JP2001239803A - Rolling bearing unit for supporting wheel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent defects such as cracks from being generated when a cylindrical part is caulked and widened to form a caulking part in order to fix an inner ring to a hub made of carbon steel. SOLUTION: A cylindrical part 10b of a hub 2a made of carbon steel is caulked and widened to fix an inner ring 3. The cylindrical part 10b is not hardened by quenching, and the hardness is set to about Hv 200 to 300. The mean sectional area of the crystal grain on the part is suppressed to not more than 0.030 mm2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The rolling bearing unit for supporting wheels according to the present invention is used to rotatably support wheels of an automobile with respect to a suspension device.

[0002]

2. Description of the Related Art The wheels of an automobile are supported on a suspension system by rolling bearing units for supporting wheels. In such a rolling bearing unit for supporting a wheel, for the purpose of cost reduction and reduction in size and weight by reducing the number of parts, a structure in which a nut is not used for connecting and fixing a hub and an inner ring is disclosed in, for example, JP-A-11-129703. As described in Japanese Unexamined Patent Publication (Kokai) No. HEI 10-301, it is conventionally known. FIGS. 5 and 6 show a conventionally known wheel supporting rolling bearing unit 1 described in this publication.
Is shown.

[0003] This conventionally known wheel supporting rolling bearing unit 1 comprises a hub 2, an inner ring 3, an outer ring 4,
And a plurality of rolling elements (5, 5). Of these, the outer end of the outer peripheral surface of the hub 2 (outside refers to the outer side in the width direction of the vehicle when assembled to the vehicle, and is the left side of each of the drawings except for FIGS. 3 and 8; Is inside, and the right side of each figure except FIGS. 3 and 8). The first flange 6 for supporting the wheel is formed in the closer part. A first inner raceway 7 is formed on the outer peripheral surface of the intermediate portion of the hub 2, and a step 8 having a smaller outer diameter is formed on the inner end of the hub 2. Then, the inner ring 3 is externally fitted to the stepped portion 8,
It is fixed by. The first inner raceway 7 is formed directly on the outer peripheral surface of the intermediate portion of the hub 2 and the hub 2
May be formed on the outer peripheral surface of a separate inner ring externally fitted to the intermediate portion of the inner ring. In such a case, the portion of the end of the hub 2 that protrudes inward in the axial direction from the separate inner ring becomes a step for fitting the inner ring 3 to the outside.

To this end, a cylindrical portion 10 for forming the caulking portion 9 is formed at the inner end of the hub 2. The thickness of the cylindrical portion 10 becomes smaller toward the leading edge in a state before the cylindrical portion 10 is crimped outward in the diameter direction as shown in FIG. For this reason, the inner end surface of the hub 2 has a tapered hole 1 whose inner diameter gradually decreases toward the inner part.
1 are formed.

In order to fix the inner ring 3 to the inner end of the hub 2 and to widen the tip of the cylindrical portion 10 as described above, the hub 2 is fixed so as not to move in the axial direction. Then, as shown in FIG. 6, the pressing die 12 is strongly pressed against the distal end of the cylindrical portion 10. At the center of the tip end surface (the left end surface in FIG. 6) of the pressing die 12, a truncated cone-shaped convex portion 13 which can be pushed into the inside of the cylindrical portion 10 is formed. The concave portion 14 is formed so as to surround the entire circumference of the convex portion 13. The cross-sectional shape of the concave portion 14 is such that the cross-sectional shape of the caulking portion 9 obtained by plastically deforming the distal end portion of the cylindrical portion 10 by the concave portion 14 is such that the thickness dimension increases from the base end portion toward the distal end portion. The composite curved surface is formed such that the radius of curvature becomes smaller toward the outer diameter side so that the thickness gradually decreases, and particularly, the thickness dimension decreases sharply at the tip end.

When the pressing die 12 having the projections 13 and the depressions 14 having the above-mentioned shapes and dimensions is pressed against the distal end of the cylindrical portion 10, the distal end of the cylindrical portion 10 is swaged outward in the diameter direction. Thus, the caulked portion 9 can be formed. Then, the inner ring 3 is sandwiched between the caulked portion 9 and the step surface 23 of the step 8 formed at the inner end of the hub 2,
The inner ring 3 can be fixed to the hub 2.

