Bearing unit with cage
By optimizing the cage topology and using additive manufacturing technology, a cage with a square cross-section cavity and a grease reservoir was designed, which solved the problems of friction loss and grease leakage and improved the performance of high-speed and high-precision bearing units.
Patent Information
- Application Number
- CN202510253836.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-03-08
- Filing Date
- 2025-03-05
- Publication Date
- 2025-09-09
AI Technical Summary
It is known that the friction loss between the cage and the rolling elements is large and the grease leakage problem is serious, which makes it difficult to meet the requirements of high-speed and high-precision bearing units.
An optimized cage topology is adopted and the cage is produced by additive manufacturing technology. The cavity with a square cross-section is designed to reduce the contact area with the rolling element. A grease reservoir is set in the cavity to use centrifugal force to provide lubricant.
It effectively reduces the friction loss between the cage and the rolling elements, prevents grease leakage, and improves the high-speed operation performance and precision of the bearing unit.
Smart Images
Figure CN120608923A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a bearing unit having a retaining cage. In particular, the bearing unit is an angular contact bearing unit for applications requiring high precision, such as machine tools. Background Art
[0002] Known bearing units with cages include:
[0003] - radial outer ring,
[0004] - radial inner ring,
[0005] - a plurality of rolling elements (especially balls) interposed between the inner ring and the outer ring so that the inner ring and the outer ring can rotate relative to each other, and
[0006] - Cage, which holds the balls in their corresponding circumferential positions.
[0007] A known type of cage comprises a one-piece annular body defining a reference axis, the body of the cage delimiting substantially cylindrical cavities or pockets distributed around the reference axis. The balls are housed in these cavities, which define the positioning and retention of said balls.
[0008] These cages are often used in high-speed, high-vibration bearing units, particularly for applications in the industrial sector (e.g., in machine tool spindles), and are typically manufactured by injection molding polymer materials, including to compensate for poor lubrication conditions. Because the bearing units require a high degree of precision, the cages used in these applications must also meet these precision requirements. Therefore, the cages are precision-machined using machine tools and must have a very simple geometry.
[0009] One disadvantage of this type of cage is the friction losses between the cage and the rolling elements held in the corresponding pockets of the cage. Summary of the Invention
[0010] It is an object of the present invention to provide a bearing unit with a cage which does not have the above-mentioned disadvantages.
[0011] The present invention thus describes a bearing unit with a cage having the features set out in the independent claims appended to this description.
[0012] Further preferred and / or particularly advantageous embodiments of the invention are described with reference to the features set out in the accompanying dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention is described below with reference to the accompanying drawings, which show non-limiting example embodiments of the invention, in which:
[0014] - Figure 1 is an axonometric view of a first preferred embodiment of a bearing unit according to the present invention,
[0015] - Figure 2 yes Figure 1 Axonometric view of the cage of the bearing unit in
[0016] - Figure 3 Shown Figure 2 Details of the cage in the
[0017] - Figure 4 Shown Figure 2 Further details of the cage are given in the . DETAILED DESCRIPTION
[0018] exist Figure 1 In the drawings, reference numeral 30 denotes the entire bearing unit according to a preferred embodiment of the present invention.
[0019] The bearing unit 30 has a central axis of rotation X and comprises:
[0020] - a stationary radial outer ring 31,
[0021] - a rotating radial inner ring 33,
[0022] - an array of rolling elements 32 (in particular balls) between a radially outer ring 31 and a radially inner ring 33, and
[0023] A cage 40 for holding the rolling elements 32 in position, said cage being centered on the radially outer ring 31 .
[0024] Throughout the present specification and claims, unless otherwise indicated, terms and expressions indicating position and orientation (such as "radial" and "axial") are to be understood with reference to the central rotation axis X of the bearing unit 30. For simplicity, the term "ball" may be used by way of example in this specification and the accompanying drawings instead of the more general term "rolling element", and the same reference numerals will be used.
[0025] Reference Figure 2 , the cage 40 according to the invention has an annular shape defining a main axis of inertia or reference axis, which coincides with the central axis of rotation X of the bearing unit 30 .
[0026] The cage 40 has a one-piece annular body 41 forming two rings 42 connected by bridges 43 , one ring 42 at each axial end.
[0027] The annular body 41 of the cage 40 may be made of any suitable material, in particular any material suitable for additive manufacturing, such as plastic, ceramic or metallic materials. An example of a preferably used material is a composite material based on cotton fibers impregnated with phenolic resin.
[0028] The two rings 42 and the bridges 43 define a plurality of through cavities 44 or cells, which are separated in pairs by the bridges 43 and each of which is framed by the two rings 42. Radially outer surfaces 44' of the cavities 44 define the boundaries of the cavities relative to the two rings 42 and the pairs of bridges 43. The cavities 44 accommodate corresponding rolling elements 32 (particularly balls) to position and retain them.
[0029] Each cavity 44 has a polar plane PP and an equatorial plane PE, both perpendicular to the annular body 41. Each cavity 44 has a center O at the intersection of these two planes. The centers O of the cavities are all located at equal distances from the central axis of rotation X.
[0030] The object of the present invention is to optimize the topology of a cage 40 , in particular a cage for an ultra-precision angular contact bearing unit capable of operating optimally at high speeds (NDm speed factor of approximately 3 million).
