Wheel bearing device

Abstract

To provide a bearing device for a wheel which enables improvement of repletion of resin in injection molding of a retainer and can inhibit increase of bearing torque.SOLUTION: A bearing device 1 for a wheel includes: a resin retainer 7 which has an annulus part 7a formed into an annular shape and multiple column parts 7b which extends from the annulus part 7a in an axial direction and arranged at constant intervals in a circumferential direction and in which a pocket Pt having a curve surface 7c along an outer peripheral surface of a rolling element (8) is formed by the adjacent column parts 7b and the annulus part 7a and the rolling element (8) is retained in each pocket Pt. The column part 7b has: a root part 7f extending from the annulus part 7a in the axial direction; and a branch part 7b extending from the root part 7f in the axial direction. The branch part 7b is formed only at the outer diameter side of the root part 7f.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a wheel bearing device. [Background technology]

[0002] Conventionally, wheel bearing devices that rotatably support wheels in suspension systems for automobiles and the like have been known. In wheel bearing devices, an inner member including a hub ring is rotatably supported on an outer member via a plurality of rolling elements (here, balls). The plurality of balls are evenly distributed in the circumferential direction by a cage and are held in a state in which adjacent balls are prevented from contacting each other.

[0003] Among such wheel bearing devices, there are known ones that make it possible to extend the bearing life while eliminating the problem of insufficient cage strength by reducing the circumferential thickness of the column sections of the cage that separate adjacent balls and by forming cutouts in the column sections to increase the number of balls, as described in Patent Documents 1 and 2, for example.

[0004] In the cages described in Patent Documents 1 and 2, the circumferential thickness of the bar portions of the cage is reduced, and notches are formed in the portions where adjacent balls are closest to each other. In other words, there are no bar portions between adjacent balls at their closest points. This shortens the circumferential distance between the balls, thereby increasing the number of balls that can be installed in the cage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 0592839 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-180630 Summary of the Invention [Problem to be solved by the invention]

[0006] In the cages described in Patent Documents 1 and 2, the bar portion is bifurcated into two parts, one on the inner diameter side and one on the outer diameter side, by a notch. In Patent Document 1, as shown in FIG. 7(A), the axial length a1 of the bar portion on the inner diameter side, starting from the end of the annular portion on the axially opposite side of the bar portion, is approximately the same as the axial length b1 to the center position of the ball. In Patent Document 2, as shown in FIG. 7(B), the axial length a2 of the bar portion on the inner diameter side, starting from the end of the annular portion on the axially opposite side of the bar portion, is longer than the axial length b2 to the center position of the ball. This shape of the bar portion on the inner diameter side raises concerns about insufficient resin filling during injection molding of the cage because the resin does not reach the tip of the bar portion, which could result in unstable quality of the cage.

[0007] Furthermore, with the trend toward lower fuel consumption in vehicles in recent years, wheel bearing devices are also required to have lower torque. Improvements are needed for cages because shear resistance in the grease occurs between the cage and balls when the wheel bearing device rotates, leading to increased bearing torque.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a wheel bearing device that can improve the filling efficiency of resin during injection molding of a cage and can suppress an increase in bearing torque. [Means for solving the problem]

[0009] That is, a first invention is a wheel bearing device comprising: an outer member having a double-row outer raceway surface formed on its inner circumference; an inner member having a double-row inner raceway surface formed opposite to the double-row outer raceway surface; double-row rolling elements interposed between the raceway surfaces of the outer member and the inner member so as to be rollable; and a resin cage having an annular portion formed in an annular shape and a plurality of pillar portions extending axially from the annular portion at regular intervals in the circumferential direction, wherein adjacent pillar portions and the annular portion form pockets having curved surfaces that follow the outer peripheral surfaces of the rolling elements, and the rolling elements are held in the pockets, wherein the pillar portions have root portions extending axially from the annular portion and branch portions extending axially from the root portion, and the branch portions are formed only on the outer diameter side of the root portion.The inner diameter surface of the branch portion is located on the outer diameter side of the center position of the rolling element. This is what we have decided. [Effects of the Invention]

[0010] The present invention has the following effects.

