Abstract:
The rolling bearing has a first bearing ring, a second bearing ring and a plurality of rolling bodies which are arranged between the first bearing ring and the second bearing ring. The rolling bodies are arranged in at least four rows. At least two rows have a first reference diameter and at least two further rows have a second reference diameter which is different from the first reference diameter, and those rows which have the same reference diameter are arranged symmetrically with respect to a predefined plane which is aligned perpendicular to a longitudinal direction of the bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 of PCT/DE2007/000070 filed Jan. 17, 2007, which in turn claims the priority of DE 10 2006 004273.5 filed Jan. 31, 2006, the priority of both applications is hereby claimed and both applications are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The present invention is aimed at a symmetrical rolling bearing and in particular at a multi-row symmetrical rolling bearing. 
     The invention is described with reference to a wheel bearing unit for driven or non-driven wheels of motor vehicles, such as for example of pickup trucks, light trucks or SUVs (sports utility vehicles). It is however pointed out that the present invention may also be used in other rolling bearings. 
     The prior art discloses rolling bearings which have an outer ring, an inner ring and rolling bodies arranged between the rings. It is also known from the prior art to arrange the rolling bodies in a plurality of rows. For example, DE 100 60 638 A1 discloses a double-row rolling bearing. In this way, it is possible to distribute the loads acting on the bearing between a plurality of rows of rolling bodies, and therefore to a plurality of rolling bodies. 
     The use of balls in double-row rolling bearings as disclosed by DE 100 60 638 A1 is disadvantageous because this is unsuitable for high axle loads. The use of tapered rollers in double-row wheel bearings has the disadvantage that a high frictional torque is generated in this way. 
     Rolling bearings having more than two rows are relatively complex to produce and, in addition, it is necessary to determine geometric dimensions which are suitable for production. 
     The present invention is therefore based on the problem of providing a rolling bearing which is firstly suitable for high axle loads and which can secondly be produced and assembled with a justifiable amount of expenditure. In addition, it is intended to provide a rolling bearing which can be exchanged for a conventional rolling bearing with tapered rollers. 
     SUMMARY OF THE INVENTION 
     The rolling bearing according to the invention has a first bearing ring and a second bearing ring. Arranged between the bearing rings is a plurality of rolling bodies. According to the invention, the rolling bodies are arranged in at least four rows, with at least two rows have a first pitch circle diameter and two further rows have a second pitch circle diameter which differs from the first pitch circle diameter. Here, those rows which have, in each case, the same pitch circle diameter are arranged symmetrically with respect to a plane which is to a longitudinal direction of the bearing. 
     The pitch circle diameter is to be understood to mean the spacing from an axis of symmetry of one rolling body to an axis of symmetry of a rolling body which is situated exactly opposite the rolling body in the same row. 
     As a result of the provision of at least four rows, the load acting on the bearing can be distributed between a plurality of rows and therefore between a plurality of rolling bodies. The bearing is therefore suitable overall for absorbing higher loads. 
     As a result of the provision of different pitch circle diameters, the bearing can be adjusted in a particularly suitable way for absorbing forces acting in different directions. Those rows with the greater pitch circle diameter are suitable for absorbing greater forces. In addition, by using different pitch circle diameters, it is possible to obtain the advantage of conical rolling bodies, that is to say a higher load capacity, without it being necessary for this purpose to accept the disadvantages of conical rolling bodies, that is to say higher friction, a higher weight and a movement of the bearing rings relative to one another. 
     The rows are arranged symmetrically with respect to a plane which is to a longitudinal direction of the bearing, which plane is preferably a central plane. The rolling bearing according to the invention is therefore a symmetrical rolling bearing. 
     The rolling bearing preferably has an overall width of more than 35 mm. In extensive tests, it was found that rolling bearings with an overall width of more than 35 mm are particularly suitable for absorbing the forces acting on the bearing. 
     The pitch circle diameters of the outer rows are preferably greater than the pitch circle diameters of the inner rows. With this embodiment, it is possible to obtain the function of tapered rolling bodies whose diameter decreases from the outside to the inside. 
