JP5105722B2 - Wheel bearing device - Google Patents

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 a wheel bearing device for a driven wheel, a concave portion that is recessed in the axial direction is formed on the end face of the hub on the outboard side in order to reduce the weight. When such a recess is formed deeply, the strength of the outer peripheral portion of the recess in the shaft portion of the hub may be insufficient. That is, the outer peripheral portion of the concave portion serves as a root portion of the wheel mounting flange, and high stress is repeatedly generated at the base portion of the wheel mounting flange when the vehicle suddenly turns.

Therefore, in order to improve fatigue strength as a countermeasure against damage, a method of subjecting the inner surface of the recess to high-frequency heat treatment or a method of performing shot peening (for example, Patent Document 1) has been proposed.
Further, in order to increase the fatigue strength, a method of tempering the entire part and increasing the hardness has been proposed (for example, Patent Document 2).

  FIG. 11 shows an example of a general manufacturing method of a hub in a conventional third-generation wheel bearing device. The bar material W0 shown in FIG. 6A is cut to a predetermined size to obtain a billet W1 that is a material of one hub (FIG. 5B). The billet W1 is a hot forging process that passes through a plurality of processes (forging 1 pass, forging 2 pass, forging 3 pass) and gradually approaches the shape of the hub. A finished material W4 is obtained (FIGS. (C) to (E)).

The forged finished material W4 is shot blasted for scale reduction, normalized or tempered as necessary (Fig. (F)), then turned (Fig. (G)), and raceway surface And the like (FIG. (H)). What is necessary is secondary turning of the flange surface, etc. ((I) in the figure). Thereafter, grinding is performed to finish the hub 14, and the wheel bearing device is assembled.
JP 2005-145313 A JP-A-2005-003061

  Conventional high-frequency heat treatment for improving fatigue strength is performed after hub forging and turning. Therefore, in the high frequency heat treatment, there is a possibility that the number of processes increases or the runout accuracy of the wheel mounting flange is deteriorated due to thermal strain or the like.

In shot peening, there is a problem that the number of processes increases.
In the case of increasing the hardness by refining the entire part, the number of processes is increased and the overall workability (for example, machinability and cold workability such as caulking) decreases due to the increased hardness. In addition, slip torque may be reduced due to a decrease in the biting property of the hub bolt.

  In the conventional method shown in FIG. 11, normalization or tempering is performed to improve the overall fatigue strength of the hub 14. In addition, since heating is performed again after forging is completed and cooled, energy consumption increases. There are cases where normalization and tempering are omitted, but if these are omitted, the crystal grains of the structure are large, the strength and toughness are lowered, and the fatigue strength is weak.

  In recent years, in order to improve fuel efficiency and reduce environmental impact, wheel bearing devices are also strongly desired to be smaller and lighter, and while maintaining fatigue strength and life, they are also smaller and lighter. It is necessary to plan. Therefore, it is necessary to make the concave portion of the hub end surface as large as possible.

  The object of the present invention is to improve the strength and fatigue strength in the vicinity of the concave portion of the hub shaft portion against high stress and repeated stress while providing a concave portion on the end surface of the hub to reduce weight, and An object of the present invention is to provide a wheel bearing device in which an increase in energy cost for reforming and a decrease in productivity due to an increase in processes are suppressed.

A wheel bearing device according to the present invention includes an inner member and an outer member that are rotatable with respect to each other via a double row of rolling elements, and the inner member includes a hub having a wheel mounting flange, and a shaft of the hub. An inner ring fitted to the outer periphery of the part, and the hub has a pilot part projecting from a root part of the wheel mounting flange on an end face on the outboard side, and guiding a wheel and a braking component. In the wheel bearing device in which a portion closer to the center than the pilot portion on the end surface on the board side is a concave portion recessed in the axial direction, the hub has a carbon content of 0.4 to 0. This hub is a hot forged product made of 8% by mass carbon steel, and this hub has a standard structure in which the base material part is a ferrite pearlite structure, and a part of the non-standard structure on the surface in the recess of the end face. 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 mixed structure of two or more of these structures. The fine ferrite / pearlite structure is a structure obtained by normalizing the ferrite / pearlite structure, and the hardness of the portion of the non-standard structure is 25 to 40 HRC. The hub referred to here may be a hub that is independent of the bearing, or may be a hub that forms a raceway surface and constitutes a part of the bearing.

