JP2007038805A - Bearing device for wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing device for a wheel capable of improving strength and fatigue strength around a seat surface contacted by a constant speed joint joining nut of a hub against high stress and repeating stress, preventing lowering of fastening shaft force of the nut by improving wear resistance of the seat surface, and suppressing lowering of productivity due to an increase of processes. <P>SOLUTION: In this bearing device, the hub 14 has a through hole 21 into which a stem part 42a of an outer ring 42, etc. of a constant speed joint 41 is inserted in a center part. An opening peripheral edge of the though hole 21 at an end face of the hub 14 becomes the seat surface 45 contacted by the nut 43 or a washer 44, and the seat surface 45 is provided in a spot facing part 46. The hub 14 is a hot forging product of a steel product and a base material part is a standard structure. The surrounding of the seat surface 45 of the hub 24 is made as non-standard structure parts 30. The non-standard structure 30 is made as any one of a fine ferrite-pearlite structure, an upper part bainite structure, a lower part bainite structure and a tempered martensite structure, or a mixed structure having at least two or more kinds of the 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 for supporting the driving wheel for rotating the inner ring, a through hole through which the stem portion of the joint member of the constant velocity joint is inserted is provided at the center of the hub. The opening peripheral edge of the through-hole on the end face of the hub on the outboard side becomes a seat surface to which a nut screwed to the male screw portion at the tip of the stem portion or a washer laid under the nut comes into contact.
This seating surface is finished by machining, but has a countersink shape at the boundary with the forging skin. The corner between the countersink and the peripheral surface of the countersink becomes a high-stress part when the automobile turns, which may cause a decrease in durability. That is, the periphery of the counterbore portion is near the root portion of the wheel mounting flange, but the root portion of the wheel mounting flange is stressed by a large amplitude runout in the wheel mounting flange during a sharp turn of the automobile. Becomes larger. The corner portion of the countersink portion is likely to cause stress concentration and becomes high stress when the automobile turns.
Moreover, the seating surface of the nut may be worn by fretting with the nut, which may lead to a decrease in axial force that couples the constant velocity joint.

  Therefore, an attempt was made to reinforce the periphery of the seat surface in the hub. Conventionally, it is not a reinforcement measure around the seat surface, but as a measure for strengthening the fatigue strength of the base part of the pilot part that guides the wheel and braking parts of the hub, a high frequency is applied to the root part of the wheel mounting flange. A method of performing heat treatment (for example, Patent Document 1) and a method of performing shot peening have been proposed (for example, Patent Document 2). 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 3).

  FIG. 9 shows an example of a general manufacturing method of a hub in a conventional third generation type 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 forging finish in which a plurality of processes (forging 1 pass, forging 2 passes, forging 3 passes) are gradually brought closer to the shape of the hub as a hot forging process, and the hub is roughly shaped in the final forging process. A product W4 is obtained (FIGS. (C) to (E)).

Forged finished product W4 is shot blasted for scale reduction, normalized or tempered as necessary (Fig. (F)), then turned (Fig. (G)), raceway surface, etc. Is subjected to high-frequency heat treatment ((H) in the figure). 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 2004-182127 A JP 2005-145313 A JP-A-2005-003061

  Conventional high-frequency heat treatment for improving fatigue strength may not be applied depending on the shape of the treated portion. In other words, when applied to a countersink that serves as a seating surface of a nut for constant velocity joint coupling of a hub, if the radius of curvature of the corner between the bottom surface and the peripheral surface of the countersink is small, it is partially caused by high-frequency heating. However, there are cases in which the treatment cannot be performed due to problems such as melting locally due to excessively high temperature.

In addition, in high-frequency heat treatment or shot peening, the number of processes may increase, or the deflection accuracy of the wheel mounting flange may be deteriorated due to thermal strain or the like.
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. 9, 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.

