Abstract:
The invention demonstrates how energy saving working cylinders are loaded with fluid under pressure in order, for example, to power devices for tensioning (toggle joint tensioning apparatus), and/or compressing and/or jointing and/or stamping and/or embossing and/or punching and/or welding, if necessary, under the interposition of gearing parts such as guides, parallelogram gears, toggle joint articulations or the like, with the fluid supply being controlled in such a way during the no-load stroke (idle stroke) of the piston ( 4 ) that only the forces of inertia and/or weight and/or the forces of friction of moveable parts are overcome and pressure is not applied from the fluid until the power stroke of the piston ( 4 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a procedure for loading a piston-cylinder unit with fluid under pressure, primarily for use in the manufacture of motor vehicle bodywork. 
     The invention also concerns a control module for loading a piston-cylinder unit with fluid under pressure, primarily for use in the manufacture of motor vehicle bodywork. 
     The invention also concerns a piston-cylinder unit as a working cylinder to be loaded with fluid under pressure, primarily for use in the manufacture of motor vehicle bodywork. 
     Finally, the invention concerns the use of a working cylinder of this kind to power devices for tensioning and/or compressing and/or joining and/or stamping and/or embossing and/or punching and/or welding, if necessary, under the interposition of a toggle joint or other gearing parts, e.g. for use in the manufacture of motor vehicle bodywork. 
     Piston-cylinder units are referred to in the industry for short as “working cylinders”. Where the term “working cylinder” is used in the following, it is understood to mean not only a cylinder but also an operable drive unit comprising at least one cylinder and at least one piston guided in this cylinder so as to be longitudinally displaceable and to seal it and having a piston rod disposed on one side of the said piston, which piston rod is preferably sealed and made to project from the said cylinder chamber and which powers devices primarily for tensioning and/or compressing and/or joining and/or stamping and/or embossing and/or punching and/or welding. In the case of such devices e.g. the piston rod often drives under interposition of at least one toggle joint other device parts such as a tensioning arm which cooperates with an opposing member or an expanding mandrel or a centring mandrel or a jointing device or a stamp, a device part for punching or also device parts, for example, under interposition of a toggle joint, actuatable welding electrodes. 
     Devices for tensioning, compressing, joining, stamping, embossing, punching and welding are used in many forms in, for example, the manufacture of motor vehicle bodywork. Tensioning devices are often constructed as “toggle tensioning devices” and hold body sheets in position until they are permanently fastened on by means of spot-welding, adhesion, clinching, etc., while other devices, for example, function as under-floor clamps and power a centring mandrel under interposition of a link mechanism, e.g. a parallelogram gear, to align one with the other and centre a number of sheets. Examples of these are to be found in, amongst others, catalogs of Tünkers Maschinenbau GmbH “Product Range”, “Tensioning Technology for Professional Series Manufacture”, “Tensioning Systems, Handling, Forming Technology, Stamping, Edging, Pressure Joining, Embossing” and in patent specifications DE 196 16 441 C1, DE 198 24 579 C1 and DE 199 30 990 C1. 
     In all these procedures, control systems, working cylinders and devices full pressure is need only for the last part of the working stroke. This means that for 90 percent and more of the setting stroke of the piston concerned and its piston rod—idle stroke—only a weak force is necessary, for example, to overcome friction and certain mass inertia and gravitational forces. Supply with fluid under pressure, for example, hydraulic fluid or compressed air and so the pump output and its driving power, however, is in the present state of the art needed for the entire stroke of the assigned piston with piston rod, for example, toggle joint and the like, which means that the greater part of the driving power is lost. 
     SUMMARY OF THE INVENTION 
     The invention is based on the problem of doing away with the disadvantages of the state of the art and helping to considerably improve the energy balance and save costs in all areas, that means, both in the case of the procedures known so far for the loading of working cylinders, primarily for use in the manufacture of motor vehicle bodywork and in the case of the control module for fluid under pressure for loading working cylinders of this kind and in the case of the use of working cylinders for devices for tensioning, compressing, joining, stamping, embossing, punching and welding. 
