Bearing cage made of composite material with improved performance and associated bearing unit

Abstract

Bearing cage made of composite material having improved behavior and associated bearing unit Bearing cage (3) comprising an annular body (7) having a plurality of pockets or housings (8) for bearing bodies of a bearing; the annular body (7) having an axis of symmetry (A) and being made of a synthetic plastic material reinforced by fibers comprising a plurality of radial layers (18) of reinforcing fibers (11) embedded in a synthetic plastic material (13) and arranged to form with the axis of symmetry of the cage, when the cage (3) is observed in a plan view, a predefined angle (β);in which an annular contact area (22) of each pocket or housing (8) configured to cooperate in contact, during use, with a bearing body (6) has an axial width extending radially with respect to the axis of symmetry (A) of the cage delimited by at least one layer or band (18c), or more, in which the predefined angle of the reinforcing fibers (11) thereof is equal to substantially 90°. [Figures 2 and 5];

Description

Title of the invention: Composite material bearing cage having improved performance and associated bearing unit. Technical field of the invention

[0001] The present invention relates to a bearing cage obtained from a fiber-reinforced composite synthetic plastic material, as well as an associated bearing unit comprising such a cage. Prior art

[0002] It is well known that a rolling bearing unit comprises a rolling bearing having an outer ring, an inner ring and a plurality of rolling bodies (for example balls) interposed between the inner and outer rings to make them relatively rotatable with low friction, and a rolling bearing cage to retain the rolling bodies in position, the cage being arranged in the radial space delimited between the inner ring and the outer ring.

[0003] A bearing housing retainer cage comprises an annular body delimited by its inner and outer cylindrical lateral surfaces and a plurality of pockets or housings, each configured to house and freely retain a respective bearing body of the roller bearing. The cage body may be made of a fiber-reinforced thermosetting or thermoplastic material, for example, a phenolic resin (or any other suitable synthetic material, for example, a polyamide) loaded with short or long reinforcing fibers such as carbon, Kevlar®, or glass fibers, or natural fibers such as cotton, hemp, or flax, and supports the pockets or housings, which are located radially through it, for example, consisting of radial through holes.

[0004] Generally, a preform consisting of a hollow tube is obtained by molding the synthetic material, then the hollow tube is radially cut into a plurality of slices, each of which constitutes a cage body. Before or after the cutting operation, the pockets or recesses are actually drilled through the axial portions of the tube forming the preform that will form the cage bodies.

[0005] The hollow tube constituting the preform can be produced by a process known as "continuous filament winding" (CFW), by tightly winding one or more filaments of composite material consisting of continuous fibers impregnated with a synthetic plastic resin onto a metal mandrel tool.

[0006] Here and hereafter, "plastic resin" means a synthetic material that is either thermosetting or thermoplastic, for example the impregnation of the fibers can be carried out either by a liquid thermosetting resin or by a solid thermoplastic powder.

[0007] After a predefined number of superimposed radial layers of pre-impregnated fibers have been obtained, the preform is hardened in a known way, for example in an oven, to cause the consolidation (irreversible consolidation in the case of a thermosetting resin, reversible consolidation in the case of a thermoplastic resin) of the synthetic material impregnating the fibers in a solid matrix, in which the wound fibers remain embedded to constitute a reinforcing material.

[0008] Hardening can occur as disclosed, for example, in FR3053624A1.

[0009] In a pending patent application of the same Applicant, it is proposed to produce the cage body in a synthetic material having a glass transition temperature greater than or equal to 120 °C, for example in an epoxy resin, reinforced with high tensile strength fibers such as carbon fibers, glass fibers, Kevlar® fibers or other known fibers having equivalent performance, for example instead of conventional cotton fibers.

[0010] Although epoxy resin reinforced with long carbon fibers is a composite material already used for several applications (tooling and aerospace), it can present a number of disadvantages when used for the production of bearing cages, even if it can also offer considerable advantages.

