Optimized surface-mounted angular contact ball bearing

Abstract

A surface mounted angular contact ball bearing includes an inner ring having an axial end connectable with a first member and an outer surface including axially spaced first and second inner raceways. An outer ring is arranged about the inner ring and has an axial end connectable with a second member and an inner surface including a first outer raceway and a second outer raceway axially arranged between and facing the inner raceways. A first set of balls is disposed between the first inner raceway and the first outer raceway, and a second set of balls is disposed between the second inner raceway and the second outer raceway. The inner and outer rings and the two sets of balls are such that the contact angle of each set of balls is greater than 35 degrees, preferably between 40 degrees and 60 degrees. In addition, the number of balls per ball group provides a bearing fill percentage greater than 75%.

Description

Technical Field

[0001] The present invention relates to bearings, and more particularly to angular contact ball bearings. Background Art

[0002] Angular contact ball bearings are known and are configured to support axial and radial loads. The angular contact bearings include an inner ring, an outer ring disposed around the inner ring, and one or more rows or groups of balls disposed between the inner and outer rings. The raceways of the two rings and the relative radial dimensions of the rings are configured such that each ball contacts the raceway at an angle ( / obliquely) with respect to the vertical plane. Thus, the angular contact bearings can support and transmit axial loads between the inner and outer rings and thereby between two members coupled by the bearing. Typically, the inner ring is disposed around an internal member (such as a shaft or axle), and the outer ring is disposed within the cylindrical surface of an external member, which can be a hub, a housing, etc. Summary of the Invention

[0003] In one aspect, the present invention is a face-mounted angular contact ball bearing for rotatably coupling a first member and a second member. The ball bearing includes an inner ring having a centerline, opposite first and second axial ends, an inner circumferential surface, and an outer circumferential surface. One of the first and second axial ends is capable of being connected to the first member. The outer circumferential surface includes a first inner raceway and a second inner raceway. The second inner raceway is axially spaced from the first inner raceway and faces the first inner raceway. An outer ring is disposed around the inner ring and has opposite first and second axial ends, an outer circumferential surface, and an inner circumferential surface. One of the first and second axial ends is capable of being connected to the second member. The inner circumferential surface includes a first outer raceway and a second outer raceway. The first outer raceway and the second outer raceway are axially disposed between the first inner raceway and the second inner raceway such that the first outer raceway faces the first inner raceway and the second outer raceway faces the second inner raceway. A first set of balls is disposed between the first inner raceway and the first outer raceway, and a second set of balls is disposed between the second inner raceway and the second outer raceway. Each ball in the first and second sets of balls has a ball diameter. Further, the inner ring, the outer ring, the first set of balls, and the second set of balls are each configured and dimensioned such that each ball in the first set of balls has a first contact angle with the first inner raceway and the first outer raceway having a value greater than 35 degrees, and each ball in the second set of balls has a second contact angle with the second inner raceway and the second outer raceway having a value greater than 35 degrees. Further, the number of balls in each of the first and second sets of balls provides a bearing fill percentage greater than 75%.

[0004] Preferably, the value of each contact angle is between 40% and 60%, and the fill percentage is greater than 80%. Further, each of the inner ring and the outer ring preferably has one or more annular shoulders that provide at least a major portion of a separate one of the first inner raceway and the second inner raceway. Each shoulder has a radial height relative to the remainder of the outer circumferential surface or the inner circumferential surface, and the value of the radial height is at least 40% of the ball diameter. Description of the Drawings

[0005] The foregoing invention content and the detailed description of the preferred embodiments of the present invention will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the present invention, the currently preferred illustrative embodiments are shown in the drawings. However, it should be understood that the present invention is not limited to the exact configurations and means shown. In the drawings:

[0006] Figure 1 is a sectional axial view of the upper part of a bearing assembly shown as rotatably coupling a first member and a second member according to the present invention;

[0007] Figure 2 is a side plan view of the bearing assembly;

[0008] Figure 3 is a sectional axial view of the bearing assembly;

[0009] Figure 4 is an enlarged sectional axial view of the bearing assembly showing the raceways and the contact angle;

[0010] Figure 5 is a sectional axial view of the upper part of the inner ring of the bearing assembly;

[0011] Figure 6 is Figure 5 an enlarged view of a part of showing details of the inner raceway;

[0012] Figure 7 is a sectional axial view of the upper part of the outer ring of the bearing assembly;