     In one preferred embodiment, the rolling body diameters of the rolling bodies of at least two rows differ, and the rolling body diameters of the rolling bodies of the outer rows are particularly preferably greater than the rolling body diameters of the rolling bodies of the inner rows. By means of the rolling body diameters which decrease from the outside to the inside, it is likewise possible to obtain the advantages of tapered rolling bodies without it being necessary here to accept the disadvantages stated above. However, all roller bodies can have the same roller body diameter. 
     A carrier-side outer diameter of the bearing is advantageously greater by more than 6 mm than the sum of the carrier-side pitch circle diameter and the rolling body diameter of the carrier-side rolling bodies. The carrier-side row is also referred to below as the row arranged at the vehicle inside. In order to obtain sufficient stability of the bearing and to simultaneously allow the bearing to be of as low a weight as possible, the above selection of the carrier-side outer diameter has proven, during detailed testing, to be a particularly suitable compromise. 
     In a further preferred embodiment, a flange-side outer diameter of the bearing is greater by more than 6 mm than the sum of the flange-side pitch circle diameter and the rolling body diameter of the flange-side rolling bodies. The flange-side row is also referred to below as the row arranged at the vehicle outside. The stated geometries particularly preferably apply both to the carrier-side outer diameter and also to the flange-side outer diameter of the bearing. 
     In a further preferred embodiment, the pitch circle diameter of an inner row is greater by more than 3.5 mm than the bore diameter of the rolling bearing. Here, the bore diameter preferably corresponds to the inner diameter of the bearing ring. 
     In a further preferred embodiment, the axial spacing between the first row and the second row, which is spaced apart from the first row, is smaller than the axial spacing between the second row and the third row, which is adjacent to the second row. The first and second rows and the third and fourth rows are preferably arranged in tandem formation with a central rim of the outer ring and/or inner ring situated between the second row and the third row. 
     At least one bearing ring, and preferably the inner ring, is formed from two inner ring halves. The design simplifies the assembly of the bearing. Here, the two inner ring halves are preferably braced against one another in the axial direction of the rolling bearing by means of a flanged collar. Each of the inner ring halves preferably has two raceways for the rolling bodies. It is however also possible for a single-piece inner bearing ring to be braced by means of a flanged collar. The outer ring is preferably formed in one piece. 
     Preferably, at least one raceway for the rolling bodies is provided on a flange body. In particular, the raceway is preferably a radially inner raceway. Here, the flange body is preferably braced against the inner ring or an inner ring half, so as to be rotationally fixed with respect to the latter. In this embodiment, the raceways of two rows, for example the raceways of the carrier-side rows, are situated in one inner ring half. In this embodiment, a second inner ring half is not provided, and instead, the raceways for the flange-side rows are arranged directly on or in the flange body on which the wheel flange is also arranged. In this way, the assembly expenditure for the bearing according to the invention can be reduced. 
     The rolling bodies are preferably selected from a group of rolling bodies which comprises balls, cylindrical rollers, cones and the like. It is preferable for rolling bodies of the same generic type to be situated in all the rows, though it is also possible to provide rolling bodies of different generic types in different rows. 
     In a further preferred embodiment, the pressure angles of at least two rows differ from one another. The pressure angle is to be understood to mean the angle under which pressure forces are transmitted from the outer ring via the rolling bodies to the inner ring or the inner ring halves. More precisely, the rolling bodies are braced along contact lines which run obliquely with respect to the longitudinal direction of the rolling bearing. The pressure angles are defined between the contact lines and the central plane. The pressure angles of the outer rows are preferably greater than the pressure angles of the inner rows. The pressure angles of the inner rows on the one hand and the pressure angles of the outer rows on the other hand are preferably of equal magnitude in each case. By means of the different pressure angles, it is possible to optimally adapt the load absorption of the bearing. 
     In a further preferred embodiment, the rolling bearing has a device for measuring the wheel rotational speed. The device may for example be a magnetic disk which outputs an alternating signal to a sensor as a result of rotation. 