[0031] Reference Figure 3 and Figure 4 The present invention focuses on optimizing the cavity 44 and the contact with the rolling elements to reduce the friction generated by the contact between the cage and the rolling elements, and uses a specially designed local reservoir to promote the flow of grease.
[0032] To this end, each cavity 44 has a plurality of cells 45 or recesses having a substantially square cross-section arranged circumferentially along a radially outer cylindrical surface 44' of the cavity 44. The cells 45 are circumferentially equidistant from one another. The cells 45 have a substantially cylindrical bottom surface 46 that is delimited radially outwardly of the cylindrical surface 44' of the cavity 44 by a pair of axial surfaces 47 and a pair of tangential surfaces 48.
[0033] These cavities are designed to:
[0034] - reducing the surface area of the cavity 44 in contact with the corresponding rolling element. In fact, since the cells are concave, that is, they are formed by removing material from the annular body 41, the cylindrical surface 44' of the cavity 44 in contact with the ball is reduced, since the bottom surface 46 of the cell 45 cannot come into contact with the rolling element;
[0035] - Ensuring prevention of grease leakage from the contact area with the rolling elements, as is the case in known solutions where the cavity is cylindrical and the geometry of the component parts does not form a lubricant reservoir.
[0036] According to the above mentioned Figure 3 and Figure 4 In a preferred embodiment shown, there are four cells 45, each extending circumferentially over an angular width α (e.g., 45°). The end edge 45' of each cell 45 is spaced an angular distance β, e.g., 22.5°, from the polar plane PP of cavity 44. Consequently, the second end 45" of each cell 45 is also spaced the same angular distance β, 22.5°, from the equatorial plane PE. Thus, in this embodiment, the cells 45 are angularly equidistant from both planes PP and PE.
[0037] Overall, the four cells 45 therefore angularly cover 180° of the full 360° of the cylindrical surface 44' of the cavity 44. Thus, according to this embodiment, the cylindrical surface 44' of the cavity 44 in contact with the rolling elements is reduced by 50%.
[0038] This improved performance of the cage is due to the optimization of the cage topology, a process that combines design tools and FEM calculations and enables the realization of highly customized shapes. The principles of topology optimization have been applied to the cage of super-precision angular contact ball bearings, assuming that the component parts are manufactured using additive manufacturing technology. This enables the realization of all possible complex geometries resulting from the optimized topological design.
[0039] Thus, although the invention is applicable to any method of manufacturing a bearing unit cage, given the specific geometry of the cage, as described above, the aforementioned invention is particularly suitable for cages of bearing units whose bodies are obtained by additive manufacturing.
[0040] Finally, the present invention provides the following advantages:
[0041] - the entire cage can be obtained using known injection molding processes, or preferably using other processes such as additive manufacturing,
[0042] - reducing the surface area of the cavities directly affected by contact with the rolling elements and thus reducing the friction losses between the cage and the rolling elements,
[0043] A reservoir for containing grease is formed, which reservoir can provide lubricant to the contact area centrifugally due to the movement of the cage.
[0044] In addition to the embodiments of the present invention described above, many other variations exist. The embodiments are provided by way of example only and do not limit the scope of the invention, its applications, or possible configurations of the invention. Indeed, although the description provided above enables one skilled in the art to implement the invention according to at least one example configuration of the invention, many variations of the described components may be used without departing from the scope of the invention as defined in the appended claims, interpreted literally and / or according to their legal equivalents.
Claims
1. A bearing unit (30) having a central axis of rotation (X) and comprising: - a fixed radial outer ring (31), - a rotating radial inner ring (33), - an array of rolling elements (32) placed between the radially outer ring (31) and the radially inner ring (33), and a cage (40) for retaining the rolling elements (32), the cage (40) being centered on the radially outer ring (31) and further comprising: - an annular body (41), in a single piece, forming two rings (42) connected by a bridge (43), - a plurality of cavities (44) for receiving and retaining corresponding rolling bodies (32), said cavities (44) being separated in pairs by said bridges (43) and each cavity being framed by said two rings (42), The bearing unit (30) is characterized in that each cavity (44) has a plurality of cells (45) or recesses with a substantially square cross section arranged circumferentially along a radially outer cylindrical surface (44') of the cavity (44).
2. The bearing unit (30) according to claim 1, characterized in that The cells (45) are equidistant from each other in the circumferential direction.
3. The bearing unit (30) according to claim 1 or 2, characterized in that Each cell (45) has a bottom surface (46) that is substantially cylindrical and radially outward of the cylindrical surface (44') of the corresponding cavity (44).
4. The bearing unit (30) according to claim 3, characterized in that The bottom surface (46) is defined by a pair of axial surfaces (47) and a pair of tangential surfaces (48).
5. Bearing unit (30) according to any one of the preceding claims, characterized in that The number of the cavities (45) is four.
6. The bearing unit (30) according to claim 5, characterized in that Each cell (45) extends in the circumferential direction over an angular width (α) equal to 45°.
7. The bearing unit (30) according to claim 5 or 6, characterized in that The end edge (45') of each cell (45) has an angular distance (β) equal to 22.5° relative to the polar plane (PP) of said cavity (44).
8. Bearing unit (30) according to any one of the preceding claims, characterized in that The annular body (41) of the retaining frame (40) is made of a material suitable for additive manufacturing technology.
9. The bearing unit (30) according to claim 8, characterized in that The material is a composite material based on phenolic resin impregnated with cotton fibers.