Bearing unit with retaining cage

Abstract

Bearing unit (30) having a central rotation axis (X) and a retaining 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 centred on the radially outer ring (31), and - the cage (40) is provided with a radially outer cylindrical surface (40a), which has one or more scores and / or one or more reliefs configured to improve a lubrication film between the cylindrical surface (40a) centring the cage (40) on the radially outer ring (31), and a guide surface (31a) of the outer ring itself.

Description

[0001] 1 202400205

[0002] BEARING UNIT WITH RETAINING CAGE

[0003] DESCRIPTION

[0004] Technical field of the invention

[0005] The present invention relates to a bearing unit with a retaining cage. In particular, the bearing unit is an angular-contact bearing unit for applications requiring high precision, for example machine tools.

[0006] Prior art

[0007] Known bearing units with a retaining cage comprise:

[0008] - a radially outer ring,

[0009] - a radially inner ring,

[0010] - a plurality of rolling bodies, in particular balls, interposed between the inner ring and the outer ring to enable the relative rotation thereof, and

[0011] - a retaining cage, which holds the balls in their respective circumferential positions and is centred on the radially outer ring.

[0012] The retaining cage of a known type comprises a one-piece annular body that defines a reference axis, the body of the cage delimiting substantially cylindrical cavities or pockets distributed about the reference axis. The balls are housed in these cavities, which define the positioning and holding of said balls.

[0013] These retaining cages are usually used in high-velocity, high-rotational- precision bearing units, in particular for applications in the industrial sector, for example in machine tool spindles, and are typically made by injection moulding a polymer material, including to compensate for poor lubrication conditions. As the bearing unit requires a high degree of precision, the cages for these applications must also meet this accuracy requirement.

[0014] When the bearing is in use, including in consideration of the high rotational speeds reached, the retaining cages can both vibrate and impact with the rolling bodies and the rings, and such vibrations and impacts, especially within specific speed ranges, can cause clicking, i.e. repetitive high-pitched 2 202400205 noises, which, although tolerated by end users because this defect does not lead to premature failure, are nonetheless perceived as a lack of quality.

[0015] In order to try to reduce the clicking caused by the cages, and therefore also the vibration thereof, the radially outer rings of some bearings were provided with ring guides in some applications discussed herein, this measure nonetheless being generally applicable. However, especially in some specific speed ranges, these ring guides did not have the desired effects. On the contrary, it was found that friction between the retaining cages and the ring guides caused circular, whirling or unstable motion in the retaining cages themselves, and even more clicking.

[0016] There is currently no known solution to this technical issue. It is possible to design a cage that is guided by the balls and not by the outer ring. This solution stops the cage from clicking, but using the balls for guidance can in some instances limit the operating conditions of the bearing itself.

[0017] In general, oil lubrication exhibits a lower likelihood of clicking in the cage compared to grease lubrication, but this choice also cannot be considered a permanent solution to the technical problem.

[0018] Summary of the invention

[0019] One purpose of the present invention is to provide a bearing unit with a retaining cage in which the clicking noise is absent or at least very reduced.

[0020] Consequently, the present invention describes a bearing unit with a retaining cage, having the features set out in the independent claim attached to the present description.

[0021] Other preferred and / or particularly advantageous embodiments of the invention are described according to the features set out in the attached dependent claims.

[0022] Brief description of the drawings

[0023] The invention is described below with reference to the attached 3 202400205 drawings, which show non-limiting example embodiments thereof, in which:

[0024] - Figure 1 is a sectional view of an embodiment of a bearing unit according to the present invention,

[0025] - Figure 2 illustrates a detail of a retaining cage of the bearing unit in Figure 1 according to a first embodiment of the invention,

[0026] - Figure 3 illustrates a detail of a retaining cage of the bearing unit in Figure 1 according to a variant of the first embodiment of the invention,

[0027] - Figure 4 illustrates a detail of a retaining cage of the bearing unit in Figure 1 according to a second embodiment of the invention, and

[0028] - Figure 5 illustrates a detail of a retaining cage of the bearing unit in Figure 1 according to a variant of the second embodiment of the invention.

[0029] Detailed description

[0030] In Figure 1, reference sign 30 denotes a bearing unit as a whole, according to a preferred embodiment of the invention.

[0031] The bearing unit 30 has a central rotation axis X and comprises:

[0032] - a stationary radially outer ring 31,

[0033] - a rotary radially inner ring 33,

[0034] - a row of rolling bodies 32, in particular balls, interposed between the radially outer ring 31 and the radially inner ring 33, and

[0035] - a cage 40 to hold the rolling bodies 32 in place, said cage being centred on the radially outer ring 31.

[0036] In particular, the cage 40 has a cylindrical surface 40a which is centred on a corresponding cylindrical radially inner guide surface 31a of the radially outer ring 31.

[0037] Throughout the present description and in the claims, terms and expressions indicating positions and orientations, such as "radial" and "axial", are to be understood with reference to the central rotation axis X of the bearing unit 30, unless otherwise specified. For the sake of simplicity, the term "ball" 4 202400205 may be used by way of example in the present description and in the attached drawings instead of the more generic term "rolling body", and the same reference signs shall be used.

[0038] In order to reduce the clicking noise of the cage, the cylindrical surface 40a of the cage has specific machining, scoring and / or reliefs, all intended to improve the lubrication film between the cylindrical surface 40a centring the cage 40 on the radially outer ring 31 and the guide surface 31a of the outer ring itself, in order to reduce the friction between the two components and to avoid generating the whirling or unstable motion that cause the clicking noise. Two preferred embodiments of the invention that improve lubrication performance are described below. Each embodiment can be implemented in several variants, and two variants for each are described below by way of example.

