Compact integrated perimeter thrust bearing

A bearing for providing rotation of at least one intermediate part relative to a first part and a second part includes a first bearing race formed in the first part, the first bearing race having a raceway corresponding to a first diameter, and a second bearing race and a third bearing race formed in the at least one intermediate part, the second bearing race and third bearing race having a raceway corresponding to a second diameter, wherein the first diameter is different from the second diameter. Further, a fourth bearing race is formed in the second part, the fourth bearing race having a raceway corresponding to the first diameter. A first plurality of roller elements are arranged between the first raceway and the second raceway, and a second plurality of roller elements are arranged between the third raceway and the fourth raceway.

TECHNICAL FIELD

The present invention relates generally to bearings and, more particularly, to an integrated angular contact thrust bearing system.

BACKGROUND ART

Bearing assemblies are typically separate, independent assemblies that are mounted to components to be rotated.FIGS. 1A-1Cillustrate a perspective view, side view and cross-sectional view of a conventional thrust bearing10in the form of a duplex-pair bearing and includes, for example, an outer portion12having a first diameter, and an inner portion14having a second (smaller) diameter. The outer portion12may be coupled to a first object (e.g., a hub) while the inner portion14may be coupled to a second object (e.g., an axle spindle) to enable relative rotation between the first and second objects.

Arranged within the bearing assembly10is a first roller element set16and a second roller element set18, each roller element set16and18including a plurality of roller elements20circumferentially spaced apart from one another between the outer portion12and the inner portion14. Each roller element set may include a cage22for maintaining the circumferential spacing between adjacent roller elements20. Each roller element20of the roller element sets16and18ride on an outer race24(which is adjacent to the outer part12) and an inner race26(which is adjacent to the inner part14). The outer and inner races24and26are configured to correspond to a diameter of the roller elements20. A rolling surface of the inner race26may be axially offset28from a rolling surface of the outer race24to provide axial stiffness in one direction. By opposing the offset between the first roller element set16and the second roller element set18, axial stiffness in both directions can be achieved.

While conventional thrust bearings provide a satisfactory means for rotating one object relative to another while providing axial stiffness, in applications requiring compact profiles such bearings can become a limiting factor as they can occupy a significant volume. In the case of variable inclination continuous transvers stub (VICTS) antennas, each rotating component typically includes a separate bearing that requires mounting features and additional volume. This results in a less efficient antenna for a given volume.

SUMMARY OF INVENTION

A thrust bearing assembly in accordance with the present disclosure includes a plurality of raceways arranged in a stacked configuration. Raceways sharing a common roller element have different diameters from one another, thereby providing opposite contact angles for each raceway pair and roller element of the bearing of the stack. The resulting bearing occupies less volume than conventional bearing assemblies and therefore is advantageous in applications that are space-limited.

The bearing system in accordance with the present disclosure can be used, for example, in Continuous Transverse Stub (CTS) and Variable Inclination Continuous Transverse Stub (VICTS) antenna arrays. Additionally, any rotating system requiring axial stiffness in both directions, as well as radial stiffness, with volume constraints will also benefit from the bearing system.

In accordance with one aspect of the invention, a bearing for providing rotation of at least one intermediate part relative to a first part and a second part includes: a first bearing race formed in the first part, the first bearing race having a raceway corresponding to a first diameter; a second bearing race and a third bearing race formed in the at least one intermediate part, the second bearing race and third bearing race having a raceway corresponding to a second diameter, wherein the first diameter is different from the second diameter; a fourth bearing race formed in the second part, the fourth bearing race having a raceway corresponding to the first diameter; a first plurality of roller elements arranged between the first raceway and the second raceway; and a second plurality of roller elements arranged between the third raceway and the fourth raceway.

In accordance with one aspect of the invention, a diameter of the first plurality of roller elements is an average of the first diameter and the second diameter.

In accordance with one aspect of the invention, a diameter of the second plurality of roller elements is an average of the first diameter and the second diameter.

In accordance with one aspect of the invention, at least one ofi) the first race and the first part are formed from the same material,ii) the second race, the third race and the at least one intermediate part are formed from the same material, oriii) the fourth race and the second part are formed from the same material.

In accordance with one aspect of the invention, at least one race is formed from at least one of aluminum, steel, titanium, ceramic or plastic.

In accordance with one aspect of the invention, the first plurality of roller elements and the second plurality of roller elements are formed from aluminum, steel, titanium, ceramic or plastic.

