JP7668133B2 - Wheel bearing device - Google Patents

Description

The present invention relates to a wheel bearing device.

In wheel bearing devices, when excessive loads are input from the wheels due to cornering, running over curbs, etc. while the vehicle is traveling, the contact ellipse between the ball and the raceway surface may ride up on the shoulder of the raceway ring, causing an indentation on the shoulder and generating abnormal noise. To solve the problem of such indentations, in JP 2015-224655 A (Patent Document 1), the raceway surface is machined by cutting hardened steel. As a result, when the groove depth is h and the diameter of the rolling elements is d, it is possible to machine the raceway surface so that h/d exceeds 0.50, ensuring the shoulder height and preventing the contact ellipse from riding up on the shoulder and the occurrence of indentations on the shoulder.

JP 2015-224655 A

In recent years, as vehicles have become more powerful and larger, there has been a trend toward lower-profile tires (not just genuine wheels, but also replacement with aftermarket parts). This means that not only in unforeseen circumstances such as running over a curb, but also during normal vehicle driving, the load acting on the wheel is not absorbed by the tire's deflection alone, but is instead input directly to the wheel. In this way, there are an increasing number of occasions where wheel bearing devices are subjected to excessive loads that are greater than expected.

When an excessive load is applied and exceeds the elastic limit of the raceway surface in a bearing device, an indentation is created on the raceway surface, which may cause abnormal noise or early peeling of the raceway surface, resulting in failure of the bearing device. To prevent indentations caused by excessive loads, there are the aforementioned conventional techniques, or a method of enlarging the bearing device itself to a size appropriate to the excessive load. However, due to layout constraints on the vehicle side, it is difficult to enlarge the bearing device, and measures against unexpected excessive loads have not been sufficient.

The object of the present invention is to provide a wheel bearing device that can suppress the occurrence of indentations in the raceway groove when an excessive load or impact load is applied, without hindering weight reduction.

The wheel bearing device of the present invention is a wheel bearing device for supporting a wheel so as to be rotatable, and includes an inner member, an outer member, and a plurality of rolling elements. The inner member has a first raceway groove. The outer member has a second raceway groove. The plurality of rolling elements are interposed between the first raceway groove and the second raceway groove. At least one of the first raceway groove and the second raceway groove includes a first region, a second region, a third region, a fourth region, and a fifth region. The first region is distributed along the depth direction from the surface of the at least one raceway groove with a first yield stress. The second region is located in a region deeper than the first region in the depth direction and is distributed along the depth direction with a second yield stress lower than the first yield stress. The third region is located in a region deeper than the second region in the depth direction and is distributed along the depth direction with a third yield stress lower than the second yield stress. The fourth region is distributed so that the yield stress decreases with increasing depth from the surface from the first region to the second region. The fifth region has a distribution in which the yield stress decreases with increasing depth from the surface, from the second region to the third region.

In the above wheel bearing device, at least one raceway groove has a first region, a fourth region, a second region, a fifth region, and a third region, which are distributed in order along the depth direction at least in the shoulder portion.

In the above wheel bearing device, the difference between the first yield stress and the second yield stress is smaller than the difference between the second yield stress and the third yield stress.

In the above wheel bearing device, the first raceway groove portion of the inner member and the second raceway groove portion of the outer member are made of medium carbon steel containing 0.40% to 0.80% by mass of carbon, or high carbon chromium bearing steel such as SUJ2.

The present invention makes it possible to realize a wheel bearing device that can suppress the occurrence of indentations in the raceway groove when an excessive load or impact load is applied, without hindering weight reduction.

