Wheel bearing device

Abstract

The present invention addresses the problem of providing a wheel bearing device with a reduced outer diameter of an outer member and reliably having a non-heat-treatment hardened layer even in the reduced portion. An outer ring 2 has an outer-side thermohardening layer 20 along an outer raceway surface 2c / 2d. A ball 7 makes contact with the outer raceway surface 2d at a contact angle α. The outer-side thermohardening layer 20 has a hardened layer depth C in the contact angle α direction from a shoulder portion 2f of the outer raceway surface 2c / 2d, and has a hardened layer depth A in a radial direction from an intersection P2 between the outer raceway surface 2d and a virtual line passing through the ball center and extending in a direction orthogonal to the axial direction. The hardened layer depth A is between 0.5 mm and 4.0 mm. The outer ring 2 has a thickness Ta equal to or less than 6 mm in the radial direction of the portion passed through by the virtual line passing through the ball 7 center and extending in a direction orthogonal to the axial direction. The outer ring 2 has a thickness Tc equal to or greater than the hardened layer depth C + 1.0 mm in the contact angle α direction between the shoulder portion 2f of the outer raceway surface 2d and the outer peripheral surface of the outer ring 2.

Description

Wheel bearing device

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

[0002] Conventionally, double-row angular contact ball bearings have been commonly used as bearing assemblies for automobile wheels, and include an outer member, an inner member, and balls held in raceways formed on the outer member and the inner member, respectively.

[0003] Wheel bearing devices are broadly divided into a first-generation structure in which a wheel bearing consisting of a double-row angular contact ball bearing or the like is fitted between the knuckle and hub wheel that make up the suspension; a second-generation structure in which a vehicle body mounting flange or wheel mounting flange is formed directly on the outer periphery of the outer member; a third-generation structure in which one of the inner rolling surfaces is formed directly on the outer periphery of the hub wheel; and a fourth-generation structure in which an inner rolling surface is formed directly on the outer periphery of both the hub wheel and the outer joint member of a constant velocity universal joint.

[0004] In conventional wheel bearing devices, a known configuration is one in which the inner member has a wheel mounting flange integrally formed at one end for mounting the wheel, and has one inner raceway surface on its outer periphery facing the double-row outer raceway surfaces, a hub ring having a small diameter step extending axially from the inner raceway surface, and an inner ring fitted onto the small diameter step of the hub ring and having an inner raceway surface formed thereon (see, for example, Patent Document 1).

[0005] In conventional angular contact ball bearings, it is desirable to further reduce the outer diameter of the outer member to reduce weight. When the outer diameter of the outer member is reduced, it is necessary to design the outer member so that the thickness in the contact angle direction is greater than that directly above the bottom of the outer raceway surface of the outer member. However, it is known that the depth of the hardened layer formed on the outer raceway surface of the outer member is greatest at the shoulder, followed by the depth in the contact angle direction, and smallest at the bottom.

[0006] Therefore, it was necessary to design the wall thickness from the shoulder to the outer diameter of the outer member taking into consideration the depth of the hardened layer at the shoulder.If the depth of the hardened layer at the shoulder is greater than the wall thickness from the shoulder to the outer diameter of the outer member, burn-through may occur, which could reduce the strength of the entire outer member.

[0007] Japanese Patent Application Laid-Open No. 2007-113718

[0008] Therefore, the present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a wheel bearing device in which the outer diameter of the outer member is reduced so that a non-heat-treated hardened layer can be reliably formed even in the portion where the outer diameter is reduced.

