JP2008207597A - Wheel bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wheel bearing device of which the high durability is ensured, by including a part with improved fatigue strength in a non-hardened portion. <P>SOLUTION: A wheel bearing device 1 includes an outer member 10, an inner member 20, and a roller 50. The inner member 20 includes a hub ring 30 made of steel and having a wheel mounting flange 31 formed. The hub ring 30 has a hardened portion 39 hardened to attain at least 50 HRC as a result of quench hardening and a non-hardened portion 33 which is a portion other than the hardened portion 39. Compressive stress in a range of 50-500 MPa remains in the surface of the non-hardened portion 33. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wheel bearing device, and more particularly, to a wheel bearing device for rotatably supporting a wheel with respect to a vehicle body.

  In recent years, further improvements in fuel consumption and running stability have been demanded for vehicles such as automobiles. Therefore, the wheel bearing device that supports the wheel rotatably with respect to the vehicle body is being reduced in size and weight. As a result, the parts constituting the wheel bearing device tend to be smaller and thinner. On the other hand, with the increase in output and performance of vehicles such as automobiles, the load on the wheel bearing device is also increasing. Under such circumstances, in wheel bearing devices, it is becoming difficult to further reduce the size, thickness, and durability of parts.

On the other hand, in the parts constituting the wheel bearing device, a region where strength is insufficient is subjected to a partial curing process using induction hardening to form a cured portion, and the strength of the region In particular, a measure for ensuring rotational bending fatigue strength has been proposed (see, for example, Patent Document 1).
JP 2002-87008 A

  However, in the measure for forming the hardened portion in a region where the strength is insufficient, the strength of the non-hardened portion which is a portion other than the hardened portion may be a problem, and it is necessary to form a further hardened portion. As described above, in the countermeasure for forming a large number of hardened portions, the manufacturing process of the wheel bearing device, particularly the heat treatment process becomes complicated, resulting in an increase in manufacturing cost. In addition, when a thin portion having a small thickness or a region adjacent to the thin portion is subjected to a hardening process such as induction hardening, a new problem that heat treatment deformation occurs in the thin portion may occur. On the other hand, among the components constituting the wheel bearing device, it is considered that a measure for securing strength by eliminating the non-cured portion by curing the entire component is effective. However, if the entire part is a hardened part, subsequent processing becomes difficult, and thus it is not always effective to adopt such measures.

  Therefore, an object of the present invention is to provide a wheel bearing device in which high durability is ensured by providing a component with improved fatigue strength of a non-hardened portion.

  The wheel bearing device according to the present invention has an outer member in which an annular outer rolling surface is formed in a double row on an inner peripheral surface, and an annular inner rolling surface facing the outer rolling surface in a double row. The formed inward member, the outer rolling surface, and a rolling element that is in contact with the inner rolling surface and is arranged to roll on an annular track are provided. Either the outer member or the inner member is made of steel and includes a wheel flanged member in which a wheel mounting flange that is a flange for mounting a wheel is formed. Furthermore, the wheel flanged member has a hardened part hardened to 50 HRC or more by quenching and hardening, and a non-hardened part that is a part other than the hardened part. And the compressive stress of 50 MPa or more and 500 MPa or less remains on the surface of the non-hardened part.

  In general, in a member with a flange for a wheel that constitutes a wheel bearing device, a countermeasure is adopted in which a hardened portion is formed in a portion where the strength is insufficient. However, in this measure, the strength of the non-cured portion that is a portion other than the cured portion may be a problem, and it is necessary to form a further cured portion. On the other hand, in consideration of problems such as manufacturing cost, heat treatment deformation, workability as described above, measures to form a large number of hardened parts, or measures to set the whole wheel flanged member as a hardened part are not necessarily effective measures. That's not true.

  On the other hand, in the wheel bearing device of the present invention, a compressive stress of 50 MPa or more and 500 MPa or less remains on the surface of the non-cured portion of the wheel flanged member. Therefore, the occurrence of cracks on the surface of the non-hardened part and the subsequent propagation of cracks are suppressed, and the fatigue strength of the non-hardened part is improved, so even if a moment load is repeatedly applied from the wheel to the wheel mounting flange. The occurrence of cracks from the non-hardened part is suppressed, and the occurrence of fretting damage is suppressed. As a result, the wheel bearing device of the present invention has high durability secured by including the wheel flanged member with improved fatigue strength of the non-cured portion.

  Preferably, in the wheel bearing device, an insertion hole for inserting another member is formed in the wheel flanged member in a region including the central axis of the raceway of the rolling element. A side wall is contained in the above-mentioned non-hardened part.

  An insertion hole for connecting the other member and the wheel bearing device may be formed in the wheel flanged member by inserting another member such as a shaft. In this case, a relatively large stress may be repeatedly applied to the surface of the side wall of the insertion hole. Therefore, depending on the magnitude of this stress, a crack may occur on the surface of the side wall of the insertion hole, and the crack may propagate to cause damage to the wheel flanged member. On the other hand, the fatigue strength in the vicinity of the surface of the side wall of the insertion hole is improved and the occurrence of breakage is caused by the side wall of the insertion hole being included in the non-hardened portion where the compressive stress of 50 MPa or more and 500 MPa or less remains on the surface Can be suppressed.

  In the wheel bearing device, preferably, the surface hardness of the base portion of the wheel mounting flange on the side on which the wheel is mounted as viewed from the wheel mounting flange is 35 HRC or less.