On the other hand, on the inner peripheral surface of the outer race 4, a first outer raceway 15 opposed to the first inner raceway 7 formed on the outer peripheral surface of the intermediate portion of the hub 2, and the outer peripheral surface of the inner race 3 Second outer raceway 1 opposed to second inner raceway 16 formed at
7 are formed. The rolling elements 5, 5 are rotatably held between the first and second inner raceways 7, 16 and the first and second outer raceways 15, 17 by retainers 18, 18, respectively. In this state, a plurality is provided.
In the illustrated example, balls are used as the rolling elements 5 and 5. However, in the case of a heavy-weight rolling bearing unit for an automobile, tapered rollers may be used as these rolling elements.

In order to assemble the above-described rolling bearing unit 1 for supporting a wheel to an automobile, the outer ring 4 is fixed to a suspension device by a second flange 19 formed on the outer peripheral surface of the outer ring 4 and the first ring is fixed to the suspension device. The wheel is fixed to the flange 6 of.
As a result, the wheels can be rotatably supported by the suspension device.

In order to form the wheel bearing rolling bearing unit 1 having the structure and operation described above, the cylindrical portion 10 is plastically deformed (caulked and expanded) to form the caulked portion 9. Preferably, an oscillating press device 20 as shown in FIG. 8 is used. This oscillating press device 20
It includes a pressing die 12, a holding jig 21, and a holder 22.
When the cylindrical portion 10 is swaged and widened to form the swaged portion 9, the pressing die 12 is displaced while the hub 2 is pressed upward through the holder 22. That is, in a state where the center axis of the pressing die 12 and the center axis of the hub 2 are inclined by the angle θ, the pressing die 12 is displaced about the center axis of the hub 2. When the caulking portion 9 is formed by such a swing press, a part of the pressing die 12 in the circumferential direction presses the cylindrical portion 10, and the working of the caulking portion 9 is partially performed. And proceed continuously in the circumferential direction. For this reason, the load applied to the cylindrical portion 10 at the time of working can be reduced as compared with the case where the caulked portion 9 is formed by general forging. The holding jig 21 prevents the inner ring 3 and the hub 2 from swaying in the radial direction when the caulking portion 9 is processed by the pressing die 12.

[0010] Further, in the conventional structure as described above, by quenching and hardening the portion indicated by the oblique lattice in FIG. 5 on a part of the outer peripheral surface of the hub 2, it is possible to improve the durability of the portion. It is described in JP-A-11-129703. That is, the first inner raceway 7 portion, the first flange 6
The hardening process is performed on the base end portion and the base half portion of the step portion 8 to increase the hardness of the portion to about Hv550 to 900. On the other hand, the hardness of the cylindrical portion 10 that should form the caulking portion 9 is as low as about Hv 200 to 300, so that the cylindrical portion 10 is easily plastically deformed.

Incidentally, of the portions subjected to the quenching process indicated by the diagonal lattice, the first inner raceway 7 receives a large surface pressure based on the contact with the rolling surface of the rolling element 5. Therefore, it is hardened to secure the rolling fatigue life. In addition, regardless of the moment load received from the first flange 6 to which the wheel is fixed,
The base is hardened to prevent deformation.
Also, the outer peripheral surface of the step portion 8 deforms regardless of the fitting pressure of the inner ring 3 and the radial load applied to the inner ring 3 from the plurality of rolling elements 5. Is hardened in order to prevent the occurrence of fretting wear on the outer peripheral surface of the step portion 8 which is a fitting portion with the inner ring 3. The step surface 23 of the step 8 prevents the step surface 23 from being deformed irrespective of an axial load applied to the inner ring 3 by a caulking operation described later. The stepped surface 23, which is the contact surface with the end surface, is hardened to prevent fretting wear from occurring. The corner R, which is a continuous portion between the outer peripheral surface of the step portion 8 and the step surface 23, is hardened to prevent deformation due to stress concentration.

Japanese Patent Application Laid-Open No. H10-95203 discloses that, as shown in FIG. 9, the outer diameter of a portion of the inner end of the hub 2a protruding from the fitting portion of the inner race 3 is determined by using the fitting portion. A structure that is slightly smaller than the outer diameter is described. That is, the outer peripheral surface of the cylindrical portion 10a formed at the inner end of the hub 2a is slightly shifted toward the second inner raceway 16 from the inclined surface 24 formed at the inner end opening of the inner race 3. In part,
A step 25 having a slight step H of about 02 to 1 mm is formed. Then, a portion of the cylindrical portion 10a having a reduced outer diameter is swaged outward in the diameter direction so as to suppress the inclined surface 24. Thus, the cylindrical part 10
a is swaged outward in the diameter direction.
5 is a starting point of a portion that is bent in accordance with the swaging operation. For this reason, the cylindrical portion 10a is
It is difficult for excessive force to be applied, and damage such as cracks is less likely to occur in the swaged portion.

