Hub unit bearing

Abstract

To realize a structure capable of securing sufficient sealing performance by a side lip of a seal ring, regardless of inclination of a central axis of a hub to a central axis of an outer ring.SOLUTION: An inclination angle α to a virtual plane P orthogonal to a central axis of a hub 3, of a radial inner face 13a of a projecting portion 13 constituting an axial slide surface 11 is determined to be larger than an inclination angle of a radial outer face 13b of the projecting portion 13 to the virtual plane P over the whole periphery in a circumferential direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a hub unit bearing for rotatably supporting a wheel and a braking rotating body of an automobile with respect to a suspension device.

Background Art

[0002] A wheel and a braking rotating body of an automobile are rotatably supported with respect to a suspension device by a hub unit bearing. The hub unit bearing includes an outer ring having a double-row outer ring raceway on an inner peripheral surface, a hub having a double-row inner ring raceway on an outer peripheral surface and a rotation flange protruding radially outward from a portion located axially outside the outer ring, and a plurality of rolling elements arranged so as to be rollable between the double-row outer ring raceway and the double-row inner ring raceway.

[0003] Note that the axial outside refers to the outside in the vehicle body width direction in a state where the hub unit bearing is assembled to an automobile, and conversely, the center side in the vehicle body width direction in a state where the hub unit bearing is assembled to an automobile is referred to as the axial inside.

[0004] The hub unit bearing further includes a seal ring that closes an opening on the axial outside of a rolling element installation space existing between the inner peripheral surface of the outer ring and the outer peripheral surface of the hub. Japanese Patent Application Laid-Open No. 2010-261598 (Patent Document 1) describes a seal ring having a plurality of seal lips whose tip portions are in sliding contact with the surface of the hub. Among the plurality of seal lips, the outermost radially seal lip is called a side lip, and its tip portion is in sliding contact with an axially sliding contact surface provided on a radially inner portion of an axially inner surface of the rotation flange.

[0005] As described in Japanese Patent Application Laid-Open No. 2017-180599 (Patent Document 2), a finishing process using a general grinding wheel (rotary grinding wheel) is performed on a portion of the outer peripheral surface of the hub where the tip portion of the seal lip is in sliding contact. When performing a finishing process on the outer peripheral surface of the hub using a general grinding wheel, concentric grinding marks are formed on the axially sliding contact surface in which concave portions and convex portions are alternately arranged in the radial direction.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-261598 [Patent Document 2] Japanese Patent Publication No. 2017-180599 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, when the moment load acting on the rotating flange changes due to changes in driving conditions such as road surface conditions and vehicle speed, the inclination angle of the hub's central axis relative to the outer ring's central axis also changes.

[0008] Figure 4 shows the portion of the hub unit bearing where the seal ring 104 is installed, specifically the portion located on the upper vertical side. When the central axis of the hub 101 is tilted counterclockwise with respect to the central axis of the outer ring 100, the axial sliding contact surface 103, located on the radially inner portion of the axial inner surface of the rotating flange 102 of the hub 101, moves axially outward and radially inward in the portion located on the upper vertical side, as indicated by arrow A in Figure 4. As a result, in the portion located on the upper vertical side, the clearance between the side lip 105 on the seal ring 104 and the axial sliding contact surface 103 becomes smaller, potentially reducing the sealing performance of the side lip 105.

[0009] In contrast, if the central axis of the hub 101 is tilted clockwise with respect to the central axis of the outer ring 100 as shown in Figure 4, the axial sliding surface 103 moves axially inward and radially outward in the portion located vertically upward, as indicated by arrow B. Therefore, the interference fit between the side lip 105 and the axial sliding surface 103 increases in the portion located vertically upward. However, in the portion of the seal ring 104 that is located vertically downward, the axial sliding surface 103 moves axially outward and radially inward, which reduces the interference fit between the side lip 105 and the axial sliding surface 103, potentially reducing the sealing performance of the side lip 105.

[0010] In view of the circumstances described above, the present invention aims to realize a hub unit bearing structure that can ensure sufficient sealing performance through the side lip of the seal ring, regardless of the inclination of the hub's central axis relative to the central axis of the outer ring. [Means for solving the problem]

[0011] A hub unit bearing according to one aspect of the present invention comprises an outer ring, a hub, a plurality of rolling elements, and a seal ring.