[0011] For example, in a composite cage body obtained through CFW processes, it is possible to configure the preform forming tube with a sequence of carbon fiber layers oriented at different angles to each other, both to prevent the composite preform forming tube from exhibiting strongly anisotropic behavior and to improve its mechanical properties and, consequently, the mechanical properties of the final cage body.

[0012] However, by adopting such a type of composite element to make a moving component such as a bearing cage, it has been shown that once the composite material is subjected to high centrifugal forces and the characteristic impact contact with the bearing bodies present in a bearing cage, it can be subjected to delamination which causes a sharp temperature increase in the application, of which total bearing failure can be a direct consequence.

[0013] Delamination can affect the performance of composite roller bearing cages and can also generate scrap during the production cycle, thereby increasing production costs. In fact, in the contact area with the balls, different machining surface conditions between each layer of fibers can be observed, especially when there are significant differences in fiber orientation within the different layers. This can lead to uneven cutting by the drilling tool and a risk of delamination initiation, which can propagate during cage operation and result in the failure of both the cage and the bearing housing it. Summary of the invention

[0014] The objective of the present invention is to overcome the disadvantages of the prior art by providing a bearing cage made of fiber-reinforced composite material having an improved service life and preserving the mechanical properties of the cage under all conditions of use.

[0015] An objective of the invention is further to produce a bearing cage made of fiber-reinforced composite material having improved interlaminar cohesion, particularly in its most critical portions, for example where impact contacts with the bearing bodies of the rolling bearing may occur, to avoid delamination, particularly in CFW composite material cages, during operation at high rotational speeds and under high loads.

[0016] An objective of the invention is also to provide a high-precision rolling bearing unit equipped with a cage made of composite material suitable for use in applications with particularly high stresses, such as those requiring high rotational speeds and / or subjected to high loads.

[0017] According to the invention, a bearing cage made of composite material having improved mechanical behavior and an associated bearing unit are provided, as defined in the attached claims. Brief description of the figures

[0018] Other features and advantages of the present invention will become clear from the following description of non-limiting examples thereof, made with reference to the figures in the accompanying drawings, in which:

[0019] - Figure [1] schematically represents, in radial cross-section, a unit of bearing housing equipped with a bearing body retention cage made according to the invention;

[0020] - [Fig.2] schematically represents, at an enlarged scale, a restraint cage bearing body for a bearing housing provided according to the present invention;

[0021] - [Fig.3] schematically represents how the retaining cage of [Fig.2] can be produced;

[0022] - [Fig. 4] schematically represents a detailed perspective view of a tube forming preform obtained by the process of [Fig. 3] where some layers of composite material have been removed, to improve understanding; and

[0023] - [Fig. 5] schematically represents in radial cross-section and at a On a fairly large scale, a circumferential portion of the bearing cage of the [Fig.2], Detailed description of the invention

[0024] With reference to Figures 1 to 5, reference number 1 indicates a rolling bearing unit ([Fig.1]) comprising a rolling bearing 2 of any known type and a rolling bearing cage 3, made of a composite material.

[0025] The bearing assembly comprises an inner ring 4, an outer ring 5 and a plurality of elements or bearing bodies 6, in the non-limiting embodiment shown, consisting of balls.

[0026] The bearing bodies 6 are arranged, in the example shown, in a ring of balls around an axis of symmetry A of the bearing housing, which is also the axis of symmetry of the cage 3 ([Fig. 2]). In different embodiments, not shown for simplicity, the bearing housing 2 may comprise two rings of bearing bodies arranged side by side, and the bearing bodies may be, interchangeably, balls, cylindrical or tapered rollers, or small cylinders, depending on the operating requirements.

[0027] In any case, the bearing cage 3 ([Fig.2]) comprises an annular body 7 and a plurality of pockets or housings 8, each of them being configured to freely house, in a known manner, a respective bearing body 6 of the bearing 2 to properly maintain the bearing bodies 6 spaced from each other by a predefined pitch.