  Thereby, workability in cutting and the like is improved, heat treatment deformation can be suppressed, and deterioration of surface runout accuracy of the brake rotor mounting surface of the wheel mounting flange due to heat treatment deformation can be prevented.

  In the above wheel bearing device, the inner member preferably includes a hub wheel that is a wheel flanged member and an inner ring fitted into the hub wheel. Thereby, an inner raceway surface is formed, and an inner ring excellent in durability, particularly in rolling fatigue life can be employed. As a result, the durability of the wheel bearing device can be further improved.

  Preferably, in the above wheel bearing device, the inboard side end portion, which is the end portion of the hub wheel opposite to the side on which the wheel is mounted as viewed from the wheel mounting flange, is plastically deformed radially outwardly. Is forming. The inner ring is fixed to the hub ring in the axial direction by the caulking portion.

  In this way, the so-called self-retain structure eliminates the need to manage the preload by firmly tightening with a nut or the like as in the prior art, so that it can be easily incorporated into the vehicle, and The preload amount can be maintained for a long time.

  Preferably, in the wheel bearing device, the caulking portion is formed by plastic deformation of an inboard side end portion having a surface hardness of 25 HRC or less.

  Thereby, the hardness variation of a crimping part is suppressed. Moreover, since sufficient workability can be ensured, it is possible to suppress the occurrence of microcracks on the surface of the crimped portion by plastic working, and the reliability of the wheel bearing device is improved.

  In the wheel bearing device, preferably, the surface hardness of the base of the wheel mounting flange opposite to the side on which the wheel is mounted as viewed from the wheel mounting flange is 54 HRC or more and 64 HRC or less.

  Thereby, it becomes possible to give sufficient mechanical strength to the rotational bending load applied to the wheel mounting flange, and the strength and durability of the wheel flanged member are further improved.

  In the wheel bearing device, preferably, the steel constituting the wheel flanged member is a medium carbon steel containing carbon of 0.40% by mass or more and 0.80% by mass or less. Thereby, the ease of forging, machinability, heat treatment property, or economic efficiency is improved, and it is particularly suitable for partial quench hardening by induction hardening.

  As is apparent from the above description, according to the wheel bearing device of the present invention, a wheel bearing device having high durability is provided by providing a component with improved fatigue strength of the non-hardened portion. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic sectional view showing a configuration of a wheel bearing device according to an embodiment of the present invention. With reference to FIG. 1, the wheel bearing apparatus in this Embodiment is demonstrated.

  With reference to FIG. 1, the wheel bearing device 1 according to the present embodiment includes an outer ring 10, a hub ring 30 and an inner ring 40 that are race members, and a plurality of rollers 50 as rolling elements. The outer ring 10 constitutes an outer member, and the hub ring 30 and the inner ring 40 constitute an inner member 20.

  The outer ring 10 as an outer member is an annular track member having an annular outer raceway surface 10A formed in two rows on the inner peripheral surface 11. The outer rolling surface 10A includes a first outer rolling surface 12A and a second outer rolling surface 13A. The outer ring 10 is made of JIS standard S53C, which is steel, for example. In the outer ring 10, the region including the first outer rolling surface 12 </ b> A and the region including the second outer rolling surface 13 </ b> A are quenched and hardened by induction hardening or the like, and have a hardness of 58 HRC or higher. 19 is formed.

  On the other hand, the hub ring 30 as an inner member is a track member that is arranged so that a part thereof is surrounded by the outer ring 10. In addition, the inner ring 40 as an inward member has an annular first inner ring 41 fitted on the outer side of the small diameter portion 34 having a smaller outer diameter than the wheel mounting flange 31 in the hub ring 30, and the first inner ring 41. And an annular second inner ring 42 which is adjacent to each other so that the central axes thereof coincide with each other and is fitted to the outside of the small-diameter portion 34. The small diameter portion 34 of the hub wheel 30 has a cylindrical shape, and is an inboard side that is an end portion opposite to the side on which the flange 31 is formed when viewed from the first inner ring 41 and the second inner ring 42. The end portion is plastically deformed radially outward to form a caulking portion 34A. The first inner ring 41 and the second inner ring 42 are fixed to the hub wheel 30 in the axial direction by the caulking portion 34A. Here, the inboard-side end portion is a region to be plastically deformed by caulking processing for forming the caulking portion 34A.

  The first inner ring 41 and the second inner ring 42 are made of, for example, JIS standard SUJ2, which is steel. The entire inner ring 41 and the second inner ring 42 are hardened and hardened to have a hardness of 58 HRC or more. Furthermore, the 1st inner side rolling surface 41A and the 2nd inner side rolling surface 42A which comprise the inner side rolling surface 40A are formed in the outer peripheral surface of the 1st inner ring | wheel 41 and the 2nd inner ring | wheel 42, respectively. The first inner rolling surface 41A and the second inner rolling surface 42A are opposed to the first outer rolling surface 12A and the second outer rolling surface 13A, respectively.

  The hub wheel 30 is made of JIS standard S53C, which is steel, for example. In the hub wheel 30, the region including the surface of the small diameter portion 34 that comes into contact with the inner ring 40 is hardened and hardened by induction hardening or the like to form a hardened portion 39 having a hardness of 58 HRC or higher.

  Further, in the hub wheel 30 which is a member with a flange for a wheel, an insertion hole 38 for inserting another member such as a shaft penetrates in an axial direction in a region including the central axis of the track of the roller 50. Is formed. A plurality of grooves extending in the axial direction are formed on the surface of the side wall of the insertion hole 38 (inner peripheral surface of the hub wheel 30). As a result, the side wall of the insertion hole 38 forms a serration portion 37.