[0009] That is, a wheel bearing device comprising: an outer member having a double-row outer raceway surface on its inner circumference; an inner member having a double-row inner raceway surface opposing the double-row outer raceway surface; and double-row rolling elements accommodated in a rollable manner between the raceway surfaces of the outer member and the inner member, wherein the outer member has a hardened layer that has been heat-hardened along the outer raceway surface provided on the outer side, the rolling elements provided in the outer side row contact the outer raceway surface provided on the outer side at a contact angle α, the hardened layer has a hardened layer depth C in the direction of the contact angle α from a shoulder portion of the outer raceway surface provided on the outer side, and a hardened layer depth A in the radial direction from an intersection of an imaginary line that passes through the center of the rolling elements provided in the outer side row and extends in a direction perpendicular to the axial direction with the outer raceway surface provided on the outer side, and the hardened layer depth A is 0.5 mm to 4.0 mm, The radial thickness Ta of the outer member at a portion where an imaginary line passing through the center of the rolling elements provided in the outer side row and extending in a direction perpendicular to the axial direction passes is: Thickness Ta≦6 mm; and the radial thickness Tc of the outer member in the direction of the contact angle α between the shoulder portion of the outer raceway surface provided on the outer side and the outer peripheral surface of the outer member is: Thickness Tc≧Hardened layer depth C+1.0 mm.

[0010] The present invention has the following effects: That is, according to the wheel bearing device of the present invention, the thickness T in the direction of the contact angle α between the shoulder portion of the outer raceway surface and the outer peripheral surface of the outer member is thick enough to form an unhardened layer, so that the outer diameter of the outer member can be reduced and a non-heat-treated hardened layer can be reliably formed even in the portion where the outer diameter is reduced.

[0011] 1 is a partial cross-sectional view of a wheel support bearing device according to a first embodiment of the present invention; FIG. 2 is a partial cross-sectional view of an inner portion of the wheel support bearing device according to the first embodiment of the present invention; and FIG. 3 is an enlarged partial cross-sectional view of an outer end portion of the wheel support bearing device according to the first embodiment of the present invention.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0013] A wheel bearing device 1 shown in FIG. 1 is one embodiment of a wheel bearing device according to the present invention, and is used to rotatably support a wheel in a suspension system of a vehicle such as an automobile.

[0014] As shown in FIG. 1 , the wheel bearing device 1 has a configuration known as a third generation, and includes an outer ring 2 as an outer member, a hub ring 3 and an inner ring 4 as inner members, two rolling rows of inner ball rows 5 and outer ball rows 6, an outer seal member 10, a sensor holder 12, and a magnetic encoder 14.

[0015] Here, the inner side refers to the vehicle body side of the wheel support bearing device 1 when it is attached to the vehicle body, and the outer side refers to the wheel side of the wheel support bearing device 1 when it is attached to the vehicle body. The axial direction refers to the direction along the rotation axis X of the wheel support bearing device 1, with one axial end side being the inner side and the other axial end side being the outer side. The direction perpendicular to the rotation axis X of the wheel support bearing device 1 is referred to as the radial direction. In the following, the term "cross section" will be explained as referring to a cross section that passes through the rotation axis X of the wheel support bearing device 1 and is parallel to the rotation axis X of the wheel support bearing device 1.

[0016] 1, an inner-side outer raceway surface 2c and an outer-side outer raceway surface 2d are formed on the inner peripheral surface of the outer ring 2. A vehicle body mounting flange 2e for mounting the outer ring 2 to a vehicle body member is integrally formed on the outer peripheral surface of the outer ring 2.

[0017] An inner-side opening 2a is formed at the inner-side end of the outer ring 2, into which a sensor holder 12 (see the two-dot chain line in FIG. 1 ) can be fitted. An outer-side opening 2b is formed at the outer-side end of the outer ring 2, into which an outer-side seal member 10 can be fitted. The outer-side seal member 10 is fitted into the outer-side opening 2b, closing it. The annular space inside the bearing is sealed by fitting the sensor holder 12 into the inner-side opening 2a, which is the opening at one axial end of the annular space formed by the outer ring 2 and the hub wheel 3, and fitting the outer-side seal member 10 into the outer-side opening 2b, which is the opening at the other axial end of the annular space.

[0018] Furthermore, a reduced diameter portion 2g is provided on the outer diameter surface of the outer ring 2 midway in the axial direction. The reduced diameter portion 2g is provided by cutting the outer diameter surface of the outer ring 2 in order to reduce the weight of the outer ring 2. The reduced diameter portion 2g is formed in the axial direction between the inner-side outer raceway surface 2c and the outer-side outer raceway surface 2d. The reduced diameter portion 2g has a tapered portion 2h that reduces in diameter from the outer side to the inner side, and a small diameter portion 2i that continues from the inner-side end of the tapered portion 2h. The tapered portion 2h is formed linearly in a cross section parallel to the axial direction in FIG. 1. Note that the inclination of the tapered portion 2h is not limited to this; for example, it may be formed curvedly in a cross section parallel to the direction of the rotation axis X in FIG. 1.

