JP2008169941A - Wheel bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wheel bearing system which can reduce time/energy required for the manufacturing of a bearing part and improve rolling fatigue life. <P>SOLUTION: The surface layer part of the track surface of at least either of the outward member 2 or the inward member 1 is locally cooled and is subjected to temper processing at the time of or after the hot forging. Furthermore, a processing layer which has been subjected to high-frequency heat treatment is provided to the surface layer part of the track surfaces 8, 9, 6 of the outward member 2 and the inward member 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wheel bearing device for automobiles, for example, and more particularly to a wheel bearing device that improves the rolling fatigue life by miniaturizing the structure after heat treatment of a surface layer portion of a raceway surface.

The inner ring and steel ball of the ball type hub bearing are made of high carbon chrome steel such as SUJ2, and hardened to the core by quenching and tempering. Some tapered roller types use case-hardened steel such as SCr435 for inner rings and tapered rollers, and the surface is hardened by carburizing heat treatment or the like.
On the other hand, the outer ring and hub ring with the body mounting flange and wheel mounting flange are made of medium and high carbon steel such as S53C for ease of forming because the shape is made by forging, and the track is made by high frequency heat treatment after turning. Only a part of the surface such as the surface is hardened to 50 HRC or more and 64 HRC or less (the raceway / hub ring seal land is 58 HRC or more and 64 HRC or less, and the inner ring fitting portion of the hub ring shaft portion is 50 HRC or more).

This high-frequency heat treatment has many advantages in terms of time and energy savings and functions in terms of the following (1) to (6) (for example, Non-Patent Document 1).
(1) Heat treatment location can be controlled (2) High surface hardness and excellent wear resistance and fatigue strength can be obtained (3) Surface residual compressive stress is large and excellent fatigue strength can be obtained (4) Decarburization (5) There is little oxide scale of heat treatment (6) Since it is heating for a short time, austenite grains are difficult to grow and the structure is fine and excellent toughness is obtained.
JP 2005-3061 A Handbook of heat treatment technology (edited by Japan Heat Treatment Technology Association, published by Nikkan Kogyo Shimbun, pages 181 to 195)

Since the above-mentioned high-frequency heat treatment is heating for a short time, it is known that the structure before heat treatment at the place where the heat treatment is performed and the uneven distribution of carbon and alloy elements are easily reflected in the characteristics of the quenched structure ( Non-Patent Document 1, page 183). The following problems (1) to (3) appear when the austenitizing time is short due to this short time heating and the austenitizing is poor.
(1) Incomplete structure (2) Hardness after quenching varies (3) Effective hardened layer depth becomes shallow As a structure that tends to austenite, so-called tempered martens having a tempered (quenched and tempered) structure A site organization is mentioned (refer nonpatent literature 1, 187 pages-188 pages). Since normal hub bearings are subjected to induction heat treatment while being forged, the structure is a ferrite / pearlite structure and is not as suitable for induction heat treatment as a tempered martensite structure.

When heating at a higher output for a longer time to eliminate the previous problem, the heated part may overheat, resulting in coarsening of the structure (crystal grains) and generation of microcracks in the overheated part. In that case, it adversely affects the rolling life of the bearing. In particular, the shoulder of the outer ring raceway groove of the ball-type hub bearing has a convex shape, and the energy of high frequency induction heating tends to concentrate, and the bearing tilts when the vehicle is turning, causing the shoulder of the outer ring raceway groove to roll. Since the moving body rolls at a high surface pressure, the rolling life is likely to decrease due to coarsening of the structure (crystal grains) and microcracks in the overheated part. In some cases, the JIS grain size number was coarsened to about “2” to “3”.
As the adjustment of the structure, countermeasures can be taken by performing normalization and tempering (for example, Patent Document 1), but the heating process of the heat treatment is performed once (normalization) or twice (tempering). Therefore, time and energy were required.

  An object of the present invention is to provide a wheel bearing device capable of reducing the time and energy required for producing bearing parts and improving the rolling fatigue life.

