WO2005071051A1

WO2005071051A1 - Grease lubricated rolling element bearing with oil film for initial lubrication and method of lubrication the bearing

Info

Publication number: WO2005071051A1
Application number: PCT/US2005/001205
Authority: WO
Inventors: Mark A. Joki
Original assignee: The Timken Company
Priority date: 2004-01-14
Filing date: 2005-01-13
Publication date: 2005-08-04

Abstract

A bearing assembly A for rotation about an axis x, where the assembly A comprises an outer race 2 about the axis x and has a pair of raceways 10 presented toward the axis x. An inner race formed of two cones 24 is located within the outer race 2. The cones 24 have a pair of raceways 32 presented away from the axis x. The raceways 10 encircle the raceways 32. Rolling elements 40 are positioned between and contacting the raceways 10 and 32. Prior to initial operation, a first lubricant 102 is added to the assembly A for initial operation. A second lubricant 100 is added to the assembly A for continuing operation. The second lubricant 102 is formulated with a thickening agent and is more viscous than the first lubricant 100 and releases a low viscosity oil into the assembly A during operation.

Description

GREASE LUBRICATED ROLLING ELEMENT BEARING WITH OIL FILM FOR INITIAL LUBRICATION AND METHOD OF LUBRICATION THE BEARING

Related Application This application derives and claims priority from United States provisional application 60/537,244 filed 14 January 2004. Technical Field This invention relates in general to bearings and more particularly to a lubricated bearing assembly and method of lubricating bearing assemblies. Background Art Grease is a common, but high viscosity, lubricant used in sealed bearing units. Most varieties of grease are typically formulated with a thickening agent so that they will bleed (i.e. release) a lower viscosity oil at a very slow rate to provide lubrication to the bearing over a long life. The grease is activated to release the oil by high temperature conditions, such as occurs during operation of a sealed bearing. However, upon initial operation of a sealed bearing unit relying upon a grease lubricant, there may be insufficient oil released from the grease to sufficiently lubricate the contacting surfaces of the rolling elements in the bearing. This results in excessive frictional torque and associated wear during initial operation. Brief Description of the Drawings Fig. 1 is a partial sectional view of a bearing assembly constructed in accordance with and embodying the present invention; Fig. 2 is a partial sectional view of a bearing assembly constructed in accordance with and embodying the present invention, and showing grease and oil within the bearing assembly. Best Modes for Carrying Out the Invention Referring now to the drawings, a sealed bearing assembly A (Fig. 1 ) is organized about an axis x of rotation. It includes an outer race 2 having a generally cylindrical external surface 4. The outer race 2 is hollow and generally tubular and has a pair of tapered raceways 10 which face inwardly toward the axis x of rotation and taper downwardly toward an intervening surface 12 located generally midway between the ends of the race 2. Actually, the outer race 2 constitutes a double cup of the type identified with double row tapered roller bearings. The raceways 10 lead out to end bores 14 which create annular extensions 16 beyond the raceways 10. The outer race 2 also has a bore 18, or port, which opens into the interior of the race 2 through the intervening surface 12, its axis y being perpendicular to the axis x of rotation. The bore 18 lies within the thickest portion of the outer race in the region between the two raceways 10. Indeed, the bore 18 opens outwardly through a spot surface 22 which is milled or otherwise machined perpendicular to the axis y of the bore 18. Of course, the axis y is not limited to being perpendicular to the axis x of rotation, and may intersect the axis x at an oblique angle to the axis x. In each such configuration, the bore 18 will be aligned with the y axis. The bearing assembly A also includes an inner race that revolves within the tubular outer race 2. Actually, the inner race takes the form of two cones 24, each of which is surrounded by a different raceway 10 of the outer race 2 (Fig. 2). Each cone 24 contains a bore 26 that at one end leads out to a back face 28 and at the other end to a front face 30. Indeed, the two cones 24 abut at their front faces 30 within the interior of the outer race 2, so the back faces 28 are presented outwardly at the ends of the bearing assembly A. On its outwardly presented surface, each cone 24 has a tapered raceway 32 which is presented opposite one of the raceways 10 of the outer race 2 and tapers in the same direction, that is, downwardly toward the mid-region of the outer race 2. At the large end of its raceway 32 each cone 24 has a thrust rib 34 which projects radially beyond the raceway 32 and extends axially out to the back face 28, which is in fact on the end of the trust rib 34. The thrust rib 34 revolves within the region of the outer race 2 that is circumscribed by one of the annular extensions 16 on the outer race 2. At is small end, the tapered raceway 32 leads out to a retaining rib 36 which projects radially slightly beyond that end of the raceway 32, and the front face 30 for the cone 24 exists on the end rib 36. The raceways 10 and 32 of the outer race 2 and the cones 24, respectively, are thus arranged in pairs, there being within each raceway 10 of the outer race 2 a corresponding raceway 32 on one of the cones 24. In addition to the outer race 2 and the two cones 24, the bearing assembly A has a complement of rolling elements in the form of tapered rolling elements 40 arranged in two rows, there being a separate row of rolling elements 40 between each pair of raceways 10 and 32. Within each row, the side faces of