In accordance with one aspect of the invention, the bearing includes: a support structure arranged relative to the first part; and a biasing member arranged between the support structure and the first part, the biasing member urging the first part toward the second part to preload the first part, the at least one intermediate part and the second part.

In accordance with one aspect of the invention, the bearing includes an outer housing, wherein the first part, the at least one intermediate part and the second part are arranged between the base structure and the outer housing.

In accordance with one aspect of the invention, the biasing member comprises a spring.

In accordance with one aspect of the invention, the spring comprises a wave spring.

In accordance with one aspect of the invention, a difference between the first diameter and the second diameter is between four-thousandths of an inch and eight-thousandths of an inch.

In accordance with one aspect of the invention, the at least one intermediate part comprises a plurality of intermediate parts arranged in a stacked configuration between the first part and the second part, each of the plurality of intermediate parts including two raceways corresponding to either the first diameter or the second diameter, wherein raceways of adjacent parts correspond to different diameters.

In accordance with one aspect of the invention, an antenna includes at least one platter and a bearing as described herein, wherein the at least one platter is mechanically coupled to an intermediate part of the bearing.

In accordance with one aspect of the invention, the at least one platter comprises a plurality of platters, and the at least one intermediate part comprises a plurality of intermediate parts, each of the plurality of platters mechanically connected to a respective one of the plurality of intermediate parts.

In accordance with one aspect of the invention, a method of manufacturing a thrust bearing integral with an object to be rotated is provided, the object including a first part, at least one intermediate part, and a second part. The method includes: forming a first bearing race in the first part, the first bearing race having a raceway corresponding to a first diameter; forming a second bearing race and a third bearing race in the at least one intermediate part, the second bearing race and third bearing race having a raceway corresponding to a second diameter, wherein the first diameter is different from the second diameter; forming a fourth bearing race in the second part, the fourth bearing race having a raceway corresponding to the first diameter; arranging a first plurality of roller elements between the first raceway and the second raceway; and arranging a second plurality of roller elements between the third raceway and the fourth raceway.

DETAILED DESCRIPTION OF INVENTION

The bearing assembly in accordance with the present disclosure will be described in the context of an antenna array, such as a VICTS antenna array. The bearing assembly in accordance with the present disclosure, however, is applicable to any rotating system requiring a thrust bearing, where space is limited and/or where cost is a significant consideration.

Referring initially toFIGS. 2A-2D, illustrated are a perspective view, top view, side view and cross-sectional view of an exemplary VICTS antenna array50in which the thrust bearing in accordance with the present disclosure may be utilized. As best seen inFIG. 2D, the exemplary VICTS antenna array50includes a first (upper) plate52having a one-dimensional lattice of continuous radiating stubs52a, and a second (lower) plate54having one or more line sources emanating into a parallel-plate region formed and bounded between the first and second plates52and54. Mechanical rotation of the upper plate52relative to the lower plate54serves to vary the inclination of incident parallel-plate modes, launched at the line source(s), relative to the continuous transverse stubs52ain the upper plate52, and in doing so constructively excites a radiated planar phase-front whose angle relative to the mechanical normal of the array is a simple continuous function of the relative angle of (differential) mechanical rotation between the two plates. Common rotation of the two plates52and54in unison moves the phase-front in the orthogonal azimuth direction.

Accordingly, the radiating stub aperture of the VICTS antenna is comprised of a collection of identical, parallel, uniformly-spaced radiating stubs52aover its entire surface area. The stub aperture serves to couple energy from a parallel-plate region (formed between the upper-most conductive surface of the array network and the lower-most conductive surface of the radiating stub aperture structure).

In order provide relative rotation between each rotating component of the VICTS antenna50(e.g., between the first and second plates52and54), separate thrust bearing assemblies have been conventionally utilized. While such configuration provides satisfactory operation, the use of separate bearing assemblies tends to occupy a significant volume within the antenna array. As will be appreciated, in any mechanical design one of the most important requirements is the allowable volume for the designed object. Any reduction in the volume occupied by the object can be considered an improvement.

