Wheel bearing device

Abstract

To provide a bearing device for a wheel which can prevent hardening crack by heat treatment without increasing a thickness of counter bore parts in an axial direction.SOLUTION: A bearing device 1 for a wheel has an inner side counter bore part 2h and an outer side counter bore part 2m which are respectively located adjacent to an inner side outer ring raceway surface 2c and an outer side outer ring raceway surface 2d and in which their inner peripheral surfaces protrude to a radial inner side relative to groove bottom diameters of the inner side outer ring raceway surface 2c and the outer side outer ring raceway surface 2d. For example, the inner side counter bore part 2h has: a first inclined surface 2i extending to the radial inner side from an end on an opening side toward the inner side outer ring raceway surface 2c side; and a second inclined surface 2l which is located on at least the opening side of both ends of the first inclined surface 2i and extends to the radial inner side toward the inner side outer ring raceway surface 2c side.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a wheel bearing device.

Background Art

[0002] A wheel bearing device for rotatably supporting a wheel is known. In the wheel bearing device, a hub ring, which is an inner member connected to the wheel, is rotatably supported by an outer ring, which is an outer member, via rolling elements. The hub ring and the outer ring are mainly made of a steel material such as S53C. The hub ring and the outer ring are processed in the order of hot forging, turning, high-frequency heat treatment, and grinding from the steel material of the raw material. In the hub ring and the outer ring, the raceway surface on which the rolling elements roll is surface-hardened to a hardness of, for example, 58 HRC to 63 HRC in terms of HRC (Rockwell C scale) by high-frequency heat treatment. The rolling elements are made of high-carbon chromium bearing steel. The rolling elements are surface-hardened to a hardness of, for example, 62 HRC to 67 HRC by quenching.

[0003] In high-frequency heat treatment, the current that heats the hub ring and the outer ring preferentially flows on the surfaces of the hub ring and the outer ring. Therefore, in a portion where a plurality of surfaces such as the corners and ends of the hub ring and the outer ring are connected, the current flowing on the plurality of surfaces concentrates on the corners and ends. Further, the corners and ends are sharper, and the heat capacity of the portion where the current flows becomes smaller. Therefore, the corners and ends that are sharply angled are heated to a high temperature due to the concentration of the current, and are likely to crack. Therefore, a wheel bearing device that alleviates the concentration of the current and prevents cracking is known. For example, it is as described in Patent Document 1.

[0004] The wheel bearing device described in Patent Document 1 has a curved chamfer formed on the axially inward shoulder of the first raceway of the outer ring. In other words, the first raceway and the shoulder adjacent to the first raceway are connected by a curved surface. Therefore, the outer ring does not have any corners between the first raceway and the shoulder. As a result, in high-frequency heat treatment, the current flowing across the surface of the outer ring is less likely to concentrate in the area where the first raceway and the shoulder are connected, and the smaller the radius of curvature of the curved surface of the chamfer, the larger the heat capacity of the area through which the current flows, thus preventing cracking. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-211308 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, in order to extend the lifespan of wheel bearing devices, there is a need for raceway surfaces that are less susceptible to indentations caused by impact loads generated when automobiles and other vehicles are in motion. To increase the resistance of the raceway surfaces of the hub ring and outer ring of a wheel bearing device to indentations, it is necessary to increase the hardening depth in the direction normal to the raceway surface. In the wheel bearing device, the deeper the hardening depth of the raceway surfaces of the hub ring and outer ring, the greater the heating range by high-frequency heat treatment. Therefore, in the wheel bearing device described in Patent Document 1, depending on the hardening depth, the counterbore portion between the first raceway and the opening of the outer ring, which protrudes radially from the inner circumferential surface of the first raceway and the opening, is included in the heating range by high-frequency heat treatment. The counterbore portion, which has the function of holding the rolling elements in the first raceway, is configured to have a thinner axial thickness than the shoulder portion from the viewpoint of weight reduction. For this reason, the wheel bearing device had the potential to crack if the counterbore portion was included in the heating range.

[0007] This invention has been made in view of the above circumstances, and aims to provide a wheel bearing device that can prevent heat cracking due to heat treatment without increasing the axial thickness of the counterbore portion. [Means for solving the problem]

[0008] The inventors investigated a configuration for a wheel bearing device that can prevent heat cracking due to heat treatment without increasing the axial thickness of the counterbore. After diligent investigation, the inventors arrived at the following configuration.

[0009] That is, the wheel bearing device of the first invention includes a cylindrical outer member having an annular double row of outer raceway surfaces on its inner circumferential surface with their axes coincided, an inner member having a double row of inner raceway surfaces on its outer circumferential surface facing the double row of outer raceway surfaces, a double row of rolling elements rotatably housed between the two raceway surfaces of the outer member and the inner member, at least one of the double row of outer raceway surfaces, and a counterbore portion adjacent to the double row of outer raceway surfaces, the inner circumferential surface of which protrudes inward from the groove bottom diameter of the outer raceway surface. The counterbore portion includes a first inclined surface extending radially inward from the end of the outer member on the opening side toward the outer raceway surface, and a second inclined surface located at least on the opening side of both ends of the first inclined surface and extending radially inward toward the outer raceway surface.