[0019] The inner end of the outer peripheral surface of the hub wheel 3 is formed with a small-diameter step 3a that is smaller in diameter than the outer end. A wheel mounting flange 3b for mounting a wheel is formed integrally with the outer end of the hub wheel 3. A plurality of bolt holes 3d are formed in the wheel mounting flange 3b. Hub bolts for fastening the hub wheel 3 to a wheel or brake component are press-fitted into the bolt holes 3d. The wheel mounting flange 3b is an example of a hub flange that extends radially outward. Wheel bolts may be used instead of hub bolts for fastening.

[0020] An outer inner raceway surface 3c is provided on the outer peripheral surface of the hub wheel 3 so as to face the outer outer raceway surface 2d on the outer side of the outer ring 2. In other words, the hub wheel 3 forms the inner raceway surface 3c on the outer side of the inner member.

[0021] The inner ring 4 is provided on the small diameter step 3a of the hub wheel 3. The inner ring 4 is press-fitted into the small diameter step 3a with a predetermined interference. Furthermore, the hub wheel 3 and the inner ring 4 are integrated by a crimped portion 3e, which is plastically deformed by crimping the inner end of the small diameter step 3a of the hub wheel 3, and prevents the inner ring 4 from slipping out of the hub wheel 3 in the axial direction.

[0022] The inner ring 4 applies preload to the rolling rows, that is, the inner ball row 5 and the outer ball row 6. The outer peripheral surface of the inner ring 4 is provided with an inner-side inner raceway surface 4a that faces the inner-side outer raceway surface 2c of the outer ring 2. In other words, the inner ring 4 forms the inner raceway surface 4a on the inner side of the inner member.

[0023] The inner ball row 5 and outer ball row 6, which are rolling rows, are formed by a plurality of balls 7, which are rolling elements, held in a cage 8. The inner ball row 5 is rollably sandwiched between the inner raceway surface 4a of the inner ring 4 and the inner-side outer raceway surface 2c of the outer ring 2. The outer ball row 6 is rollably sandwiched between the inner raceway surface 3c of the hub ring 3 and the outer-side outer raceway surface 2d of the outer ring 2. In other words, the inner ball row 5 and the outer ball row 6 are rollably housed between the raceway surfaces of the outer ring 2, which is the outer member, and the hub ring 3 and inner ring 4, which are inner members. The outer ring 2 rotatably supports the hub ring 3 and inner ring 4 via the inner ball row 5 and outer ball row 6.

[0024] In the wheel bearing device 1, a double-row angular contact ball bearing is formed by the outer ring 2, hub ring 3, inner ring 4, inner ball row 5, and outer ball row 6. The wheel bearing device 1 may also be formed by a double-row tapered roller bearing.

[0025] A support ring 13 is fitted to the inner end, which is one axial end of the inner ring 4. The support ring 13 has a cylindrical portion 13a that is press-fit onto the outer diameter of the inner ring 4, and a standing portion 13b that extends from the inner end of the cylindrical portion 13a toward the inner diameter, and a magnetic encoder 14 is integrally joined by vulcanization adhesion to the inner side surface of the standing portion 13b. The magnetic encoder 14 is made of synthetic rubber mixed with magnetic powder such as ferrite, and is magnetized with N poles and S poles alternately at equal pitches in the circumferential direction. The magnetic encoder 14 is an example of an encoder.

[0026] A sensor holder 12 (see dash-dot line in FIG. 1 ) is attached to an inner-side opening 2a, which is an opening on one axial end of the outer ring 2, so as to cover the inner-side opening 2a. A rotational speed sensor 15 (see dash-dot line in FIG. 1 ) is attached to the sensor holder 12 at a position facing the magnetic encoder 14. The rotational speed sensor 15 and the magnetic encoder 14 are arranged opposite each other in the axial direction with a predetermined air gap (axial clearance) between them via the sensor holder 12. The rotational speed sensor 15 detects the displacement of the magnetic encoder 14, making it possible to detect the rotational speed of the inner ring 4. The rotational speed sensor 15 is an example of a sensor that detects the displacement of an encoder.

