Deep-groove ball bearing

Abstract

High-speed, deep-groove ball bearing (10), the bearing (10) having a main axis (A) of rotation and symmetry, and being provided with an outer ring (20) and an inner ring (30) provided with respective raceways (21) (31), and with a row (40) of a number (N) of rolling bodies (41) arranged inside the raceways (21) (31) to enable the relative rotation of the outer ring (20) and of the inner ring (30), a parameter ratio (X) between a dimension of a diameter (φ44) of a primitive circumference (44) of the balls (41) and the product of the number (N) of balls (41) and a dimension of a diameter (φ41) of the balls (41) themselves falls within a range of values from 0.50 to 0.60.

Description

[0001] DEEP-GROOVE BALL BEARING

[0002] Technical field

[0003] The present invention relates to a deep-groove ball bearing.

[0004] Prior art

[0005] Known deep-groove ball bearings are available in a wide range of sizes and in numerous different forms, and can be used in a range of different applications. While remaining generally applicable, the present document makes explicit reference to deep-groove ball bearings used in the powertrains of electric vehicles, which are therefore substantially characterized by very high rotational speeds.

[0006] Deep-groove ball bearings are able to bear, including at high rotational speeds, both radial loads and axial loads, and comprise:

[0007] - an outer ring provided with an inner raceway,

[0008] - an inner ring coaxial with the outer ring and provided with an outer raceway,

[0009] - a row of rolling bodies arranged inside the raceways to enable the relative rotation of the outer ring and of the inner ring.

[0010] The specific shape of these raceways, referred to as “deep groove”, enables these roller bearings, which would be basically purely radial, to also bear axial loads.

[0011] Again in drivetrains of electric vehicles, the roller bearings of the type described above have numerous uses, all of which not only involve very high rotational speeds, but are also the subject of pressing demands from manufacturers of these electric vehicles to achieve increasingly high rotational speeds without affecting rigidity characteristics or external dimensions, at equal load capacity.

[0012] Summary of the invention

[0013] The present invention is intended to provide a deep-groove ball bearing that enables rotational speeds that are even higher than the rotational speeds currently being reached, without affecting the external dimensions or the rigidity and robustness constraints thereof.

[0014] The present invention provides a deep-groove ball bearing with the features set out in the attached claims.

[0015] Brief description of the drawings

[0016] The invention is described below with reference to the attached drawings, which show a non-limiting example embodiment thereof, in which:

[0017] - Figure l is a side view of a preferred embodiment of the deep-groove ball bearing according to the present invention, and

[0018] - Figure 2 is a cross section taken along the line II-II in Figure 1.

[0019] Detailed description

[0020] In Figures 1 and 2, the deep-groove ball bearing as a whole is denoted by reference sign 10.

[0021] The bearing 10 is particularly suitable for use in a powertrain of an electric vehicle (not illustrated), has a main axis A of rotation and symmetry, and comprises:

[0022] - an outer ring 20 provided with an inner raceway 21,

[0023] - an inner ring 30 coaxial with the outer ring and provided with an outer raceway 31, and

[0024] - a row 40 of rolling bodies, or balls 41, a given number N of which are arranged inside the raceways 21 and 31 to enable the relative rotation of the outer ring 20 and of the inner ring 30, and have respective centres 42 of rotation and respective external diameters cp4i of specific dimensions that pass through the related centres 42 of rotation.

[0025] The bearing 10 further comprises a cage 50 that is provided with a cell 51 for each ball

[0026] 41 to hold the balls 41 inside the raceways 21 and 31, not only positioning the centres 42 of the balls 41 themselves on a primitive circumference 44 having a diameter 44, which is referred to as the “pitch diameter” in technical language, and positioned in a substantially intermediate position between the raceways 21 and 31, but also arranging the balls 41 themselves, in relation to one another along said circumference 44, at a pitch 46 that, in the preferred embodiment of the present invention, is equal to a dimension of the circumference 44 divided by the number N of balls 41. In other words, the N balls 41 are uniformly distributed about the axis A along the primitive circumference 44.

[0027] The raceways 21 and 31 of the bearing 10 are deeply recessed inside the rings 20 and 30, providing the bearing 10 with a specific shape that is able to bear both radial loads and axial loads in both axial directions.

[0028] To increase both the maximum rotational speed that can be reached by the bearing 10 and the rigidity of the bearing 10 itself, without however modifying in any way the external dimensions of the bearing 10 or the load capacity of the bearing 10, i.e. without affecting any strictly application parameters, which are usually constrained by the requirements of the application or of the client, some structural parameters of the bearing 10 have been selected and associated in a surprising manner, i.e. in a manner not achievable solely by design.

[0029] The specific structural geometric features on which the inventive activity has been focused, and which have been associated using relationships studied and created specifically for the stated objectives of this invention, are as follows: the pitch 46 between the balls 41 along the circumference 44,

[0030] - the number N of balls 41 , and

[0031] - the diameter cp4i of the balls 41.

[0032] For a deep-groove ball bearing of a powertrain of an electric vehicle, acting synergistically on the geometric features set out above has made it possible to determine, using a series of experimental tests carried out by the applicant, that the increase in the maximum rotational speed that can be reached by the bearing 10 and the increase in the rigidity of the bearing 10 itself are obtained when a parameter X, defined as the ratio between the diameter cp44 of the primitive circumference 44 and the product of the number N and the diameter cp4i of the balls 41, falls within a range from 0.50 to 0.60.

