Abstract:
A rolling bearing, particularly a rotor bearing, or main bearing, for a wind power generating plant, the bearing having at least two mutually concentric rings separated from each other by a gap in which one or more rows of rolling elements roll along raceways on both rings, such that the two rings are rotatable in mutually opposite directions about their common axis, wherein each ring has at least one connection surface for connection to a foundation, wherein the connection surfaces extend parallel to one another and are passed through approximately perpendicularly by a plurality of fastening bores for receiving fastening bolts extending through them or screwed into them, wherein the raceway of at least one rolling-element row is formed on a part separate from the ring concerned and is pushed away from the ring concerned in a direction perpendicular to the connection surfaces, by at least one resilient element.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention is directed to a rolling bearing, particularly a rotor bearing or main bearing for a wind power generating plant, having at least two mutually concentric rings that are separated from each other by a gap in which one or more rows of rolling elements roll along raceways on both rings, such that the two rings can be rotated in mutually opposite directions about their common axis, wherein each ring has at least one planar, annular, preferably raised connection surface for connection to a machine part, plant part, chassis or foundation, wherein the connection surfaces extend parallel to one another and are passed through approximately perpendicularly by a plurality of fastening bores for receiving fastening bolts that are inserted all the way through them or screwed into them. 
         [0003]    2. Description of the Prior Art 
         [0004]    Since larger machines and plants are generally more advantageous commercially than smaller ones, there has been a steady trend toward increasingly large capacities. Particularly clear evidence of this phenomenon can be seen in the steadily increasing overall size and power rating of wind power generating plants, although similar effects can also be noted elsewhere, for instance in the ever-greater size of ships and aircraft. This trend carries with it a need for increasingly large rolling bearings for such equipment. In wind power generating plants, this relates primarily to the main bearing for supporting the rotor, the yaw or nacelle bearing for pivoting the nacelle, and finally, the blade bearings for changing the pitch of the rotor blades. The blade bearings are in turn responsible for most of the strain on the main or rotor bearing, since the latter must absorb the repeated wind pressure from the blade bearings in the axial direction; it must support the entire weight of the rotor in the radial direction, including the hub and the rotor blades; and finally, it has to rotate the most constantly. Consequently, triple-row roller bearings are used preferentially as main bearings for wind power generating plants, due in particular to their much longer service life than that of other rolling bearing designs. 
         [0005]    In all mountings where loads are transmitted across oblique contact angles, the bearings are subject to increased expansion due to the compliance of the adjacent structure. The effects can be seen in the form of greater leakage of lubricating agents, increased sliding movements by the rollers when idle, greater ovalization of the bearing rings, etc. In triple-row bearings, however, which transmit the loads to a radial raceway with a contact angle of 0° and the tilting moments and axial loads to two axial rows with a contact angle of 90°, these effects are smaller, regardless of whether rollers or balls are used as the load-transmitting elements. 
         [0006]    Triple-row roller bearings have a relatively narrow axial clearance, however, which is troublesome particularly in wind turbine applications. 
         [0007]    Furthermore, roller bearings are much more sensitive than ball bearings to standstill vibrations. Efforts are therefore being made to develop bearings for such applications that operate under bias as much as possible. 
         [0008]    The axial play of the bearing can be narrowed further by the bolt clamping forces exerted on the bearing rings by the fastening bolts, and undesirably high biases can occur in the axial rows if the ring geometry is unfavorable. 
         [0009]    To incorporate a bearing of this kind, therefore, an extremely delicate compromise must be reached among the various requirements: On the one hand, these bearings should run very smoothly; on the other hand, they should ideally be adjusted free of play. With rotor bearings several meters in diameter, such adjustment and fine-tuning of play is very labor-intensive, and even relatively small changes in environmental conditions, e.g. temperature changes, can disrupt the sensitive balance struck between freedom from play and moderate bias. 
         [0010]    Added to this is the fact that load distributions on the individual axial raceways and the radial raceway can differ greatly, depending on the load case. For example, load situations can actually arise where an axial row is largely or completely load-free, and the rolling elements in that row do not roll sufficiently or even stand still. In this case, the rolling elements drag over the raceway and the worrisome phenomenon of flat wear can develop, particularly in the form of abrasions. From the disadvantages of the described prior art comes the problem initiating the invention: in a rolling bearing of this species, to eliminate the described disadvantages that occur particularly in the case of large bearing diameters of approximately one meter or more. 