[0011] That is, according to the first aspect of the present invention, the fillability of the resin into the column portion is improved and the shear resistance of the grease between the ball and the column portion is reduced, thereby improving the fillability of the resin during injection molding of the cage and suppressing an increase in bearing torque. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing the overall configuration of a wheel bearing device; [Figure 2] FIG. 4 is an enlarged cross-sectional view showing the configuration of the ball and the cage. [Figure 3] FIG. [Figure 4] FIG. 3 is a cross-sectional view showing the overall configuration of the cage. [Figure 5] FIG. 4 is an enlarged cross-sectional view showing the axial length of the inner diameter side end portion of the cage. [Figure 6] FIG. [Figure 7] FIG. 10 is an enlarged cross-sectional view showing the axial length of a column portion on the inner diameter side of a conventional cage. DETAILED DESCRIPTION OF THE INVENTION

[0013] A wheel bearing device 1, which is one embodiment of the wheel bearing device according to the present invention, will be described below with reference to FIGS.

[0014] As shown in FIG. 1, the wheel bearing device 1 rotatably supports a wheel in a suspension system of a vehicle such as an automobile. The wheel bearing device 1 includes an outer ring 2 as an outer member, a hub ring 3 as an inner member, an inner ring 4, two rolling rows of inner ball rows 5 and an outer ball row 6, an inner seal member 9 as a sealing member, and an outer seal member 10 as a sealing member. Here, in this specification, the "inner side" refers to the side of the wheel bearing device 1 that faces the vehicle body when the wheel bearing device 1 is mounted on the vehicle body, and the "outer side" refers to the side of the wheel when the wheel bearing device 1 is mounted on the vehicle body. In addition, the direction parallel to the rotation axis of the wheel bearing device 1 is referred to as the "axial direction," the direction perpendicular to the rotation axis of the wheel bearing device 1 is referred to as the "radial direction," and the direction along an arc centered on the rotation axis of the wheel bearing device 1 is referred to as the "circumferential direction." Additionally, the side away from the inside of the bearing along the rotation axis is referred to as the "axially outer side," and the side approaching the inside of the bearing along the rotation axis is referred to as the "axially inner side."

[0015] The outer ring 2 supports the hub ring 3 and the inner ring 4 via an inner ball row 5 and an outer ball row 6. The outer ring 2 is formed in a substantially cylindrical shape. An inner side opening 2a is formed at the inner side end of the outer ring 2, into which an inner side seal member 9 can be fitted. An outer side opening 2b is formed at the outer side end of the outer ring 2, into which an outer side seal member 10 can be fitted.

[0016] An inner-side outer raceway surface 2c and an outer-side outer raceway surface 2d are provided on the inner diameter surface of the outer ring 2. A vehicle body mounting flange 2e for mounting to a knuckle of a suspension system is integrally formed on the outer peripheral surface of the outer ring 2.

[0017] The hub ring 3 supports a vehicle wheel for free rotation. The hub ring 3 is formed in a cylindrical shape. At the inner end of the hub ring 3, a small diameter step 3a is formed on the outer circumferential surface, with a reduced diameter. At the outer end of the hub ring 3, a wheel mounting flange 3b for mounting a wheel is formed integrally. Hub bolts 3d are inserted into the wheel mounting flange 3b at positions evenly spaced around the circumference. The hub ring 3 is also arranged so that the outer inner raceway surface 3c faces the outer outer raceway surface 2d of the outer ring 2. An inner ring 4 is fitted into the small diameter step 3a of the hub ring 3.

[0018] The inner ring 4 applies preload to the inner ball row 5 and the outer ball row 6. An annular inner raceway 4a is formed in the circumferential direction on the outer peripheral surface of the inner ring 4. The inner ring 4 is fixed to the inner end of the hub ring 3 by crimping. In other words, the inner raceway 4a is formed by the inner ring 4 on the inner side of the hub ring 3. The inner ring 4 is positioned so that its inner raceway 4a faces the outer raceway 2c on the inner side of the outer ring 2.

[0019] In the inner ball row 5 and the outer ball row 6, a plurality of balls 8, which are rolling elements, are held in an annular shape by a resin cage 7. The inner ball row 5 is rollably interposed between the inner raceway surface 4a of the inner ring 4 and the inner-side outer raceway surface 2c of the outer ring 2. The outer ball row 6 is rollably interposed between the inner raceway surface 3c of the hub ring 3 and the outer-side outer raceway surface 2d of the outer ring 2.

[0020] The cage 7 holds the balls 8. The cage 7 is made of synthetic resins with excellent oil resistance, wear resistance, and lubricity, such as polyamide 46 (PA46), polyamide 66 (PA66), polyamide 9T (PA9T), polyether ether ketone (PEEK), polyphenylene sulfide (PPS), etc. Furthermore, the resin may contain glass fiber, carbon fiber, etc. as a reinforcing material.

