MX2007015299A - Thrust bearing - Google Patents

Abstract

A thrust bearing assembly includes an upper thrust bearing and a lower thrust bearing for use in an engine assembly of a vehicle and which, are preferably, identically configured. The upper and lower thrust bearings each include an arcuate bearing shell with a concave inner surface and a convex outer surface and each may be formed with a pair of axially spaced flanges extending radially outwardly of the bearing shells. The flanges may be formed as one piece with the bearing shell and the thickness of one of the flanges is greater than that of the other of the flanges. The thicker flanges are load bearing and preferably contoured, whereas the thinner flanges are not. The bearings are installed with the thick flange of each bearing matched radially opposite the thin flange of the companion bearing to minimize fatigue and failure normally attributed to repeated seating and unseating of the bearing assemblies having flanges of equal thickness caused by changing bending loads imparted by a shaft.

Description

PUSH BEARING BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a thrust bearing assembly as part of an engine assembly for use in a vehicle and a method of aligning a thrust bearing in the engine assembly.

DESCRIPTION OF THE RELATED ART The crankshafts are articulated in the engine blocks by a series of axially spaced motor bearings. Each motor bearing includes an upper bearing half seated in an arcuate notch of the block and a concomitant lower bearing half, held firmly against the upper half of a bearing by a bearing bearing cap bolted to the engine block. At least one of the motor bearings in the assembly is designed to absorb the axial thrust forces imported by the crankshaft during operation. The so-called thrust bearing differs from the other motor bearing in the sense that it has two axially spaced thrust flanges projecting radially outwards. The thrust bearing has opposing axially directed thrust faces which are seated on their rear sides against block bearing surfaces and splices associated lobes of the crankshaft, when necessary, to provide the thrust bearing. These thrust flanges typically have a uniform thickness and are often formed with grooves and oil contours to impart a hydrodynamic action of the oil film to the bearing. During the operation of the engine, the loads on the crankshaft tend to force it in axially opposite directions, explaining the aforementioned thrust loads imparted to the pushing flanges of the thrust bearing. As the thrust loads are applied in an axial direction, it will be appreciated that the forwardmost set of the upper and lower thrust flanges will be confronted by the crankshaft and will be firmly seated against the associated support surface of the block. It will be appreciated that the most forward assembly of the upper and lower flanges will be confronted by the crankshaft lobe and will be firmly seated against their associated support surfaces of the block. However, this reverse force also has the effect of unsetting the forwardmost set of thrust flanges. While the unsecured thrust flanges are reset the next time the axial thrust forces imported by the crankshaft change, this constant series of settlements and settlements has the damaging effect of repeatedly bending and thus subjecting the thrust bearing of the base to stress. the thrust flanges, which can lead to a premature failure of the thrust bearing. Additionally, repeated settling and settling may cause the thrust bearing to become misaligned, which may also result in unwanted stress and malfunction of the thrust bearings. It is an object of the present invention to minimize or eliminate the undesirable seating and unsetting of the thrust bearings and thus prolong the life of the thrust bearings.

BRIEF DESCRIPTION OF THE INVENTION AND ADVANTAGES The present invention provides a thrust bearing having an arch arched bearing part with a concave inner surface and a convex outer surface. The inner and outer surfaces extend arcuately between the opposite ends and extend axially between opposite edges. A pair of flanges is formed as a single piece with the domed bearing part and extends radially outwardly from the domed bearing part from the opposite edges thereof. The thickness of one of the flanges is greater than that of the other of the flanges. Such a thrust bearing is used in combination with another such thrust bearing and is oriented in such a way that the thin flange of a bearing is disposed radially opposite the thick flange of the complementary bearing to control the thrust loads and the forces of settling and unsetting on the thrust bearings.

When installed on an engine to articulate a crankshaft with the thick and thin flanges arranged in opposite directions, the thrust forces exerted by the crankshaft in an axial direction confront the thick flange of one of the bearings, causing it to sit firmly on the block. Also, the thrust forces exerted by the crankshaft in the opposite direction confront the thick flange of the other bearing, also causing it to sit firmly on the block. Once settled, it is very convenient to keep the bearings seated and to protect them against any forces, which would cause them to disengage. The present invention provides such protection. This invention has the advantage of notching the outer axial faces of the axially thin flanges inwards of the faces of the thick flanges and thus doing so, the crankshaft confronts only the thick flanges, avoiding contact with the thin flanges. This being so, this construction and this arrangement of the bearings insulate the bearings from any axial "unsetting" forces that may otherwise be imparted by the crankshaft to the thin flanges and cause the complementary bearings to change from this initial fully seated condition. Avoiding the repeated settling and settlement condition further isolates the bearings from bending forces which, over time, could lead to weakening or damage to the bearings.

