JP2007051748A - Wheel bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wheel bearing device, which improves the strength of a hub in the neighborhood of an inner race contact surface of the hub to be brought into contact with the end face of the inner race on an outboard side, reduces the wear of that portion, and suppresses the drop of the productivity. <P>SOLUTION: The hub 14 comprises a stem portion 14a for fitting the inner race 15 of the bearing 1 thereon, and a flange 17 for mounting the wheel thereon. The end face of the inner race 15 on the outboard side is brought into contact with the inner race contact surface 40 elongating from an end portion of the external surface of the stem portion on the wheel mounting flange 17 side of the hub 14. The hub 14 is made of a steel material by hot forging, and has a standard structure in its base material. A region from at least the neighborhood of the inner race contact surface 40 in the external surface of the stem portion 14a of the hub 14 to the inner race contact surface 40 has a non-standard structure portion 30. The non-standard structure is any one of a fine ferrite-pearite structure, an upper bainite structure, a lower bainite structure, and a tempered martensite structure, or a mixed structure of at least two or more kinds of these structures. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bearing device for a wheel that has been improved in strength for passenger cars, freight cars, and the like.

  In the wheel bearing device, there is a portion where the stress increases when the automobile turns sharply. In a hub of a type in which the hub is provided independently of the bearing and the inner ring of the bearing is fitted to the outer periphery, the inner ring abutting surface formed near the root of the wheel mounting flange and the inner ring width surface abuts with the shaft portion. Corners between the outer peripheral surfaces show high stress when the vehicle turns sharply.

Therefore, in order to improve fatigue strength as a countermeasure against damage, a method has been proposed in which the entire part is tempered and the hardness is increased (for example, Patent Document 1). Further, there are a method for applying roller burnishing, a method for applying high-frequency heat treatment, and a method for performing shot peening.
JP-A-2005-003061

  However, in the case of the conventional method of refining the whole part and increasing the height, the number of processes is increased and the overall workability (for example, machinability and cold workability such as caulking) is improved by increasing the hardness. ) May decrease, and slip torque may decrease due to a decrease in biting performance of the hub bolt. In the roller burnish, the inner ring abutment surface of the hub cannot be processed, and due to fretting and creep, the inner ring abutment surface wear → axial force reduction, further creep → shaft wear, from the edge-shaped wear end Crack → Durability may be lowered. In addition, in high-frequency heat treatment, shot peening, and the like, the number of processes increases, the dimensions deteriorate due to thermal strain, and the deflection accuracy of the flange may deteriorate. In the case of high-frequency heat treatment, grinding is necessary as post-processing.

  On the other hand, in recent years, in order to improve fuel efficiency and reduce environmental load, it is strongly desired to reduce the size and weight of wheel bearing devices, and to reduce the size and weight while maintaining fatigue strength and life. It is necessary to plan.

  The object of the present invention is to improve the strength and fatigue strength in the vicinity of the inner ring contact surface of the hub with which the inner ring width surface on the outboard side abuts against high stress and repeated stress. It is an object of the present invention to provide a wheel bearing device in which wear can be reduced and a decrease in productivity due to an increase in processes is suppressed.

  The wheel bearing device of the present invention comprises a bearing in which rolling elements are interposed between the inner ring and the outer ring in a double row, and a hub having a shaft portion for fitting the inner ring of the bearing to the outer periphery and a wheel mounting flange. In the wheel bearing device in which the width surface of the inner ring on the outboard side is in contact with the inner ring contact surface extending from the end on the wheel mounting flange side to the outer diameter side of the outer peripheral surface of the hub portion of the hub, This hub is a forged product, and the hub has a standard structure in the base material portion, and a non-standard structure portion in a range extending from the vicinity of the inner ring contact surface to the inner ring contact surface on the outer peripheral surface of the shaft portion. And the non-standard structure is one of a fine ferrite / pearlite structure, an upper bainite structure, a lower bainite structure, a tempered martensite structure, or at least a mixture of two or more of these structures. Characterized in that it is a tissue.

