Abstract:
A clutch release bearing ( 21 ) that is in contact with a disk spring is provided. The clutch release bearing ( 21 ) includes at least one curved contact surface ( 12, 28, 30, 33 ) that is located at a radial distance from the axis of rotation ( 4 ) of the clutch release bearing ( 21 ) and is used for contacting at least one end ( 39 ) of at least one spring tongue ( 40 ) of the disk spring.

Description:
BACKGROUND 
     The invention relates to a clutch release bearing in contact with a disk spring, wherein the clutch release bearing has at least one curved contact surface, which is located at a radial distance from the axis of rotation of the clutch release bearing and which is used for contacting at least one end of at least one spring tongue of the disk spring. 
     DE 37 438 53 A1 describes a clutch release bearing of the class-defining type. The contact surface is constructed either on the inner ring or on an outer ring of the clutch release bearing. The ends of the spring tongues are in touching contact with the contact surface. Here, the contact surface is either an annular surface extending about the axis of rotation or alternatively several segment-like contact surfaces adjacent to each other on the peripheral side are constructed on the clutch release bearing. If several of the segment-like contact surfaces are constructed on the clutch release bearing, as described in DE 37 438 53 A1, for example, ribs are provided between the contact surfaces for engagement between the spring tongues. 
     When the clutch disengages, the peripheral contact surface on the bearing ring of the release bearing is pressed with force onto the spring tongue(s). The spring tongues therefore move in the axial direction. The contact, at which the spring tongues meet the contact surface, shifts during the moving on the contact surface radially inward in the direction of the axis of rotation of the release bearing or radially away from the axis of rotation. The contact also shifts with increasing wear in the clutch. 
     The ends of the spring tongues meeting the contact surface are therefore often curved, so that they bulge convexly outward to the contact surface on the bearing and so that these always run with a linear contact to the contact surface often also curved convexly in the direction of the end on the spring tongue during the inward and outward yielding. An example of such a release bearing arrangement is described in DE 37 438 53 A1. 
     However, there are also clutch or vehicle manufacturers that, for various reasons, use disk springs, whose ends of the spring tongues are constructed straight. Such a release bearing arrangement is described in EP 015 383 59 A1. The ends usually stand in contact with a curved contact surface. These release bearing arrangements as a rule have an optimum linear contact at only one operating point, wherein this linear contact transforms into a two-point contact in a radial direction and becomes increasingly less in the other radial direction and finally ends at a single-point contact. When the clutch is actuated, the contact is shifted radially outward into a single-point contact and for movement due to wear it is shifted into a two-point contact. Such reductions of the contact lead to high surface pressures and promote unacceptable wear due to the contact on the contact and touching faces. The contact effects on the release bearing arrangements of the state of the art are described with  FIGS. 1 and 2 . 
       FIG. 1  shows schematically the touching and contact relationships during the contact of a spring tongue for the release bearing arrangement as described in EP 015 383 59 A1. As an example, a part of an outer surface of a toroidal body  1  is considered as the curved contact surface. The toroidal body  1  is shown simplified by grid lines  2  and  3 . The axial bulge of the contact surface is symbolized by the grid lines  2 . The grid lines  2  run in planes, in which the axis of rotation  4  extends and which are aligned with the axis of rotation  4 . Peripheral curvatures of the contact surface in planes, which are intersected at a right angle by the axis of rotation  4 , are symbolized by the grid lines  3 . The contact face of the non-curved end of a spring tongue is symbolized with the surface  5 . 
     The surface line marked with  3 . 1  symbolizes the surface line  3 . 1  projecting farthest in the axial direction at the axial peak  3 . 1  of the contact surface. In  FIG. 2 , a longitudinal section through the body along the axis of rotation  4 , the surface line  3 . 1  marks the turn-around point (peak) of a curve described in the longitudinal section by one of the grid lines  2 . 
     The contact of the face  5  with the surface line  3 . 1  at the peak of the curve results in an optimum linear contact  6 . The line described by the linear contact  6  is curved in  FIG. 1  corresponding to the profile of the surface line  3 . 1 . If the surface  5  tilted in the direction of the arrow  7  extends on the contact surface, in the end a two-point contact with the contacts  8  and  9  is produced. If the face  5  tilted in the direction of the arrow  10  extends on the contact surface, the linear contact becomes increasingly smaller until the face  5  and the contact surface are finally in a single-point contact at point  11 . 
