Self-aligning antifriction bearing and cage for said self-aligning antifriction bearing

The invention relates to a self-aligning antifriction bearing (1) comprising at least one first row (9) of rolling bodies (11) and a second row (10) of rolling bodies (11) adjacent to said first row (9) of rolling bodies (11), whereby every row (9, 10) comprises balls (5) and rollers (6) disposed peripherally about a central axis of the self-aligning antifriction bearing (1). The bearing is characterized in that the balls (5) have a greater outer diameter (28) than the rollers (6).

FIELD OF THE INVENTION

Self-aligning antifriction bearing comprising at least a first row of rolling elements and comprising a second row of rolling elements adjacent to the first row of rolling elements.

BACKGROUND TO THE INVENTION

The self-aligning roller bearings and barrel roller bearings denoted by the term self-aligning antifriction bearings are used in applications in which an angular error between the housing and the shaft has to be compensated. Through the use of the rolling element roller with line contact between the outer and inner ring, these bearings are suitable for high loads. If the load upon the antifriction bearing is low, the rollers tend to slide between the raceways due to the absence of rolling contact. The rotation speed of the cage carrying the rolling elements falls to normal under rolling contact. In the event of an abrupt rise in load upon the rolling element, the antifriction bearing, the rolling element, which then enters into engagement between the outer and inner ring, must accelerate the whole of the cage carrying all the other rolling elements, within fractions of a second, to the correct rotation speed. This acceleration process generates high forces in the cage. The resultant slippage between the accelerated rollers and the raceways of the outer and inner ring leads to damage to the rolling elements and to the raceways.

The aforesaid problem arises, for example, in applications in which the rolling elements, in normal operation, are only put under low load. In the event of abrupt increases in load, the self-aligning antifriction bearings are briefly subjected to peak loads which can lead to the effect described above.

In DE 8803970 U1, a radial antifriction bearing is described, in which rollers and balls are jointly used as rolling elements. The self-aligning antifriction bearing of the generic type is provided with at least a first row of rolling elements and a second row of rolling elements adjacent to the first row of rolling elements. Each of the rows has a row of barrel rollers disposed peripherally about a bearing center axis of the self-aligning antifriction bearing. In addition, in the self-aligning antifriction bearing, a row of balls is disposed. In the bearing according to DE 8803970 U1, the basic load rating is said to be increased by the additional row of balls. The consequences of brief increases in load are not solved with this realization.

In such types of bearings of the prior art, the balls, because of their punctual contact surface with the raceways during operation of the self-aligning antifriction bearing, are intent upon assuming a kinematically optimal position. This generally leads to constrained axial motions on the part of the balls. The balls are consequently supported, especially laterally, in the cage pockets against the forces arising from the constrained motions. Increased friction, combined with higher operating temperatures and wear in the ball pockets, are the result. The mountings for the balls in the pockets are endangered and may possibly suffer premature wear. A cage described in DE 8803970 U1, due to the ball pockets situated axially between the pockets for the rollers, can only be produced at relatively high cost.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a self-aligning antifriction bearing and a cage for said self-aligning antifriction bearing with which the above-described drawbacks can be prevented.

The object according to the invention is achieved according to the subject of claim1and further embodiments of the invention according to the dependent claims. The self-aligning antifriction bearing is provided with at least a first row of rolling elements and with a second row of rolling elements adjacent to the first row of rolling elements. Each of the rows has balls and barrel rollers, or otherwise spherically shaped rollers., disposed peripherally about the bearing center axis of the self-aligning antifriction bearing. It is here conceivable for each of the rollers to be followed in the peripheral direction by one of the balls. Alternatively, the balls are mutually separated in the peripheral direction by two or more of the rollers.

The balls are here provided with an equal nominal diameter common to all the balls in the bearing. The smallest external diameter of the balls which is within the permitted tolerance of the diameter of the balls is greater than a largest external diameter of the barrel rollers. The rollers here have a nominal diameter which is common to all the rollers in the bearing. The largest external diameter of the rollers is the largest diameter which deviates within the tolerance from the nominal diameter of the rollers.

Each imaginary first rolling contact plane of the balls per row, which plane is concentric to the bearing center axis and is drawn annularly about the center axis and runs centrally through the balls, and each imaginary second rolling contact plane of the rollers per row, which plane is concentric to the center axis and intersects the rollers at the largest external diameter, are in each of the rows axially spaced apart along the bearing center axis. Preferably, the first rolling contact planes of the balls from row to row lie axially closer together than the second rolling contact planes of the rollers from row to row. Hence, the first rolling contact planes of the balls are disposed along the center axis and thus axially between the second rolling contact planes of the barrel rollers. The closer together the rolling contact planes of the mutually adjacent ball rows are moved in the direction of the transverse center plane of the bearing, the smaller are the constrained forces upon the balls. The fact that the balls and the rollers lie peripherally together respectively in a row means that the cage is easier to produce and the bearing is narrower, and thus lighter, in total, and also cheaper to produce.