[0027] 2 and 3, the hardened layers provided on the inner-side outer raceway surface 2c and the outer-side outer raceway surface 2d on the inner circumferential surface of the outer ring 2. In this embodiment, the hardened layer formed along the outer-side outer raceway surface 2d will be particularly described in detail.

[0028] As shown in Figure 2, the hardened layer is composed of an outer thermosetting layer 20 that has been induction-hardened along the outer outer raceway surface 2d. Induction hardening is a type of heat hardening process, and by performing induction hardening, a hardened layer with a certain depth is formed from the surface of the outer raceway surface 2d. Here, the hardened layer depth in the direction of the contact angle α from the shoulder 2f of the outer raceway surface 2d of the outer thermosetting layer 20 is defined as C. Here, the shoulder 2f refers to the boundary between the outer raceway surface 2d and the inner diameter surface 2j of the outer ring 2 that connects the outer raceway surfaces 2c and 2d. The contact angle α refers to the angle between the radial direction and the line of action of the force transmitted to the balls 7 by the outer raceway surface 2d.

[0029] The contact angle α is an angle inclined with respect to the rotation axis X and is set to, for example, 40° or more. The outer thermoset layer 20 is a layer that has been induction hardened to have a hardness of 500 or more. The hardness of the layer of the outer ring 2 that has not been induction hardened is 30 HRC or less.

[0030] The relationship between the hardened layer depth C of the outer thermoset layer 20 and the thickness Tc in the direction of the contact angle α between the shoulder 2f of the outer raceway surface 2d and the outer peripheral surface of the outer ring 2 is as follows: Thickness Tc ≥ Hardened layer depth C + 1.0 mm

[0031] That is, the outer thermohardened layer 20 is configured so as not to be larger than the wall thickness Tc. This ensures that the outer thermohardened layer 20 is formed over a hardened layer depth C in the direction of the contact angle α between the shoulder portion 2f and the outer peripheral surface of the outer ring 2, preventing burn-through that reaches the outer peripheral surface of the outer ring 2. In other words, a non-thermohardened layer can be reliably provided in the direction of the contact angle α. This configuration makes it possible to avoid reduced bearing life due to deterioration in grain size caused by quench cracking or overheating. In other words, quench cracking and deterioration in grain size are minimized, improving the indentation resistance of the outer side of the outer ring 2.

[0032] Furthermore, the outer thermoset layer 20 is formed so that the hardened layer depth B in the contact angle α direction from the intersection P1 of an imaginary line passing through the center of the ball 7 and extending in the contact angle α direction with the outer raceway surface 2d is shorter than the hardened layer depth C in the contact angle α direction from the shoulder 2f of the outer raceway surface 2d of the outer thermoset layer 20.

[0033] Furthermore, the hardened layer depth A in the radial direction from an intersection P2 between an imaginary line that passes through the center of the ball 7 and extends in a direction perpendicular to the rotation axis X direction (radial direction) and the outer raceway surface 2d is shorter than the hardened layer depth B in the contact angle α direction from an intersection P1 between an imaginary line that passes through the center of the ball 7 and extends in the contact angle α direction and the outer raceway surface 2d.

[0034] The relationship between the hardened layer depth A of the outer thermosetting layer 20 and the thickness Ta from the intersection P2 with the shoulder 2f of the outer raceway surface 2d to the outer diameter of the outer ring 2 in the radial direction is as follows: Thickness Ta ≥ Hardened layer depth A + 1.0 mm

[0035] Here, the thickness Ta from the intersection point P2 to the outer diameter of the outer ring 2 in the radial direction is 6 mm or less. The thickness Ta is the length from the intersection point P2 to the intersection point S4 between an imaginary line passing through the center of the ball 7 and extending in a direction perpendicular to the axial direction and the outer peripheral surface of the outer ring 2. Furthermore, the hardened layer depth A of the outer thermoset layer 20 is preferably formed in the range of 0.5 mm to 4 mm. This configuration makes it possible to avoid a reduction in bearing life due to deterioration in grain size caused by quench cracking or overheating.