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. Since the recess is provided on the end surface of the hub, the hub can be reduced in weight. In this case, the recess on the end face of the hub is located on the inner circumference of the wheel mounting flange of the hub, and a large amplitude flexure is repeatedly generated in the wheel mounting flange when the automobile turns. High stress is repeatedly generated in the shaft portion of the hub which is the root portion of the flange due to the bending of the wheel mounting flange. Since the flange root portion of the hub shaft portion is around the recess, it is difficult to ensure the strength if the recess is deepened. However, when the inner surface of the recess on the end face of the hub is the non-standard structure against such high stress that repeatedly occurs, the strength and fatigue strength are improved by the refinement of the structure and the increase in hardness, and cracks are generated from the recess. Occurrence is suppressed. That is, the effect of crack generation → increased displacement of the wheel mounting flange → increase in vehicle vibration → damage of the wheel bearing device is suppressed, and the life is extended. Therefore, the strength and fatigue strength of the hub shaft near the recess can be improved against high stress and repeated stress while sufficiently reducing the weight of the recess on the end surface of the hub.

  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. By such structure refinement and hardness increase, the strength and fatigue strength of the non-standard structure part are improved, and it withstands high stress amplitude, that is, increased in strength, compared to a hub consisting only of a normal standard structure, Long life can be achieved. Therefore, the weight can be reduced 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. Further, there is no problem of thermal distortion in the case of high-frequency heat treatment or the like.
The non-standard tissue portion may be provided at least in the concave portion of the end surface of the hub. For example, the non-standard tissue portion may be provided on the entire surface of the hub. Unlike the case of using a non-standard structure, the deterioration of workability such as machinability and caulking properties can be minimized.

  The concave portion of the hub end surface has a shape that becomes deeper as it reaches the axial center of the hub, and the deepest portion is equal to the position of the wheel mounting flange or is deeper in the axial direction than the wheel mounting flange. It may be. Even in such a deep recess, the strength and fatigue strength can be ensured by providing the non-standard structure portion on the inner surface.

The portion of the non-standard structure provided in the concave portion of the hub end surface may be substantially the entire surface of the concave portion, or may be the bottom side portion of the concave portion. This bottom portion is, for example, a portion closer to the bottom than the center of the depth.
From the viewpoint of improving strength and fatigue strength, it is preferable to provide a non-standard structure portion on substantially the entire surface of the recess, but when the location where strength is required on the inner surface of the recess is the bottom portion of the recess Even if the non-standard structure portion is provided only on the bottom portion, the strength and fatigue strength can be improved against high stress and repeated stress.

The inner member may be composed of a hub and an inner ring fitted to the outer periphery of the inboard side end of the hub, and each of the hub and the inner ring may have a raceway surface in each row.
Further, the hub may be a hub that is independent of a finished product of, for example, a double row bearing. That is, the hub may not have a raceway surface, and the inner ring may have a double row raceway surface.

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 set to 20 HRC or more, preferably 25 HRC or more, which is about the center value 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 40 HRC or less in order to ensure machinability.
The material used is carbon steel (C content 0.4 to 0.8 mass% ), but in the case of S53C or the like, the hardness of the standard structure portion 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.

A wheel bearing device according to the present invention includes an inner member and an outer member that are rotatable with respect to each other via a double row of rolling elements, and the inner member includes a hub having a wheel mounting flange, and a shaft of the hub. An inner ring fitted to the outer periphery of the part, and the hub has a pilot part projecting from a root part of the wheel mounting flange on an end face on the outboard side, and guiding a wheel and a braking component. In the wheel bearing device in which a portion closer to the center than the pilot portion on the end surface on the board side is a concave portion recessed in the axial direction, the hub has a carbon content of 0.4 to 0. This hub is a hot forged product made of 8% by mass carbon steel, and this hub has a standard structure in which the base material part is a ferrite pearlite structure, and a part of the non-standard structure on the surface in the recess of the end face. 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 mixed structure of two or more of these structures. among is any one of, the fine ferrite-pearlite structure is a woven set obtained by normalizing the ferrite-pearlite structure, due to the 25~40HRC the hardness of the portion of the non-standard structure, the recess on the end surface of the hub It is possible to improve the strength and fatigue strength of the hub shaft near the recess against high stress and repeated stress while reducing the weight. And it is possible to suppress a decrease in productivity due to an increase or step up the energy cost for the reformer.

