DE102011014078A1 - Roller bearing cage, has contour designed such that maximum diameter and guide regions are present at discrete number of points, where radii of regions of cage are smaller than radius of board, so that tapering gap results in slide bearing - Google Patents

Abstract

The cage has rolling body bags guided to boards of an outer bearing ring at its outer surface. An S-shaped outer contour (5) of the cage is non-circularly designed such that maximum diameter (1) and guide regions (2) are present at a discrete number of points, which are evenly distributed over a periphery, where the outer contour between the guide regions is reduced in the diameter. Radii of contact regions are smaller than radius of the guide board of the outer ring, so that a tapering gap results in a slide bearing.

Description

The invention relates to an outboard bearing cage for high-speed rolling bearings whose outer surface is out of round and its guide surfaces thereby subject in conjunction with additional weights of reduced thermal and centrifugal diameter increase and allow improved lubrication.

In most rolling bearings, the individual rolling elements are guided through a cage and separated from each other. This is especially the case with bearings designed for highest speeds, especially with spindle bearings. The cage is guided by the rotating rolling elements and in the relevant case of an outboard guided cage by the sliding contact on board the outer ring. In this case, a certain radial clearance between the cage and guide board of the outer ring is required to ensure the sliding bearing function by which the cage is mounted. On the one hand, the cage should be able to rotate as freely as possible in the bearing in order to generate the least possible friction, on the other hand good guidance of the cage is necessary to ensure a certain smoothness. The guide clearance of the cage must be set exactly and remain constant during operation. In practice, however, this game changes significantly by thermal and centrifugal expansion of the cage.

According to the current state of the art cages for high-speed bearings, especially for spindle bearings, made of hard tissue or plastic (especially PEEK). The hard tissue cage has the advantage over the plastic material of the lower thermal expansion coefficient and the higher modulus of elasticity. In operation, it therefore expands less than the pure plastic cage. However, its disadvantage is its lower heat resistance and its higher coefficient of friction compared to the PEEK cage. The bearing friction, to which the cage contributes a significant portion, and the associated heat generation, is currently the main cause of their speed limitation in fast-rotating spindle bearings.

Plastic cages (eg made of PEEK) have very good friction properties and a higher temperature resistance than hard tissue cages. Basically, the use of PEEK cages makes it possible to design low-friction bearings and thus an increase in the achievable speeds and stiffnesses. However, PEEK cages are subject to significant expansion at high speeds and temperature increases. This has the disadvantage that reduced in external ring cages, the radial guide clearance of the cage and the cage clamped in extreme cases and melts by the friction. Furthermore, compared to the hard tissue cage, plastic cages have lower lubricant storage capacity and transportability. It is therefore difficult to lubricate the guide area between the cage and outer ring from the outside through the narrow guide gap with a sufficient amount of lubricant.

One approach to improving the poor dimensional stability of plastic cages is the use of fiber filled material. The plastic during the injection molding process, short glass fibers are added, which are then largely distributed anisotropically in the finished cage blank. The prediction of cage behavior is therefore difficult and the effect of the fiber is not optimal.

One in the published patent application DE 10 2007 033 904 A1 described approach to reduce the cage friction is reduction of the outer diameter in the axial extent of the cage in the region of the edge of the contact area of the cage on the outboard. The solid contact between the cage and edge of the bearing shelf and the associated high Coulomb friction should be avoided. However, the reduction of the guide game with increasing speed can not be prevented.

The object of the invention is therefore to largely prevent the thermal and centrifugal expansion of the guide surfaces of the bearing cage, to improve the lubricant supply of the cage guide area and thus to enable safe storage operation and minimizing the cage friction, in particular through the use of plastic materials.

The object is achieved by a designed according to claims 1 to 5 rolling bearing cage.

The new cage according to the invention has the advantage that the outer diameter in the region of the guide surfaces and thus the guide play of the cage remains largely constant at different speeds and operating temperatures. As a result, the guide play optimally, d. H. so that a low friction and smooth running adjusts. It can be an unfilled standard PEEK material used which has low friction and high temperature resistance. The release of partial areas of the guide surface also allows an improved lubricant supply to the guide surfaces.

In the following, two embodiments of the invention are described with reference to drawings. Show it

1 a cage according to the invention with three guide areas in the side view with fiber reinforcement.

2 a detailed view of the in 1 shown cage in axial section.

The cage is designed in such a way that it distributes a discrete number of recesses (approximately in the middle uniformly distributed over the circumference) in the axial extent (FIG. 6 ), in which the rolling elements are guided. These recesses may be cylindrical, rectangular, trapezoidal or spherical and thus accommodate different Wälzkörperformen, such as balls, cylindrical rollers or tapered rollers. Before and behind these rolling body pockets, the cage has continuous outer lateral surfaces which serve as guide surfaces ( 2 . 2 ' ) serve. Depending on the design of the bearing outer ring, both or only one of the surfaces can be used to guide the cage.

