Optimized end-mounted angular contact ball bearing

Abstract

A face-mounted angular contact ball bearing comprises an inner ring having an axial end connectable to a first member and an outer surface defining axially spaced first and second inner raceways. An outer ring is disposed around the inner ring and has an axial end connectable to a second member and an inner surface defining first and second outer raceways axially disposed between and facing the inner raceways. A first set of balls is disposed between the first inner and outer raceways, and a second set of balls is disposed between the second inner and outer raceways. The inner and outer rings and the two sets of balls are formed such that the contact angles of each set of balls are greater than 35 degrees, preferably between 40 and 60 degrees.In addition, the number of balls in each ball set results in a bearing fill percentage of greater than seventy-five percent.

Description

BACKGROUND OF THE INVENTIONThe present invention relates to bearings and more particularly to angular ball bearings.Angular contact ball bearings are known and are designed to support both axial and radial loads. A angular contact ball bearing includes an inner ring, an outer ring disposed about the inner ring, and one or more rows or sets of balls disposed between the inner and outer rings. The raceways of the two rings, as well as the relative radial size of the rings, are formed such that each ball contacts the raceways at an angle with respect to a vertical plane. Thus, the angular contact ball bearing is capable of supporting and transferring axial loads between the inner and outer rings and thereby between two elements coupled by the bearing. Typically, the inner ring is disposed about an inner member, such as a shaft or axle, and the outer ring is disposed within a cylindrical surface of an outer member, which may be a hub, a housing, etc.SUMMARY OF THE INVENTIONIn one aspect, the present invention is an end-mounted angular contact ball bearing assembly for rotatably coupling a first member and a second member. The ball bearing assembly includes an inner ring having a centerline, opposing first and second axial ends, one of the first and second axial ends being connectable to the first member, an inner circumferential surface and an outer circumferential surface having a first inner raceway and a second inner raceway axially spaced from and facing the first inner raceway. An outer ring is disposed about the inner ring and has opposing first and second axial ends, one of the first and second axial ends being connectable to the second member, an outer circumferential surface, and an inner circumferential surface having a first outer raceway and a second outer raceway. The first and second outer raceways are axially disposed between the first and second inner raceways 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 race and the first outer race, and a second set of balls is disposed between the second inner race and the second outer race, each ball of the first and second sets of balls having 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 sized such that a first contact angle between each ball of the first set of balls and the first inner and outer raceways has a value greater than thirty-five degrees and a second contact angle between each ball of the second set of balls and the second inner and outer raceways has a value greater than thirty-five degrees. In addition, a number of the balls of each of the first and second sets of balls yields a bearing fill percentage greater than seventy-five percent.Preferably, each contact angle has a value between forty and sixty percent and the fill percentage is greater than eighty percent. Also, each of the inner and outer rings preferably has one or more annular shoulders providing at least a majority of a separate one of the first and second inner raceways, each shoulder having a radial height with respect to the remainder of the outer or inner circumferential surface, and the radial height having a value of at least forty percent of the ball diameter.BRIEF DESCRIPTION OF THE VARIOUS VIEWS OF THE DRAWINGSThe foregoing summary, as well as the detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the accompanying drawings. For purposes of illustrating the invention, the drawings, which are schematic, show embodiments that are presently preferred. It is to be understood, however, that the present invention is not limited to the arrangements and means in exactly the form shown herein. In the drawings:FIG. 1 is a broken-away axial cross-sectional view of an upper portion of a bearing assembly according to the present invention, showing how first and second members are rotatably coupled together;FIG. 2 is a side view of the bearing assembly;FIG. 3 is a broken-away axial cross-sectional view of the bearing assembly;FIG. 4 is an enlarged broken-away axial cross-sectional view of the bearing assembly showing the raceways and contact angles;FIG. 5 is a broken-away axial cross-sectional view of an upper portion of an inner ring of the bearing assembly;FIG. 6 is an enlarged view of a portion of FIG. 5 showing the details of the inner raceways;FIG. 7 is a broken-away axial cross-sectional view of an upper portion of an outer ring of the bearing assembly;FIG. 8 is an enlarged view of a portion of FIG. 7 showing the details of the outer raceways;FIG. 9 is a broken-away axial cross-sectional view of the bearing assembly shown with a one-piece outer ring; andFIG. 