  The plurality of rollers 50 are in contact with the first outer rolling surface 12A of the outer ring 10 and the first inner rolling surface 41A of the first inner ring 41, and at a predetermined pitch in the circumferential direction by the annular cage 60A. The arranged row, the second outer rolling surface 13A of the outer ring 10 and the second inner rolling surface 42A of the second inner ring 42 are in contact with each other at a predetermined pitch in the circumferential direction by the annular cage 60B. It is arranged so as to be able to roll on a double row (two rows) annular track with the arranged rows.

  Further, a seal member 70 is disposed between both end portions of the outer ring 10 in the axial direction and the end portions of the first inner ring 41 and the second inner ring 42 facing each other. Thereby, leakage of the lubricating grease sealed in the space between the outer ring 10 and the first inner ring 41 and the second inner ring 42 and entry of dust and the like from the outside into the space are prevented.

  With the above configuration, the outer ring 10, the hub ring 30, and the inner ring 40 can rotate relative to each other.

  Further, a hub wheel bolt hole 31 </ b> A is formed in the wheel mounting flange 31 of the hub wheel 30. And the wheel attachment flange 31 and the wheel (not shown) which comprise a wheel are mutually fixed by the volt | bolt 71 inserted in 31 A of hub wheel bolt holes. On the other hand, the outer ring 10 has an outer ring flange 15, and an outer ring through hole 15 </ b> A is formed in the outer ring flange 15. The outer ring flange 15 and a suspension device (not shown) fixed to the vehicle body are fixed to each other by a bolt (not shown) inserted into the outer ring through hole 15A. With the above configuration, the wheel bearing device 1 is interposed between the wheel and the vehicle body, and rotatably supports the wheel with respect to the vehicle body.

  That is, the wheel bearing device 1 according to the present embodiment is opposed to the outer ring 10 as an outer member in which an annular outer rolling surface 10A is formed in a double row on the inner peripheral surface 11 and the outer rolling surface 10A. An inner rolling surface 20A in which an annular inner rolling surface 40A is formed in a double row, an outer rolling surface 10A, and an inner rolling surface 40A are in contact with each other, and are arranged to be freely rollable on an annular track. And a roller 50 as a moving body.

  The inner member 20 is made of steel and includes a hub wheel 30 which is a wheel flanged member formed with a wheel mounting flange 31 which is a flange for mounting a wheel (not shown). The hub ring 30 has a hardened portion 39 hardened to 50 HRC or more by quenching and hardening, and a non-hardened portion 33 that is a portion other than the hardened portion 39. And the austenite grain size of the steel which comprises the non-hardened part 33 is 8th or more.

  In the wheel bearing device 1 according to the present embodiment, the austenite grain size of the steel constituting the non-hardened portion 33 of the hub wheel 30 that is a wheel flanged member is 8 or more, so that the microstructure of the steel is reduced. The fatigue strength of the non-hardened portion 33 is improved by miniaturization. As a result, the wheel bearing device 1 according to the present embodiment is provided with a flanged member in which the fatigue strength of the non-cured portion 33 is improved, thereby ensuring high durability. In order to secure higher durability, it is preferable that the austenite grain size of the steel constituting the non-hardened portion 33 is No. 10 or more.

  Here, the austenite grain size of steel is the grain size number of the crystal grain size determined by the test method specified in JIS standard G0551, and means the grain size number of so-called prior austenite crystal grains.

  Further, when the particle size number is less than 8, considering the stress generally applied to the wheel flanged member, the fatigue strength is not necessarily sufficient. Therefore, the particle size number is preferably 8 or more. On the other hand, if the particle size number exceeds 12, the problem that the hardenability deteriorates may occur. Therefore, the particle size number is preferably 12 or less.

  Furthermore, the condition that the austenite grain size of the steel is No. 8 or more is satisfied if, for example, the non-hardened portion is investigated in three places by a method according to JIS G0551, and the grain size is No. 8 or more in all places. Can be determined.

  Further, the wheel bearing device 1 according to the present embodiment includes an outer ring 10 in which an annular outer rolling surface 10A is formed in a double row on the inner peripheral surface 11, and an annular inner rolling facing the outer rolling surface 10A. Rollers 50 as rolling elements that are in contact with the inner member 20, the outer rolling surface 10A, and the inner rolling surface 40A, the surfaces 40A of which are formed in a double row, are arranged on a ring-shaped track so as to be freely rollable. And.

  The inner member 20 is made of steel and includes a hub wheel 30 which is a wheel flanged member formed with a wheel mounting flange 31 which is a flange for mounting a wheel (not shown). The hub ring 30 includes a hardened portion 39 hardened to 50 HRC or more by quenching and hardening, and a non-hardened portion 33 that is a portion other than the hardened portion 39. And the ferrite area ratio of the steel which comprises the non-hardening part 33 is 3% or less.

  In the wheel bearing device 1 in the present embodiment, the ferrite area ratio of steel constituting the non-hardened portion 33 of the hub wheel 30 that is a wheel flanged member is 3% or less. Therefore, the strength is low, the occurrence of cracks due to repeated stress, or the presence of ferrite that can be a propagation path of cracks is suppressed, and the fatigue strength of the non-hardened portion 33 is improved. As a result, the wheel bearing device 1 according to the present embodiment is provided with a flanged member in which the fatigue strength of the non-cured portion 33 is improved, thereby ensuring high durability.