  The wheel bearing device of the present invention includes an outer member having a double-row raceway surface on the inner periphery, an inner member having a double-row raceway surface facing the raceway surface on the outer periphery, and the outer member and the inner member. In the wheel bearing apparatus, the outer member and the inner member are hot-forged, and the outer member and the inner member. The surface layer portion of the raceway surface of at least one of the members is locally cooled during the hot forging or after the hot forging and subjected to a tempering treatment, and further, the outer member and the inner member The surface layer of the orbital surface is provided with a treatment layer subjected to high-frequency heat treatment.

  According to this configuration, the surface layer portion of the raceway surface is locally cooled during hot forging or after hot forging and subjected to a tempering treatment, whereby a non-standard structure can be obtained. This non-standard structure includes (1) tempered martensite structure (tempered structure), (2) upper bainite structure, lower bainite structure, (3) fine ferrite pearlite structure (tempered structure), (4) It is synonymous with any one of the two or more mixed tissues of (1) to (3). By applying high-frequency heat treatment to such a non-standard structure, that is, the surface layer portion, the structure after the heat treatment can be refined and the rolling fatigue life can be improved. In addition, it is possible to reduce the time and energy required for manufacturing the bearing component compared to the conventional technology.

In the present invention, the treatment layer that has been subjected to the high-frequency heat treatment preferably has a crystal grain size number of 8 or more. This crystal grain size is synonymous with the size of a crystal grain represented by a cross section observed with a microscope, and is represented by a crystal grain size number obtained by a comparison method or a cutting method. The crystal grain size number is defined in Japanese Industrial Standard (abbreviation JIS).
When the crystal grain size of the treatment layer that has been subjected to the high-frequency heat treatment is 8 or more in terms of the crystal grain size number, the stress concentration generated at the grain boundaries of the prior austenite crystals is alleviated. Thereby, it becomes difficult to open a fatigue crack and it becomes possible to suppress the fall of a rolling fatigue life. Conversely, when the crystal grain size of the treatment layer is less than 8 in terms of the crystal grain size number, the effect of alleviating stress concentration on the crystal grain boundaries of prior austenite is small.

  In the present invention, it is preferable that the surface hardness of the raceway surface provided with the treatment layer is 58 HRC or more and 64 HRC or less. In this case, the stress concentration generated at the grain boundaries of the prior austenite crystal is relaxed, the fatigue cracks are difficult to open, and the rolling fatigue life can be improved. Further, the life can be easily determined based on the surface hardness of the raceway surface.

  In the wheel bearing device of the present invention, the surface layer portion of the raceway surface is locally cooled at the time of hot forging or after hot forging to obtain a non-standard structure. By subjecting this non-standard structure to high-frequency heat treatment, the structure after heat treatment can be refined and the rolling fatigue life can be improved. In addition, it is possible to reduce the time and energy required for manufacturing the bearing component compared to the conventional technology.

  An 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. The following description also includes a description of a method for manufacturing a wheel bearing device. 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 wheel 14 and an inner ring 15 fitted to the outer periphery of the inboard side end of the shaft portion 14a of the hub wheel 14. The hub ring 14 and the inner ring 15 are formed with the raceway surfaces 6 and 7 on the inner member 1 side, respectively. An inner ring fitting surface 16 having a step and a small diameter is provided on the inboard side end of the outer periphery of the shaft portion 14 a of the hub wheel 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 wheel 14 by a caulking portion 14b obtained by caulking the inboard side end of the shaft portion 14a of the hub wheel 14 to the outer diameter side.