The invention has the additional advantage of making it possible for the complementary bearings to be constructed identically for cost-saving manufacturing simplicity.

THE DRAWINGS These and other advantages of the present invention will be readily appreciated as it is better understood with reference to the following detailed description and the accompanying drawings, in which: Figure 1 is a perspective view of a bearing assembly of thrust that has a top thrust bearing and a lower thrust bearing; Figure 2 is a cross-sectional view of any one of the upper thrust bearing and the lower thrust bearing; Figure 3 is a cross-sectional view of the thrust bearing assembly shown assembled in a motor assembly; and Figure 4 is a cross-sectional view of one of the outer faces of the thrust bearing having contours.

DETAILED DESCRIPTION A thrust bearing assembly is generally shown with 10 in Figure 1. The thrust bearing assembly 10 includes a top thrust bearing 12 and a lower thrust bearing 14. A cross-sectional view of the lower thrust bearing 14 it is illustrated in Figure 2. It is to be appreciated that the upper and lower thrust bearings 12, 14 are substantially identical, as will be described later. Both upper and lower thrust bearings 12, 14 include a domed arched bearing part 16 with a concave inner surface 18 and a convex outer surface 20. The domed bearing part 16 extends between the first and second ends 22, 24, as shown in figure 1, and extends axially between opposite edges 26, 28. The pair of flanges, a thick flange 30 and a thin flange 32, extends radially outwardly from the domed bearing part 16 from the opposite edges. 26, 28 thereof. The flanges 30, 32 are formed as a part, or part, with the domed bearing part 16 of the same material. The material is formed and cut into desired lengths. The material is then folded to form the flanges 30, 32 and can then be bent into arcs. Alternatively, the flanges 30, 32 can be made separately from the domed bearing part 16 and mechanically joined thereto (3-piece construction), as is customary in the art and considered by the invention. Each of the upper and lower thrust bearings 12, 14 has the thick flange 30 and the thin flange 32 extending radially from the outer surface 20. Each of the flanges has an axial thickness 34., 35 associate. The thickness 34 of one of the flanges 30 is greater than the thickness 35 of the other flanges 32. When the bearings 12, 14 are disposed in the thrust bearing assembly 10, the first and second ends 22, 24 of the bearing upper and lower thrust 12, 14 are positioned substantially in abutment contact, with the first opposite end 22 of the upper thrust bearing 12 arranged in abutting contact with the first opposite end 22 of the lower thrust bearing 14, and the second opposite end 24 of the upper thrust bearing 12 disposed in abutting contact with the second end 24 of the lower thrust bearing 14. When so arranged, the thick flange 30 of the upper thrust bearing 12 is radially aligned or spliced in opposition to the thin flange 32 of the lower thrust bearing 14, as illustrated in FIGS. 1 and 3. Each of the thick flanges 30 and the thin flanges 32 has an inner face 36 and an outer face 38. L The outer face 38 may be contoured as is known in the art and as shown in Fig. 4. Preferably, the outer face 38 of the thick flange 30 is contoured, while the outer face 38 of the thin flange 32 is free of such contours. In addition to being contoured, the outer face 38 is preferably formed with a series of oil grooves 40. The oil grooves 40 channel a lubricant to and from the outer contoured surface 38 to develop a protective hydrodynamic oil film through of face 38 contoured during operation to reduce friction and wear. The outer faces 38 of the thin flange 32 may also include similar oil grooves to facilitate lubrication in the event of contact. Aligning the ends 22, 24, as disclosed above, results in the outer faces 38 of the upper and lower thrust bearings 12, 14 being deviated from one another by the thickness 34 of the thick flange 30. The outer face 38 of the thick flange 30 of the upper thrust bearing 12 is in a different plane than the outer face 38 of the thin flange 32 of the lower thrust bearing 14, as best shown in Figure 3. Since the faces external bearings 38 are in different planes, when a force is exerted in one direction on the upper thrust bearing 12, the lower thrust bearing 14 is not disengaged. This result is obtained because the thin flange 32 of the upper thrust bearing 12 is not in contact with the adjacent support surfaces to transmit the force. Therefore, once one of the thrust bearings 12, 14 is seated, it will not disengage due to a force in the opposite direction. Also, the thrust bearings 12, 14 have less wear and fatigue, because they are subjected to only one force in one of the directions. Once the upper and lower thrust bearings 12, 14 are properly seated; the opposite bearing is insulated from the force in the direction to unseat the bearing due to the thin flange 32. The outer faces 38 of the thick and thin flanges 30, 32 may also include a bearing material 42 disposed thereon.