1 is a cross-sectional view showing a state in which a wheel is attached to a wheel bearing device in one embodiment. FIG. 2 is an enlarged view of a main part of FIG. 1 . FIG. 3 is an enlarged view showing an area RA in FIG. 2 . This is a stress-depth diagram showing the internal stress generated by an impact load and the material yield stress (= proof stress) when a secondary hardening with high heat input is performed after a primary hardening with low heat input. 5 is a flow diagram showing a method for manufacturing the wheel bearing device according to the embodiment. FIG. This is a stress-depth diagram showing the internal stress generated by an impact load and the material yield stress (= proof stress) when hardened with low heat input. This is a stress-depth diagram showing the internal stress generated by an impact load and the material yield stress (= proof stress) when hardened with high heat input. This is a stress-depth diagram showing the internal stress generated by an impact load and the material yield stress (= proof stress) when primary quenching is performed with low heat input. This is a stress-depth diagram showing the internal stress generated by an impact load and the material yield stress (= proof stress) when a secondary hardening with low heat input is performed after a primary hardening with high heat input.

The following describes an embodiment of the present invention with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference symbols, and overlapping descriptions will not be repeated.

<Configuration of wheel bearing device>
First, the configuration of the wheel support bearing device according to this embodiment will be described with reference to FIGS.

As shown in FIG. 1, the wheel bearing device 40 is a second or third generation double row angular contact ball bearing type wheel bearing device. The wheel bearing device 40 has an inner member 10, an outer member 20, and multiple rolling elements 30a, 30b. The inner member 10 is the rotating member, and a wheel (wheel 52, tire 53) is attached to the inner member 10 by tightening a hub nut 55 to a hub bolt 54. A serrated shaft 51 of a constant velocity universal joint is engaged with the inner member 10. As a result, a driving force is transmitted to the inner member 10 via the serrated shaft 51.

The outer member 20 is a fixed member and is arranged around the inner member 10. Each of the multiple rolling elements 30a, 30b is, for example, a ball, and is arranged between the inner member 10 and the outer member 20. The multiple rolling elements 30a, 30b include multiple rolling elements 30a in a first row and multiple rolling elements 30b in a second row. The inner member 10, to which wheels (wheels 52, tires 53) are attached, is rotatably supported relative to the outer member 20 via the multiple rolling elements 30a, 30b.

As shown in FIG. 2, the inner member 10 is composed of a hub ring 1 and an inner ring 2. The inner ring 2 is fitted and fixed to the outer peripheral surface of the hub ring 1. As a result, the hub ring 1 and the inner ring 2 are integrated to form the inner member 10. The inner member 10 has two rows of raceway grooves (first raceway grooves) 3a, 3b on its outer peripheral surface, which correspond to the inner ring raceway. The raceway groove 3a is formed in the hub ring 1, and the raceway groove 3b is formed in the inner ring 2.

The hub wheel 1 has a cylindrical portion 1a and a hub flange 1b. The cylindrical portion 1a has a cylindrical shape. The hub flange 1b protrudes in the outer circumferential direction from the outer circumferential surface of the cylindrical portion 1a. The hub flange 1b is a flange for mounting a wheel (wheel 52, tire 53) and a brake rotor 56. Hub bolts 54 are attached to the hub flange 1b at predetermined intervals in the circumferential direction. As shown in FIG. 1, the wheel (wheel 52, tire 53) and brake rotor 56 are fastened to the hub flange 1b by tightening a hub nut 55 to the hub bolt 54.

The cylindrical portion 1a of the hub wheel 1 has a serrated hole (spline hole) 1c that penetrates in the axial direction. As shown in FIG. 1, the serrated hole 1c of the hub wheel 1 can engage with a serrated shaft 51 of an outer joint member of a constant velocity universal joint.

The outer member 20 has a sleeve 11 and a flange 12. The sleeve 11 has a cylindrical shape. The flange 12 protrudes in the outer circumferential direction from the outer circumferential surface of the sleeve 11. The flange 12 is for fixing to a suspension device (not shown) such as a knuckle of a vehicle body (chassis). The flange 12 has screw holes 13 formed at predetermined intervals in the circumferential direction. The outer member 20 is fixed to the knuckle or the like using a screw member inserted into the screw hole 13.