[0028] The annular body 7 has an axis of symmetry A and a predefined axial width or length. The pockets or recesses 8 are located radially throughout the annular body 7, through respective inner and outer cylindrical lateral surfaces 9 and 10 ([Fig. 2]) of the annular body 7, substantially perpendicular to them, and, in the example shown, consist of simple cylindrical radial holes. The lateral surfaces 9 and 10 radially delimit the annular body 7 from each other.

[0029] The annular body 7 is made of a fiber-reinforced synthetic plastic material and is preferably obtained by a process known in the art as CFW (continuous filament winding), schematically represented by a in a non-limiting manner to [Fig.3], solely for illustrative purposes and for a better understanding of the invention.

[0030] With reference to [Fig.3], in a CFW production process, a plurality of reinforcing fibers 11 are unwound in a known manner from reels 12, are impregnated in a known manner with a resin / synthetic plastic material 13, for example, by passing them through the plastic material 13 maintained in a fluid state, then the impregnated reinforcing fibers 11b are wound around a mandrel 14 at a predefined inclination with respect to the axis of symmetry Al of the mandrel 14, until a preform forming tube 15 is obtained (Figures 3, 4) consisting of different layers 18 of impregnated fibers, for example having different orientations, the layers being stacked one on top of the other.Alternatively, pre-preg (pre-impregnated) fibers, or pre-preg sheets or strips 18 (not shown) of carefully arranged fibers having the same orientation in each sheet or strip can be used, by arranging the sheets or strips 18 having fibers of different orientations stacked one on top of the other to obtain the preform forming tube 15.

[0031] The axis of symmetry Al of the mandrel tool 14 coincides with the axis of symmetry A of the cage 3 to be obtained and with the winding axis of the fibers 11 around the mandrel tool 14.

[0032] To obtain a plurality of annular bodies 7 from a single preform tube 15, the latter is hardened in any known and appropriate way (for example according to FR3053624A1), in order to polymerize the synthetic plastic material or resin 13 to form a solid matrix 21 ([Fig.4]), then is cut radially into slices each consisting of an axial section 16 ([Fig.4]) of the preform tube 15 cut in a radial direction in the preform tube 15, for example along the dashed lines ([Fig.4]), such that each axial section 16 of the preform tube 15 has the same axial width / length as a cage 3 to be obtained.

[0033] Before or after the cutting step, but generally after the hardening step, a plurality of radial holes configured to form the pockets or housings 8 are drilled through each axial section 16 of the tube forming preform 15.

[0034] Consequently, as shown in [Fig.4] and 2, each section 16 comes to constitute, after the cutting step, an annular body 7.

[0035] Each annular body 7, therefore, comprises a plurality of superimposed layers 18 of reinforcing fibers 11 embedded in a synthetic plastic material 13 and arranged with respect to the axis of symmetry A / Al according to a predefined pattern.

[0036] In certain embodiments, the preforming tube 15 can be obtained either from a polymerized fiber-reinforced thermosetting resin or from a polymerized thermoplastic resin. In the latter case, the hardening step of the preforming tube 15 would no longer be necessary, since the thermoplastic powder for impregnating / coating the fibers must be melted (and therefore also polymerized) directly on the mandrel 14, for example by means of a laser beam or by means of a hot air stream.

[0037] According to one feature of the invention, the impregnated / embedded fibers 11b of each layer 18 are arranged, for example by selecting a correct winding angle, to form, in a plan view, with the axis of symmetry A of the final cage 3 and, with reference to the process of [Fig.3], the axis of symmetry Al of the mandrel 14, a predefined angle [3 ([Fig.2]), which may differ from the angle [3 formed in a plan view with the axis of symmetry A / Al by the fibers 11b of each layer 18 immediately adjacent to it.

[0038] After cutting the preform tube 15 into axial sections 16, the annular body 7 of each cage 3 which will be obtained by further producing the radial holes constituting the pockets or housings 8 will be formed, consequently, by a plurality of radially superimposed layers 18 of fibers 11b arranged / wound around the axis of symmetry A of the resulting cage 3 with the same pattern and the same inclination as those present in the preform tube 15.