[0013]

According to the conventional structure described above, a small and lightweight rolling bearing unit for supporting a wheel may be realized at low cost, but sufficient durability and reliability are ensured. In order to reduce the cost sufficiently, it is necessary to improve the yield by preventing the caulking portion 9 for fixing the inner ring 3 to the hubs 2 and 2a from generating damage such as cracks. is there. The present invention, in view of such circumstances, to prevent the occurrence of damage such as cracks in the swaged portion,
The present invention has been made to realize a wheel supporting rolling bearing unit capable of sufficiently reducing costs by a sufficient yield improving effect.

[0014]

In the rolling bearing unit for supporting a wheel according to the present invention, the rolling bearing unit for supporting a wheel according to the first aspect of the present invention has one end similar to the above-mentioned conventional rolling bearing unit for supporting a wheel. A first flange is formed on the outer peripheral surface of the hub, and a first inner raceway is provided on the outer peripheral surface of the intermediate portion through an integral or separate inner race. An inner race having a second inner raceway formed on a surface thereof, and an outer race having formed thereon a first outer raceway facing the first inner raceway and a second outer raceway facing the second inner raceway on an inner circumferential surface. And a plurality of rolling elements provided between the first and second inner raceways and the first and second outer raceways, respectively. An inner ring externally fitted to the hub is formed by caulking a cylindrical portion formed at least at a portion of the other end of the hub that protrudes from the inner ring externally fitted to the hub in a radially outward direction. Is fixedly connected to this hub. Further, the wheel supporting rolling bearing unit according to the second aspect also has a first flange formed at one end outer peripheral surface and a second flange formed at an intermediate outer peripheral surface, similarly to the above-described conventional wheel supporting rolling bearing unit. A hub provided with one inner raceway directly or via a separate inner race, and a step provided at the other end of the hub and having an outer diameter smaller than that of the portion provided with the first inner raceway. A second inner raceway formed on the outer peripheral surface and an outer race fitted on this step, and a first outer raceway and the second inner raceway facing the first inner raceway on the inner peripheral surface. The second outer ring raceway facing, the second flange on the outer peripheral surface, the outer race respectively formed, between the first, the second inner raceway and the first, the second outer raceway, respectively And a plurality of rolling elements. At the other end of the hub, a cylindrical portion formed at least at a portion protruding from the inner ring externally fitted to the step portion is swaged outward in the diametrical direction. The inner ring thus formed is pressed down toward the step surface of the step, and the inner ring externally fitted to the step is connected and fixed to the hub.

In particular, in the rolling bearing unit for supporting a wheel according to the present invention, the hub is made of carbon steel, and a portion of the cylindrical portion that is plastically deformed in accordance with the operation of forming the caulked portion (caulking). The average cross-sectional area of the crystal grains (during processing) is set to 0.030 mm ² or less. Preferably, the average cross-sectional area of the crystal grains in this portion is 0.020 mm ² or less, more preferably 0.0156 mm ² or less, and still more preferably 0.012 mm ² or less. Preferably, when the first inner raceway is formed directly on the outer peripheral surface of the intermediate portion of the hub, the carbon content of the carbon steel is preferably 0.1%.
When the first inner raceway is formed on the outer peripheral surface of an inner race separate from the hub, the content of 45 to 1.10% by weight is defined as follows.
A C content of 0.20 to 1.10% by weight,
Use each. As such a carbon steel, for example, S
53C, S35C and the like can be used.