       SUMMARY OF THE INVENTION 
       [0011]    This problem is solved by the fact that a raceway of at least one rolling-element row is formed on a raceway ring that is separate from the connection ring concerned and that is pushed away from the particular connection ring, in a direction perpendicular to the connection surfaces, by a device comprising at least one resilient and/or elastically compressible element. 
         [0012]    A spring element of this kind makes it possible to produce and/or adjust a bias, particularly in a direction perpendicular to the connection surface of the ring concerned. As a result, the rolling elements of a rolling-element row remain under a load created by the bias even when no external loads are being applied to the row, thus reliably keeping the rolling elements from sliding. At the same time, unduly high bias is prevented by the compliance of the springs. Finally, a measure of this kind makes it possible to avoid any narrowing of the bearing play by the clamping force of the fastening bolts and/or due to slight unevenness in a connected machine part or plant part. The direction of bias from the connection ring concerned refers to the local direction in the region of the closest-together surfaces of the connection ring and the raceway ring. In the region of these directly confronting surfaces the two rings are pushed away from each other, i.e., apart. This can be effected by a pressure means, and has the additional advantage that one or more such pressure means can be disposed on the side of the raceway ring, particularly its front side, that faces the raceway per se, i.e., can be aimed, in a direction parallel to the axis, straight at the rolling elements rolling along the raceway. This eliminates the possibility of tilting, twisting or the like. By the same token, these pressure means or their anchoring means do not extend all the way through the raceway ring, thus ensuring a continuous raceway surface uninterrupted by anchoring means or the like. Finally, such preferably pressure-exerting spring elements are particularly easy to produce: for example, they can be disposed in trough- or groove-shaped depressions in the connection ring, and are thus extremely space-saving. For controllable pressure means, for example hydraulic pressure means, the drive lines concerned can be led out in rectilinear extension, hence in a row perpendicular to the raceway concerned, and can be contacted or connected there—preferably in the region of the end face of the particular connection ring that faces the connection surface—if not in the ring itself, for example by means of a circumferential connection channel. Since the necessary pressure-application or adjustment mechanism can thus be installed in the axial direction immediately under the raceway concerned, the connection elements of the particular connection ring can be configured as through-bores without it being necessary to increase the cross section of the particular ring. The risk of fracture is considerably reduced by the fact that the guide means or anchoring means are loaded primarily in compression rather than in tension. 
         [0013]    It has proven advantageous for one or preferably both of the connection rings to have an axial extent that is smaller than the outer diameter of the radially outer connection ring, for example smaller than the maximum diameter of the gap, preferably smaller than the inner diameter of the radially inner connection ring, and which is preferably smaller than the outer radius of the outer ring, particularly smaller than the inner radius of the inner ring. By means of the raceway ring according to the invention, such delicate bearing rings, with their limited inherent rigidity, can be used without further modifications even in wind power generating plants or the like, since any deformation due to loads and/or an uneven connecting structure are tolerated by the movable raceway ring. 
         [0014]    The rolling elements of at least one row can be configured as rollers. Although rollers are subject to the risk of flat wear in the case of partial unloading, they will not slide or drag, because they are maintained in friction-locked contact with the raceways by the bias according to the invention. 
         [0015]    It is within the scope of the invention that plural rows of rolling elements are provided, particularly at least three. In this way, for example, a respective row of rolling elements is provided for forces in each of the two axial directions and another row is provided for radial forces. 
         [0016]    Additional advantages are gained if the raceway ring has an approximately rectangular cross-sectional geometry, with the longer main axis extending parallel to the particular connection surface. Such a geometry facilitates a minimal axial height for a bearing according to the invention, so the two connection surfaces of two oppositely rotatable components can be disposed a minimal distance apart, which is important for many use cases. 
         [0017]    The invention can be developed further by having the direction of pressure application of at least one resilient and/or elastically compressible element extend parallel to the fastening bores in the particular connection ring. In particular, this eliminates effects of the clamping forces of these fastening means. If, for example, the connection ring per se is deformed by these forces, then the raceway ring can move in relation to it and thus compensate for stress-induced local deformations. 
         [0018]    The raceway ring is preferably pushed toward the connection surface of the particular connection ring. The raceway ring is then located on the side of the particular rolling-element row facing away from this connection surface, and can, for example, be adjusted or serviced from this relatively accessible side. 