[0013] Figure 8 is Figure 7 an enlarged view of a part of showing details of the outer raceway;

[0014] Figure 9 is a sectional axial view of the bearing assembly showing a one-piece outer ring; and

[0015] Figure 10 is another axial sectional view of the upper part of a bearing shown as rotatably coupling a first member and a second member through an intermediate member. Detailed Description

[0016] In the following description, the use of certain terms is for convenience only and is not limiting. The words "lower", "upper", "upward", "below", and "downward" denote directions in the accompanying drawings to which reference is made. The words "inner", "inward", and "outer", "outward" respectively refer to directions toward and away from the designated centerline or geometric center of the described element, and the specific meanings are readily understood from the context of the description. Further, as used herein, the words "connect" and "couple" each are intended to include both direct connection between two members without any other member intervening therebetween and indirect connection with one or more other members intervening between the members. The terms include the specifically mentioned words above, their derivatives, and words having similar meanings.

[0017] Reference is now made in detail to the drawings, in which the same numbers are always used to indicate the same elements, and in Figures 1 to 10 is shown a face-mounted angular contact ball bearing assembly 10 for rotatably coupling a first member 1 and a second member 2 such that at least one of the members 1, 2 rotates about a central axis A C rotation. The first member 1 and the second member 2 are preferably separate components of a joint of a robot, such as the shoulder and arm of a joint of a robot manipulator for the semiconductor manufacturing industry, but may be components of any other suitable mechanical assembly that is desired to rotatably couple two members 1, 2 with maximum load capacity and stiffness. In any case, the angular contact ball bearing assembly generally includes an inner ring 12, an outer ring 14 disposed around the inner ring 12, a first set 16 of balls 17, and a second set 18 of balls 17, each ball set 16, 18 being rollably disposed between the inner ring 12 and the outer ring 14. Due to the configuration of the raceways, the construction and dimensions of the inner ring 12 and the outer ring 14, and the diameter BD of the balls 17 ( Figure 4 ), the face-mounted angular contact bearing assembly 10 has significantly greater stiffness and the ability to support axial and moment loads as compared to previously known bearings for such applications, as described in detail below.

[0018] Referring first to Figure 1 and Figures 4 to 6 , the inner ring 12 has a centerline L C coaxial with the central axis A C , opposite first and second axial ends 12a and 12b, an inner circumferential surface 13A defining a central hole 11, opposite outer circumferential surfaces 13B, and a radial thickness TR MIN between the minimum outer diameter OD I of the outer surface 13B and the inner surface 13A Figure 5)。One of the first axial end 12a and the second axial end 12b of the inner ring 12 can be mounted to or connected with the first member 1 such that the inner ring 12 is "surface-mounted" to the first member 1, and one end 12a or 12b abuts directly against the first member 1 or against an intermediate member 3 (e.g., spacer) located between the inner ring 12 and the first member 1; Figure 10 ) arranged. Preferably, the inner ring 12 has a plurality of mounting holes 21 which axially extend from one of the first axial end 12a and the second axial end 12b and are circumferentially spaced apart around the center line L C . Each mounting hole 21 is configured to receive a fastener with a clearance or to be threadedly engaged by a fastener 5 ( Figure 1 ) to directly connect the inner ring 12 with the first member 1 or to connect the inner ring 12 with the first member 1 through the intermediate member 3 (as Figure 10 shown).

[0019] In addition, the outer circumferential surface 13B includes a first inner raceway 20 and a second inner raceway 22. The second inner raceway 22 is axially spaced apart from and faces the first inner raceway 20. Preferably, each of the first inner raceway 20 and the second inner raceway 22 has a radius R RI ( Figure 6 ), and the value of the radius R RI is no more than three percent greater than half of the value of the ball diameter BD, as will be discussed below. More specifically, the inner ring 12 includes two annular shoulders 24 which radially extend outwardly from the remainder of the outer circumferential surface 13B of the inner ring 12 and are axially spaced apart. Each annular shoulder 24 provides at least a majority, i.e., at least 75% and preferably more than 90% of the total raceway surface area, of a separate one of the first inner raceway 20 and the second inner raceway 22, and each annular shoulder 24 has a radial height RH I relative to the remainder of the outer circumferential surface 13B. The dimensions of the two shoulders 24 are designed such that the value of the radial height RH I is at least 40% of the ball diameter BD and preferably about 48% of the ball diameter BD so that the bearing assembly 10 can form a relatively large contact angle, as will be discussed below.

