Bearing unit with cage

Abstract

A bearing unit (30) having a central axis of rotation (X) and a cage (40) for a plurality of rolling bodies (32) interposed between a radially outer ring (31) and a radially inner ring (33) wherein the cage (40) is provided with:-a one-piece annular body (41) forming two rings (42) connected by a bridge (43); -a plurality of cavities (44) for accommodating and retaining respective rolling bodies (32), the cavities (44) being separated in pairs by bridges (43) and each cavity being framed by two rings (42), the radially outer surface (45) of the cavity (44) delimiting the boundary of the cavity itself with respect to the two rings (42) and the pair of bridges (43), with alternating curved surface portions, and enclosed within a first cylindrical surface (C ') and a second cylindrical surface (C' '), the cylindrical surfaces (C', C '') being concentric with respect to the center (O) of the cavity (44).

Description

Technical Field

[0001] The present invention relates to a bearing unit having a retention 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] The main disadvantage of this type of cage is the friction between the balls and their cavities due to the cylindrical geometry of the cavities in contact with the balls. 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 an axonometric view of the cage of the bearing unit in , and

[0016] - Figure 3 Shown Figure 2 Details of the cage. DETAILED DESCRIPTION

[0017] exist Figure 1 In the drawings, reference numeral 30 denotes the entire bearing unit according to a preferred embodiment of the present invention.

[0018] The bearing unit 30 has a central axis of rotation X and comprises:

[0019] - a stationary radial outer ring 31,

[0020] - a rotating radial inner ring 33,

[0021] - an array of rolling elements 32 (in particular balls) between a radially outer ring 31 and a radially inner ring 33, and

[0022] A cage 40 for holding the rolling elements 32 in position, said cage being centered on the radially outer ring 31 .

[0023] 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.

[0024] Reference Figure 2 and Figure 3 , 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 .

[0025] The cage 40 has a one-piece annular body 41 forming two rings 42 connected by bridges 43 .

[0026] 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.

[0027] The two rings 42 and the bridges 43 define a plurality of cavities or pockets 44, which are separated in pairs by the bridges 43, and each through-going cavity 44 or pocket is framed by the two rings 42. Radially outer surfaces 45 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.

[0028] 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.

[0029] The radially outer surface 45 of each cavity 44 has an innovative shape specifically designed to reduce friction between the rolling elements and the cavity and also to enable better distribution of the grease.

[0030] In particular, the novel shape of the surface 45 of the cavity 44 includes:

[0031] - a plurality of corrugations ( / waves) 46, 46', 46" or curved surface portions, convex towards the center O of the cavity 44 and tangent to the cylindrical surface C' inside the surface 45 of the cavity 44. According to a preferred embodiment, there are six corrugations 46, 46', 46". symmetrically positioned about the equatorial plane PE. Preferably, the three corrugations 46', 46" situated in the first half-space relative to the equatorial plane PE are angularly separated from each other by 45°. In particular, one corrugation 46' is situated on the polar plane PP and the other two corrugations 46" are symmetrical about the polar plane PP. The 45° angle between two consecutive corrugations has been defined by topological optimization. In other words, this is a process based on building the design of the cage by 3D printing, reducing the material therein to achieve the most efficient result. Obviously, taking into account the symmetry of the corrugations about the equatorial plane PE, the same ratios as described above also apply to the three corrugations 46 situated in the second half-space relative to the equatorial plane. The corrugations 46, 46', 46" serve as contact surfaces with the respective balls 32 fitted in the cavities 44 and are the only contact surfaces between the balls and the cavities. This significant reduction in contact surface reduces friction and therefore reduces heat generation;

[0032] - curvilinear sections 47, arranged along the equatorial plane PE and symmetrical about the polar plane PP. Likewise, these sections are curvilinear surface portions facing each other on either side of the equatorial plane PE. Thus, the curvilinear sections 47 are formed on the rings 42 of the annular body 41 of the cage 40, concave towards the centre O of the cavity 44 and tangent to the cylindrical surface C' inside the surface 45 of the cavity 44. The two curvilinear sections 47 are intended to increase the rigidity of the cage along the equatorial plane PE of the cavity 44, increasing the cross-section of the two rings 42. This prevents stress concentrations in this zone. The two sections 47 also serve as guides for the balls inside the cavity 44; and