  In addition, in the wheel bearing device of each of the above-described configurations of the present invention, the structure obtained by cooling at the end of the hot forging step can be obtained by cooling a reheated normal hot forged product. good.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an example of a wheel bearing device, and this example is applied to support a third generation driven wheel. This wheel bearing device has an inner member 1 and an outer member 2 that are rotatable with respect to each other via a double row of rolling elements 3, and the rolling elements 3 are held by a cage 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 inner member 1 and the outer member 2 have double-row raceway surfaces 6 and 7 and raceway surfaces 8 and 9, respectively. This wheel bearing device is a double-row angular contact ball bearing type, the rolling elements 3 are formed of balls, and the raceway surfaces 6 and 7 are formed so that the contact angles are outward. Both ends of the bearing space between the inner member 1 and the outer member 2 are sealed with seals 10 and 11.

  The outer member 2 is composed of a single integral part, and a vehicle body mounting flange 12 is provided at an arbitrary position in the width direction. The outer diameter surface portion of the outer member 2 closer to the inboard side than the vehicle body mounting flange 12 is a surface to which a knuckle (not shown) serving as a suspension device of the vehicle body is fitted. 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. 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 member 1 is composed of two parts, a hub 14 and an inner ring 15 fitted to the outer periphery of the inboard side end of the shaft portion 14a of the hub 14. The hub 14 and the inner ring 15 are formed with the raceway surfaces 6 and 7 on the inner member 1 side. An inner ring fitting surface 16 having a step and a small diameter is provided at the inboard side end on the outer periphery of the shaft portion 14 a of the hub 14, and the inner ring 15 is fitted to the inner ring fitting surface 16. The inner ring 15 is fixed in the axial direction with respect to the hub 14 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.

The hub 14 has a wheel mounting flange 17 on the outer periphery of the end on the outboard side of the shaft portion 14a. A hub bolt is inserted into each bolt press-fitting hole 18 provided at a plurality of locations in the circumferential direction of the wheel mounting flange 17. 19 is attached in a press-fit state.
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 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.

  A portion closer to the center than the pilot portion 20 on the end face of the hub 14 on the outboard side is a recess 40 that is recessed in the axial direction. The recess 40 may have a concave spherical shape that becomes deeper as it reaches the axial center of the hub 14, and the bottom side portion 40b may have a spherical shape with a smaller radius of curvature than the opening side portion 40a. The deepest portion of the recess 40 is recessed deeper in the axial direction than the side surface on the inboard side of the wheel mounting flange 17, and reaches the axial position in the vicinity of the track surface 6 on the outboard side of the hub 14. The boundary between the bottom side portion 40b and the opening side portion 40a is located near the axial position of the side surface of the wheel mounting flange 17 on the inboard side.

  The hub 14, the inner ring 15, and the outer member 2, which are parts constituting the inner member 1, are all hot forged products of steel. Of these, the hub 14 has a non-standard tissue portion 30 that is substantially the entire inner surface of the recess 40 at the end face. The base material portion of the hub 14 has a standard structure. 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 (not shown) into a fixed 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 material W4, which is a forged finished product having 14 rough shapes, is obtained (FIGS. (B) to (D)).

  The forged finished material W4 is turned as shown in FIG. 4A, and the raceway surface 6 and the inner ring fitting surface 16 are subjected to high-frequency heat treatment (FIG. 4B). Thereafter, the raceway surface 6 and the like are ground ((D) in the figure). What is required is secondary turning of the surface of the wheel mounting flange 17 and the like before grinding ((C) in the figure). The hub 14 for which the raceway surface has been ground is assembled into a wheel bearing device (FIG. 5E).

  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 concave portion 40 of the hub end surface, which is a modification target portion, at the end of the forging process. Or after the forging process (forging 2 pass) before the final forging process (forging 3 pass) as shown in FIG. 3 (C), the material is reformed by partially blowing the coolant to the site to be reformed. .

  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 spraying the coolant, the coolant may be sprayed while rotating the material W4 serving as the hub 14 around its 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 material W4.
The coolant may be sprayed by using a ring-shaped cooling jacket (not shown) having a large number of ejection holes, or by spraying from a single nozzle if the material W4 to be the hub 14 is rotated. It may be a thing.

  When rotating the material W4 that becomes 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. In addition, when cooling the recessed part 40 which is not penetrating the inner diameter side of the pilot part 20 of the hub 14 as in the example of FIG. 1, it is preferable to spray upward so that the refrigerant does not accumulate. In FIG. 3 (D), it is shown to be ejected downward, but this is upside down.