[0010] In the first invention, the counterbore portion of the wheel bearing device has a first inclined surface at the end of the outer member on the opening side. Furthermore, the first inclined surface has a second inclined surface at least on the opening side. The counterbore portion has only obtuse angles that suppress overheating due to current concentration during high-frequency heat treatment due to the first and second inclined surfaces. In other words, the counterbore portion does not have any acute angle portions that are prone to overheating due to current concentration during high-frequency heat treatment. This makes it possible to prevent cracking due to heat treatment without increasing the axial thickness of the counterbore portion.

[0011] Furthermore, from another perspective, the wheel bearing device of the second invention preferably includes the following configuration: 1 In a radial cross-sectional view, the inclined surface ,straight It is linear or arc-shaped.

[0012] In the second invention, the first inclined surface is a curved or straight surface that protrudes radially in a radial cross-sectional view. It is formed in The second inclined surface connects to at least one of the surface located on the raceway side and the surface located on the opening side. In other words, at the end of the first inclined surface, the counterbore portion has a more obtuse angle or a convex curved surface formed by the second inclined surface, where the corners that are prone to overheating during high-frequency heat treatment are formed. This makes it possible to prevent quench cracking due to heat treatment without increasing the axial thickness of the counterbore portion.

[0013] Furthermore, from another perspective, the wheel bearing device of the third invention preferably includes the following configuration: The second inclined surface is located at both ends of the first inclined surface, and the second inclined surface on the outer raceway surface side is connected to the outer raceway surface.

[0014] In the third invention, the counterbore portion has a second inclined surface on the outer raceway surface side of the first inclined surface that is connected to the outer raceway surface, so that the opening side of the counterbore portion, which is prone to overheating during high-frequency heat treatment, can be made into an inclined surface. This makes it possible to prevent quench cracking due to heat treatment without increasing the axial thickness of the counterbore portion.

[0015] Furthermore, from another perspective, the wheel bearing device of the fourth invention preferably includes the following configuration: The first inclined surface is a straight line in radial cross-sectional view, with respect to the axis in an inclination range of 30 to 60 degrees.

[0016] In the fourth invention, the angle of the first inclined surface with respect to the surfaces located on both sides of the first inclined surface is determined by the inclination of the first inclined surface with respect to the axis. That is, in the counter bore portion, the angular range of the connection portion between the first inclined surface and the second inclined surface is limited to a range in which overheating due to high-frequency heat treatment is unlikely to occur. Thereby, it is possible to prevent cracking due to heat treatment without increasing the axial thickness of the counter bore portion.

[0017] Also, from another perspective, it is preferable that the wheel bearing device of the fifth invention includes the following configuration. At least a part of the counter bore portion has a surface hardness of 58 HRC to 63 HRC by high-frequency heat treatment.

[0018] In the fifth invention, the counter bore portion has no acute-angle portion where overheating due to high-frequency heat treatment is likely to occur due to the first inclined surface and the second inclined surface. Therefore, the counter bore portion can harden the surface to a surface hardness of 58 HRC to 63 HRC by high-frequency heat treatment while suppressing cracking. Thereby, the counter bore portion can improve its strength by high-frequency heat treatment.

Advantages of the Invention

[0019] According to one embodiment of the present invention, it is possible to prevent cracking due to heat treatment without increasing the axial thickness of the counter bore portion.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a perspective view showing the overall configuration of a wheel bearing device according to Embodiment 1 of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the overall configuration of a wheel bearing device according to Embodiment 1 of the present invention. [Figure 3] FIG. 3 is a partially enlarged cross-sectional view showing the inner-side counter bore portion in the outer ring of the wheel bearing device according to Embodiment 1 of the present invention. [Figure 4]FIG. 4 is a partially enlarged cross-sectional view showing an outer counter bore portion in an outer ring of the wheel bearing device according to Embodiment 1 of the present invention. [Figure 5] FIG. 5 is a partially enlarged cross-sectional view showing an inner counter bore portion in an outer ring of the wheel bearing device according to Embodiment 2 of the present invention. [Figure 6] FIG. 6 is a partially enlarged cross-sectional view showing an outer counter bore portion in an outer ring of the wheel bearing device according to Embodiment 2 of the present invention. [Figure 7] FIG. 7 is a partially enlarged cross-sectional view showing an inner counter bore portion in an outer ring of the wheel bearing device according to another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] (Embodiment 1) Hereinafter, a wheel bearing device 1 which is an exemplary Embodiment 1 of the wheel bearing device according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view showing the overall configuration of the wheel bearing device 1. FIG. 2 is a cross-sectional view showing the overall configuration of the wheel bearing device 1.

[0022] As shown in FIG. 1, the wheel bearing device 1 is a bearing device that rotatably supports a wheel in a suspension device of a vehicle such as an automobile. In the present embodiment, the wheel bearing device 1 is a wheel bearing device for a driven wheel. The wheel bearing device 1 includes an outer ring 2 which is an outer member, a hub ring 3 and an inner ring 4 which are inner members, two rows of inner side ball rows 5 (see FIG. 2) which are rolling element rows, an outer side ball row 6 (see FIG. 2), an inner side seal member 7 and an outer side seal member 8 (see FIG. 2). Here, the inner side represents the vehicle body side of the wheel bearing device 1 when attached to the vehicle body, and the outer side represents the wheel side of the wheel bearing device 1 when attached to the vehicle body. Further, the axial direction represents the direction along the rotation axis of the wheel bearing device 1.