10 is another axial cross-sectional view of an upper portion of a bearing showing how first and second members are rotatably coupled together by intermediate members.DETAILED DESCRIPTION OF THE INVENTIONIn the following description, for convenience only, certain terminology will be used, which is not limiting. The words "lower", "upper", "upward", "downward", and "downward" denote directions in the drawings to which reference is made. The words "inner", "inward" and "outer", "outward" refer to directions leading to or from a designated center line or a geometric center of a described element, wherein the concrete meaning is easily recognizable from the context of the description. Furthermore, as used herein, the words "connected" and "coupled" are intended to include direct connections between two elements without other elements therebetween, as well as indirect connections between elements with one or more other elements therebetween. The terminology includes the words expressly mentioned above, their derivatives, and words of similar import.Reference will now be made in detail to the drawings, wherein like reference numerals are used to designate like elements throughout. In Figs. 1-10, an end-mounted angular contact ball bearing assembly 10 is shown for rotatably coupling a first member 1 and a second member 2 such that at least one member 1, 2 rotates about a central axis AC. The first and second elements 1, 2 are preferably separate components of a joint of a robot machine, such as a shoulder and an arm of a joint of a handling robot used in the semiconductor manufacturing industry. However, it is also possible to use components of any other suitable mechanical arrangement in which it is desired to rotatably couple two elements 1, 2 having maximum load-bearing capacity and rigidity. In any event, the angular contact ball bearing assembly basically includes an inner ring 12, an outer ring 14 disposed about the inner ring 12, a first set 16 of balls 17, and a second set 18 of balls 17, each ball set 16, 18 rollingly disposed between the inner and outer rings 12, 14. Due to the arrangement of the raceways and the arrangement and dimensioning of the inner and outer rings 12, 14 and the diameter BD (FIG. 4 ) of the balls 17, the end-mounted angular bearing assembly 10 has a substantially higher stiffness and ability to support axial and torque loads compared to previously known bearings used for such applications, as will be described in detail below.First, refer to Figs. 1 and 4-6. The inner ring 12 has a center line LC coaxial with the center axis AC, opposing first and second axial ends 12 a, 12 b, an inner circumferential surface 13A defining a center bore 11, an opposing outer circumferential surface 13B, and a radial thickness TRI (FIG. 5 ) between a minimum outer diameter ODMINof the outer surface 13B and the inner surface 13A. One of the first and second axial ends 12 a, 12 bof the inner ring 12 is mountable to or connectable to the first element 1 such that the inner ring 12 is "mounted" "face-on" to the first element 1 and the one end 12 aor 12 bis arranged either directly against the first element 1 or against an intermediate element 3 (e.g. a spacer; FIG. 10 ) located between the inner ring 12 and the first element 1. Preferably, the inner ring 12 comprises a plurality of mounting holes 21 extending axially from one of the first and second axial ends 12 a, 12 band spaced circumferentially about the centerline LC, each mounting hole 21 being configured to accommodate a fastener with play or to be threadably engaged by a fastener 5 (FIG. 1 ) to connect the inner ring 12 to the first member 1, either directly or through the intermediate member 3, as shown in FIG. 10.Further, the outer peripheral surface 13B includes a first inner raceway 20 and a second inner raceway 22 axially spaced from and facing the first inner raceway 20. Preferably, for reasons discussed below, each of the first and second inner races 20, 22 has a radius RRI (FIG. 6 ) with a value no greater than three percent greater than half the value of the ball diameter BD. More specifically, the inner ring 12 has two annular shoulders 24 that extend radially outward from a remainder of the outer circumferential surface 13B of the inner ring 12 and are axially spaced apart from each other. Each annular shoulder 24 provides at least a majority of a separate one of the first and second inner raceways 20, 22, i.e., at least seventy-five percent, and preferably more than ninety percent of the total raceway surface, and has a radial height RHIwith respect to the remainder of the outer circumferential surface 13B. The two shoulders 24 are sized such that the radial height RHIhas