  Here, if the ferrite area ratio exceeds 3%, the ferrite phase is connected to other adjacent ferrite phases, and the tendency to become a crack initiation point or a crack propagation path becomes strong. Therefore, the ferrite area ratio is preferably 3% or less.

In addition, a ferrite area ratio means the area ratio with respect to the said whole surface of the ferrite in the surface which cut | disconnected the non-hardening part of the member with a flange for wheels which comprises the bearing apparatus for wheels. More specifically, it can be measured as follows. First, a test piece is cut out from the non-hardened portion of the wheel flanged member. And after grind | polishing the surface of the said test piece, the surface is corroded by corrosive liquid, for example, picral (picric acid alcohol solution). Then, the corroded surface is observed by, for example, 3 fields of view of 1 mm × 1 mm (= 1 mm ² ) with an optical microscope, and the average value of the ferrite area ratio with respect to the whole is calculated.

  Furthermore, it is preferable that the area ratio of ferrite that can be a crack initiation point or a propagation path of the crack is small, and the ferrite area ratio is preferably 0. That is, it is desirable that ferrite is not observed as a result of observing three fields of view by the measurement method.

  Further, the wheel bearing device 1 according to the present embodiment includes an outer ring 10 in which an annular outer rolling surface 10A is formed in a double row on the inner peripheral surface 11, and an annular inner rolling facing the outer rolling surface 10A. Rollers 50 as rolling elements that are in contact with the inner member 20, the outer rolling surface 10A, and the inner rolling surface 40A, the surfaces 40A of which are formed in a double row, are arranged on a ring-shaped track so as to be freely rollable. And.

  The inner member 20 is made of steel and includes a hub wheel 30 which is a wheel flanged member formed with a wheel mounting flange 31 which is a flange for mounting a wheel (not shown). The hub ring 30 has a hardened portion 39 hardened to 50 HRC or more by quenching and hardening, and a non-hardened portion 33 that is a portion other than the hardened portion 39. And the carbide area ratio of the steel which comprises the non-hardened part 33 is 10% or less.

  In the wheel bearing device 1 according to the present embodiment, the carbide area ratio of steel constituting the non-hardened portion 33 of the hub wheel 30 that is a wheel flanged member is 10% or less. Therefore, the steel structure constituting the non-hardened portion 33 is uniform, and the fatigue strength of the non-hardened portion 33 is improved. As a result, the wheel bearing device 1 according to the present embodiment is provided with a flanged member in which the fatigue strength of the non-cured portion 33 is improved, thereby ensuring high durability.

  Here, if the carbide area ratio exceeds 10%, the tendency of the fatigue strength to decrease accompanying the decrease in the homogeneity of the steel constituting the non-hardened portion 33 increases. Therefore, the carbide area ratio is preferably 10% or less.

The carbide area ratio means that the non-hardened portion of the wheel flanged member constituting the wheel bearing device is cut, and the fatigue strength of the carbide (cementite; Fe ₃ C) on the cut surface is reduced. Carbide having a size that can cause the steel structure to be inhomogeneous to the extent that it is observable with a general optical microscope, more specifically, the area ratio of carbide with a diameter or width exceeding 1 μm to the entire surface. Say. This carbide area ratio can be measured, for example, as follows. First, a test piece is cut out from the non-hardened portion of the wheel flanged member. And after grind | polishing the surface of the said test piece, the surface is corroded by corrosive liquid, for example, picral. And about the corroded surface, for example, with an optical microscope, three visual fields of 1 mm × 1 mm (= 1 mm ² ) are observed, and the average value of the carbide area ratio relative to the whole is calculated.

  Furthermore, the area ratio of the carbide that lowers the fatigue strength is preferably small, and the carbide area ratio is preferably zero. That is, it is desirable that no carbide is observed as a result of observation of three fields of view by the measurement method.

  Further, the wheel bearing device 1 according to the present embodiment includes an outer ring 10 in which an annular outer rolling surface 10A is formed in a double row on the inner peripheral surface 11, and an annular inner rolling facing the outer rolling surface 10A. Rollers 50 as rolling elements that are in contact with the inner member 20, the outer rolling surface 10A, and the inner rolling surface 40A, the surfaces 40A of which are formed in a double row, are arranged on a ring-shaped track so as to be freely rollable. And.

  The inner member 20 is made of steel and includes a hub wheel 30 which is a wheel flanged member formed with a wheel mounting flange 31 which is a flange for mounting a wheel (not shown). The hub ring 30 includes a hardened portion 39 hardened to 50 HRC or more by quenching and hardening, and a non-hardened portion 33 that is a portion other than the hardened portion 39. And the non-diffusible hydrogen content of the steel which comprises the non-hardening part 33 is 0.8 ppm or less.

  In the wheel bearing device 1 according to the present embodiment, the non-diffusible hydrogen content of the steel constituting the non-hardened portion 33 of the hub wheel 30 that is a wheel flanged member is suppressed to 0.8 ppm or less. Therefore, the presence of hydrogen that can promote the generation and propagation of cracks is suppressed, and the fatigue strength of the non-hardened portion 33 is improved. As a result, the wheel bearing device 1 according to the present embodiment is provided with a flanged member in which the fatigue strength of the non-cured portion 33 is improved, thereby ensuring high durability.

  Here, when the non-diffusible hydrogen content exceeds 0.8 ppm, the tendency to promote crack generation and propagation becomes strong, and therefore the non-diffusible hydrogen content is preferably 0.8 ppm or less.