     SUMMARY 
     The object of the invention is to create a clutch release bearing, which generates optimum contact to the spring tongues, in order to reduce, in particular, the wear in the arrangement. 
     This objective is met with a clutch release bearing according to the features of Claim  1  and is constructed by the features of additional dependent claims. 
     The release bearing has several contact surfaces following one after the other on the peripheral side. The contact surfaces are either directly adjacent to each other and transition one into the other at bevels or the contact surfaces are separated from each other, so that, e.g., functional elements of the release bearing are arranged between the contact surfaces. 
     For example, a construction of the invention provides that between at least two of the contact surfaces following one after the other on the peripheral side, an axial rib-like projection is formed, wherein the axial projection is provided for engaging in a peripheral spacing between two of the peripheral spring tongues adjacent to each other. The projection is tapered like a roof in the axial direction. 
     The disk springs have an arbitrary number of spring tongues, which are distributed with equal spacing relative to each other or with different spacings on the periphery. The spring tongues of a disk spring have either the same shape or a different shape relative to each other. Preferably one of the ends or alternatively also several ends of a spring tongue are allocated to each of the contact surfaces. 
     Each of the contact surfaces is curved in the planes running longitudinally with the axis of rotation—but not in the peripheral direction. The contact surface is described by an arbitrary number of straight-line surface lines adjacent to each other and aligned parallel to each other in planes intersected at a right angle by the axis of rotation. Each of the surface lines is aligned tangential and in a straight line to an imaginary circle lying in one of the planes. The axis of rotation of the clutch release bearing intersects the circle in the center thereof at a right angle. 
     The contact surface is bulged convexly toward the end and is described by surface lines that correspond through one radius to the profile of the curve of an ellipse or that are convexly curved differently in any manner. 
     One construction of the invention provides that the contact surface is described by at least one segment of an outer surface of a cylinder. The axis of symmetry of the cylinder is aligned tangential to a circumferential line running about the axis of rotation and runs parallel to the surface lines. The parallel spacing between the axis of symmetry and each of the surface lines of the contact surface is preferably at least 5 mm and thus corresponds to the radius of the cylinder. 
     The contact surfaces are either fixed to the inner ring or to the outer ring of the clutch release bearing. Here, the contact surfaces are fixed either directly to the material of the relevant ring or to at least one thrust-carrying piece or the like. As materials for the inner ring, outer ring, or for the annular thrust-carrying piece, preferably a tempering steel such as C45; CF 53, C75 or a deep-drawing grade tool steel, such as C80 U, is used. 
     The contact surface carrying piece is produced, for example, as a deep-drawn, stamped, or extruded part and is subjected to a heat treatment. The contact surfaces are alternatively provided with a wear-resistant, heat-resistant surface with low roughness made from hard-material coatings, which are comprised of, e.g., plastic, hard materials, or ceramic or nickel-aluminum alloys. Also provided are layers made from materials with the trade name “Triondur”—coatings based on chromium or nitride chromium layers. The layers are deposited, for example, through plasma coating, sintering, chemical coating, or through spraying in a flame spraying, electric-arc spraying, plasma spraying, or high-speed spraying method or through cathode evaporation or sputtering, or a vacuum-supported or plasma-supported method. 
     The thrust-carrying piece or some other suitable component is made selectively, for example, from plastic, hard metal, hardened sheet steel, or some other suitable materials or various combinations of these materials. The thrust-carrying pieces are selectively snapped, bonded, welded, injection-molded (through spraying, casting, or similar deposition) onto the corresponding bearing ring or fixed in another suitable way with a positive, non-positive, or material fit on the bearing ring. Possible attachments are, e.g., non-positive connection through press fit, positive connection through snap-on connections, and material connections through soldering, ultrasonic welding, and hot stamping and bonding. 