Two rows of raceway grooves (second raceway grooves) 14a, 14b corresponding to the outer ring raceway are formed on the inner circumference of the sleeve 11. Each of the multiple rolling elements 30a in the first row is interposed between the raceway groove 3a and the raceway groove 14a. Each of the multiple rolling elements 30a in the first row is held by the first retainer 31a so that they can roll freely. Each of the multiple rolling elements 30b in the second row is interposed between the raceway groove 3b and the raceway groove 14b. Each of the multiple rolling elements 30b in the second row is held by the second retainer 31b so that they can roll freely.

Seal rings 32a, 32b are installed between the outer peripheral surface of the inner member 10 and the inner peripheral surface of the outer member 20. This isolates the space in which the rolling elements 30a, 30b are held from the outside. The seal ring 32a is disposed between the outer peripheral surface of the hub wheel 1 and the inner peripheral surface of the inner member 20. The seal ring 32b is disposed between the outer peripheral surface of the inner ring 2 and the inner peripheral surface of the inner member 20.

The hub ring 1 and the outer member 20 are each made of medium carbon steel containing 0.40% to 0.80% by mass of carbon, for example S53C. The inner ring 2 and the rolling elements 30a, 30b are made of high carbon chromium bearing steel, for example SUJ2, and are hardened to the core by deep hardening. Deep hardening is a type of overall hardening in which the entire workpiece is hardened. However, the inner ring 2 may be made of medium carbon steel containing 0.40% to 0.80% by mass of carbon, and may be induction hardened.

<Stress distribution in the depth direction of the raceway groove>
Next, the stress distribution in the depth direction of the shoulder portions of the raceway grooves 3a, 14a, 14b will be described with reference to FIGS.

In this embodiment, the shoulders SP of each of the raceway grooves 3a, 14a, and 14b are subjected to low heat input quenching and high heat input quenching, which will be described later. Here, low heat input quenching refers to high-frequency quenching using low power and high-frequency current, and high heat input quenching refers to high-frequency quenching using high power and low-frequency current. The shoulders SP of each of the raceway grooves 3a, 14a, and 14b are the parts shown by thick lines in Figures 2 and 3. By the above heat treatment, a heat treatment hardened layer is formed in the area from the surface of each of the raceway grooves 3a, 14a, and 14b to the position shown by the dashed line in Figure 2. Furthermore, by the above heat treatment, the stress distribution in the depth direction of the shoulders SP of each of the raceway grooves 3a, 14a, and 14b becomes as shown in Figure 4.

The depth direction of the shoulder portion SP of each of the raceway grooves 3a, 14a, and 14b means a direction perpendicular to a tangent at any point on the surface of the shoulder portion SP of each of the raceway grooves 3a, 14a, and 14b in a cross section passing through the axis C of the wheel bearing device 40, as shown by the arrow A in FIG. 3. In this embodiment, the stress distribution in the depth direction A of the shoulder portion SP of the raceway groove 14a will be described as an example.

As shown in FIG. 4, the horizontal axis indicates the depth position from the surface of the raceway groove 14a in the outer member 20 in the depth direction A, and the vertical axis indicates the stress value. The solid line in the graph in FIG. 4 represents the stress generated internally in the shoulder portion SP of the outer member 20 when an impact load acts on the wheel bearing device 40 (internal stress generated when an impact load acts). The thick dashed line in the graph in FIG. 4 represents the material yield stress (= proof stress) inside the outer member 20.

The outer member 20 has five regions R1 to R5 in the distribution of material yield stress in the depth direction A from the surface of the shoulder portion SP of the raceway groove 14a. The five regions R1 to R5 are arranged in the following order from the surface of the shoulder portion SP of the raceway groove 14a toward the depth: first region R1, fourth region R4, second region R2, fifth region R5, and third region R3.

