Method of assembling ball bearing assembly

Abstract: A method of assembling a ball bearing assembly includes the steps of forming a one-piece metallic ball bearing cage having an initial configuration with ball pockets and bridge portions (16) between the ball pockets, at least a portion of the bridge portions (16) having a predetermined chordal length. The bearing balls (52) are positioned within an annulus between inner and outer bearing rings (68, 70), the bearing balls (52) being separated by an average chordal distance less than said predetermined chordal length and then the ball bearing cage is inserted into the annulus such that circumferential movement of the bearing balls (52) allows the bridge portions (16) of the ball bearing cage to pass between adjacent bearing balls (52) as the bearing balls (52) sequentially enter the ball pockets.

Description: This invention relates generally to ball bearing cages and, more particularly, to a method of assembling one-piece metallic ball bearing cages that are installed in a ball bearing assembly by "popping" or "snapping" over bearing balls. See, for example, US 1 496 516. One common type of ball bearing cage comprises two halves joined together by welding, riveting or mechanical interlock. These two-piece ball bearing cages require insertion of the two halves from opposite ends of the ball bearing after the bearing balls have been loaded between the bearing rings. Welding is difficult due to potential arcing through the bearing balls, and riveting is difficult due to the many small rivets that must be inserted. Additional cost results from inspection and rejection of defective bearing assemblies. Additional problems are associated with two-piece ball bearing cages due to space requirements. Such ball bearing cages require sufficient circumferential distance between bearing balls to permit welding, riveting or mechanical interlock of the two halves. As a result, fewer bearing balls may be inserted, reducing the load capacity of the bearing assembly. Also, when multiple rows of bearing balls are used, the rows must be separated to provide space for the ball bearing cages, adding to the axial length of the bearing assembly. Another type ball bearing cage comprises a sheet metal ring having an initial undulatory configuration with open ball pockets spaced apart by U-shaped connecting portions. After being inserted between the bearing rings, with bearing balls placed in the pockets, the U-shaped connecting portions are upset, causing the sides of the connecting portions to spread and conform to the contour of the bearing balls. However, forming the ball bearing cages directly against the bearing balls often results in excess gripping of the bearing balls or in insufficient ball retention. Ball bearing cages may also employ a one-piece design having resilient fingers or lips which snap over the bearing balls as the bearing balls enter the ball pockets to provide a simple pop-in assembly. Such one-piece ball bearing cages are difficult to form of metal with sufficient ball contacting surface to retain the bearing balls. Moulded polymer ball bearing cages of similar one-piece pop-in design may provide improved wrap-around and ball conformity. However, such polymer ball bearing cages are limited to low temperature and low strength applications. A method of assembling a ball bearing assembly is described in EP-A-0 608 629, which comprises part of the state of the art, according to Article 54(3) EPC. According to the present invention there is provided a method of assembling a ball bearing assembly, the method comprising the steps of forming a one-piece metallic ball bearing cage having an initial configuration with ball pockets and bridge portions between the ball pockets, at least a portion of the bridge portions having a predetermined chordal length; characterised by positioning bearing balls within an annulus between inner and outer bearing rings, the bearing balls being separated by an average chordal distance less than said predetermined chordal length; and inserting the ball bearing cage into said annulus such that circumferential movement of the bearing balls allows the bridge portions of the ball bearing cage to pass between adjacent bearing balls as the bearing balls sequentially enter the ball pockets. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a cross-sectional view illustrating tooling and a portion of a partially formed one-piece ball bearing cage; Fig. 2 is a cross-sectional view illustrating an alternative bridge portion of a partially formed one-piece ball bearing cage; Fig. 3 is a sectional view along the line 3-3 of Fig. 1 illustrating the tooling and a portion of the partially formed one-piece ball bearing cage; Fig. 4 is a cross-sectional view illustrating tooling and a portion of a fully formed one-piece ball bearing cage; Fig. 5 is a cross-sectional view similar to Fig. 4 illustrating a subsequent position of the tooling relative to the fully formed one-piece ball bearing cage; Fig. 6 is a pictorial view illustrating the fully formed one-piece ball bearing cage; Fig. 7 is an elevational view, partially in section, illustrating a partially assembled ball bearing assembly and tooling for inserting the ball bearing cage; Fig. 8 is a side view, partially in section, of the