CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of German Application Nos. 297 19 343.0 filed Oct. 31, 1997, 198 13 386.3 filed Mar. 26, 1998 and 198 41 381.5 filed Sep. 10, 1998, which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     In normal reciprocating piston-type machines the position of the pistons in the respective engine cylinders depends exclusively from the angular position of the crankshaft. According to a conventional arrangement for changing the compression ratio as a function of operational conditions, the connecting rod of each piston is subdivided into two connecting rod parts which are coupled with one another by a central joint. Further, a control arm is articulated at one end to the connecting rod and is secured, at its other end, to a pivotal support slidable on the machine housing. 
     The above-outlined constructions are described, for example, in German Offenlegungsschriften (applications published without examination) 29 35 073, 29 35 977, 30 30 615 (to which corresponds U.S. Pat. No. 4,437,438) and 37 15 391 (to which corresponds U.S. Pat. No. 4,957,069). In the structures described therein the control arm is directly coupled to the central joint, giving rise to substantial structural and operational problems. The central joint has a substantial width and thus has a large weight which, at the given spatial availabilities, cannot be compensated for by counterweights mounted on the crankshaft. On the whole, it is a disadvantage of the prior art structures that the moved masses, that is, the piston and the connecting rod, are increased and therefore greater mass forces have to be overcome. 
     To avoid the above-noted disadvantages, it is known to change the compression ratio by supporting the crankshaft in eccentric rings which are angularly displaceably (rotatably) supported in the cylinder block and are connected with a setting drive. By rotating the eccentric rings, the position of the crankshaft is shifted such that in the upper dead center position the pistons have a greater or lesser distance from the cylinder roof. For this purpose, German Offenlegungsschrift 30 04 402 provides that each eccentric ring is coupled with a toothed gear meshing with a pinion mounted on a setting shaft which extends parallel to the crankshaft and which is coupled with a setting drive. Apart from a substantial structural and technological input, increased space is needed for accommodating the eccentric rings and the gears disposed in their vicinity. 
     Further, German Offenlegungsschrift 36 01 528 describes an arrangement wherein the eccentric rings which support the crankshaft bearings are connected with a partial cylinder shell arranged concentrically to the eccentric rings and extending over the entire length of the cylinder block. The partial cylinder shell is provided on its exterior with a toothed segment which meshes with a setting worm extending transversely to the crankshaft and connected with a setting drive. Despite a favorable structural length of the crankshaft support, such a system has the disadvantage that a very compact structural component for the synchronous shifting of the eccentric rings is provided, and that because of the eccentricity of the crankshaft axis relative to the support axis of the eccentric rings, torques appearing during operation may be taken up only through the setting worm. Since in such a construction only a few teeth are in a meshing relationship with a small degree of overlap, the stress on the component materials is substantial because of the fluctuating loads generated during operation. Even a small play between the toothed segment and the setting worm may lead to a rapidly progressing wear. 
     Further, German Offenlegungsschrift 36 44 721 describes a system in which each eccentric ring is connected with a laterally projecting lever carrying a bearing block on its free end. Laterally of and parallel to the crankshaft a setting shaft is supported which has a setting drive and which is provided with a fork-like jaw straddling the bearing block of an eccentric ring. Since the bearing blocks cannot be guided in a play-free manner, such a system too, is disadvantageous because the fluctuating torques exerted on the eccentric rings during operation lead in this region to a significant stress on the system which is coupled with an increasing wear in the zone of the bearing block guidance. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved internal-combustion engine of the above-outlined type from which the discussed disadvantages are eliminated. 
     This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the internal-combustion engine includes a cylinder block; a plurality of cylinders arranged in line in the cylinder block; a piston accommodated for reciprocating motion in the respective cylinders; a crankshaft received in the cylinder block; a connecting rod coupling each piston with the crankshaft; and a plurality of eccentric rings surrounding and supporting the crankshaft. Each eccentric ring is rotatable about a common ring axis radially spaced from the crankshaft axis. Further, ring-supporting bearing housings are accommodated in the cylinder block for supporting the eccentric rings. A ring-turning assembly adjusts in unison the angular position of the eccentric rings to radially shift the crankshaft, whereby the upper dead center position of the pistons is altered for varying the compression ratio thereof. The ring-turning assembly includes a setting drive for exerting a force upon actuation thereof; a ring-turning component connected to at least some of the eccentric rings; and a coupling element connecting the setting drive with the ring-turning components for transmitting the force exerted by the setting drive to the ring-turning components for rotating the eccentric rings. 
