Abstract:
A roller cage for an axial-thrust bearing in a rotating machine has a substantially flat annular body with a first face, a second face, a radially inner surface, a radially outer surface, and a plurality of radially-arrayed substantially rectangular roller pockets with axially oriented sidewalls and endwalls. The cage also has features which provide enhanced flow of lubricant, present within the rotating machine, through the radially arrayed roller pockets during operation of the rotating machine. Rollers are retained within the pockets by a single projection on the sidewall of each pocket at the first face and another single projection on the other sidewall at the second face. Cage design in conjunction with inner and outer race design assures direction of lubricant flow to locations with greatest lubrication and cooling requirements. Because of its simple straight-surface design the cage of the invention is relatively simple to fabricate from polymers by polymer molding processes or from metals by fine flow blanking or ribbon forming and coining techniques.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to axial-thrust bearings and more particularly to high performance thrust roller bearings which provide enhanced removal of frictional heat and replenishment of a lubricant film by assuring lubricant flow through the bearings to other components of a rotating machine. 
     In automotive transmission units as well as in other high-speed rotary machines, lubricant circulation is the primary mechanism for dissipation of frictional heat. The rollers are aligned on the radii of the bearing, and the sidewalls of the pockets are offset but parallel to the radii. The rollers, being narrower than the pockets are slightly loose within the pockets, and while driving the cage during acceleration and being driven by the cage during deceleration, the rollers tend to contact the sidewalls at the outer end rather than along the full length of the roller. This results in almost point contact between the outer end of the rollers and rectangular roller pockets of the roller cage at the outer ends of the roller pockets and leads to increased local heat generation and wear of the cage and rollers. Apart from that, the sliding local contact between the rollers, the cage, and the races produces frictional heat and, in cases of inadequate lubricant flow, can generate temperatures sufficient to degrade seals, lubricants, and friction linings. This may result in constriction of fluid paths due to accretion of wear particles and lubricant breakdown products, accelerated wear of moving components due to further decrease of already inadequate lubricant flow, and increased rates of frictional heat generation. Since much of the lubrication of components mounted radially outboard of the thrust bearing relies on lubricant which must pass through the bearing, any factor which impedes such flow or degrades its effectiveness is potentially catastrophic to the life of the transmission. Moreover, there is a tendency for lubricant to follow the path of least resistance through the bearing, thereby contributing to lubricant starvation of other critical areas of the bearing. Thus, lubricant, in order to provide the maximum protection, must be directed away from paths of least resistance and into those parts of the bearing which carry the greatest load and which generate the greatest frictional heat effects. For applications requiring higher power density, higher rotational speeds, and increased roller loading, it is important to minimize or to completely avoid the above lubrication inadequacies. 
     The foregoing illustrates limitations known to exist in present high performance roller thrust bearings for use in rotating machines. Thus, 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 a roller cage for an axial-thrust bearing in a rotating machine, comprising a substantially flat annular body having a first face, a second face, a radially inner surface, and a radially outer surface; a plurality of radially-arrayed substantially rectangular roller pockets with axially oriented sidewalls and endwalls; and means for directing a flow of lubricant through the radially arrayed roller pockets during operation of the rotating machine. 
     The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic elevation sectional view showing the enhanced path of lubricant through a roller thrust bearing of the invention in a rotating machine; 
     FIG. 2 is a schematic partially sectional perspective view of a portion of a roller thrust bearing of the invention; 
     FIGS. 3a and 3b are schematic fragmentary perspective views of a roller cage of the invention from inner and outer vantage points, respectively; 
     FIG. 4 is a schematic transverse elevation sectional view through a roller and roller pocket, along line 4--4 of FIG. 3, illustrating inclined solid portions together with roller retention and axial pumping features of a preferred embodiment of the roller cage; 
     FIG. 5 is a fragmentary radial sectional view through a roller bearing of the invention at a midpoint of a solid portion between two roller pockets of the roller cage; 
     FIG. 6 is a fragmentary radial sectional view through a roller bearing of the invention at a midpoint of a roller pocket, without a roller, of the roller cage; 
     FIG. 7a. is a schematic elevation sectional view of a roller pocket in a roller cage with the molding tool in place; 
     FIG. 7b. is a schematic elevation sectional view of a roller pocket in a roller cage with the molding tool withdrawn from the pocket to illustrate the axial draw molding permitted by the invention; and 
     FIG. 8 is a fragmentary schematic sectional plan view of a roller and roller pocket, along line 8--8 of FIG. 7, illustrating further detail of the roller pocket form. 