[0016]

In the case of the rolling bearing unit for supporting a wheel according to the present invention configured as described above, the average sectional area of the carbon steel crystal grains constituting the cylindrical portion on which the caulked portion is to be formed is set to 0.030.
Since suppressed and mm ² or less, with the task of forming the crimped portion spread caulking the cylindrical portion diametrically outward, that damage such as cracks occurs in the crimped portion, effectively prevent it can. As a result, according to the present invention, the cost of the wheel supporting rolling bearing unit can be sufficiently reduced while ensuring durability and reliability. If the average cross-sectional area of the crystal grains of the carbon steel is suppressed to 0.030 mm ² or less, the caulked portion does not have a defect that causes a practical problem. However, when the average cross-sectional area is close to 0.030 mm ² , a small wrinkle may be generated in the obtained swaged portion to such an extent that there is no practical problem as a rolling bearing unit for supporting a wheel. When the average cross-sectional area is close to 0.020 mm ² , wrinkles are smaller and the frequency of occurrence is lower, but wrinkles still occur very rarely.
On the other hand, when the average cross-sectional area is 0.0156 mm ² or less, wrinkles hardly occur. Furthermore,
When the average cross-sectional area is 0.012 mm ² or less, wrinkles are not generated on the obtained swaged portion.

[0017]

1 to 3 show an example of an embodiment of the present invention. The feature of the present embodiment lies in a structure for preventing deformation and wear of each part, and for preventing formation of a crack or the like in a part of the hub 2b when the caulking part 9 is formed. The structure, manufacturing method and operation of other parts
Since it is the same as the case of the prior art shown in FIGS. 5 to 9, the illustration and description of the equivalent parts are omitted or simplified, and the following description focuses on the characteristic parts of the present invention and the parts different from the above-described prior art. explain. In the rolling bearing unit for supporting a wheel according to the present invention, the first inner raceway 7 is formed on the outer peripheral surface of the intermediate portion of the hub 2b, as shown in FIG.
2 as well as a structure directly formed on the hub 2b,
As shown in FIG. 4, there is a hub in which a separate inner race 3a having a first inner raceway 7 formed on the outer peripheral surface is externally fitted to an intermediate portion of the hub 2c. In the case of the structure as shown in FIG. 4, a portion projecting inward from the inner end surface of the separate inner race 3a at the inner end of the hub 2c is formed on the outer peripheral surface of the second inner raceway 16. Is formed as a stepped portion 8a for externally fitting the inner ring 3 formed with. The inner end surface of the separate inner ring 3a serves as a step surface 23a.

Rolling bearing unit 1a for supporting wheels of the present embodiment
Is made of carbon steel, and a surface portion (a diagonal lattice portion in FIG. 1) including a step portion 8 for externally fitting the inner ring 3 is hardened by a quenching process (the hardness of the portion is reduced). Hv
550 to 900). The hardened portion is not limited to the base half portion of the step 8 as in the case of the conventional structure shown in FIG. It is the part that reaches the base end. The outer peripheral surface of the cylindrical portion 10b provided at the inner end of the hub 2b has a large diameter at the base end side (the left side in FIGS. 1 and 2) and the distal end side of the cylindrical portion 10b (the right side in FIGS. ) Is provided with a step 25 having a small diameter. The step H of the step 25 is about 0.02 to 0.12 mm. The step 25 has a curved surface having an arcuate cross section and is smoothly continuous with at least the small-diameter side portion (the outer peripheral surface of the cylindrical portion 10b near the front end).

In particular, in the case of the hub 2b constituting the wheel supporting rolling bearing unit 1a of the present invention, the hub 2b
Of these, the cylindrical portion 10b for forming the caulking portion 9 for fixing the inner ring 3 to the hub 2b (a portion that is not hardened and hardened and is a portion on the right side of the chain line α in the figure) is formed. The average cross-sectional area of the crystal grains of the carbon steel before forming the caulked portion 9 was 0.0
12mm ² or less. Fig. 3 (A) is 0.012mm
² ｝. The reason for setting the average cross-sectional area of the crystal grains of the carbon steel constituting the cylindrical portion 10b to a predetermined value in this manner is as follows.
After forging the hub 2b, the cooling time is adjusted to room temperature.

Further, in the case of the hub 2b constituting the wheel supporting rolling bearing unit 1a of this embodiment, the cylindrical portion 10
In step b, the above-mentioned quenching process is not performed on the step portion 25 and the portion closer to the front end than the step portion 25. That is, the hardened and hardened portion indicated by the oblique lattice in FIG. 1 is closer to the base end of the cylindrical portion 10b than the stepped portion 25 (stepped surface 2).
3 and ends at the left portion of FIGS. 1 and 2). Therefore, the carbon steel constituting the intermediate portion or the tip portion of the step portion 25 and the cylindrical portion 10b is much softer in a raw or semi-green state than the hardened and hardened portion indicated by the diagonal lattice. (Hv is about 200 to 300).