The non-standard structure is, for example, a structure obtained by cooling during the hot forging process or at the end of the process for self-reheating or re-heating holding tempering.
Specifically, the fine ferrite / pearlite structure is obtained by partially cooling the part by immersing it in a coolant at the end of the hot forging step. Alternatively, when the hot forging process includes a plurality of forging processes, cooling is performed before the final forging process, and then the final forging process is performed. The tempered martensite structure is obtained by partially cooling the part to below the martensite start point at the end of the hot forging process and then performing reheat tempering. The upper bainite structure and the lower bainite structure are obtained by controlling to a predetermined cooling rate at the end of the hot forging step and cooling to about room temperature. The lower bainite structure can be obtained by lowering the cooling rate than that of the upper bainite structure.

According to the wheel bearing device having this configuration, the following effects can be obtained. When the vehicle is turning, for example, a large amplitude of flexure is repeatedly generated in the wheel mounting flange, and high stress is repeatedly generated at the corner between the inner ring contact surface and the outer peripheral surface of the hub, which is the root portion of the flange. When the corner between the inner ring contact surface and the outer peripheral surface of the hub is the above-mentioned non-standard structure against such repeated high stress, the strength and fatigue strength are improved by refining the structure and increasing the hardness. The occurrence of cracks is suppressed. That is, the effect of crack generation → increase in displacement of the stress generation site → increase in vehicle vibration → damage of the wheel bearing device is suppressed, thereby extending the life.
That is, the fine ferrite pearlite structure, the upper bainite structure, the lower bainite structure, any of the tempered martensite structure, or at least a portion of the non-standard structure of the mixed structure of two or more of these structures, Compared to the base material portion made of the standard structure, the structure is fine and the hardness is equal to or higher than that. This refinement and increased hardness improves the fatigue strength of the non-standard structure part, and can withstand higher stress amplitude, that is, higher strength and longer life compared to a hub consisting only of a normal standard structure. Can be Therefore, it can be reduced in size and weight as compared with a wheel bearing device having a normal standard structure. Accordingly, the input weight for manufacturing the wheel bearing device can be reduced, the cost can be reduced, and it can be provided at a low cost.

Since the part of the non-standard structure is obtained by cooling during the hot forging process or at the end of the process, it is only necessary to add a simple process, and a decrease in productivity due to an increase in the process can be suppressed. Moreover, since the heat of hot forging is used, the energy used for the process for the structure modification can be reduced.
The portion to be the non-standard structure may be the entire surface of the hub, but only at a necessary portion of the outer peripheral surface of the shaft portion of the hub ranging from the vicinity of the inner ring contact surface to the inner ring contact surface. , Deterioration of workability such as machinability is minimized.

  Further, since the hardness of the non-standard structure is higher than that of the standard structure, wear on the inner ring contact surface of the hub is reduced, and creep due to wear is suppressed. For this reason, the wear of the inner ring contact surface due to creep → axial force reduction, further creep generation → shaft wear → cracking from edge-shaped wear ends → durability degradation is suppressed.

  In this invention, you may provide the part of the said non-standard structure | tissue to the location where the inner ring | wheel on the inboard side in the outer peripheral surface of the said axial part fits. By providing a non-standard tissue portion over a wide range of the shaft portion, the strength and fatigue strength of the shaft portion are further improved.

In this invention, when the inner ring is fixed to the hub in the axial direction by pressing the width surface of the inner ring by a caulking portion that caulks the inboard side end of the shaft portion of the hub to the outer diameter side. It is preferable that the outer peripheral surface near the inboard side end of the shaft portion is a portion of the same standard structure as the base material.
When the vicinity of the inboard side end is a non-standard structure, it is difficult to process the crimped portion, but by using the standard structure, it is possible to prevent the workability of the crimping process from being lowered.