    
    
     DETAILED DESCRIPTION 
     Briefly, the thrust bearing assembly 100 illustrated in FIGS. 1, 2, 5, and 6 consists of an annular outer race 20 with a flat radially projecting member and a cylindrical outer wall, an annular inner race 30 with a flat radially projecting member and a cylindrical inner wall, an annular roller cage 10, and cylindrical rollers 40. The roller cage 10 has an inner rail 12, an outer rail 11, and a plurality of substantially rectangular roller pockets 15. The size and number of pockets 15 and rollers 40 depends on the size and load capacity of the bearing 100. The roller diameters are sufficient to support the inner race 30 and outer race 20 clear of the cage 10 during operation. The clearance between the races and cage is sufficient to permit passage of a thin film of lubricant over and through the cage 10 to provide lubrication to the rollers 40 and the races 20, 30, and to remove frictional heat from the assembly. This lube flow may be driven solely by centrifugal force if the lubricant is supplied at the center of the device; however, in order to assure flow through other than paths of least resistance, this invention includes a roller cage with features for controlling and directing lubricant flow. Note that &#34;up&#34; and &#34;down&#34; are used herein only to describe directions with respect to the figures shown. They are not intended to represent absolute directions nor to indicate any required orientation of the bearing in its applications. 
     FIG. 1 shows a longitudinal section taken through a roller pocket of a roller thrust bearing 100 of the invention installed in a rotating machine, and FIG. 2 shows a partially sectional perspective view of the bearing 100. The bearing is shown with its outer race 20 supporting a rotating member &#34;R&#34; and resting on its inner race 30 on a stationary member &#34;S&#34; of the machine. The roller 40 supports the outer race 20 above the inner race 30 with sufficient clearance for the roller cage 10, supported by and supporting a film of lubricant between the cage and the races, to be free of both races. Lubricant flow &#34;L&#34; is downward between the inner wall of inner race 30 and the inner surface of the cage 10, under the inner rail 12 at the recesses 32 of the first face A (FIGS. 2 and 3), axially through the roller pocket 15 around the roller 40, over the outer rail 11 at the recesses 32 of the second face B and downward between the outer surface of the cage 10 and the cylindrical outer wall of the outer race 20. Preferably there is a slight axial taper of the inner and outer surfaces of the cage 10 to conform to a similar slight taper of the cylindrical inner and outer walls of the inner race and outer race, respectively. This taper increases radial pilot contact areas between the cage and races during radial runout to reduce stress and minimize cage-to-race pilot zone wear. Moreover, during transmission of radial runout load through the thrust bearing assembly, the matching tapers cause slight coning (or dishing) of the cage 10. This causes the inner and outer rails to ride in close proximity to the races. 
     Inner rail 12 and outer rail 11 have seal portions on opposite faces (second and first faces, respectively) of the cage 10 comprising labyrinthine dams 12&#39; and 11&#39;, respectively, which consist of a plurality of circumferential sharp-edged grooves, which, in radial cross-section, may have a crenellated appearance, as shown, a sawtooth form, or other flow-impeding cross section. These seal portions provide a resistance to radial flow of lubricant across them when the rotating machine is operating due to their close fit to the races 20, 30 and to their multiple grooves, which induce tangential flow of lubricant and discourage radial flow. This directs the flow axially between the axial portions of the inner race 30 and the outer race 20 and the inner and outer surfaces of the roller cage 10 to prevent lubricant starvation of critical areas of the bearing. This enhances sealing and promotes lube flow into the corners of the races 20, 30 between the cylindrical axially oriented walls and the radial annular surfaces of the races. Such enhanced lube flow through the more heavily stressed cage-to-race pilot contact zones helps to flush dirt and wear particles out of these critical areas while also extracting friction-generated heat from the bearing. 