[0020] In addition, the inner ring 12 is preferably a two-part ring including a first ring portion 26 and a second ring portion 28, and the two ring portions 26, 28 abut axially. Specifically, the first ring portion 26 provides the first inner raceway 20 and has an outer axial end 26a that provides the first axial end 12a of the inner ring and an opposite inner axial end 26b, and the second ring portion 28 provides the second inner raceway 22 and has an outer axial end 28a that provides the second axial end 12b of the inner ring and an inner axial end 28b that is arranged to abut against the inner axial end 26b of the first ring portion 26.

[0021] Now referring to Figure 1 、 Figure 4 、 Figure 7 and Figure 8 , the outer ring 14 has opposite first and second axial ends 14a, 14b, an outer circumferential surface 15A, opposite inner circumferential surfaces 15B, and a maximum inner diameter ID MAX of the inner surface 15B and a radial thickness TR O ( Figure 7 ). One of the first axial end 14a or the second axial end 14b may be connected to the second member 2 for face mounting, as discussed with respect to the inner ring 12, and one of the first axial end 14a or the second axial end 14b is arranged to directly abut against the radial surface 2a of the second member 2 or against an intermediate member 4 ( Figure 10 ) arranged between the outer ring 14 and the second member 2. Preferably, a plurality of mounting holes 31 extend axially from one of the first axial end 14a and the second axial end 14b and are circumferentially spaced about a centerline L C , and each mounting hole 31 is configured to receive a fastener (not shown) with clearance or to be threadedly engaged by a fastener to directly connect the outer ring 14 to the second member 2 or to connect the outer ring 14 to the second member 2 through the intermediate member 4.

[0022] In addition, the inner circumferential surface 15B of the outer ring 14 includes a first outer raceway 30 and a second outer raceway 32, and the first outer raceway 30 and the second outer raceway 32 are axially arranged between the first inner raceway 20 and the second inner raceway 22. Specifically, the two outer raceways 30, 32 are configured such that the first outer raceway 30 faces the first inner raceway 20 and the first axial end 14a of the outer ring, and the second outer raceway 32 faces the second inner raceway 22 and the second axial end 14b of the outer ring. Thus, the four raceways 20, 22, 30, 32 are configured in a "back-to-back" configuration, with a contact angle as described below outside the bearing assembly 10 with respect to the rotational axis A RIntersect, as discussed in further detail below. Preferably, as with the inner ring 12, each of the first outer raceway 30 and the second outer raceway 32 is preferably formed with a radius R RO ( Figure 8 ) The radius R RO is not more than three percent greater than half the value of the ball diameter BD, as also discussed below.

[0023] Referring to Figure 7 and Figure 8 , the outer ring 14 preferably includes two adjacent annular shoulders 34 that extend radially inwardly from the inner circumferential surface 15B of the outer ring 14 towards the remainder thereof. Each annular shoulder 34 provides at least a majority, i.e., at least 75% and preferably greater than 90% of the total raceway surface area, of a separate one of the first outer raceway 30 and the second outer raceway 32, and each annular shoulder 34 has a radial height RH O . Further, when the outer ring 14 is formed as two ring portions 36, 38, the outer ring 14 has two adjacent shoulders 34, as depicted in Figure 4 , Figure 7 and Figure 8 .

[0024] Specifically referring to Figure 9 , as an alternative, the outer ring 14 may be formed as a single ring having a single annular shoulder 40 that extends radially inwardly from the central portion of the inner circumferential surface 15B, and the single annular shoulder 40 provides at least a majority of both the first outer raceway 32 and the second outer raceway 34 on opposite axial sides 40a, 40b of the shoulder 40. The single shoulder 40 has a radial height RH O with respect to the remainder of the inner circumferential surface 15B. In either case, the radial height RH O of each of the two shoulders 34 of the outer ring 14 or the single shoulder 40 is at least 40% of the ball diameter BD and preferably greater than 48% of the ball diameter BD to allow for the formation of a relatively large contact angle, as discussed below.

[0025] Further, the balls 17 of the first set 16 are disposed between the first inner raceway 20 and the first outer raceway 30, and the balls 17 of the second set 18 are disposed between the second inner raceway 22 and the second outer raceway 32, and the balls 17 of the two sets 16, 18 are circumferentially spaced about the centerline L C of the inner ring 12. Each ball 17 in the two ball sets 16, 18 preferably has the same ball diameter BD, but in some applications, the balls 17 in one of the sets 16, 18 may have a diameter BD that is larger or smaller than the balls 17 in the other ball set 18, 16.