In the case of the rolling bearing unit 1a for supporting a wheel of the present embodiment constructed as described above, the surface portion including the base end portion of the stepped portion 8 is hardened by quenching. Damage such as deformation or wear can be prevented from occurring in the portion. Further, since the step 25 is provided on the outer peripheral surface of the cylindrical portion 10b, damage such as a crack or the like is less likely to occur in the swaged portion when the cylindrical portion 10b is swaged outward in the diameter direction.

Further, in the case of this embodiment, the average cross-sectional area of the crystal grains of the carbon steel constituting the cylindrical portion 10b which should constitute the caulking portion 9 is suppressed to a small value of 0.012 mm ^2. With the operation of forming the above-mentioned caulked portion 9 by caulking and expanding the cylindrical portion 10b outward in the diameter direction, the caulked portion 9 is formed.
It is possible to effectively prevent defects such as cracks from being generated. In this regard, an experiment performed by the present inventors will be described with reference to FIG.

In the experiment, the average cross-sectional area of the crystal grains of the carbon steel constituting the cylindrical portion 10b was 0.012 mm ² as shown in FIG. 3A and as shown in FIG. Two types, 0.050 mm ² , 10
Zero pieces (a total of 200 pieces) were prepared. Then, an operation of caulking and expanding the cylindrical portion 10b was performed for each sample, and the presence or absence of a defect of the caulked portion 9 obtained as a result was verified. As a result, no defect was found in any of the samples having an average cross-sectional area of 0.012 mm ² (pass rate: 100%). On the other hand, when the average cross-sectional area was 0.050 mm ² , a defect occurred in 40% of the samples (pass rate: 60%). From such an experiment, it was confirmed that reducing the average cross-sectional area of the crystal grains of the carbon steel constituting the cylindrical portion 10b was effective in eliminating the defects of the caulked portion 9.

Further, in the case of the present embodiment, the quenching process is not performed on the step portion 25 and the intermediate portion to the tip portion of the cylindrical portion 10b which is closer to the tip than the step portion 25. . For this reason, it is possible to more effectively prevent damage such as a crack in the step portion 25 and a portion closer to the tip than the step portion 25 during the caulking and spreading operation.
That is, at the time of the caulking operation, the step portion 25 is securely plastically deformed outward in the diameter direction, and closely adheres to the inner peripheral surface of the inner ring 3. FIG. 10 shows the operation and effect of this point.
This will be described below.

For example, the first example of the conventional structure shown in FIGS. 5 and 6 and the second example of the conventional structure also shown in FIG. 9 are combined as they are, and the step formed on the outer peripheral surface of the cylindrical portion 10a is formed. 25 is hardened and hardened, the cylindrical portion 1
When the caulking portion is formed by caulking Oa radially outward and forming a caulked portion, damage such as a crack is likely to occur in the step portion 25. That is, as shown in FIG. 10A, when the hardened layer indicated by the oblique lattice in FIG.
As shown in FIG. 10 (B), even if the cylindrical portion 10a is swaged and widened, the step portion 25 is hardly plastically deformed, and the outer peripheral surface of the base end portion of the swaged portion 9 corresponds to the step portion 25. A groove 26 as shown in FIG. Then, damage such as a crack is easily generated from the groove 26.

On the other hand, in the case of this example, the step 25
Is not quenched and hardened, so that the step 25 is easily plastically deformed, and the groove 2 as shown in FIG.
No 6 is formed. In particular, in the case of this example, since the step H of the step portion 25 is as small as 0.12 mm or less, it is possible to more reliably prevent the formation of the groove portion 26 which may cause a crack. Thus, according to the present invention, not only the cost reduction effect due to the reduction in the number of parts but also the yield improvement effect due to the reduction in the defective product occurrence rate during manufacturing is sufficiently increased, and the cost of the wheel supporting rolling bearing unit 1a is reduced. Can be sufficiently reduced.

[0027]

Since the present invention is constructed and operates as described above, it is possible to realize a rolling bearing unit for supporting a wheel which is lightweight, low-cost and has excellent durability.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing an example of an embodiment of the present invention before an end portion of a hub is swaged.

FIG. 2 is a half sectional view showing a state after completion.

