Method for manufacturing outward member and bearing device for wheel

Abstract

To suppress cracks or distortion on a portion including an outer raceway groove due to influence of heat treatment and further extract a hub bolt, in an outward member of a bearing for wheels.SOLUTION: A hub bolt 35 has a fitting shaft part 42. A flange 34 has a bolt hole 50 with a fitting hole part 52 that is in close contact with the fitting shaft part 42. An outward member 11 has a first outer peripheral surface 61, a stepped surface 62, and a second outer peripheral surface 63 located radially outward of an outer raceway groove 21. The first outer peripheral surface 61 and the stepped surface 62 are machined surfaces, while the second outer peripheral surface 63 is a non-machined surface. A first dimension L1 defined below is less than or equal to a second dimension L2 defined below. The first dimension L1 represents an axial dimension of a portion where the fitting hole part 52 and the fitting shaft part 42 are actually fitted to each other in a close contact manner. The second dimension L2 represents a dimension of an extraction distance until a head part 41 contacts the stepped surface 62 when the hub bolt 35 fitted into the bolt hole 50 is extracted.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an outer member and a wheel bearing device. [Background technology]

[0002] Patent Document 1 discloses a wheel bearing device mounted on a vehicle (automobile) to rotatably support a wheel. The wheel bearing device has a cylindrical outer member, an inner member, and multiple rolling elements located between the outer member and the inner member. The inner member has a flange located on the vehicle outer side and multiple hub bolts for fixing the wheel to the flange. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022-185382 Summary of the Invention [Problem to be solved by the invention]

[0004] When an impact load acts on a wheel bearing device, for example, a large load input from the rolling elements may cause indentations in the outer raceway grooves of the outer member. In the wheel bearing device disclosed in Patent Document 1, the pitch circle diameter of the rolling elements on the vehicle outer side is made large, which makes it possible to prevent the occurrence of such indentations.

[0005] As the pitch diameter of the rolling elements increases, the outer diameter of the outer member also increases. When attempting to remove the hub bolt from the flange bolt hole toward the vehicle's inner side for replacement, for example, the head of the hub bolt interferes with part of the outer periphery of the outer member, making it impossible to remove the hub bolt.

[0006] To prevent this type of interference, the radial thickness (wall thickness) of the outer member on the vehicle outer side can be reduced. However, if the outer member is too thin, and the portion including the outer raceway groove is subjected to heat treatment (hardening), the insufficient thickness could result in cracking or increased distortion.

[0007] Therefore, the present invention aims to provide a wheel bearing device that suppresses cracks or distortions caused by heat treatment in the part including the outer raceway groove, and yet allows the hub bolt to be removed, as well as a method for manufacturing the outer member of the wheel bearing device. [Means for solving the problem]

[0008] The method for manufacturing an outer member of the present invention is a method for manufacturing an outer member included in a wheel bearing device that is mounted on a vehicle to rotatably support a wheel, and includes the steps of: The wheel bearing device includes the outer member having a cylindrical shape, an inner member having a portion located radially inward of the outer member, and a plurality of rolling elements located between the outer member and the inner member, the inner member has a flange located on the vehicle outer side and a plurality of hub bolts for fixing the wheel to the flange, The hub bolt has, in order from the vehicle inner side, a head, a fitting shaft portion having a smaller diameter than the head, a non-fitting shaft portion having a smaller diameter than the fitting shaft portion, and a male thread portion, the flange has a bolt hole having a fitting hole portion that comes into close contact with the fitting shaft portion, the outer member has, on its inner circumference, a first outer raceway groove on a vehicle outer side and a second outer raceway groove on a vehicle inner side, and, on the vehicle outer side, a stepped surface whose diameter increases toward the vehicle inner side, and a second outer peripheral surface which is located radially outward of the first outer raceway groove and has an outer diameter larger than that of an end of the stepped surface on the vehicle outer side, an outer diameter of the step surface at the vehicle outer side end is smaller than a diameter of an inscribed circle of the heads of the plurality of hub bolts; The outer diameter of the second outer peripheral surface is larger than the diameter of the inscribed circle, The manufacturing method includes: a forming step of plastically processing the primary outer member to form a cylindrical secondary outer member; a heat treatment step of heat treating a portion of the secondary outer member that will become the outer raceway groove to obtain a tertiary outer member; a cutting step for cutting an end portion of an outer peripheral surface of the tertiary outer member on a vehicle outer side to obtain the outer member; and In the molding step, forming the secondary outer member so that a pre-cutting dimension, as defined below, is equal to or less than a first dimension, as defined below; In the cutting step, The outer end portion is machined so that a dimension after machining, defined below, is greater than a first dimension, defined below. First dimension: The axial dimension of the portion where the fitting hole and the fitting shaft are actually tightly fitted together Pre-cutting dimension: When the hub bolt fitted into the bolt hole is extracted, the dimension of the extraction distance until the head comes into contact with a part of the outer circumferential surface of the secondary outer member. Dimension after cutting: The dimension of the distance that the head of the hub bolt that fits into the bolt hole can be pulled out until it comes into contact with the stepped surface.