     The present invention is also aimed at a wheel bearing having a rolling bearing of the above-described type. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and embodiments can be gathered from the appended drawings, in which: 
         FIG. 1  is a schematic illustration of a rolling bearing according to the invention; 
         FIG. 2  is the illustration from  FIG. 1 , showing the geometries; and 
         FIG. 3  is the schematic illustration of  FIG. 1  where all of the roller bodies have the same roller body diameter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The rolling bearing shown in  FIG. 1  has four rows  11 ,  12 ,  13  and  14  in which rolling bodies  5  are arranged in each case. Here, the rolling bodies  5  are arranged in each case in rings and run in a plane perpendicular to the plane of the Figure. The individual rolling bodies  5  can run in bearing cages (not shown in detail). For simplicity, in each case only one bearing half is illustrated in  FIGS. 1 and 2 . 
     As shown in  FIG. 1 , the individual rows  11 ,  12 ,  13  and  14  have different pitch circle diameters Tk 1 , Tk 2 , Tk 3 , Tk 4  which, as mentioned in the introduction, are defined by the spacing from a rolling body center of one rolling body to an opposite rolling body, and again to the rolling body center of the latter. 
     In the embodiment shown in  FIG. 1 , the two rows  11  and  14  have greater pitch circle diameters Tk 1 , Tk 4  than the rows  12  and  13 . The pitch circle diameters of the rows  11  and  14  are equal, and the pitch circle diameters Tk 2  and Tk 3  of the rows  12  and  13  are also equal. The rolling bearing shown in  FIG. 1  is therefore symmetrical about a central plane ME both with regard to the number of rows and also with regard to the respective pitch circle diameters. 
     The rolling bodies of the rows  11  and  14  also have a greater rolling body diameter than the rows  12  and  13 . In this way, it is possible by means of the tandem arrangement of the rows  11  and  12  on the one hand and the tandem arrangement of the rows  13 ,  14  on the other hand to obtain that, in the bearing, it is possible to dispense with the tapered rollers known from the prior art, and it is also possible to utilize the advantages of tapered rollers. 
     Provided on an outer bearing ring  2  is a flange  24  which in turn serves for connecting to a carrier (not shown). Between the two rows  12  and  13 , the outer ring  2  has a substantially radially inwardly pointing central rim  23 . In the embodiment shown in  FIG. 1 , the flange  24  is arranged in the longitudinal direction not precisely in the center of the rolling bearing but rather so as to be offset in the direction of a flange  17 . 
     In this embodiment, the flange  17  is formed in one piece with a flange body  18 , on which are arranged inner ring halves  3   a  and  3   b  of a bearing inner ring  3 . More precisely, the inner ring halves  3   a ,  3   b  are braced in the axial direction of the rolling bearing by means of a flanged collar  21  and a shoulder  22  which is arranged in the flange body  18 . 
     In the embodiment shown in  FIG. 1 , in each case two raceways  9  for the rolling bodies are arranged on the two inner ring halves  3   a  and  3   b . It would however also be possible to dispense with the inner ring halves  3   a  and to instead arrange the corresponding raceways  9  in the flange body  18 . Conversely, the inner ring half  3   b  could also be dispensed with. 
     The reference numeral  19  relates to a radially outwardly pointing outer rim of the inner ring  3  or of the inner ring half  3   b . The outer rim adjoins the raceway  9  of the row  14 . 
     The reference numeral  15  relates to a seal for the rolling bearing. The seal is designed here as a cassette seal and has, on a reinforcement  20  which is arranged on the outer ring  2 , three sealing lips  15   a ,  15   b  and  15   c . One of the sealing lips  115   a  is prestressed at the periphery radially against the inner ring  3  or the inner ring half  3   b  thereof. A further sealing lip  15   b  bears axially against a sliding plate. The third sealing lip bears radially against the sliding plate. 
     Depending on the embodiment of the bearing, it would also be possible to dispense with one or both of the flanges  17 ,  24 . For example, in a further embodiment (not shown), only one flange  24  is arranged on the outer ring  2 , and the flange is provided on a vehicle-side carrier. 
     In a further embodiment, only one flange  17  is provided which can be connected to a wheel (not shown) and which is formed in one piece with the flange body  18 . 
       FIG. 2  shows the illustration from  FIG. 1 , showing the geometries. In  FIG. 2 , the reference symbol B denotes the overall bearing width and the reference symbol D denotes the bearing height, that is to say the spacing between a radially inwardly pointing surface of the inner bearing ring  3  and a radially outwardly pointing surface of the outer bearing ring  2 , neglecting the flange  24 . The reference symbol F denotes the flange-side outer diameter of the outer ring and the reference symbol E denotes the outer diameter of the rolling bearing at the vehicle inside or carrier side. 