the rolling elements 40 bear against and roll along the two raceways 10 and 32 for that row, while the large end faces of the rolling elements 40 bear against the thrust rib 34 at the end of the raceway 32 for that row. The rolling elements 40 of the two rows are confined within cages 42 which distribute the rolling elements 40 uniformly in their respective rows and thereby maintain the proper spacing between the rolling elements 40. They also retain the rolling elements 40 around the cones 24 when the cones 24 are withdrawn from the outer race 2. The ends of the bearing assembly A are closed by bearing seals 44 which fit into the annular spaces between the extensions 16 on the outer race 2 and the thrust ribs 34 on the two cones 24 that form the inner race. Each seal 44 includes a metal seal case 45 which is pressed into the end bore 14 of one of the extensions 16 for the outer race 2, an elasotmeric sealing element 47, and a metal shield 49. The sealing element 47 is bonded to the seal case 45 and establishes a live or dynamic barrier along the cylindrical surface of the thrust rib 34 for the cone 24 at which it is located. Typically, after each seal 44 is fully assembled, with its sealing element 47 being bonded to the seal case 45, and the shield 49 being within the sealing element 47, the seal 44 is then press fitted into the bearing assembly A with the shield 49 being pressed over the thrust rib 34 and the case 45 being pressed into the end bore 14 in the annular extension 16 of the outer race 2. U.S. Patent No. 4,799,808 discloses a suitable seal. Typically, the sealing element 47 comprises outwardly directed sealing lips 51 that bear against the shield 49, such that pressure within the bearing assembly A can deflect the lips 51 away from the shield 49. Such a sealing element 47 allows liquids to leak out of the bearing assembly A during operation. This is known as "venting". The sealing element 47 is typically configured such that the degree of loss of lubricant from the assembly A due to venting is generally inversely proportional to the viscosity of the lubricant in the assembly. Hence, lower viscosity liquids, such as oils, in the bearing assembly A to leak out or otherwise escape through the sealing element 47 during the operation of the assembly, while high viscosity materials will tend not to leak out. Because of the venting characteristics of typical sealed bearings, grease is typically used as the primary lubricant in sealed bearings. The extended cone 24 carries a target wheel 52 that is aligned with a sensor 54 which fits within the bore 18 of the outer race 2. When the periphery of the target wheel 52 moves past the inner end of the sensor 54 by reason of rotation, the sensor 54 produces an electrical signal which has a frequency that reflects the angular velocity of the target wheel 52. Referring now to Figure 2, in the bearing assembly A, a highly viscous lubricant 100, which is preferably a grease, is injected around the tapered rolling elements 40 of the bearing assembly A to facilitate the continuous lubrication of the assembly during operation. Typically, the amount of grease 100 added will be 10% to 70%, and preferably about 40%, of the available open volume within the bearing assembly A. Open volume being that volume within the bearing assembly A that is not subsumed by any of the components of the bearing assembly A. However, the amount of grease 100 added to the assembly A can be less than 10% of open volume within the assembly or more than 70% of open volume within the assembly A, as may be required by specific applications. Preferably, the grease 100 will constitute a standard NLGI No. 2 grease, which typically comprises an ISO VG 150 mineral oil mixed with a thickening agent such as lithium soap. However, the grease 102 may be of any number of available varieties of grease that may be more suitable for specific applications. The grease 100 acts as a lubricant to the sealed bearing assembly A by bleeding out (releasing) oil which provides a low-friction film coating at the contact points of all the moving parts within the assembly A, including the interface between the tapered rolling elements 40 and the inner raceways 10 and between the tapered rolling elements 40 and the outer raceways 32. Prior to the release of the mineral oil during operation, the grease 100 has a kinematic viscosity at 40° C of approximately 430 - 490 cSt. In contrast, the mineral oil released by the grease 100 has a kinematic viscosity at 40° C of approximately 135-165 cSt, with an average kinematic viscosity at 40° C of 150 cSt. Because it has a lower viscosity than the grease 100, the oil released by the grease 100 is more easily distributed to the raceways 10 and 32, thereby more fully lubricating the raceways to reduce friction and wear within the bearing assembly A. The grease 100 may be added to the assembly A at any time during the assembly process or after assembly by injection through the bore 18. Preferably, the grease 100 is added to the assembly A by injecting the grease directly onto the tapered rolling elements 40 just prior to seating the seals 44 in place along opposing peripheries of the assembly. In addition to the lubricant (grease) 100, a lubricant 102 that has a lower viscosity than that of the lubricant 100 is also added to the bearing assembly A. The lubricant 102 is preferably an oil. This added oil 102 may sometimes be referred to as "free oil." Typically, the amount of oil 102 added will be 0.50% to 5%, and preferably about 2%, of the total weight of the grease 100 added to the bearing assembly A. However, the amount of oil 102 added to the assembly A can be less than 0.50% or more than 5% of the total weight of the grease 100 added to the bearing assembly A, as may be required by specific applications. Preferably, the oil 102 comprises a standard ISO VG 50 oil. However, the oil 102 may be of