[0039] It should be noted that, in each layer 18, the fibers 11b can be wound around, or arranged in plan view with respect to, the axis A of the cage 3 in a parallel or crisscross pattern, so that the angles [3] of each layer 18 can adopt a positive and / or negative value. With reference to the schematic datum frame sketched in [Fig. 2], the angle [3] can vary from 0° when the fibers 11 / 11b are arranged parallel to the axis A to substantially ±90° when the fibers 11 / 11b are arranged in a plan view parallel to an axis B perpendicular to the axis A, where the term "substantially" indicates an operating tolerance of ±3°.

[0040] It is therefore possible to obtain a preform-forming tube 15 and, consequently, cage bodies 7, where all the radially superimposed or stacked layers or strips 18 are arranged to form, with the axis of symmetry A of the cage 3, when the cage 3 is viewed in a plan view, a predefined angle [3] that is identical or different from one layer or strip to another. For example, with reference to [Fig. 4], a first radially innermost layer 18b is formed with its impregnated fibers 11b arranged at an angle [3] of a first value, a second layer 18c, for example immediately adjacent to it, is formed with its impregnated fibers 11b arranged at an angle [3] of a second value and a third layer 18e immediately adjacent to layer 18c, radially outside of it, is formed with its impregnated fibers 11b arranged at an angle [3 of a third value, etc.

[0041] With reference to the schematic cross-sectional view in [Fig. 5], each pocket or housing 8 comprises an annular contact area 22 configured in a known manner to cooperate in contact, during use, with a bearing body 6 (illustrated by a dashed line) of a rolling bearing. The pockets or housings 8, as well as their annular contact areas 22 intended to cooperate with bearing bodies 6, have an axial width extending radially with respect to the axis of symmetry A of the cage 3, namely in the direction of the radial thickness of the cage 3.

[0042] The stacking of superimposed layers or strips of reinforcing fibers impregnated with synthetic plastic material delimits, consequently, a side wall 23 (figures 2 and 5) of each pocket or housing 8 over its entire radial length, the annular contact areas 22 being made up of a portion of such a side wall 23 of each pocket or housing 8.

[0043] According to the main aspect of the invention, the annular contact area 22 of each pocket or housing 8 is delimited by at least one first layer or band 18, for example according to a simplified scheme presented here purely for explanatory purposes, by the layer or band 18c, in which the predefined angle [3 formed in a plan view by its reinforcing fibers 11 with the axis of symmetry A must be equal, according to the invention, to substantially 90°, where the term "substantially" includes an operating tolerance of ±3°.

[0044] Preferably, since the average radial thickness of each layer or strip 18 can be about 0.15 mm, the annular contact area 22 of each pocket or housing 8 is delimited by a plurality of first layers or strips, for example 18c, whose reinforcing fibers 11 are arranged with respect to the axis of symmetry A of the cage 3, when the cage 3 is observed in a plan view, at a predefined angle of substantially 90°, given the operating tolerances.

[0045] As a purely illustrative example, in [Fig.5], the contact area 22 is shown as delimited / formed by at least two superimposed layers or bands 18c, not shown to scale for better understanding.

[0046] According to another aspect of the invention, the annular contact area 22 of each pocket or housing 8 is arranged so as to be delimited by a radially central annular portion 24 ([Fig. 5]) of the cage body 3 formed by one or more first layers or strips 18c arranged in a radial stacking which also delimits a portion of the side wall 23. This central portion 24 is located between the inner and outer cylindrical side surfaces 9 and 10 of the cage body 7 and, according to one embodiment of the invention, the annular contact area 22 of the pockets or housings 8 delimited by the radially central annular portion 24 of the cage body 7 is arranged closer to the outer lateral cylindrical surface 10 of the cage body 7.