  The hub wheel 14 has a wheel mounting flange 17 on the outer periphery of the end on the outboard side of the shaft portion 14 a, and each bolt press-fitting hole 18 provided at a plurality of locations in the circumferential direction of the wheel mounting flange 17 includes A hub bolt 19 is attached in a press-fit state. An annular pilot portion 20 concentric with the hub wheel 14 protrudes from the root portion of the wheel mounting flange 17 of the hub wheel 14. The pilot portion 20 includes a brake disk and a portion for guiding the wheel of the wheel that are attached to the side surface on the outboard side of the wheel mounting flange 17. 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 wheel 14, the inner ring 15, and the outer member 2 are all hot forged products of steel, and of these, the surface layer portion on the outer periphery of the raceway surface 6 of the hub wheel 14 and the double row of the outer members 2. The surface layer portions on the inner periphery of the raceway surfaces 8 and 9 are non-standard tissue portions 6H, 8H, and 9H.
The base material portion of the hub wheel 14 and the base material portion of the outer member 2 are standard structures. The inner ring 15 is entirely hardened by quenching and tempering. The non-standard structure of the non-standard structure portions 6H, 8H, and 9H is obtained by locally cooling the hub wheel 14 and the outer member 2 by being exposed to a refrigerant during or at the end of the hot forging process. For example, a fine ferrite / pearlite structure, an upper bainite structure, a lower bainite structure, or a tempered martensite structure, or at least a mixed structure of two or more of these structures.

  FIG. 2 shows a hot forging process among the manufacturing processes of the hub wheel 14. As shown in FIG. 2 (a), the hub wheel 14 is made of a bar material W0. By cutting the bar material W0 into a fixed size, as shown in FIG. 2 (b), one hub wheel 14 is provided. A billet W1 is prepared. This billet W1 is gradually a hub through a plurality of processes as hot forging processes, here forging 1 pass W2 (FIG. (C)), forging 2 pass W3 ((d)) and 3 forgings. In the final forging process (forging 3 passes), a forged finished material W4 is obtained that approximates the shape of the wheel 14 (FIGS. 3C to 3E).

FIG. 3 shows a hot forging process among the manufacturing processes of the outer member 2.
As shown in FIG. 3 (a), the outer member 2 is made of a bar material GW0. By cutting the bar material GW0 into a fixed size, as shown in FIG. A billet GW1 serving as a material is prepared. The billet GW1 is subjected to a plurality of processes as a hot forging process, here, a forging 1 pass GW2, a forging 2 pass GW3, and a forging 3 pass, gradually approaching the shape of the outer member 2, and a final forging process (forging 3). In the pass), a forged finished material GW4 having a rough shape of the outer member 2 is obtained (FIGS. (C) to (e)).

FIG. 4 shows a manufacturing process after hot forging of the hub wheel 14. This will be described with reference to FIG.
The forged finished material W4 having a rough shape of the hub wheel 14 is turned as shown in FIG. Next, as shown in FIG. 4B, in the post-turning material W <b> 4, the seal contact surface 41, the raceway surface 6, the peripheral surface portion 14 c near the raceway surface 6, and the inner ring fitting surface 16 face in the axial direction. The step surface 16a and the peripheral surface portion 16b in the vicinity thereof are subjected to high-frequency heat treatment. Thereafter, the raceway surface 6 and the like are ground. What is required is secondary turning of the surface of the wheel mounting flange 17 before grinding.

FIG. 5 shows a manufacturing process after hot forging of the outer member 2. This will be described with reference to FIG.
The forged finished material GW4 of the outer member 2 is turned (FIG. 5A). Next, as shown in FIG. 5 (b), the raceway surfaces 8 and 9 of the post-turning material GW4 are subjected to high-frequency heat treatment, and thereafter, secondary turning of the surface of the body mounting flange 12 or the like is performed as necessary. Done. Next, the raceway surfaces 8 and 9 are ground. Thereafter, the hub wheel 14 after grinding of the raceway surface 6 and the outer member 2 after grinding of the raceway surfaces 8 and 9 are assembled as a wheel bearing device (FIG. 4C).

As shown in FIG. 2 (e), the non-standard structure portion 6H of the hub wheel 14 is modified by partially blowing a refrigerant (indicated by an arrow RB) to the reforming target portion at the end of the forging process. As shown in FIG. 2 (d), after the forging process (forging 2 pass) before the final forging process (forging 3 pass) is completed, the coolant is partially blown to the reforming target portion. Quality.
The non-standard structure portions 8H and 9H of the outer member 2 are modified by partially blowing a coolant to the modification target portion at the end of the forging process, as shown in FIG. 3 (e), or As shown in FIG. 3 (d), after the forging process (forging 2 pass) before the final forging process (forging 3 pass) is completed, the material is reformed by partially blowing a 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.