[0033] Therefore, when the value of the structural parameter X:

[0034] X = [diameter 44] / (number N * [diameter cp4i]) where [diameter 44] and [diameter cp4i] represent the dimensions of the diameter cp44 and respectively of the diameter cp4i, falls within the range of values: 0.50 < X < 0.60 the bearing 10 can reach a maximum rotational speed that is much higher than the maximum rotational speed of the deep-groove bearings currently known, and the rigidity thereof may also be increased considerably. Experimental tests carried out on a series of prototypes have demonstrated that the best performance levels, i.e. with a rotational speed at least greater than 0.8 MnDm (millions of revolutions in relation to the diameter 44), are obtained precisely with a value of the structural parameter X of between 0.5 and 0.6, precisely because when the ratio between the dimensions of the diameter 44, of the diameter cp4i, and of the number N of balls 41 falls within this range the best performance levels are obtained in terms of lubrication of the bearing 10, and the risk of plastic deformation, i.e. ovalizing, of the outer ring 20 and the inner ring 30 is eliminated entirely, likewise preventing the best performance levels from being obtained any other problem during assembly of the bearing 10.

[0035] The aforementioned specific geometric structural features were not however the only features on which the inventive activity was focused, since experimental tests carried out on a series of prototypes have demonstrated, in a surprising way with respect to the current knowledge of a person skilled in the art, that, considering other specific geometric structural features of the bearing 10 and associating these other specific geometric structural features with one another by means of further relationships specifically studied and created, the aforementioned results of a much higher maximum rotational speed and a considerable increase in the rigidity of the bearing 10 can be achieved in a stable and constant manner with the bearing 10 according to the present invention.

[0036] These other specific structural geometric features are:

[0037] - a surface SI of the area of a ball 41 measured in a plane transverse to the axis A, i.e. in a section plane passing through the line II-II, and

[0038] - a surface S2 of the area of the bearing 10 as a whole, again measured in a plane transverse to the axis A, i.e. in a section plane passing through the line II-II.

[0039] In particular, the surface SI of the area of a ball 41 is equal to

[0040] SI = 7t * R2 where R2 is equal to half the dimension of the diameter cp4i, while the surface S2 of the area of the bearing 10 is equal to

[0041] S2 = (cp3o - cp2o) * S3 i.e. the product of the distance between an internal diameter >30 of the inner ring 30 and an external diameter cp2o of the outer ring 20 and the axial thickness S3 of the bearing 10 itself measured parallel to the axis A.

[0042] The stabilization of the results inherent in the increase both of the maximum rotational speed that can be achieved by the bearing 10 and the rigidity of the bearing 10 itself is obtained when a parameter Y, defined as the ratio between the dimensions of the two surfaces SI and S2, i.e.:

[0043] Y = S1 / S2 falls within the range of values:

[0044] 0.10% < Y < 6.6%

[0045] With the parameter Y as expressed above having a value within the range of values indicated above guarantees, regardless of the wide range of dimensions in which the bearing 10 can be made, not only the necessary rigidity to completely eliminate the risk of plastic deformation as described above, but also to stabilize, for each bearing 10 and regardless of the absolute dimensions thereof, the increase in both the maximum rotational speed that can be reached by the bearing 10 itself and also the increase in the rigidity of the bearing 10.

[0046] For example, while keeping the area of the surface S2 constant, for example, if for a parameter value Y equal to the upper limit of the range defined above, i.e. 6.6%, it has been determined experimentally that the bearing 10 can already achieve high rotational speeds greater than those that can be reached with the standard bearings without any loss in performance or rigidity, a progressive reduction of the area of the surface SI until the lower limit of the parameter value Y is reached, i.e. 0.10%, entails a progressive reduction in the dimensions of the balls 41, and of the overall mass thereof, enabling even higher rotational speeds of the bearing 10 to be achieved. There are numerous other variants in addition to the embodiment of the invention described above. Furthermore, said embodiments are merely examples that limit neither the scope nor the application nor the possible arrangements of the invention. Indeed, although the above description enables a person skilled in the art to carry out the present invention according to at least one example embodiment thereof, many variants of the described components can also be used without thereby departing from the scope of the invention as defined in the attached claims, which should be understood literally and / or according to the legal equivalents thereof.

Claims

C L A I M S1. Deep-groove ball bearing (10), the bearing (10) having a main axis (A) of rotation and symmetry, and comprising:- an outer ring (20) provided with an inner raceway (21), - an inner ring (30) coaxial with the outer ring (20) and provided with an outer raceway (31), and- a row (40) of rolling bodies ( 1), a given number (N) of which are arranged inside the raceways (21) and (31) to enable the relative rotation of the outer ring (20) and of the inner ring (30), and have respective centres (42) of rotation arranged along a primitive circumference (44), the roller bearing (10) being characterized in that a parameter ratio (X) between a dimension of a diameter ( 44) of the primitive circumference (44) and the product of the number (N) of balls (41) and a dimension of a diameter (cp4i) of the balls (41) themselves falls within a range of values from 0.50 to 0.

60.

2. Roller bearing according to Claim 1, characterized in that a parameter ratio (Y) between a dimension of a surface (SI) of an area of a ball (41) in a plane transverse to the axis (A), and a dimension of a surface (S2) of a transverse area of the bearing (10) falls within a range of values from a minimum of 0. 10% to a maximum of 6.6%.

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