a value of at least forty percent of the ball diameter BD, and preferably about forty-eight percent of the ball diameter BD, to allow the bearing assembly 10 to be formed with a substantially large contact angle, as will be discussed further below.Furthermore, the inner ring 12 is preferably a two-part ring, which has a first ring part 26 and a second ring part 28, wherein the two ring parts 26, 28 abut one another axially. More specifically, the first ring portion 26 forms the first inner raceway 20 and has an outer axial end 26a forming the first inner ring axial end 12a and an opposite inner axial end 26b, and the second ring portion 28 forms the second inner raceway 22 and has an outer axial end 28a forming the second inner ring axial end 12b and an inner axial end 28b disposed against the inner axial end 26b of the first ring portion 26.Now, refer to Figs. 1, 4, 7 and 8. The outer ring 14 has opposing first and second axial ends 14 a, 14 b, an outer circumferential surface 15A, an opposing inner circumferential surface 15B, and a radial thickness TRO (FIG. 7 ) between a maximum inner diameter IDMAXof the inner surface 15B and the outer surface 15A. One of the first and second axial ends 14 aor 14 bis connectable to the second member 2 so as to be frontally mounted to the inner ring 12, as discussed, and is disposed either directly against a radial surface 2 aof the second member 2 or against an intermediate member 4 (FIG. 10 ) located between the outer ring 14 and the second member 2. Preferably, a plurality of mounting holes 31 extend axially from one of the first and second axial ends 14a, 14b and are circumferentially spaced about the centerline LC, each mounting hole 31 being configured to clearance receive a fastener (neither shown) or to be threadably engaged by a fastener to connect the outer ring 14 to the second member 2 either directly or through the intermediate member 4.Further, the inner circumferential surface 15B of the outer ring 14 includes a first outer raceway 30 and a second outer raceway 32, the first and second outer raceways 30, 32 being axially interposed between the first and second inner raceways 20, 22. More specifically, the two outer raceways 30, 32 are arranged such that the first outer raceway 30 faces the first inner raceway 20 and the first outer ring axial end 14 aand the second outer raceway 32 faces the second inner raceway 22 and the second outer ring axial end 14 b. Thus, the four raceways 20, 22, 30, 32 are arranged in a "back-to-back" arrangement in which the contact angles, as will be described below, intersect the axis of rotation AR external to the bearing assembly 10, as will be discussed in more detail below. Preferably, as with the inner ring 12, each of the first and second outer raceways 30, 32 is preferably formed with a radius RRO (FIG. 8 ) that is no more than three percent greater than half the value of the ball diameter BD, as will also be discussed below.Referring to FIGS. 7 and 8, the outer ring 14 preferably includes two adjacent annular shoulders 34 that extend radially inward from a remainder of the inner circumferential surface 15B of the outer ring 14. Each annular shoulder 34 provides at least a majority of a separate one of the first and second outer raceways 30, 32, i.e., at least seventy-five percent, and preferably more than ninety percent of the total raceway surface, and has a radial height RHOwith respect to the remainder of the inner circumferential surface 15B. Furthermore, the outer ring 14 has the two adjacent shoulders 34 when the outer ring 14 is formed as two ring parts 36, 38, as illustrated in FIGS. 4, 7 and 8.With particular reference to FIG. 9, the outer ring 14 may alternatively be formed as a single ring having a single annular shoulder 40 extending radially inward from a central portion of the inner circumferential surface 15B and providing at least a majority of the first and second outer raceways 32, 34 on opposite axial sides 40 a, 40 bof the shoulder 40. The single shoulder 40 has a radial height RHOwith respect to the rest of the inner circumferential surface 15B. In either case, the radial height RHOof each of the two shoulders 34 or the single shoulder 40 of the outer ring 14 has a value of at least forty percent of the ball diameter BD, and preferably greater than forty-eight percent of the ball diameter BD, to allow for the formation of a relatively large contact angle, as discussed below.Further, the first set 16 of balls 17 is disposed between the first inner raceway 30 and the first outer raceway 40, and the second set 18 of balls 17 is disposed between the second inner raceway 32 and the second outer raceway 34, and the two sets 16, 18 of balls 17 are circumferentially spaced apart from each other about the center line LC of the inner ring 12. Each ball 17 of the two ball sets 16, 18 preferably has a ball diameter BD of the same value, but in some applications the balls 17 of one set 16, 18 may also have a larger or smaller diameter BD than the balls 17 of the other ball set 18, 16.With particular reference to FIG. 3, the bearing assembly 10 