[0021] As shown in Figure 2, the cage 7 has an annular ring portion 7a and multiple pillar portions 7b. The pillar portions 7b extend axially outward from the ring portion 7a. The pillar portions 7b are arranged at equal intervals along the circumferential direction of the ring portion 7a. Pockets Pt that independently hold balls 8 are formed in the cage 7 at equal intervals between adjacent pillar portions 7b (see Figure 3).

[0022] The balls 8 are formed of steel balls made of high carbon chromium bearing steel SUJ2, etc. The plurality of balls 8 are rotatably held in pockets Pt of the cage 7.

[0023] As shown in Figure 1, the inner seal member 9 seals the gap between the inner opening 2a of the outer ring 2 and the inner ring 4. The inner seal member 9 is, for example, a two-side lip type pack seal in which two seal lips come into contact. The inner seal member 9 includes a substantially cylindrical seal plate and a substantially cylindrical slinger.

[0024] The outer seal member 10 seals the gap between the outer opening 2b of the outer ring 2 and the hub ring 3. The outer seal member 10 has a core metal formed into a substantially cylindrical shape from a steel plate made of the same material as the seal plate, and multiple seal lips made of synthetic rubber such as NBR (acrylonitrile-butadiene rubber) are fixed to the core metal.

[0025] Next, the cage 7 will be described in detail with reference to FIGS.

[0026] 2, the annular portion 7a is located axially inward of the center position P1 of the ball 8. The column portion 7b does not branch out toward the inner diameter side of the annular portion 7a, but extends obliquely from the annular portion 7a so as to move away from the outer diameter surface 7q of the annular portion 7a toward the outer diameter side, and extends in the axial direction from the obliquely extending portion.

[0027] 3 and 4, in the area defined by the annular portions 7a on the opposing side surfaces of adjacent column portions 7b and the annular portions 7a between them, curved surfaces 7c that conform to the outer circumferential surfaces of the balls 8 are formed in a substantially hemispherical shape with the annular portions 7a at their base. Furthermore, the column portions 7b are formed with guide surfaces 7d that extend straight in the axial direction from the edges of the hemispherical curved surfaces 7c toward the tips of the column portions 7b (see FIG. 6). The guide surfaces 7d are configured to guide the balls 8 from the tips of the column portions 7b into the space surrounded by the curved surfaces 7c. Thus, the cage 7 is formed with equally spaced pockets Pt between adjacent column portions 7b, where the curved surfaces 7c and guide surfaces 7d hold the balls 8.

[0028] The balls 8 come into contact with the inner surface of the column portion 7b, thereby restricting the minimum distance on the pitch circle PCD between adjacent balls 8. The thickness of the column portion 7b is thinnest on the pitch circle PCD and gradually increases toward the inner diameter side and the outer diameter side.

[0029] The curved surfaces 7c of the pillar portions 7b are curved with the approximate center of the adjacent pillar portions 7b as the base. The spacing between adjacent pillar portions 7b is formed so that the spacing Wi between their inner diameter side ends and the spacing Wo between their radially outer ends are smaller than the spacing Wc between their approximate radial centers. This allows the pillar portions 7b to restrict the radially inward and outward movement of the balls 8 placed inside the pockets Pt. The tip portions of the pillar portions 7b are each formed with a claw portion 7e that protrudes toward the adjacent pillar portions 7b on both circumferential sides (see FIG. 6).

[0030] 2, the base portion 7b has a root portion 7f extending axially outward from the annular portion 7a and branch portions 7g extending axially outward from the outer diameter side of the root portion 7f. The branch portions 7g extend on the outer diameter side of the annular portion 7a. In other words, there are no branch portions 7g on the inner diameter side of the annular portion 7a.

[0031] The base portion 7f holds the ball 8 on the base end side of the column portion 7b. The base portion 7f has an inner diameter surface 7h and an inclined surface 7j. The inner diameter surface 7h is formed to extend axially outward from the inner diameter surface 7k of the annular portion 7a. The inclined surface 7j is formed to extend at an angle away from the inner diameter surface 7h toward the outer diameter side and is connected to the branch portion 7g (curved surface 7m).

[0032] The branch portion 7g holds the ball 8 at the tip side of the base portion 7b. The branch portion 7g is formed only on the outer diameter side of the root portion 7f. Specifically, the radial center line L of the branch portion 7g is located outer diameter side than the outer diameter surface 7q of the annular portion 7a. The branch portion 7g has a curved surface 7m, an inner diameter surface 7n, and an axial end surface S. The curved surface 7m is formed by extending from the inclined surface 7j in an arc-shaped cross section. The inner diameter surface 7n is formed by extending axially from the curved surface 7m toward the axial end surface S of the base portion 7b. In this way, the base portion 7b is configured such that no branch portion extending in the axial direction is formed on the inner diameter side of the root portion 7f. The radial center line L is a line parallel to the axial direction and passes through the radial center of the axial end surface S.