This outer guide surface of the cage is not cylindrical as usual, but viewed from the axial view, in the form of a polygonal profile, so that the cage at a discrete number greater than three, evenly distributed over the circumference points ( 2 ) the nominal guide diameter ( 1 ) is performed. In the areas between these guide surfaces ( 3 ), the outer contour of the cage is withdrawn, so that here a smaller diameter and thus a much greater radial clearance prevails. Furthermore, in these reduced diameter areas ( 3 ) Additional masses ( 4 ), which under the influence of centrifugal force locally bend the cage radially outwards. This is unproblematic due to the radial clearance present here. In this case, the cage material on the sides of the bend and thus in the region of the guide surfaces ( 2 ) tangentially, so that the guide surfaces ( 2 ) tend to shift inwards. The centrifugally induced increase in the nominal guide diameter ( 1 ) is counteracted.

The management areas ( 2 ) have a slightly smaller radius of curvature than that of the nominal guide circle. In this way results between the guide board of the bearing and the guide surfaces of the cage as in a radial sliding a narrowing gap in which a hydrodynamic lubricant film can build to guide the cage. The transitions to the diameter-reduced areas between the guide surfaces ( 3 ) via tangentially connected, S-shaped contours ( 5 ).

The attachment of additional masses ( 4 ) into the outer diameter-reduced region ( 3 ) can be accomplished by incorporating additional elements into the cage, such as threaded pins or glued dowel pins, from a material of higher density than that of the cage material. Alternatively, the attachment of the additional mass can also be done by an accumulation of material on the side facing away from the guide (inside).

At high speeds, the lubrication of the guide board is particularly important, but the narrowed guide gap, the lubricant access is difficult. The larger gap in the reduced diameter areas ( 3 ) improves the access of the lubricant mixture. For example, lubricant can be injected between the cage and the guide board in a simplified manner by means of axial oil-air lubrication, which reduces the risk of unlubricated contact on the cage guide surfaces.

In a further advantageous embodiment of the cage by a fiber winding ( 7 ) strengthened. The fiber material has a very high modulus of elasticity and a low thermal expansion coefficient. For example, carbon or glass fibers can be used. The fiber winding is in an axially introduced circumferential groove ( 8th . 8th' ) with a suitable matrix material and thereby connected to the cage. The matrix material used is, for example, a resin composition. The axial introduction of the fiber reinforcement does not affect the outer guide surfaces of the cage. Fiber windings can be introduced both on one side and on both sides. The groove can be executed in axial plan view around or the polygon shape of the outer contour following. The high modulus of elasticity of the fiber winding limits its centrifugal expansion significantly. Due to the positive and adhesive connection of the fiber insert with the cage, the outer cage expansion is also reduced. The same applies due to the low or even negative thermal expansion coefficient for thermal expansion of the guide surface.

If the outer contour of the cage and the shape of the fiber winding polygonal executed and is the cage with additional weights ( 4 ), so the additional weights in the released areas shift outward due to centrifugal forces. Due to its high modulus of elasticity, the fiber core retains a constant length as far as possible, so that its contour approximates the circular shape. The corners of the polygon profile are drawn inwards and with them the abutment surfaces of the guide board ( 2 ). A similar effect results in a heating and thus a thermal expansion of the cage. Due to its low coefficient of thermal expansion, the fiber largely retains its initial length, as a result of which the polygon corners are pulled inwards. Overall, the outer cage geometry, the fiber reinforcement web and the additional weights are designed so that the outer diameter on which the guide surfaces of the cage ( 1 ) are largely constant.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007033904 A1 [0006]

Claims (5)

Rolling bearing cage with rolling body pockets which is guided on its outer surface on one or two rims of the bearing outer ring, characterized in that the outer contour of the cage is designed out of round, that the maximum diameter ( 1 ) and thus the management areas ( 2 ) are present only at a discrete number of locations of three or more evenly distributed over the circumference, and that the outer contour between these guide areas is reduced in diameter. The radii of the contact areas are smaller than the radius of the guide edge of the outer ring, so that there is a tapering gap as in a sliding bearing. Rolling bearing cage according to claim 1, characterized in that in the middle of the diameter-reduced areas ( 3 ) Additional weights ( 4 ), which locally cause an increased centrifugal force expansion. Rolling bearing cage according to claim 1 or 2, characterized in that at least on the side on which the guide board is located, optionally on both sides in an axially recessed groove ( 8th . 8th' ) a fiber winding with a filling matrix ( 7 ) is shed. Rolling bearing cage according to claim 3, characterized in that the fiber winding ( 7 ) is performed out of round in the form of a rounded polygonal profile, that it has a larger diameter at the points of the guide areas than in the diameter-reduced areas on the outer contour. Rolling bearing cage according to claim 1, characterized in that the guide areas tangentially in an S-shaped course ( 5 ), and these in turn transition tangentially into the recessed areas.

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