     This problem is solved by a procedure for loading a piston-cylinder unit (working cylinder), primarily for use in the manufacture of motor vehicle bodywork, with at least one piston which is longitudinally and sealingly displaceable in a cylinder by fluid pressure and which is on one side assigned a piston rod which is made to project from the cylinder and which powers device parts for tensioning and/or joining and/or stamping and/or embossing and/or punching and/or welding, if necessary, under interposition of gear parts such as guide rods, parallelogram gears, toggle lever arrangements or the like, where during the idle stroke (setting stroke) of the piston the fluid feed is controlled in such a way that only the inertia and/or gravitational forces and/or frictional forces of moveable parts are overcome and the piston is not loaded with pressure from the fluid until the power stroke. 
     In order to adjust the different pressures during the idle stroke and power stroke in keeping with the output, particularly the air flow or hydraulic fluid flow rate, in the case of the procedure according to the invention one working cylinder is filled with pressure medium on both sides of the piston during the idle stroke so that during the idle stroke (setting stroke) only the differential pressure, which is the difference between the piston surface loaded by the fluid pressure and the opposite side of the piston-ring surface, acts in the direction of the working stroke. The fluid and in particular energy consumption for the pump and its drive motor, particularly compressed air and hydraulic fluid consumption, are considerably reduced, for example, by 50%, by it. 
     To initiate the actual pressure stroke (working stroke), the piston-ring side is relieved of pressure, while the piston surface remains loaded with pressure from the medium. The fluid pressure can develop thereby and, for example, load the tensioning arm of a toggle joint device or pressing device, a joining device, a stamped part, part of a device for embossing or punching, or welding dies and crimpers, for example, under interposition of a toggle joint. 
     Control of pressure medium loading in the case of the invention is either pressure-dependent or path-dependent. For example, to initiate the power stroke through the piston a valve, for example, a piston valve is actuated, relieving the pressure on the piston-ring side and maintaining the load acting on the piston surface from the full fluid pressure. The full pressure can thereby develop in the working direction in order to be able to act, for example, on a toggle tensioning device or a device for compressing, joining, stamping, embossing, punching or welding, primarily under interposition of a toggle joint. The retraction of the piston rod and thus the return movement of the piston are achieved by loading the piston-ring side with pressure from the already previously reversed valve. 
     In a further preferred embodiment, the control of the fluid during the power stroke, that is, on completion of the setting stroke (idle stroke) is derived from the movement of the piston. 
     In a very advantageous embodiment, the control of the fluid during the power stroke, that is, on completion of the setting stroke (idle stroke), is derived from the movement of the piston. 
     According to the invention control parts of the control system, for example, the piston valve and ducts, can be wholly or partly integrated in the cylinder cover and/or in the cylinder base, and, if required, also in the side walls of the cylinder, as a result of which the overall dimensions of the hitherto usual devices of the kind needed in the manufacture of motor vehicle bodywork for tensioning, compressing, joining, stamping, embossing, punching or welding, primarily using toggle levers, are not increased, so that the standards hitherto used in, for example, the automotive industry, with regard to outside dimensions are retained. The arrangement can be applied both with round and flat (rectangular) and oval or flattened-oval cylinders. 
     Working cylinders designed in accordance with the invention can be used to great advantage in many forms, particularly in the automotive industry, for example, in devices for tensioning, compressing, jointing, stamping, embossing, punching and welding in the manufacture of motor vehicle bodywork. Existing production lines can be fitted with working cylinders of the kind forming the object of the invention without structural changes, thus enabling the cost of energy for operating production lines of this kind to be considerably reduced. 
     It is particularly advantageous if in a working cylinder in accordance with the invention is used so that the piston rod controls a valve, for example, a piston valve at the end of the idle stroke (setting stroke) in such a way that the full pressure from the pressure medium acts on the active side of the piston. Working cylinders which are constructed in this way can be used to special advantage in toggle joint tensioning devices in the manufacture of motor vehicle bodywork. 
     In a particularly advantageous embodiment, a detachable coupling is provided for which does not make a connection between the piston rod and the valve but at the end of the idle stroke (setting stroke) acts automatically and controls the valve in such a way that the pressure from the pressure medium acts fully on the side of the effective piston. 
     Some embodiments are especially advantageously suitable in devices in which toggle joint arrangements are provided for, for example, for toggle lever tensioning devices, and with spot-welding devices and stamping, joining and embossing devices powered via toggle levers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages result from the following descriptions of drawings in which the invention is—partly schematically—illustrated by a number of embodiments. 