     The invention provides that in an internal-combustion engine in which the compression ratio may be altered, the support for the setting arrangement does not require an extension of the crankshaft support in the cylinder block so that the usual structural lengths for such cylinder blocks need not be increased. The ring-turning components, the bearing housings and the eccentric rings are expediently dimensioned in such a manner that an axial support for the eccentric rings is obtained. By virtue of the fact that all ring-turning components are connected to one another by means of a coupling element, a synchronous rotation of the eccentric rings is ensured. 
     According to an advantageous feature of the invention, that portion of an eccentric ring which is oriented towards the associated cylinder has, on its exterior, a circumferentially extending groove which is provided with a radially inwardly oriented bore and further, in the cylinder block a central oil channel is arranged from which branch channels extend which terminate with their open end at the ring-supporting bearing housing in the region of the groove provided in the eccentric ring. This arrangement ensures that the bearing surfaces of the eccentric rings as well as the crankshaft bearings arranged in the eccentric rings are supplied with lubricant. 
     In accordance with a further advantageous feature of the invention, at least some of the ring-supporting bearing housings are provided with a respective window through which the turning component for the associated eccentric ring passes. In this manner, a compact structure for the entire arrangement and for the turning component is obtained. The coupling element which connects the turning components with one another and with the setting drive may be, according to a further feature of the invention, formed by a setting shaft connected with the setting device and provided with pinions which mesh with the corresponding toothed elements of the respective turning components. According to a further advantageous feature of the invention, the turning components may be pivotal levers which preferably extend downwardly into the oil pan. 
     In accordance with a further advantageous feature of the invention, the turning components are formed by toothed elements carried by the eccentric rings and coupled with respective toothed transmission elements extending through windows in the ring-supporting bearing housings and mesh with pinions carried by the setting shaft. Such an arrangement allows a relocation of the turning components and the setting shaft in the cylinder block and thus the structural volume of the engine may be maintained small. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view of a preferred embodiment of the invention installed in a four-cylinder in-line engine. 
     FIG. 2 is a schematic enlarged sectional view taken along line II—II of FIG.  1 . 
     FIG. 3 is a sectional end elevational view of a structural embodiment of the arrangement shown in FIG.  2 . 
     FIG. 4 is a sectional view taken along line IV—IV of FIG.  3 . 
     FIG. 5 is a view taken in the direction of arrow V of FIG.  4 . 
     FIG. 6 is an end elevational view of a ring-turning assembly according to another preferred embodiment of the invention. 
     FIG. 7 is a sectional side elevation of the construction shown in FIG.  6 . 
     FIG. 8 is a schematic perspective view, similar to FIG. 1, of a further preferred embodiment of the invention. 
     FIG. 9 is a sectional end elevational view of a structural embodiment based on the principle illustrated in FIG.  8 . 
     FIG. 10 is a schematic end elevational view of a variant of FIG.  8 . 
     FIG. 11 is a sectional side elevational view of a sealed through-passage for the crankshaft. 
     FIG. 12 is a fragmentary sectional side elevation of a crankshaft bearing and a forked pivot lever according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning to FIG. 1, an engine crankshaft  1  is supported in axially spaced crankshaft bearings  2  which, in turn, are supported in rotatable eccentric rings  3 . The eccentric rings  3  are rotatably supported in respective ring-supporting bearing housings  4  installed in a cylinder block. Engine pistons  6  are coupled with the crankshaft  1  by respective connecting rods  5 . The crankshaft  1  is shown in an angular position in which the pistons  6 , and  64  are situated in their upper dead center position, whereas pistons  62  and  63  are situated in their lower dead center position. 
     Each eccentric ring  3  is rigidly coupled with a respective ring-turning component  7  constituted by a pivot lever which extends from the respective ring-supporting bearing housing  4  in a downward direction through a window  16  provided therein, as will be described later in further detail. The pivot levers  7  are fixedly connected to one another by means of a rod-shaped coupling element  8  so that a synchronous rotation of all the eccentric rings  3  is ensured. The rod  8  is connected with a schematically illustrated setting device  10  by means of a push-pull component  9 . 