[0023] As shown in Figure 2, the outer ring 2, which is an outer member, is a cylindrical member that supports the inner members (hub ring 3 and inner ring 4). The outer ring 2 is made of medium-high carbon steel containing 0.40 to 0.80 wt% carbon, such as S53C, which is formed into a substantially cylindrical shape. The inner opening of the outer ring 2 includes an inner seal fitting portion 2a into which the inner seal member 7 is fitted. In other words, the inner seal fitting portion 2a is the inner opening of the outer ring 2. The outer opening of the outer ring 2 includes an outer seal fitting portion 2b into which the outer seal member 8 is fitted. In other words, the outer seal fitting portion 2b is the outer opening of the outer ring 2.

[0024] The outer ring 2 has an inner outer ring raceway surface 2c and an outer outer ring raceway surface 2d, which are annular double-row outer raceway surfaces on its inner circumferential surface. The inner outer ring raceway surface 2c, which is one of the double-row outer raceway surfaces, is located on the inner side of the outer ring 2. The inner outer ring raceway surface 2c is located near the outer side of the inner seal fitting portion 2a. The outer outer ring raceway surface 2d, which is the other of the double-row outer raceway surfaces, is located on the outer side of the outer ring 2. The outer outer ring raceway surface 2d is located near the inner side of the outer seal fitting portion 2b. The inner outer ring raceway surface 2c and the outer outer ring raceway surface 2d have their axes coincide and are positioned so as to be parallel to each other in the circumferential direction. The pitch circle diameter of the inner outer ring raceway surface 2c and the pitch circle diameter of the outer outer ring raceway surface 2d are of equal size. Furthermore, the pitch circle diameter of the inner outer ring raceway surface 2c and the pitch circle diameter of the outer outer ring raceway surface 2d may be configured to be different sizes.

[0025] The outer ring 2 has a body mounting flange 2e on its outer circumference for attachment to a suspension knuckle (not shown). The body mounting flange 2e is located near the inner side seal fitting portion 2a. The inner side of the body mounting flange 2e has a cylindrical pilot portion 2g that fits into the vehicle's knuckle.

[0026] The hub ring 3, which constitutes the inner member, is a solid cylindrical member having a flange that rotatably supports the wheel of a vehicle (not shown). The hub ring 3 is made of medium-high carbon steel containing 0.40 to 0.80 wt% carbon, such as S53C. The hub ring 3 has a small-diameter stepped portion 3a at its inner end, which is a portion where the outer diameter is smaller by a predetermined range in the axial direction from the inner end. In other words, the inner end of the small-diameter stepped portion 3a is the inner end of the hub ring 3 and has a crimped portion 3b, which will be described later. The hub ring 3 has a wheel mounting flange 3c at its outer end for attaching the wheel. The wheel mounting flange 3c has hub bolts 3d at equidistant positions around the circumference. The hub ring 3 has an annular sealing sliding surface 3e in the circumferential direction and an annular outer inner ring raceway surface 3f, which is one of the inner raceway surfaces of a double row of inner raceway surfaces, on its outer circumferential surface (wheel mounting flange 3c side). The outer inner ring raceway surface 3f is located adjacent to the inner side of the seal sliding surface 3e. The outer inner ring raceway surface 3f is located radially opposite the outer outer ring raceway surface 2d of the outer ring 2.

[0027] The hub wheel 3 is hardened from the small-diameter stepped portion 3a on the inner side to the seal sliding surface 3e on the outer side by high-frequency induction hardening to a surface hardness in the range of 58 HRC to 63 HRC. As a result, the hub wheel 3 has sufficient mechanical strength against the rotational bending load applied to the wheel mounting flange 3c, improving its durability. The hub wheel 3 has a crimped portion 3b at the inner end that is plastically deformed radially outward to fix the inner ring 4, into which the inner ring 4 is fitted.

[0028] The inner ring 4 is a rolling element that provides preload to the inner ball row 5, which is located on the vehicle body side when mounted, and the outer ball row 6, which is located on the wheel side when mounted. The inner ring 4 has an annular inner inner ring raceway surface 4a on its outer circumference, which is the other inner raceway surface of the double row of inner raceways. The inner ring 4 is fixed to the small diameter stepped portion 3a of the hub ring 3 by press-fitting and crimping. In other words, the inner inner ring raceway surface 4a is formed on the inner side of the hub ring 3 by the inner ring 4. The inner inner ring raceway surface 4a of the inner ring 4 is radially opposite to the inner outer ring raceway surface 2c of the outer ring 2.