         FIG. 1  shows an axial longitudinal section of a working cylinder where the piston with the piston rod is in an intermediate position of the idle stroke in the direction Y; 
         FIG. 2  shows a longitudinal section of the working cylinder shown in  FIG. 1  in the end position of the working stroke (power stroke); 
         FIG. 3  shows a longitudinal section of a further embodiment of a working cylinder in an intermediate position of the idle stroke in the direction Y; 
         FIG. 4  likewise shows an axially longitudinal section of the working cylinder shown in  FIG. 3  in an intermediate position during the return movement of the piston in direction X (opening stroke); 
         FIG. 5  shows a toggle lever tensioning device in longitudinal section with a working cylinder in accordance with the invention; 
         FIG. 6  shows a further embodiment, partly in longitudinal section, of a working cylinder with an external control device, with an interrogation device; 
         FIG. 7  shows a further embodiment, partly in longitudinal section; 
         FIG. 8  shows a toggle lever tensioning device, partly in axially longitudinal section, partly in side view, with a working cylinder in accordance with the invention during the power stroke (tensioning), end position; 
         FIG. 9  shows the toggle tensioning device shown in  FIG. 8  in the open position (piston) in the opposite end position after completion of the opening stroke and 
         FIG. 10  shows the toggle lever tensioning device shown in  FIGS. 8 and 9  during the setting stroke (idle stroke) (intermediate position of the piston). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown on the drawing with reference number  1  is a cylinder incorporating a cylinder base  2  and a cylinder cover  3 . Cylinder base and/or cylinder cover can be detachably and replaceably connected to the actual cylinder with bolts (not shown). 
     Disposed in the cylinder  1  and able to move in a longitudinal direction in opposite directions, that is, in direction X or Y, and sealed with a sealing element  5 , is a piston  4 . Assigned to the piston  4  on one side is a piston rod  6  via which suitable device parts for tensioning  7 , compressing, joining, stamping, embossing, punching and welding are powered. These device parts  7  or the like are indicated in  FIGS. 1 and 2  only schematically. Between these device parts  7  a toggle lever arrangement can also be disposed as shown in  FIG. 5  and which is marked with the reference number  8 . The device part  7  is shown in  FIG. 5  by a tensioning arm, which cooperates with other device parts, for example, with an opposing member, also known as a jaw. The fundamental construction of such devices for tensioning, for example, toggle lever tensioning devices, for compressing, joining, stamping, embossing, punching and welding is state of the art and for simplicity&#39;s sake need not be described here. Devices of this kind can be found in the specifications shown in the enclosed bibliography and are also described in the preamble to the description of this patent application. 
     In all the embodiments as shown on the drawing the cylinder  1  can in a cross-section at right angles to its longitudinal axis be designed round, oval, rectangular, flattened-oval or otherwise. 
     In one side  9  of the cylinder in the embodiment according to  FIGS. 1 and 2  is a longitudinal duct  10  which is connected fluid-conductingly at the end portion facing the cylinder cover  3  to a transverse duct  11 , which leads at one end into the working cylinder chamber  12  and at the other end leads out of the working cylinder chamber and is connected here to a control system (not shown here) for a suitable fluid inlet and outlet. This fluid may be hydraulic fluid, compressed air or a quasi-fluid of the kind used to power working cylinders. In the manufacture of motor vehicle bodywork mainly compressed air will be used, as this is available everywhere in workshops and particularly on assembly lines, although it is not absolutely necessary for realization of the invention. 
     At a distance from its other end the longitudinal duct  10  is fluid-conductingly connected to a branch duct  13  disposed in the cylinder base, while the longitudinal duct  10  is at its other end also fluid-conductingly connected to a portion  14  of the duct which leads fluid-conductingly into a chamber  15 . 
     Disposed in the cylinder base is a further duct  16  which leads into a cylindrical hole  17 . Connected to this duct  16  is a chamber duct  18  which leads at one end fluid-conductingly to the duct  16  and at the other end into the chamber  15 . 