[0047] In a preferred embodiment of the invention, radially above and below the annular contact area 22 of the pockets or housings 8 delimited by one or more first layers or strips 18c, the cage body 7 is formed by a plurality of radially superimposed second layers or strips, for example 18b and 18d, of reinforcing fibers 11 embedded in a synthetic plastic material 13, the predefined angle of orientation of its reinforcing fibers 11 with respect to the axis of symmetry of the cage 3 seen in a plan view gradually decreasing in each subsequent layer or strip 18 in increments of finite angular amplitude, for example of about 15° and preferably of a maximum of 15°, until a minimum angular value is reached, which corresponds to the innermost and outermost second layer or strip 18, which define and delimit, respectively,the inner and outer lateral cylindrical surfaces 9, 10 of the cage body 7, that is to say, according to the simplified representation shown in [Fig.4] for purely illustrative purposes, by layers 18b and 18d, layer 18d being the outermost one.

[0048] The aforementioned minimum value of the angle [3 that the reinforcing fibers 11 of such second layers or strips 18 form in a plan view with the axis of symmetry A can be close to 15° and in a preferred embodiment is substantially identical in both the innermost and outermost layer or strip 18, namely for example layers or strips 18b and 18d, defining and delimiting the inner and outer lateral cylindrical surfaces 9, 10 of the cage body 7.

[0049] According to another feature of the invention, the composite material bearing cage 3 is made using a synthetic plastic material which has a glass transition temperature greater than or equal to 90 °C, preferably an epoxy resin.

[0050] According to another feature of the invention, the reinforcing fibers 11 are selected from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, mineral fibers such as basalt and quartz fibers, ceramic fibers, for example A12O3 or SiC fibers, metallic fibers, for example steel or aluminum fibers, organic fibers including cotton, cellulose, flax, jute, hemp and sisal fibers, any synthetic, organic or inorganic fiber similar to these in terms of tensile strength and stiffness.

[0051] According to a preferred embodiment, the reinforcing fibers 11b are continuous fibers 11 embedded in the synthetic plastic material 13 which has been made to impregnate the fibers 11.

[0052] According to one aspect of the invention, the bearing unit 1 of [Fig. 1] therefore comprises a bearing, for example bearing 2 or any other type of bearing having a plurality of bearing bodies 6 arranged in a defined radial space between the inner ring 4 and the outer ring 5 to make them relatively rotatable with low friction, and a bearing cage 3 as described above for retaining the bearing bodies 6 in a spaced manner. The bearing 2 is preferably of the high-precision bearing type, characterized by high-speed and / or high-load operation.

[0053] Research conducted by the Applicant's engineers has demonstrated that 90° inclined fiber plies (i.e., for example, layers or strips 18) positioned as close as possible to the contact area 22 of the pocket 8 with the bearing bodies 6 makes it possible to produce maximum cage 3 stiffness in the most critical areas, thereby improving the cage 3's mechanical performance at the contact point. Furthermore, the surface finish problems present in the side walls of pockets of prior art fiber-reinforced cages due to drilling and delamination are also remarkably resolved by selecting such a specific fiber ply orientation.The steepest 90° folds should be located in the center of the stacking sequence, then the orientation of the folds is gradually changed, moving towards both the outer and inner diameters, preferably ending with folds with a fiber orientation of 15°. This represents the essence of the present invention.

[0054] The main advantage of the present invention is: • avoiding any risk of cage delamination during machining; • the fact of having a better surface finish on the side wall of the cage pockets, which also means less potential friction and better performance at high rotational speeds; • avoiding or significantly reducing the risk of cage delamination in the strip layers during bearing operation. • achieving high contact loads in the ball pocket area thanks to the 90° folds.

[0055] All the objectives of the invention are therefore achieved.

