FIELD OF THE INVENTION 
       [0001]    The invention relates to a rolling bearing designed as a single-row deep groove ball bearing, as per the features of the preamble of patent claim  1 , which rolling bearing can particularly advantageously be used for mounting the secondary mass on the primary mass of a dual-mass flywheel in a motor vehicle. 
       BACKGROUND OF THE INVENTION 
       [0002]    As is known, dual-mass flywheels are arranged between the internal combustion engine and the gearbox of a motor vehicle and are provided for increasing driving comfort. A dual-mass flywheel of said type is composed substantially of a disk-shaped primary mass which is connected directly to the crankshaft of the internal combustion engine and of a disk-shaped secondary mass which is arranged coaxially with respect to said primary mass and which is connected via a clutch to the input shaft of the gearbox. Here, the two masses are coupled to one another by means of a plurality of damping means arranged between them, said damping means conventionally being in the form of two curved spiral compression springs arranged opposite one another, and said masses can rotate relative to one another counter to the action of said damping means via a friction-reducing bearing arranged on a bearing flange on the primary mass. During operation of the motor vehicle, the primary mass is actively driven by means of the rotating crankshaft of the internal combustion engine, while the secondary mass is carried along by means of the damping elements and in turn drives the gearbox input shaft. Here, the damping elements serve to dampen firstly the non-uniformities resulting from imbalances of the moving masses in the drivetrain, and secondly the rotational non-uniformities of the internal combustion engine resulting from the piston movements. 
         [0003]    Since the bearing between the secondary mass and the primary mass of the dual mass flywheel is subjected to particularly high wear in particular as a result of temperature influences from the clutch, said bearing is conventionally formed by special deep groove ball bearings in the form of DFC bearings, such as are known, for example, from DE 42 14 655 A1 and from DE 196 31 725 A1. Said deep-groove ball bearings are composed, as is known, of an inner bearing ring and of an outer bearing ring and also of a multiplicity of bearing balls which are arranged between said bearing rings and which roll in groove-like raceways in the outer lateral surface of the inner bearing ring and in the inner lateral surface of the outer bearing ring and which are held at uniform intervals from one another in the circumferential direction by a bearing cage. Since no lubricant replenishment facilities are provided for deep-groove ball bearings in dual-mass flywheels, their service life is therefore dependent on the size of the lubricant reserve provided. To fill the interior space of these deep-groove ball bearings with a lubricant quantity adequate for their entire service life, said bearings therefore have, at one side, special plastic sealing caps which engage over and under the outer bearing ring and the inner bearing ring respectively and which are formed with an additional axial cavity, by means of which the volume of the bearing interior space is increased several times over. 
         [0004]    Such plastic sealing caps on the deep-groove ball bearings of dual mass flywheels are however relatively complex to manufacture and are fragile during bearing assembly, and have furthermore proven to be disadvantageous in practice because their seal collar which bears slidingly against the inner lateral surface of the inner bearing ring has a relatively high preload and a relatively low elasticity, as a result of which a high frictional torque acts between it and the inner bearing ring. Here, said high frictional torque is a cause for almost complete premature wear of said seal collar, such that subsequently, as a result of the lack of coverage of said seal region, lubricant leakages occur via the adjoining sealing gap between the plastic sealing cap and the inner bearing ring, resulting in a shortening of the service life of the deep-groove ball bearing. 
         [0005]    To avoid said disadvantages, the German patent application with the official file reference 10 2008 048 517.9, which on the filing date of the present application had not yet been published, therefore proposes a rolling bearing for a dual mass flywheel, which rolling bearing has substantially the same design as the deep groove ball bearing described above but is formed with an axial width considerably greater than the standard dimensions in order to attain an interior space volume between the bearing rings which is adequately large to receive a lifetime filling of lubricant. Here, the interior space of the rolling bearing is sealed off by two circular-ring-shaped seals which are situated axially opposite one another and which are formed as metal-reinforced lip sealing rings, which at one side are in each case snapped into a retaining groove in the inner lateral surface of the outer bearing ring and at the other side have in each case two sealing lips which bear slidingly against the outer lateral surface of the inner bearing ring. Furthermore, a plurality of small ventilation bores are formed into said seals at the level of the bearing pitch circle, via which ventilation bores the rolling bearing can be positively ventilated if an admissible gas pressure in the interior space thereof is exceeded, which arises at relatively high temperatures as a result of gasification of the lubricant filling. 
