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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hydraulic piston-cylinder-unit for a slewing drive, especially to swing working tools, with at least one piston, which can be slid in a cylinder and exhibits fastening means, by means of which the piston can be connected in such a manner to a coupling rod that the working tool can be swung by means of a movement of the piston. 
     2. Description of the Related Art 
     Hydraulic piston-cylinder-units are widely used to drive working tools, especially to swing backhoe and face shovels of dredgers. The DE-U-94 07 859 discloses a hydraulically driven dredging shovel, which can be arranged so as to swing on a carrier, arranged on the front end of the boom of a dredger. The swinging motion of the shovel is induced by means of a piston-cylinder-unit, which is arranged in a carrier, located in the upper rim area of the shovel. The carrier is connected to a coupling rod, with which the piston-cylinder-unit engages. The carrier is preferably shaped tubularly and contains the cylinder of the piston-cylinder-unit. Furthermore, the DE-U-296 21 253 discloses a slewing adapter to swing a tool, such as a dredging shovel, wherein the piston-cylinder-unit is envisaged in a coupling mechanism, which can be swung relative to the carrier of the construction machine. In this case, too, the piston-cylinder-unit is located preferably in a tubular carrier. 
     The end areas of the coupling rod are connected to the carrier of the construction machine and to the piston-cylinder-unit so as to swing. The connection to the piston-cylinder-unit is accomplished usually by means of an extension piece, which is mounted on the piston and which projects beyond the carrier, containing the piston-cylinder-unit. 
     Such an arrangement has the disadvantage that the extension piece cannot be mounted in principle until after the piston-cylinder-unit has been slid into the carrier. The result is a relatively low degree of prefabrication of the slewing drive, since the extension piece cannot be attached to the piston rod before the cylinder has been installed in a carrier. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to improve a piston-cylinder-unit for a slewing drive to the extent that it is easier to mount. 
     This problem is largely solved by a piston-cylinder-unit of the aforementioned kind in that the cylinder exhibits fastening means, by means of which the cylinder can be connected to the working tool or to a carrier of the slewing drive. The advantage herein lies in the fact that the extension piece can be mounted, for example, by screwing or welding before the piston-cylinder-unit is attached. The reason for this lies in the fact that, according to the invention, the cylinder of the piston-cylinder-unit is not slid into a carrier, but rather it itself functions as the carrier of the piston-cylinder-unit. This goal is reached in that the cylinder exhibits fastening means, by means of which it can be attached to the working tool or also to the carrier of the slewing drive. 
     Thus, it is no longer necessary to slide the cylinder into a carrier; and correspondingly it is possible to prefabricate the piston with extension pieces. 
     Furthermore, there are cost advantages in production, since the piston rod can be produced, according to the invention, as one piece with the welded extension piece. In addition it is possible to make the effective lengths smaller than in prior art slewing drives, since the narrower design of the welded extension piece makes it possible to use a correspondingly narrower cylinder. Another important advantage is the faster assembly and disassembly or the easy replacement of the piston-cylinder-unit. 
     A preferred embodiment of the present invention provides that the cylinder of the hydraulic piston-cylinder-unit is designed as a twin plunger cylinder. In this case a piston rod is used whose end regions can be moved in one of the end regions of the cylinder. 
     The chambers of the twin plunger cylinder that are provided at both faces of the piston and are pressure-driven can exhibit different diameters. The resulting advantage lies in the fact that forces can be introduced that vary with the piston&#39;s direction of motion in accordance with the different areas; and thus different velocities of the pistons can be realized. Such an arrangement is especially advantageous when the piston-cylinder-unit according to the invention is used with a grabber, since in this case different velocities are often necessary when opening or closing the grabber. 
     Another embodiment of the present invention provides that the fastening means of the piston are designed as an extension piece, which projects beyond the cylinder and to which the coupling rod can be attached so as to swing. The piston&#39;s movement in the cylinder leads to a corresponding movement of the extension piece connected to the piston, thus resulting in a corresponding swinging of the piston-cylinder-unit or a workpiece fastened thereto when the piston moves owing to the coupling rod, hinged to the extension piece. 