  The method of holding the material W4 that becomes the hub 14 at the time of cooling does not have to prevent the cooling part from being uniformly cooled, and holds the shaft part 14a, the outer diameter part of the wheel mounting flange 17, and the pilot part. For example, 20 outer diameter portions or inner diameter portions may be held.

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. Any of the mixed tissues 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”).
As for the steel material used as a raw material, for example, the amount of C such as S53C is 0.4-0. 8 mass% carbon steel.

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. 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 are described in FIG. 5, when the non-standard tissue portion 30 is provided in the recess 40 of the hub 14 in the example of FIG. 1, the curves (1) to (6) in FIG. Of the cooling methods shown, the methods shown in curves (1) to (4) are preferred. Further, 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. The surface in the recess 40 at the end face of the hub 14 is a non-standard structure portion 30, and the non-standard structure is any one of a fine ferrite / pearlite structure, an upper bainite structure, a lower bainite structure, and a tempered martensite structure. Alternatively, since at least two or more of these structures are mixed, the strength of the portion 14c between the inner surface of the recess 40 and the outer peripheral surface of the shaft portion of the hub 14 is improved, and a long life is obtained. That is, when the automobile turns, for example, a large amplitude flexure is repeatedly generated in the wheel mounting flange 17, and high stress is repeatedly generated in the root portion of the flange 17. High stress is repeatedly generated in the outer peripheral portion 14c of the recess 40 in the shaft portion 14a of the hub 14 serving as the root portion. When the inner surface portion 30 of the recess 40 has a non-standard structure against such repeated high stress, the structure is finer and the hardness is equal to or higher than that of the base material portion made of the standard structure. The strength and fatigue strength are improved by refining the structure and increasing the hardness. Therefore, compared with a hub made of only a normal standard structure, the strength is increased, it can withstand a high stress amplitude, and the occurrence of cracks in the outer peripheral portion 14c of the recess is suppressed, and the life can be extended. 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.
Therefore, the strength and fatigue strength of the recessed portion outer peripheral portion 14c of the hub shaft portion 14b can be improved against high stress and repeated stress while making the recessed portion 40 as large as possible to reduce the weight.

  Therefore, it is possible to reduce the weight as compared with a wheel bearing device of a normal standard structure. Therefore, 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. It becomes.

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. For example, the process can be simplified as compared with the case of normalizing or tempering. Further, since the heat of hot forging is used, energy used for the processing for modifying the structure can be reduced unlike high-frequency heat treatment or the like. Further, there is no problem of thermal distortion in the case of high-frequency heat treatment or the like.
Since the non-standard texture portion 30 is the inner surface of the recess 40, a decrease in workability such as the machinability of other portions of the hub 14 and the caulking performance of the caulking portion 14b can be minimized.

In the above embodiment, the substantially entire surface of the end surface of the hub 14 in the recess 40 is the non-standard tissue portion 30, but the non-standard tissue portion 30 is, for example, as shown in FIG. Only the portion 40b may be used. Specifically, in this example, an annular inner surface portion from the vicinity of the side surface on the inboard side of the wheel mounting flange 17 to the vicinity of the deepest portion of the recess 40 is used as the non-standard tissue portion 30. Further, as described above, the non-standard tissue portion 30 is provided in the bottom side portion 40b which is a portion having a small curvature radius among the two concave spherical surfaces having different curvature radii.
Since the portion where the repeated stress from the wheel mounting flange 17 acts is mainly the portion between the wheel mounting flange 17 and the raceway surface 6 in the outer peripheral portion 17c of the recess 40, the bottom side portion as described above. Even if the non-standard tissue portion 30 is provided only on 40b, the strength and fatigue strength can be improved against high stress and repeated stress acting through the wheel mounting flange 17.

7 to 10 each show another embodiment of the present invention. Also in each of these embodiments, by providing the non-standard tissue portion 30 on the inner surface of the concave portion 40, while providing the concave portion 40 on the end surface of the hub 14 to reduce the weight, against high stress and repeated stress, The strength and fatigue strength of the hub shaft portion 14b in the vicinity of the recess 40 can be improved, and an increase in energy cost for reforming and a decrease in productivity due to an increase in processes can be 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.
7 to 10 show examples in which the non-standard tissue portion 30 is provided on substantially the entire inner surface of the recess 40. In these examples of FIGS. 7 to 10, the example of FIG. Similarly, the non-standard tissue portion 30 may be provided only on the bottom side portion 40b which is a part of the recess 40.