With continued reference toFIG. 2D, an integrated perimeter thrust bearing60in accordance with the present disclosure succeeds in reducing the overall volume (and complexity) by integrating the separate bearing assemblies into rotating components of the objects to be rotated, and by reducing the number of bearings required for multiple rotating components. For example, the integrated perimeter thrust bearing60in accordance with the present disclosure integrates bearing raceways into the rotating components, thus reducing required volume and producing a more compact system (e.g., by reducing the number of bearings). Further, alternating angular contact pairs can be integrated into the rotating component. Such alternating angular contact pairs produce opposite angular contact angles in the rotating member. Conventionally, a pair of angular contact bearings are required (with opposite contact angles—seeFIG. 1C) to realize stiffness in both axial directions for each rotating component, each pair of bearings being “grounded” (fixed) to a stationary surface. By realizing opposite angular contact angles in the rotating member, the need for a “pair” of bearings for each rotating component is eliminated thus producing a more compact system.

Such integration provides several advantages. For example, a separate bearing assembly and the features required to mount/house the bearings are eliminated, which can reduce the required radial volume. Further, by integrating a pair of angular contact bearings and sharing them between two rotating components, vertical volume is reduced.

For example, a VICTS antenna with four rotating components would require eight conventional angular contact bearings (or equivalently four duplex pairs). Using the integrated perimeter thrust bearing in accordance with the present disclosure, the number of required bearings is reduced to N+1 instead of N×2, where N=the number of rotating components.

With reference toFIGS. 3A and 3B, illustrated in cross-section is a bearing portion of the VICTS antenna50ofFIG. 2Dshowing in more detail the thrust bearing60in accordance with the present disclosure. The thrust bearing60includes a stacked arrangement of races62formed within rotating members, with roller elements64arranged between adjacent races62. The thrust bearing60in accordance with the present disclosure provides an alternating angular contact pair between rotating members, thereby providing axial stiffness in two opposing directions.FIGS. 3A and 3Billustrate the alternating angular contact pair arrangement, which is implemented via alternating raceway diameters and thrust angles (FIG. 3Bomits the roller elements64to more clearly show the alternating diameters and thrust angles).

With continued reference toFIGS. 3A and 3B, the exemplary bearing60includes a base66(e.g., a stationary base), and first bearing race62aformed in a first part50aof the VICTS antenna array50, the first bearing race having a raceway corresponding to a first diameter. The first bearing race62a, which may float relative to the base66, may not be a rotatable part of the bearing assembly. A second bearing race62band a third bearing race62care formed in an intermediate part50b(e.g., a first rotatable member) of the VICTS antenna array50, the second bearing race62band third bearing race62chaving a raceway corresponding to a second diameter, the second diameter being different from the first diameter. Preferably, a difference between the first diameter and the second diameter is between four-thousandths of an inch and eight-thousandths of an inch, although larger variations are contemplated. A fourth bearing race62dand a fifth bearing race62eare formed in another intermediate part50c(e.g., a second rotatable member) of the VICTS antenna array50, the fourth bearing race62dand fifth bearing race62ehaving a raceway corresponding to a first diameter.

The above alternating pattern can repeat for as many number of rotating members that are utilized in the system. In the exemplary embodiment shown inFIGS. 3A and 3B, there are a total of four different rotatable elements. Thus the system further includes a sixth bearing race62fand a seventh bearing race62gformed in another intermediate part50d(e.g., a third rotatable member), the sixth bearing race62fand seventh bearing race62ghaving a raceway corresponding to a second diameter, an eighth bearing race62hand a ninth bearing race62iformed in intermediate part50e(e.g., a fourth rotatable member), the eighth bearing race62hand ninth bearing race62ihaving a raceway corresponding to a first diameter, and finally a tenth bearing race62jformed in a housing (end)50fof the assembly, the tenth bearing race having a raceway corresponding to the second diameter. Roller elements64are arranged between race pairs. The housing50f, which may be a non-rotatable member, may be attached to the base66to enclose the bearing assembly. A diameter of the roller elements may be an average of the first diameter and the second diameter. Preferably, the roller elements are formed from steel (e.g., stainless steel), though other appropriate metallic, ceramic or other materials may be employed (e.g., aluminum, titanium or plastic).

Arranged between the base66and the first bearing race62ais a biasing member68, such as a wave spring. The biasing member68can apply an axial force to the bearing assembly thereby urging the first bearing race62atoward the housing50fand thus providing a desired pre-determined bearing preload.

When the components are assembled and preloaded the contact angle is realized, and thus so is the stiffness. As will be appreciated by one having ordinary skill in the art, the raceway diameters can be manipulated and any contact angle can be achieved until the required stiffness is met. Further, raceways sharing a common roller element may be offset from one another to enhance axial, radial, and moment stiffness.