  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 around the seat surface where the constant velocity joint coupling nut of the hub contacts with high stress and repeated stress, and also improve the wear resistance of the seat surface. Thus, it is an object of the present invention to provide a wheel bearing device that can prevent a decrease in the tightening axial force of the nut and can suppress a decrease in productivity due to an increase in processes.

  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. The hub has a through hole through which the stem portion of the joint member of the constant velocity joint is inserted, and the opening of the through hole on the end surface of the hub on the outboard side. In a wheel bearing device in which a peripheral edge is a seat surface to which a nut or a washer screwed to a male screw portion at the tip of the stem portion contacts, the hub is a hot forged product of steel material, and the base material portion is a standard structure The bearing surface of the hub is a part of a non-standard structure, 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. Ku is characterized in that it is a mixture of two or more tissue of at least one of these tissues.

  The seating surface may be a bottom surface of a countersink portion provided on an end surface of the hub on the outboard side. In that case, it is preferable to provide the non-standard tissue portion over the periphery of the corner between the bottom surface of the counterboring portion and the peripheral surface of the counterboring portion.

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 periphery of the seat surface where the nut for connecting the constant velocity joint on the end face of the hub contacts the vicinity of the base of the wheel mounting flange, when a large amplitude flexure occurs repeatedly in the wheel mounting flange when the car turns High stress repeatedly occurs. In particular, when the seating surface is the bottom surface of the countersink portion, high stress is repeatedly generated at the corner between the bottom surface of the countersink portion and the peripheral surface.
However, with respect to such high stress that repeatedly occurs, if the seat surface and the part extending around the corner between the bottom surface and the peripheral surface of the countersunk portion are the non-standard structure, By increasing the hardness and increasing the hardness, the strength and fatigue strength are improved, and the occurrence of cracks from the periphery of the seating surface such as the corner between the bottom surface of the countersink and the peripheral surface is suppressed. That is, the action of crack generation → increased displacement of the wheel mounting flange → 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. 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, 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.

  Further, since the hardness is increased by the non-standard structure, fretting wear on the seating surface due to contact with the nut is suppressed, and a decrease in the tightening axial force of the nut due to the wear is suppressed.

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, in the case of high-frequency heat treatment, there is no problem of overheating when the radius of curvature of the corner between the bottom surface and the peripheral surface of the countersink serving as the seat surface is small.
The non-standard structure may be the entire surface of the hub, but if only the necessary part around the seating surface is used, a decrease in workability such as machinability can be minimized.

  In the wheel bearing device according to the present invention, the inner member includes a hub having a wheel mounting flange and an inner ring fitted to the outer periphery of the shaft portion of the hub, and the hub is a joint member of a constant velocity joint at the center portion. As long as it has a through-hole through which the stem portion is inserted, it can be applied to various types. For example, the hub and the inner ring may have a row of raceways. The hub may have no raceway surface, and the inner ring may have a double row raceway surface, that is, the hub may be a hub of a component independent of a finished bearing composed of double row bearings.

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 amount 0.4 to 0.8%), but in the case of S53C, 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.

  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.

  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. The hub has a through-hole through which a stem portion such as a joint member of a constant velocity joint is inserted in the center portion, and the through-hole on the end surface of the hub on the outboard side In a wheel bearing device in which an opening periphery is a seat surface to which a nut or a washer screwed to a male screw portion at the tip of the stem portion is in contact, the hub is a hot forged product of steel material, and the base material portion is a standard structure. The bearing surface of the hub is a part of a non-standard structure, the non-standard structure is one of fine ferrite pearlite structure, upper bainite structure, lower bainite structure, tempered martensite structure, Or a mixed structure of at least two of these structures, or the non-standard structure is cooled during the hot forging process or at the end of the process to be self-reheated or subjected to recuperation holding tempering. Therefore, the strength and fatigue strength around the seating surface where the constant velocity joint coupling nut of the hub is in contact with high stress and repetitive stress due to the refinement and increased hardness of the non-standard structure. In addition, the wear resistance of the seating surface can be improved, the axial force of the nut can be prevented from being lowered, and the reduction in productivity due to the increased number of processes can be suppressed.