[0009] The wheel bearing device of the present invention comprises a cylindrical outer member, an inner member having a portion located radially inward of the outer member, and a plurality of rolling elements located between the outer member and the inner member, and is mounted on a vehicle to rotatably support a wheel, the inner member has a flange located on the vehicle outer side and a plurality of hub bolts for fixing the wheel to the flange, The hub bolt has, in order from the vehicle inner side, a head, a fitting shaft portion having a smaller diameter than the head, a non-fitting shaft portion having a smaller diameter than the fitting shaft portion, and a male thread portion, the flange has a bolt hole having a fitting hole portion that comes into close contact with the fitting shaft portion, the outer member has, on its inner circumference, a first outer raceway groove on a vehicle outer side and a second outer raceway groove on a vehicle inner side, and, on the vehicle outer side, a stepped surface whose diameter increases toward the vehicle inner side, and a second outer peripheral surface which is located radially outward of the first outer raceway groove and has an outer diameter larger than that of an end of the stepped surface on the vehicle outer side, the step surface is a machined surface, the second outer peripheral surface is a non-machined surface, an outer diameter of the step surface at the vehicle outer side end is smaller than a diameter of an inscribed circle of the heads of the plurality of hub bolts; The outer diameter of the second outer peripheral surface is larger than the diameter of the inscribed circle, The first dimension, defined below, is less than or equal to the second dimension, defined below. First dimension: The axial dimension of the portion where the fitting hole and the fitting shaft are actually tightly fitted together Second dimension: The distance by which the head of the hub bolt that fits into the bolt hole comes into contact with the stepped surface when the hub bolt is pulled out. [Effects of the Invention]

[0010] According to the present invention, cracks or distortions caused by the influence of heat treatment in the outer member of the wheel bearing device are suppressed, and the hub bolt can be removed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing an embodiment of a wheel bearing device according to the present invention. [Figure 2] 2 is an enlarged cross-sectional view of the vehicle outer side portion of the bearing device shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the outer end of the outer member before machining. [Figure 4] FIG. 4 is a cross-sectional view showing how the hub bolt is being extracted. [Figure 5] FIG. 5 is a cross-sectional view showing how the hub bolt is being extracted. [Figure 6] FIG. 6 is a cross-sectional view of the secondary outer member after plastic working. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Outline of the embodiment of the present invention> Hereinafter, an outline of an embodiment of the present invention will be listed and described. (1) A manufacturing method according to an embodiment of the present invention is a method for manufacturing an outer member of a wheel bearing device that is mounted on a vehicle to rotatably support a wheel, the method comprising: The wheel bearing device includes the outer member having a cylindrical shape, an inner member having a portion located radially inward of the outer member, and a plurality of rolling elements located between the outer member and the inner member, the inner member has a flange located on the vehicle outer side and a plurality of hub bolts for fixing the wheel to the flange, The hub bolt has, in order from the vehicle inner side, a head, a fitting shaft portion having a smaller diameter than the head, a non-fitting shaft portion having a smaller diameter than the fitting shaft portion, and a male thread portion, the flange has a bolt hole having a fitting hole portion that comes into close contact with the fitting shaft portion, the outer member has, on its inner circumference, a first outer raceway groove on a vehicle outer side and a second outer raceway groove on a vehicle inner side, and, on the vehicle outer side, a stepped surface whose diameter increases toward the vehicle inner side, and a second outer peripheral surface which is located radially outward of the first outer raceway groove and has an outer diameter larger than that of an end of the stepped surface on the vehicle outer side, an outer diameter of the step surface at the vehicle outer side end is smaller than a diameter of an inscribed circle of the heads of the plurality of hub bolts; The outer diameter of the second outer peripheral surface is larger than the diameter of the inscribed circle, The manufacturing method includes: a forming step of plastically processing the primary outer member to form a cylindrical secondary outer member; a heat treatment step of heat treating a portion of the secondary outer member that will become the outer raceway groove to obtain a tertiary outer member; a cutting step for cutting an end portion of an outer peripheral surface of the tertiary outer member on a vehicle outer side to obtain the outer member; and In the molding step, forming the secondary outer member so that a pre-cutting dimension, as defined below, is equal to or less than a first dimension, as defined below; In the cutting step, The outer end portion is machined so that a dimension after machining, defined below, is greater than a first dimension, defined below.