[0029] The inner ball row 5 and the outer ball row 6 are rolling elements arranged in a ring shape, with multiple balls, which are the rolling elements, held in a ring shape by a retainer. The inner ball row 5 is rotatably housed between the inner inner ring raceway surface 4a of the inner ring 4 and the inner outer ring raceway surface 2c of the inner ring 2. The outer ball row 6 is rotatably housed between the outer inner ring raceway surface 3f of the hub ring 3 and the outer outer ring raceway surface 2d of the outer ring 2.

[0030] Thus, the wheel bearing device 1 is composed of a double-row angular contact ball bearing consisting of an outer ring 2, a hub ring 3 and an inner ring 4, an inner ball row 5, and an outer ball row 6.

[0031] The inner side sealing member 7, which is a sealing component, is a pack seal that closes the gap between the outer ring 2 and the inner ring 4. The inner side sealing member 7 is composed of, for example, a two-side lip type pack seal in which two sealing lips are in contact. The inner side sealing member 7 comprises a substantially cylindrical sealing plate and a substantially cylindrical slinger. The sealing plate of the inner side sealing member 7 is fitted into the inner side sealing fitting portion 2a of the outer ring 2. The cylindrical portion of the slinger of the inner side sealing member 7 is fitted into the inner ring 4. The inner side sealing member 7 is configured to be slidable relative to the slinger by the sealing lip of the sealing plate contacting the slinger via an oil film. As a result, the inner side sealing member 7 prevents grease leakage from between the inner side sealing fitting portion 2a of the outer ring 2 and the inner ring 4, and prevents the intrusion of rainwater and dust from the outside.

[0032] The outer-side sealing member 8, which is a sealing component, is a sealing member that mainly closes the gap between the outer ring 2 and the hub ring 3. The cylindrical portion of the outer-side sealing member 8 is fitted into the outer-side sealing fitting portion 2b of the outer ring 2, and multiple sealing lips contact or come into close proximity with the sealing sliding surface 3e of the hub ring 3 via an oil film, thereby preventing mud, water, or foreign matter from entering between the outer ring 2 and the hub ring 3.

[0033] The wheel bearing device 1, configured in this way, consists of a double-row angular contact ball bearing comprising an outer ring 2, a hub ring 3, an inner ring 4, an inner ball row 5, and an outer ball row 6. The hub ring 3 is rotatably supported on the outer ring 2 via the inner ball row 5 and the outer ball row 6. Furthermore, the wheel bearing device 1 seals the gap between the outer ring 2 and the inner ring 4 with an inner seal member 7, and seals the gap between the outer ring 2 and the hub ring 3 with an outer seal member 8. In this way, the wheel bearing device 1 rotatably supports the hub ring 3, which is supported on the outer ring 2, while preventing grease leakage from the inside and the intrusion of rainwater and dust from the outside.

[0034] Next, the inner counterbore portion 2h and the outer counterbore portion 2m, which are the counterbore portions of the outer ring 2, will be explained using Figures 3 and 4. Figure 3 is a partially enlarged cross-sectional view showing the inner counterbore portion 2h of the outer ring 2 of the wheel bearing device 1. Figure 4 is a partially enlarged cross-sectional view showing the outer counterbore portion 2m of the outer ring 2 of the wheel bearing device 1.

[0035] As shown in Figure 2, the inner counterbore portion 2h is an engaging portion that holds the inner ball row 5, which is housed in the inner outer ring raceway surface 2c, to prevent it from falling out to the inner side. The inner counterbore portion 2h is located between the inner outer ring raceway surface 2c and the inner seal fitting portion 2a, which is the inner opening of the outer ring 2. In other words, the inner counterbore portion 2h is adjacent to the inner seal fitting portion 2a on the inner outer ring raceway surface 2c. Furthermore, the portion of the inner counterbore portion 2h that is located most radially inward (the inner circumferential surface 2j, which will be described later) protrudes radially inward from the groove bottom diameter, which is the portion located most radially outward on the inner outer ring raceway surface 2c, and from the radial fitting surface of the inner seal fitting portion 2a. In other words, the inner counterbore portion 2h constitutes the inner side (inner seal fitting portion 2a side) of the inner outer ring raceway surface 2c and the outer side (inner outer ring raceway surface 2c side) of the inner seal fitting portion 2a.

[0036] As shown in Figure 3, the inner counterbore portion 2h has a conical inner circumferential surface at the end on the inner seal fitting portion 2a side (see Figure 2). In other words, the inner counterbore portion 2h has a first inclined surface 2i at the end on the inner seal fitting portion 2a side that extends radially inward toward the inner outer ring raceway surface 2c side. The first inclined surface 2i extends radially inward from the end on the inner seal fitting portion 2a side toward the inner outer ring raceway surface 2c side. In a radial cross-sectional view, the first inclined surface 2i is a straight line whose angle θ1 with respect to the axis is in the range of 30 to 60 degrees.

[0037] Furthermore, the inner counterbore portion 2h has a cylindrical inner circumferential surface at its end on the inner outer ring raceway surface 2c side. In other words, in a radial cross-sectional view, the inner counterbore portion 2h is located on the inner outer ring raceway surface 2c side of the first inclined surface 2i and has an inner circumferential surface 2j which is a plane with a constant radial position at any position in the axial direction.

