Abstract:
A rolling bearing which has at least one bearing ring and a plurality of rollers. The bearing ring has a raceway for the rollers and at least one lateral rim for axially guiding the rollers. The roller has a front face facing the rim and the rim has a rim bearing surface facing the roller. At least sections of at least the front face or the rim bearing surface are cambered in the direction of the rim bearing surface or the front face. The camber has a logarithmic profile of camber in at least one border section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 of PCT/DE2006/002185 filed Aug. 12, 2006, which in turn claims the priority of DE 10 2005 061 103.6 filed Dec. 21, 2005. The priority of both applications is hereby claimed and both applications are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a rolling bearing. The present invention is described with reference to tapered roller bearings, although it is pointed out that the invention may also be applied to other types of bearing, such as cylindrical roller bearings or self aligning ball bearings. 
     BACKGROUND OF THE INVENTION 
     According to the state of the art roller hearings are known which, with reference to a raceway, have lateral rims for absorbing axial stress components. In this connection, according to the state of the art, cylindrical roller bearings with flat roller front faces and flat rim faces are known. These bearings give rise to edge loading of the rolling body with respect to the rim. The result of such edge loading is a reduced working life of the rolling bearing. 
     In addition, according to the state of the art, cylindrical roller bearings are known where the front face of the rolling bodies is formed in the manner of a spherical cap. In the case of these rolling bodies a central region of the front faces is not spherical, but is formed flat or with a depression. Thus the contact surface of these rolling bodies is at least on the rim shoulder to a certain degree truncated, resulting in a limited axial load capacity during rim contact. 
     SUMMARY OF THE INVENTION 
     The present invention relates a rolling bearing, which is able to withstand higher axial stresses compared to the state of the art. A special area of application of such tapered or cylindrical roller bearings is for example wind power gearing. 
     The rolling bearing according to the invention has at least one bearing ring and a plurality of rolling bodies. The bearing ring has a raceway for the rolling bodies and at least one lateral rim for axially guiding the rolling bodies. According to the invention, the rolling body has a front face with no edge facing the rim and the rim has a rim hearing surface facing the rolling body and at least the front face or the rim bearing surface is, at least along sections, curved in a convex manner in the direction of the rim bearing surface or the front face. This curvature has a logarithmic curvature profile in at least one edge section. 
     The bearing ring may consist of a bearing outer ring or a bearing inner ring. The front face of the rolling body is understood as being the end face thereof as opposed to the lateral surface, the rolling body rolling with its lateral surface along the raceway of the bearing ring. 
     As well as providing guidance, the lateral rim also serves to absorb axial loading components. 
     With respect to the rolling bodies, an edge section is understood to mean any section of the front face which is spaced apart in its entirety from the rotational axis or axis of symmetry of the rolling body. An edge section of the rim bearing surface is correspondingly understood to mean any section which is spaced apart in its entirety from the axis of symmetry of the rolling bearing. A logarithmic relationship or a logarithmic curvature profile is understood to mean any relationship which has at least one logarithmic component and in particular a logarithmic factor or summand. The front face preferably usually has a first curvature profile in at least one first edge section and a second curvature profile, which differs from the first, in a second edge section. 
     A first and a second curvature profile are understood to mean two different curvatures, that is to say curvatures which can be described by different geometric relationships. Here, however, a curvature is understood to mean only a curvature with a finite radius of curvature; a straight line is therefore not considered as a curvature. 
     For example, a first edge section which is situated closer to the rotational axis of the rolling body could have a first radius of curvature, and a second edge section which is situated further outward could have a second logarithmic curvature profile. In a preferred embodiment which is described in detail below, the first edge section has a toroidal convex curvature profile, and the second edge section has a logarithmic curvature profile. 
     The front face is preferably curved in a convex manner in the direction of the rim bearing surface at least in sections. Said curvature preferably has a first curvature profile in the first edge section and has the second curvature profile, which differs from the first, in the second edge section. This means that preferably both curvature profiles are curved in a convex manner in the direction of the rim bearing surface. It would however also be possible to provide only one logarithmic curvature profile of the front face. 
     Preferably the rolling bearing has a second bearing ring and the rolling bodies are arranged between the first and the second bearing rings. A lateral rim is preferably also arranged in the case of the second bearing ring and especially preferably on the side of the rolling bearing lying opposite the first rim. 
     The curvature preferably extends toroidally in at least one edge section. Whereas, in the spherical cap like curvature known according to the state of the art the entire front face of the rolling body has, along sections, the form of a sphere, the radius of this sphere lying on the axis of rotation of the rolling body, the toroidal curvature of the front face described here is not described by a sphere, the center of which lies on the axis of rotation of the rolling body, but for example by circular lines or ellipse lines, the centers of which are offset from the axis of rotation. More precisely, in a preferred embodiment, the centers of the toroidal curvatures are arranged in the manner of a circle around the axis of rotation of the rolling body. 
     In this connection these centers need not necessarily be the centers of circles, but they may also be centers of ellipses or similarly formed bodies. As a result of the toroidal curvature a circular curvature is present in the outer region of the rolling body and this curvature merges in an edgeless manner into a flat central region of the rolling bearing. Thus, viewing the rolling body in axial section, a flat central region adjoins an outer region with a given radius of curvature and a second curved region with the given radius of curvature adjoins this flat central region. The respective circular curvatures are preferably adjoined by the logarithmic curvature profile according to the invention. 
     In a further preferred embodiment, the curvature profile in at least one region of the front face can be described by a superposition of a toroidal relationship and of a logarithmic relationship. This makes it possible, for example, for a logarithmic curvature profile to be superposed on a toroidal curvature profile. It is however also possible for a toroidal profile and a logarithmic profile to be applied separately from one another and to merge into one another at a predefined transition point. 
     The curvature profile in at least one edge section is preferably described by the mathematical relationship 
     