[0033] The inner diameter surface 7n is located on the outer diameter side of the center position P1 of the balls 8. The inclined surface 7j is located closer to the annular portion 7a than the center position P1 of the balls 8. In other words, the pillar portions 7b are formed so as not to overlap the center position P1 of the balls 8 in the circumferential direction. With this configuration, the cage 7 reduces the spacing between the balls 8, allowing for a greater number of balls 8 to be retained. The shapes of the surfaces of the root portion 7f and the branch portions 7g can be modified as appropriate. For example, although the inclined surface 7j is illustrated as extending straight, it may have a bent or curved shape.

[0034] Next, the axial length of the root portion 7f on the inner diameter surface 7h to the tip position P2 will be described in detail with reference to Figures 5 and 6. In the following, the axial length will be described starting from the end 7p of the annular portion 7a on the axially opposite side of the root portion 7f.

[0035] 5, the cage 7 is formed so that the axial length a to the tip position P2 is shorter than the axial length d to the base end position of the branch portion 7g (the axial length to the base end position P3 of the curved surface 7m). The cage 7 is also formed so that the axial length a to the tip position P2 is longer than the axial length e to the tip position P4 on the inner diameter surface 7k of the annular portion 7a. In other words, the axial length a to the tip position P2 is shorter than the axial length d to the base end position of the branch portion 7g and longer than the axial length e to the tip position P4 on the inner diameter surface 7k of the annular portion 7a.

[0036] The pillar portion 7b is formed so that the axial length up to the axial end face S is longer than the axial length up to the center position P1 of the ball 8. As a result, the pillar portion 7b restricts the axial movement of the ball 8 by the claw portions 7e (see FIG. 6).

[0037] In this way, in the wheel bearing device 1, because no branch portions extending in the axial direction are formed on the inner diameter side of the root portion 7f, the resin fillability on the inner diameter side of the retainer 7 is improved. Furthermore, because the area of ​​contact between the balls 8 and the retainer 7 is reduced, the shear resistance of the grease between the column portions 7b and the balls 8 is reduced. Therefore, the resin fillability during injection molding of the retainer 7 is improved and an increase in bearing torque can be suppressed. Furthermore, because the resin fillability on the inner diameter side of the retainer 7 is improved, the formability of the retainer 7 is improved and the strength of the retainer 7 can be ensured. Furthermore, because no branch portions extending in the axial direction are formed on the inner diameter side of the root portion 7f, the weight of the retainer 7 can be reduced.

[0038] Next, other features and effects of the wheel bearing device 1 will be described with reference to FIGS.

[0039] The wheel bearing device 1 has grease sealed inside the bearing where the balls 8 are provided. The kinetic viscosity of the grease is 30 mm 2 / s~200mm 2 / s is preferable. If the kinematic viscosity of the grease is too low, the oil film formation will be insufficient, and there is a risk of damaging the cage 7 and the like. On the other hand, if the kinematic viscosity of the grease is too high, the viscous resistance will increase, causing an increase in temperature rise and friction loss. In the wheel bearing device 1, the kinematic viscosity is set to 30 mm as described above. 2 / s~200mm 2 / s, the dynamic viscosity of the grease is optimized.

[0040] In addition, a pocket gap f is provided between the pocket Pt and the balls 8. The pocket gap f is preferably 0.05 mm to 0.45 mm. The cage 7 can move freely relative to the balls 8 within the range of the pocket gap f. If the pocket gap f is too small, the pocket Pt and the balls 8 may interfere with each other and be damaged. On the other hand, if the pocket gap f is too large, the balls 8 may rattle within the pocket Pt, deteriorating acoustic characteristics. In the wheel bearing device 1, the pocket gap f is optimized by setting the pocket gap f to 0.05 mm to 0.45 mm as described above.

[0041] The cage 7 is an injection-molded body made of resin. During injection molding, resin is injected into a mold through a gate of the mold. The cage 7 has a gate portion 7r, which is located at a position corresponding to the gate of the mold. The cage 7 has a weld 7s formed by the joining of resin injected from the gate portion 7r.

[0042] As shown in FIG. 6, the gate portions 7r are provided on the inner diameter surface 7k of the annular portion 7a and are located on the axial extension of the column portions 7b. The welds 7s are located midway between the column portions 7b. The gate portions 7r are provided in several locations, and the number of locations is determined depending on the cage 7. The welds 7s have lower strength than other portions where no welds 7s are formed. Because the number of welds 7s increases depending on the number of gate portions 7r provided, it is preferable to minimize the number of gate portions 7r provided within the range that allows resin filling.