[0013] First dimension: The axial dimension of the portion where the fitting hole and the fitting shaft are actually tightly fitted together Pre-cutting dimension: When the hub bolt fitted into the bolt hole is extracted, the dimension of the extraction distance until the head comes into contact with a part of the outer circumferential surface of the secondary outer member. Dimension after cutting: The dimension of the distance that the head of the hub bolt that fits into the bolt hole can be pulled out until it comes into contact with the stepped surface. The first dimension, the pre-cutting dimension, and the post-cutting dimension are each dimensions assuming that the secondary outer member, the tertiary outer member, or the outer member is combined with a plurality of rolling elements and an inner member.

[0014] In the manufacturing method described above, the heat treatment step involves heat treatment of the portion of the secondary outer member that will become the outer raceway groove. Because this heat treatment is performed before the vehicle outer end is cut (before the cutting step), it is possible to perform the heat treatment while ensuring a sufficient thickness for the portion that includes the outer raceway groove. This makes it possible to suppress cracks or distortions caused by the heat treatment. In the cutting process after the heat treatment, the post-cutting dimension becomes larger than the first dimension. Therefore, even if the outer diameter of the outer side of the secondary outer member is increased in the heat treatment to ensure the thickness of the portion including the outer raceway groove, the outer diameter is subsequently reduced by cutting, resulting in a configuration that allows the hub bolt to be removed from the bolt hole in the flange.

[0015] (2) A wheel bearing device according to an embodiment of the present invention is A wheel bearing device mounted on a vehicle to rotatably support a wheel, the wheel bearing device comprising: a cylindrical outer member; an inner member having a portion located radially inward of the outer member; and a plurality of rolling elements located between the outer member and the inner member, the inner member has a flange located on the vehicle outer side and a plurality of hub bolts for fixing the wheel to the flange, The hub bolt has, in order from the vehicle inner side, a head, a fitting shaft portion having a smaller diameter than the head, a non-fitting shaft portion having a smaller diameter than the fitting shaft portion, and a male thread portion, the flange has a bolt hole having a fitting hole portion that comes into close contact with the fitting shaft portion, the outer member has, on its inner circumference, a first outer raceway groove on a vehicle outer side and a second outer raceway groove on a vehicle inner side, and, on the vehicle outer side, a stepped surface whose diameter increases toward the vehicle inner side, and a second outer peripheral surface which is located radially outward of the first outer raceway groove and has an outer diameter larger than that of an end of the stepped surface on the vehicle outer side, the step surface is a machined surface, the second outer peripheral surface is a non-machined surface, an outer diameter of the step surface at the vehicle outer side end is smaller than a diameter of an inscribed circle of the heads of the plurality of hub bolts; The outer diameter of the second outer peripheral surface is larger than the diameter of the inscribed circle, The first dimension, defined below, is less than or equal to the second dimension, defined below.