FIG. 3 is a photomicrograph showing two examples of a case where the average cross-sectional area of a crystal grain is small and a case where the average cross-sectional area is large;

FIG. 4 is a half sectional view showing another example of the structure of the rolling bearing unit for supporting a wheel to which the present invention is applied.

FIG. 5 is a half sectional view showing a first example of a conventional structure.

FIG. 6 is a partially enlarged cross-sectional view showing a state in which the inner end of the hub is swaged to fix the inner ring at the time of manufacturing the structure of the first example.

FIG. 7 is a partially enlarged cross-sectional view showing a state before the inner end of the hub is swaged.

FIG. 8 is an essential part longitudinal cross sectional view showing a state where the inner end of the hub is swaged and widened by the swing press device.

FIG. 9 is a view similar to FIG. 7, showing a second example of the conventional structure.

FIG. 10 is a partial cross-sectional view showing, in the order of steps, a state in which a defect occurs during the caulking operation when the positional relationship between the step portion and the hardened and hardened portion is inappropriate.

[Description of Signs] 1, 1a Wheel bearing rolling bearing unit 2, 2a, 2b, 2c Hub 3, 3a Inner ring 4 Outer ring 5 Rolling element 6 First flange 7 First inner ring raceway 8, 8a Step 9 Caulking section 10, 10a, 10b Cylindrical part 11 Tapered hole 12 Press mold 13 Convex part 14 Concave part 15 First outer raceway 16 Second inner raceway 17 Second outer raceway 18 Cage 19 Second flange 20 Swing press device 21 Suppression Jig 22 Holder 23, 23a Stepped surface 24 Inclined surface 25 Stepped portion 26 Groove

Claims (5)

[Claims] 1. A hub in which a first flange is formed on an outer peripheral surface of one end and a first inner raceway is provided on an outer peripheral surface of an intermediate portion through an integral or separate inner ring, and a hub is provided on the other end of the hub. An outer ring having an outer race formed with a second inner raceway on an outer peripheral surface, and a first outer raceway facing the first inner raceway and a second inner raceway facing the second inner raceway on the inner circumferential surface. An outer ring forming an outer raceway, and a plurality of rolling elements provided between the first and second inner raceways and the first and second outer raceways, respectively, and the other end of the hub The inner ring externally fitted to the hub was connected and fixed to the hub by a caulking portion formed by caulking and expanding the cylindrical portion formed at least in a portion protruding from the inner ring externally fitted to the hub radially outward. In the rolling bearing unit for supporting wheels, the hub is made of carbon steel, and the hub is made of carbon steel. A rolling bearing unit for supporting wheels, wherein the average cross-sectional area of crystal grains in a portion of the portion which is plastically deformed in association with the forming operation of the caulking portion is set to 0.030 mm ² or less. 2. A hub having a first flange formed on an outer peripheral surface of one end and a first inner raceway provided directly or through a separate inner race on an outer peripheral surface of an intermediate portion, and a hub provided at the other end of the hub. A step portion having an outer diameter smaller than that of the portion provided with the first inner ring raceway provided; an inner ring formed with a second inner ring raceway on the outer peripheral surface and fitted to the step portion; A first outer raceway facing the first inner raceway on the peripheral surface and a second outer raceway facing the second inner raceway on the outer raceway, a second flange formed on the outer circumferential surface, and an outer race formed respectively, A plurality of rolling elements are provided between the first and second inner raceways and the first and second outer raceways, respectively, and the other end of the hub is externally fitted to at least the stepped portion. The caulking part formed by caulking and expanding the cylindrical part formed at the part protruding from the inner ring In a wheel supporting rolling bearing unit in which the inner ring externally fitted to the step is pressed toward the step surface of the step and the inner ring externally fitted to the step is fixedly connected to the hub, the hub is preferably A rolling bearing for wheel support, wherein the rolling bearing is made of carbon steel, and has an average cross-sectional area of 0.030 mm ² or less of crystal grains in a portion of the cylindrical portion that is plastically deformed in association with the work of forming the caulked portion. unit. 3. The rolling bearing unit for supporting wheels according to claim 1, wherein the average sectional area of the crystal grains is 0.020 mm ² or less. 4. An average sectional area of crystal grains is 0.0156 mm ^2.
The rolling bearing unit for wheel support according to any one of claims 1 to 2, wherein: 5. The rolling bearing unit for supporting a wheel according to claim 1, wherein the average sectional area of the crystal grains is 0.012 mm ² or less.