End cap for bearing assembly

[0002] Not Applicable.

[0003] Not Applicable.

[0004] This invention relates in general to a bearing assembly for axle journals and, more particularly, to a bearing assembly having an improved end cap and to the end cap itself.

[0005] One type of bearing (FIG. 1) which finds widespread use on the journals of rail car axles, has an outer race known as a double cup, an inner race composed of two cones arranged end to end, and tapered rollers arranged in two rows between the cup and cones, there being a separate row around each cone. The bearing actually forms part of a package or assembly which further includes a backing ring that seats against a fillet or shoulder at one end of a journal and an end cap that fits over the opposite end of the journal where it is secured with three cap screws that thread into the journal. The two cones fit around the journal between the backing ring and the end cap, and the cap screws clamp the cones firmly in place, with the clamping force being transferred through the end cap. Seals fit into the ends of the cup and establish fluid barriers along the cones in some assemblies and along seal wear rings in others, with those wear rings likewise being clamped up by the cap screws—there being one wear ring between the backing ring and inboard cone and the other between the end cap and the outboard cone. The two cones should be fitted to the journal with an interference fit and relatively heavy torque should be applied to the cap screws, all to minimize fretting along the journal.

[0006] More particularly, loose cones will themselves rotate around the journal, that is to say, the cylindrical surface of the journal will roll along the surfaces of the cone bores. This in itself produces fretting and hence, the need for the interference fit between the cones and the journal. But additional flexure develops as a consequence of the journal supporting the rail car and its load in the manner of a cantilever. This flexure produces minute movement axially between the journal and the cone bores, primarily at the bore of the inboard cone. A large clamping force exerted by the cap screws and transferred through the end cap minimizes this type of fretting, but does not eliminate it.

[0007] Indeed, the flexure produces wear along the faces where the end cap abuts a mating surface, whether that face be on the outboard cone or on a wear ring, and that wear leads to greater movement and more fretting. Cap screws can tolerate only a limited amount of torque, and furthermore, when turned down with excessive torque can distort the end cap. This may produce gaps which allow water to seep onto the surface of the journal and exacerbate the fretting that occurs. In this regard, this typical end cap has an axial wall which extends along the journal and a cross wall which is formed integral with the axial wall and extends over the end face of the journal. The cap screws pass through the cross wall, and when turned down urge that wall toward the end of the journal and the surrounding axial wall toward the cones of the bearing. The cross wall generally has uniform thickness (FIG. 1) and tends to deflect more in the region of the cap screws than elsewhere. This distortion transfers to the axial wall.

[0008] An end cap for retaining an antifriction bearing on the journal of an axle has an abutment face and a cross wall around which the abutment faces extends. The end cap is secured to the journal with cap screws which pass through bolt holes in its cross wall and thread into the journal. The cross wall of the end cap is thicker between the bolt holes than it is in the regions of the bolt holes. This produces a more uniform force along the abutment face when the cap screws are tightened. The invention also resides in a bearing assembly including the end cap.

[0009] FIG. 1 is a perspective view, partially broken away and in section, of a bearing assembly having an end cap formed in accordance with the prior art;

[0010] FIG. 2 is a sectional view of a bearing assembly having an end cap constructed in accordance with and embodying the present invention;

[0011] FIG. 3 is a front view of the end cap;

[0012] FIG. 4 is a rear view of the end cap;

[0013] FIG. 5 is a sectional view of the end cap taken along line 5—5 of FIG. 3;

[0014] FIG. 6 is a sectional view of a slightly different bearing assembly with its end cap modified to accommodate it.

[0015] Referring now to the drawings (FIG. 2), a bearing B fits between a housing H and the end of an axle A and enables the axle A to rotate under the housing H, thus supporting the housing H which it carries. The bearing B, which establishes an axis X of rotation for the axle A, forms part of a bearing assembly C that is usually furnished as a package. Typically, the axle A will have flanged rail car wheels on it, and the housing H will fit into the side frame of a rail car truck. But the bearing assembly C has other applications as well, such as for the wheels of cranes, for table rolls at rolling mills and even the work rolls, and for supporting large sheaves.

[0016] The axle A at its end undergoes a reduction in diameter, thus forming a journal 2 (FIG. 2) having a cylindrical exterior surface. The journal 2 merges into the main body of the axle A at a curved shoulder or fillet 4. At its opposite end it has an end face 6 which is squared off with respect to the axis X. The journal 2 contains three threaded holes 8 which open out of the end face 6. They are located equidistantly from the axis X and at 120° intervals.