preferably further includes first and second annular cages 50, 52 each disposed between the inner and outer rings 12, 14 and having a plurality of pockets 54 circumferentially spaced about the centerline LC. Each pocket 54 of the first cage 50 includes a separate one of the balls 17 of the first set 16 of balls 17, and each pocket 54 of the second cage 52 includes a separate one of the balls 17 of the second set 18 of balls 17. furthermore, 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 a 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 a shoulder 34 of the outer ring 14 or the single central shoulder 40 of the outer ring 14.In the basic structure described above, the inner ring 12, the outer ring 14, and each ball 17 of the two sets of balls 16, 18 are each formed and sized such that a first contact angle CA 1 (FIG. 4 ) between a contact point PC of each ball 17 of the first set 16 of balls 17 on the first inner and outer raceways 20, 30 has a value greater than thirty-five degrees and a second contact angle CA 2 (FIG. 4 ) between a contact point PC of each ball 17 of the second set 18 of balls 17 on the second inner and outer raceways 22, 32 has a value greater than thirty-five degrees. More specifically, each contact angle CA1, CA2 is determined by the relative radial dimension between the inner ring 12 and the outer ring 14 for a given diameter BD of the balls 17 defining an amount of radial play, and the relatively large radial height RHI, RHO of the annular shoulders 24, 34 and 40, respectively, and the axial distance between the raceways 20, 22 and 30, 32. Preferably, each of the inner and outer rings 12, 14 is radially sized and formed with specific values of the shoulder heights RHI, RHO, as well as the specific values of the ball diameter BD and the raceway radii RRI, RRO such that each contact angle CA1, CA2is between forty degrees and sixty degrees.Further, a particular number of the balls 17 of each of the first and second sets 16, 18 of balls 17 is selected or specified to provide a bearing fill percentage of greater than seventy-five percent, and preferably greater than eighty percent. As is known, the percentage of filling of a bearing is the percentage of the circumference of the pitch circle of the bearing occupied by all balls of a ball set, the pitch circle being a theoretical circle through the center of all balls of the ball set about which each ball moves during bearing rotation. Moreover, each of the inner ring 12 and the outer ring 14 is expressly radially sized such that a value of each radial thickness RTI, RTOis at least twice greater than a value of the ball diameter BD, and preferably the value of each radial thickness RTI, RTOis at least three times greater than the ball diameter value.With the combination of the relatively large contact angles CA1, CA2, the significant bearing fill percentage, and the relatively large radial thickness RT1, RT2of the rings 12, 14, the end-mounted angular contact ball bearing 10 has significant stiffness and the ability to handle increased axial and moment loads. More specifically, the relatively high contact angles CA1, CA2 substantially increase the stiffness of the bearing assembly 10 under relatively high axial and torque loads. The high filling percentage of the two sets 16, 17 of balls 17 also increases the stiffness of bearing assembly 10 and reduces the contact stresses on each ball 17, resulting in a longer life of balls 17 and thereby also bearing assembly 10. Furthermore, the shoulders 24 and 34 or 40 provide a relatively large contact area for the balls 17 in the direction of axial thrust loads thanks to their considerable radial height, which increases the moment stiffness and reduces the contact stress due to axial thrust loads.Representative, non-limiting examples of the present invention have been described above in detail with reference to the accompanying drawings. This detailed description is merely intended to teach those skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention.Moreover, combinations of features and steps disclosed in the above detailed description may not be required to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Moreover, various features of the representative examples described above, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to produce additional useful embodiments within the meaning of the present teaching.It is intended to disclose all features disclosed in the specification and / or the claims separately and independently from each other and independently from the compositions of the features in the embodiments and / or the claims for the purpose of original written disclosure and for the purpose of limiting the claimed subject matter. Moreover, it is intended that all value ranges or indications of groups of entities disclose any possible intermediate value or entity for the purpose of original written disclosure as well as for the purpose of restricting the claimed subject matter. The invention is not limited to the embodiments described above and can be varied within the scope of the following claims.