     The ring-turning components (pivot levers)  7 , the coupling element  8 , the push-pull component  9  and the setting device  10  together form a ring-turning assembly A. 
     Upon motion of the push-pull component  9  in the direction of the double-headed arrow  11 , the pivot levers  7  are pivoted back and forth in the direction of the arrow  11 , causing a unison rotation of the eccentric rings  3 , whereby the height level of the pistons  6  in their upper and lower dead center positions is also changed. 
     FIG. 2 illustrates the operation of the ring-turning assembly A in more detail, with reference to a single eccentric ring  3 . The rotary axis  13  of the crankshaft  1  is eccentric with respect to the rotary axis (ring axis)  14  of the eccentric ring  3  and is, by means of the pivot lever  7 , rotated into the shown position from an assumed mid position (in which the pivot lever  7  is oriented vertically downwardly). In this manner, the crankshaft axis  13  is lifted by a distance a relative to the stationary ring axis  14  of the eccentric ring  3 . As a result of the shift of the crankshaft axis  13 , upon rotation of the crankshaft  1  the piston crown  15  of the piston  6 , in the upper dead center position is, by the distance a, closer to the cylinder roof, whereby the compression ratio is accordingly increased. If by means of the pivot lever  7  the eccentric ring  3  is turned in the opposite direction, the crankshaft axis  13  is lowered by a corresponding distance with respect to the stationary ring axis  14 , whereby in the upper dead center position the distance of the piston crown  15  from the cylinder roof is increased and accordingly, the compression ratio is reduced. 
     As it may be observed from FIG. 2, the ring-supporting bearing housing  4  has a lid  4 . 1  provided with a window  16  through which the pivot lever  7  projects. As seen in FIGS. 1,  2  and  3 , it is expedient to so orient the pivot levers  7  that in each instance they project downwardly into the crank case. 
     Advantageously, the ring-turning assembly A is so designed that the ratio of the diameter D KW  of the crankshaft bearing  2  to the diameter D A  of the ring-supporting bearing housing  4  equals D KW /D A =0.5 to 0.75. Further, expediently, the ratio of the length L of the pivot lever  7  to the diameter D A  has a magnitude of L/D A =1.2 to 1.8. The ratio of the eccentricity e between the crankshaft axis  13  and the ring axis  14  to the diameter D A  has a magnitude of e/D A =0.04 to 0.08. The ratio of the eccentricity e to the length L is expediently e/L=0.03 to 0.07. 
     FIG. 3 is a sectional view of the lower region of an cylinder block B, showing details of the support for the crankshaft  1 , the crankshaft bearing  2 , the eccentric ring  3  and the ring-supporting bearing housing  4 . 
     The ring-supporting bearing housing  4  for the eccentric ring  3  is formed by a divided bearing block, whose upper part is constituted by a shell in the cylinder block, while its lower part is constituted by a bearing lid  4 . 1 . Departing from the conventional bearing lids, the bearing lid  4 . 1  has a slot-shaped window  16  through which the pivot lever  7  projects downwardly into an oil pan. Since the width of the support arrangement is determined by the required width of the crankshaft bearing, the width of the bearing surface of the bearing lid  4 . 1 , reduced by the width of the window  16  is sufficient for taking up the forces generated, so that the structural length of the engine is not enlarged when using the ring-turning assembly A according to the embodiment of FIGS. 1,  2  and  3 . 
     Each eccentric ring  3  is divided into a lower ring part  3 . 1  and an upper ring part  3 . 2 . The two rings parts are attached to one another by screws and serve for holding the respective crankshaft bearings  2 . The upper eccentric ring part  3 . 2  has a circumferentially extending groove  17  provided with a radially inwardly extending bore  18 . In the cylinder block B a central oil channel  19  is provided from which branch channels  20  extend in the region of the ring-supporting bearing housings  4 . The branch channels  20  open in the region of the groove  17  of the respective eccentric rings  3 . By virtue of such an arrangement the lubricant supply for the bearing faces of the ring-supporting bearing housings  4  as well as for the respective crankshaft bearings  2  is ensured. 