The bearing material 42 can be chamfered to form the contours on the outer face 38. The bearing material 42 is relatively softer than the underlying base metal of the domed bearing part 16 and flanges 30, 32, which are typically made of steel. Copper or aluminum based bearing materials can typically be used in thrust bearing applications in the present invention, although the invention contemplates other bearing materials that also include polymer-based material. The bearing material 42 can be added to the material before bending the flanges 30, 32 or after the flanges 30, 32 have been bent. Preferably, the bearing material 42 is present only on the outer faces 38 of the thick flanges 30. If the material is present on both outer faces 38, then the bearing material 42 in the thin flange can be machined to reduce the thickness 35 of the thin flange 32 relative to the thick flange 30. Referring to Figure 3 , an engine assembly for use in a vehicle (not shown) is generally shown with the 44. The engine assembly has the thrust bearing assembly 10 incorporated therein. The upper and lower thrust bearings 12, 14 are preferably identical in shape, but arranged opposite one another in reverse orientation, in such a way that the contoured thick flange 30 of the upper thrust bearing 12 is arranged opposite the thin flange 32 of the lower thrust bearing 14. The thin flange 32 of the upper thrust bearing 12 is disposed oppositely to the thick flange 30 of the lower thrust bearing 14. The motor assembly 44 includes an upper support surface 46, a shaft 48 received within the upper support surface 46 and a lower support surface 50. The upper support surface 46 is preferably a motor block and the lower support surface 50 is preferably a bearing cap. The shaft 48 is preferably a crankshaft 48. The thrust bearing assembly 10 rotatably supports the shaft 48 between the upper thrust bearing 12 and the lower thrust bearing 14, when in splicing contact, as described above. An interstice 52 is defined between the thick and thin flanges 30, 32 of the upper and lower thrust bearings 12, 14, respectively. The interstice 52 of the upper thrust bearing 12 receives the upper support surface 46 and the gap 52 of the lower thrust bearing 14 receives the lower support surface 50. In the preferred embodiment, the shaft 48 is the crankshaft having front and rear lobes. rear 54, 56 adjacent to the bearing assembly 10. The terms "front" and "rear" are used to indicate opposite ends or direction of the crankshaft in relation to the front and rear sides of the engine, which may be arranged from the front side to the side rear in the vehicle, or transverse, as the case may be. The front lobe 54 is closer to the front side of the motor assembly 44 and the rear lobe 56 is closer to the rear side of the motor assembly 44. The thick flange 30 of the upper thrust bearing 12 preferably butts the rear lobe 56 of the shaft 48 and the thick flange 30 of the lower thrust bearing 14 preferably butts the forward lobe 54 of the shaft 48. Alternatively, the bearings 12, 14 can be reversed, such that the thick flange 30 of the upper thrust bearing 12 contacts the the leading lobe 54 and the thick flange 30 of the lower thrust bearing 14 contact the rear lobe 56. In the preferred embodiment, the upper and lower thrust bearings 12, 14 define a clearance 58 between the thin flange 32 and the upper and lower support surfaces 46, 50, respectively. The free space 58 is defined when the thick flange 30 abuts the respective upper and lower support surfaces 46., 50, when the upper and lower support surfaces 46, 50 are positioned in the respective interstices 52. The thick flange 30 has the thickness 34 greater than a sum of the thickness 35 of the thin flange 32 and the free space 58. The space free 58 allows the isolation of the upper and lower thrust bearings 12, 14, when the force is applied opposite to the thick flange 30 of each thrust bearing 12, 14 respectively. The thick flange 30 of the upper thrust bearing 12 is the load bearing surface for a forward force and the thick flange 30 of the lower thrust bearing 14 is the load bearing surface for a rear force. The thin flanges 32 do not receive the load and are therefore non-load bearing flanges. It should be appreciated that even thin flanges 32 can be omitted without departing from the present invention. When the forward force is applied to the shaft 48, the lower thrust bearing 14 does not receive that force due to the clearance 58 adjacent the thin flange 32 and therefore the thick flange 30 of the upper thrust bearing 12 receives it. Also, when the back force is applied to the shaft 48, the upper thrust bearing 12 does not receive that force due to the clearance 58 adjacent the thin flange 32 and therefore the thick flange 30 of the lower thrust bearing 14 receives it. This reduces the amount of wear and fatigue in the thrust bearing assembly 10 and prevents premature failure. This also ensures that the bearing assembly 10 remains properly seated. In operation, the upper thrust bearing 12 is positioned having the upper support surface 46 extending between the thick and thin flanges 30, 32. Preferably, the upper thrust bearing 12 is positioned with the thick flange 30 towards a rear side of the assembly. of motor 44 and the thin flange 32 towards a front side of the motor assembly 44. After the upper thrust bearing 12 has been positioned, the shaft 48 is positioned adjacent to the upper thrust bearing 12. The lower thrust bearing 14 it is then positioned having the lower support surface 50 extending between the thick and thin flanges 30, 32. Preferably, the lower thrust bearing 14 is positioned with the thick flange 30 towards the front side of the motor assembly 44 and the thin flange 32. towards the rear side of the motor assembly 44. The upper and lower thrust bearings 12, 14 are positioned, such that the flange Thick 30 of one is spliced radially in opposition to the thin flange 32 of the other. The lower support surface 50 is secured to the upper support surface 46 for positioning the lower thrust bearing 14 in abutment contact with the upper thrust bearing 12. Once secured, the thrust bearing assembly 10 rotatably supports the shaft 48. A rear force is then applied to the shaft 48 towards the rear side of the motor assembly 44 to seat the thick flange 30 of the lower thrust bearing 14 against the lower support surface 50. A forward force is then applied to the opposite direction to the shaft 48 towards the front side of the motor assembly 44 to seat the thick flange 30 of the upper thrust bearing 12 against the upper supporting surface 46. During the operation of the motor, these leading and trailing forces are constantly generated and absorbed. by the thrust bearing assembly 10. The thick flanges 30 of the upper and lower thrust bearings 12, 14 bear the load of this s forces and the clearance 58 surrounding the thin flanges 32 prevents the upper and lower thrust bearings 12, 14 from disengagement. Since the thrust bearing assembly 10 is not disengaged, bending and fatigue of the thrust bearings are reduced. bearings 12, 14, as described above.