         [0019]    A particularly advantageous arrangement is obtained if the raceway ring pushes the rolling elements that roll along it against a nose ring of the other connection ring. In this case, the raceway ring is not disposed on the nose ring, but on the respective other connection ring, and therefore pushes toward the center plane of the bearing, with the result that the elastic pushing means face toward an outer bearing end side and ideally can be accessed from that side, for maintenance purposes, for example. 
         [0020]    By virtue of the invention, it is possible for two rows of rolling elements to be maintained under bias in the axial direction by a raceway ring, one rolling-element row of the two preferably being on the near side of the nose ring and the other one on the far side of the nose ring. Such an arrangement results when a respective row of rolling elements runs along each of the two flanks of a circumferential flange. These two rows of rolling elements are then, so to speak, lined up one after the other in the axial direction and can be placed under bias together by means of a single clamping device. 
         [0021]    The invention is further distinguished by at least one piston element, to which pressure is applied by a resilient and/or elastically compressible element and which is thereby pressed against the raceway ring. Since the raceway ring absorbs the pressure force of one or more piston elements and distributes it over its annular base plane, it is quite possible to use a plurality of discrete, mutually separated, particularly piston-shaped pressure elements instead of a single pushing device distributed over the entire circumference. Such a piston can be and remain separate from the raceway ring per se, it can be connected thereto, or it can even be produced integrally therewith. The choice of the best variant is guided primarily by the ability to achieve optimal mechanical behavior for the assembly as a whole and by ease of installation (and removal) of the assembly. 
         [0022]    At least one such piston element can be guided in a guide opening of the particular connection ring, particularly in a bore thereof. The particular cross-sectional fit between the piston element and such a receiving guide opening can be configured as a transition fit, to keep both friction and play to a feasible minimum. 
         [0023]    It is further provided according to the invention that at least one piston element is sealed with respect to its guide opening, for example by means of at least one fully circumferential sealing ring. This serves to keep lubricant from the raceway region from getting into the area behind the piston and potentially altering the resilience characteristics. 
         [0024]    The maximum deflection of at least one piston element can be limited, particularly by an adjustable stop. The maximum play of the raceway ring can be limited in this way, so the bearing will basically keep working even if a spring means is defective in addition, the bearing according to the invention is thus given defined characteristics, which will characterize its behavior in the worse case of maximal excursion of the raceway ring. 
         [0025]    The invention can be realized by having at least one resilient element configured as a disc spring or as a disc spring pack whose disc springs are preferably stacked one behind the other in the longitudinal direction of the fastening bores. The discs are preferably metal rings whose cross section is not planar, however, but instead extends along a very shallow conical surface. In a disc spring pack, these rings can be stacked so that the opening angles of the conical surfaces of adjacent rings open upward and downward in alternation. To stabilize a pack of this kind, the rings concerned can be passed through by a rear portion or shaft region of the piston or a rod anchored therein, a bolt screwed therein or the like. The effect of arrangement parallel to the fastening bores is a pressing force that is perpendicular to the particular raceway plane. 
         [0026]    According to a preferred further development of the invention, at least one disc spring or at least one disc spring pack is located on the same radial straight line as a fastening bore of the particular connection ring. These are the locations where the influence of the tensions created in the particular connection ring by the fastening bolts is greatest, so the effect of the biasing device according to the invention is maximal there. 
         [0027]    A further design rule is that at least one disc spring pack must be passed through by a piston element that pushes against the raceway ring. To receive the spring force from the disc spring pack, the piston element has a rear abutment surface for the disc spring pack; to achieve this purpose, this abutment surface is larger than the central opening in a disc spring. 
         [0028]    In the context of another embodiment of the invention, it is provided that at least one resilient, elastically compressible and/or adjustable element has at least one chamber that is or can be filled with a fluid, particularly with a hydraulic oil. If this chamber is filled with the particular medium and then placed under pressure, a corresponding pressure force is exerted against the inner surface of the chamber. If—as the invention further provides—the chamber is located at the back end of a piston element, this pressure force acts in the region of the piston element on the back side thereof and thereby pushes it against the raceway ring placed against the front side thereof, to press said raceway ring against the row of rolling elements located there. 
         [0029]    Finally, it is within the teaching of the invention that at least one elastically compressible element is seated in a depression, particularly in a bore or in a fully circumferentially groove. Whereas a piston element cushioned by means of disc springs can be guided in an opening that is open at the back and the chamber can be made sealable at the back for a hydraulic pressure medium, particularly hydraulic oil, the arrangement can also be realized in such a way that an opening that is closed at the back is provided in the connection ring to receive an elastically compressible element, for example made of hard rubber or, if appropriate, a still harder material, which pushes directly against the back side of a piston element seated in front of or in this opening, or the back side of the raceway ring. 
