Composite rolling bearing cage with improved behavior

Abstract

A rolling bearing cage (3) comprises an annular body (7) having a plurality of pockets or seats (8) for rolling bodies of a rolling bearing; the annular body has an axis of symmetry (A) and is made of a fiber-reinforced synthetic plastic material comprising a plurality of radial layers (18) of reinforcing fibers (11) embedded in a synthetic plastic material (13), and the reinforcing fibers of the plurality of radial layers are configured to form a predetermined angle (beta) with the axis of symmetry of the cage when the cage is viewed in a plan view; wherein the annular contact area (22) of each cavity or seat, which is configured to be in contact fit with a rolling body (6) in use, has an axial width which is defined by at least one or more layers or strips (18c) and extends in the radial direction relative to the symmetry axis of the cage, the predetermined angle of the reinforcing fibers of the at least one or more layers or tapes is substantially equal to 90 DEG.

Description

Technical Field

[0001] The present invention relates to a rolling bearing cage obtained from a fiber-reinforced composite synthetic plastic material and an associated rolling bearing unit including such a cage. Background Technology

[0002] As is well known, a rolling bearing unit includes a rolling bearing and a rolling bearing cage. The rolling bearing has an outer ring, an inner ring, and a plurality of rolling elements (e.g., balls) between the inner and outer rings so that they can rotate relative to each other with low friction. The rolling bearing cage holds the rolling elements in place and is configured in a radial space defined between the inner and outer rings.

[0003] A rolling bearing cage includes an annular body defined between its inner and outer cylindrical surfaces, and multiple pockets or seats, each configured to rotatably accommodate and retain a corresponding rolling element of the rolling bearing. The cage body can be made of fiber-reinforced thermosetting or thermoplastic materials, such as those carrying short or long reinforcing fibers (e.g., carbon fibers). It is made of phenolic resin (or any other suitable synthetic material, such as polyamide) of natural fibers or glass fibers, such as cotton, hemp, or flax, and the cage body is supported by a cavity or seat (e.g., formed by radial through holes) disposed radially through the cage body.

[0004] Typically, a preform consisting of a hollow tube is obtained by molding a synthetic material. The hollow tube is then cut radially into multiple slices, each slice forming the cage body. Before or after the cutting operation, the cavity or seat is actually drilled through the axial portion of the preform that will form the cage body.

[0005] The hollow tube that makes up the preform can be produced by a process called “continuous wire winding” (CFW), which involves tightly winding one or more composite filaments made of continuous fibers impregnated with synthetic plastic resin onto a metal mandrel tool.

[0006] Here and in the following text, "plastic resin" should be understood as a thermosetting synthetic material or a thermoplastic synthetic material, for example, the impregnation of fibers can be made from liquid thermosetting resin or solid thermoplastic powder.

[0007] After obtaining a predetermined number of superimposed radial layers of preimpregnated fibers, the preform is cured in a known manner (e.g., in an oven) to solidify the synthetic material of the impregnated fibers (irreversibly in the case of thermosetting resins and reversibly in the case of thermoplastic resins) into a solid matrix, in which the wound fibers remain embedded to form a reinforcing material.

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

[0009] In a pending patent application by the same applicant, a method using, for example, high tensile strength fibers (such as carbon fiber, glass fiber, etc.) was proposed. The cage body is produced from a synthetic material (e.g., epoxy resin) with a glass transition temperature equal to or greater than 120°C, which is used to reinforce the cage body instead of conventional cotton fibers (or other known fibers with equivalent properties).

[0010] Although epoxy resin reinforced with long carbon fibers is a composite material that has been used in several applications (tooling and aerospace), it may have many disadvantages when used to produce rolling bearing cages, even though it may also offer considerable advantages.

[0011] For example, in a composite cage body obtained via the CFW method, a preformed tube can be constructed using a series of carbon fiber layers oriented at different angles relative to each other, in order to both prevent the composite preformed tube from exhibiting strong anisotropic behavior and improve the mechanical properties of the composite preformed tube, and thus improve the mechanical properties of the final cage body.