  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 a third generation type driving wheel support. 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 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 through hole 21 through which the stem portion 42a of the outer ring 42 serving as one joint member of the constant velocity joint 41 is inserted is provided at the center of the hub 14. The opening peripheral edge of the through-hole 21 on the end face on the outboard side of the hub 14 becomes a seat surface 45 with which a nut 43 screwed to the male screw portion at the tip of the stem portion 42a or a washer 44 laid under the nut 43 comes into contact. By tightening the nut 45, the step surface 42 b of the constant velocity joint outer ring 42 is pressed against the width surface of the inner ring 15, and the wheel bearing device and the constant velocity joint 41 are coupled.

The seat surface 45 of the hub 14 is formed from the bottom surface of the counterbore 46. A recess 47 is provided on the end surface of the hub 14 on the outboard side on the inner diameter side of the pilot portion 20, and the countersunk portion 46 is provided at the bottom of the recess 47. Due to the formation of the recess 47, the pilot portion 20 has a cylindrical shape.
The inner surface of the recess 47 is a forged skin or a turning surface, and the inner surface, that is, the bottom surface and the peripheral surface of the countersink portion 46 are turning surfaces. The counterbore part 46 is not limited to a deeply formed part as shown in the figure, and may be a part having a depth to the extent that the forged skin portion has been cut.

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, and of these, the seat surface 45 of the hub 14 and its periphery are nonstandard. It is a part 30 of the tissue. The non-standard tissue portion 30 is provided from the seating surface 45 to the periphery of the corner 46a between the bottom surface and the peripheral surface of the countersink 46 constituting the seating surface 45. As a result, the peripheral surface of the counterbore 46 is also a non-standard tissue portion 30. 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 locally cooling the hub 14 by being exposed to a refrigerant 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. The material W4 of the forged finished product which becomes 14 rough shape is obtained (the figure (B)-(D)).

  The forged finished material W4 is turned as shown in FIG. At this time, turning of the counterbore 46 that becomes the seating surface 45 of the hub 14 is also performed. Next, the raceway surface 6 and the inner ring fitting surface 16 are subjected to high-frequency heat treatment ((B) in the figure). 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 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. In order to prevent the refrigerant from accumulating, it is preferable to eject upward.

  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 or inner diameter portion of the pilot portion 20 may be retained. You may make it hold centering by using the through-hole 21 of the hub 14 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. As shown in FIG. 5, the mixed structure can be selected depending on the cooling method.
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 locally provided, such as the seating surface 45 and its periphery in the example of FIG. 1, each curve (1) of FIG. Of the cooling methods indicated by (6), the methods indicated by curves (1)-(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 having this configuration, the following effects can be obtained. Since the periphery of the seat surface 45 with which the nut 43 for constant velocity joint connection on the end face of the hub 14 contacts is near the root of the wheel mounting flange 17, the wheel mounting flange 17 bends with a large amplitude when the vehicle turns. When this occurs repeatedly, high stress is repeatedly generated. In particular, when the seat surface 45 is the bottom surface of the countersunk portion 46, high stress is repeatedly generated at the corner 46a between the bottom surface and the peripheral surface of the countersink portion 46.
However, with respect to the high stress repeatedly generated, the portion over the periphery of the seat surface 45 and the corner 46a of the countersunk portion 46 is the non-standard tissue portion 30. By increasing the hardness and increasing the hardness, the strength and fatigue strength are improved, and the occurrence of cracks from the periphery of the seating surface 45 such as the corner 46a of the countersink 46 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, 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. 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, 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.