In the wheel bearing device of each configuration of the present invention, the hardness of the non-standard tissue portion and the standard tissue portion may be set as appropriate, for example, the non-standard tissue hardness is 20 to 40 HRC, The base material portion may have a hardness of 13 to 25 HRC.
The lower limit of the hardness of the non-standard structure portion is preferably 20 HRC or more, preferably 25 HRC or more, which is about the center of the base material hardness, in order to improve fatigue strength by increasing hardness. The upper limit of the hardness of the non-standard structure portion is preferably 40 HRC or less in order to ensure machinability.
The material used is carbon steel (C content 0.4 to 0.8%), but in the case of S53C, the hardness of the standard part is 13 to 25 HRC. In the case of performing cold working such as caulking, or taking into account the portion into which the hub bolt is press-fitted, it is preferable that the maximum is 25 HRC.

  In addition, in the wheel bearing device having the above-described configuration, the structure obtained by cooling at the end of the hot forging step may be cooled by reheating a normal hot forged product.

  The wheel bearing device of the present invention comprises a bearing in which rolling elements are interposed between the inner ring and the outer ring in a double row, and a hub having a shaft portion for fitting the inner ring of the bearing to the outer periphery and a wheel mounting flange. In the wheel bearing device in which the width surface of the inner ring on the outboard side is in contact with the inner ring contact surface extending from the end on the wheel mounting flange side to the outer diameter side of the outer peripheral surface of the hub portion of the hub, This hub is a forged product, and the hub has a standard structure in the base material portion, and a non-standard structure portion in a range extending from the vicinity of the inner ring contact surface to the inner ring contact surface on the outer peripheral surface of the shaft portion. And the non-standard structure is one of a fine ferrite / pearlite structure, an upper bainite structure, a lower bainite structure, a tempered martensite structure, or at least a mixture of two or more of these structures. Because of the structure, it is possible to improve the strength and fatigue strength near the inner ring contact surface of the hub where the inner ring width surface on the outboard side contacts with high stress and repeated stress, and wear of the inner ring contact surface And can contribute to weight reduction of the wheel bearing device. In addition, the non-standard structure is a structure obtained by cooling at the end of the hot forging process or at the end of the process for self-recuperation, or by recuperation holding and tempering. Reduction is suppressed.

A first embodiment of the present invention will be described with reference to FIGS. The wheel bearing device includes a double-row bearing 1 and a hub 14 for fitting the bearing 1 to the outer periphery. The bearing 1 is obtained by interposing rolling elements 3 in a double row between an inner ring 15 and an outer ring 2. The rolling elements 3 are held by a holder 4 for each row. The term “double row” as used herein refers to two or more rows and may be three or more rows, but in the illustrated example, it is two rows. The rolling element 3 is a tapered roller, but may be a ball. The outer ring 2 is integral and has a vehicle body mounting flange 12 on the outer periphery. At a plurality of locations in the circumferential direction of the vehicle body mounting flange 12, vehicle body mounting holes 13 including bolt insertion holes or screw holes are provided. The inner ring 15 is provided for each row. Both ends of the bearing space between the inner ring 15 and the outer ring 2 are sealed with seals 10 and 11.
In this specification, the side closer to the outer side in the vehicle width direction when attached to the vehicle body is referred to as the outboard side, and the side closer to the center in the vehicle width direction is referred to as the inboard side.

  The hub 14 has a shaft portion 14a for fitting the inner ring 15 to the outer periphery and a wheel mounting flange 17. The wheel mounting flange 17 is provided with bolt press-fit holes 18 at a plurality of locations in the circumferential direction, and hub bolts 19 are attached to the respective bolt press-fit holes 18 in a press-fit state. A through hole 21 through which a stem portion (not shown) of the outer ring of the constant velocity joint is inserted is provided at the center of the shaft portion 14a. An inner ring contact surface 40 extending toward the outer diameter side is provided at the end of the outer peripheral surface of the shaft portion 14a on the wheel mounting flange side, and the width surface of the inner ring 15 on the outboard side contacts the inner ring contact surface 40. . The inner ring 15 is fixed to the hub 14 in the axial direction between the inner ring abutment surface 40 by a caulking portion 14b obtained by caulking the inboard side end of the shaft portion 14a of the hub 14 to the outer diameter side. . Alternatively, the inner ring 15 may be fixed by pressing the stepped surface provided on the constant velocity joint outer ring against the width surface of the inner ring 15 without providing the crimping portion 14b.