[0012] However, it has been shown that by using this type of composite material element to implement moving components (such as the cage of a rolling bearing), the composite material element may undergo delamination once it is subjected to high centrifugal forces and characteristic impact contact with the rolling elements present in the bearing cage. This leads to a high temperature rise in the application, which may result in complete failure of the bearing as a direct consequence.

[0013] Delamination issues can impair the performance of composite rolling bearing cages and may also lead to scrap during the production cycle, thereby increasing production costs. In fact, in the contact area with the balls, especially where there are strong differences in fiber orientation between different layers, varying surface finishes between each fiber layer can be observed. This can lead to uneven cutting by the drilling tool and the risk of initial delamination, which may propagate during cage operation and cause cage and bearing failure. Summary of the Invention

[0014] The purpose of this invention is to overcome the shortcomings of the prior art by providing a fiber-reinforced composite rolling bearing cage, which has an improved service life and retains the mechanical properties of the cage under all operating conditions.

[0015] Furthermore, the present invention aims to provide a fiber-reinforced composite rolling bearing cage with improved interlaminar cohesion, particularly in its most critical parts, such as where impact contact with the rolling elements of the rolling bearing may occur, to avoid delamination during operation at high speeds and high loads (especially in CFW composite cages).

[0016] Another objective of this invention is to provide a high-precision rolling bearing unit equipped with a composite material cage, which can be used in applications with particularly high stress, such as applications requiring high speed and / or bearing high loads.

[0017] According to the present invention, a composite material rolling bearing cage having improved mechanical behavior, as defined in the appended claims, and an associated rolling bearing unit are provided. Attached Figure Description

[0018] Other features and advantages of the invention will become apparent from the following description of a non-limiting example of the invention with reference to the accompanying drawings, wherein:

[0019] - Figure 1 A rolling bearing unit with a rolling element cage made according to the present invention is schematically shown in radial section;

[0020] - Figure 2 A rolling element cage for a rolling bearing according to the present invention is shown schematically at an enlarged scale;

[0021] - Figure 3 It schematically shows that it can be produced Figure 2 The method of cage maintenance;

[0022] - Figure 4 It schematically shows the use of Figure 3 Detailed three-dimensional images of the preformed tube obtained by the method, wherein some composite material layers have been removed for better understanding; and

[0023] - Figure 5 Schematably shown in radial cross-section and at a fairly large scale Figure 2 The circumferential portion of the rolling bearing cage. Detailed Implementation

[0024] Reference Figures 1 to 5 Reference numeral 1 in the attached figure indicates the rolling bearing unit ( Figure 1 The rolling bearing unit includes any known type of rolling bearing 2 and a rolling bearing cage 3 made of composite material.

[0025] The rolling bearing includes an inner ring 4, an outer ring 5, and a plurality of rolling elements or rolling bodies 6, which, in the non-limiting embodiment shown, are composed of balls.

[0026] In the example shown, the rolling element 6 is configured as a spherical cap about an axis of symmetry A of the rolling bearing, which is also the axis of symmetry of the cage 3. Figure 2 In different embodiments not shown for simplicity, the rolling bearing 2 may include two rolling element crowns arranged side by side, and the rolling elements may be, indifferently, balls, cylindrical rollers, tapered rollers, or small cylinders, depending on the operation requirements.

[0027] In any case, the rolling bearing cage 3 ( Figure 2 It includes an annular body 7 and multiple cavities or seats 8, each cavity or seat being configured to freely accommodate the corresponding rolling element 6 of the rolling bearing 2 in a known manner during use, so as to properly keep the rolling elements 6 spaced apart from each other by a predetermined pitch.

[0028] The annular body 7 has an axis of symmetry A and a predetermined axial width or length. A cavity or seat 8 is disposed radially through the annular body 7, passing through the corresponding inner cylindrical lateral surface 9 and outer cylindrical lateral surface 10, which are substantially perpendicular to the annular body 7. Figure 2 In the example shown, the cavity or seat 8 is composed of a simple cylindrical radial hole. Lateral surfaces 9 and 10 define the annular body 7 radially between them.