[0038] Furthermore, the inner counterbore portion 2h has an annular stepped surface facing axially towards the inner seal fitting portion 2a. In other words, in a radial cross-sectional view, the inner counterbore portion 2h has a side surface 2k located on the inner seal fitting portion 2a side of the first inclined surface 2i.

[0039] Furthermore, the inner counterbore portion 2h has a substantially conical inner circumferential surface that connects the first inclined surface 2i and the inner circumferential surface 2j, and the first inclined surface 2i and the side surface 2k. In other words, in a radial cross-sectional view, the inner counterbore portion 2h has a second inclined surface 2l that extends radially inward toward the inner outer ring raceway surface 2c at the end of the first inclined surface 2i on the inner outer ring raceway surface 2c side and the end on the inner seal fitting portion 2a side. The second inclined surface 2l is a curved surface in a radial cross-sectional view. Therefore, in a radial cross-sectional view, the first inclined surface 2i and the inner circumferential surface 2j, and the first inclined surface 2i and the side surface 2k are smoothly connected by the second inclined surface 2l.

[0040] Thus, the inner counterbore portion 2h is configured such that the angle between the inner circumferential surface 2j and the first inclined surface 2i, and the angle between the side surface 2k and the first inclined surface 2i, are obtuse angles. Furthermore, the connection portion between the inner circumferential surface 2j and the first inclined surface 2i, and the connection portion between the side surface 2k and the first inclined surface 2i, are rounded by the second inclined surface 2l so as not to have any corners.

[0041] As shown in Figure 4, the outer counterbore portion 2m is an engaging portion that holds the outer ball row 6, which is housed in the outer ring raceway surface 2d, so as not to fall out to the outer side. The outer counterbore portion 2m is located between the outer ring raceway surface 2d and the outer seal fitting portion 2b, which is the outer opening of the outer ring 2. In other words, the outer counterbore portion 2m is adjacent to the outer seal fitting portion 2b side of the outer ring raceway surface 2d. Furthermore, the portion of the outer counterbore portion 2m that is located most radially inward (the inner circumferential surface 2o, which will be described later) protrudes radially inward from the groove bottom diameter, which is the portion located most radially outward on the outer ring raceway surface 2d, and from the radial fitting surface of the outer seal fitting portion 2b. In other words, the outer counterbore portion 2m constitutes the outer side (outer seal fitting portion 2b side) of the outer outer ring raceway surface 2d and the inner side (outer outer ring raceway surface 2d side) of the outer seal fitting portion 2b.

[0042] The outer counterbore section 2m, like the inner counterbore section 2h, has a first inclined surface 2n, an inner circumferential surface 2o, a side surface 2p, and a second inclined surface 2q.

[0043] The first inclined surface 2n of the outer counterbore portion 2m is a conical inner circumferential surface that extends radially inward toward the outer outer ring raceway surface 2d, located at the end on the outer seal fitting portion 2b side in a radial cross-sectional view. The first inclined surface 2n is a straight line in a radial cross-sectional view, with an angle θ2 with respect to the axis ranging from 30 to 60 degrees.

[0044] The inner circumferential surface 2o of the outer counterbore portion 2m is located on the outer ring raceway surface 2d side of the first inclined surface 2n in a radial cross-sectional view. The inner circumferential surface 2o is a cylindrical inner circumferential surface whose radial position is constant at any position in the axial direction.

[0045] The side surface 2p of the outer counterbore portion 2m is located on the outer seal fitting portion 2b side of the first inclined surface 2n in a radial cross-sectional view.

[0046] The second inclined surface 2q of the outer counterbore portion 2m is, in a radial cross-sectional view, a substantially conical inner circumferential surface that extends radially inward toward the outer outer ring raceway surface 2d at the end of the first inclined surface 2n on the outer outer ring raceway surface 2d side and the end on the outer seal fitting portion 2b side. The second inclined surface 2q is a curved surface in a radial cross-sectional view. Therefore, in a radial cross-sectional view, the first inclined surface 2n and the inner circumferential surface 2o, and the first inclined surface 2n and the side surface 2p are smoothly connected by the second inclined surface 2q.

[0047] In the outer counterbore section 2m configured in this way, the angle between the inner circumferential surface 2o and the first inclined surface 2n, and the angle between the side surface 2p and the first inclined surface 2n are both obtuse angles. Furthermore, the connection portion between the inner circumferential surface 2o and the first inclined surface 2n, and the connection portion between the side surface 2p and the first inclined surface 2n are rounded by the second inclined surface 2q so that they do not have corners.

[0048] Next, the effects of high-frequency heat treatment on the inner counterbore section 2h and the outer counterbore section 2m will be explained. Note that the effects of high-frequency heat treatment on the inner counterbore section 2h and the outer counterbore section 2m are substantially the same. Therefore, the effects of high-frequency heat treatment on the inner counterbore section 2h will be explained, and the explanation of the effects of high-frequency heat treatment on the outer counterbore section 2m will be omitted.