  In addition, the non-diffusible hydrogen content of the steel which comprises the non-hardening part 33 can be measured as follows, for example. That is, the hydrogen content can be measured by, for example, a DH-103 type hydrogen analyzer manufactured by LECO. The specification of this LECO DH-103 type hydrogen analyzer is shown below.

Analysis range: 0.01 to 50.00 ppm
Analysis accuracy: ± 0.1 ppm or ± 3% H (whichever is greater)
Analysis sensitivity: 0.01ppm
Detection method: thermal conductivity method Sample mass size: 10 mg to 35 g (maximum: diameter 12 mm × length 100 mm)
Heating furnace temperature range: 50 ° C to 1100 ° C
Reagents: Anhydrone Mg (ClO ₄ ) ₂ , Ascarite NaOH
Carrier gas: nitrogen gas, gas dosing gas: hydrogen gas, both gases have a purity of 99.99% or more and a pressure of 40 PSI (2.8 kgf / cm ² ).

  The outline of the measurement procedure is as follows. A sample collected with a dedicated sampler is inserted into the hydrogen analyzer together with the sampler. Internal diffusible hydrogen is directed to the thermal conductivity detector by a nitrogen carrier gas. This diffusible hydrogen is not measured in this embodiment. Next, the sample is taken out from the sampler and heated in a resistance heating furnace, and non-diffusible hydrogen is guided to the thermal conductivity detector by nitrogen carrier gas. And non-diffusible hydrogen content can be known by measuring thermal conductivity in a thermal conductivity detector.

  In order to further improve the fatigue strength, the non-diffusible hydrogen content is preferably 0.5 ppm or less.

  Further, the region within 1 mm from the surface of the serration portion 37 of the hub wheel 30 in the present embodiment is the above-mentioned austenite grain size condition, ferrite area ratio condition, carbide area ratio condition, and non-diffusible hydrogen content. It is preferable that the non-cured portion 33 satisfies at least one of the above conditions.

  Thereby, the fatigue strength of the serration part 37 near the surface of the side wall of the insertion hole 38, that is, the serration part 37 can be improved, and the occurrence of breakage from the serration part 37 can be suppressed.

  In consideration of the general magnitude of stress applied to the wheel flanged member from the above-mentioned other members and the distribution of stress inside the wheel flanged member, the region with high fatigue strength is the area of the insertion hole. 1 mm from the surface of the side wall is sufficient. Therefore, it is preferable that a region within 1 mm from the surface satisfies the above conditions.

  Further, the wheel bearing device 1 according to the present embodiment includes an outer ring 10 in which an annular outer rolling surface 10A is formed in a double row on the inner peripheral surface 11, and an annular inner rolling facing the outer rolling surface 10A. Rollers 50 as rolling elements that are in contact with the inner member 20, the outer rolling surface 10A, and the inner rolling surface 40A, the surfaces 40A of which are formed in a double row, are arranged on a ring-shaped track so as to be freely rollable. And.

  The inner member 20 is made of steel and includes a hub wheel 30 which is a wheel flanged member formed with a wheel mounting flange 31 which is a flange for mounting a wheel (not shown). The hub ring 30 includes a hardened portion 39 hardened to 50 HRC or more by quenching and hardening, and a non-hardened portion 33 that is a portion other than the hardened portion 39. Then, a compressive stress of 50 MPa or more and 500 MPa or less remains on the surface of the non-cured portion 33.

  In the wheel bearing device 1 according to the present embodiment, a compressive stress of 50 MPa or more and 500 MPa or less remains on the surface of the non-cured portion 33 of the hub wheel 30 that is a wheel flanged member. Therefore, the occurrence of cracks on the surface of the non-hardened portion 33 and the subsequent propagation of cracks are suppressed, and the fatigue strength of the non-hardened portion 33 is improved, so that a moment load is repeatedly applied from the tire to the wheel flange. However, the occurrence of cracks from the non-hardened portion 33 is suppressed, and the occurrence of fretting damage is suppressed. As a result, the wheel bearing device 1 according to the present embodiment is provided with a flanged member in which the fatigue strength of the non-cured portion 33 is improved, thereby ensuring high durability.

  Here, if the compressive stress remaining on the surface is less than 50 MPa, the effect of improving fatigue strength and the effect of suppressing the occurrence of fretting damage are small, and therefore, it is necessary to be 50 MPa or more. In order to further improve the fatigue strength and further suppress the occurrence of fretting damage, the compressive stress remaining on the surface is preferably 100 MPa or more. On the other hand, when the compressive stress remaining on the surface exceeds 500 MPa, other factors at the time of applying the compressive stress, such as work hardening, are remarkable, and cracks are likely to occur. Therefore, the compressive stress is preferably 500 MPa or less.

  In addition, the measurement of the compressive stress is confirmed by measuring the region of 50 μm below the surface of the non-hardened portion 33 in the direction of the largest stress applied to the non-hardened portion 33, for example, the axial direction, using an X-ray stress measuring device can do.

  Further, the serration portion 37 of the hub wheel 30 in the present embodiment is preferably a non-cured portion 33 that satisfies the above-described stress condition. That is, the side wall of the insertion hole 38 is preferably included in the non-hardened portion 33 that satisfies the above-described stress condition. Thereby, the fatigue strength near the surface of the side wall of the insertion hole 38 is improved, and the occurrence of breakage from the serration portion 37 can be suppressed.