[0026] Specifically referring toFigure 3 , the bearing assembly 10 preferably further includes a first annular cage 50 and a second annular cage 52. The first annular cage 50 and the second annular cage 52 are each disposed between the inner ring 12 and the outer ring 14 and have a plurality of cells 54 spaced circumferentially about the centerline L C The individual balls 17 of the first group 16 are received in the respective cells 54 of the first cage 50, and the individual balls 17 of the second group 18 are received in the respective cells 54 of the second cage 52. In addition, each cage 50, 52 is angled such that each cage 50, 52 has an outer axial end disposed between the inner surface 15B of the outer ring 14 and one shoulder 24 of the inner ring 12 and an inner axial end disposed between the outer surface 13B of the inner ring 12 and either one shoulder 34 of the outer ring 14 or a single central shoulder 40 of the outer ring 14.

[0027] With the basic structure as described above, each of the inner ring 12, the outer ring 14, and the balls 17 of the two sets 16, 18 is formed and dimensioned such that each ball 17 of the first set 16 has a first contact angle CA C between the contact points P 1 ( Figure 4 ) having a value greater than 35 degrees, and each ball 17 of the second set 18 has a second contact angle CA C between the contact points P 2 ( Figure 4 ) having a value greater than 35 degrees. Specifically, for a given ball diameter BD of the balls 17, each contact angle CA 1 , CA 2 is established by the relative radial dimensioning between the inner ring 12 and the outer ring 14, which establishes the amount of radial clearance, the relatively large radial height RH I of the annular shoulder 24 and the relatively large radial height RH O of the annular shoulder 34 or 40 and the axial spacing between the raceways 20, 22 and 30, 32. Preferably, each of the inner ring 12 and the outer ring 14 is dimensioned radially and formed with a shoulder height RH I , RH O of a specific value, as well as a ball diameter BD and a raceway radius R RI , R RO of a specific value, such that each contact angle CA 1 , CA 2 is between 40 degrees and 60 degrees.

[0028] In addition, a specific number of balls 17 in each of the first set 16 of balls 17 and the second set 18 of balls 17 is selected or designated to provide a bearing fill percentage greater than 75% and preferably greater than 80%. As is well known, the fill percentage (or packing percentage) of a bearing is the percentage of the circumference of the pitch circle of the bearing occupied by all the balls of the ball set, the pitch circle being a theoretical circle passing through the centers of all the balls of the ball set, and each ball traveling around this pitch circle during bearing rotation. In addition, each of the inner ring 12 and the outer ring 14 is specifically dimensioned radially such that each radial thickness RT I 、RT O has a value that is at least two times greater than the value of the ball diameter BD, and preferably, each radial thickness RT I 、RT O has a value that is at least three times greater than the value of the ball diameter.

[0029] Utilizing the relatively large contact angles CA 1 、CA 2 of the rings 12, 14, a relatively large bearing fill percentage, and the combination of relatively large radial thicknesses RT1, RT2, the face-mounted angular contact bearing 10 has significant stiffness and the ability to handle increased axial and moment loads. More specifically, the relatively high contact angles CA 1 、CA 2 substantially increase the stiffness of the bearing assembly 10 under relatively heavy axial and moment loads. The high fill percentage of the two sets 16, 18 of balls 17 also increases the stiffness of the bearing assembly 10 and reduces the contact stress on each ball 17, thereby obtaining a longer life for the balls 17 and thus also a longer life for the bearing assembly 10. In addition, the shoulders 24 and 34 or 40 having a relatively large radial height provide a relatively large contact surface area for the balls 17 in the direction of the axial thrust load, which increases the moment stiffness and reduces the contact stress caused by the axial thrust load.

[0030] Representative non-limiting examples of the present invention have been described in detail above with reference to the accompanying drawings. This detailed description is only intended to teach those skilled in the art further details of the preferred aspects for practicing this teaching, and is not intended to limit the scope of the present invention.

[0031] In addition, the combinations of features and steps disclosed in the above detailed description may not be necessary for practicing the present invention in the broadest sense, but merely teach representative examples for specifically describing the present invention. Further, the above representative examples and the various features of the appended individual independent claims and dependent claims may be combined in ways not specifically and explicitly enumerated to provide additional useful embodiments of this teaching.