     Longitudinally-displaceably and sealingly guided in the hole  17  is a piston valve  19  a certain longitudinal portion of which projects into the cylinder return chamber  21  and is longitudinally-displaceably and sealingly guided in the chamber  15  by a piston  20 . The chamber  15  is divided by this into two cylinder chambers, into one  22  of which the chamber duct  18  leads fluid-conductingly, while duct portion  14  leads fluid-conductingly into cylinder chamber  23 . 
     The piston valve  19  incorporates a longitudinal duct  24  which in the embodiment shown extends coaxially to the longitudinal axis of the piston valve  19  over part of its length and incorporates a fluid-conducting branch duct  25  running at right angles to the longitudinal axis and connected to the longitudinal duct  24 . 
     The working cylinder shown in  FIGS. 1 and 2  is built into the toggle lever tensioning device shown in  FIG. 5 . The working cylinder shown in  FIGS. 1 ,  2  and  5  operates as follows: 
     In the position shown in  FIG. 1  the transverse duct  11  is connected to a fluid source (not shown), which supplies a fluid under pressure, for example, compressed air. This causes the working cylinder chamber  12  to be loaded with pressure by the compressed medium via the longitudinal duct  10 , the branch duct  13 , the branch duct  13  and the branch duct  25  and the longitudinal duct  24  in the piston valve  19  also to the cylinder return chamber  21  with the same pressure from the compressed medium. This means that both the working cylinder chamber  12  and the cylinder return chamber  21  are loaded simultaneously by the fluid under pressure. This causes the fluid pressure to act on the piston  4  from both sides. Since, however, the fluid pressure on the side on which the piston rod  6  is located loads a smaller surface, that is, the annular surface, a stroke displacement force results in the direction Y, that is, the working direction, and this is determined by the difference between the fluid-effective piston surfaces. As a result, the piston  4  and the piston rod  6  and any connected device parts, for example, the toggle lever arrangement  8  and the device parts  7 , e.g. as tensioning arm or other device parts such as are necessary for compressing, joining, stamping, embossing, punching and welding, move with only relatively low driving force during the idle stroke. As a result, the driving energy needed during the idle stroke (setting stroke) reduces in proportion to the compressed medium-effective surfaces in the working cylinder. For example, by 50 percent. This can also be determined by the choice of fluid-effective piston surfaces, for example, by varying the cross-section of the piston rod  6  correspondingly. For example, in the case of toggle lever tensioning devices or other devices the piston rod may be enlarged in diameter in order to still further reduce the energy to be used during the idle stroke (setting stroke). If the piston  4  comes up against the end face of the piston valve  19 , the piston valve is displaced accordingly in a longitudinal direction, until it has reached the position shown in  FIG. 2 . In this position the branch duct  13  is blocked off from the cylinder return chamber  21  and fluid-conductingly connected to the duct  16  via the longitudinal duct  24  in the piston valve  19  and its branch duct  25 , causing the cylinder return chamber  21  to be evacuated of air. This evacuation can be carried out by means of a suitable control system (not shown). 
     The inward movement of the piston rod  6 , that is, a movement in direction X (opening stroke), is carried out by corresponding control of the control device not shown, causing the piston-ring side, that is, the cylinder return chamber  21 , to be loaded with pressure from the compressed medium through the valve previously already reversed and shown in the present as piston valve  19 . In this case the duct  16  is connected to the pressure from the compressed medium via the control system. The fluid is thereby conducted in to the cylinder return chamber  21  via the duct  16  and the longitudinal duct  24  in the piston valve  19 . The pressure from the compressed medium is also transmitted to the chamber portion  22  via the chamber duct  18  and loads the piston  20  and thereby holds the piston valve  19  in the position shown in  FIG. 2 . 
     When the idle stroke (setting stroke) is initiated in direction Y, the fluid pressure is again transmitted via transverse duct  11  and the duct  10  to the branch duct  13  and also via the duct portion  14  in the chamber  15  and loads the piston  20 , causing this to be displaced into its position shown in  FIG. 1 , whereupon the working cycle previously described can be repeated. 
     In the embodiment in accordance with  FIGS. 3 and 4  the same reference numbers are used for parts having the same function. 
     Disposed in the cylinder base  2  at right angles to the stroke of piston  4  is a valve chamber  26  in which a piston valve  27  is longitudinally-displaceably in both directions and sealingly disposed in its longitudinal direction. 