         [0006]    However, a disadvantage of said seals for deep groove ball bearings of dual mass flywheels is that the ventilation bores can only be formed by means of complex laser boring, and therefore necessitate the purchase of a correspondingly expensive laser boring device and suitable holding tools. Likewise, laser boring requires additional working steps such as the cleaning of the sealing rings after the lasering of the ventilation bores, and a visual inspection, as a result of which the manufacturing costs of such seals increase toward uneconomical levels. Furthermore, in practice, it has been found that such ventilation bores tend to become blocked as a result of dirt accumulation or gumming of the lubricant, such that said bores can no longer perform the function for which they are intended and, if the admissible gas pressure in the interior space of the bearing is exceeded, the lubricant is forced out via the elastic sealing lips of the sealing rings, likewise leading to a shortening of the service life of the deep groove ball bearing. 
       OBJECT OF THE INVENTION 
       [0007]    Taking the discussed disadvantages of the known prior art as a starting point, it is therefore the object of the invention to design a rolling bearing, in particular single-row deep groove ball bearing for a dual mass flywheel, which is provided with wear-resistant seals which are cheap to manufacture and which simultaneously ensure reliable ventilation of the rolling bearing if an admissible gas pressure in the interior space thereof is exceeded. 
       DESCRIPTION OF THE INVENTION 
       [0008]    According to the invention, said object is achieved in the case of a rolling bearing as per the preamble of claim  1  in that at least one of the two seals is designed as an angle-profile-shaped lip seal whose dimensionally stable radial seal leg is fastened to the outer bearing ring and is arranged so as to form a gap seal with an axial side of the inner bearing ring, and whose elastic axial sealing lip engages under the inner bearing ring and bears slidingly against the inner lateral surface of the latter and is simultaneously designed as an overpressure valve, by means of which the rolling bearing, if an admissible gas pressure in the interior space thereof is exceeded, can be positively ventilated via the gap seal and via the sealing lip which lifts up from the inner lateral surface of the inner bearing ring at least in regions. 
         [0009]    Preferred embodiments and advantageous refinements of the rolling hearing designed according to the invention will he described in the subclaims. 
         [0010]    According to claim  2 , it is provided in the rolling bearing designed according to the invention that preferably only the seal at the secondary mass side is designed as an angle-profile-shaped lip seal, whereas the seal at the primary mass side is formed by a lip sealing ring which is known per se and which at one side is snapped into a receiving groove in the inner lateral surface of the outer bearing ring and which at the other side has two sealing lips which bear slidingly against the outer lateral surface of the inner bearing ring. Such a seal pairing has proven to be particularly cheap and functionally adequate because the known lip seals provide optimum sealing against the escape of lubricant from the bearing and simultaneously prevent the ingress of dirt from the nearby clutch bell into the hearing. It would however also be conceivable for both seals of the rolling bearing to be formed as angle-profile-shaped lip seals. 
         [0011]    According to claim  3 , it is a further feature of the rolling bearing designed according to the invention that the radial seal leg of the angle-profile-shaped lip seal is stiffened by a metal reinforcement and can be snapped with its free edge section into a further encircling receiving groove in the inner lateral surface of the outer bearing ring. Here, the metal reinforcement serves to provide the radial stiffness of the lip seal which is otherwise composed of a vulcanized-on elastomer, and ensures that the gap seal formed to the axial side of the inner bearing ring has a uniform gap dimension. 
