oil through the piston  27  and the piston rod  28  forwardly in the extended condition. 
     In this arrangement, the piston  27  has a check valve ( 273 ) (see  FIG. 3 ), which possibly opens when the piston  27  is slightly retracted, upon pressurization by the return oil flow, from the piston rod side, and enables the through-flow rearwardly. 
       FIG. 6  shows a vehicle  200  with a loading crane  101  mounted thereon, having a hydraulically actuable jib  100  with jib extensions.