     The push-pull component  9 , together with the associated setting device  10  is arranged laterally on the cylinder block and extends from the oil pan. 
     FIG. 4 shows the entire bearing and support arrangement for the crankshaft  1  and the ring-turning assembly A. It is seen that the windows  16  provided in the bearing lids  4 . 1  and the thickness of the pivot levers  7  measured parallel to the crankshaft axis  13  are coordinated to one another such that an axial guidance of the eccentric rings  3  is effected. 
     At the output (driving) end of the engine, the crankshaft  1  has a stub  21  which is concentric to the crankshaft axis  13  and which is provided with a toothing  22  on its exterior. An inner toothing  23  of a flywheel  24  which is concentric with the ring axis  14  is in a meshing relationship with the toothing  22 . The rotation of the crankshaft  1  is transmitted to the driven (output) components by the toothings  22 ,  23 . When the eccentric rings  3  are turned about the ring axis  14 , the toothing  22  rolls on the inner toothing  23 ; thus, a force transmission in any angular position of the eccentric rings  3  is ensured. 
     It is, however, also feasible to support the flywheel  24  on a separate axle which is fixedly secured to the cylinder block and which is oriented parallel to the crankshaft axis  13 . The force transmission between the crankshaft  1  and the flywheel  24  may then be effected by means of a roller chain which, to compensate for the different lengths resulting from the radial shifts of the crankshaft, is tensioned by a chain adjuster which may be, for example, hydraulically operated. 
     The control-side free end  25  of the crankshaft  1  is, in the FIG. 4 construction, fixedly connected with a toothed-belt pulley  26  by means of which the usual accessories such as generator, fan, water pump, etc. are driven. Since the pulley  26  is concentric with the crankshaft axis  13  and is fixedly connected with the crankshaft  1 , suitable tensioning elements have to be provided for the toothed belt to compensate for the inherent length changes resulting from the turning of the eccentric rings  3  and to maintain the toothed belt at all times at a constant tension for driving the accessories. In the embodiment according to FIG. 4 for the pulley  26  a separate bearing  26 . 1  is provided which is held in the cylinder block by means of a flexible sealing disk  26 . 2  sealing the through passage in the end face of the cylinder block. At the same time, the radial shifting motions of the crankshaft  1  with respect to the cylinder block  2  upon adjustment of the compression ratio are not affected. 
     It is also feasible to provide the crankshaft  1  at its control-side free end, similarly to the flywheel  24 , with a stub having an external toothing which meshes with an inner toothing of the pulley  26  if the latter is rotatably supported on the cylinder block concentrically with the ring axis  14 . It is likewise feasible to support the pulley  26  separately and to drive it by a chain provided with a chain adjuster as it was described earlier in connection with the flywheel  24 . 
     FIG. 5 shows in plan view the construction of the coupling element (coupling rod assembly)  8  and the push-pull component  9  connected therewith. The illustrated free ends of the pivot levers  7  are secured between the clamping sleeves  27  which are firmly tightened to one another by means of a throughgoing tensioning screw  28  and thus constitute the coupling rod assembly  8  which passes through support blocks  9 . 1  of the fork-shaped push-pull component  9 . The support blocks  9 . 1  are connected with one another by means of a transverse web  9 . 2  which forms a unitary, one-piece structure with the support blocks  9 . 1 , resulting in a very rigid construction of the push-pull component  9 . Consequently, in conjunction with the support and design of the coupling rod assembly  8 , accurately uniform adjustments of all pivot levers  7  are ensured. Further, the push-pull component  9  has a traveling nut  9 . 3  threadedly engaging a rotary spindle  10 . 1  of the setting device  10 , so that upon rotation of the spindle  10 . 1  the push-pull component  9  is linearly displaceable parallel to the arrow  11 . 
     FIGS. 6 and 7 show another preferred embodiment of a device for rotating the eccentric rings  3 . In this embodiment too, each eccentric ring  3  is connected with a separate pivot lever  7  which may be connected to one another by means of a coupling rod  8 . At least one of the pivot levers  7  carries a circular segment-shaped toothing element  29  which is rigidly affixed to the pivot lever  7  and whose center coincides with the ring axis  14 . A pinion  30  keyed to the setting shaft  31  of the setting drive  10 . 2  meshes with the toothing element  29 . 