         [0012]    According to claim  4 , the rolling hearing designed according to the invention is furthermore characterized in that, in relation to the outer bearing ring, the inner bearing ring has an axial width which is reduced by the thickness of the radial seal leg of the lip seal and by the gap dimension of the gap seal. In this way, it is ensured that the rolling bearing has a continuously uniform axial width when the lip seal has been inserted. Furthermore, the inner bearing ring is formed, on its inner lateral surface, with a bearing seat width which is reduced by approximately the length of the axial sealing lip of the lip seal, in order to provide the necessary installation space for the axial sealing lip. That part of the inner lateral surface of the inner bearing ring which is in sliding contact with the axial sealing lip may either have the same diameter as the bearing seat, such that the bearing flange on the primary mass should be formed with an undercut corresponding to the thickness of said sealing lip, or the inner lateral surface of the inner bearing ring is provided with a stepped undercut such that, when the lip seal has been inserted, the underside of the axial sealing lip is at approximately the same level as the bearing seat. 
         [0013]    Furthermore, in one expedient refinement of the rolling bearing designed according to the invention as per claim  5 , it is provided that that part of the inner lateral surface of the inner hearing ring which is in sliding contact with the axial sealing lip of the lip seal is additionally formed with an encircling groove and with a bevel running to the axial side of the inner bearing ring, in order thereby to reduce the frictional surface of the axial sealing lip against the inner bearing ring. An approximately wedge-shaped annular contour is thus formed on the inner lateral surface of the inner bearing ring between the encircling groove and the bevel, against which wedge-shaped annular contour the axial sealing lip of the lip seal bears only with low-friction linear contact with respect to the inner bearing ring. The elasticity of the axial sealing lip and unavoidable lubricant leakages escaping via the gap seal furthermore ensure that the axial sealing lip has virtually no wear over the service life of the rolling bearing. 
         [0014]    Finally, it is also proposed in claims  6  and  7 , as an advantageous in a variant of the rolling bearing designed according to the invention, that the lip seal has, on the inner side of its radial seal leg, an additional pre-sealing lip, and that an additional centrifugal groove is formed into the outer lateral surface of the inner bearing ring directly in front of the pre-sealing lip of the lip seal. Here, the additional pre-sealing lip has a profile cross section approximately in the shape of a monopitch roof and is intended to prevent liquid or low-viscosity lubricant from being able to directly drip down into the gap seal between said seal leg and the axial side of the inner bearing ring. In contrast, the centrifugal groove in the outer lateral surface of the inner bearing ring preferably has a semi-circular profile cross section and, during bearing operation, forms a separation edge which is intended to prevent lubricant from creeping into the gap seal under centrifugal force. Furthermore, such a centrifugal groove may also be formed into the outer lateral surface of the inner bearing ring directly in front of the lip seal at the primary mass side, in order, on this side of the bearing too, to form a separation edge to prevent the lubricant from creeping under the sealing lips under centrifugal force. 