The balls bear the radial load alone when the bearing is under low load. In the event of higher or peak loads, the rollers lend support. As a result of the point contact between raceway and ball, higher Hertzian stresses are generated than with a line contact between roller and raceway. The comparatively higher stress in the rolling contact with the balls at low load leads to less slippage between the rolling elements. Mixed friction or solid friction in the contact between the raceways and the rolling elements are prevented. This effect is further enhanced by the fact that just the balls, and not, therefore, the entire number of rolling elements, are engaged. The load is thus distributed to fewer rolling elements, whereby the stresses in the rolling contact are increased. The roller ring, comprising roller and cage, is dragged along by the balls under low load.

At the moment of peak load, the minimally larger balls which are present in the load zone are elastically deformed in accordance with their spring load-deflection curve, to the point where the rollers lend support. This prevents the formation of stresses in the bearing which would lead to a plastic deformation of the balls and the raceways in rolling contact with the balls. The abrupt acceleration forces upon the roller ring are prevented, since the roller ring is already set in operating speed by the rollers. The nominal diameter of the balls is greater than the diameter of the rollers, preferably within a range of 0.005% to 0.4% of the largest nominal diameter of the rollers.

With one embodiment, the invention provides a cage for at least one of the rows of the self-aligning antifriction bearing. Preferentially, however, a cage is used which guides both the rows simultaneously. The cage has ball pockets comprising, respectively, a lateral opening. This cage is also known to experts as a cam or double-cam cage. Each of the openings of the pockets of a row is configured on a side of the cage which is facing away from the other of the rows. The, in the peripheral direction of the bearing, tangential free apertural measure of the opening is smaller than the external diameter of the ball, so that the ball is also detained against the side of the opening in the pocket. The opening is also of use when the balls are snap-locked into the cage from outside, since the pocket, which around the periphery of the pocket is not closed, expands further elastically and the snap-in forces are thereby smaller. The catch flange is thus protected from damage when the balls are installed in the cage.

Preferentially, each of the ball pockets has respectively a flange on a radially outward facing rim. The largest clear distance, at least between portions of the flange which lie tangentially opposite one another in the peripheral direction and are in this case farthest removed from one another, is less than the sum of the external diameter of the ball in the pocket, plus a greatest possible motional play in the pocket. The motional play is a clear distance between the pocket and the respective ball in the pocket radially beneath the flange. The flange thus embraces the ball above the pitch circle diameter of the row of balls. Included in the largest clear distance between the portions of the flange is also a greatest possible free motional play between the ball in the pocket and the flange, so that the ball in the pocket is held freely movable relative to the flange to the extent of the motional play, yet is held radially outward by the flange.

Preferably, the entire radially outwardly directed rim of each of the ball pockets is bounded by the flange. The flange thus extends from one end of the pocket at the opening, around the ball, as far as the opposite end of the pocket at the opening.

According to a further embodiment of the invention, the flange has an inner surface portion of a circular cylinder, the inner surface portion facing the ball in the pocket and, peripherally, partially encompassing the ball as far as the opening. The surface portion is described by a radius. The height of the surface portion, directed transversely to the radius, decreases from that of the opening on the farthest side of the pocket in the direction of the opening.

DETAILED DESCRIPTION OF THE DRAWINGS

InFIG. 1, a preferred embodiment of a self-aligning antifriction bearing1is shown. The self-aligning antifriction bearing1is provided with an outer ring2, an inner ring3and with rolling elements11disposed between the outer and inner ring. The rolling elements11are configured as balls5and as rollers6and are guided by a common cage4. In further applications, however, a split cage is also conceivable, which guides each row9and10of rolling elements11separately.

The balls5are minimally larger in diameter than the rollers6. The rollers6and balls5are respectively disposed alternately in the peripheral direction in one of rows9and10, so that, in the peripheral direction of the self-aligning antifriction bearing1, each of the balls5in one of rows9and10is adjoined by one of the rollers6. In addition, each of the balls5of the first row9is adjoined by a gap12between a ball5and a roller6of the second row10. When dimensioning the diameter of the balls5and the diameter8of the rollers6, care should be taken to ensure that, in the event of a low antifriction bearing load, the rollers between two adjacent balls in rolling contact do not simultaneously touch both raceways13and14. In the event of a first, low bearing load, the load is borne solely by the balls5, while the rollers6roll without any load.

When setting out the diameter difference7(FIG. 2a) from the ball5to the roller6, care should be taken to ensure that, in the event of a possible second bearing load of the self-aligning antifriction bearing1, which here increases to the maximal bearing load, the balls5do not plastically deform. A possible practical measurement for the diameter difference7between the larger ball5and the smaller roller6is, for example, a measure of two hundredths of a millimeter.