  The wheel bearing device of FIG. 7 is of an angular ball bearing type for supporting a driven wheel, and the inner member 1 is a double row in which the hub 14 and the outer periphery of the shaft portion 14a of the hub 14 are fitted. It consists of an inner ring 15. The inner ring 15 is provided for each row, and 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 is fixed to the hub 14 in the axial direction by a caulking portion 14 b provided on the hub 14. The outer member 2 is composed of one integral part, and the outer diameter surface is a cylindrical surface throughout, and does not have the vehicle body mounting flange 12 in the example of FIG.

  The wheel bearing device of FIG. 8 is of a tapered roller bearing type for supporting a driven wheel, and the inner member 1 is a double row in which the inner member 1 is fitted to the outer periphery of the hub 14 and the shaft portion 14a of the hub 14. It consists of an inner ring 15. The inner ring 15 is provided for each row. The outer member 1 is composed of a single component.

  The wheel bearing device of FIG. 9 is an angular ball bearing type for supporting a driven wheel, as in the example of FIG. 7, and the inner member 1 includes a hub 14 and an outer periphery of a shaft portion 14 a of the hub 14. And a double row of inner rings 15 fitted to each other. The inner ring 15 is provided for each row. In this example, the inner rings 15 in both rows are of the same size. Other configurations are the same as the example of FIG.

  The wheel bearing device of FIG. 10 is such that the outer member 2 has a vehicle body mounting flange 12 on the outer periphery in the example of FIG. Other configurations are the same as those in the example of FIG.

  In each of the above embodiments, the non-standard tissue portion 30 is partially provided on the surface of the component constituting the inner member 1, but the component constituting the inner member 1, the surface of the hub 14. May be used as the non-standard tissue portion 30.

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. It is sectional drawing of the wheel bearing apparatus which concerns on other embodiment. It is sectional drawing of the wheel bearing apparatus which concerns on other embodiment. It is sectional drawing of the wheel bearing apparatus which concerns on other embodiment. It is process explanatory drawing which shows the forge process of the hub of the conventional wheel bearing apparatus, and a subsequent process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Inner member 2 ... Outer member 3 ... Rolling elements 6-9 ... Track surface 12 ... Body mounting flange 14 ... Hub 14a ... Shaft part 14b ... Clamping part 14c ... Recess inner surface and hub shaft outer peripheral surface Intermediate part 17 ... Inner ring 17 ... Wheel mounting flange 20 ... Pilot part 30 ... Non-standard structure part 40 ... Recess 40b ... Bottom side part

Claims (7)

An inner member and an outer member that are rotatable with respect to each other via double row rolling elements, the inner member having a hub having a wheel mounting flange, and an inner ring fitted to the outer periphery of the shaft portion of the hub, The hub has a pilot portion that projects from a root portion of the wheel mounting flange on the end surface on the outboard side, and guides the wheel and the brake component, and the pilot portion on the end surface on the outboard side of the hub In the wheel bearing device in which the center side portion is a recess recessed in the axial direction,
The hub has a carbon content of 0.4-0. This hub is a hot forged product made of 8% by mass carbon steel, and this hub has a standard structure in which the base material part is a ferrite pearlite structure, and a part of the non-standard structure on the surface in the recess of the end face. 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 mixed structure of two or more of these structures The wheel bearing device is characterized in that the fine ferrite / pearlite structure is a structure obtained by normalizing the ferrite / pearlite structure, and the hardness of the portion of the non-standard structure is 25 to 40 HRC. According to claim 1, before Symbol nonstandard tissue, a wheel bearing apparatus is a tissue obtained by the or recuperation holding tempered to self recuperator is cooled at the end of the process or during the process of hot forging .   3. The recess according to claim 1, wherein the concave portion has a shape that becomes deeper as it reaches the axial center of the hub, and the deepest portion is equal to the position of the wheel mounting flange or is more axial than the wheel mounting flange. Wheel bearing device that is deeply recessed in the direction.   4. The wheel bearing device according to claim 1, wherein the portion of the non-standard structure is a substantially entire surface of the concave portion. 5.   4. The wheel bearing device according to claim 3, wherein the portion of the non-standard structure is a bottom portion of the recess.   6. The inner surface according to claim 1, wherein the inner member includes a hub and an inner ring fitted to an outer periphery of an inboard side end of the hub. Is a bearing device for wheels.   The wheel bearing device according to any one of claims 1 to 5, wherein the hub does not have a raceway surface, and the inner ring has a double-row raceway surface.

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