     The piston valve  27  has at its ends piston-shaped thickened portions and approximately in its middle longitudinal portion  28  a diameter reduction, thus producing an annular chamber  29  around its circumference. 
     Connected to the valve chamber  26  and spaced apart in turn are a transverse duct  11  and a duct  16  which can be alternately connected to the pressure from the compressed medium via a suitable fluid control system (not shown) or also evacuated of air. 
     The longitudinal duct  10  disposed in the cylinder wall  9  is in turn connected via a transverse duct  11  to the working cylinder chamber  12  and also leads fluid-conductingly into a duct  30  which leads fluid-conductingly into the valve chamber  26  in the area of the annular chamber  29 . 
     The duct  16  is likewise connected via a duct portion  31  to a part of the valve chamber  26  into which a push rod  32  projects longitudinally displaceably and sealingly, which push rod is integrally connected to a piston  33  disposed longitudinally displaceably and sealingly in a chamber  34  and constantly loaded in a direction away from the piston valve  27  by a pretensioned compression spring element  35 . The compression spring element  35  is braced at one end against a partition wall  36  and at the other end against the piston  33 . 
     On the side of the piston facing away from the compression spring element emerges a branch duct  37 , which is connected fluid-conductingly to a duct portion  38 , which can be fluid-conductingly connected to the transverse duct ( FIG. 3 ). The duct portion  38  leads fluid-conductingly into the cylinder return chamber  21 . 
     The embodiment shown in  FIGS. 3 and 4  operates as follows: 
     In the representation according to  FIG. 3  the piston  4  performs an idle stroke in direction Y. The transverse duct  11  is connected to a suitable fluid source, for example, compressed air, by means of a control system (not shown), causing the duct portion  38  to be loaded with fluid pressure, thereby causing the cylinder return chamber  21  and also the working cylinder chamber  12  to be loaded with pressure from the compressed medium via the annular chamber  29  and the duct  30  and the transverse duct  11 . As a result, the piston  4  and the piston rod  6  and any connected device parts not shown in  FIGS. 3 and 4 , for example, a toggle lever arrangement  8  with a device part  7 , for example, a tensioning arm ( FIG. 5 ) are moved by the differential force resulting from the pressure-effective piston surfaces. If the piston  4  reaches the position in which the full power stroke is performed, the pressure from the compressed medium is transmitted into the chamber  34  via the duct portion  38  and the branch duct  37  and loads the piston  33  which then, overcoming the restorative force of the compression spring element  35 , presses the push rod  32  against the piston valve  37 , thereby blocking off the transverse duct  11  from the annular chamber  29 , so that the cylinder return chamber  21  is no longer loaded by the pressure from the compressed medium. As a result, in this position the full pressure from the compressed medium acts on the pressure-effective surface of the side of the piston  4  not provided with the piston rod  6 , whereupon the device concerned, for example, a toggle lever tensioning device, or a device for compressing, joining, stamping, embossing, punching or welding can perform its full working stroke. The cylinder return chamber  21  is then relieved of pressure. 
     In the embodiment according to  FIG. 6  a multi-port valve  39  is incorporated in a system control system (not shown) outside the actual working cylinder and cooperates with a fluid source (likewise not shown), for example, a compressed air source or a hydraulic fluid source, to which a compressed medium is fed under pressure in a suitable manner, for example, via at least one motor-powered pump. 
     Again, the same reference numbers were used for parts having the same function. 
     The duct portion  38  can be connected to the cylinder return chamber  21  and the transverse duct  11  to the working cylinder chamber  12  via the multi-port valve  39 . During the idle stroke in turn only the differential pressure acts on the piston  4  and displaces the piston during the working stroke in direction Y. 