partially assembled ball bearing assembly and tooling of Fig. 7; Fig. 9 is an elevational view illustrating a subsequent position of the partially assembled ball bearing assembly and portions of the tooling of Fig. 7; Fig. 10 is an elevational view illustrating a subsequent position of the partially assembled ball bearing assembly and tooling of Fig. 8; and Fig. 11 is an elevational view similar to Fig. 7 illustrating a subsequent position of the ball bearing assembly and tooling. Referring to the drawings, Figure 1 illustrates a portion of a partially formed one-piece ball bearing cage 10 and tooling, comprising movable anvils 12 that may be used to complete a fully formed one-piece ball bearing cage. To form the partially formed ball bearing cage 10, a flat, thin ring of metal is first formed using any known forming method. For example, the flat ring may be stamped or punched as a "washer" from a wide strip of sheet of flat metal. Alternatively, the flat ring may be formed from a narrow flat strip of metal which is coiled edgewise ("the hard way") into a split ring. The ends of the split ring may be joined by welding or other means, with a butt, puzzle-cut or lap joint, coined to an even thickness and trimmed to size to provide a uniform section. Next, the flat, thin ring is modified into the partially formed ball bearing cage 10 by forming initial ball pockets 14 and bridge material 16 between adjacent, initial ball pockets 14. Conventional multistage dies or other means may be used to progressively gather the thin ring into an undulating configuration as the overall diameter of the ring is reduced. Subsequent die stages may progressively form initial ball pockets 14 and bridge material 16. Preferably, initial ball pockets 14 have a spherically concave bottom surface 18 to conform to a bearing ball; however, other concave configurations may be used with similar effect. Side walls 20 and 22 of initial pocket portions 14 are not spherically concave, thus facilitating use of conventional multistage dies. Bridge material 16 may include flat portions 24 and 26 providing a tent or peaked configuration, as shown in Figure 1, or may have a rounded portion 28 providing a curved arch configuration, as shown in Figure 2. The flat portions 24 and 26 or rounded portion 28 extend upward from the side walls 20 and 22 to provide sufficient material to form a desired bridge configuration of the finished ball bearing cage, as described below. Movable anvils 12 are positioned within the initial ball pockets 14. Preferably, a rounded surface 30 of movable anvils 12 defines a band of a sphere having a diameter slightly greater than that of the bearing balls with which the finished ball bearing cage is to be used, to ensure that the bearing balls are freely rotatable. The rounded surface 30 is mounted on an anvil post 32, which may be cylindrical. As shown in Figure 3, the movable anvils 12 include recessed side portions 34 that are recessed with respect to spherical extension 35 of the rounded surface 30 to provide an overall "lollipop" shape. Recessed side portions 34 may be flat or may be cylindrically curved, as shown, to conform to the bore and outside diameter of the ball bearing cage. As shown in Figure 4, a fully formed ball bearing cage 36 is formed by flattening the bridge portion 16 (Figures 1 and 2) with suitable dies to form a flat bridge 38 and to cause the side walls 20 and 22 (Figures 1 and 2) to wrap around the rounded portion 30, forming curved upper walls 40. Bridge ends 42 and 44 are spread against the anvil posts 32, which provide stop surfaces limiting the length of the flat bridge 38, ensuring that final ball pockets 46 enclose more than a 180 degree circumference of the rounded surface 30. As a result, the final ball pockets 46 retain bearing balls both axially and radially with respect to the ball bearing cage. Flattening of the bridge portion 16 between initial ball pockets 14 (Figure 1) thus creates a narrowed access to the final ball pockets 46 to achieve the desired retainment feature. The bore and outside diameter of the partially formed ball bearing cage 10 (Figure 1) are contained during this bridge flattening operation in order to prevent radial growth or undesirable distortion of the ball bearing cage. The anvil posts 32 provide a controlled clearance between the bridge ends 42 and 44 of each final ball pocket 46 to ensure that a desired amount of force is required to remove the bearing cage from a ball bearing assembly. To facilitate removal of the movable anvils 12 from the fully formed ball bearing cage 36 without distorting the ball bearing cage, the anvils are moved by rotation about axes perpendicular to the ball bearing cage or by another form of motion, for example, by tilting the movable anvils 12, such that final ball pockets 46 no longer enclose more than a 180 degree circumference of the rounded surface 30 of the movable anvils 12. For illustrative purposes only, Figure 5 shows the movable anvils 12 rotated 90 degrees relative to their position in Figure 4; generally, a rotation of 30 degrees is sufficient. The rotation of the anvils may be effected by a ring gear and pinions or by other known means. Figure 6 shows the fully formed ball bearing cage 36 after removal of the movable anvils 12. If the flat, thin ring is