While blowing the refrigerant, while rotating the materials W3 and W4 serving as the hub wheel 14 and the materials GW3 and GW4 serving as the outer member 2 around the axis of each material so that the cooling is uniformly performed on the entire circumference. A refrigerant may be sprayed. Further, the refrigerant spraying device (not shown) may be rotated without rotating the materials W3, W4, GW3, and GW4.
The coolant may be sprayed by using a ring-shaped cooling jacket (not shown) having a large number of ejection holes, or the materials W3 and W4 that become the hub wheel 14 and the material GW3 that becomes the outer member 2. If the GW 4 is rotated, it may be sprayed from one nozzle.

  When the materials W3 and W4 to be the hub wheel 14 and the materials GW3 and GW4 to be the outer member 2 are rotated 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 holding method of the raw materials W3 and W4 and the raw materials GW3 and GW4 at the time of cooling may be sufficient as long as the cooling unit is not inhibited from being uniformly cooled. For example, the shaft portion 14a may be retained, the outer diameter portion of the wheel mounting flange 17 may be retained, or the outer diameter portion or the inner diameter portion of the pilot portion 20 may be retained. When the hub wheel 14 has a through hole at the center as in the case of a drive wheel described later with reference to FIG. 8, the centering holding may be performed using this through hole as a guide.

By cooling, the structure of the non-standard structure portions 6H, 8H, and 9H is changed to any one of the fine ferrite / pearlite structure, the upper bainite structure, the lower bainite structure, and the tempered martensite structure, or at least of these structures. Whether to use two or more mixed tissues can be selected by a cooling method as shown in FIG.
In FIG. 6, 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.

6, 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. FIG. 2 (e) (or FIG. 2 (d)) and FIG. 3 (e) (or FIG. 3 (d)) at the end of the hot forging process, that is, until the hot forging process is finished and cooling is performed. In this way, the parts (materials) to be reformed are partially cooled by soaking in the refrigerant, limiting the cooling time, and allowing self-reheating after cooling to obtain a fine ferrite / pearlite structure as the non-standard structure. It is done. 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 FIGS. 2 and 3, when the hot forging process is composed of a plurality of stages of forging processes, before the final forging process (FIGS. 2 (e) and 3 (e)) (FIG. 2 ( d) and FIG. 3 (d)), a part of the parts (materials W3 and GW3) is cooled, and then the final forging process (FIGS. 2 (e) and 3 (e)) 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 ° C. or higher and about 600 ° C. or lower, the structure becomes sorbite. When the temperature of recuperation tempering is about 350 ° C. or more and 400 ° C. or less, 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. 6, in the case of providing a non-standard tissue portion near the seal contact surface 41 and the inner ring fitting surface 16 of the hub wheel 14 in the example of FIG. Of the cooling methods shown in (1) to (6), the method shown in the cooling curves (3) and (4) or the method shown in the cooling curves (5) and (6) is preferable. When the non-standard structure portion is provided on the raceway surface 6 of the hub ring 14, it is most preferable to obtain a tempered martensite structure by the method shown in the cooling curves (3) and (4).

According to the wheel bearing device of this configuration, the following effects can be obtained.
The surface layer portion 6H on the outer periphery of the raceway surface 6 of the hub wheel 14 and the surface layer portions 8H and 9H on the inner periphery of the double-row raceway surfaces 8 and 9 of the outer member 2 are made non-standard structures, and the non-standard structures are made fine. One of a ferrite pearlite structure, an upper bainite structure, a lower bainite structure, and a tempered martensite structure, or at least a mixed structure of at least two of these structures was used. By applying high-frequency heat treatment to this non-standard structure, the structure after heat treatment is made finer than the base material part (or the high-temperature heat-treated standard structure) of the standard structure, and the rolling fatigue life is improved. Can do.
For example, when the non-standard structure is the tempered martensite structure (sorbite) shown in the cooling curves (3) and (4) of FIG. 6, finer martensite is obtained as a hardened layer by high-frequency heat treatment of the sorbite. be able to.