       
         
           
             
               h 
               ⁡ 
               
                 ( 
                 x 
                 ) 
               
             
             = 
             
               cDw 
               ⁢ 
               
                   
               
               ⁢ 
               
                 
                   ln 
                   ( 
                   
                     1 
                     
                       1 
                       - 
                       
                         
                           k 
                           ⁡ 
                           
                             ( 
                             
                               x 
                               l 
                             
                             ) 
                           
                         
                         p 
                       
                     
                   
                   ) 
                 
                 . 
               
             
           
         
       
     
     Here, Dw denotes the diameter of the rolling body, l denotes the distance between a contact point between the front face and the rim bearing surface on the one hand and the raceway of the bearing ring or the end point of the front face on the other hand, and h(x) denotes the profile height, that is to say the distance by which the front face is remote from a tangent to the front face at the contact point in the direction of the raceway. With respect to the rim bearing surface, l denotes the spacing between the contact point and the rim shoulder. 
     Here, it is preferable for the numerical value for c to be between 0.00001 and 1, for the numerical value for k to be between 0.5 and 2.5, and for the numerical value for p to be between 1 and 10. In practical application, it must however be ensured that the denominator is always greater than 0. 
     Preferably the aperture angle between the raceway and the rim bearing surface is greater than 90°. In the case of evenly curved surfaces, in order to determine the rim aperture angle, a straight line is considered, said line running in the radial direction of the rolling bearing through the starting point and the end point of the curvature. As a result of this embodiment, instead of a contact area between the front face of the rolling bearing and the rim bearing surface, there is a contact point with a gap gradually opening outwards. In this way a frictionally favorable contact is established, resulting in favorable penetration of lubricant and thus a smaller amount of friction. 
     In addition, as a result of the inventive constructional form of the rim bearing surface and the front face of the rolling body, an effectively round geometry is obtained in the region of contact and thus a high tolerance with respect to tilting or skewing of the roller is achieved. 
     In a further preferred embodiment both the front face and the rim bearing surface are curved at least along sections. Particularly preferably both the rim bearing surface and the front face of the rolling body have a crowned form with a given toroidal radius. In this connection this toroidal radius of the two curvatures may be the same, although the two radii may also vary with respect to each other. The curvature of the rim bearing surface can also have a logarithmic curvature profile in one section. 
     Preferably both the front face and the rim bearing surface are curved in a convex manner in the direction of the respective other surface or face. In this way particularly favorable penetration of lubricant may be achieved. It is also possible, however, for one of the two surfaces to be curved in a concave manner, in which case the corresponding convex radius of curvature is particularly preferably smaller than the concave radius of curvature. 
     Preferably the front face of the rolling body lies at least at a distance on a circular line. This means that, as mentioned above, the curvatures of the rolling body, in axial section, are formed by circular lines, the centers of these circular lines being situated offset at a given distance from the axis of rotation of the rolling body preferably in the direction of the curvature. 
     Preferably at least one component of the rolling bearing according to the invention is produced by means of a hard turning process. By using the hard turning process it is possible to achieve low-cost production of the torus radii mentioned. 
     Preferably the rolling bearing is chosen from a group of rolling bearings which includes cylindrical roller bearings, tapered roller bearings, self aligning ball bearings, radial bearings, axial bearings and the like. 
     In a further preferred embodiment the radius of curvature at least of the rim bearing surface or the front face, according to the amount, is at least three times as great as the diameter of the rolling body. Through this selection of the radius of curvature it is possible to achieve a particularly efficient contact between the front face and the rim bearing surface. The radius of curvature of one of the two surfaces may, however, also be infinite, i.e. in this case the curvature may be represented by a straight line. 
     Stated more precisely, if the radius of curvature in the case of one of the two surfaces becomes infinite, in axial section a straight line is obtained instead of a spherical formation. This straight line is again the generatrix of a cone of the rim bearing surface or the front face of the rolling body, depending on whether the straight line is turned about the axis of symmetry of the rolling body or about the axis of symmetry of the rolling bearing in its entirety. 
     It is however also possible to envisage a plane instead of a conical surface if the rim bearing surface is perpendicular to the bearing axis. 
     In a preferred embodiment the curvatures of the rim bearing surface and the front face are formed such that substantially only one contact point occurs between the rim bearing surface and the front face. In this connection particularly preferably this contact point in the radial direction of the rolling body is situated at least at the same distance from the axis of symmetry of the rolling body as the center of the circular line which describes the curvature of the front face. 
     In general this means that preferably the center of the circular lines for different rolling bodies according to the invention are arranged on a torus center line which extends parallel with respect to the axis of symmetry of the rolling body. With respect to this torus center line the contact point lies, in the radial direction of the rolling body, outside thereof. This means that the touching or contact line is inclined at a given angle with respect to the torus center line. This angle of inclination lies between 0° and 30° and preferably between 0° and 10°. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and embodiments will become clear from the accompanying drawings. 