     FIGS. 3a and 3b. show perspective views from the inner edge and the outer edge, respectively, of a portion of a roller cage 10, according to the invention, which is designed to impel, control, and direct lubricant flow. The cage 10 has a radially inner surface and a radially outer surface, an inner rail 12, an outer rail 11, radial roller pockets 15 with unique roller retainer vanes 18, and solid portions 13 between the pockets 15. The retainer vanes 18 have the dual purposes of retaining rollers 40 in the pockets 15 and of axially pumping lubricant, in the example shown in FIG. 2, from the inner race 30 to the outer race 20. The upper faces of the solid portions 13 of the cage are slightly inclined upward from the trailing unvaned edge of one pocket which is lower than the inner and outer rails 12, 11, to the trailing distal edge of the retainer vanes 18, of substantially equal height with the rails, of the trailing pocket. On the bottom faces of solid portions 13, the incline is also upward from the leading distal edge of the retainer vane 18 to the leading unvaned edge of the trailing pocket 15. Thus, even if the inner and outer races 30, 20 were resting directly on the rails, they would not be in contact with the solid portions 13. 
     The cage 10 also has notches 31 on its inner radial surface, and other notches 33 on its outer radial surface. These notches 31, 33 also have at least one inclined edge and intersect approximately with the centers of the recesses 32 ahead of the race/roller contact zones of the trailing pockets. The recesses 32 are substantially contiguous with the tilted surfaces of the solid portions 13 at opposite faces of the roller cage. The inclined edges of the notches 31 in FIG. 3a act as vanes to pump the lubricant axially downward as indicated by the lube flow path &#34;L&#34;, and the inclined edges of notches 33 in FIG. 3b also pump the lubricant axially downward as shown. In both cases, the pumping action requires rotation in the direction &#34;D&#34; shown. Thus, acting with the retainer vanes 18, the notches create a serpentine flow around the cage and through the roller pockets. Because of the directional design of the notches 31, lubricant arriving at the inner surface of the cage 10 is pumped axially downward and passes under the recesses 32 of the inner rail 12 at the first face. It flows radially outwardly to the solid portion 13 and into the trailing roller pockets 15. The lubricant in the pockets 15 is lifted by the retainer vanes 18 to the second face and exits over the unvaned trailing edges of the pockets via the solid portions 13. The upward tilt of the solid portions 13 toward the tip of the vanes provides a squeegee effect to the lubricant spreading it along the radial portion of the outer race 20 and causing it to flow over the recesses 32 of the outer rail 11, at the second face of the cage 10, to the outer surface of the cage 10, as seen in FIGS. 3a and 3b. The notches 33 then pump the lubricant axially down the outer surface of the cage to the gap between the outer wall of the outer race 20 and the radial portion of the inner race 30. If necessary, under certain operating conditions, the lubricant can be pumped to flow radially inwardly from the outer surface through the pockets to the inner surface, by forming the sweep of the recesses 32 and the inclination of the solid portions 13 in the appropriate direction with respect to the direction of rotation. This is determined by the operating speed of the bearing and whether the lubricant source lies outboard of the bearing and above or below the bearing. In either case, the enhanced lubricant flow through the bearing improves lubrication of outboard or inboard components, reduces friction and wear, and carries away frictional heat. 
     The invention is designed to assure that a flow of lubricant passes between the axial cylindrical wall of one race and the proximal radial surface of the cage impelled by slanted edges of notches on the cage face, the notches being aligned with the approximate centers of solid portions of the cage between the roller pockets. From there, it crosses a rail of the cage at a recess and flows against one solid portion into a trailing roller pocket 15 ahead of the roller 40. After the roller passes, the lubricant is impelled axially through the pocket 15 by the retainer vane and onto the trailing solid portion where it is propelled by the squeegee action of the trailing retainer vane 18 to cross a rail of the cage at a recess substantially contiguous with the solid portion 13. From there, it is pumped, by an inclined edge of a notch on a radial surface of the cage, between that surface and the axial cylindrical wall of the other race to exit the bearing. 
