Patent Application
20110229068
The invention relates to a radial roller bearing according to the features of patent claim 1 which form the preamble, and it can be advantageously realized, in particular, on single track ball roller bearings for high speeds and high requirements for a low noise level, such as in motor vehicle transmissions or within the secondary drive of internal combustion engines.
It is generally known in roller bearing technology that the radial roller bearings which are used most frequently are single track and multiple track groove ball bearings, since they are distinguished above all by an equally high radial and axial loadbearing capacity and have the highest rotational speed limits of all radial bearings on account of their low friction. Said groove ball bearings comprise substantially an outer bearing ring and an inner bearing ring and a number of balls, which are arranged between the bearing rings as rolling bodies, which roll in each case in groove-shaped raceways in the inner side of the outer bearing ring and in the outer side of the inner bearing ring and are guided at uniform spacings from one another by a bearing cage. Here, said radial ball bearings are filled with the balls by the eccentric mounting method which has been disclosed by DE 168 499 and in which the two bearing rings are arranged eccentrically with respect to one another and the free space which is produced as a result between the bearing rings is fitted with the balls.
However, it has been shown in practice that limits are nevertheless placed on groove ball bearings of this type in relation to the loadbearing capacity of the bearing on account of the low maximum number of balls which can be installed and/or the low maximum filling level of approximately 60%. In the past, a multiplicity of solutions were therefore proposed, in which the number of balls and, therefore, the loadbearing capacity of groove ball bearings was to be increased, for example, by the arrangement of filling openings in the raceways. Moreover, another possibility to increase the number of rolling bodies on a radial roller bearing has been disclosed by DE 43 34 195 A1. In this radial roller bearing, which is formed per se as a single track groove ball bearing, the rolling bodies are not formed by balls, however, but rather by what are known as ball rollers, which are configured as balls with two side faces, which are flattened symmetrically from a basic ball shape and are arranged parallel to one another. Here, the width of said ball rollers between their side faces is smaller than the spacing between the inner side of the outer bearing ring and the outer side of the inner bearing ring, with the result that, during filling of the bearing, the ball rollers can be introduced into the bearing, axially with respect to the bearing, through the spacing between the inner ring and the outer ring and can then be rotated by 90° into the raceways of the bearing rings. Since smaller spacings can be achieved between the individual rolling bodies as a result of this mounting method, a higher number of rolling bodies overall can therefore be introduced into the radial roller bearing.
Since, in ball roller bearings of this type, however, exact axial guidance of the ball rollers is required and, above all, automatic rotation of the ball rollers transversely with respect to the running direction is to be avoided during bearing operation, a plurality of embodiments of corresponding bearing cages are also proposed in the document cited last. Here, one cage embodiment, which is particularly suitable for applications with high requirements, for low noise is a plastic snap action cage which is open on one side and comprises a circumferential solid-walled side ring with pocket webs which extend axially away from it on one side and merge at the level of a plane which is defined by the center points of the ball rollers into in each case two elastically yielding pocket tabs. Here, said pocket tabs are spaced apart from one another by an intermediate space and form in each case in pairs a plurality of cage pockets which spatially surround the running faces of the ball rollers.
However, it has proven disadvantageous that the entire kinematic behavior of the ball rollers which occurs at different bearing loadings has not been taken into consideration in a snap action cage which is configured in this way. It has thus been determined, for example, that ball rollers as rolling bodies in radial roller bearings roll without offsetting movements stably in their raceways at relatively high speeds and uniform load on account of the gyroscopic effect which occurs, and do not require any axial guidance by the bearing cage. If, however, the bearing rotational speed drops below a permissible minimum rotational speed or the bearing is suddenly accelerated greatly, what is known as a tumbling effect occurs, in particular, in the loadfree zone of the bearing, during which tumbling effect the ball rollers tend to roll in their raceways in an undulating manner transversely with respect to the running direction. Here, first of all contact occurs between the running faces of the ball rollers and the side ring of the snap action cage, by way of which contact friction heat is generated and which contact is the cause of a disadvantageous rise in the operating temperature in the radial roller bearing. Here, the friction between the ball rollers and the bearing cage and the tumbling movements of the ball rollers can become so pronounced that the ball rollers ultimately even snap out of their cage pockets which are open on one side, via the elastically yielding pocket tabs, and stand transversely with respect to their raceways, with the result that destruction of the bearing cage and premature failure of the bearing occur. The ball rollers within a bearing cage of this type likewise have no possibility to orient themselves to the respective contact angle in the case of mixed radial and axial loading of the bearing, without contact between the ball rollers and the side ring of the snap action cage and the resulting disadvantageous consequences likewise occurring.