Obviously, many modifications and variations of the present invention are possible in light of the teachings mentioned above. The invention may be practiced in a manner different from that specifically described within the scope of the appended claims.

Claims (37)

NOVELTY OF THE INVENTION CLAIMS

1. - A thrust bearing assembly comprising: an upper thrust bearing including an arched arching bearing part with a concave inner surface and a convex outer surface extending arcuately between a first and a second end and extending axially between opposite edges; a lower thrust bearing including a curved arched bearing part with a concave inner surface and a convex outer surface extending arcuately between a first and a second end and extending axially between opposite edges; each of said upper and lower thrust bearings having a thick radially extending flange of said said outer surface thereof from one of said edges; each of said upper and lower thrust bearings having a thin flange extending radially from said outer surface thereof of said other of said edges; and said thick flange having a thickness greater than said thin flange.

2. The thrust bearing assembly according to claim 1, further characterized in that each of said thick flanges is formed as a single piece with said respective domed bearing pieces of said upper and lower thrust bearings.

3. - The thrust bearing assembly according to claim 2, further characterized in that each of said thin flanges are formed as a single piece with said respective arcuate bearing pieces of said upper and lower thrust bearings.

4. The thrust bearing assembly according to claim 3, further characterized in that said first and said second ends of said upper and lower thrust bearings are substantially in splice contact.

5. The thrust bearing assembly according to claim 4, further characterized in that said first end of said upper thrust bearing is in abutting contact with said first end of said lower thrust bearing and said second end of said thrust bearing. The upper thrust bearing is in abutting contact with said second end of said lower thrust bearing, such that said thick flange of said upper thrust bearing is radially spliced in opposition to said thin flange of said lower thrust bearing.

6. - The thrust bearing assembly according to claim 5, further characterized in that each of said thick flanges and said thin flanges has an inner face and an outer face.