     To initiate the power stroke, the control is reversed so that the cylinder return chamber  21  is not longer loaded with pressure from the fluid but only the working cylinder chamber  12 , as a result of which the full pressure from the compressed medium is available when initiating the power stroke, for example, in a toggle lever tensioning device or a device for compressing, joining, stamping, embossing, punching or welding. The reference number  40  refers to an only schematically indicated device for detecting the position of the piston rod  6 . This device may be a cassette known from toggle lever tensioning devices, where the respective position of the piston rod  6  can be detected by means of pneumatic switches, microswitches, inductive switches or the like, for example, via a switching flag  41 . The device  40  may also be assigned direct to cylinder  1  in the form of a cassette, for example, be disposed in a recess in the cylinder, as shown, for example, in  FIG. 5 , where the device for detecting the various positions of the piston rod  6  and thus indirectly also the angular position of the tensioning arm is disposed in a slot  43  located on the rear of the tensioning head  42 . This slot  43  may preferably extend in a longitudinal direction of the tensioning head  42  and so parallel to the direction of stroke of the piston rod  6  or also at right angles to this. The device  40  preferably extensively seals the slot fluid-tight and dust-tight against ingress from outside. The device can also be constructed as an adaptive cassette, where by selecting certain positions one or more times these positions can be stored and reversed electronically in a memory in order to assign various angular positions to, for example, a tensioning arm. The device parts  44 ,  45  can be displaced relative to each other in order to allow for various working positions, for example, tensioning positions. The device parts  44 ,  45  may be switches, e.g. electrical switches or inductive switches which are energized through the switching flag  41 . The data are interrogated via a suitable electrical or electronic plug  46  and transmitted by wire to, for example, a remote control station, data processing system or the like. These data can be incorporated into a production control system or automatic control system and be located in, for example, a production line employed in the manufacture of motor vehicle bodywork. In the same way, however, these different means can also be used in devices for compressing, joining, stamping, embossing, punching and welding. 
     In all the embodiments there is a seal, indicated by the reference number  47 , through which the piston rod  6  can be fluid-tightly made to project from the working cylinder. 
     In the embodiment according to  FIG. 7  the piston  4  is assigned a control pin  49  which can be moved against the restorative force of a compression spring element  48  and which is displaceably and sealingly disposed longitudinally in a hole in the piston  4  and which cooperates at its front end with the piston valve  19  in such a way that, when the idle stroke is completed, the control pin  49  comes up against the front end of the piston valve  19  and pushes this in direction Y, that is, into the cylinder cover  3 . This can begin shortly beforehand, preferably at the beginning of the power stroke, whereupon the feed of compression medium to the piston-ring side  21  is interrupted and the cylinder return chamber  21  evacuated of air so that the pressure from the fluid loads only the piston side and, for example, loads a toggle lever tensioning device, crimpers, a combined tensioning and welding device provided with toggle lever joints, a stamping or embossing device or the like. In the embodiment shown the pressure spring element is braced under pretension at one end against the piston  4  and at the other against a piston-shaped thickened portion. 
       FIGS. 8 to 10  show a further embodiment of the invention. The same reference numbers were used for parts having the same function as in the afore-described drawings. Reference number  50  refers to a coupling rod running parallel to the longitudinal axis of the piston rod  6  and guided longitudinally displaceably in a hole  51  in the wall  52  and sealed tightly against compressed medium with a seal  53 . 
     The coupling rod  50  is connected at one end with the piston valve  19  materially or functionally as a single element, for example, by a screw thread. Otherwise the coupling rod  50  projects into a space  54  in the tensioning head and is disposed at a distance from the outer periphery of the piston rod  6 . At its end portion facing away from the piston valve  19  the coupling rod  50  has a diameter enlargement  55 . Also disposed in this area is a cup-shaped spring sleeve  56  having a single-piece flange  57  projecting outwards at its end portion facing away from the diameter enlargement  55 . The spring sleeve  56  slides on the outer periphery of the round-section coupling rod  50  by a hole  58 . 
     Provided for in the spring sleeve  56  is a pretensioned compression spring element  59  which in the present case is constructed as a helical compression spring. The compression spring element  59  is resiliently braced at one end against the diameter enlargement  55  and at the other end by its front end in the deepest part of the spring sleeve  56 . The compression spring element  59  is guided and retained axially and radially by the spring sleeve over a large part of its axial length. The compression spring element  59  has the tendency to expand and move the spring sleeve  56  by its front end up against a stop  60  which is connected as a single piece to the coupling rod  50 . The stop  60  can be in the form of a transverse pin, a bolt, an expanding mandrel or the like which is rigidly disposed in a hole running at right angles to the longitudinal axis of the coupling rod  50  and limits the displacement of the spring sleeve in direction X. 