     FIG. 4 shows a cross-section through a roller 40 and roller pocket 15 in a preferred embodiment of the cage 10. In this embodiment, roller retention in the pocket 15 is provided by at least one retainer vane 18 at each face on diagonally opposite edges of the pocket 15. The retainer vanes 18 may or may not extend the full length of the pocket between the endwalls thereof; and, because of their shape, act as axial pumping vanes through the pocket 15 for lubricant flowing between the races and the cage 10 to further enhance flow. In addition, as alluded to above, the solid portions 13 between the roller pockets 15 are formed with a slight tilt &#34;T&#34; from the tip of the retainer vanes 18 back to the unvaned edge of the trailing pocket to assure a supply of lubricant to the roller in the trailing pocket and to the sharp edges of the retainer vanes. A low-angle tilt of the solid portions 13 has been found to be adequate for most applications. 
     As seen in FIGS. 2, 5, and 6, inner race 30 has an outwardly projecting edge 38 on its inner cylindrical wall and outer race 20 has a similar inwardly projecting edge 28 on its outer cylindrical wall. The radius of edge 38 of the inner race 30 is slightly larger than the inner radius of the roller cage 10, so that it snaps in place when the cage 10 is forced over it. Similarly, the radius of edge 28 of the outer race 20 is slightly less than the outer radius of the cage 10 to also snap in place when forced over the cage. The inner edge of the cage has a slight radius on one face, and the outer edge of the cage has a slight radius on the opposite face, to permit this assembly and to provide a near sharp corner retention of the cage within the races once the races are snapped in place. This one-way snap fit simplifies handling in that it eliminates the danger of disorientation of the cage 10 within the races 20, 30 when the cage and rollers are assembled within the races. The single face radii and opposed sharp edges at the inner and outer surfaces of the cage provide both tactile and visual indications of the cage orientation. This is important; because the pumping action of the cages is specific to the direction of rotation. The necessity for proper orientation is well recognized, and one need only refer to FIG. 1 and consider the flow restriction that would result if the bearing assembly were turned upside-down. 
     A method and tooling for molding the cage 10 with the pockets 15, the retainer vanes 18, and the tilted solid portions 13 between the pockets is shown in FIGS. 7a and 7b. Here, the core pins 60, 80 are seen to be reverse images of each other such that they fit together seamlessly and define pockets 15 with laterally reversed features. This provides the sharp edged retainer vanes 18, the straight sidewalls of the pockets, and the tilted solid portions 13 resulting in the faceted first and second faces of the cage 10. The annular form of the cage is provided by the mold body 70, 90, shown only in FIG. 7b, from which the core pins are axially extended and withdrawn to define the pockets. The cavity of the annular mold body is made with a top member 70 and a bottom member 90 both of which have tilted surfaces between the core pins 60, 80 to match with those of the core pins and to blend smoothly to the sharp edges of the retainer vanes. The axial-draw tooling used with this design permits molding with stronger high-temperature polymers than can be used with radial draw tooling, since there is no interference between the tool and the retainer vanes during withdrawal of the tool from the mold. 
     FIG. 8 illustrates the slightly trapezoidal shape of the roller pockets 15, which is preferred in order to provide line contact between the rollers 40 and the cage 10 at the leading edges of the pockets 15. This reduces the uneven pressure and wear between the rollers and the roller pockets of the cage caused by a purely rectangular roller pocket shape. With rectangular pockets, because of the clearance of the pocket 15 around the roller 40; upon acceleration, the rollers tend to drive the pocket sidewalls at their outer ends, as indicated by the divergence between the roller centerline C/L r  and the pocket centerline C/L p , due to the offset of the sidewalls of the pockets 15 from the radii of the cage 10. During deceleration, the pocket sidewalls of the cage 10 also tend to drive the rollers at their outer ends, in which case, the roller centerline would lag the pocket centerline (not illustrated). Thus, both conditions lead to potentially damaging non-uniform loading and stress concentrations within the bearing assembly. This condition is described in U.S. Pat. No. 4,077,683, issued Mar. 7, 1978 and commonly assigned herewith. 
     The roller bearing made according to the invention provides the advantage of always having a film of lubricant flowing through the roller pockets and over the solid portions of the cage even under overload conditions which deform the races sufficiently to cause them to ride against the inner and/or outer rails of the roller cage. The provision of the notches on the inner and outer radial surfaces of the cage and the recesses on the inner and outer rails at the first and second faces of the cage, respectively, together with the retainer vanes, assures a continuously pumped flow of lubricant through the always open flow path over the cage rails and through the pockets.