[0049] The inner outer ring raceway surface 2c and the outer outer ring raceway surface 2d are subjected to high-frequency heat treatment so that a hardened layer H is formed on the surface in the range of 58 HRC to 63 HRC. When the depth of the formed hardened layer H is approximately 2.5 mm to 4.0 mm, the inner counterbore portion 2h of the outer ring 2 is also subjected to high-frequency heat treatment by the high-frequency heat treatment of the inner outer ring raceway surface 2c and the outer outer ring raceway surface 2d.

[0050] In the inner counterbore section 2h, induced current flows through the inner circumferential surface 2j, the first inclined surface 2i, the side surface 2k, and the second inclined surface 2l due to high-frequency heat treatment. The inner circumferential surface 2j and the first inclined surface 2i are smoothly connected by the second inclined surface 2l. Therefore, the induced current flowing through the inner circumferential surface 2j and the first inclined surface 2i is less likely to accumulate on the second inclined surface 2l, which is located between the inner circumferential surface 2j and the first inclined surface 2i and connects them. Also, since there are no sharp angles with low heat capacity between the inner circumferential surface 2j and the first inclined surface 2i, overheating is less likely. Similarly, the side surface 2k and the first inclined surface 2i are smoothly connected by the second inclined surface 2l. Therefore, the induced current flowing through the side surface 2k and the first inclined surface 2i is less likely to accumulate on the second inclined surface 2l, which is located between the side surface 2k and the first inclined surface 2i and connects them.

[0051] Thus, in a radial cross-sectional view, the inner counterbore portion 2h has a first inclined surface 2i at the inner end of the outer ring 2 on the opening side, and the first inclined surface 2i is connected to at least one of the inner circumferential surface 2j located on the inner outer ring raceway surface 2c side of the first inclined surface 2i and the side surface 2k located on the opening side of the first inclined surface 2i by a second inclined surface 2l. In a radial cross-sectional view, the second inclined surface 2l is an arc shape projecting radially. The first inclined surface 2i is a straight line in a radial cross-sectional view, with an angle θ1 with respect to the axis of the outer ring 2 in the range of 30 to 60 degrees. At least a portion of the inner counterbore portion 2h has a hardened layer H hardened to a surface hardness of 58 HRC to 63 HRC by high-frequency heat treatment.

[0052] The inner counterbore portion 2h is connected by a second inclined surface 2l, which is a curved surface projecting radially from at least one of the inner circumferential surface 2j located on the inner outer ring raceway surface 2c side and the side surface 2k located on the opening side, where the first inclined surface 2i is connected. Therefore, the inner counterbore portion 2h does not have any sharp angles that would cause overheating due to high-frequency heat treatment due to the first inclined surface 2i and the second inclined surface 2l. Thus, the surface of the inner counterbore portion 2h can be hardened to a surface hardness of 58 HRC to 63 HRC by high-frequency heat treatment.

[0053] Furthermore, the angle of the first inclined surface 2i with respect to the side surface 2k located on the opening side of the first inclined surface 2i and the inner outer ring raceway surface 2c is determined by the inclination of the first inclined surface 2i with respect to the axis. In other words, the angle range of the corner at the connection portion between the first inclined surface 2i and the second inclined surface 2l of the inner counterbore portion 2h is limited to a range in which overheating is unlikely during high-frequency heat treatment. The same applies to the outer counterbore portion 2m. As a result, the wheel bearing device 1 can prevent cracking of the inner counterbore portion 2h and the outer counterbore portion 2m due to heat treatment without increasing the axial thickness of the inner counterbore portion 2h and the outer counterbore portion 2m in order to increase the heat capacity of the inner counterbore portion 2h and the outer counterbore portion 2m.

[0054] (Embodiment 2) Below, an exemplary embodiment 2 of the wheel bearing device according to the present invention, the wheel bearing device 1A, will be described with reference to Figures 5 and 6. Figure 5 is a partially enlarged cross-sectional view showing the inner side counterbore portion 2hA of the outer ring 2 of the wheel bearing device 1A. Figure 6 is a partially enlarged cross-sectional view showing the outer side counterbore portion 2mA of the outer ring 2 of the wheel bearing device 1A. In the following description, components identical to those in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted; only the parts that differ from Embodiment 1 will be described.

[0055] As shown in Figure 5, the inner counterbore portion 2hA of the outer ring 2 of the wheel bearing device 1A is located between the inner outer ring raceway surface 2c and the inner seal fitting portion 2a, which is the inner opening of the outer ring 2. In other words, the inner counterbore portion 2hA is adjacent to the inner seal fitting portion 2a side of the inner outer ring raceway surface 2c. Furthermore, the portion of the inner counterbore portion 2hA that is located most radially inward (the second inclined surface 2lA corresponding to the inner circumferential surface) protrudes radially inward from the groove bottom diameter of the inner outer ring raceway surface 2c and the radial fitting surface of the inner seal fitting portion 2a.

[0056] The inner counterbore portion 2hA has a conical inner circumferential surface. In other words, in a radial cross-sectional view, the inner counterbore portion 2hA has a first inclined surface 2iA that extends radially inward toward the inner outer ring raceway surface 2c, from the end on the inner outer ring raceway surface 2c side to the end on the inner seal fitting portion 2a side. In a radial cross-sectional view, the first inclined surface 2iA extends from the end on the inner seal fitting portion 2a side to the vicinity of the inner outer ring raceway surface 2c side.