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

[0030] Reference Figure 3In the CFW production method, multiple reinforcing fibers 11 are unwound from a spool 12 in a known manner and impregnated with a synthetic plastic resin / material 13 in a known manner, for example, by immersing them in a plastic material 13 held in a fluid state. The impregnated reinforcing fibers 11b are then wound around a mandrel tool 14 at a predetermined inclination relative to the axis of symmetry A1 of the mandrel tool 14 until a preformed tube 15 is obtained, consisting of impregnated fibers (e.g., with different orientations) in different layers 18. Figure 3 , Figure 4 These layers are stacked on top of each other. Alternatively, semi-cured sheet (pre-impregnated) fibers, or semi-cured sheets or strips 18 (not shown) with neatly ordered fibers having the same orientation in each sheet or strip, can be used to stack sheets or strips 18 with fibers having different orientations on top of each other to obtain a preformed tube 15.

[0031] The axis of symmetry A1 of the mandrel tool 14 coincides with the axis of symmetry A of the cage 3 to be obtained, and also coincides with the axis around which the fiber 11 is wound around the mandrel tool 14.

[0032] To obtain multiple annular bodies 7 from a single preformed tube 15, the preformed tube 15 is cured in any known and suitable manner (e.g., according to FR3053624A1) to polymerize the synthetic plastic material or resin 13 to form a solid matrix 21. Figure 4 Then it is cut into slices in the radial direction, each slice being cut from the preformed tube 15 in the radial direction (e.g., along the dotted line). Figure 4 The axially stretched portion 16 of the preformed tube 15 Figure 4 The structure, such as each axially stretched portion 16 of the preformed tube 15, has the same axial width / length as the cage 3 to be obtained.

[0033] Before or after the cutting step, but usually after the curing step, a plurality of radial holes are drilled through each axially stretched portion 16 of the preformed tube 15 to form a cavity or seat 8.

[0034] Therefore, as Figure 4 and Figure 2 As shown, each stretching portion 16 forms an annular body 7 after the cutting step.

[0035] Therefore, each annular body 7 includes reinforcing fibers 11 embedded in a synthetic plastic material 13 and configured according to a predetermined pattern relative to the axis of symmetry A / A1.

[0036] In some embodiments, the preformed tube 15 may be obtained from a polymerized fiber-reinforced thermosetting resin or a polymerized thermoplastic resin. In the latter case, the curing step of the preformed tube 15 will no longer be necessary because the thermoplastic powder used for impregnating / embedding the fibers needs to be melted (and thus polymerized) directly on the mandrel 14, for example by a laser beam or by a stream of hot air.

[0037] According to the features of the invention, the impregnated / embedded fibers 11b of each layer 18 are configured (e.g., by selecting an appropriate winding angle) in a plan view with respect to the axis of symmetry A of the final cage 3 and a reference. Figure 3 The method forms a preset angle β with the axis of symmetry A1 of the mandrel 14. Figure 2 The preset angle β can be different from the angle β formed by the fibers 11b of each layer 18 adjacent to the layer in the plan view with respect to the axis of symmetry A / A1.

[0038] After the preformed tube 15 is cut into axially stretched portions 16, an annular body 7 of each retainer 3 is formed by fibers 11b of multiple radially superimposed layers 18 arranged / wound around the axis of symmetry A of the resulting retainer 3 in the same pattern and angle as present in the preformed tube 15. The annular body 7 is obtained by further providing radial holes that constitute a cavity or seat 8.

[0039] It should be noted that in each layer 18, fibers 11b can be wound around the axis A of the cage 3 according to a parallel or intersecting pattern, or configured relative to the axis A of the cage 3 in a plan view, such that the angle β of each layer 18 can be positive and / or negative. (Refer to...) Figure 2 The schematic reference system depicted in the diagram allows angle β to vary from 0° (when fiber 11 / 11b is configured parallel to axis A) to essentially ±90° (when fiber 11 / 11b is configured parallel to axis B and perpendicular to axis A in the plan view), wherein the term “essentially” indicates a working tolerance of ±3°.