         [0015]    In summary, the deep groove ball bearing designed according to the invention for a dual mass flywheel therefore has the advantage over deep groove ball bearings known from the prior art that it has a lip seal which is simultaneously designed as an overpressure valve which, despite being in sliding contact with the inner bearing ring, is almost free from wear owing to the elasticity of its axial sealing lip, and which ensures reliable ventilation of the rolling bearing if an admissible gas pressure in the interior space thereof is exceeded. In this way, it is simultaneously possible to dispense with the cumbersome formation of individual ventilation bores which are at risk of becoming blocked, such that the lip seal is extremely cheap to manufacture overall. Furthermore, it is possible, by dimensioning the axial scaling lip of the lip seal differently, to correspondingly limit the level of the admissible gas pressure in the interior space of the rolling bearing. Likewise, it is possible for the lip seal to be mounted in a simple and reliable manner on the rolling bearing without the risk of sealing lips being folded over, and said lip seal, as a result of the fact that it is visible from the outside, simultaneously allows the rolling bearing to be mounted reliably and in the correct position in the dual mass flywheel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A preferred embodiment of the rolling bearing designed according to the invention will be explained in more detail below with reference to the appended drawings, in which: 
           [0017]      FIG. 1  shows a cross section through a dual mass flywheel having a rolling bearing designed according to the invention; 
           [0018]      FIG. 2  shows an enlarged overall illustration of a rolling bearing designed according to the invention; 
           [0019]      FIG. 3  shows an enlarged illustration of the detail X of the rolling bearing designed according to the invention as per  FIG. 2 ; 
           [0020]      FIG. 4  shows an enlarged illustration of the detail X as per  FIG. 2  with a variant of the rolling bearing designed according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       [0021]      FIG. 1  shows a schematic illustration of a dual mass flywheel  1  for a motor vehicle, said dual mass flywheel being composed substantially of a disk-shaped primary mass  2  which is connected directly to the crankshaft of the internal combustion engine and of a disk-shaped secondary mass  3  which is arranged coaxially with respect to said primary mass  2  and which is connected via a clutch to the input shaft of the gearbox. Here, the two masses  2 ,  3  are coupled to one another by means of a plurality of damping means (not illustrated in any more detail) arranged between them, and can rotate relative to one another counter to the action of said damping means via a rolling bearing  5  arranged on a bearing flange  4  on the primary mass  2 . 
         [0022]    It is also clear from  FIG. 2  that the rolling bearing  5  arranged in the dual mass flywheel  1  is composed substantially of an inner bearing ring  6  and of an outer bearing ring  7  arranged coaxially with respect to said inner bearing ring and also of a multiplicity of bearing balls  8  which are arranged between said bearing rings  6 ,  7  and which roll in groove-like raceways in the outer lateral surface  11  of the inner bearing ring  6  and in the inner lateral surface  12  of the outer bearing ring  7  and which arc held at uniform intervals from one another in the circumferential direction by a bearing cage  13 . Here, the interior space  14  of the rolling bearing  5  is sealed off by two circular-ring-shaped seals  15 ,  16  which are situated axially opposite one another and is completely filled with a rolling bearing lubricant (not illustrated in any more detail), the quantity of which is configured for the entire service life of the bearing. 
         [0023]    It is also clear from  FIG. 3  that the seal  16  at the secondary mass side is designed according to the invention as an angle-profile-shaped lip seal  17  whose dimensionally stable radial seal leg  18  is fastened to the outer bearing ring  7  and forms a gap seal  20  with an axial side  19  of the inner bearing ring  6 , and whose elastic axial sealing lip  21  engages under the inner bearing ring  6  and bears slidingly against the inner lateral surface  22  of the latter. Here, the axial sealing lip  21  is simultaneously designed as an overpressure valve, by means of which the rolling bearing  5 , if an admissible gas pressure in the interior space  14  thereof is exceeded, as a result of gasification of the lubricant filling, is positively ventilated via the gap seal  20  by virtue of the sealing lip  21  lifting up from the inner lateral surface  22  of the inner bearing ring  6  at least in regions. The seal  15  at the primary side is in contrast designed, as can be clearly seen, as a lip seal such as is known per se, which lip seal is held in an encircling receiving groove  23  in the inner lateral surface  12  of the outer bearing ring  7 . 
         [0024]    It can also be seen from  FIG. 3  that the radial seal leg  18  of the angle-profile-shaped lip seal  17  is stiffened by a metal reinforcement  24  and can be snapped with its free edge section  25  into a further encircling receiving groove  26  in the inner lateral surface  12  of the outer bearing ring  7 . Here, the metal reinforcement  24  serves to provide the radial stiffness of the lip seal  17  which is otherwise composed of a vulcanized-on elastomer, and ensures that the gap seal  20  formed to the axial side  19  of the inner hearing ring  6  has a uniform gap dimension. 