     In addition, the cylinder may exhibit one or several slotted recesses, through which the extension piece extends. The extension piece exhibits a cover element, by means of which the recess can be covered in all positions of the piston. The cover element can be screwed or also welded to the extension piece and serves primarily to prevent the piston-cylinder-unit from becoming dirty. In addition, it prevents an inadvertent engagement with the slotted recess of the cylinder. 
     According to a preferred design of the present invention, the extension piece is screwed or welded to the piston. One advantage of the welded design lies in the fact that a narrow extension piece can be used that in turn necessitates a narrow cylinder. Another advantage of welding lies in cost reduction. In both cases (screwed or welded) it is possible to attach the extension piece to the piston prior to installation of the piston-cylinder-unit. Especially in this case the resulting advantage is also that the piston-cylinder-unit of the invention can be quicky assembled and disassembled; and, when the requirements change, it can be easily replaced with a piston-cylinder-unit of a different design. 
     According to a preferred embodiment of the present invention, each opposite side of the piston exhibits one extension piece each, which extends radially from said piston. The resulting advantage lies in the fact that special tools, for example with several components, to be moved synchronously, such as grabbers, can be driven by means of the piston-cylinder-unit of the invention. 
     Another embodiment of the present invention provides that the piston of the hydraulic piston-cylinder-unit exhibits a cross borehole. In this case the coupling rods of a slewing drive are connected to the piston of the piston-cylinder-unit according to the configuration of the borehole. 
     Another embodiment of the present invention provides that the fastening element of the cylinder comprises straps, which have boreholes to mount the cylinder. In this case the straps can extend radially from the cylinder or can be configured at any other arbitrary position, for example in the bottom region of the cylinder. The straps are welded preferably to the outer jacket of the cylinder. The boreholes in the straps serve to connect the piston-cylinder-unit to a tool, for example to a shovel, or also to the carrier of the slewing drive. 
     It is especially advantageous if the cylinder of the hydraulic piston-cylinder-unit of the invention consists of two end members and at least one center member, which is connected to the end members so as to disconnect. Such a design of the cylinder offers the possibility of being able to select freely the length of the cylinder and thus also the slewing angle through the appropriate choice of the center member. The center member is flanged preferably to the end members. 
     The center member can exhibit the slotted recess, whose purpose serves the passing through of the extension piece of the piston. 
     Another embodiment of the present invention provides that the center member exhibits a strap, by means of which the piston-cylinder-unit can be swung in the carrier. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other details and advantages of the invention are explained in detail with reference to the embodiments depicted in the drawings. 
     FIG. 1A is a front view, which is a sectional view in part, of one embodiment of the piston-cylinder-unit with an extension piece. 
     FIG. 1B is a side view of the embodiment of FIG.  1 A. 
     FIG. 2A is a front view of an embodiment of the piston rod with two opposite extension pieces, which extend radially. 
     FIG. 2B is a side view of the embodiment of FIG.  2 A. 
     FIG. 3A is a longitudinal view of one embodiment of the piston-cylinder-unit with cross borehole. 
     FIG. 3B is a side view of the embodiment of FIG.  3 A. 
     FIG. 4A is a front view of one embodiment of the piston-cylinder-unit with flanged center member. 
     FIG. 4B is a side view of the embodiment of FIG.  4 A. 
     FIG. 5A is a front view of one embodiment of the piston-cylinder-unit with flanged center member, where the center member exhibits a strap to swing the piston-cylinder-unit. 
     FIG. 5B is a side view of the embodiment of FIG.  5 A. 
     FIG. 6A is a side view of a dredging shovel with the piston-cylinder-unit of the invention according to FIG.  1 . 
     FIG. 6B is a front view of a dredging shovel with the piston-cylinder-unit of the invention according to FIG.  1 . 
