Thrust bearing assembly

A thrust washer has a radially directed annular portion providing a first raceway and an axially directed annular flange. A subassembly comprising a plurality of rollers, in rolling contact with the raceway, retained axially and radially in a roller cage, has a pilot surface facing the axially directed annular flange. A bushing or rolling element between the pilot surface and the axially directed annular flange reduces friction between the pilot surface and the flange while maintaining concentricity of the subassembly relative to the thrust washer.

BACKGROUND OF THE INVENTION 
This invention relates generally to thrust bearings and, more particularly, 
to a thrust bearing assembly having a thrust washer and caged rollers for 
receiving an axial load between relatively rotatable members. 
One common type of thrust bearing assembly comprises a cage and roller 
subassembly positioned between thrust washers and piloted on flanges of 
the thrust washers. The relative rotation between the thrust washers and 
the cage and roller subassembly produces heat, wear and drag associated 
with friction within the thrust washer assembly. The heat, wear and drag 
are amplified by increasing rotational speed, out-of-square geometry of 
adjacent members backing up the thrust bearing assembly, and eccentricity 
of the elements of the thrust bearing assembly, as well as other factors. 
The foregoing illustrates limitations known to exist in present thrust 
bearing assemblies. Thus, it is apparent that it would be advantageous to 
provide an alternative directed to overcoming one or more of the 
limitations set forth above. Accordingly, a suitable alternative is 
provided including features more fully disclosed hereinafter. 
SUMMARY OF THE INVENTION 
In one aspect of the present invention, this is accomplished by providing a 
thrust bearing assembly comprising a thrust washer having a radially 
directed annular portion providing a raceway and an axially directed 
annular flange. A subassembly comprising a plurality of rollers, in 
rolling contact with the raceway, and a roller cage retaining the rollers 
axially and radially, has a pilot surface facing the axially directed 
annular flange. Friction reducing means between the pilot surface and the 
axially directed annular flange reduces friction between the pilot surface 
and the flange while maintaining concentricity of the subassembly relative 
to the thrust washer. 
The foregoing and other aspects will become apparent from the following 
detailed description of the invention when considered in conjunction with 
the accompanying drawing figures.

DETAILED DESCRIPTION 
Referring now to the drawings, FIG. 1 illustrates prior art thrust bearing 
assembly 10 comprising first thrust washer 12, second thrust washer 14, 
roller and roller cage subassembly 16, and outer cup 18. 
Roller cage 20 of subassembly 16 is piloted on axially directed annular 
first flange 22, integrally formed with first thrust washer 12, and/or on 
axially directed annular second flange 24, integrally formed with second 
thrust washer 14. Rollers 26 of subassembly 16 roll on first raceway 28 
and second raceway 30 of radially directed portions of first and second 
thrust washers 12 and 14, respectively. Thrust bearing assembly 10 is held 
together by lip 32 of outer cup 18 and lip 34 on second flange 14, which 
wrap around first thrust washer 12 and roller cage 20, respectively. 
Thrust bearing assembly 40 of FIG. 2 illustrates an embodiment of the 
present invention comprising first thrust washer 42, second thrust washer 
44, roller and roller cage subassembly 46, and outer cup 48. 
Roller cage 50 of subassembly 46 is radially spaced from axially directed 
annular first flange 52, integrally formed with first thrust washer 42, 
and is adjacent to axially directed annular second flange 54, integrally 
formed with second thrust washer 44. Rollers 56 of subassembly 46 roll on 
first raceway 58 and second raceway 60 of radially directed portions of 
first and second thrust washers 42 and 44, respectively. Thrust bearing 
assembly 40 may be held together by various means, such as, for example, 
lip 62 of outer cup 48 and lip 64 on second flange 54 which wrap around 
first thrust washer 42 and roller cage 50, respectively, and flange 65 of 
outer cup 48 which also wraps around roller cage 50. Lips 62 and 64 may be 
formed by spinning, dimpling, staking or other means. 
The radial space between roller cage 50 and first flange 52 is sufficient 
to contain a friction reducing element, such as first bushing 66, for 
example, for improved piloting of subassembly 46. First bushing 66 may be 
molded of a suitable polymer, such as, for example, polyetheretherketone 
or VESPEL (available from DuPont, Wilmington, Del.), or may be machined or 
otherwise formed of bronze or other material providing low friction and 
low wear for sliding contact with adjacent elements of the bearing 
assembly, such as, for example, first thrust washer 42, roller cage 50 and 
outer cup 48. If desired, additional piloting of roller cage 50 may be 
provided by sliding engagement with second flange 54. 
As best shown in FIG. 3, first bushing 66 may have beveled surface 68 or 
may be otherwise configured to provide clearance for an internal radius 
connecting the radially directed portion of first thrust washer 42 
(including first raceway 58) with the axially directed portion forming 
first flange 52. The radial thickness and the axial length of first 
bushing 66 depend on the size, speed of rotation and load of thrust 
bearing assembly 40. For a typical configuration with a 2-inch outside 
diameter, for example, the radial thickness and axial length may be, 0.030 
and 0.250 inches, respectively. 
Thrust bearing assembly 70 of FIG. 4 illustrates a second embodiment of the 
present invention similar to thrust bearing assembly 40. In addition to 
first bushing 66, thrust bearing assembly 70 includes a second friction 
reducing element, such as second bushing 72, for example, between second 
flange 54 and roller cage 74, to further improve piloting of roller cage 
74. Compared to subassembly 46 of FIG. 2, subassembly 76 of FIG. 4 
provides increased radial clearance between roller cage 74 and second 
flange 54 for location of second bushing 72. 
In addition to the configurations of FIGS. 2 and 4, the present invention 
may employ a single friction reducing element for piloting a roller and 
roller cage subassembly at its inside diameter. In that configuration, 
second bushing 72, for example, would be used without first bushing 66. 
The roller cage for that configuration would have a modified form to 
position the rollers on the desired raceway surfaces and to provide a 
desired radial spacing at its outside diameter to facilitate additional 
piloting or other requirements. 
FIG. 5 illustrates a third embodiment of the present invention similar to 
that of FIGS. 2 and 4 but incorporating a different type of friction 
reducing element. In place of first bushing 66, thrust bearing assembly 80 
includes a plurality of rolling elements such as, for example, needle 
rollers or balls 82, within retainer or cage 84, to reduce friction during 
piloting of roller cage 50. Balls 82 provide rolling contact with first 
thrust washer 42 and roller cage 50, further reducing friction. A rolling 
element friction reducing means may also be employed in place of second 
bushing 72. 
The present invention is applicable to a wide range of thrust bearing 
configurations with various types of roller cages. The bushing or other 
friction reducing element may be positioned between the roller cage and 
piloting flange of any thrust washer to effect the present invention. The 
piloting flange may be a separate annular axially directed surface rigidly 
attached to the thrust washer or may be integrally formed with the thrust 
washer by bending, crimping, machining or other means. 
From the above description, it will be apparent that the present invention 
provides improved piloting of a roller and roller cage subassembly in many 
forms of thrust bearing assemblies. Heat, wear and drag resulting from 
friction between elements of the thrust bearing assembly are substantially 
reduced. In addition, the present invention may permit higher rotational 
speed of the thrust bearing assembly and increased out-of-square geometry 
of backup members or eccentricity of the elements of the thrust bearing 
assembly.