[0057] Furthermore, the inner counterbore portion 2hA has a substantially conical inner circumferential surface that connects the first inclined surface 2iA to the inner outer ring raceway surface 2c, and to the side surface 2k. In other words, in a radial cross-sectional view, the inner counterbore portion 2hA has a second inclined surface 2lA extending radially inward toward the inner outer ring raceway surface 2c at the end of the first inclined surface 2iA on the inner outer ring raceway surface 2c side and at the end on the inner seal fitting portion 2a side. In addition, each of the second inclined surfaces 2lA is a curved surface in a radial cross-sectional view. Therefore, in a radial cross-sectional view, the inner counterbore portion 2hA is smoothly connected to the first inclined surface 2iA to the inner outer ring raceway surface 2c, and to the side surface 2k, respectively, by the second inclined surface 2lA. Therefore, on the inner circumferential surface of the inner counterbore portion 2hA, the second inclined surface 2lA on the inner seal fitting portion 2a side is located most radially outward, and the second inclined surface 2lA on the inner outer ring raceway surface 2c side is located most radially inward.

[0058] Thus, the inner counterbore portion 2hA is configured such that the angle between the inner outer ring raceway surface 2c and the first inclined surface 2iA, and the angle between the side surface 2k and the first inclined surface 2iA, are both obtuse angles. Furthermore, the connection portion between the inner outer ring raceway surface 2c and the first inclined surface 2iA, and the connection portion between the side surface 2k and the first inclined surface 2iA, are rounded by the second inclined surface 2lA so as not to have any corners.

[0059] As shown in Figure 6, the outer counterbore portion 2mA is located between the outer ring raceway surface 2d and the outer seal fitting portion 2b, which is the outer opening of the outer ring 2. In other words, the outer counterbore portion 2mA is adjacent to the outer seal fitting portion 2b side of the outer ring raceway surface 2d. Furthermore, the portion of the outer counterbore portion 2mA that is located most radially inward (the second inclined surface 2qA, which corresponds to the inner circumferential surface) protrudes radially inward from the groove bottom diameter of the outer ring raceway surface 2d and the radial fitting surface of the outer seal fitting portion 2b.

[0060] The outer counterbore section 2mA, like the inner counterbore section 2hA, has a first inclined surface 2nA, a side surface 2p, and a second inclined surface 2qA.

[0061] The first inclined surface 2nA of the outer counterbore portion 2mA is a conical inner circumferential surface that extends radially inward toward the outer ring raceway surface 2d, from the end on the outer ring raceway surface 2d side to the end on the outer seal fitting portion 2b side, in a radial cross-sectional view. The first inclined surface 2nA extends from the end on the outer ring raceway surface 2b side to the vicinity of the outer ring raceway surface 2d side, in a radial cross-sectional view.

[0062] The second inclined surface 2qA of the outer counterbore portion 2mA is, in a radial cross-sectional view, a substantially conical inner circumferential surface that extends radially inward toward the outer ring raceway surface 2d at the end of the first inclined surface 2nA on the outer ring raceway surface 2d side and the end on the outer seal fitting portion 2b side. The second inclined surface 2qA is a curved surface in a radial cross-sectional view. Therefore, in a radial cross-sectional view, the first inclined surface 2nA and the outer ring raceway surface 2d, and the first inclined surface 2nA and the side surface 2p are smoothly connected by the second inclined surface 2qA. Thus, on the inner circumferential surface of the outer counterbore portion 2mA, the second inclined surface 2qA on the outer seal fitting portion 2b side is located radially outward, and the second inclined surface 2qA on the outer ring raceway surface 2d side is located radially inward.

[0063] In the outer counterbore section 2mA configured in this way, the angle between the outer ring raceway surface 2d and the first inclined surface 2nA, and the angle between the side surface 2p and the first inclined surface 2nA are both obtuse angles. Furthermore, the connection portion between the outer ring raceway surface 2d and the first inclined surface 2nA, and the connection portion between the side surface 2p and the first inclined surface 2nA are rounded by the second inclined surface 2qA so that they do not have corners.

[0064] Therefore, the inner counterbore section 2hA and the outer counterbore section 2mA do not have any sharp angles that would cause overheating due to high-frequency heat treatment. As a result, the wheel bearing device 1A can prevent cracking due to heat treatment of the inner counterbore section 2hA and the outer counterbore section 2mA without increasing the axial thickness of the inner counterbore section 2hA and the outer counterbore section 2mA in order to increase their heat capacity.

[0065] (Other embodiments) Note that the first inclined surfaces 2i, 2iA, 2n, and 2nA are straight inclined surfaces in a radial cross-sectional view. However, the first inclined surface may also be an arc-shaped inclined surface projecting radially in a radial cross-sectional view. Figure 7 is a partially enlarged cross-sectional view showing the inner counterbore portion 2hB of the outer ring of the wheel bearing device 1B.