any number of available varieties of oil that may be more suitable for specific applications. Like the mineral oil that releases from the grease 100, the oil 102 is of substantially lower viscosity than the grease 100, has a kinematic viscosity at 40° C of approximately 45- 55 cSt, with an average kinematic viscosity at 40° C of 50 cSt. Significantly, the addition of the oil 102 enables more complete lubrication of the bearing assembly A during the assembly's initial operation, prior to the release of the mineral oil from the grease 100 that occurs as the assembly operates. Hence, the addition of the oil 102 reduces internal friction among the internal moving parts of the bearing assembly A during the period of initial operation when the grease 102 has not yet released sufficient mineral oil to fully lubricate the assembly. The oil 102 may be added to the bearing assembly A at any time during the assembly process. However, because of its low viscosity, the oil 102 is preferably added to the assembly A after all assembly steps are completed with the exception of placing the sensor 54 into the bore 18. (See Fig. 2). In this way, the oil 102 can be injected by an injector 104 into the bearing assembly A through the bore 18, and the sensor 54 can then be fitted in the bore 18 to hold the oil 102 within the assembly A. Even more preferably, the oil 102 is injected through the bore 18 and directly onto the tapered rolling elements 40 and the raceways 10 and 32. Indeed, this enables the most effective initial distribution of the oil 102 throughout the most critical moving parts in the assembly. Of course, the injector 104 is shown only by way of example. In fact, the oil 102 need not be injected into the assembly A only by the disclosed injector 104, but may be placed in the bearing assembly A via a multitude of devices, such as, for example, tubes, spray nozzles, and troughs. The sealed bearing assembly A may be coupled to a road wheel and to the suspension system of an automotive vehicle, such as a steering knuckle or a trailing swing arm, thereby enabling the wheel to rotate about the axis x of rotation, which is, of course, the axis of the bearing assembly A. The bearing assembly A may be used with either driven or non-driven wheels, and insofar as the former is concerned, it further serves to couple a drive shaft of drive axle to the road wheel. The bearing assembly A may also be used with either front or rear wheels. Moreover, use of the bearing assembly A is not limited to road wheels, and is not even limited to wheels, but may be used in any application where rotation about an axis is desired. Variations on the basic construction and process are available. For example, the bearing assembly A need not be confined to the application of motor vehicles, but may be utilized wherever one member rotates relative to another member. Moreover, the outer race 2 may rotate and the two cones 24 that form the inner race may remain fixed or both the outer race 2 and both cones 24 that form the inner race may rotate at different angular velocities. Also, the bearing need not be a tapered roller bearing, but can be another type of antifriction bearing, such as a cylindrical roller bearing or a spherical roller bearing or even an angular contact ball bearing. In addition, the present invention is not limited to double row bearings, but may be used in conjunction with all forms of sealed bearings, including single row bearings and multi-row bearings. This invention may also be used in bearing assemblies that do not exhibit venting. The seals 44 may be formed of any variety of materials and shapes, so long as they minimize the exposure of the internal portion of the bearing assembly A to outside contaminants. Likewise, the sealing elements 47 may be formed of any variety of materials so long as the sealing element 47 is capable of forming a seal within the seal 44. The seal case 45 and the shield 49 may also be formed of a variety of materials, including but not limited to various metals, plastics and ceramics, so long as the case 45 and shield 49 provide the structural integrity and durability required of the specific bearing application. The present invention does not require the inclusion of the sensor 54. Further, the sensor 54 need not be located in the bore 18, but may be positioned in another bore in the assembly, so long as the sensor can be properly aligned with the target wheel 52. Similarly, the present invention does not require the inclusion of the target wheel 52, and the target wheel 52 need not be located in the position depicted in Fig. 1 , but may be positioned in another location within the assembly A, so long as the wheel 52 can be properly aligned with the sensor 54. Moreover, the bore 18 may remain open or may be closed with a plug. Furthermore, more than two lubricants may be used in the bearing assembly, or alternately, lubricants other than grease 100 and oil 102 may be used for lubrication, so long as at least one of lubricants offers sufficient lubrication for initial operation. The grease 100 and the oil 102 may be added to the bearing assembly A through any opening in the assembly. Further, one or more ports may be formed in the assembly that can be used for the injection of lubricants into the assembly, where the ports may or may not have other functions as well. Additionally, the dimensions of the bearing assembly A can vary significantly, including, but not limited to, widening or thinning of each of the components together or relative to one another, so long as the general operation of the apparatus is not defeated. Finally, each of the components of the invention can be manufactured from a variety of materials, including, but not limited to, plastics and metals, so long as the apparatus maintains the same functionality and the necessary structural integrity. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