[0017] The bearing B fits around the journal 2 of the axle A and within the housing H which is located generally over the journal 2. It includes (FIG. 2) an inner race in the form of inboard and outboard cones 12, an outer race in the form of a double cup 14, rolling elements in the form of tapered rollers 16 arranged in two rows between the cones 12 and the cup 14, there being a separate row around each cone 12, and a spacer ring 18 located between the two cones 12. Each cone 12 has a tapered raceway 20 and a thrust rib 22 at the large end of the raceway 20. The thrust rib 22 extends out to a back face 24 which is squared off with respect to the axis X. The two cones 12 fit over the journal 2 with their back faces 24 being presented away from each other, An interference fit on the order of 0.0025 to 0.0045 inches exists between the cones 12 and the journal 2. The cup 14 fits within housing H which is configured to confine it—and the bearing B—axially, but nevertheless allows it to rotate in minute increments, that is to say, creep in the circumferential direction. The cup 14 has two raceways 28 which surround the raceways 20 of the two cones 12 and taper downwardly toward an intervening surface. At their opposite or large ends the raceways 28 open into end bores 30 within which the thrust ribs 22 of the cones 20 are located. The tapered rollers 16 are arranged in two rows between the opposed raceways 20 and 28 of the cones 12 and cup 14, respectively. Generally speaking, line contact exists between the raceways 20 and 28 and the tapered side faces of the rollers 16. Moreover, the large ends of the rollers 16 bear against the thrust ribs 22 of the cones 12 which prevent the rollers 16 from moving up the raceways 20 and 28 and out of the ends of the bearing B. The rollers 16 are on apex, meaning that within each row, the conical envelopes formed by the rollers 16 of that row have their apices at a common point along the axis X. The spacer 18 establishes the distance between the raceways 20 of the two cones 12 and thus determines the setting for the bearing B. That setting is one of slight end play, and thus slight radial and axial free motion exists between the two cones 12 and the cup 14. Since the rollers 16 of the two rows taper downwardly toward each other, thus giving the bearing B the indirect configuration, the bearing B will carry radial load as well as thrust loading in either axial direction.

[0018] In addition to the bearing B, the bearing assembly A includes (FIG. 2) a backing ring 34 which has a contoured surface 36 that conforms to and fits against the fillet 4 at the inboard end of the journal 2. The backing ring 34 also has an abutment surface 38 which is squared off with respect to the axis X and is presented toward the bearing B. Indeed, the abutment surface 38 abuts the back face 24 on the inboard cone 12 of the bearing B.

[0019] The bearing assembly A also includes an end cap 42 (FIG. 2) which fits over the end face 6 of the journal 2 and bears against the back face 24 of the outboard cone 12. It may be cast from ductile iron or from steel or it may be a steel forging, but in any event, it is an integral unit that includes a cross wall 44 and an axial wall 46 which is directed away from the cross wall 44, terminating at an abutment face 48 that is squared off with respect to the axis X. The axial wall 46 fits around the outboard end of the journal 2—indeed, far enough to enable the abutment face 48 to bear against the back face 24 on the outboard cone 12. When the end cap 42 is so disposed, its cross wall 44 lies slightly beyond the end face 6 on the journal 2.

[0020] The end cap 42 is secured to the journal 2 with cap screws 50 which pass through the cross wall 44 and engage the threaded holes 8 in the journal 2. When tightened, the cap screws 50 urge the end cap 42 toward the backing ring 34 to clamp the two cones 12 and the spacer ring 18 of the bearing B tightly between the backing ring 34 and end cap 42.

[0021] The cross wall 44 of the end cap 42 has a front face 54 (FIG. 3) that is presented away from end face 6 of the journal 2 and a rear face 56 (FIG. 4) which is present toward the end face 6. The axial wall 46, on the other hand, has an inside face 58 (FIG. 5) which is cylindrical, thus creating within the end cap 42, a bore that leads from the rear face 56 of the cross wall 44 out to the abutment face 48. The axial wall 46 also has an outside face 60 which extends from the abutment face 48 to the front face 54 of the cross wall 44. It has a taper, with its greatest diameter being toward the abutment face 48. Thus, the axial wall 46 has its greatest thickness at the abutment face 48.

[0022] The front face 54 (FIGS. 3 & 5) includes a peripheral surface 64 and a triangular land 66 that lies within the peripheral surface 64, but is raised from it. The peripheral surface 64 merges into the outside face 60 of the axial wall 46. The triangular land 66 at each of its corners has a circular boss 68 that projects slightly beyond the land 66 and terminates at a raised surface 70. Indeed, the peripheral edge of the land 66 merges into and coincides with the corner edges of the bosses 68, so that the bosses 68 form rounded corners on the land 66. The three bosses 68 are arranged at 120° intervals and each contains a bolt hole 72 that is large enough to loosely receive one of the cap screws 50. The holes 72 lie equidistantly from the axis X and are arranged in a pattern that corresponds with that of the threaded holes 8 in the journal 2. Thus, the end cap 42 may be rotated to a position in which its holes 72 align with the threaded holes 8 in the journal 2. While the peripheral surface 64 and the land 66 lie in parallel planes that are perpendicular to the axis X, the raised surfaces 70 of the bolt bosses 68 lie in planes that are slightly inclined with respect to the peripheral surface 64 and land 66, each having its greatest elevation where it is closest to the axis X and its least along the rounded corner of the land 66. (FIG. 5—inclination exaggerated). Thus, the raised surfaces 70 of the bolt bosses 68 slope downwardly toward the axial wall 46. For a bolt boss 68 having a one inch radius, the difference in elevation between the regions closes and farthest from the axis X should range between 0.008 in. and 0.023 in.