       In these drawings: 
         FIG. 1  is a partial view illustrating the basic geometrical layout of the rolling bearing; and 
         FIG. 2  is a further partial illustration of the rolling bearing according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic sectional representation of a rolling bearing  1  according to the invention, illustrating the geometrical layout thereof. In this connection the reference number  5  refers to a rolling body for a tapered roller bearing, although only a part of the front face  11  of this rolling body is shown. 
     This front face  11  of the rolling body  5  has a central section  11   a  as well as a first edge region  11   b  and a second edge region  11   c . In this embodiment the central section  11   a  extends substantially in the form of a straight line and the first and the second edge regions  11   b ,  11   c  are each curved. The reference number  6  refers to a lateral rim of a bearing ring which has a rim bearing surface  6   a  which faces the front face  11  of the rolling body  5 . 
     In the embodiment shown in  FIG. 1  the central section  11   a  of the front face  11  does not make contact against the rim bearing surface  6   a  of the rim  6 . Therefore the central region  11   a  of the front face  11 , instead of extending in the form of a straight line, may also extend in substantially any other preferred manner, having, for example, a depression in the center. 
     The reference letter L refers to the axis of symmetry of the rolling body  5 . As mentioned in the introduction, the first edge section  11   b  of the front face  11  of the rolling body  5  is curved toroidally. In the embodiment shown in  FIG. 1  the edge section  11   b  of the front face  11 , in axial section, is curved substantially in the manner of a circle and has a radius of curvature ρ s . Thus the edge section  11   b  in the embodiment shown in  FIG. 1  is curved in a convex manner in the direction of the rim bearing surface  6   a.    
     The rim  6  or the rim bearing surface  6   a  of the rim  6  is also curved toroidally, this curvature having a radius of curvature ρ f . The reference number  19  refers to a circular line on which the edge section  11   b  of the front face  11  lies. The center of this circular line lies on the torus center line  14 . The distance between the raceway  4   a  in the region of the front face  11  and the torus center line  14  corresponds approximately to the height h of the rim. 
     This torus center line  14  is situated at the distance a from the axis of symmetry L of the rolling body. The rolling body shown in  FIG. 1  has the geometrical configuration shown in  FIG. 1  in any random axially sectioned view. This means that the circular line  19  must also be turned about the axis of symmetry L in order to describe the front face  11  in its totality. In a transition zone or at a transition point  3  the first edge section  11   b  curved in the manner of a circle and the central region  11   a  extending in the manner of a straight line merge with each other. Since the center of the circular curvature lies on the torus center line  14 , a tangent to the circular line  19  would extend at the point  3  precisely on the central section  11   a . Thus no edge is present on the front face  11 . 
     The circle radii ρ f  and ρ s  are preferably in each case at least as great as three times the diameter Dw of the rolling body. The arrows indicating the radii ρ f  and ρ s  define at the same time the contact line  10  which extends through the contact point  8 . This contact line  10  is inclined at an angle μ relative to the direction of the torus center line  14  and thus also the direction of the axis of symmetry L. By selecting this inclination the position of the contact point on the front face can be substantially freely chosen. Preferably, however, the contact point  8  lies at approximately half the height of the rim  6 . 
     The reference number  4  distinguishes a central region of the bearing ring with the raceway  4   a  (not shown in greater detail) for the rolling body. 
     As mentioned in the introduction, the second edge section  11   c  is described by a logarithmic profile and follows the mathematical relationship likewise mentioned in the introduction. 
     Here, in  FIG. 1 , the reference letter x relates to the variable, with x having the value 0 at the contact point  8  between the rim bearing surface  6   a  and the front face  11 , and with it therefore also being true that h(x)=0 in this region, which means that the logarithmic component does not yet carry any weight here, and therefore the contact point still lies on the circular first edge section  11   b . The circular curvature profile and the logarithmic curvature profile therefore merge into one another at the contact point  8 . 
     The closer x becomes to the value l, the greater the value assumed by the factor x/c. The value of k·(x/l) ρ  therefore also becomes greater, resulting in the steep profile of the second edge section  11   c  in the vicinity of the raceway  4   a . Here, l denotes the distance between the contact point  8  and the raceway  4   a  in a direction which is tangential with respect to the front face  11  at the contact point  8 . 
     Said logarithmic end profiling generates a contact which is largely free from edge stress peaks between the rim bearing surface  6   a  and the front face  11 , and which can therefore be more highly loaded. 
     It is however also possible for 2 circular curvatures to be provided, with the first edge section  11   b  having the profile shown in  FIG. 1  and with the second edge section having a circular profile with a smaller radius of curvature. The applicant reserves to aim divisional applications at such a profile of the front face. 
     Also conceivable would be other profiles which lead to a comparatively steep profile of the front face in the direction of the edge or the lateral surface of the rolling body. 
     A gap which is open to the outside at both sides proceeding from the center of contact is generated between the rim bearing surface  6   a  and the front face of the rolling body. 
     All the features disclosed in the application documents are claimed as essential for the invention in so far as they are novel individually or in combination with respect to the state of the art. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 List of reference numbers/letters 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Rolling bearing 
               