Claims 1. A bearing assembly for accommodating rotation about an axis, said bearing assembly comprising: a. an outer race about the axis, the outer race having a raceway presented toward the axis; b. an inner race located within the outer race, the inner race having a raceway presented away from the axis and toward the raceway of the outer race; c. a rolling element positioned between and contacting the raceways of the inner and outer races; d. a first lubricant within the bearing assembly for initial operation of the assembly; e. a second lubricant within the bearing assembly for continuing operation of the assembly, the second lubricant being more viscous than the first lubricant; and f. a seal for isolating the interior of the bearing assembly from external contaminants.

2. The bearing assembly of Claim 1 , wherein the first lubricant is applied to the rolling element prior to initial operation of the bearing assembly.

3. The bearing assembly of Claim 1 , wherein the seal is configured to allow for limited external venting of the assembly and associated loss of lubricant from within the assembly, the degree of loss of lubricant being generally inversely proportional to the viscosity of the lubricant in the assembly.

4. The bearing assembly of Claim 1 , wherein the amount of first lubricant in the assembly is less than five percent by weight of the amount of the second lubricant in the assembly.

5. The bearing assembly of Claim 1 , wherein the first lubricant comprises an oil.

6. The bearing assembly of Claim 5, wherein the oil has a kinematic viscosity at 40° C of less than or equal to 75 cSt.

7. The bearing assembly of Claim 1 , wherein the second lubricant comprises a grease.

8. The bearing assembly of Claim 7, wherein the grease has a kinematic viscosity at 40° C greater than or equal to 250 cSt.

9. The bearing assembly of Claim 1 , further comprising a port through which lubricants may be injected into the assembly.

10. The bearing assembly of Claim 9, wherein the first lubricant is injected into the assembly through the port after the second lubricant has been added to the assembly.