  An annular pilot portion 20 concentric with the hub 14 protrudes from the base portion of the wheel mounting flange 17 of the hub 14. The pilot portion 20 includes a brake pilot 20a serving as a portion for guiding a brake disc that is attached to be overlaid on the side surface on the outboard side of the wheel mounting flange 17, and a wheel pilot 20b that protrudes further to the outboard side than the brake pilot 20a. Consists of. The pilot unit 20 may be divided into a plurality of portions provided with notches at a plurality of locations in the circumferential direction.

  The hub 14, the inner ring 15, and the outer ring 2 are all hot forged products of steel. Of these, the hub 14 has a non-standard tissue portion 30 that extends from at least the vicinity of the inner ring contact surface 40 to the inner ring contact surface 40 on the outer peripheral surface of the shaft portion. The base material portion of the hub 14 has a standard structure. The axial range of the non-standard tissue portion 30 extends to a position where the inner ring 15 on the inboard side is fitted on the outer peripheral surface of the shaft portion 14a, but up to a middle portion of the width dimension of the inner ring 15 on the inboard side. The outer peripheral surface closer to the inboard side than this is a part of the same standard structure as the base material. The entire inner ring abutment surface 40 is a non-standard tissue portion 30, but the inner ring abutment surface 40 may have only the inner peripheral portion as a non-standard tissue portion.

  The non-standard structure of the non-standard structure portion 30 is a structure obtained by, for example, locally cooling the hub 14 by bathing a coolant during or at the end of the hot forging process. For example, fine ferrite pearlite Any one of a structure, an upper bainite structure, a lower bainite structure, and a tempered martensite structure, or at least a mixed structure of two or more of these structures.

FIG. 3 shows a hot forging process among the manufacturing processes of the hub 14, and FIG. 4 shows a manufacturing process after hot forging of the hub 14.
As shown in FIG. 3A, a billet W1 as a material for one hub 14 is prepared by cutting a bar material or a pipe material (not shown) to a predetermined size. The billet W1 is subjected to a plurality of processes as a hot forging process, here, a forging 1 pass, a forging 2 pass, and a forging 3 pass, and gradually approaching the shape of the hub. A forged finished material W4 having a rough shape of 14 is obtained ((B) to (D) in the figure).

  The forged finished material W4 is turned as shown in FIG. After that, what is necessary is completed by grinding the shaft portion 14a and the like. (Figure (B)). The completed hub 14 is assembled into a wheel bearing device (FIG. 3C).

  As shown in FIG. 3D, the portion 30 of the non-standard structure of the hub 14 is modified by partially blowing a coolant to the modification target portion at the end of the forging process, or FIG. After the forging process (forging 2 pass) before the final forging process (forging 3 pass) as shown in FIG.

  As the refrigerant, a liquid, its mist or gas, for example, oil, low temperature air or the like is used. Also, depending on the application, lubricants, media, rust preventives, etc. may be mixed in the refrigerant to reduce the scale by material lubrication / mold release effect, mold wear prevention, cooling effect, shot blasting after forging, etc. The omission, the antirust effect, etc. may be obtained.

At the time of blowing the refrigerant, the refrigerant may be blown while rotating the materials W3 and W4 serving as the hub 14 around the axis so that the cooling is uniformly performed on the entire circumference. Moreover, you may rotate a refrigerant | coolant spraying apparatus (not shown), without rotating the raw materials W3 and W4.
The coolant may be sprayed by using a ring-shaped cooling jacket (not shown) having a large number of ejection holes, or if the materials W3 and W4 to be the hub 14 are rotated, one nozzle is provided. It may be sprayed from.