         [0030]    The bias can be produced not only by means of disc spring packs or other spring designs, but also by means of permanently elastic elements or, alternatively, by pneumatic or hydraulic means. The bias created is transmitted to the row of rolling elements via the raceway ring. It has proven advantageous to adjust the magnitude of the load applied by the bias to a value that is within a range of 2% to 20% of the dynamic load capacity. At values above this range the negative influence on service life can predominate, whereas below this range it is impossible to ensure that the bias will be effective. 
         [0031]    The spring elements are inserted in cylindrical depressions in the retaining ring, the nose ring or the raceway ring. If they are inserted in the retaining ring, the bias can be influenced from the outside, for example by means of bolts. If the bias is produced pneumatically or hydraulically, the energy can be supplied via a corresponding ring conduits [singular/plural sic] and the bias regulated centrally. Smoothness of operation can also be influenced in this way, and any wear on the raceways can be at least partially compensated. 
         [0032]    It is also conceivable to have the spring elements inserted in one or more annularly circumferential grooves. Such a groove can also be used to guide the raceway ring and receive the spring elements. In this case, a particularly suitable spring element is an elastic profile that can be inserted in a groove of this kind. 
         [0033]    The raceways of large slewing bearings are typically hardened, particularly inductively hardened. This can also be done with the raceway ring according to the invention. Due to process limitations, there is a narrow spot at which the hardness is reduced between the beginning and the end of a raceway hardened in the forward-feed process. This so-called hardness gap can be lowered with respect to the rest of the particular raceway by abrasive grinding, so the rolling elements rolling over it do not transmit a load at that location. If the raceways and the intermediate ring are inductively hardened gaplessly by a special method that requires at least two induction heads, then there is no hardness gap and no need to abrasively grind the raceway, which has an advantageous effect on the smoothness of operation of the bearing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Further features, details, advantages and effects based on the invention will become apparent from the following description of a preferred embodiment of the invention and by reference to the drawing. Therein: 
           [0035]      FIG. 1  is a sectional view through a rolling bearing according to the invention, partially cut away; 
           [0036]      FIG. 2  is an enlargement of detail  11  from  FIG. 1 ; 
           [0037]      FIG. 3  is a modified embodiment of the invention in a representation corresponding to  FIG. 2 ; and 
           [0038]      FIG. 4  is a further modified embodiment of the invention in a representation corresponding to  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]      FIG. 1  is a section taken transversely through an annular rolling bearing  1  according to the invention. This is a large rolling bearing, of the kind used, for example, in wind power generating plants, for example as the rotor bearing or main bearing thereof. Clearly, similar designs could also be used for other purposes: for example, as the blade bearings or the yaw or nacelle bearing of a wind power generating plant. 
         [0040]    In the case illustrated, the viewer will recognize an outer ring  2  configured as a nose ring and, disposed concentrically therein, an inner ring  3 , which is preferably divided into two subrings  4 ,  5  abutting each other along a plane  6 . The ring  3  formed by these adjoining subrings  4 ,  5  has an approximately C-shaped cross section and surrounds the nose or a circumferential flange  7  of the nose ring  2  on the top and bottom surfaces  8 ,  9  thereof with a gap  10 , such that the two rings  2 ,  3  can be rotated in mutually opposite directions. 
         [0041]    In the exemplary embodiment shown, provided in the gap  10  is a total of three rows of rolling elements  11 ,  12 ,  13 , all of which roll along the flange  7 , specifically on its planar top surface  8 , its planar bottom surface  9 , and also on a concavely cylindrical face  14  that connects these two surfaces  8 ,  9  to each other. Should the nose ring be configured as the inner ring, on the other hand—which can also be contemplated—then connecting face  14  on the flange  7  would be cylindrical rather than concavely cylindrical. 
         [0042]    The rolling elements  11 ,  12 ,  13  in this exemplary embodiment are rollers, but tapered rolling elements are also conceivable, as are balls. The individual rolling elements  11 ,  12 ,  12 ,  13  are held in their positions relative to each other by cages  15 . 