Claims

Demands

1. A composite material bearing cage (3) having improved behavior, comprising an annular body (7) and a plurality of pockets or housings (8), each configured to house, in a rotational manner, a respective bearing body (6) of a bearing (2), the annular body (7) having an axis of symmetry (A) and a predefined axial width and the pockets or housings (8) being located radially throughout the annular body, through respective internal and external cylindrical lateral surfaces (9, 10) of the annular body radially delimiting it,the annular body (7) being made of a fiber-reinforced synthetic plastic material comprising a plurality of superimposed layers or strips (18) of reinforcing fibers (11) embedded in a synthetic plastic material (13) and arranged with respect to said axis of symmetry (A) in a predefined pattern to form with the axis of symmetry (A) of the cage, when the cage (3) is viewed in a plan view, a predefined angle (|3); wherein each pocket or housing (8) comprises an annular contact area (22) configured to cooperate in contact, during use,with a bearing body (6) of a rolling bearing (2) and having an axial width extending radially with respect to said axis of symmetry (A) of the cage; characterized in that said annular contact zone (22) of each pocket or housing (8) is delimited by at least one first layer or strip (18c) in which said predefined angle (|3) of its reinforcing fibers (11) is equal to substantially 90°, taking into account the operating tolerances.

2. Bearing cage made of composite material according to claim 1, characterized in that the operating tolerances are such that said predefined angle (|3) of the reinforcing fibers (11) of said at least one first layer or strip (18c) is equal to 90° ± 3°.

3. A bearing cage made of composite material according to claim 1 or 2, characterized in that said annular contact zone (22) of each pocket or housing (8) is delimited by a plurality of said first layers or strips (18c) whose fibers reinforcement (11) are arranged with respect to said axis of symmetry (A) of said cage, when the cage (3) is observed in a plan view, at a predefined angle (|3) of substantially 90° given the operating tolerances.

4. Bearing cage made of composite material according to any one of the preceding claims, characterized in that said annular contact area (22) of each pocket or housing (8) is delimited by a radially central annular portion (24) of the cage body (7) formed by said at least one first layer or strip or by a plurality of said first layers or strips (18c) arranged in a radial stack, said central portion (24) being contained between said inner and outer cylindrical lateral surfaces (9, 10) of the cage body (7).

5. Bearing cage made of composite material according to claim 4, characterized in that said annular contact area (22) of the pockets or housings (8) delimited by said radially central annular portion (24) of the cage body (7) is arranged closer to the outer lateral cylindrical surface (10) of the cage body.

6. Bearing cage made of composite material according to any one of the preceding claims, characterized in that radially above and below said annular contact zone (22) of the pockets or housings (8) delimited by at least one first layer or strip (18c), said cage body (7) is formed by a plurality of second radially superimposed layers or strips (18b;18d) of reinforcing fibers (11) embedded in a synthetic plastic material (13), the predefined angle (|3) of orientation of its reinforcing fibers (11) with respect to the axis of symmetry (A) of the cage (3) seen in a plan view gradually decreasing in each subsequent layer or band (18) in increments of finite angular amplitude, until a minimum value is reached, which corresponds to the second innermost and outermost layer or band (18), which define and delimit, respectively, said inner (9) and outer (10) lateral cylindrical surfaces of the cage body.;

7. Bearing cage made of composite material according to claim 6, characterized in that said predefined angle (|3) of orientation of the reinforcing fibers (11) of the second layers or bands (18b, 18d) defining and delimiting said internal and external lateral cylindrical surfaces (9, 10) of the cage body (7) is substantially identical.

8. Bearing cage made of composite material (3) according to any one of the preceding claims, characterized in that the synthetic plastic material (13) has a glass transition temperature greater than or equal to 90 °C and preferably consists of an epoxy resin.

9. A bearing cage made of composite material according to any one of the preceding claims, characterized in that the reinforcing fibers (11) are selected from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, mineral fibers, such as basalt and quartz fibers, ceramic fibers, preferably A12O3 or SiC fibers, metallic fibers, for example steel or aluminum fibers, organic fibers including cotton, cellulose, flax, jute, hemp and sisal fibers, any synthetic, organic or inorganic fiber similar to these in terms of tensile strength and stiffness.

10. A bearing unit (1) comprising a bearing (2) comprising an outer ring (5), an inner ring (4) and a plurality of bearing bodies (6) arranged in a defined radial space between the inner ring and the outer ring to make them relatively rotatable with low friction, and a bearing cage (3) for retaining the bearing bodies in a spaced manner by means thereof, characterized in that the bearing cage (3) is made according to any one of the preceding claims.

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