     In the embodiment according to FIG. 3 as well in the embodiment according to FIGS. 6 and 7, the setting drive is self-locking so that during operation the pistons  6  which momentarily execute expansion or compression strokes, take up, by virtue of the eccentricity between the crankshaft axis  13  and the pivot axis  14 , the torques applied to the eccentric rings  3 , and the compression ratio set by the setting drive  10  is reliably maintained. 
     FIG. 8 illustrates another preferred embodiment in which the ring-turning assembly A′ includes a toothing element  29 ′ which is affixed to the circumferential surface of an eccentric ring  3  and which meshes with a pinion  30 . The pinion  30 , in turn, is carried by the setting shaft  31  coupled to the setting drive  10 . 2 . As illustrated schematically in FIG.  8  and shown in more detail in FIG. 9, the respective ring-supporting bearing housing  4  is provided with a window  16  in a region which is laterally and above the rotary axis  14  of the eccentric rings  3 , so that the pinion  30 , by projecting through the window  16 , meshes with the toothing element  29 ′ of the eccentric ring  3 . In other details the construction and mode of operation of the embodiment of FIG. 8 is identical to that shown in FIG.  1  and described in connection therewith. 
     To be able to observe the actual dimensional relationships in an cylinder block, the schematically shown construction of FIG. 8 has to be modified to some extent. Thus, the required free space for the circular travel path of the cranks of the crankshaft must be ensured. For this purpose the setting shaft  31  must extend at a suitable distance from the rotary axis  13  of the crankshaft  1  as illustrated in FIG.  9 . The basic structure for the support of the crankshaft  1  corresponds to that described in connection with FIG.  3 . While, however, the ring-turning assembly of FIG. 3 uses simple pivot levers  7  and the FIGS. 6 and 7 modifications use pivot levers  7  with a toothing element  29 , in the FIG. 9 embodiment it is the eccentric ring  3  which is provided with a toothing element  29 ′ immediately on its outer circumference in its upper region as indicated in FIG.  8 . Here too, the ring-supporting bearing housing  4  is formed by a part of the fire wall of the cylinder block and is, laterally and above the crankshaft axis  13 , provided with a window  16 ′ into which the toothing element  29 ′ projects. Within the confines of the window  16 ′ an intermediate pinion  30 . 1  is freely rotatably supported which meshes with the toothing element  29 ′ carried by the eccentric ring  3  and with the pinion  30  carried by the setting shaft  31 . By providing the intermediate pinion  30 . 1  the setting shaft  31  extending in the longitudinal direction of the engine may be relocated outwardly to such an extent that the cranks of the crankshaft  1 , together with the connecting rods coupled therewith and with the respective engine pistons, may operate unobstructed in the required free space. 
     FIG. 10 schematically shows a variant of the embodiment illustrated in FIG.  9 . In the FIG. 10 embodiment, instead of the intermediate pinion  30 . 1  a toothed rack  30 . 2  is used which is guided in the cylinder block. The toothed rack  30 . 2  meshes with the toothing element  29 ′ of the eccentric ring  3  and with the pinion  30  of the setting shaft  31 . By virtue of such an arrangement the setting shaft  31  may be supported, together with its pinion  30 , on the exterior of the cylinder block, without significant alterations of the structural volume. 
     As a variant of the embodiments of FIGS. 9 and 10, in a cylinder block having windows  16  as in FIGS. 9 and 10, pivot levers  7  with toothing element  29  in accordance with the embodiment of FIGS. 6 and 7 may be used. 
     In the above-described embodiments each eccentric ring  3  is provided with a respective ring-turning arrangement. Dependent upon the number of the cylinders or the size of the engine, it might be expedient to directly engage by the ring-turning assembly only some eccentric rings  3 , for example, those two eccentric rings  3  which are at the opposite ends of the crankshaft  1 . Upon actuation of the setting device  10 , those eccentric rings  3  too, which are not in direct engagement with the ring-turning assembly will rotate as well. 
     While in FIG. 4 the control-side crankshaft end  25  passing through the cylinder block, is sealed by a flexible sealing disk  26 . 2  which yields to the necessary transverse shift of the crankshaft  1  when the compression ratio is changed, FIG. 11 shows another embodiment of the control-side seal. 