     Alternative materials for the thrust-carrying pieces with contact surfaces or alternatively at least for the contact surfaces are thermoplastics or duroplastics. Preferred thermoplastics are, for example, high temperature-resistant polyamides, polyaryl ether ketones (PEAK). From the range of polyamides, preferably polyamide 46 (PA 46) or semi-aromatic polyamides, preferably polyphthalamide (PPA) or polyhexamethylene terephthalamide (PA6T) or copolymers, polyhexamethylene isophthalamide (PA6T/6I) and/or polyhexamethylene adipamide (PA6T/66, PA6T/6I/66) or polymethylpentamethylene terephthalamide (PA6T/MPMDT) with friction and wear reducing, as well as strength increasing additives can be used. Selected as suitable additives are carbon fibers and/or aramide fibers in a weight percentage of 1 to 40%, preferably carbon fibers with a weight percentage of 20 to 30%, aramide fibers with a weight percentage of 1 to 15%, and also solid lubricants, such as molybdenum disulfide with a weight percentage of 1 to 5%, together with or alternatively graphite in a weight percentage of 1 to 10%, together with or alternatively polytetrafluoroethylene (PTFE) in a weight percentage of 1 to 30%, preferably a PTFE percentage of 5 to 15 weight %, together with or alternatively polyphenylene sulfone (PPSo2, Ceramer) in a weight percentage of 1 to 30%, preferably 1 to 15 weight %. 
     The contact surface is formed through non-cutting shaping in the bearing rings and thrust-carrying pieces made from sheet metal preferably at the ends. 
     Hard metals are, for example, tungsten carbides or titanium-containing metals, which are provided with bonding agents and are sintered accordingly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below with reference to embodiments. Shown are: 
         FIG. 1  a view showing the principle and the different contact relationships in the contact of a spring tongue with a contact surface on release bearings of the state of the art, 
         FIG. 2  a partial section view aligned with the axis of rotation through the toroidal body according to  FIG. 1 , 
         FIG. 3  a view showing the geometric relationships on the contact surfaces of an embodiment of the invention, 
         FIG. 4  a longitudinal section view along the axis of rotation through an embodiment of a clutch release bearing, 
         FIG. 5  a partial section view of an embodiment of a bearing ring, in which contact surfaces are formed on the peripheral side directly adjacent to each other, 
         FIG. 6  a front view of a thrust-carrying piece with several peripheral contact surfaces separated from each other by ribs, 
         FIG. 7  a longitudinal section view through the thrust-carrying piece according to  FIG. 6  along the line VII-VII, 
         FIG. 8  the detail Z from  FIG. 7 , enlarged and not true to scale, with the description of the geometry of one of the contact surfaces, 
         FIG. 9  a sectioned partial view of a bearing ring with an attached thrust-carrying piece, 
         FIG. 10  another partial view of a bearing ring with an attached thrust-carrying piece in section, 
         FIG. 11  a sectioned partial view of a bearing ring with an attached thrust-carrying piece, 
         FIG. 12  a partial section view longitudinally through another embodiment of an inner ring, on which contact surfaces are formed directly, 
         FIG. 13  a partial section view through an inner ring produced through cold forming with stamped contact surfaces. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The illustrations in  FIGS. 1 and 2  are described in the section “Background of the Invention.” 
       FIG. 3  shows a rough schematic of an example for the geometric relationships of a contact surface  12 . The contact surface  12  is a partial face of a cylinder  13 . The axis of symmetry  18  of the cylinder  13  tangentially crosses the circumferential line  19  of a circle  14  or a circular plane  14  at an intersecting point  18   a . The axis of rotation  15  of a release bearing not shown in more detail intersects the circular plane  14  in the center  16  of the circle  14 . The contact surface  12  is described by an arbitrary number of surface lines  17  and is curved in planes aligned with the axis of rotation  15 . The surface lines  17  of the contact surface  12  are aligned to each other and to the axis of symmetry  18  of the cylinder  13  and thus also in the plane of the image parallel to each other. Because the contact surface  12  is a partial face of a cylinder  13 , R is the radius of the cylinder and therefore equal as the spacing for all surface lines  17  relative to the axis of symmetry  18 . 
     The spacing between each surface line and an imaginary axis in the same position as the axis of symmetry becomes increasingly greater as an alternative to the construction described above the farther the surface line is removed from the peak line  20 . On cam-shaped contact surfaces, as an alternative this spacing becomes increasingly smaller the farther the surface line is removed from the peak line. 