  Furthermore, in the hub wheel 30 in the present embodiment, the surface hardness of the base portion 31B of the wheel mounting flange 31 on the side (outboard side) on which the wheel is mounted as viewed from the wheel mounting flange 31 is 35 HRC or less. . Thereby, workability in cutting and the like is improved, heat treatment deformation can be suppressed, and deterioration of surface runout accuracy of the brake rotor attachment surface 31C of the wheel attachment flange 31 due to heat treatment deformation is suppressed.

  Further, in the hub wheel 30 in the present embodiment, the inboard which is the end of the hub wheel 30 on the side (inboard side) opposite to the side on which the wheel is mounted (outboard side) when viewed from the wheel mounting flange 31. A side end portion plastically deforms radially outward to form a caulking portion 34A. The inner ring 40 is fixed to the hub wheel 30 in the axial direction by the caulking portion 34A.

  In this way, the so-called self-retain structure eliminates the need to manage the preload by firmly tightening with a nut or the like as in the prior art, so that it can be easily incorporated into the vehicle, and The preload amount can be maintained for a long time.

  Further, in the hub wheel 30 in the present embodiment, the caulking portion 34A is formed by plastic deformation of an inboard side end portion having a surface hardness of 25 HRC or less. Thereby, the hardness variation of the caulking part 34A is suppressed. In addition, since sufficient workability can be ensured, it is possible to suppress the occurrence of micro cracks on the surface of the caulking portion 34A due to plastic working, and the reliability of the wheel bearing device 1 is improved. Yes.

  Further, in the hub wheel 30 in the present embodiment, the wheel mounting flange 31 has a root portion 31D on the side (outboard side) opposite to the side on which the wheel is mounted (outboard side) as viewed from the wheel mounting flange 31. R is formed, and the surface hardness is 54 HRC or more and 64 HRC or less.

  Thereby, it becomes possible to give sufficient mechanical strength to the rotational bending load applied to the wheel mounting flange 31, and the strength and durability of the hub wheel 30 are further improved.

  Here, the root portion of the wheel mounting flange 31 is a root portion in which the wheel mounting flange 31 protrudes in a direction crossing the central axis in a cross section including the central axis of the raceway of the roller 50 that is a rolling element, Usually, it refers to a region where the surface of the flange is formed in a curved shape, a region where a so-called R is formed, or a region where a chamfered portion is formed.

  Further, the steel constituting the hub wheel 30 in the present embodiment is a medium carbon steel containing carbon of 0.40 mass% or more and 0.80 mass% or less. Thereby, the ease of forging, machinability, heat treatment property, or economic efficiency is improved, and it is particularly suitable for partial quench hardening by induction hardening.

  Next, the manufacturing method of the wheel bearing apparatus 1 in this Embodiment is demonstrated. FIG. 2 is a flowchart showing an outline of a method for manufacturing the wheel bearing device in the present embodiment. Moreover, FIG. 3 is a flowchart which shows the outline of the hub wheel manufacturing process in which the hub ring as an inward member which is a member with a wheel flange is manufactured among the manufacturing methods of the wheel bearing apparatus in this Embodiment. .

  Referring to FIG. 2, the method for manufacturing wheel bearing device 1 in the present embodiment includes an outer member preparation step, an inner member preparation step, a rolling element preparation step, and an assembly step. In the outer member preparation step, referring to FIG. 1, an outer ring 10 in which an outer circumferential rolling surface 10 </ b> A is formed in a double row on the inner peripheral surface 11 is prepared. In the inner member preparation step, the hub wheel 30 and the inner ring 40 constituting the inner member 20 in which the annular inner rolling surface 40A is formed in a double row are prepared. In the rolling element preparation step, a roller 50 as a rolling element is prepared.

  In the assembly process, first, the inner rolling surface 40A is opposed to the outer rolling surface 10A, and the rollers 50 are disposed on an annular track in contact with the outer rolling surface 10A and the inner rolling surface 40A. Thus, the outer ring 10, the inner ring 40, and the rollers 50 are combined. Thereafter, a lubricant such as lubricating grease is put in a space (bearing space) sandwiched between the outer ring 10 and the inner ring 40, and then both end portions of the inner peripheral surface 11 of the outer ring 10 and the first end facing the both end portions. When the seal member 70 is press-fitted between the inner ring 41 and the end of the second inner ring 42, the lubricant is sealed in the bearing space. Then, the inner ring 40 of the assembly assembled as described above is press-fitted into the hub wheel 30 manufactured in the hub wheel manufacturing process (FIG. 3) described later. Thereafter, the inboard side end portion of the hub wheel 30 is plastically deformed radially outward to form a caulking portion 34 </ b> A, and the caulking portion 34 </ b> A causes the inner ring 40 to move relative to the hub wheel 30. As a result, the assembly of the wheel bearing device 1 is completed.

  And either one of the outer member preparation step or the inner member preparation step is made of steel, and a wheel flange for manufacturing a wheel flanged member formed with a wheel attachment flange, which is a flange for attaching a wheel. Includes an attached member manufacturing process. More specifically, in the present embodiment, the inward member preparation step includes a hub wheel manufacturing step as an inner member preparation step in which the hub wheel 30 as a wheel flanged member is manufactured.