Proceeding from the described disadvantages of the known prior art, the invention is therefore based on the object of designing a radial roller bearing, particular a single track ball roller bearing, which is configured with a plastic bearing cage, by way of which sufficient axial guidance of the ball rollers is ensured at all times, even at low bearing rotational speeds or at a high bearing acceleration, and transverse positioning of the ball rollers in their raceways can be avoided, and which plastic bearing cage affords the possibility that the ball rollers are automatically oriented to the respective bearing contact angle without contact with the bearing cage, the case of mixed radial and axial loading of the bearing.
According to the invention, this object is achieved in a radial roller bearing according to the preamble of claim 1, in such a way that the plastic bearing cage comprises two axially divided pocket cage halves of substantially mirror-symmetrical configuration which can be assembled positively, nonpositively or with a material-to-material fit via complementary connecting elements which are arranged so as to lie opposite one another on their dividing faces, and form a separate cage pocket in the mounted state for each ball roller, which cage pocket encloses said ball roller completely, and in which cage pocket the ball rollers have a defined two-sided axial tilting clearance for automatic orientation to the respective bearing contact angle via low-friction linear contacts between their side faces and those longitudinal webs of the cage pockets which lie opposite them.
Preferred refinements and developments of the radial roller bearing which is configured according to the invention are described in the subclaims.
Accordingly, it is proposed as claimed in claim 2 in the case of the radial roller bearing which is configured according to the invention that the contour of the cage pockets corresponds substantially to the cross-sectional contour of the ball rollers, the spacing between the longitudinal webs of the cage pockets being greater, however, than the extent of the width of the ball rollers between their side faces. Here, the transverse webs between the cage pockets are of arched configuration in accordance with the diameter of the ball rollers or with the radius of their running faces and are connected via rounded transition regions to the longitudinal webs of the cage pockets.
Moreover, as claimed in claims 3 and 4, the radial roller bearing which is configured according to the invention is also distinguished by the fact that the linear contacts between the side faces of the ball rollers and the longitudinal webs of the cage pockets can preferably be produced via compensator webs, which are integrally formed onto the inner sides of the longitudinal webs, extend over the entire diameter of the side faces of the ball rollers and are wedge-shaped in profile cross-section. Here, the height of these wedge-shaped compensator webs corresponds in each case approximately to the spacing of the side faces of the ball rollers from those longitudinal webs of the cage pockets which lie opposite, a small air gap remaining between the compensator webs and the side faces of the ball rollers, however, in order to avoid permanent contact between the ball rollers and the bearing cage. For as long a guidance length as possible, moreover, the crest lines of the compensator webs are advantageously arranged on the pitch circle of the ball rollers and are of rounded configuration in order to prevent premature wear.
As claimed in claim 5, it is a further feature of the radial roller bearing which is configured according to the invention that the axial tilting clearance corresponds to an angular range of up to 35° on both sides of the longitudinal center axes of the ball rollers for automatic orientation of the ball rollers to the respective bearing contact angle within the cage pockets. As a result of the arrangement of the longitudinal webs of the cage pockets, which is spaced apart from the side faces of the ball rollers, the ball rollers can therefore perform axial tilting movements without contact with the bearing cage in a pivoting range of overall approximately 70°, which is delimited by the surfaces of the compensator webs on the longitudinal webs of the cage pockets.
Finally, claim 6 also proposes, as an advantageous refinement of the radial roller bearing which is configured according to the invention, that the complementary connecting elements which are arranged so as to lie opposite one another on the dividing faces of the pocket cage halves are preferably configured on one cage half as journals, which can be pressed into corresponding holes on the other cage half and can be connected to said holes by ultrasonic welding. As an alternative to this, however, it is also possible to connect the two cage halves by way of suitable latching elements on their dividing faces or by adhesive bonding, or to combine the stated connection types with one another.
In comparison with the roller bearings which are known from the prior art, the radial roller bearing which is configured according to the invention therefore has the advantage that it has a plastic bearing cage which can be assembled from two mirror-symmetrical parts, cannot be dismantled and by way of which it is possible in a simple way to arrange the ball rollers in the same completely enclosing cage pockets and to guide them axially in such a way that the tumbling movements of the ball rollers in their cage pockets, which occur at low bearing rotational speeds or at high bearing acceleration, are avoided effectively. At the same time, it is possible, as a result of low friction linear contacts between the ball rollers and the bearing cage and as a result of defined axial tilting clearances within the cage pockets, that the ball rollers are oriented automatically to the respective contact angle of the ball roller bearing without contact with the bearing cage.
One preferred embodiment of the radial roller bearing which is configured according to the invention will be explained in greater detail in the following text with reference to the appended drawings, in which:
A radial roller bearing, which is configured as a single track ball roller bearing 1, is clearly apparent from
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Furthermore,
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| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 060 957.9 | Dec 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/065980 | 11/27/2009 | WO | 00 | 5/26/2011 |