Claims

An end-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, first and second axial ends opposing each other, one of the first and second axial ends connectable to the first member, an inner circumferential surface and an outer circumferential surface having a first inner raceway and a second inner raceway axially spaced from and facing the first inner raceway; an outer ring disposed about the inner ring and having opposed first and second axial ends, one of the first and second axial ends being connectable to the second member, and having an outer circumferential surface and an inner circumferential surface having a first outer raceway and a second outer raceway, the first and second outer raceways being axially disposed between the first and second inner raceways such that the first outer raceway faces the first inner raceway and the second outer raceway faces the second inner raceway; and 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 of the first and second sets of balls having a ball diameter; wherein the inner ring, the outer ring, the first set of balls, and the second set of balls are each configured and sized such that a first contact angle between each ball of the first set of balls and the first inner and outer raceways has a value greater than thirty-five degrees and a second contact angle between each ball of the second set of balls and the second inner and outer raceways has a value greater than thirty-five degrees; and wherein a number of the balls of each of the first and second sets of balls yields a bearing fill percentage greater than seventy-five percent.The ball bearing assembly of claim 1, wherein: the inner ring includes two annular shoulders extending radially outward from a remainder of the outer circumferential surface of the inner ring and axially spaced apart from one another, each annular shoulder providing at least a majority of a separate one of the first and second inner raceways and having a radial height with respect to the remainder of the outer circumferential surface, the radial height having a value of at least forty percent of the ball diameter; and the outer ring has two adjacent annular shoulders extending radially inward from a remainder of the inner circumferential surface of the outer ring, each annular shoulder providing at least a majority of a separate one of the first and second outer raceways and having a radial height with respect to the remainder of the inner circumferential surface, or having a single annular shoulder extending radially inward from a central portion of the inner circumferential surface, providing at least a majority of both the first and second outer raceways and having a radial height with respect to the remainder of the inner circumferential surface, the radial height of each of the two shoulders or the single shoulder of the outer ring being at least forty percent of the ball diameter.The ball bearing assembly of claim 2, wherein the value of each radial height is greater than forty-eight percent of the value of the ball diameter.The ball bearing assembly of claim 1, wherein the value of each contact angle is between forty degrees and sixty degrees.The ball bearing assembly of claim 1, wherein the number of balls of each of the first and second sets of balls yields a bearing fill percentage greater than eighty percent.The ball bearing assembly of claim 1, wherein the inner ring includes first and second ring portions, the first ring portion forming the first inner raceway and having an outer axial end forming the first axial end of the inner ring and an opposing inner axial end, the second ring portion forming the second inner raceway and having an outer axial end forming the second axial end of the inner ring and an inner axial end disposed against the inner axial end of the first ring portion.The ball bearing assembly of claim 1, wherein the inner ring has a radial thickness between a 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 a maximum inner diameter of the inner circumferential surface of the outer ring and the outer circumferential surface of the outer ring, and a value of each radial thickness is at least twice greater than a value of the ball diameter.The ball bearing assembly of claim 1, wherein each of the inner ring and the outer ring includes a plurality of mounting holes extending axially from one of the first and second axial ends and spaced circumferentially about the centerline, each mounting hole configured to clearance receive a fastener or to be threadably engaged by a fastener to connect the inner ring to the first member and the outer member to the second member.The bearing assembly of claim 1, wherein each of the first and second inner raceways and each of the first and second outer raceways has a radius, a value of each raceway radius being no more than three percent greater than half the value of the ball diameter.The bearing