[0032] For the purposes of the original written disclosure and for the purposes of limiting the claimed subject matter, all features disclosed in the specification and / or claims are intended to be disclosed separately and independently of each other, without reliance on combinations of features in the embodiments and / or claims. Further, for the purposes of the original written disclosure and for the purposes of limiting the claimed subject matter, all value ranges or indications of entity groups are intended to disclose each possible intermediate value or intermediate entity. The present invention is not limited to the above embodiments and may vary within the scope of the appended claims.

Claims

1. A surface-mounted angular contact ball bearing assembly for rotatably coupling a first member and a second member, the ball bearing assembly comprising: an inner ring having a centerline, opposing first and second axial ends, an inner circumferential surface and an outer circumferential surface, one of the first and second axial ends being connectable to the first member, the outer circumferential surface including a first inner raceway and a second inner raceway, the second inner raceway being axially spaced from and facing the first inner raceway; an outer ring arranged around the inner ring and having opposite first and second axial ends, an outer circumferential surface and an inner circumferential surface, one of the first and second axial ends being connectable to the second member, the inner circumferential surface comprising a first outer raceway and a second outer raceway, the first outer raceway and the second outer raceway being axially arranged between the first and second inner raceways so that the first outer raceway faces the first inner raceway and the second outer raceway faces the second inner raceway; as well as a first set of balls disposed between the first inner raceway and the first outer raceway and a second set of balls disposed between the second inner raceway and the second outer raceway, each ball in the first set of balls and the second set of balls having a ball diameter; wherein the inner race, the outer race, the first group of balls, and the second group of balls are each configured and dimensioned such that a first contact angle between each ball in the first group of balls and the first inner raceway and the first outer raceway has a value greater than 35 degrees, and a second contact angle between each ball in the second group of balls and the second inner raceway and the second outer raceway has a value greater than 35 degrees; and wherein the number of balls in each of the first set of balls and the second set of balls provides a bearing fill percentage greater than 75%.

2. The ball bearing assembly according to claim 1, characterized in that: the inner ring including two annular shoulders extending radially outwardly from a remainder of the outer circumferential surface of the inner ring and spaced axially apart, each annular shoulder providing at least a majority of a single one of the first inner raceway and the second inner raceway and having a radial height relative to the remainder of the outer circumferential surface, the radial height being at least 40% of the ball diameter; and The outer ring includes two adjacent annular shoulders extending radially inward from the remainder of the inner circumferential surface of the outer ring, each annular shoulder providing at least a majority of a single one of the first outer raceway and the second outer raceway and having a radial height relative to the remainder of the inner circumferential surface, or the outer ring includes a single annular shoulder extending radially inward from the central portion of the inner circumferential surface, providing at least a majority of both the first outer raceway and the second outer raceway and having a radial height relative to the remainder of the inner circumferential surface, the radial height of each of the two shoulders of the outer ring or the single shoulder being at least 40% of the ball diameter.

3. The ball bearing assembly according to claim 2, characterized in that The value of each radial height is greater than 48% of the value of the ball diameter.

4. The ball bearing assembly according to claim 1, characterized in that The value of each contact angle is between 40 degrees and 60 degrees.

5. The ball bearing assembly according to claim 1, characterized in that The number of balls in each of the first set of balls and the second set of balls provides a bearing fill percentage greater than 80%.

6. The ball bearing assembly according to claim 1, characterized in that The inner ring includes a first ring portion and a second ring portion, wherein the first ring portion provides the first inner raceway and has an outer axial end portion providing a first axial end of the inner ring and an opposite inner axial end portion, and the second ring portion provides the second inner raceway and has an outer axial end portion providing a second axial end of the inner ring and an inner axial end portion arranged against the inner axial end portion of the first ring portion.

7. The ball bearing assembly according to claim 1, characterized in that The inner ring has a radial thickness between a minimum outer diameter of an outer circumferential surface of the inner ring and an inner circumferential surface of the inner ring, the outer ring has a radial thickness between a maximum inner diameter of an inner circumferential surface of the outer ring and an outer circumferential surface of the outer ring, and the value of each radial thickness is at least twice the value of the ball diameter.

8. The ball bearing assembly according to claim 1, characterized in that Each of the inner race and the outer race has a plurality of mounting holes extending axially from one of the first axial end and the second axial end and spaced circumferentially about the centerline, each mounting hole being configured to receive a fastener with clearance or to be threadedly engaged by a fastener so as to connect the inner race with the first member and the outer member with the second member.