     FIG. 7A is a side view of a dredging shovel with the piston-cylinder-unit of the invention according to FIG.  3 . 
     FIG. 7B is a front view of a dredging shovel with the piston-cylinder-unit of the invention according to FIG.  3 . 
     FIG. 8 is a partial sectional front view of a grabber with a piston rod according to FIG.  2 . 
     FIG. 9 is a side view of the piston-cylinder-unit of the invention with grabber and 
     FIG. 10 is a cross sectional view of a grabber with several piston rod units. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     FIG. 1A is a front view, which is a sectional view in part, and a side view of a first embodiment of the piston-cylinder-unit  10  of the invention, where a piston  20  can be slid in the twin plunger cylinder  30 . The top side of the twin plunger cylinder  30  exhibits a slotted recess  33 , through which the extension piece  22  extends. 
     The extension piece  22  is screwed to the piston  20 . Said extension piece exhibits a borehole to receive a coupling rod, which is attached so as to swivel. 
     Furthermore, the extension piece  22  is connected to the cover element  24 , which is designed as a sheet metal strip. Thus, an unintentional engagement with the slotted recess  33  is prevented; and in all positions of the piston  20  dirt is effectively prevented from getting into the piston-cylinder-unit  10 . 
     FIG. 1B is a side view of the straps  32 , which are arranged on the outside of the twin plunger cylinder  30  and by means of which the piston-cylinder-unit  10  or the twin plunger cylinder  30  can be fastened. The straps  32  have vertical boreholes  34 . The straps  32  are welded to the twin plunger cylinder  30 . 
     FIG. 2A is a front view and FIG. 2B is a side view of another embodiment of the piston rod  20 , which exhibits two opposite extension pieces  22 ′ and  22 ″, which extend radially from the piston  20 . Each of the extension pieces  22 ′ and  22 ″ exhibits a borehole to receive a coupling rod. Such a piston rod  20  is provided, for example, for the special application with synchronously moved tools. 
     FIGS. 3A and 3B depict another embodiment of a piston-cylinder-unit  10 , in which the piston rod  20  can be slid in the twin plunger cylinder  30 . As evident from FIG. 3B, the piston  20  has two horizontally extending extension pieces  22 ′ and  22 ″, through which the borehole  23  extends. The bottom region of the twin plunger cylinder  30  has straps  32  to fasten the piston-cylinder-unit  10 , each of said straps exhibits a vertical borehole  34 . 
     FIG. 4A is a front view and FIG. 4B is a side view of one embodiment of the piston-cylinder-unit  10  of the invention, where the end members  36 ,  36 ′ of the twin plunger cylinder  30  are connected together by means of a flanged center member  38 . The result is the possibility of making arbitrary adjustments to the length of the cylinder and thus also the slewing angle of the slewing drive through the choice of the center member  38 . According to FIGS. 4A and 4B, the piston  20  exhibits an extension piece  22 , for which the top side of the center piece has a corresponding recess  33 . 
     FIGS. 5A and 5B also depict an embodiment, where the end members  36 ,  36 ′ of the twin plunger cylinder are connected together by means of the center member  38 . The flanged center member  38  exhibits the straps  50 , which exhibit a borehole and serve to pivot-mount the piston-cylinder-unit or an attached tool to a carrier. As already explained with respect to FIGS. 4A and 4B, the piston rod  20  exhibits an extension piece  22 , which extends through a slotted recess  33  of the center piece  38 . 
     FIG. 6A is a side view and FIG. 6B is a front view of a dredging shovel  70 . The dredging shovel  70  is connected by means of the straps  80  to a carrier  90 , for example, the dredger boom so as to swing. 
     The upper region of the dredging shovel  70  of the dredger has the invention&#39;s piston-cylinder-unit  10 , which is screwed to the dredging shovel  70  by means of the straps  32 . The extension piece  22  projects beyond the upper side of the piston-cylinder-unit  10 . Said extension piece is connected to the carrier  90  by means of coupling rods  40 , which are arranged to the right and left of said extension piece. A movement of the piston (not illustrated) by raising the pressure in the appropriate chamber of the twin plunger cylinder  30  results in a displacement of the extension piece  22 , which leads to the dredging shovel  70  being swung relative to the carrier  90  owing to the arrangement of the coupling rod  40 . 