formed from a split ring, as described above, a weld joint 48 is preferably located in the final ball pockets 46, as shown, rather than in the flat bridge 38, to improve resistance to fatigue. At least one of the flat bridges 38 has predetermined chordal length A, measured at pitch circle 50 of bearing balls 52, which is greater than the space between adjacent bearing balls 52. As a result, the fully formed ball bearing cage 36 must be deformed to allow adjacent bearing balls 52 to pass between the bridge ends 42 and 44 and enter the final ball pockets 46. The ball bearing cage may be formed of steel, brass, bronze or similar metal. If a relatively soft material is used, the number of pressing stages required to form the partially formed ball bearing cage 10 and fully formed ball bearing cage 36 may be reduced. For example, the initial ball pockets 14 of the partially formed ball bearing cage 10 may have a simplified curved surface, and the rounded portion 30 of the movable anvils 12 may serve as a die to form the spherically concave bottom surface 18 in addition to their function in forming the flat bridge 38 and curved upper walls 40. The fully formed ball bearing cage 36 should have sufficient resiliency to snap back to its fully formed configuration after being deformed during installation of the bearing balls 52 in the final ball pockets 46, to provide a pop-in installation. If the ball bearing cage is formed of mild steel, carburizing, hardening and tempering of fully formed ball bearing cage 36 may be employed to create residual compressive stress and improve resiliency and fatigue resistance. Preferably, carburizing does not exceed one-third the thickness of the ball bearing cage and tempering ensures that the surface of the cage is softer than the surface of bearing balls 52. Figures 7 and 8 illustrate tooling that may be used to insert the fully formed ball bearing cage 36 to complete a ball bearing assembly. A top plate shank 60 is mounted in a vertical press such that a top plate 62 is movable vertically, perpendicular to a bearing end face 64 of a ball bearing 66, as shown by arrow B. Bearing balls 52 are within an annulus between inner and outer bearing rings 68 and 70 and are separated by an average chordal distance less than the chordal length of at least one flat bridge 38. The ball bearing 66 may be the type with a wide inner bearing ring 68 relative to outer bearing ring 70, as illustrated, or may be of other configurations. A pivot plate 72 is pivotably mounted on opposite sides of the top plate 62 by means of trunnion blocks 74 and trunnion pins 76. The pivot plate 72 includes a stop bar 77 and stop washer 79 and is biased by a compression spring 78, or by other biasing means, against the top plate 62 into the position illustrated in Figure 7. A loading punch 80 includes a ring shaped shoulder 82 and is fixed to the pivot plate 72 by clamps 84 at opposite sides of the pivot plate 72. A centre pilot 86 is fixed to the top plate 62 and extends through a bore 88 in the loading punch 80 and a corresponding bore in the pivot plate 72. Figure 8 illustrates a subsequent position of the tooling and ball bearing assembly of Figure 7. The vertical press moves the top plate shank 60, top plate 62 and centre pilot 86 vertically, as a unit, such that the centre pilot 86 is advanced into a bore 90 of the inner bearing ring 68, as illustrated in Figure 9, thereby maintaining proper alignment of the ball bearing 66. A shoulder portion 92 of the loading punch 80 then engages a cage portion 94, as illustrated in Figure 10, such that adjacent bearing balls 52 move circumferentially, along pitch circle 50, allowing the adjacent flat bridge 38 to pass between the bearing balls 52 as the balls enter final ball pockets 46. After this initial insertion of the cage portion 94, further advancement of the tooling compresses the compression spring 78 and pivots the loading punch 80 such that additional portions of fully formed ball bearing cage 36 are pressed downward against the bearing balls 52. The bearing balls 52 move circumferentially, along pitch circle 50, allowing the balls to enter the remaining final ball pockets 46. Insertion is said to be "sequential" because the bearing balls 52 do not all enter the ball pockets simultaneously, that is, at least one bearing ball 52 (for example, a bearing ball adjacent cage portion 94) precedes the others, which may or may not enter simultaneously. Although a simple pivoted loading punch is illustrated, having an abutment surface initially angled and subsequently parallel with respect to the bearing end face 64, other types of tooling may be used to press the ball bearing cage and force the flat bridges 38 between adjacent bearing balls. For example, a V-shaped or curved abutment surface may be pressed against two cage portions to initially insert the bearing balls 52 at those two cage portions rather than at a single cage portion 94. The ball bearing cage 36 may remain substantially as shown in Figure 6 during insertion, or may be temporarily bent to a "potato chip" configuration to facilitate insertion over the bearing balls 52. The fully formed ball bearing cage 36 is made of a resilient material such that it returns to its fully formed configuration after the bearing balls 52 enter the final ball