[0012] The outer ring has a double row of outer ring raceways on its inner circumferential surface.

[0013] The hub has a double row of inner ring raceways and a rotating flange.

[0014] The aforementioned double-row inner raceway is provided on the outer surface of the hub.

[0015] The rotating flange has an axial sliding contact surface on the radially inner portion of its axially inner surface, and protrudes radially outward.

[0016] The plurality of rolling elements are arranged to be able to roll freely between the double row of outer ring raceways and the double row of inner ring raceways.

[0017] The seal ring has a side lip whose tip is in sliding contact with the axial sliding contact surface.

[0018] Each of the axial sliding contact surfaces has a texture formed by alternately arranging concave portions and convex portions extending in the circumferential direction in the radial direction.

[0019] Particularly, in the hub unit bearing according to one aspect of the present invention, over the entire circumference in the circumferential direction, the inclination angle of the radially inner surface of the convex portion with respect to the virtual plane orthogonal to the central axis of the hub is larger than the inclination angle of the radially outer surface of the convex portion with respect to the virtual plane.

[0020] In the hub unit bearing according to one aspect of the present invention, the inclination angle of the radially inner surface of the convex portion with respect to the virtual plane can be less than 5 times the inclination angle of the radially outer surface of the convex portion with respect to the virtual plane, preferably greater than 1.5 times and less than 3 times.

Advantages of the Invention

[0021] According to the hub unit bearing of one aspect of the present invention, regardless of the inclination of the central axis of the hub with respect to the central axis of the outer ring, the sealing performance by the side lip of the seal ring can be sufficiently ensured.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a cross-sectional view showing a hub unit bearing according to an example of an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of part X in FIG. 1. [Figure 3] FIG. 3 is an enlarged view showing part Y in FIG. 2 with the axial direction exaggerated. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a main part for explaining problems caused by a change in the inclination angle of the central axis of the hub with respect to the central axis of the outer ring.

Embodiments for Carrying Out the Invention

[0023] Figures 1 to 3 show an example of an embodiment of the present invention. The hub unit bearing 1 in this example comprises an outer ring 2, a hub 3, a plurality of rolling elements 4, and a seal ring 5. The hub unit bearing 1 in this example has a structure for a driven wheel and uses balls as the rolling elements 4.

[0024] In the following explanation, with respect to the hub unit bearing 1, the axial, radial, and circumferential directions refer to the axial, radial, and circumferential directions of the outer ring 2 unless otherwise specified. When there is no inclination of the central axis of the hub 3 with respect to the central axis of the outer ring 2, the axial, radial, and circumferential directions of the outer ring 2 coincide with the axial, radial, and circumferential directions of the hub 3. Furthermore, the axial outer side refers to the outer side in the width direction of the vehicle body when the hub unit bearing 1 is assembled to the vehicle, and the axial inner side refers to the inner side in the width direction of the vehicle body when the hub unit bearing 1 is assembled to the vehicle.

[0025] The outer ring 2 is made of a hard metal such as medium carbon steel. The outer ring 2 has double rows of outer ring raceways 6 on its inner circumferential surface and a stationary flange 7 projecting radially outward in the axial middle section. The stationary flange 7 has support holes 8 that penetrate axially at multiple locations in the circumferential direction in the radial middle section.

[0026] In this example, the support hole 8 is made up of a threaded hole. The outer ring 2 is supported and fixed to the suspension system by screwing support bolts, which are inserted through holes provided in the knuckle of the suspension system, into the support holes 8 of the stationary flange 7 from the axial inside, and does not rotate even when the wheel rotates.

[0027] The hub 3 comprises a double row of inner ring raceways 9 and a rotating flange 10, and is positioned coaxially with the outer ring 2 on the radially inner side of the outer ring 2.

[0028] The double-row inner ring track 9 is provided on the outer surface of the hub 3.

[0029] The rotating flange 10 is provided on the hub 3 so as to protrude radially outward from the portion located axially outward from the axially outward end of the outer ring 2. The rotating flange 10 has an axial sliding contact surface 11 on the radially inward portion of its axially inward surface.