         [0043]    The gap  10  is preferably filled with a lubricant, for example grease. To prevent this from leaking out of mouth regions  16  of the gap  10 , these regions  16  are sealed, preferably each by a respective circumferential sealing ring  17 , which is inserted by its cross-sectionally rearward region in a circumferential groove  18  of a connection ring  2 ,  3  and which by virtue of its inherent elasticity is pressed by its frontward cross-sectional region, which preferably tapers to a sealing lip  19 , against a surface region of the respective other ring  3 ,  2  and extends therealong. 
         [0044]    Each of the two rings  2 ,  3  has two substantially planar end faces  20 ,  21 ,  22 ,  23 , one of which per ring  2 ,  3  serves as a connection surface. These two connection surfaces  20 ,  23  are raised above the adjacent end face  22 ,  21  of the respective other ring  3 ,  2 , thus enabling a bearing  1  of this kind to be fitted between planar connection surfaces of two plant and/or machine parts without any problems and without the need for grinding. The two connection surfaces  20 ,  23  are parallel to each other. 
         [0045]    To secure a respective connection ring  2 ,  3  to a respective such plant part or machine part or foundation, each connection ring  2 ,  3  has a plurality of fastening bores  24 ,  25 , which are distributed coronally along the respective ring  2 ,  3  and pass perpendicularly through the connection surface  20 ,  23  concerned. Whereas in the illustrated example these fastening bores  24 ,  25  are configured as bores that extend all the way between these two end faces  20 ,  21  or  22 ,  23 , many or all of the fastening bores  24 ,  25  could also be configured as blind bores provided with an internal thread. 
         [0046]    Whereas all the raceways of the nose ring  2  are formed directly on its circumferential flange  7 , particularly by machining its molded body, into which the fastening bores  24  are also machined, particularly drilled, only two of the three raceways of the C-shaped ring  3  are formed directly on the latter, particularly by machining its molded body, into which the fastening bores  25  are also machined, particularly drilled. In the example shown, the ring concerned is subring  5 , comprising connection surface  23 . 
         [0047]    The third raceway of the cross-sectionally C-shaped ring  3  preferably is not disposed directly thereon, i.e., neither on subring  5  comprising connection surface  23  nor on the other subring  4 ; subring  4  thus has no raceway in the present example. Instead, a raceway  26  concerned—along which the rolling elements  11  travel—is disposed on a dedicated raceway ring  27  located in the region of a channel  28  of the particular cross-sectionally C-shaped ring  3 , particularly on its subring  4 . 
         [0048]    In the example illustrated, this raceway ring  27  has a rectangular cross section whose longer sides are the flat sides  26 ,  29  of the raceway ring  27 , while its shorter sides are, respectively, a cylindrical jacket surface  30  of the raceway ring  27  and a concavely cylindrical jacket surface  31  thereof. The side  29  facing away from the raceway  26  would rest on a planar boundary surface  32  of the channel  28  if it were not pushed away from it and toward the rolling elements  11  by one or more piston elements  33 . 
         [0049]      FIG. 2  is an enlarged representation of such a piston element  33 . It comprises a head  34  with a planar top side  35  for contacting the planar back side  29  of the raceway ring  27 , and a rear shaft region  36  that is tapered relative to the head  34 . In the exemplary embodiment shown, the head  34  and the shaft  36  each have a circular cross section, the respective centers being aligned with each other. A stop element  37  can be screwed onto the free end of the shaft  36 , and preferably has the same cross section as the shaft  36 . 
         [0050]    This piston element  33  is guided slidably in the longitudinal direction  39  of its shaft  36  in an opening  38  of the particular ring, preferably the C-shaped ring, particularly the inner ring  3 , here specifically subring  4 . This shaft longitudinal direction  39  is therefore also the longitudinal direction of the opening  38 , which, in turn, extends perpendicularly to the connection surface  23  and thus parallel to the fastening bores  25 . 
         [0051]    Opening  38  extends all the way through the respective ring  3 ,  4  from the boundary surface  32  of the channel  28  to end face  22 , and has a stepped cross section. A region  40 —an upper region, in FIG.  2 —close to the raceway ring  27  or close to the boundary surface  32  of the channel  28  has a cross section approximately corresponding to that of the head  34 , while a region  41  of the opening  38 —a lower region, in FIG.  2 —near the end face  22  approximately corresponds in cross section to the cross section of the piston shaft  36 , and thus is tapered cross-sectionally relative to the upper region  40 . 