  Further, since the hardness of the seat surface 45 is increased by the non-standard structure, fretting wear of the seat surface 45 due to contact with the nut 43 is suppressed, and a decrease in the tightening axial force of the nut 43 due to the wear is suppressed. The

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. When the non-standard texture portion 30 is obtained by cooling during the hot forging process or at the end of the process, when the radius of curvature 46a at the corner of the countersink 46 serving as the seating surface 45 in the case of high-frequency heat treatment is small No overheating problem.
The non-standard-structure portion 30 may be the entire surface of the hub, but if only the necessary portion around the seating surface 45 is provided, a decrease in workability such as machinability can be minimized.

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 around the seat surface 45 where the nut 43 or constant washer 44 on the end face of the hub 14 contacts, the structure is refined and the hardness is increased. As a result, the strength and fatigue strength are improved and the life can be extended. Further, fretting wear is reduced by increasing the hardness of the seating surface 45, and a reduction in the axial force of the nut 43 is 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 of an angular ball bearing type for driving wheel support, 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, and the inner ring 15 on the inboard side may have a larger 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.
In this embodiment, the countersunk portion of the seating surface 45 is not provided, but a countersink portion may be provided as in the first embodiment.

  The wheel bearing device of FIG. 7 includes the hub 14 and a double row of inner rings 15 fitted on the outer periphery of the shaft portion 14a of the hub 14 as in the wheel bearing device of FIG. . The outer member 2 is composed of one integral part and does not have the vehicle body mounting flange 12. In this example, the two inner rings 15 have the same size.

  The wheel bearing device of FIG. 8 is of a tapered roller bearing type for supporting a drive 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. The outer member 2 is composed of a single component.

  In addition, 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 a fragmentary sectional view of the bearing device for wheels concerning other embodiments 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. 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 body 6-9 ... Track surface 12 ... Body mounting flange 14 ... Hub 14a ... Shaft part 14b ... Clamping part 15 ... Inner ring 17 ... Wheel mounting flange 20 ... Pilot Part 21 ... Through hole 30 ... Non-standard part 41 ... Constant velocity joint 42 ... Joint outer ring 42a ... Stem part 43 ... Nut 45 ... Seat surface 46 ... Counter-sink part 46a ... Corner

Claims (5)

  An inner member and an outer member that are rotatable with respect to each other via double row rolling elements, the inner member from 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 through-hole through which a stem portion such as a joint member of a constant velocity joint is inserted at the center, and the opening peripheral edge of the through-hole on the end surface of the hub on the outboard side is the tip of the stem portion. In a wheel bearing device that serves as a seating surface to which a nut or a washer that is screwed onto a male threaded portion comes into contact, the hub is a hot forged product of steel material, the base material portion is a standard structure, and the seating surface of the hub is A non-standard structure, 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 these Wheel bearing device characterized in that it is a mixture of two or more tissue of the tissue.   An inner member and an outer member that are rotatable with respect to each other via double row rolling elements, the inner member from 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 through-hole through which the stem portion of the joint member of the constant velocity joint is inserted, and the peripheral edge of the through-hole in the end face on the outboard side of the hub is a male screw at the tip of the stem portion In a wheel bearing device that serves as a seating surface to which a nut or a washer that is screwed onto a part contacts, the hub is a hot forged product of steel material, the base material portion is a standard structure, and the seating surface of the hub is not A bearing for a wheel, which is a part of a standard structure, and the non-standard structure is a structure obtained by cooling and self-reheating or re-tempering holding and tempering during the hot forging process or at the end of the process. apparatus.   3. The seating surface according to claim 1 or 2, wherein the seating surface comprises a bottom surface of a countersink portion provided on an end surface of the hub on the outboard side, and the space between the bottom surface of the countersink portion and the peripheral surface of the countersink portion. The wheel bearing apparatus which provided the part of the said non-standard structure | tissue over the circumference | surroundings of the corner of this.   4. The wheel bearing device according to claim 1, wherein each of the hub and the inner ring has a row of raceway surfaces. 5.   The wheel bearing device according to any one of claims 1 to 3, wherein the hub does not have a raceway surface, and the inner ring has a double row raceway surface.

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