  When rotating the materials W3 and W4 to be the hub 14 during cooling, either the vertical axis or the horizontal axis may be used. Also, the direction in which the refrigerant is ejected may be either upward or downward when the rotational vertical axis is used, and may be any direction other than the horizontal direction when the rotational horizontal axis is used.

  The method of holding the materials W3 and W4 that will become the hub 14 during cooling may be as long as it does not hinder the cooling part from being uniformly cooled, holding the shaft part 14a, holding the outer diameter part of the wheel mounting flange 17, The outer diameter portion and inner diameter portion of the pilot portion 20 may be retained. When the hub 14 has a through hole 21 at the center as in the case of driving wheels, the hub 14 may be centered and held using the through hole 21 as a guide.

By cooling, the structure of the non-standard structure portion 30 is any one of the fine ferrite pearlite structure, the upper bainite structure, the lower bainite structure, and the tempered martensite structure, or at least two or more of these structures. Which of the mixed tissues is selected can be selected by a cooling method as shown in FIG.
In FIG. 5, the horizontal axis indicates the passage of time, and the vertical axis indicates the temperature. In the figure, A ₃ is the temperature that becomes the A ₃ transformation point, and A ₁ is the temperature that becomes the A ₁ transformation point. M _s is a martensite start point (hereinafter referred to as “M _s point”), and M _f is a martensite finish point (hereinafter referred to as “M _f point”).
The steel material used as the material is carbon steel having a C content of 0.4 to 0.8%, such as S53C.

5, as shown by the curve (0), when simply cooled from forging the component temperature T1 (A greater than ₃ transformation point), the standard organization is a tissue of the conventional forging, that is, a ferrite-pearlite structure.

  Curve (1) is a cooling curve when a fine ferrite / pearlite structure is obtained as a non-standard structure. Until the end of the hot forging process, that is, until the hot forging is finished and cooling, the component (material) to be reformed is partially cooled by being exposed to a coolant as shown in FIG. By limiting the cooling time and allowing self-recuperation after cooling, a fine ferrite and pearlite structure can be obtained as the non-standard structure. The fine ferrite pearlite structure is a structure obtained by normalization, that is, a normalization structure.

  Curve (2) shows another cooling curve when a fine ferrite / pearlite structure is obtained as a non-standard structure. In this case, as shown in FIG. 3, when the hot forging process is composed of a plurality of forging processes, the component (material W3) is placed before the final forging process (FIG. 3D) (FIG. 3C). ) Is partially or wholly cooled, and then the final forging step (FIG. 3D) is performed. The final forging step is performed during the self-recuperation after the cooling. Thus, by adding one of the forging steps after cooling, dynamic strain is given and a fine ferrite / pearlite structure is obtained.

Curves (3) and (4) show cooling curves when a tempered martensite structure, which is a tempered structure, is obtained as a non-standard structure. At the end of the hot forging process, the part is partially cooled to a range below the M _s point and above the M _f point, and then reheated and tempered within a predetermined temperature range, thereby providing a tempered structure as a non-standard structure. That is, a tempered martensite structure is obtained. When the recuperating and tempering temperature is about 500 to 600 ° C., the structure becomes sorbite. When the recuperating and tempering temperature is about 350 to 400 ° C., the structure becomes troostite.

  Curves (5) and (6) show the cooling curves when upper bainite and lower bainite are obtained as non-standard structures, respectively. At the end of the hot forging process, as a controlled cooling, the structure becomes upper bainite by cooling slightly slower than the quenching cooling rate (cooling rate generated by martensite). When quenching is performed at a cooling rate slower than the cooling rate, the structure becomes lower bainite.