[0043] In this way, in the wheel bearing device 1, the gate portion 7r into which the resin is filled is provided in the annular portion 7a and positioned on the axial extension of the pillar portion 7b, thereby improving the ability to fill the pillar portion 7b with resin. Also, by preventing the formation of welds 7s in the pillar portion 7b, the formability of the cage 7 can be improved.

[0044] While the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, which are merely examples, and can of course be embodied in various other forms without departing from the spirit of the present invention. The scope of the present invention is defined by the claims, and further includes equivalents set forth in the claims and all modifications within the scope of the claims. Also, in this embodiment, the wheel bearing device 1 is configured as a wheel bearing device of a third-generation structure in which the inner raceway surface 3c is formed directly on the outer periphery of the hub ring 3, but is not limited to this and may be a second-generation structure in which a pair of inner rings are press-fitted into the hub ring, or a first-generation structure in which a double-row angular contact ball bearing is fitted between the knuckle and the hub ring. [Explanation of symbols]

[0045] 1 Wheel bearing device 2 Outer ring (outer member) 2c Outer raceway surface 2d outer raceway 3 Hub ring (inner part) 3c Inner raceway surface 4 Inner ring (inner part) 4a Inner raceway surface 5 Inner ball row 6 Outer ball row 7 Cage 7a Annular part 7b Pillar part 7f Base 7g branch 7h Inner diameter surface of base 7j Inclined surface at base 7k Inner diameter surface of the annular part 7n Inner diameter surface of branch 7p End of the annular part on the axially opposite side of the base part 7q Outer diameter surface of the annular part 7r Gate 7s Weld 8 balls (rolling elements) a Axial length from the inner diameter surface of the base to the tip position d Axial length to the base end of the branch e Axial length to the tip position on the inner diameter surface of the annular part f Pocket gap L Radial center line P1 Center position of rolling element P2 Tip position of the inner diameter surface of the base P4 Tip position on the inner diameter surface of the annular part Pt Pocket

Claims

1. an outer member having a double-row outer raceway surface formed on an inner periphery thereof; an inner member having a double-row inner raceway surface formed thereon opposite to the double-row outer raceway surface; double-row rolling elements rollably interposed between the raceway surfaces of the outer member and the inner member; a cage made of resin, the cage having an annular portion formed in an annular shape and a plurality of column portions extending in an axial direction at regular intervals in a circumferential direction from the annular portion, wherein adjacent column portions and the annular portions form pockets having curved surfaces that follow the outer peripheral surfaces of the rolling elements, and the cage holds the rolling elements in the pockets, the base portion has a root portion extending in an axial direction from the annular portion and a branch portion extending in the axial direction from the root portion, the branch portion being formed only on an outer diameter side of the root portion, The wheel bearing device according to claim 1, wherein the inner diameter surface of the branch portion is located on the outer diameter side of the center position of the rolling element.

2. 2. The wheel bearing device according to claim 1, wherein a radial center line of the branch portion is located on the outer diameter side of an outer diameter surface of the annular portion.

3. the root portion has an inner diameter surface that extends axially from the inner diameter surface of the annular portion, 3. A wheel bearing device according to claim 1, wherein an axial length from an end of the annular portion axially opposite to the root portion to a tip position on the inner diameter surface of the root portion is shorter than an axial length to a base end position of the branch portion and longer than an axial length to a tip position on the inner diameter surface of the annular portion.

4. the root portion has an inclined surface connected to the branch portion on an inner diameter side of the root portion, 4. The wheel bearing device according to claim 1, wherein the inclined surface of the base portion is located closer to the annular portion than the center position of the rolling element.

5. Grease is sealed inside the bearing in which the rolling elements are arranged, The grease has a kinematic viscosity of 30 mm ２ / s~200mm ２ 5. The wheel bearing device according to claim 1, wherein the torque is 0.1 / s.

6. 6. The wheel bearing device according to claim 1, wherein a pocket clearance between the rolling element and the pocket is 0.05 mm to 0.45 mm.

7. the cage is an injection-molded body having a gate portion, and the gate portion is located corresponding to a gate of a mold into which resin is injected during injection molding; 7. The wheel bearing device according to claim 1, wherein the gate portion is provided on the annular portion and is located on an axial extension of the pillar portion.

8. the cage has a weld formed by the resin filling from the gate portion joining together, 8. The wheel bearing device according to claim 7, wherein the weld is located midway between the pillar portions.

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