[0023] On its rear face 56 face the cross wall 44 has (FIGS. 4 & 5) three ribs 78 which radiate from the axis X, where they merge, and extend out to the inside face 58 of the axial wall 46. The bolt holes 72 lie between the ribs 78. In addition the rear face 56 has recessed surfaces 80 which lie between the ribs 78 where they also extend out to the cylindrical inside face 58 of axial wall 46. The bolt holes 72 open out of the rear face 56 through the recessed surfaces 80 and are centered between the ribs 78. The recessed surfaces 80 lie in a common plane that is perpendicular to the axis X. The cross wall 44 has its greatest thickness at the ribs 78 and its least thickness at the recessed surfaces 74, particularly the regions of the surfaces 76 that underlie the peripheral surface 64 on the front face 54.

[0024] Finally, the bearing assembly C includes seals 82 (FIG. 2) which fit into the end bores 30 of the double cup 14 and around the thrust ribs 22 on the two cones 12. The seals 82 establish live fluid barriers that close the annular ends of the bearing B, keeping grease within the interior of the bearing B and excluding contaminants from it. U.S. Pat. No. 4,819,949 entitled Shielded Seal Assembly discloses a seal which, with minor alterations, is suitable for use as each seal 82.

[0025] To install the bearing assembly C on the journal 2 of the axle A, the backing ring 34 is advanced over the journal 2 and its contoured surface 36 is brought against the fillet 4. The bearing B comes as a subpackage, it being unitized by the seals 82. The cones 12 of the packaged bearing B are next advanced over the journal 2 within enough force to overcome the interference fit, with the advance continuing until the back face 24 of the inboard cone 12 bears firmly against the abutment face 38 on the end of the backing ring 34. In this condition, the backing ring 34 is captured firmly between the fillet 4 and the inboard cone 12. Next the end cap 42 is fitted over the outboard end of the journal 2 with its abutment face 48 against the back face 24 of the outboard cone 12. After the end cap 42 is rotated to align its bolt holes 72 with the threaded holes 8 in the journal 2, the cap screws 50 are inserted through the holes 72 and engaged with the threaded holes 8. The cap screws 50 are turned down until their heads bear snugly against the raised surfaces 70 on the bolt bosses 68. Enough torque is applied to the cap screws 50 to clamp the cones 12 and the spacer ring 18 firmly between the end cap 42 and the backing ring 34 and to hold the backing ring 34 firmly against the fillet 4. The torque deflects the end cap 42 in its thinnest section, that is in the regions backed by the recessed surfaces 80. Lesser deflections occur at the ribs 78. As the cross wall 44 of the end cap 42 deflects the raised surfaces 70 on the bolt bosses 68 more closely approach an orientation perpendicular to the axis X and thus the undersides of the heads for the cap screws 50 seat generally uniformly along the raised surfaces 70 of the bolt bosses 68. This minimizes the prospect of water migrating along the cap screws 50 to the journal 2.

[0026] More importantly, the deflection of the cross wall 44 imparts a more uniform distribution of force along the abutment face 48 on the axial wall 46. Whereas end caps with cross walls of generally uniform thickness concentrate the clamping force in the regions immediately outwardly from the cap screws, the end cap 42, by reason of the somewhat flexible regions between the ribs 78 of its cross wall 44, effect a more uniform distribution of the clamping force. The end cap 42 undergoes less distortion in its axial wall 46, and the prospect of gaps developing between the abutment face 48 on the axial wall 46 and the back face 24 of the outboard cone 12 is diminished and indeed eliminated. In short, the recessed surfaces 80 and the ribs 78 in the cross wall 44 render the end cap 42 flexible in a manner that effects a generally uniform distribution of the clamping force along abutment face 48.

[0027] A modified end cap 86 (FIG. 6) is suitable for use in a bearing assembly D that differs in some respects from the bearing assembly C, in the sense that the bearing assembly D is the predecessor of the bearing assembly C. The bearing assembly D includes a bearing B which is essentially the same as the bearing B for the assembly C, except that the thrust ribs 22 on its cones 12 are not as long. The bearing assembly D has a backing ring 88 that fits against the fillet 4 at the end of the journal 2. It also has two seal wear rings 90, one that fits between the backing ring 88 and the inboard cone 12 and the other that fits between the end cap 86 and the outboard cone 12.

[0028] The backing ring 88 contains a counterbore 92 to receive the inboard wear ring 90, whereas the end cap 86 has another counterbore 94 that receives the end of the outboard wear ring 90. The base of the counterbore 94 constitutes an abutment surface for transferring the clamping force imparted by the cap screws 50 to the outboard wear ring 90 which in turn transfers it to the outboard cone 12.

[0029] The bearing assembly D contains seals 96 which fit into the end bores 30 of the double cup 14 and establish fluid barriers around the seal wear ring 90. U.S. Pat. No. 4,819,949 shows a seal suitable for use as each of the seals 96.