11. The bearing assembly of Claim 9, wherein the port is configured to accept a speed sensor for the assembly.

12. The bearing assembly of Claim 1 , wherein the outer race comprises two or more raceways, each of said two or more outer race raceways being presented toward the axis; the inner race comprises two or more raceways, each of said two or more inner race raceways being presented away from the axis; and each of said two or more outer race raceways encircles one of said two or more inner race raceways.

13. The bearing assembly of Claim 12, further comprising a port through which lubricants may be injected into the assembly, said port being configured to accept a speed sensor for the assembly.

14. The bearing assembly of Claim 13, wherein the first lubricant is injected into the assembly through the port after the second lubricant has been added to the assembly.

15. A bearing assembly for accommodating rotation about an axis, said bearing assembly comprising: a. an outer race about the axis, the outer race having a pair of raceways presented toward the axis; b. an inner race located within the outer race, the inner race having a pair of raceways presented away from the axis, one raceway of the outer race encircling one raceway of the inner race and the other raceway of the outer race encircling the other raceway of the inner race; c. rolling elements positioned between and contacting the raceways of the inner and outer races, a contact point being defined at the meeting of each rolling element and the raceways; d. a first lubricant within the bearing assembly for initial operation of the assembly; e. a second lubricant within the bearing assembly for continuing operation of the assembly, the second lubricant being more viscous than the first lubricant; and f. a seal for isolating the interior of the bearing assembly from external contaminants; wherein the assembly is configured such that lubricant applied within the assembly will be distributed along the raceways to the contact points during operation of the assembly, and the first lubricant is applied prior to initial operation of the bearing assembly at a location within the assembly to accomplish distribution of the first lubricant to the contact points.

16. The bearing assembly of Claim 15, wherein the seal is configured to allow for limited external venting of the assembly and associated loss of lubricant from within the assembly, the degree of loss of lubricant being inversely proportional to the viscosity of the lubricant in the assembly.

17. A method for lubricating a bearing assembly, the method comprising: a. forming a bearing assembly, the assembly comprising an outer race about an axis, the outer race having a raceway presented toward the axis; an inner race located within the outer race, the inner race having a raceway presented away from the axis, the raceway of the outer race encircling the raceway of the inner race; a rolling element positioned between and contacting the raceways of the inner and outer races; and a seal positioned between the first and second members, said seal being configured to isolate the interior of the bearing assembly from external contaminants; b. adding a first lubricant within the bearing assembly for initial operation of the assembly; and c. adding a second lubricant within the bearing assembly for continuing operation of the assembly, the second lubricant being more viscous than the first lubricant.

18. The method of Claim 17, wherein the first lubricant is applied to the rolling element prior to initial operation of the bearing assembly.

19. The method of Claim 17, wherein the assembly has a port through which lubricants may be injected into the assembly.

20. The method of Claim 19, wherein the first lubricant is injected into the assembly through the port after the second lubricant has been added to the assembly.

21. The method of Claim 19, wherein the port is configured to accept a speed sensor for the assembly.

22. A bearing assembly for accommodating rotation about an axis, said bearing assembly comprising: a. an outer race about the axis, the outer race having a raceway presented toward the axis; b. an inner race located within the outer race, the inner race having a raceway presented away from the axis and toward the raceway of the outer race; c. a rolling element positioned between and contacting the raceways of the inner and outer races; d. a first lubricant within the bearing assembly for initial operation of the assembly; e. a second lubricant within the bearing assembly for continuing operation of the assembly, the second lubricant comprising a thickening agent; and f. a seal for isolating the interior of the bearing assembly from external contaminants.

23. The bearing assembly of Claim 25, wherein the first lubricant is applied to the rolling element prior to initial operation of the bearing assembly.

24. The bearing assembly of Claim 25, wherein the seal is configured to allow for limited external venting of the assembly and associated loss of lubricant from within the assembly, the degree of loss of lubricant being generally inversely proportional to the viscosity of the lubricant in the assembly.

25. The bearing assembly of Claim 25, wherein the amount of first lubricant in the assembly is less than five percent by weight of the amount of the second lubricant in the assembly.

26. The bearing assembly of Claim 25, wherein the first lubricant comprises an oil.

27. The bearing assembly of Claim 25, wherein the second lubricant comprises a grease.

28. The bearing assembly of Claim 30, wherein the thickening agent comprises lithium soap.