While the exemplary bearing60shown inFIGS. 3A and 3Bhas a total of 10 races and five roller element sets, it should be appreciated that less races and roller elements can be used without departing from the scope of the invention. For example, in order to provide axial stiffness in two opposing directions, the stacked assembly should have at least two roller element sets and four races. Thus, the bearing60may include only a first race formed in a first part with a raceway corresponding to the first diameter, a second and third race formed in an intermediate part with raceways corresponding to the second diameter, and a third race formed in an outer part with a raceway corresponding to the first diameter. Further, a first plurality of roller elements may be arranged between the first and second races, and a second plurality of roller elements may be arranged between the third and fourth races.

Due to the change in diameter and/or offset between raceways that share a roller element64, different contact angles are achieved. For example, and with additional reference toFIG. 4, line70illustrates where the raceways contact the roller elements64(the contact angle). In order for the bearing to provide high axial, radial and moment stiffness in all directions, and be considered and angular contact bearing, opposing contact angles are realized. In the thrust bearing in accordance with the present disclosure, opposing contact angles are accomplished by varying the diameter of the “integrated” raceways to achieve the desired contact angle.

For applications with extreme temperature excursions material selection becomes more important. A majority of pre-assembled independent bearing assemblies use steel races that, when used with devices formed from material other than steel (e.g., aluminum), can result in a large coefficient of thermal expansion (CTE) mismatch. Such mismatch is undesirable, particularly in applications that are subjected to large temperature swings. Various methods have been used to overcome the CTE mismatch. For example, component material may be changed to match the CTE of the steel bearing. This can be costly due to large assemblies with mismatched materials.

Further, separate (non-integrated) bearing assemblies require hard mounting to the rotating components. Given the large CTE mismatch that exists between aluminum and steel, for example, (both frequently used for rotating components and bearing assemblies respectively) the aluminum rotating component can deform the bearing raceways and cause the bearing to lock or seize up preventing rotation at extreme cold or hot temperatures. The integrated perimeter thrust bearing assembly in accordance with the present disclosure eliminates CTE mismatch between the bearing assembly and the rotating component by integrating at least part of the bearing system into the rotating component (e.g., the bearing race may be integrated within a surface of the rotating component). Thus, the same material is used for both the component and the bearing and therefore a CTE mismatch does not exist.

For example, if the first rotatable member50bis formed from aluminum, then the race62bis also formed from aluminum (the race is formed in the rotatable member). Similarly, if the first rotatable member50bis formed from steel then the race62bmay also be formed from steel. The same applies for each race62and corresponding support structure of the bearing60.

Additionally, as the diameter of the rotating components increases, the tolerances become increasingly difficult to produce and maintain, particularly for preloaded bearings. To address the tolerance issue of large bearings, as noted above the bearing system in accordance with the present disclosure can utilize a biasing member68, such as a wave spring, which is much easier to manufacture than preloaded bearings (particularly at larger diameters). As is well known, a wave spring is a spring formed from pre-hardened flat wire in a process called “on-edge-coiling”, also known as “edge winding”. During this process, waves are added to the wire to give it a spring effect.

More specifically, instead of hard mounting the system to a stationary “ground” plate, the thrust bearing system can be mounted on a wave spring. This allows the bearing system to tolerate additional runout and therefore alleviates the ultra-tight machined raceway tolerances necessary to preload the bearing, thereby providing advantages in both manufacturing and cost.

Also, as the diameter of the rotating components increases, the cost of the bearing grows significantly. By integrating the raceways within the rotating components, the overall part count is reduced, and the need to manufacture two parts (the bearing and the rotating component) with approximately the same diameter is reduced to one rotating part with an integrated bearing raceway.

Another advantage of the integrated perimeter thrust bearing assembly in accordance with the present disclosure is that it can be easily serviced. More particularly, conventional bearing assemblies require a special fixture and/or special tools to disassemble and re-assemble the bearing, and such servicing is almost exclusively done by the bearing supplier. In contrast to the conventional bearing, since the preload is supplied by a biasing member (e.g., a wave spring), the integrated perimeter thrust bearing assembly can easily be dis-assembled, serviced, and re-assembled in any laboratory with no special tools or fixtures. This provides advantages in timing/scheduling as the bearing does not need to be returned to the supplier for any rework.