     As seen in FIG. 11, the crankshaft  1  is, at its control-side free terminus  25  projecting from the cylinder block, provided with a shaft stub  33  which is coaxial with the crankshaft axis  13  and which, in a manner similar to FIG. 4, is coupled with a non-illustrated belt pulley  26 . 
     For sealing the passage of the crankshaft  1  through the cylinder block, on the stub shaft  33  a sealing disk  34  is mounted for rotation relative to the stub shaft  33 . The sealing disk  34  has a hub  35  and a radially outwardly oriented disk part  36  extending from the hub  35 . The hub  35  is supported on the stub shaft  33  by a bearing (such as a needle bearing)  37  and is further provided with a sealing element  38 , for example, a shaft seal ring which seals the inner space of the cylinder block in cooperation with the stub shaft  33 . 
     The sealing disk  34  is held in a sealing housing  39  at the two faces of the disk part  36  for movement relative to the sealing housing  39 . The latter is fixedly attached to the cylinder block and is formed essentially of a bearing lid  39 . 1  provided with an aperture  39 . 2  in which the disk part  36  is held and covered by a closure  39 . 3 . The bearing lid  39 . 1  and the closure  39 . 3  are, at their faces oriented towards the disk part  36 , provided each with a circumferentially extending seal  40  pressed against the surfaces of the disk part  36 . 
     If, as described earlier, for example, in conjunction with FIG. 2, by pivoting the pivot levers  7  the crankshaft  1  is displaced transversely to its rotary axis  13  in the cylinder block, the disk part  36  is shifted likewise within the sealing housing  39  while preserving the desired sealing function. The clamping forces exerted by the seals  40  on the disk part  36  are normally sufficient to maintain the sealing disk  34  in a frictional engagement in the sealing housing  39  so that the latter is moved not by the rotation of the crankshaft  1  but only as a result of a transverse motion of the crankshaft  1  relative to the sealing housing  39 , effected by the pivot levers  7 . 
     To avoid a stress on the seals  40  by a torque generated by the friction between the bearing  37  and the sealing element  38  and applied to the sealing disk  34 , the disk part  36  is expediently provided at its circumference with a slot  41  through which an arresting pin  42  projects which is held in the closure  39 . 3  and/or in the bearing lid  39 . 1 . The arresting pin  42  secures the sealing disk  34  against being entrained into rotation as a result of a friction between bearing and seal. 
     The above-described sealing arrangement may find application not only in the described environment but generally for any environment in which a rotary shaft is transversely moveable in a machine housing. 
     FIG. 12 shows an embodiment in which the bearing lid  4 . 3  is of closed design. The pivot lever  7 . 1  connected with the associated eccentric ring portion  3 . 1  is of forked configuration for straddling the closed bearing lid  4 . 3  at both lateral surfaces thereof and, at the same time, for supporting the eccentric ring  3  in the axial direction. By virtue of the closed bearing lid  4 . 3  an axially throughgoing carrying and sliding surface is obtained which may be supplied with lubricant in a simple manner. Such a fork-like pivot lever  7 . 1  too, may be coupled with a toothing segment and may be actuated in accordance with the embodiment shown in FIGS. 6 and 7. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.
An internal-combustion engine includes a cylinder block; a plurality of cylinders arranged in line in the cylinder block; a piston accommodated for reciprocating motion in the respective cylinders; a crankshaft received in the cylinder block; a connecting rod coupling each piston with the crankshaft; and a plurality of eccentric rings surrounding and supporting the crankshaft. Each eccentric ring is rotatable about a common ring axis radially spaced from the crankshaft axis. Further, ring-supporting bearing housings are accommodated in the cylinder block for supporting the eccentric rings. A ring-turning assembly adjusts in unison the angular position of the eccentric rings to radially shift the crankshaft, whereby the upper dead center position of the pistons is altered for varying the compression ratio thereof. The ring-turning assembly includes a setting drive for exerting a force upon actuation thereof; ring-turning components connected to at least some of the eccentric rings; and a coupling element connecting the setting drive with the ring-turning components for transmitting the force exerted by the setting drive to the ring-turning components for rotating the eccentric rings.