A further embodiment (not represented) provides for a plurality of rollers to be disposed between two balls. It should here be borne in mind that, as the number of load-bearing rollers5in the load zone of the bearing under the first bearing load decreases, the self-aligning antifriction bearing1, and a shaft supported by means of the self-aligning antifriction bearing1, runs radially less and less smoothly.

InFIGS. 2aand2b,the self-aligning antifriction bearing1is shown in part-sections. InFIG. 2a,the load-bearing ball5, under a first bearing load, is represented of such a small size that the load is borne solely by the balls5. InFIG. 2b,the contact of a non-load-bearing roller6under the first bearing load is represented. In this representation, the diameter difference7is exaggerated and is therefore not shown true to scale.

FIG. 3shows a further illustrative embodiment of a self-aligning antifriction bearing15, comprising a one-part cage16which simultaneously guides a first row9and a second row10of rolling elements11. Each of the rolling element rows9and10runs on a common outer raceway14. To each of the rows9and10there is respectively assigned, on the inner bearing ring, a separate inner raceway13. As can be seen, in particular, from a representation of the cage16as an individual part detached from the self-aligning antifriction bearing15, and from the arrangement of the pockets18and19according toFIG. 4, each of the balls5of the first row9is adjoined by a roller6of the second row10. The roller pockets18and the ball pockets19of each of the rows9and10have openings20and21, respectively, on the lateral end faces of the cage16, the openings20and21of one of the rows9or10being configured jointly on a side of the pockets18and19which is facing away from the other of the rows9or10.

FIG. 5shows a self-aligning antifriction bearing22comprising the cage16, the balls5and the rollers6. The imaginary rolling contact planes23of the balls5of both the first row9and the second row10are disposed axially between the rolling contact planes24of the rollers6of the first row9and of the second row10. Consequently, the rolling circle planes23in one of rows9or10are axially distanced from the rolling circle planes24in the same row9or10. The rolling contact planes23are of annular configuration and are here bounded in the radially outward direction by the outer rolling circle23adrawn about the balls5and in the radially inward direction by the enveloping circle23bencompassed by the balls5. The rolling contact planes23are inclined relative to a radial plane R1drawn through the enveloping circle23b.The rolling contact planes24of the rollers6are of annular configuration and are here bounded in the radially outward direction by the outer rolling circle24adrawn about the rollers6and in the radially inward direction by the enveloping circle24bencompassed by the rollers6. The rolling contact planes24are inclined relative to a radial plane R2drawn through the enveloping circle24b.

FIGS. 6 to 8show details of the ball pocket19, as this is preferably configured on the cages4and16. The tangential free apertural measure25between the ends19aand19bof the pocket19which lie tangentially opposite one another in the peripheral direction about the center axis of the bearing is less than the, within the diameter tolerance of the balls5, smallest external diameter28of the ball5. The radially outward facing rim19cof the pocket19merges into a flange26. The clear distance of the mutually opposing surface portions26awhich is largest tangentially in the peripheral direction of the cage4,16and which is described by twice the radius27is at least less than the sum of double the radius29. The radius29corresponds to the sum of the external diameter28and the motional play30. The radius27here jointly includes the motional play31between the ball5and the flange26.

The surface portion26aof the flange26which is facing the ball5is a surface portion of a circular cylinder described by the radius27.

The radius27here extends from an axis31which lies in the rolling contact plane23and which is drawn through the center point32of the ball5. Starting from a side26bof the flange26which is farthest distanced from the opening21, the height H1, H2, H3between the body edges39and40, which is directed transversely to the radius27, increases in the direction of the ends19a, b,up to the maximum height Hx. The flange26is followed in the radially inward direction by a surface portion19dof an inner face of the pocket, having the radius29.

FIG. 9shows an ideal state, depicted in schematic and exaggerated representation and not true to scale, of the arrangement and size relationships of rollers6and balls5in a self-aligning antifriction bearing. The, within the tolerances of the nominal measure of a ball dimension, smallest possible external diameter28of the balls5is greater than the, within the tolerances of a roller dimension, largest possible external diameter8of the roller6. The rollers6and balls5are disposed with even spacing T on the periphery of the self-aligning antifriction bearing. In each case, a ball5lies peripherally adjacent to a roller6. The distance33in the radian measure between two balls which succeed each other peripherally and which are here mutually separated by one of the rollers6is sufficiently small that the radial distance34between the roller6and the raceway13remains. The radial distance34is formed between the roller6, here situated in the vertex35of a load zone36, and the inner raceway13. InFIG. 9, the load zone36is described schematically by the line36a,which, without numerical specification, indicates in the vertex35the highest value of Hertzian stress.

InFIG. 10, at variance with the invention, the distance37in the radian measure between the balls5is too large, so that, due to the axial sag38of the raceway13and, where appropriate, due to high elastic deformation of the balls5under a first bearing load, the radial distance between the raceways13and14corresponds to or is smaller than the diameter8of the roller6.

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