[0036] Furthermore, the intersection S1 between an imaginary line passing through the shoulder 2f of the outer raceway surface 2d and extending in the contact angle α direction and the outer peripheral surface of the outer ring 2 is located radially inward relative to the outer peripheral surface S2 of the outer end of the outer ring 2. In other words, the intersection S1 is provided so as to be located in the reduced diameter portion 2g of the outer ring 2. This makes it possible to reduce weight by forming the reduced diameter portion 2g by cutting the outer diameter surface of the outer ring 2, while also avoiding reduced bearing life due to deterioration of grain size caused by quench cracking or overheating.

[0037] In other words, the hardened layer depth C from the shoulder 2 f in the direction of the contact angle α is 65% or less of the thickness Tc from the shoulder 2 f to the outer diameter of the outer ring 2 in the direction of the contact angle α. By configuring in this manner, a sufficient thickness can be obtained to prevent hardening while ensuring the hardened layer thickness at the shoulder 2 f.

[0038] Furthermore, the intersection S3 of the outer raceway surface 2d between an imaginary line passing through the center of the ball 7 and extending in the contact angle α direction and the outer peripheral surface of the outer ring 2 is located on the outer diameter side of the intersection S1. In other words, the intersection S3 is formed in the reduced diameter portion 2g, in the tapered portion 2h. In order to obtain a sufficient thickness to prevent burn-through while ensuring the thickness of the hardened layer at the intersection P1 between the imaginary line passing through the center of the ball 7 and extending in the contact angle α direction and the outer raceway surface 2d, the cutting depth of the outer diameter surface of the outer ring 2 is made relatively shallow.

[0039] The relationship between the hardened layer depth B from the intersection point P1 to the outer diameter of the outer ring 2 in the direction of the contact angle α and the wall thickness Tb from the intersection point P1 in the direction of the contact angle α is as follows: Wall thickness Tb ≥ Hardened layer depth B + 1.0 mm

[0040] In other words, the hardened layer depth B from the intersection point P1 in the direction of the contact angle α is formed to be 60% or less of the thickness Tb from the intersection point P1 to the outer diameter of the outer ring 2 at the contact angle α. By configuring in this manner, it is possible to obtain a wall thickness sufficient to prevent burn-through while ensuring the thickness of the hardened layer at the intersection point P1.

[0041] As described above, the wheel bearing device 1 according to the present invention is a wheel bearing device 1 including an outer ring 2 having double-row outer raceway surfaces 2c and 2d on its inner circumference, a hub ring 3 and an inner ring 4 having double-row inner raceway surfaces 3c and 4a that face the double-row outer raceway surfaces 2c and 2d, and double-row balls 7, 7 that are accommodated so as to roll freely between the raceway surfaces of the outer ring 2 and the hub ring 3 and inner ring 4, and the outer ring 2 has an outer-side thermosetting layer 20 that has been subjected to a thermosetting treatment along the outer raceway surfaces 2c and 2d provided on the outer side. The balls 7 in the outer row contact the outer raceway 2d provided on the outer side at a contact angle α, and the outer thermoset layer 20 has a hardened layer depth C in the direction of the contact angle α from the shoulder 2f of the outer raceway surfaces 2c and 2d provided on the outer side, and a hardened layer depth A in the radial direction from an intersection P2 between an imaginary line passing through the center of the balls provided in the outer row and extending in a direction perpendicular to the axial direction and the outer raceway surface 2d provided on the outer side, and the hardened layer depth A is The hardened layer depth A is 0.5 mm to 4.0 mm, the radial thickness Ta of the outer ring 2 at a portion where an imaginary line passing through the center of the balls 7 in the outer side row and extending in a direction perpendicular to the axial direction passes is: Thickness Ta≦6 mm, and the thickness Tc of the outer ring 2 in the direction of the contact angle α between the shoulder 2f of the outer raceway surface 2d provided on the outer side and the outer peripheral surface of the outer ring 2 is: Thickness Tc≧Hardened layer depth C+1.0 mm. With this configuration, the outer-side thermohardened layer 20 is formed over the hardened layer depth C in the direction of the contact angle α between the shoulder 2f and the outer peripheral surface of the outer ring 2, preventing burn-through that reaches the outer peripheral surface of the outer ring 2 and avoiding reduced bearing life due to deterioration in grain size caused by quench cracking and overheating. In other words, quench cracking and deterioration in grain size are minimized, and the indentation resistance of the outer side of the outer ring 2 is improved.