[0030] Each axial sliding surface 11 has grooves 37 formed by alternating recesses 12 and protrusions 13 in the radial direction, each extending in the circumferential direction and having a substantially triangular cross-sectional shape. The grooves 37 are formed in a logarithmic spiral pattern.

[0031] Furthermore, in at least a portion of the circumferential direction, the inclination angle α of the radially inner surface 13a of the convex portion 13 with respect to a virtual plane P perpendicular to the central axis O of the hub 3 is made greater than the inclination angle β of the radially outer surface 13b of the convex portion 13 with respect to the virtual plane P (α > β). As a result, the vertex T of each convex portion 13 is located radially inward from the radially central position of the convex portion 13. In this example, the inclination angle α of the radially inner surface 13a is made greater than the inclination angle β of the radially outer surface 13b of the convex portion 13 with respect to the virtual plane P, over the entire circumference.

[0032] The inclination angle α of the radially inner surface 13a can be greater than the inclination angle β of the radially outer surface 13b, and less than 5 times (β < α < 5β), preferably greater than 1.5 times the inclination angle β of the radially outer surface 13b, and less than 3 times (1.5β < α < 3β). If the inclination angle α of the radially inner surface 13a is greater than 5 times the inclination angle β of the radially outer surface 13b, the radial length of the radially outer surface 13b may become unnecessarily long.

[0033] The inclination angle α of the radial inner surface 13a is not particularly limited, but can be 0.01 degrees or more and 0.31 degrees or less, preferably 0.015 degrees or more and 0.25 degrees or less, and more preferably 0.02 degrees or more and 0.15 degrees or less.

[0034] In this example, the inclination angle α of the radial inner surface 13a is set to approximately twice the inclination angle β of the radial outer surface 13b. Note that Figure 3 exaggerates the grooves 37 by increasing the axial magnification by approximately 30 times compared to the radial magnification.

[0035] The hub 3 has a concave curved surface 14 with an arc-shaped cross-section on the portion of its outer circumferential surface adjacent to the axially inward side of the axial sliding surface 11, and a cylindrical radial sliding surface 15 on the portion of its outer circumferential surface adjacent to the axially inward side of the concave curved surface 14. In other words, the axial sliding surface 11, the concave curved surface 14, and the radial sliding surface 15 constitute a sealing sliding surface 16 that slides against the sealing lip of the seal ring 5, namely the side lip 25, radial lip 26, and grease lip 27.

[0036] The seal sliding surface 16, including the axial sliding surface 11, is composed of a ground surface that has been ground using an abrasive wheel. That is, when manufacturing the hub wheel 21 that constitutes the hub 3, the portion of the intermediate material obtained by forging a metal material into which the seal sliding surface 16 is to be formed is subjected to heat treatment such as high-frequency induction hardening to form a hardened layer, and then the portion is ground using a full-size abrasive wheel to form the seal sliding surface 16.

[0037] In this particular example, after grinding with a full-form grinding wheel, additional processing such as laser processing, coining, or etching is performed on the portion where the axial sliding contact surface 11 is to be formed. This makes the inclination angle α of the radially inner surface 13a of the convex portion 13 constituting the axial sliding contact surface 11 greater than the inclination angle β of the radially outer surface 13b.

[0038] The axial height of the protrusions 13 constituting the axial sliding contact surface 11, i.e., the axial depth h of the recesses 12, is not particularly limited, but can be 0.5 μm or more and 3.2 μm or less, preferably 0.8 μm or more and 2.5 μm or less, and more preferably 1.0 μm or more and 2.5 μm or less.

[0039] The rotating flange 10 has mounting holes 17 that penetrate axially at multiple locations in the circumferential direction in the radial middle section. Studs 18 for connecting and fixing braking rotating bodies such as discs and drums, and wheels constituting wheels, to the rotating flange 10 are press-fitted and serrated into each of the mounting holes 17. In other words, in this example, the mounting holes 17 are cylindrical holes.