     FIGS. 7A and 7B depict an arrangement of a dredging shovel  70  according to FIGS. 6A and 6B, where the embodiment of FIGS. 3A and 3B was used as the piston-cylinder-unit  10 . In this case the coupling rods  40  are attached to the extension pieces, which extend laterally from the piston. The coupling rods  40  are connected to the piston of the piston-cylinder-unit  10  so as to swing by means of a bolt, extending through the borehole  23 . As already explained in FIGS. 6A and 6B, the piston-cylinder-unit  10  is screwed by means of the straps  32  to said dredging shovel on the upper side of the dredging shovel  70 . 
     FIG. 8 depicts another embodiment of the invention, where a piston-cylinder-unit  10  is used, where the piston  20  is designed according to FIGS. 2A and 2B. Thus, the opposing extension pieces  22 ′,  22 ″ extend radially on two sides of the piston. Attached to said extension pieces by means of suitable boreholes are coupling rods  40  in order to drive the grab tongs  100  of a grabbing device synchronously. 
     FIG. 9 is a side view of a grabbing device with a piston-cylinder-unit  10  of the invention. The piston-cylinder-unit  10  comprises the piston  20 , which can move in the twin plunger cylinder  30 . Said piston exhibits the extension piece  22 , which is connected to two coupling rods  40  so as to swing. Furthermore, the half scoop  110  of the grabbing device is attached to the coupling rods  40  so as to swivel. 
     The top end region of the piston-cylinder-unit  10  exhibits straps  32  as the fastening means; said straps have boreholes  34  to mount the piston-cylinder-unit  10  on a carrier. 
     Furthermore, FIG. 9 shows that the bottom chamber of the twin plunger cylinder  30  exhibits a smaller diameter and thus a smaller cross sectional area than the chamber, bordering the piston  20  in the top end region of the twin plunger cylinder  30 . Different forces and speeds with respect to the up and down motion of the piston  20  and thus opening and closing of the half scoop  110  can be realized as a function of the different cross sectional areas. 
     FIG. 10 depicts an arrangement, wherein several piston-cylinder-units  10  of the invention are configured parallel to each other. Each piston-cylinder-unit  10  exhibits a twin plunger cylinder  30 , in which the piston  20  can be moved. From said piston extends radially the extension piece  22 , which is connected by means of the coupling rods  40  to the half scoop  110  so as to swing. For the sake of clarity the picture in FIG. 10 shows only one piston  20  with extension piece  22  and coupling rods  40  and only one half scoop  110 . 
     Each of the other half scoops (not illustrated) extends radially and outwardly from the individual piston-cylinder-units  10 . The individual piston-cylinder-units  10  are connected to each other or to a frame by means of the fastening means  120 . 
     In addition to the illustrated design with several piston-cylinder-units  10  it is also possible to use only one piston-cylinder-unit. Thus to be able to swing and simultaneously actuate many half scoops  110 , it is necessary in this case that the pistons  20  exhibit four radially extending extension pieces  22 , which are connected so as to swivel by means of coupling rods  40  to the appropriate half scoops  110 . 
     In addition to the illustrated embodiment of FIG. 10 that exhibits four piston-cylinder-units  10 , it is also possible to provide, as necessary, more or fewer piston-cylinder-units or half scoops. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.

Summary:
The invention relates to a hydraulic piston-cylinder-unit ( 10 ) for a slewing drive with at least one piston, which can be slid in a cylinder and exhibits fastening means, by means of which the piston can be connected in such a manner to a coupling rod that the working tool can be swung by means of a movement of the piston. In accordance with the invention the cylinder exhibits fastening means, by means of which the cylinder can be connected to the working tool or to a carrier of the slewing drive.