assembly of claim 1, wherein: the one of the first and second axial ends of the inner ring is arrangeable against the first member or an intermediate member disposed between the inner ring and the first member when the inner ring is connected to the first member; and the one of the first and second axial ends of the outer ring is arrangeable against the second member or an intermediate member disposed between the outer ring and the second member when the outer ring is connected to the second member.A 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, first and second axial ends opposing each other, one of the first and second axial ends connectable to the first member, an inner circumferential surface and an outer circumferential surface having a first inner raceway and a second inner raceway axially spaced from and facing the first inner raceway; an outer ring disposed about the inner ring and having opposed first and second axial ends, one of the first and second axial ends being connectable to the second member, and having an outer circumferential surface and an inner circumferential surface having a first outer raceway and a second outer raceway, the first and second outer raceways being axially disposed between the first and second inner raceways such that the first outer raceway faces the first inner raceway and the second outer raceway faces the second inner raceway; and 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 of the first and second sets of balls having a ball diameter; wherein the inner ring, the outer ring, the first set of balls, and the second set of balls are each formed and sized such that a first contact angle between each ball of the first set of balls and the first inner and outer raceways has a value greater than thirty five degrees and a second contact angle between each ball of the second set of balls and the second inner and outer raceways has a value greater than thirty five degrees; and wherein the inner ring has two annular shoulders extending radially outward from a remainder of the outer circumferential surface of the inner ring and spaced axially from one another, each annular shoulder providing at least a majority of a separate one of the first and second inner raceways and having a radial height with respect to the remainder of the outer circumferential surface, the outer ring having two adjacent annular shoulders, which extend radially inwardly from a remainder of the inner circumferential surface of the outer ring, each annular shoulder providing at least a major portion of a separate one of the first and second outer raceways and having a radial height with respect to the remainder of the inner circumferential surface, or having a single annular shoulder extending radially inwardly from a central portion of the inner circumferential surface and providing both the first and second outer raceways and having a radial height with respect to the remainder of the inner circumferential surface, each radial height having a value of at least forty percent of the ball diameter.A 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, first and second axial ends opposing each other, one of the first and second axial ends being connectable to the first member, and having an inner circumferential surface and an outer circumferential surface having a first inner raceway and a second inner raceway axially spaced from and facing the first inner raceway; an outer ring disposed about the inner ring and having opposed first and second axial ends, one of the first and second axial ends being connectable to the second member, an outer circumferential surface and an inner circumferential surface having a first outer raceway and a second outer raceway, the first and second outer raceways being axially disposed between the first and second inner raceways such that the first outer raceway faces the first inner raceway and the second outer raceway faces the second inner raceway; and 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 of the first and second sets of balls having a ball diameter; wherein the inner ring, the outer ring, the first set of balls, and the second set of balls are each formed and sized such that a first contact angle between each ball of the first set of balls and the first inner and outer raceways has a value greater than thirty-five degrees and a second contact angle between each ball of the second set of balls and the second inner and outer raceways has a value greater than thirty-five degrees; and wherein the inner ring has a radial thickness between a 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 a maximum inner diameter of the inner circumferential surface of the outer ring and the outer circumferential surface of the outer ring, and a value of each radial thickness is at least twice greater than a value of the ball diameter.

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