       FIG. 4  shows a clutch release bearing  21  made of an outer ring  22 , an inner ring  23 , balls  24  in a cage  25 , and a guide and centering sleeve of the clutch release housing  26 . The inner ring  23  has contact surfaces  28  on a rim  27  displaced radially inward through cold forming. The contact surfaces  28  are stamped into the rim  27 . Corresponding contact surfaces can also be constructed on the guide and centering sleeve as an alternative to the just mentioned variant. 
       FIG. 5  shows a bearing ring  29 , an inner ring or an outer ring, on which contact surfaces  30  of the release bearing according to the invention are stamped, which are directly adjacent to each other and which transition one into the other at bevels  31 . 
       FIG. 6  and  FIG. 7  show an annular thrust-carrying piece  32  with peripheral contact surfaces  33  spaced apart from each other. The surface lines of the contact surfaces  33  are aligned tangentially. Between the contact surfaces  33  there are axial projections  34 , which taper at the ends into a roof shape. 
       FIG. 8  shows the curvature  35  of the contact surface  33  in a plane aligned parallel to the axis of rotation  4 , in this case the plane of the drawing of  FIG. 8 . The curvature  35  is described by a radius R. The surface lines in a plane perpendicular to the plane of the drawing are aligned in a straight line without curvature. The thrust-carrying piece  32  is fixed at the end to an inner or outer ring by bonding or welding. 
       FIG. 9  shows an embodiment of an inner ring  36  with a thrust-carrying piece  37 . The thrust-carrying piece has several contact surfaces  33  and is pressed and/or bonded tightly to the inner ring  36 . 
       FIG. 10  shows the contact of one end  39  of an only partially shown spring tongue  40  to a contact surface  33 . The spring tongues  40  or their ends  39  are in the end positions radially inward or radially outward in linear contacts  41  or  42  with the contact surface  33 . The ends  39  are spring mounted in the end positions each by the angle α of arbitrary size. The angle α is preferably 7°-8°. The thrust-carrying piece  43  with the contact surfaces  33  is welded to an inner ring  44 . 
       FIG. 11  shows a detail of an inner ring  45 , on which a thrust-carrying piece  46  is snapped and held by at least one snap-on element  38 . The snap-on element  38  is, for example, a snap-on rim or the snap-on elements are snap-on tabs. Alternatively, the thrust-carrying piece  46  is injection molded. 
       FIGS. 12 and 13  show inner rings  47  and  48 , on whose material the contact surfaces  33  are formed directly on a radial rim  49  and  50 . The inner ring  47  also has axial projections  51  formed with the inner ring  47  for the positive-fit engagement between the spring tongues of a disk spring. The inner ring  48  is a shaped part, which is produced, for example, through a combined method including deep drawing, pressing, and/or rolling, as well as stamping. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Toroidal body 
           2  Grid line 
           3  Grid line 
           3   a  Surface line 
           4  Axis of rotation 
           5  Surface 
           6  Linear contact 
           7  Arrow 
           8  Contact 
           9  Contact 
           10  Arrow 
           11  Point 
           12  Contact surface 
           13  Cylinder 
           14  Circle/circular plane 
           15  Axis of rotation 
           16  Center 
           17  Surface line 
           18  Axis of symmetry 
           18   a  Intersection point 
           19  Circumferential line 
           20  Peak line 
           21  Clutch release bearing 
           22  Outer ring 
           23  Inner ring 
           24  Balls 
           25  Cage 
           26  Release bearing housing 
           27  Rim 
           28  Contact surface 
           29  Bearing ring 
           30  Contact surface 
           31  Bevel 
           32  Thrust-carrying piece 
           33  Contact surface 
           34  Projection 
           35  Curvature 
           36  Inner ring 
           37  Thrust-carrying piece 
           38  Snap-on element 
           39  End of a spring tongue 
           40  Spring tongue 
           41  Linear contact 
           42  Linear contact 
           43  Thrust-carrying piece 
           44  Inner ring 
           45  Inner ring 
           46  Thrust-carrying piece 
           47  Inner ring 
           48  Inner ring 
           49  Radial rim 
           50  Radial rim 
           51  Projection