               
                 2 
                 Bearing ring 
               
               
                 3 
                 Transition zone 
               
               
                 4 
                 Central region of bearing ring 2 
               
               
                 4a 
                 Raceway 
               
               
                 5 
                 Rolling body 
               
               
                 6 
                 Lateral rim 
               
               
                 6a 
                 Rim bearing surface 
               
               
                 8 
                 Contact point 
               
               
                 10 
                 Contact line 
               
               
                 11 
                 Front face 
               
               
                 11a 
                 Central section of front face 11 
               
               
                 11b 
                 First edge section of front face 11 
               
               
                 11c 
                 Second edge section of front face 11 
               
               
                 14 
                 Torus center line 
               
               
                 19 
                 Circular line 
               
               
                 L 
                 Axis of symmetry of rolling body 
               
               
                 ρ s , ρ f   
                 Radius of curvature 
               
               
                 a 
                 Distance between axis of symmetry of rolling body 5 and torus 
               
               
                   
                 center line 14 
               
               
                 h 
                 Rim height 
               
               
                 b 
                 Radial distance between contact point 8 and end of front face 11 
               
               
                 Dw 
                 Diameter of rolling body 
               
               
                 μ 
                 Angle between axis of symmetry and contact line 10 
               
               
                 x 
                 Variable 
               
               
                 h(x) 
                 Profile height 
               
               
                 I 
                 Distance between contact point 8 and raceway 4a 
               
               
                 α 
                 Rim aperture angle