[0042] Furthermore, the thickness Ta satisfies the following relationship: thickness Ta ≥ hardened layer depth A + 1.0 mm. This configuration ensures that the depth A of the outer thermoset layer 20 in the direction perpendicular to the axial direction and passing through the center of the ball 7 is smaller than the radial thickness Ta of the portion of the ball 7 where an imaginary line passing through the center of the ball 7 and extending perpendicular to the axial direction passes. This prevents burn-through that reaches the outer peripheral surface of the outer ring 2.

[0043] The outer thermoset layer 20 has a hardened layer depth B in the contact angle α direction from an intersection P1 between an imaginary line passing through the center of the balls 7 provided in the outer side row and extending in the contact angle α direction and the outer raceway surface 2d, and the thickness Tb in the contact angle α direction of the portion of the outer ring 2 passed by the imaginary line passing through the center of the balls 7 and extending in the contact angle α direction is: Thickness Tb ≧ Hardened layer depth B + 1.0 mm. By configuring in this manner, the depth B of the outer thermoset layer 20 in the contact angle α direction from an intersection P1 between the imaginary line passing through the center of the balls 7 and extending in the contact angle α direction and the outer raceway surface 2d is reliably smaller than the thickness Tb in the contact angle α direction of the portion of the outer ring 2 passed by the imaginary line passing through the center of the balls 7 and extending in the contact angle α direction, thereby preventing burn-through that reaches the outer peripheral surface of the outer ring 2.

[0044] Furthermore, an intersection S1 between an imaginary line passing through a shoulder 2f of an outer raceway surface 2d provided on the outer side of the wheel bearing device 1 and extending in the direction of the contact angle α and the outer peripheral surface of the outer member is located on the inner diameter side of an outer peripheral surface S2 of the outer end of the outer ring 2. By configuring in this manner, it is possible to form the outer-side thermoset layer 20 while forming a reduced diameter portion 2g to reduce the weight of the outer ring 2d.

[0045] Furthermore, an intersection S3 between an imaginary line passing through the center of the ball 7 and extending in the direction of contact angle α on the outer raceway 2d provided on the outer side of the wheel bearing device 1, and the outer peripheral surface of the outer ring 2, is located on the outer diameter side of an intersection S1 between an imaginary line passing through the shoulder 2f of the outer raceway 2d provided on the outer side of the wheel bearing device 1 and extending in the direction of contact angle α, and the outer peripheral surface of the outer ring 2. By configuring in this manner, it is possible to form a reduced diameter portion 2g for weight reduction while ensuring a thickness Tb that is greater than the hardened layer depth B of the outer thermoset layer 20 formed along the outer raceway surface 2d.

[0046] Furthermore, an intersection S4 between an imaginary line passing through the center of the ball 7 and extending in a direction perpendicular to the axial direction on the outer raceway surface 2d provided on the outer side of the wheel bearing device 1, and the outer peripheral surface of the outer ring 2, is located on the outer diameter side of an intersection S3 between an imaginary line passing through the center of the ball 7 and extending in the contact angle α direction on the outer raceway surface 2d provided on the outer side of the wheel bearing device 1, and the outer peripheral surface of the outer ring 2. By configuring in this way, it is possible to ensure a thickness Tc that is greater than the hardened layer depth A of the outer thermoset layer 20 formed along the outer raceway surface 2d.