Moreover, the surface hardness of the raceway surfaces 6, 8, and 9 is set to 58 HRC or more and 64 HRC or less among the processing layers obtained by subjecting the non-standard structure to high frequency heat treatment. This location corresponds to a Japanese Industrial Standard (abbreviation JIS) grain size number of 8 or more. The crystal grain size is synonymous with the size of a crystal grain represented by a cross section observed with a microscope, and this is represented by a crystal grain size number N obtained by a comparison method or a cutting method. Here, the crystal grain size number N is defined as m = 8 × 2 ^N using the number m of crystal grains per 1 mm ² in cross-sectional area when the object is observed at a magnification of 100 times.

When the crystal grain size of the treatment layer that has been subjected to the high-frequency heat treatment is 8 or more in terms of the crystal grain size number, the stress concentration generated at the grain boundaries of the prior austenite crystals is alleviated. Thereby, it becomes difficult to open a fatigue crack and it becomes possible to suppress the fall of a rolling fatigue life. Conversely, when the crystal grain size of the treatment layer is less than 8 in terms of the crystal grain size number, the effect of alleviating stress concentration on the crystal grain boundaries of prior austenite is small.
Further, when the surface hardness of the raceway surfaces 6, 8, and 9 provided with the treatment layer is set to 58 HRC or more and 64 HRC or less, the stress concentration generated at the grain boundary of the prior austenite crystal is relaxed, as described above. Fatigue cracks are difficult to open, and it is possible to suppress a decrease in rolling fatigue life. Further, the life can be easily determined based on the surface hardness of the raceway surface. Therefore, quality control of parts can be simplified.

  Further, according to the wheel bearing device of this configuration, it is possible to suppress a decrease in rolling fatigue life, and therefore, it is possible to reduce the 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 portions 6H, 8H, and 9H are 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 and tempering the entire part. Further, since the heat of hot forging is used, it is not necessary to prepare another heat source or the like, and the energy used for the processing for modifying the structure can be reduced. In addition, the high-frequency heat treatment is mainly a raceway surface and has a small processing range, so that it consumes less power. In addition, when the plurality of hub wheels 14 and the plurality of outer members 2 are overlapped in the axial direction and subjected to high-frequency heat treatment, the number of treatments per unit time can be increased and the number of man-hours can be reduced. Therefore, the manufacturing cost can be reduced.
Since the non-standard structures 6H, 8H, and 9H are a part of the hub wheel 14 and a part of the outer member 2, a decrease in machinability such as machinability can be minimized and added. Since the tightening portion 14b is left in the state of the standard structure, it is avoided that the caulking workability is deteriorated.

The embodiment of the present invention shown in FIG. 7 is an example of a second-generation type wheel bearing device, which is for supporting a driven wheel and rotating an outer ring.
In the following description, the same reference numerals are given to portions corresponding to the matters described in the preceding forms in each embodiment, and overlapping description may be omitted. When only a part of the configuration is described, the other parts of the configuration are the same as those described in the preceding section. Not only the combination of the parts specifically described in each embodiment, but also the embodiments can be partially combined as long as the combination does not hinder.

The inner member 1 includes double rows of inner rings 15. The outer member 2 has a wheel mounting flange 17 and a pilot portion 20.
In this embodiment, the surface layer portions 8H and 9H in the inner circumference of the double-row raceway surfaces 8 and 9 of the outer member 2 are made non-standard structures, and the non-standard structures are made of fine ferrite / pearlite structure, upper bainite structure, lower part Either a bainite structure or a tempered martensite structure, or at least a mixed structure of two or more of these structures was used. By applying high-frequency heat treatment to this non-standard structure, the structure after heat treatment is made finer than the base material part (or the high-temperature heat-treated standard structure) of the standard structure, and the rolling fatigue life is improved. Can do. Further, when the plurality of outer members 2 are stacked in the axial direction and subjected to high-frequency heat treatment, the number of treatments per unit time can be increased, and the number of man-hours can be reduced. Therefore, the manufacturing cost can be reduced. In addition, the same effects as the embodiment shown in FIG.