[0040] The braking rotating body and wheel are connected and fixed to the rotating flange 10 by inserting the pilot portion 19, which is provided at the axially outer end of the hub 3, through the central hole provided at the center of each, and inserting the studs 18 through the through holes provided at multiple locations in the circumferential direction in the radial middle of each, and then screwing hub nuts onto the tips of the studs 18.

[0041] The mounting holes for the rotating flange can also be made of threaded holes. In this case, the braking rotating body and the wheel are joined and fixed to the rotating flange by screwing hub bolts, which are inserted through holes in the braking rotating body and through holes in the wheel, into the mounting holes.

[0042] In this example, the hub 3 is formed by combining the inner ring 20 and the hub ring 21.

[0043] The inner ring 20 is made of a hard metal such as bearing steel. The inner ring 20 has an inner ring raceway 9 on its outer circumferential surface that is axially inward.

[0044] The hub wheel 21 is made of a hard metal such as medium carbon steel. The hub wheel 21 comprises an inner ring raceway 9 on the axial outer side, a rotating flange 10, and a pilot portion 19.

[0045] The hub wheel 21 has a small-diameter stepped portion 22 located axially inward from the inner ring raceway 9 on the axially outer side, which has a smaller outer diameter than the adjacent portion on the axially outer side, and into which the inner ring 20 is fitted. Furthermore, the hub wheel 21 has a stepped surface 23 facing axially inward at the axially outer end of the small-diameter stepped portion 22, and a crimped portion 24 that is bent radially outward from the axially inner end of the small-diameter stepped portion 22.

[0046] The hub 3 is constructed by fitting the inner ring 20 onto the small-diameter stepped portion 22 of the hub ring 21, and by clamping the inner ring 20 from both axial sides between the stepped surface 23 of the hub ring 21 and the crimping portion 24, thereby joining and fixing the inner ring 20 and the hub ring 21.

[0047] Furthermore, the hub ring and the inner ring can also be joined by screwing a nut onto the axially inward end of the hub ring that protrudes from the axially inward end of the inner ring.

[0048] In this example, since the hub unit bearing 1 is a hub unit bearing for the driven wheel, the hub 3 is constructed to be solid.

[0049] However, the hub unit bearing of the present invention can also be applied to a hub unit bearing for a drive wheel. In this case, the hub has a splined hole in its center that penetrates axially. The tip of a drive shaft, which is driven by an engine or electric motor, is spline-engaged into the splined hole. When the automobile is running, the hub is rotated by the drive shaft, thereby rotating the wheel and braking rotating body which are coupled and fixed to the rotating flange of the hub.

[0050] Multiple rolling elements 4 are arranged to roll freely between the double-row outer ring raceway 6 and the double-row inner ring raceway 9, each held by a cage 38. As a result, the hub 3 is rotatably supported radially inward of the outer ring 2.

[0051] The seal ring 5 has a side lip 25 whose tip is in sliding contact with the axial sliding surface 11. The seal ring 5 in this example further has a radial lip 26 whose tip is in sliding contact with a concave curved surface 14, and a grease lip 27 whose tip is in sliding contact with the radial sliding surface 15.

[0052] In this example, the seal ring 5 comprises a core metal 28 and a sealing material 29.

[0053] The core metal 28 is formed into an annular shape by bending a metal plate such as a mild steel plate. The core metal 28 has a fitting cylinder portion 30 that is fitted and fixed to the axially outer end of the outer ring 2 by interference fit, and a support plate portion 31 that is bent radially inward from the axially outer end of the fitting cylinder portion 30.

[0054] The sealing material 29 is made of an elastic material such as an elastomer like rubber and is bonded and fixed to the surface of the support plate portion 31 of the core metal 28 by vulcanization adhesive. The sealing material 29 has a base portion 32, as well as a side lip 25, a radial lip 26, and a grease lip 27. In Figure 2, the side lip 25, radial lip 26, and grease lip 27 are shown in their free state. In Figure 3, the side lip 25 is shown in a state where it has elastically deformed and is sliding against the axial sliding surface 11.

[0055] The base portion 32 covers the surface of the support plate portion 31, specifically the axial outer surface, the inner circumferential surface, and the radially inner end of the axial inner surface of the support plate portion 31.