7. - The thrust bearing assembly according to claim 6, further characterized in that said outer face of said upper thrust bearing is axially offset from said outer face of said lower bearing, when in abutting contact thereof.

8. - The thrust bearing assembly according to claim 7, further characterized in that said outer faces are contoured.

9. - The thrust bearing assembly according to claim 8, further characterized in that said contoured outer face is further defined as oil grooves located on said outer faces of said thick flanges.

10. The thrust bearing assembly according to claim 7, further characterized in that it additionally comprises a bearing material disposed on said outer faces of at least one of said thin and thick flanges.

11. - The thrust bearing assembly according to claim 10, further characterized in that said bearing material is arranged on said outer faces of said thick flanges.

12. - The thrust bearing assembly according to claim 1, further characterized in that it additionally comprises a bearing material disposed on said inner surfaces of said upper and lower thrust bearings.

13. - An engine assembly for use in a vehicle, said assembly comprising: a top support surface; a tree received within said face of said upper support surface; a thrust bearing assembly that rotatably supports said shaft on said upper support surface; said thrust bearing assembly having an upper thrust bearing and a lower thrust bearing in splice contact; said upper thrust bearing including a curved arched bearing part with a concave inner surface and a convex outer surface extending arcuately between a first and a second end and extending axially between opposite edges; said lower thrust bearing including an arched arching bearing part with a concave inner surface and a convex outer surface extending arcuately between a first and a second end and extending between opposite edges; each of said upper and lower thrust bearings having a thick flange formed as a part therewith and extending radially from said outer surface thereof from said other of said edges; each of said upper and lower thrust bearings having a thin flange formed as a part therewith of a continuous material and extending radially from said outer surface thereof from said other of said edges; and said thick flange having a thickness greater than thin flange.

14.- The motor assembly in accordance with the claim 13, further characterized in that said upper and lower thrust bearings define a gap between said thick flange and said thin flange.

15. - The motor assembly according to claim 14, further characterized in that said first end of said upper thrust bearing is in abutting contact with said first end of said lower thrust bearing and said second end of said upper thrust bearing is in splicing contact with said second end of said lower thrust bearing, such that said thick flange of said upper thrust bearing is radially spliced in opposition to said thin flange of said lower thrust bearing.

16. - The motor assembly according to claim 15, further characterized in that said thick flange of said upper thrust bearing splices a rear lobe of said shaft and said thick flange of said lower thrust bearing splices a forward lobe of said shaft .

17. - The motor assembly according to claim 14, further characterized in that said upper thrust bearing defines a clearance between said thin flange and said upper support surface, when said thick flange abuts said upper support surface after that said upper support surface is positioned in said gap.

18.- The motor assembly in accordance with the claim 17, further characterized in that said thick flange is further defined as having a thickness greater than a sum of a thickness of said thin flange and said free space.

19. - The motor assembly according to claim 14, further characterized in that said lower thrust bearing defines a clearance between said thin flange and said lower support surface, when said thick flange abuts said lower support surface, after which said lower support surface is positioned in said gap.

20. - The motor assembly according to claim 19, further characterized in that said thick flange said is further defined as having a thickness greater than a sum of a thickness of said said thin flange and said free space.

21. - The motor assembly according to claim 13, further characterized in that each of said thick flanges and said thin flanges has axially an inner face and an outer face.

22. - The motor assembly according to claim 21, further characterized in that it additionally comprises a bearing material disposed on said outer faces of said thick flanges.

23. - The motor assembly according to claim 13, further characterized in that it additionally comprises a bearing material disposed on said inner surface of said upper and lower thrust bearing.

24. - The motor assembly according to claim 13, further characterized in that said upper support surface is further defined as a motor block.

25. The motor block assembly according to claim 24, further characterized in that said lower support surface is further defined as a bearing cap.

26. - The engine block assembly according to claim 25, further characterized in that said shaft is further defined as a crankshaft.

27. - A method of aligning a thrust bearing assembly in an engine assembly of a vehicle, the engine assembly including at least one upper support surface, a shaft received within the upper support surface, and a surface lower support, said method comprising: providing the thrust bearing assembly for rotatably supporting the shaft on the upper support surface, the thrust bearing assembly having an upper thrust bearing and a lower thrust bearing; provide the upper thrust bearing and the lower thrust bearing with a concave inner surface and a convex outer surface extending arcuately between opposite ends and extending axially between opposite edges, each of the upper and lower thrust bearings having a flange thicker radially extending from the outer surface thereof from one of the edges and a thin radially extending flange from the outer surface thereof from the other edge, the thick flange having a thickness greater than that of the thin flange; positioning the upper thrust bearing having the upper support surface extending between the thick and thin flanges; position the tree adjacent to the upper thrust bearing; positioning the lower thrust bearing having the lower support surface extending between the first and thin flanges; and securing the lower support surface to the upper support surface to position the lower thrust bearing in abutment contact with the upper thrust bearing.