  Although various cooling methods have been described with reference to FIG. 5, when the non-standard tissue portion 30 is provided in the local range of the outer peripheral surface of the shaft portion 14 a and the inner ring contact surface 40 in the example of FIG. Of the cooling methods indicated by the curves (1) to (6), the methods indicated by the curves (1) to (4) are preferred. When the entire surface of the part is the non-standard texture portion 30, the method shown in the cooling curves (5) and (6) may be used.

  According to the wheel bearing device of this configuration, the following effects can be obtained. When the vehicle turns, for example, the wheel mounting flange 17 is repeatedly bent with a large amplitude, and a high stress is applied to the corner portion 41 between the inner ring contact surface 40 and the outer peripheral surface of the hub 14 serving as the root portion of the flange 17. Repeatedly occurs. When the corner portion 41 between the inner ring contact surface 40 and the outer peripheral surface of the hub 14 is the above-mentioned non-standard structure with respect to such high stress that repeatedly occurs, the strength and fatigue strength can be increased by refining the structure and increasing the hardness. Is improved, and the occurrence of cracks is suppressed. That is, the action of crack generation → increased displacement of the wheel mounting flange 17 → increased vibration of the vehicle → damage of the wheel bearing device is suppressed and the life is extended.

  That is, the fine ferrite pearlite structure, the upper bainite structure, the lower bainite structure, any of the tempered martensite structure, or at least a portion of the non-standard structure of the mixed structure of two or more of these structures, Compared to the base material portion made of the standard structure, the structure is fine and the hardness is equal to or higher than that. This refinement and increased hardness improves the fatigue strength of the non-standard structure part, and can withstand higher stress amplitude, that is, higher strength and longer life compared to a hub consisting only of a normal standard structure. Can be Therefore, it can be reduced in size and weight as compared with a wheel bearing device having a normal standard structure. Accordingly, the input weight for manufacturing the wheel bearing device can be reduced, the cost can be reduced, and it can be provided at a low cost.

  Since the non-standard-structure portion 30 is obtained by cooling during the hot forging process or at the end of the process, it is only necessary to add a simple process, and a decrease in productivity due to an increase in the process can be suppressed. Moreover, since the heat of hot forging is used, the energy used for the process for the structure modification can be reduced. The non-standard tissue portion 30 may be the entire surface of the hub 14, but a range extending from the vicinity of the inner ring contact surface 40 to the inner ring contact surface 40 on the outer peripheral surface of the shaft portion 14 a of the hub 14. If only the necessary parts are used, deterioration of workability such as machinability can be minimized.

  Further, since the hardness of the non-standard structure is higher than that of the standard structure, the wear of the inner ring contact surface 40 of the hub 14 that comes into contact with the inner ring 152 on the outboard side is reduced, and creep due to wear is suppressed. Is done. For this reason, the wear of the inner ring contact surface 40 due to creep → axial force reduction, further creep generation → shaft wear → cracking from edge-shaped wear ends → durability degradation is suppressed.

6 to 8 each show another embodiment of the present invention. Also in each of these embodiments, by providing the non-standard tissue portion 30 in a range extending from at least the vicinity of the inner ring contact surface 40 to the inner ring contact surface 40 on the outer peripheral surface of the shaft portion 14a of the hub 14, the structure By miniaturization and increased hardness, the strength and fatigue strength are improved and the life can be extended. Further, by increasing the hardness of the inner ring contact surface 40, wear due to creep is reduced, and an increase in creep and a decrease in durability of the shaft portion 14a due to this are suppressed.
In each of these embodiments, the matters other than those specifically described are the same as those of the first embodiment described with reference to FIGS.

  The wheel bearing device of FIG. 6 is the wheel bearing device according to the first embodiment shown in FIGS. 1 to 5 for a driven wheel, and the shaft portion 14a of the hub 14 is the same as in the example of FIG. The central through hole 21 is not provided.