The first region R1 is distributed along the depth direction A from the surface of the track groove 14a to a predetermined depth while maintaining the first yield stress ST1 (hardened layer formed by step S2 described later). The second region R2 is located in a region deeper than the first region R1 in the depth direction A (region farther from the surface) (hardened layer formed by step S3 described later). The second region R2 is distributed along the depth direction A to a predetermined depth while maintaining a second yield stress ST2 lower than the first yield stress ST1. The third region R3 is located in a region deeper than the second region R2 in the depth direction A (region farther from the surface) (unhardened layer). The third region R3 is distributed along the depth direction A to a predetermined depth while maintaining a third yield stress ST3 lower than the second yield stress ST2.

The difference between the first yield stress ST1 in the first region R1 and the second yield stress ST2 in the second region R2 is smaller than the difference between the second yield stress ST2 in the second region R2 and the third yield stress ST3 in the third region R3.

The fourth region R4 is located between the first region R1 and the second region R2 in the depth direction A (an intermediate layer between the first region R1 and the second region R2). The fourth region R4 is adjacent to both the first region R1 and the second region R2. The yield stress in the fourth region R4 is distributed so that the yield stress decreases with increasing depth (movement) from the surface from the first region R1 to the second region R2. Specifically, the yield stress in the fourth region R4 gradually decreases with increasing depth from the surface, from the yield stress ST1 in the portion in contact with the first region R1 to the yield stress ST2 in the portion in contact with the second region R2.

The fifth region R5 is located between the second region R2 and the third region R3 in the depth direction A (incomplete hardening layer). The fifth region R5 is adjacent to both the second region R2 and the third region R3. The yield stress in the fifth region R5 is distributed so that the yield stress decreases with increasing depth (away) from the surface from the second region R2 to the third region R3. Specifically, the yield stress in the fifth region R5 gradually decreases with increasing depth from the surface, from the yield stress ST2 in the portion adjacent to the second region R2 to the yield stress ST3 in the portion adjacent to the third region R3.

The crystal grains in the first region R1 are finer and smaller than the crystal grains in the second region R2. This results in a hardened layer in the first region R1 that is harder than the second region R2.

Meanwhile, the internally generated stress when an impact load is applied, shown by the solid line, is distributed in the depth direction A from the surface so that it is greater in the surface layer and smaller in the deeper areas. When comparing the internally generated stress and the yield stress at the same depth position from the surface, the yield stresses of all regions R1 to R5 are greater than the internally generated stress when an impact load is applied.

Although the above description has been given using the raceway groove 14a as an example, the stress distribution in the depth direction from the surface of each of the raceway grooves 3a and 14b is similar to that of the raceway groove 14a. It is preferable that at least the shoulder portion SP of each of the raceway grooves 3a, 14a, and 14b has the stress distribution shown in FIG. 4. That is, as shown in FIG. 4, at least the shoulder portion SP of each of the raceway grooves 3a, 14a, and 14b is preferably distributed in the order of the first region R1, the fourth region R4, the second region R2, the fifth region R5, and the third region R3 along the depth direction from the surface of at least the shoulder portion SP of each of the raceway grooves 3a, 14a, and 14b. It is also preferable that all of the yield stresses of the regions R1 to R5 along the depth direction from the surface of at least the shoulder portion SP of each of the raceway grooves 3a, 14a, and 14b are greater than the internally generated stress when a shock load is applied.

In addition, the stress distribution in the depth direction from the surface may be as shown in Figure 4 not only in the shoulder portion SP of each of the track grooves 3a, 14a, and 14b but also in the entire track grooves 3a, 14a, and 14b.

<Method of manufacturing wheel bearing device>
Next, a manufacturing method of the wheel bearing device according to this embodiment will be described with reference to FIGS.

As shown in FIG. 5, the manufacturing method of the wheel bearing device 40 in this embodiment mainly includes a preparation process (step S1) of the inner member 10 and the outer member 20, a low heat input quenching process (step S2), a high heat input quenching process (step S3), a tempering process (step S4), and an assembly process (step S5).