28. - The method according to claim 27, further characterized in that the step of positioning the upper thrust bearing is further defined as the positioning of the upper thrust bearing with the thick flange towards a rear side of the motor assembly and the flange thin towards one front side of the motor assembly.

29. - The method according to claim 28, further characterized in that the step of positioning said lower thrust bearing is further defined as the positioning of the lower thrust bearing with the heavy flange towards the front side of the motor assembly and the flange thin towards the back side of the motor assembly.

30. - The method according to claim 29, further characterized in that it further includes the step of applying a force to the shaft toward the rear side of the motor assembly to seat the thick flange of the lower thrust bearing against the lower support surface.

31. - The method according to claim 30, further characterized in that it further includes the step of applying a force to the shaft toward the front side of the motor assembly to seat the thick flange of the upper thrust bearing against the upper support surface.

32. - A thrust bearing comprising: an arched arching bearing part having a concave inner surface and a convex outer surface extending arcuately between opposite ends and extending axially between opposite edges; a pair of flanges formed as a single piece with said domed bearing part extending radially outwardly of said bearing from said opposite edges thereof; each of said flanges having an associated axial thickness and said thickness of one of said flanges is greater than the other of said flanges; and said relatively thicker flange said having a contoured outer face and said relatively thinner flange having an outer face that is substantially free of contours.

33. - A method of aligning a thrust bearing assembly in an engine assembly of a vehicle, the engine assembly including at least one upper support surface, a shaft received within the upper support surface and a surface of lower support, said method comprising: providing the thrust bearing assembly for rotatably supporting the shaft on the upper support surface, the thrust bearing assembly having an upper thrust bearing and a lower thrust bearing; providing the upper thrust bearing and the lower thrust bearing with a concave inner surface and a convex outer surface extending arcuately between opposite ends and extending axially between opposite edges, each of the upper and lower thrust bearings having a flange which supports loads extending radially from the outer surface; positioning the upper thrust bearing adjacent to the upper support surface; position the tree adjacent to the upper thrust bearing; positioning the lower thrust bearing adjacent to the lower support surface; securing the lower support surface to the upper support surface to position the lower thrust bearing in abutment contact with the upper thrust bearing; and insulating each of the upper and lower thrust bearings of a force in opposite directions, such that the load-bearing flanges of each of the thrust bearings receive the force in one direction only to prevent disentangling the thrust bearing assembly.

34.- The method according to claim 33, further characterized in that the step of positioning the upper and lower thrust bearings is further defined as the positioning of the load bearing flange of the upper thrust bearing axially spaced from the flange of load support of the lower thrust bearing.

35. - The method according to claim 34, further characterized in that the step of providing the upper and lower thrust bearing further includes the step of providing each of the upper and lower thrust bearings having a non-load bearing flange that extends radially outwardly of the bearing from an opposite edge of the load-bearing flange. 36. - The method according to claim 35, further characterized in that the step of providing the upper and lower thrust bearings having the non-load bearing flange is further defined as the provision of the load bearing flange that has a thickness greater than that of the non-load bearing flange. 37. - A thrust bearing assembly, comprising: a top thrust bearing including an arched vault with a concave inner surface and a convex outer surface extending arcuately between a first and a second and extending axially between opposite edges: a lower thrust bearing including an arched arching bearing part with a concave inner surface and a convex outer surface extending arcuately between a first and a second end and extending axially between opposite edges; said upper thrust bearing including a flange extending radially from said outer surface of said upper thrust bearing adjacent one of said edges and having an axially outer thrust face spaced axially outward from a very axially outer face from said bearing of lower thrust; and said lower thrust bearing including a flange extending radially from said outer surface of said lower thrust bearing adjacent said one of said edges of said lower thrust bearing on an axially opposite side to said flange of said upper thrust bearing, and having an outer face axially of the thrust axially spaced out from a very axially outer face of said upper thrust bearing.