9. The ball bearing assembly according to claim 1, characterized in that Each of the first inner raceway and the second inner raceway and each of the first outer raceway and the second outer raceway has a radius, each raceway radius having a value no greater than three percent greater than half the value of the ball diameter.

10. The ball bearing assembly according to claim 1, characterized in that: When the inner ring is connected to the first member, one of the first axial end and the second axial end of the inner ring can be arranged against the first member or against an intermediate member arranged between the inner ring and the first member; and When the outer ring is connected to the second member, one of the first axial end and the second axial end of the outer ring can be arranged against the second member or against an intermediate member arranged between the outer ring and the second member.

11. An angular contact ball bearing assembly for rotatably coupling a first member and a second member, the ball bearing assembly comprising: an inner ring having a centerline, opposing first and second axial ends, an inner circumferential surface and an outer circumferential surface, one of the first and second axial ends being connectable to the first member, the outer circumferential surface including a first inner raceway and a second inner raceway, the second inner raceway being axially spaced from and facing the first inner raceway; an outer ring arranged around the inner ring and having opposite first and second axial ends, an outer circumferential surface and an inner circumferential surface, one of the first and second axial ends being connectable to the second member, the inner circumferential surface comprising a first outer raceway and a second outer raceway, the first outer raceway and the second outer raceway being axially arranged between the first and second inner raceways so that the first outer raceway faces the first inner raceway and the second outer raceway faces the second inner raceway; as well as a first set of balls disposed between the first inner raceway and the first outer raceway and a second set of balls disposed between the second inner raceway and the second outer raceway, each ball in the first set of balls and the second set of balls having a ball diameter; wherein the inner race, the outer race, the first set of balls, and the second set of balls are each formed and dimensioned such that a first contact angle between each ball in the first set of balls and the first inner raceway and the first outer raceway has a value greater than 35 degrees, and a second contact angle between each ball in the second set of balls and the second inner raceway and the second outer raceway has a value greater than 35 degrees; and wherein the inner ring comprises two annular shoulders extending radially outward from the remainder of the outer circumferential surface of the inner ring and spaced apart in the axial direction, each annular shoulder providing at least a majority of a single one of the first inner raceway and the second inner raceway and having a radial height relative to the remainder of the outer circumferential surface, the outer ring comprises two adjacent annular shoulders extending radially inward from the remainder of the inner circumferential surface of the outer ring, each annular shoulder providing at least a majority of a single one of the first outer raceway and the second outer raceway and having a radial height relative to the remainder of the inner circumferential surface, or the outer ring comprises a single annular shoulder extending radially inward from the center portion of the inner circumferential surface, providing both the first outer raceway and the second outer raceway and having a radial height relative to the remainder of the inner circumferential surface, each radial height having a value of at least 40% of the ball diameter.

12. An angular contact ball bearing assembly for rotatably coupling a first member and a second member, the ball bearing assembly comprising: an inner ring having a centerline, opposing first and second axial ends, an inner circumferential surface and an outer circumferential surface, one of the first and second axial ends being connectable to the first member, the outer circumferential surface including a first inner raceway and a second inner raceway, the second inner raceway being axially spaced from and facing the first inner raceway; an outer ring arranged around the inner ring and having opposite first and second axial ends, an outer circumferential surface and an inner circumferential surface, one of the first and second axial ends being connectable to the second member, the inner circumferential surface comprising a first outer raceway and a second outer raceway, the first outer raceway and the second outer raceway being axially arranged between the first and second inner raceways so that the first outer raceway faces the first inner raceway and the second outer raceway faces the second inner raceway; as well as a first set of balls disposed between the first inner raceway and the first outer raceway and a second set of balls disposed between the second inner raceway and the second outer raceway, each ball in the first set of balls and the second set of balls having a ball diameter; wherein the inner race, the outer race, the first set of balls, and the second set of balls are each formed and dimensioned such that a first contact angle between each ball in the first set of balls and the first inner raceway and the first outer raceway has a value greater than 35 degrees, and a second contact angle between each ball in the second set of balls and the second inner raceway and the second outer raceway has a value greater than 35 degrees; and Wherein, the inner ring has a radial thickness between the minimum outer diameter of the outer circumferential surface of the inner ring and the inner circumferential surface of the inner ring, the outer ring has a radial thickness between the maximum inner diameter of the inner circumferential surface of the outer ring and the outer circumferential surface of the outer ring, and the value of each radial thickness is at least twice the value of the ball diameter.

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