         [0052]    The upper region  40  is longer in axial extent than the height of the head-like broadening  34  of the piston element  33 . Since—as will be explained further below—the piston element  33  is constantly being pressed upward, where it butts against the bottom side  29  of the raceway ring  27 , in the normal case the top side  35  of the head  34  is always flush with or above the boundary surface  32  of the channel  28 . An annular space  44  thus remains free below a step  42  of the piston element  33 , between its head  34  and shaft  36 , on the one side and above a step  43  of the opening  38  between its widened upper region  40  and its tapered lower region  41 . 
         [0053]    This annular space  44  serves to accommodate a pack of annular disc springs  45  stacked one on top of the other. These annular discs are not flat, however, but are slightly conically deformed. They rest atop one another with the their conical openings directed alternatingly upward and downward, so that they are in contact with each other only along their inner or outer edges. The topmost and bottommost disc springs  45  rest each against a respective step  42 ,  43  and push them apart, as a result of which the piston element  33  is subjected to an upward pressure—in this case, toward connection surface  23 —and thus pushes the raceway ring  27  against the particular row of rolling elements  11 . Where appropriate, a (respective) washer could further be provided between an (or each) outermost disc spring  45  and the respective step  42 ,  43 . 
         [0054]    The tapered region  41  of the opening  38  can be tapered again in its lower region, particularly to a smaller cross section than the stop element  37  at the free bottom end of the piston shaft  36 ; an additional step  46  created in this way then forms an abutment for the stop element  37 , which is ultimately braced by the step  46  if the disc spring pack  45  becomes overloaded. 
         [0055]    In addition, the bottommost portion of the tapered region  41  could be provided below the step  46  with an internal thread, so that the opening  38  can be sealed by screwing in a cap  47 , bolt or the like. 
         [0056]    The raceway ring  27  is preferably surface-hardened, particularly in the region of its raceway  26  and/or its bottom side  29 . If the axial extent of the raceway ring  27  is not too large, the raceway ring  27  could also be through-hardened. 
         [0057]    The spring constant and the number of disc springs  45  per pack are adjusted so that in the case of normal operation the bias exerted on the raceway ring  27  by this disc spring pack  45  and passed along to the rolling elements  11  is equal to approximately 2% to 20% of the dynamic load capacity of this rolling-element row  11 . 
         [0058]      FIG. 3  shows a modified embodiment of the invention, in which a bearing  1 ′ corresponds on the whole to bearing  1  from  FIG. 1 . Here, however, the piston elements  33 , through-passing openings  38  and disc spring packs  45  are absent. Instead, provided here in the region of a channel  28 ′ below a raceway ring  27 ′ is a groove  48  that extends all the way along a ring  3 ′ or subring  4 ′, and in which an elastic profile  49  is seated. The raceway ring  27 ′ then rests directly on the top surface of this profile. To guide raceway ring  27 ′, the latter can have on its bottom side  29 ′ a preferably formed-on, or alternatively fastened-on, circumferential attachment  50  whose width is approximately equal to the width of the groove  48  and whose height is slightly greater than the difference between the depth of the groove  48  and the height of the profile  49  seated therein. 
         [0059]    A further modified embodiment of the invention can be found in  FIG. 4 , where a bearing  1 ″ corresponds on the whole to bearing  1  from  FIG. 1 . Here, piston elements  33 ″ and the respective openings  38 ″ to receive them are provided; there are no disc spring packs  45 , however. 
         [0060]    Instead, the openings  38 ″ are connected in their bottom regions by a groove  51  in the nature of an annular channel, which runs all the way around a ring  3 ″ or subring  4 ″ and which in turn is sealed by a ring  52  seated and fixed therein, for example by welding or gluing. The openings  38 ″ form with the annular channel  51  a closed cavity into which a preferably fluid medium, for example hydraulic oil, can be funneled through a feed line (not shown) and placed under pressure. 
         [0061]    So that this medium, particularly hydraulic oil, cannot leak up out of the openings  38 ″, the piston elements  33 ″ seated therein are sealed. For this purpose, they each have a cylindrical shape with a cross section approximately corresponding to that of the openings  38 ″, but comprise on their jacket side one or more fully circumferential grooves  53  in each of which a respective sealing ring  54  is inserted. 
         [0062]    The pressure of the medium, particularly hydraulic oil, can be used to adjust the contact pressure of a raceway ring  27 ″ against a particular rolling-element row  11 ″. This can be done just once, during the filling of the annular space  51 ; or at each maintenance; or, if appropriate, in an ongoing manner, for example by means of a pressure regulator.