As shown in FIG. 2, in the preparation process for the inner member 10, a hub ring 1 having an annular raceway groove 3a on its outer peripheral surface and an inner ring 2 having an annular raceway groove 3b on its outer peripheral surface are prepared. In the preparation process for the outer member 20, an outer member 20 is prepared in which annular raceway grooves 14a, 14b are formed in double rows on its inner peripheral surface. In the rolling element preparation process, rolling elements (balls) 30a, 30b are prepared.

The hub ring 1 and the outer member 20 are each made of medium carbon steel containing 0.40% to 0.80% by mass of carbon, such as S53C. The inner ring 2 and the rolling elements 30a, 30b are made of high carbon chromium bearing steel, such as SUJ2.

The raceway groove 3a of the hub wheel 1 and the raceway grooves 14a, 14b of the outer member 20 prepared as described above are subjected to, for example, induction hardening (steps S2, S3) followed by tempering (step S4). This forms a predetermined hardened layer on the surface of each of the raceway grooves 3a, 14a, 14b. The induction hardening process includes, for example, a low heat input hardening process (step S2) followed by a high heat input hardening process (step S3).

The first-stage low-heat-input quenching process (step S2) is intended to refine the crystal grains in at least the surface layer of the shoulder portion SP of the track grooves 3a, 14a, and 14b. The first-stage low-heat-input quenching process (step S2) may refine the crystal grains in the entire surface layer of each of the track grooves 3a, 14a, and 14b.

The second stage high heat input hardening process (step S3) is intended to prevent buckling of deep tissue. The second stage high heat input hardening process (step S3) may be performed on the entirety of each of the track grooves 3a, 14a, and 14b.

In addition to induction hardening, laser hardening may be used in the first low-heat-input hardening process (step S2). Because the crystal grains in the surface layer are sufficiently refined by the first low-heat-input hardening process (step S2), the crystal grains in the surface layer are unlikely to become coarse even if the hardening is performed to the deeper parts in the second high-heat-input hardening process (step S3). This improves the mechanical strength, i.e., the yield strength, of the surface layer, and effectively prevents indentations in the surface layer and buckling in the deeper structure.

Meanwhile, the inner ring 2 is hardened to its core by deep quenching. The hub ring 1, inner ring 2, outer member 20, and rolling elements 30a, 30b prepared as described above are assembled to form the wheel bearing device 40 (step S5).

As shown in FIG. 2, in the assembly process, first, the inner ring 2, outer member 20, and multiple rolling elements 30b are combined so that the multiple rolling elements 30b held by the retainer 31b come into contact with the raceway grooves 3b, 14b and are arranged on a circular track. Then, the hub ring 1, outer member 20, and multiple rolling elements 30a are combined so that the multiple rolling elements 30a held by the retainer 31a come into contact with the raceway grooves 3a, 14a and are arranged on a circular track. At this time, the inner ring 2 is press-fitted into the hub ring 1.

After a lubricant such as lubricating grease is poured into the space (bearing space) between the inner member 10 and the outer member 20, a seal ring 32a is press-fitted between the outer peripheral surface of the hub wheel 1 and the inner peripheral surface of the outer member 20. A seal ring 32b is press-fitted between the outer peripheral surface of the inner ring 2 and the inner peripheral surface of the outer member 20.

In this manner, the wheel bearing device 40 of this embodiment is manufactured.

＜Effects＞
Next, the effects of the wheel bearing device according to this embodiment will be described.

In this embodiment, as shown in FIG. 4, the first region R1 having a yield stress ST1 higher than the yield stress ST2 in the second region R2 is provided at a predetermined depth from the surface of each of the track grooves 3a, 14a, and 14b. As a result, even if an impact load acts and stress is generated inside each of the track grooves 3a, 14a, and 14b, it is easy to make the yield stress ST1 higher than the generated stress. Therefore, even when an impact load or an excessive load acts, the generation of indentations in the track grooves 3a, 14a, and 14b can be suppressed.

