Thrust bearing assemblies generally include a pair of axially spaced races and a circular complement of rolling bearing elements received between pathways ground into the races. The bearing is so named because, while operating, it is under a compressive load that forces or thrusts the races axially toward one another. While the load may have a significant radial component, it does not generally reverse axial direction. Consequently, such a bearing needs no structure to prevent the races from axially separating once the bearing is installed and operating. However, such a bearing still must be shipped and handled prior to installation, and it is then subjected to forces that would axially separate the races, in the absence of some structure to retain them together.
One common application for thrust bearings is the suspension of a vehicle, especially steerable McPherson struts, where the provision of a rolling bearing gives superior steering and handling feel. A vehicle suspension is an application where unitization of the bearing during installation and handling on the line is desirable. Furthermore, a vehicle suspension is a harsh environment where a sealed bearing is almost essential. There are many different approaches to both sealing and unitization in steerable McPherson strut bearings disclosed in the published patents. One approach is to mount the bearing within the elastomer material of the the upper mount of the suspension strut itself so as to wrap and seal the bearing. An example may be seen in U.S. Pat. No. 4,274,655, assigned to the assignee of the present invention. Another possibility, when the bearing can be partially protected and shielded within the pad, is to use a non-rubbing labyrinth seal, as may be seen in U.S. Pat. No. 4,541,744, assigned to the assignee of the present invention. Such an approach finds utility where it is practical to mount the bearing within the elastomer pad of the upper mount, which is not always possible.
Another approach is to mold elastomer seals directly to one of the bearing races and snap engage the seal with the other race, thereby both sealing and unitizing the bearing. Two examples may be seen in U.S. Pat. Nos. 4,120,543 and 4,400,041, also assigned to the same assignee. However, there is a great cost disadvantage to directly molding elastomer to steel, as the molding process must be carefully controlled. There is also the disadvantage that the elasticity of the elastomer is then inevitably limited by the inelasticity of the steel to which it is bonded. By far the least expensive seal is a free molded seal, used in a bearing in which some structure other than the seal itself unitizes the bearing. An example may be seen in U.S. Pat. No. 4,497,523, where free molded O-rings compressed between the bearing races provide the seal, while separate snap engaged housing members enclose the races to unitize the bearing. A disadvantage of an O-ring is that it requires the compressive operating load to keep it in sealing engagement, and it disengages almost immediately upon any axial separation of the races. While that is not a problem when separate housings prevent the races from axially separating prior to installation, separate housings themselves present a cost penalty. In addition, although it is not visible in the scale of the drawings in U.S. Pat. No. 4,497,523, a conventional O-ring presents problems of its own. It cannot be allowed to just float freely between the races, some mounting groove must be added to one of the races to confine the O-ring and to prevent it from gathering as it rubs on the other race. U.S. Pat. No. 3,567,296 illustrates such an O-ring mounting groove. Besides necessitating an extra manufacturing step, the provision of an O-ring mounting groove in one race destroys the symmetry of the bearing, a symmetry which is itself very desirable from a manufacturing and installation standpoint. Such problems with conventional free molded O-rings have even led to designs in which the O-ring is, in effect, directly molded to one of the races, despite the cost penalty, see U.S. Pat. No. 4,462,608, also assigned to the assignee of the present invention.