pockets 46 to provide a pop-in assembly. Because at least some of the flat bridges 38 are longer than respective spaces between the bearing balls 52, the bridge ends 42 and 44 are engageable with bearing balls 52 to prevent the ball bearing cage 36 from separating from the bearing balls 52 in an axial direction with respect to the ball bearing 66. Preferably, the final bridge pockets 46 have a substantially spherical concave surface for receiving a circumferential portion of the respective bearing ball and have a slightly larger diameter to provide free rotation. From the above, it will be apparent that flattening of the bridge material 16 between and above the midpoint of the open, loop-shaped initial ball pockets 14 ensures that the final ball pockets 46 have a narrowed opening to retain the fully formed ball bearing cage 36. The movable anvils 12 provide a controlled interference fit with respect to the bearing balls 52 during insertion and a controlled clearance after insertion of the ball bearing cage 36 within the ball bearing 66 to form a ball bearing assembly. Excess gripping of the bearing balls 52 and insufficient retention are thereby prevented. The present construction and method provides a pop-in ball bearing cage having improved performance as well as reduced manufacturing cost. Because joining of cage halves is not required, costs and defects associated with welding and riveting halves are eliminated. Ball pockets may be made closer together, allowing a greater number of bearing balls in a bearing assembly of a given size, thereby increasing load capacity, and closer spacing of rows of a two row ball bearing is permitted than with two-piece ball bearing cages. Better lubrication results from increased space for holding grease and higher temperature applications are possible than with polymer ball bearing cages.

Claims: A method of assembling a ball bearing assembly, the method comprising the steps of forming a one-piece metallic ball bearing cage having an initial configuration with ball pockets and bridge portions (16) between the ball pockets, at least a portion of the bridge portions (16) having a predetermined chordal length; characterised by positioning bearing balls (52) within an annulus between inner and outer bearing rings (68, 70), the bearing balls (52) being separated by an average chordal distance less than said predetermined chordal length; and inserting the ball bearing cage into said annulus such that circumferential movement of the bearing balls (52) allows the bridge portions (16) of the ball bearing cage to pass between adjacent bearing balls (52) as the bearing balls (52) sequentially enter the ball pockets. A method according to claim 1, wherein the ball bearing cage is made of a resilient material and wherein the step of inserting the ball bearing cage resiliently deforms the ball bearing cage such that the ball bearing cage returns to said initial configuration after insertion. A method according to claim 1 or 2, wherein, after the step of inserting the ball bearing cage, ends of at least some of the bridge portions (16) are engageable with the bearing balls (52) to prevent the ball bearing cage from separating from the bearing balls (52) in an axial direction with respect to the inner and outer bearing rings (68, 70). A method according to claim 1, 2 or 3, wherein the ball pockets of the ball bearing cage each include a substantially spherical concave surface for receiving a portion of the respective bearing ball, the concave surface having a diameter larger than the diameter of the bearing ball such that the bearing ball may freely rotate within the ball pocket. A method according to claim 4, wherein each concave surface subtends an arc of more than 180 degrees to retain its bearing ball (52) within the ball bearing cage. A method according to any one of the preceding claims, wherein the step of inserting the ball bearing cage into the annulus between the inner and outer bearing rings (68, 70) comprises forcing a first bridge portion (16) between adjacent bearing balls (52) and subsequently moving the ball bearing cage such that other bridge portions (16) are forced, sequentially, between other adjacent bearing balls (52). A method according to claim 6, wherein the inner and outer bearing rings (68, 70) define a bearing end face (64), and wherein the step of inserting the ball bearing cage into the annulus between the inner and outer bearing rings (68, 70) is aided by an insertion tool having an abutment surface which is initially angled with respect to the bearing end face (64) and which is subsequently moved parallel to the bearing end face (64). A method according to claim 7, wherein the insertion tool includes biasing means for biasing the abutment surface into an angled initial position and wherein advancement of the insertion tool, axially with respect to the inner and outer bearing rings (68, 70), causes the abutment surface to engage the ball bearing cage and overcome the biasing of the biasing means to move the abutment surface to a subsequent position parallel to the bearing end face (64).

Inventors: ALLING RICHARD L, ZINKEN GUNTER J, ALLING, RICHARD L., ZINKEN, GUNTER J.
Applicants: TORRINGTON CO, THE TORRINGTON COMPANY
Application year: 1995
Main classification: F16C43
IPC codes: F16C33, F16C43