  The wheel bearing device of FIG. 7 is of an angular ball bearing type for driving wheel support, and the outer ring 2 does not have the body mounting flange 12 in the example of FIG. It is a cylindrical surface. The inner ring 15 is provided for each row, but the inner ring 15 on the inboard side is larger in thickness and axial dimension than the inner ring 15 on the outboard side. The inner ring 15 may be the same size in both rows.

  The wheel bearing device of FIG. 8 is of the angular ball bearing type for supporting the drive wheels, like the wheel bearing device of FIG. 7, but the inner rings 15 in both rows are of the same size. In this example, the caulking portion 14 b of the example of FIG. 7 is not provided in the hub 14, and the inner ring 15 is fixed in the axial direction by a constant velocity joint (not shown) coupled to the hub 14.

  7 and 8 is for driving wheel support, it may be a wheel bearing device for driven wheel support. Moreover, what was obtained by cooling the last of a hot forging process in each said embodiment may cool what heated the normal hot forging goods.

It is sectional drawing which shows the wheel bearing apparatus which concerns on 1st Embodiment of this invention. It is sectional drawing of the hub of the bearing apparatus for wheels. It is process explanatory drawing of the forge process of the hub of the bearing apparatus for wheels. It is process explanatory drawing of the process after the forge of the hub of the bearing apparatus for wheels. It is explanatory drawing of the cooling curve which obtains various non-standard structure | tissues of the hot forged components. It is sectional drawing of the wheel bearing apparatus which concerns on other embodiment of this invention. It is sectional drawing of the wheel bearing apparatus which concerns on other embodiment of this invention. It is sectional drawing of the wheel bearing apparatus which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Bearing 2 ... Outer ring 3 ... Rolling body 6-9 ... Track surface 12 ... Body mounting flange 14 ... Hub 14a ... Shaft part 14b ... Clamping part 40 ... Inner ring contact surface 15 ... Inner ring 17 ... Wheel mounting flange 20 ... Pilot part 30 ... Non-standard part

Claims (4)

A bearing having rolling elements interposed between the inner ring and the outer ring in a double row, and a hub having a shaft portion for fitting the inner ring of the bearing to the outer periphery and a wheel mounting flange. In the wheel bearing device in which the width surface of the inner ring on the outboard side contacts the inner ring contact surface extending from the end on the wheel mounting flange side to the outer diameter side,
The hub is a hot forged product of steel material, and the hub has a standard structure in a base material portion, and a range extending from at least the vicinity of the inner ring contact surface to the inner ring contact surface on the outer peripheral surface of the shaft portion. And the non-standard structure is one of a fine ferrite / pearlite structure, an upper bainite structure, a lower bainite structure, a tempered martensite structure, or at least two of these structures. A wheel bearing device characterized by a mixed structure of more than one type. A bearing having rolling elements interposed between the inner ring and the outer ring in a double row, and a hub having a shaft portion for fitting the inner ring of the bearing to the outer periphery and a wheel mounting flange. In the wheel bearing device in which the width surface of the inner ring on the outboard side contacts the inner ring contact surface extending from the end on the wheel mounting flange side to the outer diameter side,
The hub is a hot forged product of steel material, and the hub has a standard structure in a base material portion, and a range extending from at least the vicinity of the inner ring contact surface to the inner ring contact surface on the outer peripheral surface of the shaft portion. The non-standard structure is a structure obtained by cooling during the hot forging process or at the end of the process for self-reheating or reheating holding tempering. Wheel bearing device.   3. The wheel bearing device according to claim 1, wherein the portion of the non-standard structure is provided up to a place where the inner ring on the inboard side on the outer peripheral surface of the shaft portion is fitted.   4. The shaft according to claim 3, wherein the inner ring is fixed to the hub in the axial direction by pressing a width surface of the inner ring by a crimping portion obtained by crimping an inboard side end of the shaft portion of the hub to the outer diameter side. Wheel bearing device in which the outer peripheral surface near the inboard side end of the part has the same standard structure as the base material.

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