[0040] Therefore, a preformed tube 15 and a corresponding cage body 7 can be obtained, wherein all radially superimposed or stacked layers or strips 18 are configured to form a predetermined angle β with the axis of symmetry A of the cage 3 when viewed in a plan view, the predetermined angle β being the same or different between one layer or strip and another. For example, refer to Figure 4 The first layer 18b, which is the innermost layer in the radial direction, has impregnated fibers 11b arranged at an angle β of a first value. The second layer 18c (e.g., adjacent to the first layer) has impregnated fibers 11b arranged at an angle β of a second value. The third layer 18e, which is adjacent to the layer 18c and is located outside the layer 18c in the radial direction, has impregnated fibers 11b arranged at an angle β of a third value, and so on.

[0041] Reference Figure 5 A schematic cross-sectional view shows that each cavity or seat 8 includes an annular contact area 22, which is constructed in a known manner for contact engagement with the rolling elements 6 (shown in dashed lines) of the rolling bearing during use. The cavities or seats 8 and their annular contact areas 22 for engaging with the rolling elements 6 have an axial width extending radially (i.e., in the radial thickness direction of the cage 3) relative to the axis of symmetry A of the cage 3.

[0042] Therefore, the sidewalls 23 of each cavity or seat 8 are defined by a stack of reinforced fibers impregnated with synthetic plastic material, which define the entire radial length of the sidewalls. Figure 2 and Figure 5 The annular contact area 22 is formed by a portion of the sidewall 23 of each cavity or seat 8.

[0043] According to a key aspect of the invention, the annular contact area 22 of each cavity or seat 8 is defined by at least one first layer or band 18. For example, according to a simplified scheme done here only for better explanation, the annular contact area 22 of each cavity or seat 8 is defined by a layer or band 18c, in which, according to the invention, the predetermined angle β formed by the reinforcing fibers 11 of the layer or band 18c with the axis of symmetry A in a plan view must be equal to substantially 90°, wherein the term “substantially” includes a working tolerance of ±3°.

[0044] Preferably, since the average radial thickness of each layer or band 18 can be about 0.15 mm, and the annular contact area 22 of each cavity or seat 8 is defined by a plurality of first layers or bands (e.g., 18c), when the cage 3 is viewed in a plan view, the reinforcing fibers 11 of the plurality of first layers or bands are configured at a predetermined angle of substantially 90° relative to the axis of symmetry A of the cage 3, taking into account working tolerances.

[0045] For illustrative purposes only, in Figure 5 In the diagram, the contact area 22 is shown as being defined / formed by at least two superimposed layers or bands 18c, which are not shown to scale for better understanding.

[0046] According to another aspect of the invention, the annular contact area 22 of each cavity or seat 8 is configured such that it is formed by the annular radial intermediate portion 24 of the retainer 3. Figure 5The annular radial intermediate portion 24 is defined by one or more first layers or bands 18c arranged in a radial stack and also defining a portion of the sidewall 23. This intermediate portion 24 is included between the inner cylindrical lateral surface 9 and the outer cylindrical lateral surface 10 of the cage body 7, and according to one embodiment of the invention, the annular contact area 22 of the cavity or seat 8 defined by the annular radial intermediate portion 24 of the cage body 7 is configured closer to the outer cylindrical lateral surface 10 of the cage body 7.

[0047] In a preferred embodiment of the invention, above and below the annular contact area 22 of the cavity or seat 8 defined by one or more first layers or bands 18c, the retainer body 7 is formed of reinforcing fibers 11 of a plurality of radially stacked second layers or bands (e.g., 18b and 18d) embedded in a synthetic plastic material 13, wherein, when viewed in a plan view, a predetermined angle of orientation of the reinforcing fibers 11 of the plurality of radially stacked second layers or bands relative to the axis of symmetry of the retainer 3 gradually decreases in each subsequent layer or band 18 with a finite angular amplitude, for example, decreasing by about 15° or preferably not exceeding 15°, until a minimum angular value corresponding to the innermost second layer or band 18 and the outermost second layer or band 18 is reached, the innermost second layer or band 18 and the outermost second layer or band 18 respectively defining and defining the inner cylindrical lateral surface 9 and the outer cylindrical lateral surface 10 of the retainer body 7, i.e., according to Figure 4 The simplified representations of layers 18b and 18d are for illustrative purposes only, with layer 18d being the outermost layer.