  The hub wheel manufacturing process as the wheel flanged member manufacturing process, with reference to FIG. 3, a steel material preparation process, a hot forging process as a hot working process, a tempering process, a turning process, It includes a bolt hole forming step, an induction heat treatment step as a partial quench hardening step, a broaching step, and a finishing step. In the steel material preparation step, a steel material made of steel to constitute the hub wheel 30 that is a wheel flanged member, for example, a steel material made of medium carbon steel containing 0.40 mass% or more and 0.80 mass% or less of carbon is prepared. The In the hot forging process, the steel material is heated to a temperature range of, for example, 1050 ° C. or higher and 1300 ° C. or lower and hot forged to be formed into a steel member having a schematic shape of the hub wheel 30 shown in FIG. The In the tempering step, the steel member is tempered. In the turning process, the surface region including the surfaces of the wheel mounting flange 31 and the small diameter portion 34 of the steel member is turned. In the bolt hole forming step, a hub wheel bolt hole 31A is formed by drilling the wheel mounting flange 31 using a drill or the like.

  In the induction heat treatment step, a part of the tempered steel member is hardened and hardened. Specifically, referring to FIG. 1, the region including the surface of the small diameter portion 34 that is in contact with the inner ring 40, which is a region other than the surface of the side wall of the insertion hole 38, is hardened by induction hardening, A hardened portion 39 having a hardness of 58 HRC or higher is formed, and the surface hardness of the base portion 31D on the inboard side of the wheel mounting flange 31 is set to 54 HRC or higher and 64 HRC or lower. In order to satisfy such hardness conditions, for example, in the induction heat treatment step, after the induction hardening step in which induction hardening is performed, the entire tempering step in which the entire hub wheel 30 is tempered, and A partial tempering step in which a part of the region where induction hardening is performed is heated by induction heating and tempered may be performed.

  In the broaching process, referring to FIG. 1, serrations 37 are formed by forming a plurality of axially extending grooves on the surface of the side wall of insertion hole 38 formed in the hot working process. Then, in the finishing process, a finishing process (finishing process) such as a grinding process is performed on the steel member, whereby the hub wheel 30 as a wheel flanged member is completed.

  Next, the details of the tempering step will be described. FIG. 4 is a diagram showing an example of a heating pattern (temperature history given to the steel member) in the tempering step of the present embodiment. In FIG. 4, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 4, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature.

Referring to FIG. 4, the refining process includes a quenching process and a tempering process. In the quenching process, after the steel member produced in the hot forging process is heated to a temperature of A ₁ point or higher, for example, 800 ° C. or higher and 900 ° C. or lower and held for 1 hour or longer and 3 hours or shorter, It is hardened by being cooled from a ₁ point or more temperature range in M _S point or lower. The said cooling can be implemented by immersing a steel member in the oil for hardening from the temperature range more than A ₁ point, for example (oil cooling).

Thereafter, in the tempering step, the hardened steel member is heated to a temperature below A ₁ point, for example, a temperature of 400 ° C. or more and 700 ° C. or less, and held for 1 hour or more and 3 hours or less, then room temperature. It is tempered by being cooled down. By adjusting the heating temperature and the holding time, particularly the heating temperature, the surface hardness of the base portion 31B on the outboard side of the wheel mounting flange 31 is 35 HRC or less, and the inboard side end portion of the hub wheel 30 is The tempering step can be performed so that the surface hardness is 25 HRC or less. In order to satisfy the hardness condition of the end portion on the inboard side of the hub wheel 30, for example, after the tempering step is performed, the inboard side end of the hub wheel 30 is further induced by induction heating using a high-frequency current. A local tempering step may be performed in which the part is locally heated and tempered.

  The cooling in the tempering step may be performed by leaving the steel member in air at room temperature (air cooling), or by spraying cooling water on the steel member as necessary. May be done (shower cooling).

  By performing the tempering process as described above, the steel constituting the steel member has a tempered martensite (tempered troostite or / and tempered sorbite) structure. And with reference to FIG. 1, since the structure | tissue is hold | maintained in the non-hardening part 33 which is area | regions other than the hardening part 39 which is an area | region hardened and hardened in the subsequent induction hardening process, a ferrite and carbide | carbonized_material are Almost no ferrite is present (the area ratio of ferrite is 3% or less and the area ratio of carbide is 10% or less). Preferably, a homogeneous structure is obtained in which no ferrite or carbide is present. As a result, it is possible to manufacture the hub wheel 30 (inward member) as the wheel flanged member of the present embodiment that is excellent in the fatigue strength of the non-cured portion 33.

  In the tempering process, if the heating temperature in the quenching process is less than 800 ° C., the solid solution of the carbide before quenching cooling becomes insufficient, and there is a risk that ferrite and carbide remain, The heating temperature is preferably 800 ° C. or higher. Further, if the heating temperature exceeds 900 ° C., the austenite crystal grains before quenching cooling become large, and the austenite crystal grain size number after quenching may be less than 8, so that the temperature is 900 ° C. or less. It is preferable that

  Moreover, when the tempering step is performed as described above, when heated in the quenching step, a steel member is produced from an atmosphere gas containing hydrogen atoms (for example, a mixed gas of carbon monoxide, carbon dioxide and hydrogen). Hydrogen that may penetrate into the steel is released to the outside by heating the steel member to 400 ° C. or higher in the tempering step, and the non-diffusible hydrogen content is reduced to 0.8 ppm or less. As a result, it is possible to manufacture the hub wheel 30 (inward member) as the wheel flanged member of the present embodiment that is excellent in the fatigue strength of the non-cured portion 33.

  Furthermore, by performing the tempering process as described above, the heating temperature in the quenching process is set to 900 ° C. or less, and the grain size number of the austenite crystal grains to be generated is maintained at 8 or more. As a result, it is possible to manufacture the hub wheel 30 (inward member) as the wheel flanged member of the present embodiment that is excellent in the fatigue strength of the non-cured portion 33.