Between the first region R1 and the third region R3, a second region R2 is provided, which has a yield stress ST2 greater than the yield stress ST3 of the third region R3. This makes it possible to suppress buckling in deep areas and also to suppress the occurrence of indentations due to buckling.

Furthermore, according to this embodiment, there is no need to increase the size of the wheel bearing device 40 in order to suppress indentations caused by impact loads or excessive loads. Therefore, it is possible to suppress the occurrence of indentations on the raceway surface when an excessive load or impact load acts on the bearing device, without hindering weight reduction.

Furthermore, according to this embodiment, as shown in Figures 2 and 4, at least one of the raceway grooves 3a, 14a, 14b has a first region R1, a fourth region R4, a second region R2, a fifth region R5, and a third region R3, which are distributed in order along the depth direction at least in the shoulder portion SP. This makes it possible to prevent indentations from being made on the shoulder even if the contact ellipse between the rolling elements 30a, 30b and the raceway surface rides up onto the shoulder portion SP of the raceway grooves 3a, 14a, 14b.

Furthermore, according to this embodiment, as shown in FIG. 4, the difference between the first yield stress ST1 in the first region R1 and the second yield stress ST2 in the second region R2 is smaller than the difference between the second yield stress ST2 in the second region R2 and the third yield stress ST3 in the third region. This makes it possible to suppress plastic deformation in the surface and deep parts of the shoulder portion SP, and to suppress the occurrence of indentations.

In addition, according to this embodiment, the hub wheel 1 and the outer member 20 are made of medium carbon steel containing 0.40% by mass or more and 0.80% by mass or less of carbon. This makes it possible to suppress the occurrence of indentations on the raceway surface when an excessive load or impact load acts on the bearing device, without hindering weight reduction in the hub wheel 1 and the outer member 20, which are made of medium carbon steel.

Next, the inventors' investigation will be explained as an example using Figures 6 to 9.

First, the inventors investigated the relationship between the yield stress when hardening with low heat input and the internal stress when impact load is applied. The results are shown in Figure 6. As shown in Figure 6, when hardening with low heat input, there are areas in both the surface and deep parts where the yield stress is lower than the internal stress when impact load is applied. Therefore, when impact load is applied, there is a risk of plastic deformation of the track groove in both the surface and deep parts. Plastic deformation in the surface part causes indentation, and plastic deformation in the deep part causes buckling. Buckling in the deep part is the so-called geological image of land subsidence, where plastic deformation occurs in the internal structure and propagates to cause indentation in the surface part. Figure 6 shows the internal stress (thick dashed line) under normal driving conditions other than when impact load is applied, but in this case, the yield stress when hardening with low heat input is not lower than the internal stress.

In the case of low heat input hardening, by increasing the frequency of the current passed through the hardening coil, the hardening depth becomes shallower, but the yield stress of the surface layer can be increased, for example, as shown in Figure 8. However, in this case, the area in the deeper part where the yield stress is lower than the internally generated stress when an impact load is applied expands, making buckling more likely to occur.

The inventors also investigated the relationship between the yield stress when hardening with a high heat input and the internal stress generated when an impact load is applied. The results are shown in Figure 7. As shown in Figure 7, when hardening with a high heat input is performed, the yield stress in the deep part is greater than the internal stress generated when an impact load is applied. This suppresses buckling in the deep part. However, in this case, the yield stress in the surface layer is smaller than the internal stress generated when an impact load is applied. For this reason, when an impact load is applied, the surface layer undergoes plastic deformation and is prone to indentations.

In contrast, in this embodiment, low heat input quenching is performed first, followed by high heat input quenching. For this reason, low heat input quenching is performed so that the yield stress in the surface layer is significantly greater than the internal stress generated when an impact load is applied, as shown in FIG. 8. In this state, the area in the deep part where the yield stress is lower than the internal stress generated when an impact load is applied becomes wider, making buckling more likely to occur. However, in this embodiment, high heat input quenching is performed after this. This high heat input quenching is performed so that the yield stress in the deep part is greater than the internal stress generated when an impact load is applied, as shown in FIG. 4. This suppresses the occurrence of buckling in the deep part.