         [0025]    It can likewise be seen in  FIG. 3  that, in relation to the outer bearing ring  7 , the inner bearing ring  6  has an axial width which is reduced by approximately the thickness of the radial seal leg  18  of the lip seal  17 , and has, on its inner lateral surface  22 , a bearing seat width which is reduced by approximately the length of the axial sealing lip  21 . Here, that part of the inner lateral surface  22  of the inner bearing ring  6  which is in sliding contact with the axial sealing lip  21  has the same diameter as the bearing seat (not shown in any more detail) of said inner bearing ring, such that the bearing flange  4  on the primary mass  2  is formed, as indicated in  FIG. 1 , with an undercut corresponding to the thickness of said sealing lip  21 . 
         [0026]    Finally, it can also be seen in  FIG. 3  that that part of the inner lateral surface  22  of the inner bearing ring  6  which is in sliding contact with the axial sealing lip  21  of the lip seal  17  is additionally formed with an encircling groove  27  and a bevel  28  running to the axial side  19  of the inner bearing ring  6 , in order thereby to reduce the frictional surface of the axial sealing lip  21  against the inner bearing ring  6 . A wedge-shaped annular contour is thus formed on the inner lateral surface  22  of the inner bearing ring  6  between the encircling groove  27  and the bevel  28 , against which wedge-shaped annular contour the axial sealing lip  21  of the lip seal  17  bears only with low-friction linear contact with respect to the inner bearing ring  6 . 
         [0027]      FIG. 4  furthermore illustrates a further advantageous variant of the rolling bearing  5  designed according to the invention, in which the lip seal  17  has, on the inner side of its radial seal leg  18 , an additional pre-sealing lip  29  with a profile cross section in the shape of a monopitch roof, by means of which pre-sealing lip liquid lubricant can be prevented from directly dripping down into the gap seal  20  between said seal leg and the axial side  19  of the inner bearing ring  6  when the bearing is at a standstill. Furthermore, in this variant, an additional centrifugal groove  30  with a semi-circular profile cross section is formed into the outer lateral surface  11  of the inner bearing ring  6  directly in front of the pre-sealing lip  29  of the lip seal  17 , which centrifugal groove forms a separation edge to prevent lubricant from creeping into the gap seal  20  under centrifugal force. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Dual Mass Flywheel 
           2  Primary Mass 
           3  Secondary Mass 
           4  Bearing Flange on  2   
           5  Rolling Bearing 
           6  Inner Bearing Ring 
           7  Outer Bearing Ring 
           8  Bearing Balls 
           9  Raceway in  6   
           10  Raceway in  7   
           11  Outer Lateral Surface of  6   
           12  Inner Lateral Surface of  7   
           13  Bearing Cage 
           14  Interior Space of  5   
           15  Seal 
           16  Seal 
           17  Lip Seal 
           18  Radial Seal Leg of  17   
           19  Axial Side of  6   
           20  Gap Seal 
           21  Axial Sealing Lip of  17   
           22  Inner Lateral Surface of  6   
           23  Receiving Groove in  12   
           24  Metal Reinforcement of  18   
           25  Edge Section of  18   
           26  Receiving Groove in  12   
           27  Groove in  22   
           28  Bevel on  22   
           29  Pre-Scaling Lip on  18   
           30  Centrifugal Groove in  11
A single-row deep groove ball bearing made substantially of an inner ring and an outer ring disposed coaxially thereto and balls disposed between the rings. The balls roll in deep groove tracks in an outer face of the inner ring and in an inner face of the outer ring, and the balls are held at equal distances to each other in the circumferential direction by a housing. The interior of the bearing is sealed by two circular ring-shaped seals axially opposite each other. At least one of the seals is a lip seal, which has an angular profile. A shape-stable radial seal leg of the seal is attached to the outer ring and forms a gap seal with an axial side of the inner ring, and a sealing lip, which is an overpressure valve, is disposed under the inner ring and slidingly contacts the inner face of the inner ring.