[0056] The side lip 25 has its tip in sliding contact with the axial sliding surface 11 over its entire circumference. In this example, the side lip 25 extends from the portion of the base 32 that covers the radially intermediate portion of the axially outer surface of the support plate portion 31 in a direction that is both axially and radially outward.

[0057] The thickness of the tip of the side lip 25 is not particularly limited, but can be 0.2 mm or more and 0.8 mm or less, preferably 0.3 mm or more and 0.6 mm or less, and more preferably 0.35 mm or more and 0.45 mm or less.

[0058] The radial lip 26 has its tip in sliding contact with the concave curved surface 14 over its entire circumference. In this example, the radial lip 26 extends outward in the axial direction from the portion of the base 32 that covers the radially inner end of the support plate portion 31.

[0059] The grease slip 27 has its tip in sliding contact with the radial sliding surface 15 over its entire circumference. In this example, the grease slip 27 extends from the portion of the base 32 that covers the radially inner end of the support plate portion 31 in a direction that is both axially inward and radially inward.

[0060] Such a seal ring 5 exists between the inner circumferential surface of the outer ring 2 and the outer circumferential surface of the hub 3, and closes the axially outer opening of the rolling element installation space 33 where the rolling elements 4 are arranged. This prevents foreign matter such as mud and water from entering the rolling element installation space 33 through the axially outer opening, and prevents grease sealed in the rolling element installation space 33 from leaking into the outside space through the axially outer opening. In this example, grease is also filled in the space between the side lip 25 and the radial lip 26, and in the space between the radial lip 26 and the grease lip 27.

[0061] The hub unit bearing 1 in this example further includes a cover 34 that closes the axially inner opening of the rolling element mounting space 33. The cover 34 has a cylindrical portion 35 that is fitted and fixed to the axially inner end of the outer ring 2 by interference fit, and a bottom plate portion 36 that closes the axially inner end of the cylindrical portion 35. Such a cover 34 prevents foreign matter from entering the rolling element mounting space 33 through the axially inner opening of the rolling element mounting space 33, and prevents grease sealed in the rolling element mounting space 33 from leaking into the outside space through the axially inner opening of the rolling element mounting space 33. Alternatively, the axially inner opening of the rolling element mounting space can be closed with a combination seal ring instead of the cover 34.

[0062] In this example, in the hub unit bearing 1, macroscopically, that is, when considering the entire sliding contact area between the tip of the side lip 25 and the axial sliding contact surface 11, the contact pressure between the tip of the side lip 25 and the axial sliding contact surface 11 increases as it approaches the external space, that is, as it moves radially outward. On the other hand, microscopically, that is, when considering each individual protrusion 13, the apex T of the protrusion 13 is located radially inward from the radial center of the protrusion 13. Therefore, the peak of the contact pressure between the tip of the side lip 25 and the axial sliding contact surface 11 is located radially inward from the radial center of the protrusion 13.

[0063] According to the hub unit bearing 1 in this example, regardless of the inclination of the central axis of the hub 3 with respect to the central axis of the outer ring 2, sufficient sealing performance can be ensured by the side lip 25 of the seal ring 5.

[0064] In other words, in this example, the inclination angle α of the radially inner surface 13a of the convex portion 13 with respect to the virtual plane P is greater than the inclination angle β of the radially outer surface 13b of the convex portion 13 with respect to the virtual plane P (α>β) over the entire circumference. As a result, the central axis of the hub 3 is tilted with respect to the central axis of the outer ring 2, and at one position in the circumferential direction, when the axial sliding contact surface 11 moves axially outward and radially inward (in the direction indicated by arrow A in Figure 2), the tip of the side lip 25 is likely to catch on the radially inner surface 13a of the convex portion 13. When the tip of the side lip 25 catches on the radially inner surface 13a of the convex portion 13, the relative radially outward movement of the tip of the side lip 25 with respect to the axial sliding contact surface 11 is inhibited. Then, the base end of the side lip 25 undergoes elastic deformation, and the pressing force of the tip of the side lip 25 against the axial sliding contact surface 11 increases. As a result, it is possible to prevent the interference fit between the side lip 25 and the axial sliding surface 11 from becoming too small.