In addition, by performing hardening with a high heat input, the crystal grains in the surface layer may become slightly larger, and the yield stress in the surface layer may decrease. However, if the crystal grains in the surface layer are sufficiently refined by the previous hardening with a low heat input, the grains will not become coarse even if hardening with a high heat input is performed. Therefore, even if hardening with a high heat input is performed, the yield stress of the surface layer can be maintained higher than the internal stress generated when a shock load is applied. As a result, as shown in FIG. 4, the yield stress is higher than the internal stress generated when a shock load is applied throughout the entire depth direction from the surface of the raceway grooves 3a, 14a, and 14b, making it difficult for indentations to occur. In this way, the improvement in the yield strength (mechanical strength) due to the improvement (refining) of the crystal grain size in the surface layer by hardening with a low heat input and the improvement in the yield strength of the deep structure by hardening with a high heat input work together to effectively suppress the occurrence of indentations in the surface layer.

A method can be considered in which the order of low heat input quenching and high heat input quenching is reversed, and low heat input quenching is performed after high heat input quenching. However, in this case, as shown in Figure 9, the heat-affected layer from low heat input quenching remains in the middle part (hatched part in Figure 9), and a quench boundary (incomplete combustion quenched structure, low hardness part) is generated in the middle part. This can cause buckling in the structure in the middle part. Therefore, from the viewpoint of suppressing the occurrence of indentations due to buckling, it is preferable to perform low heat input quenching followed by high heat input quenching.

The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 Hub ring, 1a Cylindrical part, 1b Hub flange, 1c Serration hole, 2 Inner ring, 3a, 3b, 14a, 14b Raceway groove, 10 Inner member, 11 Sleeve, 12 Flange, 13 Screw hole, 20 Outer member, 30a, 30b Rolling element, 31a First retainer, 31b Second retainer, 32a, 32b Seal ring, 40 Wheel bearing device, 51 Serration shaft, 52 Wheel, 53 Tire, 54 Hub bolt, 55 Hub nut, R1 First region, R2 Second region, R3 Third region, R4 Fourth region, R5 Fifth region, SP Shoulder.

Claims (4)

A wheel bearing device for rotatably supporting a wheel, comprising:
an inner member having a first raceway groove;
an outer member having a second raceway groove;
a plurality of rolling elements interposed between the first raceway groove and the second raceway groove,
At least one of the first raceway groove and the second raceway groove is
a first region having a first yield stress distributed from a surface of the at least one raceway groove along a depth direction;
a second region located in a region deeper than the first region in the depth direction and distributed along the depth direction with a second yield stress lower than the first yield stress;
a third region located in a region deeper than the second region in the depth direction and distributed along the depth direction with a third yield stress lower than the second yield stress;
a fourth region having a yield stress that decreases with increasing depth from the surface from the first region to the second region;
a fifth region having a yield stress that decreases with increasing depth from the surface from the second region to the third region;
A wheel bearing device , wherein the yield stress is greater than the internally generated stress when an impact load is applied in all of the first region, the second region, the third region, the fourth region and the fifth region . The wheel bearing device according to claim 1, wherein the at least one raceway groove has the first region, the fourth region, the second region, the fifth region, and the third region, which are distributed in order along the depth direction, at least in the shoulder portion. The wheel bearing device according to claim 1 or 2, wherein the difference between the first yield stress and the second yield stress is smaller than the difference between the second yield stress and the third yield stress. The wheel bearing device according to any one of claims 1 to 3, wherein the first raceway groove portion of the inner member and the second raceway groove portion of the outer member are made of medium carbon steel containing 0.40% by mass or more and 0.80% by mass or less of carbon.

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