     The reference symbol A denotes the bore diameter of the rolling bearing. The reference symbols Dw denote the individual diameters of the respective rolling bodies; for example, the reference symbol Dw 1  denotes the diameter of a rolling body  5  in the row  11 . The reference symbols Tk 1 -Tk 4  denote the individual pitch circle diameters of the respective rows. The reference symbols Db 1 -Db 4  denote the respective rim diameters of the individual rows. For clarity, however, only the reference symbols Tk 1  and Db 4  are plotted. 
     The reference symbols Dl 1 -Dl 4 , with only the diameter Dl 1  being shown, denote the respective raceway base diameters, and is measured from that section of a raceway  31  which lies radially at the inside. The reference symbol n denotes the width of the central rim between the rows  12  and  13 . 
     The reference symbol m denotes the rim width of the inner ring or of the inner ring half  3   b  on that side which faces toward the vehicle inside. The reference symbols α 1 -α 4  denote in each case the pressure angles. 
     The overall bearing width B is greater than the sum of all the rolling body diameters plus the rim widths m of the inner ring and the central rim width n. In addition, the overall bearing width is greater than 35 mm. 
     The in each case outer rows have greater pitch circle diameters. This means that the pitch circle diameter Tk 1  of the row  11  is greater than the pitch circle diameter Tk 2  of the row  12 , and the pitch circle diameter Tk 4  of the row  14  is greater than the pitch circle diameter Tk 3  of the row  13 . 
     In the embodiment shown in  FIG. 2 , the carrier-side outer diameter E of the outer ring is greater than the sum of the pitch circle diameter Tk 4  and the diameter Dw 4  of the rolling bodies in the row  14 . The carrier-side outer diameter E is preferably at least 6 mm greater than the sum stated above. 
     The pitch circle diameter Tk 3  is preferably at least 3.5 mm greater than the bore diameter A. The flange-side outer diameter F is preferably greater by more than 6 mm than the pitch circle diameter Tk 1  of the row  11  plus the rolling body diameter Dw 1 . 
     Furthermore, in the embodiment shown in  FIG. 2 , the respective pressure angles α 1  and α 4  of the rows  11  and  14  are greater than the pressure angles α 2 , α 3  of the rows  12  and  13 . Here, the angles are specified in relation to the central plane ME. This means that the pressure angles of the outer rows, that is to say the angles under which the forces are transmitted from the outer ring to the inner ring, are greater in the outer rows than the pressure angle of the inner rows. It would however also be possible for the pressure angles of all the rows to be equal. 
       FIG. 3  is identical to  FIG. 1  except the roller body diameters Dw 1 , Dw 2 , Dw 3 , and Dw 4  are illustrated as being the same. 
     All the features disclosed in the application are claimed as being essential to the invention if novel, individually or in combination, over the prior art. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Wheel bearing 
           2  Outer bearing ring 
           3  Inner bearing ring 
           3   a ,  3   b  Inner ring halves 
           5  Rolling body 
           9  Raceway 
           11 ,  12 ,  13 ,  14  Rows 
           15  Sealing device 
           15   a ,  15   b ,  15   c  Sealing lip 
           17  Flange 
           18  Flange body 
           20  Reinforcement 
           21  Flanged edge 
           22  Shoulder 
           23  Central rim of the outer ring 
           24  Flange 
           31  Radially inner section of a raceway 
         ME Central plane 
         A Bore diameter 
         B Overall bearing width 
         D Bearing height 
         E Vehicle-inner-side or carrier-side outer diameter 
         F Flange-side outer diameter 
         M Bearing center 
         n Central rim width 
         m Rim width of the inner ring 
         Db 1 -Db 4  Rim diameter of the individual rows 
         Dl 1 -Dl 4  Raceway base diameter 
         Dw 1 -Dw 4  Diameter of the respective rolling bodies 
         Tk 1 -Tk 4  Pitch circle diameter 
         α 1 , α 2 , α 3 , α 4  Pressure angle