[0048] The minimum value of the angle β formed by the reinforcing fiber 11 of this second layer or band 18 with the axis of symmetry A in the plan view can be close to 15°, and in a preferred embodiment, the angle β is substantially the same in the innermost layer or band 18 and the outermost layer or band 18 (i.e., layers or bands 18b and 18d) of the inner cylindrical lateral surface 9 and the outer cylindrical lateral surface 10 that define and delineate the cage body 7.

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

[0050] According to another feature of the invention, the reinforcing fiber 11 is selected from the group consisting of: carbon fiber, glass fiber, Fibers, such as mineral fibers like basalt and quartz fibers, ceramic fibers like Al2O3 or SiC fibers, metal fibers like steel or aluminum fibers, organic fibers including cotton, cellulose, flax, jute, hemp, and sisal fibers, and any synthetic organic or inorganic fibers with tensile strength and stiffness similar to these fibers.

[0051] According to a preferred embodiment, the reinforcing fiber 11b is a continuous fiber 11 embedded in a synthetic plastic material 13, the synthetic plastic material 13 having been impregnated with the fiber 11.

[0052] According to one aspect of the invention, Figure 1 The rolling bearing unit 1 thus includes a rolling bearing (e.g., rolling bearing 2 or any other type of rolling bearing) and a rolling bearing cage 3 as described above. The rolling bearing has a plurality of rolling elements 6 arranged in a radial space defined between an inner ring 4 and an outer ring 5 to allow the inner ring 4 and the outer ring 5 to rotate relative to each other with low friction. The rolling bearing cage 3 is used to keep the rolling elements 6 spaced apart. The rolling bearing 2 is preferably a high-precision bearing type characterized by high speed and / or high operating load.

[0053] Studies conducted by the applicant's engineers have shown that 90° inclined fiber sheets (i.e., layers or strips 18) located as close as possible to the contact area 22 between the cavity 8 and the rolling element 6 allow for maximum stiffness of the cage 3 in most critical areas, resulting in better mechanical properties of the cage 3 at the contact level. In parallel, by selecting this specific orientation of the fiber sheets, the problem of poor surface conditions in the cavity sidewalls of prior art fiber-reinforced cages due to drilling and delamination is also surprisingly solved. The steepest 90° sheets are located in the middle of the lay-up sequence, and then the orientation of the sheets gradually changes towards both the outer and inner diameters, thus completing, preferably with a 15° gradual change in fiber orientation. This is the core of the invention.

[0054] The main advantages of this invention include:

[0055] • Avoid any risk of rack delamination during machining;

[0056] • The sidewalls of the cage cavity have a good surface finish, which means less friction and better performance at high speeds;

[0057] • Avoid or significantly reduce the risk of cage delamination during bearing operation.

[0058] • High contact load is achieved in the spherical cavity grid region due to the 90° plies.

[0059] Therefore, all the objectives of this invention have been achieved.

Claims

1. A composite rolling bearing cage (3) with improved behavior, comprising an annular body (7) and a plurality of cavities or seats (8), each cavity or seat (8) being configured to rotatably accommodate a corresponding rolling element (6) of a rolling bearing (2) in use, the annular body (7) having an axis of symmetry (A) and a predetermined axial width, and the cavity or seat (8) being disposed radially through the annular body and passing through corresponding inner cylindrical lateral surfaces (9) and outer cylindrical lateral surfaces (10) that radially define the annular body, the annular body (7) being made of a fiber-reinforced synthetic plastic material comprising reinforcing fibers (11) embedded in a plurality of stacked layers or strips (18) of synthetic plastic material (13), the reinforcing fibers (11) of the plurality of stacked layers or strips (18) being configured according to a predetermined pattern relative to the axis of symmetry (A) to form a predetermined angle (β) with the axis of symmetry (A) of the cage when viewed in a plan view, wherein, Each cavity or seat (8) includes an annular contact area (22) configured to engage with the rolling elements (6) of the rolling bearing (2) in use, and having an axial width extending radially relative to the axis of symmetry (A) of the cage. Its features are, The annular contact area (22) of each cavity or seat (8) is defined by at least one first layer or band (18c), wherein the predetermined angle (β) of the reinforcing fibers (11) of the at least one first layer or band (18c) is substantially equal to 90°, taking into account working tolerances.