[0065] On the other hand, in the portion located radially opposite to the aforementioned circumferential position, the axial sliding surface 11 moves axially inward and radially outward (in the direction indicated by arrow B in Figure 2). Here, the inclination angle β of the radially outer surface 13b of the convex portion 13 with respect to the virtual plane P is smaller than the inclination angle α of the radially inner surface 13a of the convex portion 13 with respect to the virtual plane P (β < α). Therefore, even when the tip of the side lip 25 attempts to move radially inward relative to the axial sliding surface 11, the tip of the side lip 25 is less likely to catch on the radially outer surface 13b of the convex portion 13. In other words, the relative movement of the tip of the side lip 25 radially inward with respect to the axial sliding surface 11 can be made smooth, and the interference fit between the side lip 25 and the axial sliding surface 11 can be increased based on the axially inward movement of the axial sliding surface 11.

[0066] As described above, in the hub unit bearing 1 of this example, even if the inclination angle of the central axis of the hub 3 with respect to the central axis of the outer ring 2 changes due to changes in driving conditions such as road surface conditions and vehicle speed, sufficient interference fit between the side lip 25 and the axial sliding contact surface 11 can be secured around the entire circumference. In other words, sufficient sealing performance by the side lip 25 can be ensured.

[0067] The hub unit bearing 1 in this example has a uniform-diameter PCD type structure in which the pitch circle diameter of the rolling elements 4 in the axial inner row is equal to the pitch circle diameter of the rolling elements 4 in the axial outer row. However, the present invention can also be applied to a hub unit bearing of a different-diameter PCD type in which the pitch circle diameter of the rolling elements in the axial inner row is larger or smaller than the pitch circle diameter of the rolling elements in the axial outer row. Furthermore, although balls are used as rolling elements 4 in the hub unit bearing 1 in this example, tapered rollers can be used instead of balls. [Explanation of Symbols]

[0068] 1 Hub unit bearing 2 Outer ring 3 Hubs 4 Rolling elements 5 Seal ring 6 Outer ring track 7. Stationary flange 8 Support hole 9. Inner track 10 Rotating flanges 11 Axial sliding surface 12 recesses 13 Convex part 13a Radial inner surface 13b Radial outer surface 14. Concave curved surface 15 Radial sliding surface 16 Seal sliding contact surface 17 mounting holes 18 studs 19 Pilot Section 20 Inner circle 21 Hub Wheel 22 Small diameter stepped section 23 Step surface 24 Crimping part 25 Side Lip 26 Radial Lip 27 Grease Lip 28 Mandrel 29. Sealant 30 Fitting cylinder 31 Support plate part 32 Base 33 Rolling element installation space 34 Cover 35 Cylindrical section 36 Bottom plate part 37th line 38 Retainer 100 Outer ring 101 Hub 102 Rotating flange 103 Axial sliding surface 104 Seal ring 105 Side Lip

Claims

1. An outer ring having a double row of outer ring raceways on its inner circumference, A hub having a double row of inner ring raceways on its outer surface, and a rotating flange having an axial sliding contact surface on the radially inner portion of its axially inner surface, and projecting radially outward, A plurality of rolling elements are arranged to roll freely between the double-row outer ring raceway and the double-row inner ring raceway, A seal ring having a side lip that slides against the axial sliding surface at its tip, Equipped with, The aforementioned axial sliding surface has grooves in which recesses and protrusions extending in the circumferential direction are alternately arranged in the radial direction. Along the entire circumference, the inclination angle of the radially inner surface of the protrusion with respect to a virtual plane perpendicular to the central axis of the hub is greater than the inclination angle of the radially outer surface of the protrusion with respect to the virtual plane. Hub unit bearing.

2. The inclination angle of the radially inner surface of the protrusion with respect to the virtual plane is less than five times the inclination angle of the radially outer surface of the protrusion with respect to the virtual plane. The hub unit bearing according to claim 1.

3. The inclination angle of the radially inner surface of the protrusion with respect to the virtual plane is greater than 1.5 times and less than 3 times the inclination angle of the radially outer surface of the protrusion with respect to the virtual plane. The hub unit bearing according to claim 2.

Images