[0066] As shown in Figure 7, for example, the first inclined surface 2iB of the inner counterbore portion 2hB is configured in a protruding arc shape in a radial cross-sectional view. In a radial cross-sectional view, the first inclined surface 2iB of the inner counterbore portion 2hB is configured in an arc shape, which makes the angle between the first inclined surface 2iB and the adjacent surfaces at both ends of the first inclined surface 2iB more obtuse. Furthermore, the connection portion between the inner outer ring raceway surface 2c and the first inclined surface 2iB, and the connection portion between the side surface 2k and the first inclined surface 2iB, are rounded by the second inclined surface 2lB so that they do not have corners. This makes it possible to prevent quench cracking due to heat treatment without increasing the axial thickness of the inner counterbore portion 2hB.

[0067] Furthermore, the inner counterbore sections 2h, 2hA and the outer counterbore sections 2m, 2mA are constructed by combining first inclined surfaces 2i, 2iA, 2n, 2nA and second inclined surfaces 2l, 2lA, 2q, 2qA so as not to have any sharp angles that would cause overheating due to high-frequency heat treatment. However, the inner and outer counterbore sections may also be inner circumferential surfaces that, in radial cross-sectional view, consist of a single circular arc from the end on the opening side to the end on the raceway surface side.

[0068] Furthermore, the wheel bearing device 1 is a third-generation structure with an inner ring rotation specification, comprising an outer ring 2 as an outer member, an inner ring 4 as an inner member, and a hub ring 3 fitted together, with a hub ring 3 having one inner ring 4 fitted as an inner member. However, it may also be a first-generation structure consisting of an outer ring 2 as an outer member and a pair of inner rings 4 as an inner member, or a second-generation structure with an inner ring rotation specification consisting of an outer ring 2 as an outer member and a pair of inner rings 4 as an inner member, with this pair of inner rings 4 fitted around the outer circumference of the hub ring 3.

[0069] Furthermore, although the wheel bearing device 1 has been described as a wheel bearing device for a driven wheel, it may also be a wheel bearing device for a drive wheel. Also, the wheel bearing device 1 in this application is a wheel bearing device 1 for inner ring rotation in which a hub wheel 3 and an inner ring 4 having a wheel mounting flange 3c rotate. However, the wheel bearing device may also be a wheel bearing device for outer ring rotation in which an outer ring having a wheel mounting flange rotates.

[0070] Furthermore, the outer member of the wheel bearing device 1 is composed of a substantially cylindrical outer ring 2. However, the outer member does not have to be cylindrical. It is acceptable as long as it can accommodate the inner member inside.

[0071] Furthermore, the inner member of the wheel bearing device 1 is composed of a solid cylindrical hub ring 3 with a flange and a substantially cylindrical inner ring 4. However, the hub ring of the inner member does not have to be a solid cylinder. The hub ring of the inner member may be a hollow cylinder with a flange.

[0072] Although embodiments of the present invention have been described above, the present invention is not limited in any way to these embodiments, but is merely illustrative. It can be implemented in various other forms without departing from the spirit of the invention, and the scope of the present invention is indicated by the claims, and further includes all modifications within the meaning and scope of equivalents as described in the claims. [Explanation of Symbols]

[0073] 1. Wheel bearing device 2 Outer ring 2a Inner side opening 2b Outer side opening 2c Inner side outer raceway surface 2d Outer side outer raceway surface 2e Body mounting flange 2g pilot section 2h, 2hA, 2hB Inner side counterbore section 2i, 2iA, 2iB, 2n, 2nA 1st slope 2j, 2o inner surface 2k, 2p side 2l, 2lA, 2lB, 2q, 2qA 2nd slope 2m, 2mA outer side counterbore section 3 Hub wheels 4. Inner Ring 5. Inner ball row 6 Outer ball rows 7. Inner side sealing member 8. Outer side sealing member

Claims

1. A cylindrical outer member having a double row of annular outer raceway surfaces on its inner circumferential surface, An inner member having a double row of inner raceway surfaces on its outer surface that are opposite to the double row of outer raceway surfaces, A double row of rolling elements is housed so as to be rotatable between the raceway surfaces of the outer member and the inner member, A wheel bearing device having a counterbore portion adjacent to the double-row outer raceway surface, wherein the inner circumferential surface protrudes inward from the groove bottom diameter of the outer raceway surface, The aforementioned counterbore section is The outer member has a first inclined surface extending radially inward from the end on the opening side toward the outer raceway surface, a second inclined surface located at both ends of the first inclined surface and extending radially inward toward the outer raceway surface, and a hardened layer hardened by heat treatment. At least a portion of the first inclined surface or the second inclined surface is located in the hardened layer. Wheel bearing device.

2. In the wheel bearing device according to claim 1, The first inclined surface is, In a radial cross-sectional view, it is either linear or arc-shaped. Wheel bearing device.

3. In the wheel bearing device according to claim 1 or 2, The first inclined surface is, In a radial cross-sectional view, the inclination with respect to the axis falls within the range of 30 to 60 degrees. That is, Wheel bearing device.

4. In the wheel bearing device according to claim 1 or 2, At least a portion of the counterbore section is It has a surface hardness of 58 HRC to 63 HRC due to high-frequency heat treatment. Wheel bearing device.

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