[0039] With reference to Figure 2, according to a first embodiment of the invention, a cylindrical radially outer groove 41 is provided on the cylindrical surface 40a of the cage 40, close to an annular end surface 40b and between two protrusions 42, which are also cylindrical and radially external. Preferably, the groove 41 has a cross-section with a profile that is substantially convergent in the radially inward direction. Conversely, the protrusions 42 have a crosssection with a profile that is substantially convergent in the radially outward direction. The groove 41 serves as a reservoir for accumulating lubricating grease, which improves the lubrication film between the cylindrical surface 40a centring the cage 40 on the radially outer ring 31 and the guide surface 31a of the outer ring itself. The shape of the groove keeps the lubricating grease to the sides of the surfaces in contact, i.e. circumferentially towards the outside. This helps to ensure that there is always a lubricating film present, reducing direct contact between the surfaces and therefore friction.

[0040] With reference to Figure 3, according to a variant of the first embodiment, there may be more than one groove, for example two cylindrical 5 202400205 radially outer grooves 41, each formed between two protrusions 43, which are also cylindrical and radially external. Preferably, the grooves 41 have a crosssection with a profile that is substantially convergent in the radially inward direction. Conversely, the protrusions 43 have a cross-section with a profile that is substantially convergent in the radially outward direction. As in the variant in Figure 2, the grooves 41 act as reservoirs for accumulating lubricating grease.

[0041] With reference to Figure 4, in a second embodiment of the invention, the cylindrical surface 40a of the cage 40 has a cylindrical radially outer relief 44 close to the annular end surface 40b. The relief 44 has a cross-section with a profile that is substantially convergent in the radially outward direction. The convergent shape of the relief 44 helps to maintain the film of lubricating grease between the cylindrical surface 40a centring the cage 40 on the radially outer ring 31 and the guide surface 31a of the outer ring itself. More precisely, the convergent profile creates a high-pressure zone that helps to form a hydrodynamic film of lubricating grease, and this solution also reduces friction between the contacting surfaces.

[0042] With reference to Figure 5, according to a variant of this embodiment, the cylindrical surface 40a of the cage 40 also has a cylindrical radially outer relief 45 close to the annular end surface 40b. The relief 45 has a profile convergent in the radially outward direction but, unlike the previous variant, has a cross-section ending in a flat cylindrical radially outer surface 45a. Similarly, the convergent profile of the relief 45 helps to maintain the film of lubricating grease between the cylindrical surface 40a centring the cage 40 on the radially outer ring 31 and the guide surface 31a of the outer ring itself. More precisely, the convergent profile creates a variation in pressure between the surfaces in contact. This helps to keep the lubricating grease in a high-pressure zone, encouraging the formation of a thicker and more uniform film of lubricating grease, as in the variant in Figure 4. In addition, the radially outer 6 202400205 flat cylindrical surface 45a of the relief 45 improves the stability of the lubricating film.

[0043] Ultimately, according to the first embodiment of the invention (Figures 2 and 3) the presence of the groove 41 (or grooves) results in a greater accumulation of lubricating grease between the surfaces in contact, i.e. between the cylindrical surface 40a centring the cage 40 on the radially outer ring 31 and the guide surface 31a of the outer ring itself.

[0044] Conversely, in the second embodiment of the invention (Figures 4 and 5) the presence of the relief 44, 45 ensures greater hydrodynamic support for the lubricating grease.

[0045] The two embodiments nonetheless have the same technical effect, i.e. reducing friction between the surfaces in contact.

[0046] In addition to the embodiments of the invention as described above, it should be understood that there are numerous other variants. Said embodiments are provided solely by way of example and do not limit the scope of the invention, its applications or its possible configurations. Indeed, although the description provided above enables the person skilled in the art to carry out the present invention at least according to one example configuration thereof, numerous variations of the components described could be used without thereby departing from the scope of the invention, as defined in the attached claims interpreted literally and / or according to their legal equivalents.

Claims

7 202400205C LA I M S1. Bearing unit (30) having a central rotation axis (X) and comprising:- a stationary radially outer ring (31),- a rotatable radially inner ring (33),- a row of rolling bodies (32), interposed between the radially outer ring (31) and the radially inner ring (33), and- a retaining cage (40) for retaining the rolling bodies (32), centred on the radially outer ring (31), the bearing unit (30) being characterized in that the cage (40) is provided with a radially external cylindrical surface (40a), which has one or more scores and / or one or more reliefs configured to improve a lubrication film between the cylindrical surface (40a), centering the cage (40) on the radially outer ring (31), and a guide surface (31a) of the outer ring itself.

2. Bearing unit (30) according to claim 1, wherein the cylindrical surface (40a) of the cage (40), in proximity to an annular end surface (40b), has at least one cylindrical, radially external groove (41), included between two protrusions (42, 43) which are also cylindrical and radially external.

3. Bearing unit (30) according to claim 2, wherein the at least one groove (41) has a cross-section with a profile substantially convergent in a radially internal direction and the protrusions (42, 43) have a cross-section with a profile substantially convergent in a radially outward direction.

4. Bearing unit (30) according to claim 1, wherein the cylindrical surface (40a) of the cage (40), in proximity to an annular end surface (40b), has a cylindrical and radially external relief (44, 45).

5. Bearing unit (30) according to claim 4, wherein the relief (44) has a cross-section with a profile substantially convergent in a radially outward direction.2024002056. Bearing unit (30) according to claim 4, wherein the relief (45) has a cross-section with a substantially convergent profile that ends with a cylindrical surface (45a), that is radially external and flat.

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