2. The composite material rolling bearing cage according to claim 1, characterized in that, The working tolerance is such that the predetermined angle (β) of the reinforcing fiber (11) of the at least one first layer or strip (18c) is equal to 90° ± 3°.

3. The composite material rolling bearing cage according to claim 1 or 2, characterized in that, The annular contact area (22) of each cavity or seat (8) is defined by a plurality of first layers or bands (18c), the reinforcing fibers (11) of the plurality of first layers or bands (18c) being configured at a predetermined angle (β) of substantially 90° relative to the axis of symmetry (A) of the retainer when viewed in a plan view, taking into account working tolerances.

4. The composite material rolling bearing cage according to any one of the preceding claims, characterized in that, The annular contact area (22) of each cavity or seat (8) is defined by an annular radial intermediate portion (24) of the cage body (7), the annular radial intermediate portion (24) being formed by the at least one first layer or band or by a plurality of first layers or bands (18c) arranged in a radially stacked manner, the intermediate portion (24) being included between the inner cylindrical lateral surface (9) and the outer cylindrical lateral surface (10) of the cage body (7).

5. The composite material rolling bearing cage according to claim 4, characterized in that, The annular contact area (22) of the cavity or seat (8) defined by the annular radial intermediate portion (24) of the cage body (7) is configured to be closer to the outer cylindrical lateral surface (10) of the cage body.

6. The composite material rolling bearing cage according to any one of the preceding claims, characterized in that, Above and below the annular contact area (22) of the cavity or seat (8) defined by at least one first layer or band (18c), the retainer body (7) is formed of a plurality of radially superimposed second layers or bands (18b; 18d) of reinforcing fibers (11) embedded in a synthetic plastic material (13), wherein, when viewed in a plan view, a predetermined angle (β) of the orientation of the plurality of radially superimposed second layers or bands (18b; 18d) of reinforcing fibers (11) relative to the axis of symmetry (A) of the retainer (3) gradually decreases in each subsequent layer or band (18) with a finite angular amplitude step until reaching a minimum value corresponding to the innermost second layer or band (18) and the outermost second layer or band (18), which respectively define and delineate the inner cylindrical lateral surface (9) and the outer cylindrical lateral surface (10) of the retainer body.

7. The composite material rolling bearing cage according to claim 6, characterized in that, The predetermined angle (β) at which the orientation of the reinforcing fibers (11) of the second layer or band (18b, 18d) of the inner cylindrical lateral surface (9) and the outer cylindrical lateral surface (10) of the cage body (7) is substantially the same.

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

9. The composite material rolling bearing cage according to any one of the preceding claims, characterized in that, The reinforcing fiber (11) is selected from the group consisting of: carbon fiber, glass fiber, Fibers, such as mineral fibers like basalt and quartz fibers, ceramic fibers preferably Al2O3 or SiC fibers, metal fibers such as steel or aluminum fibers, organic fibers including cotton, cellulose, flax, jute, hemp and sisal fibers, and any synthetic organic or inorganic fibers with tensile strength and stiffness similar to these fibers.

10. A rolling bearing unit (1) comprising a rolling bearing (2) and a rolling bearing cage (3), the rolling bearing (2) further comprising an outer ring (5), an inner ring (4), and a plurality of rolling elements (6) arranged in a radial space defined between the inner ring and the outer ring such that the inner ring and the outer ring can rotate relative to each other with low friction, the rolling bearing cage (3) for holding the rolling elements spaced apart from the rolling bearing cage (3), characterized in that, The rolling bearing cage (3) is made according to any one of the preceding claims.

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