[0047] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, which are merely examples, and it goes without saying that the present invention can be embodied in various other forms without departing from the spirit of the present invention. The scope of the present invention is indicated by the claims, and further includes the equivalent meanings set forth in the claims, and all modifications within the scope of the claims.

[0048] The present invention can be used in a wheel bearing device.

[0049] DESCRIPTION OF SYMBOLS 1 Wheel bearing device 2 Outer ring (outer member) 2c, 2d Outer raceway surface 2f Shoulder portion 2g Reduced diameter portion 2h Tapered portion 2i Small diameter portion 3 Hub ring (inner member) 3c, inner raceway surface 4 Inner ring (inner member) 4a Inner raceway surface 5 Inner ball row 6 Outer ball row 7 Balls (rolling elements) 8 Cage 10 Outer seal member 20 Outer thermoset layer Ta, Tb, Tc Thickness of outer ring A, B, C Hardened layer depth of outer thermoset layer

Claims

1. A wheel bearing device comprising: an outer member having a double-row outer raceway surface on its inner circumference; an inner member having a double-row inner raceway surface opposing the double-row outer raceway surface; and double-row rolling elements housed in a rollable manner between the raceway surfaces of the outer member and the inner member, wherein the outer member has a hardened layer that has been heat-hardened along the outer raceway surface provided on the outer side, the rolling elements provided in the outer row contact the outer raceway surface provided on the outer side at a contact angle α, the hardened layer has a hardened layer depth C in the direction of the contact angle α from a shoulder portion of the outer raceway surface provided on the outer side, and a hardened layer depth A in the radial direction from an intersection of an imaginary line that passes through the center of the rolling elements provided in the outer row and extends in a direction perpendicular to the axial direction with the outer raceway surface provided on the outer side, and the hardened layer depth A is 0.5 mm to 4.0 mm, A wheel bearing device in which the radial thickness Ta of the outer member at a portion where an imaginary line passing through the center of the rolling elements provided in the outer side row and extending in a direction perpendicular to the axial direction passes is: Thickness Ta≦6 mm; and the thickness Tc of the outer member in the direction of the contact angle α between the shoulder portion of the outer raceway surface provided on the outer side and the outer peripheral surface of the outer member is: Thickness Tc≧Hardened layer depth C+1.0 mm.

2. A wheel bearing device according to claim 1, wherein the thickness Ta satisfies the following relationship: thickness Ta≧hardened layer depth A+1.0 mm.

3. A wheel bearing device as described in claim 1, wherein the hardened layer has a hardened layer depth B in the contact angle α direction from the intersection of an imaginary line passing through the center of the rolling elements provided in the outer side row and extending in the contact angle α direction with the outer raceway surface provided on the outer side, and the thickness Tb in the contact angle α direction of the portion of the outer member passed by the imaginary line passing through the center of the rolling elements provided in the outer side row and extending in the contact angle α direction is: thickness Tb ≧ hardened layer depth B + 1.0 mm 4. A wheel bearing device as claimed in any one of claims 1 to 3, wherein the intersection of an imaginary line passing through a shoulder of the outer raceway surface provided on the outer side of the wheel bearing device and extending in the direction of the contact angle α with the outer circumferential surface of the outer member is located on the inner diameter side of the outer circumferential surface of the outer end of the outer member.

5. A wheel bearing device as described in claim 4, wherein the intersection of an imaginary line passing through the center of the rolling element and extending in the direction of the contact angle α on the outer raceway surface provided on the outer side of the wheel bearing device with the outer peripheral surface of the outer member is located on the outer diameter side of the intersection of an imaginary line passing through the shoulder of the outer raceway surface provided on the outer side of the wheel bearing device and extending in the direction of the contact angle α on the outer peripheral surface of the outer member.

6. A wheel bearing device as described in claim 5, wherein the intersection of an imaginary line passing through the center of the rolling element and extending in a direction perpendicular to the axial direction on the outer raceway surface provided on the outer side of the wheel bearing device and the outer peripheral surface of the outer member is located on the outer diameter side of the intersection of an imaginary line passing through the center of the rolling element and extending in the direction of the contact angle α on the outer raceway surface provided on the outer side of the wheel bearing device and the outer peripheral surface of the outer member.

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