  Further, by performing a turning process or a broaching process after the tempering process, a compressive stress of 50 MPa or more and 500 MPa or less can remain on the surface of the non-cured portion 33. As a result, it is possible to manufacture the hub wheel 30 (inward member) as the wheel flanged member of the present embodiment that is excellent in the fatigue strength of the non-cured portion 33.

  As described above, the wheel bearing device 1 in the present embodiment can be manufactured by the method for manufacturing the wheel bearing device in the present embodiment.

  In the above embodiment, the case where the tapered roller is employed as the rolling element has been illustrated and described. However, the rolling element that can be employed in the wheel bearing device of the present invention is not limited to this and is a cylindrical roller. It may be a ball or a ball. In the above embodiment, the case where the inner ring 40 is fixed to the hub ring 30 by caulking is described. However, the inner ring 40 may be fixed to the hub ring 30 by a fixing member such as a bolt. Good. In the above embodiment, the case where the hub wheel 30 is a hub wheel for a drive wheel provided with the insertion hole 38 as a through hole penetrating the hub wheel 30 in the axial direction has been described. The hub wheel constituting the bearing device is not limited to this, and may be a hub wheel for a driven wheel that does not have the through hole.

  Further, as the material of the hub wheel 30, steel containing 0.4% by mass or more and 0.8% by mass or less of carbon, for example, JIS standard S53C, SAE1070 or the like can be adopted. Further, as the material of the inner ring 40, for example, SUJ3, SCr420, SCM420, etc. can be adopted in addition to the JIS standard SUJ2. Further, as the material of the outer ring 10, for example, SAE1070 or the like in addition to JIS standard S53C can be adopted. Further, as the material of the roller 50, for example, SUJ3, SCr420, SCM420, etc. can be adopted in addition to the JIS standard SUJ2.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The wheel bearing device of the present invention can be particularly advantageously applied to a wheel bearing device that requires high durability in order to rotatably support a wheel with respect to a vehicle body such as an automobile.

It is a schematic sectional drawing which shows the structure of the wheel bearing apparatus in one embodiment of this invention. It is a flowchart which shows the outline of the manufacturing method of the wheel bearing apparatus in one embodiment of this invention. It is a flowchart which shows the outline of a hub wheel manufacturing process among the manufacturing methods of the wheel bearing apparatus in one embodiment of this invention. It is a figure which shows an example of the heating pattern (temperature history given to a steel member) in the refining process of one embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Wheel bearing apparatus, 10 Outer ring, 10A Outer rolling surface, 11 Inner peripheral surface, 12A 1st outer rolling surface, 13A 2nd outer rolling surface, 15 Outer ring flange, 15A Outer ring through-hole, 19 Hardening part, 20 Inner member, 30 hub wheel, 31 wheel mounting flange, 31A hub wheel bolt hole, 31B, 31D root part, 31C brake rotor mounting surface, 33 non-hardened part, 34 small diameter part, 34A caulking part, 37 serration part, 38 Insertion hole, 39 Hardened portion, 40 Inner ring, 40A Inner rolling surface, 41 First inner ring, 41A First inner rolling surface, 42 Second inner ring, 42A Second inner rolling surface, 50 rollers, 60A, 60B Cage , 70 sealing member, 71 bolts.

Claims (8)

An outer member in which an annular outer rolling surface is formed in a double row on the inner peripheral surface,
An inner member in which an annular inner rolling surface facing the outer rolling surface is formed in a double row,
The outer rolling surface and the inner rolling surface are in contact with each other, and provided with rolling elements that are arranged to roll on an annular track,
Either the outer member or the inner member is made of steel, and includes a wheel flanged member formed with a wheel mounting flange that is a flange for mounting a wheel.
The wheel flanged member is:
By being hardened by quenching, a cured portion cured to 50 HRC or more;
It has a non-cured part that is a part other than the cured part,
A wheel bearing device in which a compressive stress of 50 MPa or more and 500 MPa or less remains on the surface of the non-hardened portion. In the flanged member for wheels, an insertion hole for inserting another member is formed in a region including the central axis of the track of the rolling element,
The wheel bearing device according to claim 1, wherein a side wall of the insertion hole is included in the non-hardened portion.   3. The wheel bearing device according to claim 1, wherein a surface hardness of a base portion of the wheel mounting flange on a side where the wheel is mounted as viewed from the wheel mounting flange is 35 HRC or less. The inner member is
A hub wheel that is a member with a flange for the wheel;
The wheel bearing device according to any one of claims 1 to 3, comprising an inner ring fitted into the hub ring. The inboard side end that is the end of the hub wheel on the side opposite to the side on which the wheel is mounted as seen from the wheel mounting flange forms a crimped portion by plastic deformation radially outward,
The wheel bearing device according to claim 4, wherein the inner ring is fixed to the hub wheel in the axial direction by the caulking portion.   The wheel bearing device according to claim 5, wherein the caulking portion is formed by plastic deformation of the inboard side end portion having a surface hardness of 25 HRC or less.   7. The surface hardness of a root portion of the wheel mounting flange on the side opposite to the side on which the wheel is mounted as viewed from the wheel mounting flange is 54 HRC or more and 64 HRC or less. Wheel bearing device.   The wheel bearing device according to any one of claims 1 to 7, wherein the steel is a medium carbon steel containing carbon of 0.40 mass% or more and 0.80 mass% or less.

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