[0033] - A first arcuate surface portion 48 and a second arcuate surface portion 49, respectively, between the two corrugations 46, 46', 46" and between the corrugation 46 and the curved section 47. The second arcuate surface portion 49 is longer than the first arcuate surface portion 48. These arcuate surface portions 48, 49 are concave toward the center O of the cavity 44 and are tangent to the second cylindrical surface C" outside the surface 45 of the cavity 44. The first arcuate surface portion 48 and the second arcuate surface portion 49 define cavities 50 between the balls 32 and the cage 40, which serve as reservoirs for containing grease. These cavities 50 are used to retain grease and release the grease during the rotation of the balls, so that the raceways of the balls and rings 31, 33 of the bearing unit 30 are always lubricated, avoiding metal-to-metal contact between the balls and the raceways. In addition, the lubrication reservoir also serves to lubricate the contact between the cavity and the balls, reducing friction between these components.

[0034] Advantageously, the contact points between the corrugations 46, 46', 46" and the arcuate surface portions 48, 49 and between the second arcuate surface portion 49 and the curved section 47 are suitably rounded to remove sharp edges and thus eliminate / reduce stresses in the material under static and dynamic conditions.

[0035] It can therefore be summarized that the cavity 44 has a radially outer surface 45 having alternating curvilinear surface portions and being substantially enclosed within two cylindrical surfaces C′, C″ concentric about the center O of the cavity 44 .

[0036] Although the present 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 bearing unit cages whose bodies are obtained by additive manufacturing.

[0037] Finally, the present invention provides the following advantages:

[0038] - the entire cage can be obtained using known injection molding processes, or preferably using other processes such as additive manufacturing,

[0039] - the geometry of the outer surface of the cavity allows reducing the contact surface between the rolling elements and the cavity, thus reducing friction,

[0040] - some of the internal space of the cavity is designed to form a reservoir for holding lubricant,

[0041] - Thus, the lubrication between the balls and the raceways (on the outer and inner rings) is optimized by the above-mentioned lubrication reservoir.

[0042] 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 rotatable 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 by the fact that the radially outer surface (45) of the cavity (44), which delimits the cavity itself relative to the two rings (42) and the pair of bridges (43), presents an alternation of curvilinear surface portions and is enclosed within a first cylindrical surface (C') and a second cylindrical surface (C"), the cylindrical surfaces (C', C") being concentric relative to the center (O) of the cavity (44).

2. The bearing unit (30) according to claim 1, characterized in that The radially outer surface (45) of the cavity (44) comprises a plurality of corrugations (46, 46', 46") having a convex surface facing the center (O) of the cavity (44) and being tangent to a first cylindrical surface (C') inside the surface (45), wherein the corrugations (46, 46', 46") function as contact surfaces with corresponding rolling bodies (32) located inside the cavity (44).

3. The bearing unit (30) according to claim 2, characterized in that The number of the corrugations (46, 46', 46") is six and they are located in symmetrical positions relative to the equatorial plane (PE).

4. The bearing unit (30) according to claim 3, characterized in that Three corrugations (46', 46") located in a half space relative to the equatorial plane (PE) are angularly spaced 45 degrees from each other, one corrugation (46') is located on the polar plane (PP) and the other two corrugations (46") are symmetrical relative to the polar plane (PP).

5. The bearing unit (30) according to claim 1, characterized in that The radially outer surface (45) of the cavity (44) comprises a curved section (47) positioned along the equatorial plane (PE) and symmetrical with respect to the polar plane (PP), facing each other on either side of the equatorial plane (PE), having a concave surface facing the center (O) of the cavity (44) and being tangent to a first cylindrical surface (C') inside the surface (45).

6. The bearing unit (30) according to claim 5, characterized in that The radially outer surface (45) of the cavity (44) has a first arcuate surface portion (48) and a second arcuate surface portion (49), the first arcuate surface portion (48) and the second arcuate surface portion (49) respectively included between two corrugations (46, 46', 46") and between the corrugation (46) and the curved section (47), presenting a concave surface facing the center (O) of the cavity (44) and being tangent to a second cylindrical surface (C") outside the surface (45).

7. The bearing unit (30) according to claim 6, characterized in that The length of the second arcuate surface portion (49) is greater than the length of the first arcuate surface portion (48).

8. The bearing unit (30) according to claim 6 or 7, characterized in that The first arcuate surface portion (48) and the second arcuate surface portion (49) define a chamber (50) between the rolling element (32) and the cage (40) for use as a reservoir for containing grease.

9. 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.

10. The bearing unit (30) according to claim 9, characterized in that The material is a composite material based on phenolic resin impregnated with cotton fibers.

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