  The embodiment of the present invention shown in FIG. 8 is an example of a second-generation type wheel bearing device, which is a tapered roller bearing type for driving wheel support, and the inner member 1 is a hub wheel 14. The hub wheel 14 includes a double row of inner rings 15 fitted to the outer periphery of the shaft portion 14a. The inner ring 15 is provided for each row. The outer member 2A consists of one part.

  Also in this embodiment, the surface layer portions 8H and 9H in the inner periphery of the double-row raceway surfaces 8 and 9 of the outer member 2A are made non-standard structures, and the non-standard structures are made of fine ferrite / pearlite structure, upper bainite structure, lower part Either a bainite structure or a tempered martensite structure, or at least a mixed structure of two or more of these structures was used. By applying high-frequency heat treatment to this non-standard structure, the structure after heat treatment is made finer than the base material part (or the high-temperature heat-treated standard structure) of the standard structure, and the rolling fatigue life is improved. Can do. In addition, the same effects as those of the embodiment shown in FIGS.

  The embodiment of the present invention shown in FIG. 9 is an example of a fourth generation type wheel bearing device, and the inner member 1 is a joint outer ring 32 in which the hub wheel 14 and one joint member of the constant velocity joint 31. The raceway surfaces 6 and 7 in each row are formed on the hub wheel 14 and the joint outer ring 32. The outer member 2 is made of one component and has a vehicle body mounting flange 12.

  In this embodiment, the surface layer portions 8H and 9H in the inner periphery of the double-row raceway surfaces 8 and 9 of the outer member 2, and the surface layer in the inner periphery of the raceway surfaces 6 and 7 in each row on the hub wheel 14 and the joint outer ring 32 are provided. Portions 6H and 7H are non-standard tissues. The non-standard structure was 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. By applying high-frequency heat treatment to this non-standard structure, the structure after heat treatment is made finer than the base material part (or the high-temperature heat-treated standard structure) of the standard structure, and the rolling fatigue life is improved. Can do. In addition, the same effects as those of the embodiment shown in FIGS.

  In each of the above embodiments, a part of the non-standard tissue is partially provided on the surface of the parts constituting the inner member 1 or the outer member 2, but these inner member 1 or outer member are provided. 2, for example, the entire surface of the hub wheel 14, the outer member 2, etc. can be a non-standard tissue part. 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 of the wheel bearing apparatus which concerns on one Embodiment of this invention. It is process explanatory drawing showing the forge process of the hub ring of the bearing apparatus for wheels in steps. It is process explanatory drawing showing the forge process of the outer ring | wheel of the bearing apparatus for wheels in steps. It is process explanatory drawing showing the process after the forge process of the hub wheel in steps. It is process explanatory drawing showing the process after the forge process of the same outer ring in steps. It is explanatory drawing of the cooling curve which obtains various non-standard structure | tissues. 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 ... Inner member 2 ... Outer member 3 ... Rolling elements 6-9 ... Track surface 6H, 8H, 9H ... Non-standard structure | tissue part 14 ... Hub ring

Claims (3)

An outer member having a double-row raceway surface on the inner periphery, an inner member having a double-row raceway surface facing the raceway surface on the outer periphery, and interposed between the outer member and the inner member raceway surface In a wheel bearing device comprising a double row rolling element, wherein the outer member and the inner member are hot forged,
The surface layer portion of the raceway surface of at least one of the outer member and the inner member is locally cooled during the hot forging or after the hot forging and subjected to a tempering treatment, A wheel bearing device, characterized in that a treatment layer subjected to high-frequency heat treatment is provided on a surface layer portion of a raceway surface of the outer member and the inner member.   2. The wheel bearing device according to claim 1, wherein the treatment layer subjected to the high-frequency heat treatment has a crystal grain size number of 8 or more.   3. The wheel bearing device according to claim 1, wherein the surface hardness of the raceway surface provided with the treatment layer is 58 HRC or more and 64 HRC or less.

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