     Connected firmly to the piston rod  6 , in the present case to the fork head of the toggle lever arrangement  8  assigned to the piston rod  6 , is a coupling  62  which accordingly moves in direction Y or X during the lifting movement of the piston rod  6 . The coupling  62  is in the present case constructed as a sheet metal element set at right angles to the longitudinal axis of the piston rod  6  and having a through-hole which is larger than the outside diameter of the spring sleeve  56  so that the spring sleeve can slide through this hole in the coupling  56 . However, the hole in the coupling  66  is smaller than the outside diameter of the flange  57  of the coupling sleeve so that the coupling  62  can engage the flange  57  from below and, when moving in direction Y and at the same time compressing the compression spring element  59 , carry it with it ( FIG. 8 ).  FIG. 10  shows how the coupling  62  slides over the spring sleeve  56 , while  FIG. 9  shows an arrangement where the spring sleeve under corresponding relaxation of the compression spring element  59  has been displaced in direction X against the stop  60 . The hole  63  in the coupling  62  is also suitably dimensioned to enable it to slide over the stop  60 . 
     The arrangement is such that immediately on completing the idle stroke (setting stroke) in direction Y the coupling  62  comes up against the underside of the flange  57  of the spring sleeve  56  and under compression of the compression spring element  59  moves the coupling rod  50  over the diameter enlargement  55  in direction Y, causing the piston valve  19  also to be displaced in direction Y. This results in a control reverse as described in the preceding such that now the full pressure from the compressed medium acts on the underside (piston-side) and so the full tensioning force is available on the tensioning arm of the toggle lever tensioning device. 
     Naturally this design and this principle can also be used for other devices, for example, for clinching and punching devices, welding devices with toggle lever arrangements and devices for joining, embossing and tensioning. The compression spring element  59  here prevents sudden contact and ensures a precise but suitably cushioned reversal of the piston valve  19 . 
     The features shown in the abstract, the patent claims and the description and on the drawing can be important for realization of the invention either individually or in any desired combination. 
     LIST OF REFERENCES 
     
         
           1  Cylinder 
           2  Cylinder base 
           3  Cylinder cover 
           4  Piston 
           5  Sealing element 
           6  Piston rod 
           7  Device parts 
           8  Toggle lever arrangement 
           9  Cylinder wall 
           10  Longitudinal duct 
           11  Transverse duct 
           12  Working cylinder chamber 
           13  Branch duct 
           14  Duct portion 
           15  Chamber 
           16  Duct 
           17  Hole 
           18  Chamber duct 
           19  Piston valve 
           20  Piston 
           21  Cylinder return chamber, piston-ring side 
           22  Cylinder chamber 
           23  Cylinder chamber 
           24  Longitudinal duct 
           25  Branch duct 
           26  Valve chamber 
           27  Piston valve 
           28  Longitudinal portion, middle 
           29  Annular chamber 
           30  Duct 
           31  Duct portion 
           32  Push rod 
           33  Piston 
           34  Chamber 
           35  Compression spring element 
           36  Partition wall 
           37  Branch duct 
           38  Duct portion 
           39  Multi-port valve 
           40  Device 
           41  Switching flag 
           42  Tensioning head 
           43  Slot 
           44  Device part 
           45  Device part 
           46  Plug, electrical, electronic 
           47  Seal 
           48  Compression spring element 
           49  Control pin 
           50  Coupling rod 
           51  Hole 
           52  Wall 
           53  Seal 
           54  Space 
           55  Diameter enlargement 
           56  Spring sleeve 
           57  Flange 
           58  Hole 
           59  Compression spring element 
           60  Stop 
           61  Fork head 
           62  Coupling 
           63  Opening 
         X Direction of stroke 
         Y Direction of stroke 
       
    
     BIBLIOGRAPHY 
     
         
         Prospectus of Tünkers Maschinenbau GmbH, Ratingen, “Tensioning Technology for Professional Series Production” 
         Prospectus of Tünkers Maschinenbau GmbH, Ratingen, “Product Range” 
         Prospectus of Tünkers Maschinenbau GmbH, Ratingen, “Tensioning Systems, Handling, Forming Technology” 
         DE 196 16 441 C1 
         DE 198 24 579 C1 
         DE 199 30 990 C1