[0016] First dimension: The axial dimension of the portion where the fitting hole and the fitting shaft are actually tightly fitted together Second dimension: The distance by which the head of the hub bolt that fits into the bolt hole comes into contact with the stepped surface when the hub bolt is pulled out.

[0017] When the hub bolt is removed from the bolt hole, the first dimension is equal to or smaller than the second dimension, so the mating shaft portion is disengaged from the mating hole portion. Because the non-mating shaft portion has a small diameter, the hub bolt can be tilted and removed completely from the bolt hole. To enable this removal, the stepped surfaces of the outer member are machined to have small outer diameters. In contrast, the second outer peripheral surface of the outer member is a non-machined surface, and its outer diameter is not reduced, ensuring the thickness of the portion including the outer raceway groove. This reduces cracking or distortion caused by the heat treatment of the portion including the outer raceway groove.

[0018] (3) The wheel bearing device of (2) has, as the plurality of rolling elements, a first row of rolling elements formed by the plurality of rolling elements located on a vehicle outer side, and a second row of rolling elements formed by the plurality of rolling elements located on a vehicle inner side, The circumscribing circles of the plurality of rolling elements located on the vehicle outer side are larger than the circumscribing circles of the plurality of rolling elements located on the vehicle inner side. When an impact load acts on a wheel bearing device, the large load input from the rolling elements can cause indentations in the raceway grooves. With the above-described configuration, the circumscribed circles of the multiple rolling elements located on the vehicle outer side are large, making it possible to suppress the occurrence of indentations. As the circumscribing circle increases, the outer diameter of the outer member also increases. Even in this case, the configuration of (2) prevents the head of the hub bolt from interfering with part of the outer periphery of the outer member and preventing removal when the hub bolt is removed from the bolt hole, and allows the hub bolt to be completely removed from the bolt hole.

[0019] <Details of the embodiment of the present invention> [Overall configuration of wheel bearing device 10] Fig. 1 is a cross-sectional view showing one embodiment of a wheel bearing device of the present invention. A wheel bearing device 10 (hereinafter referred to as "bearing device 10") shown in Fig. 1 is a bearing device for a wheel used in a vehicle (automobile), and is also called a hub unit. The bearing device 10 is mounted on the vehicle to rotatably support a wheel 7.

[0020] The bearing device 10 has a cylindrical outer member 11, an inner member 12 having a portion located radially inward of the outer member 11, balls 13 which are multiple rolling elements located between the outer member 11 and the inner member 12, and an annular cage 14. The balls 13 are arranged in two rows between the outer member 11 and the inner member 12. The multiple balls 13 in each row are held by the cage 14.

[0021] When no load is applied to the bearing device 10, the central axis of the outer member 11 and the central axis of the inner member 12 coincide. These central axes are the central axis C of the bearing device 10. Figure 1 is a cross-sectional view taken along a plane including the central axis C. The bearing device 10 is mounted on a vehicle so that the central axis C is approximately horizontal.

[0022] The various directions of the bearing device 10 will be defined below. The direction along the central axis C is the "axial direction" of the bearing device 10. This axial direction also includes a direction parallel to the central axis C. The direction perpendicular to the central axis C is the "radial direction" of the bearing device 10. The direction along a circle centered on the central axis C is the "circumferential direction" of the bearing device 10. The right side in FIG. 1 is the outer side of the vehicle, and the left side in FIG. 1 is the inner side of the vehicle.

[0023] The outer member 11 has, on its outer periphery, a fixing flange 20 that is fixed to a suspension system (not shown). The outer member 11 has, on its inner periphery, a first outer raceway groove 21 located on the vehicle outer side and a second outer raceway groove 22 located on the vehicle inner side.

[0024] The inner member 12 has an inner shaft 31 and an annular inner ring 32 attached to the vehicle inner side of the inner shaft 31. The inner shaft 31 has a shaft body 33 and a flange 34 for attaching the wheel 7. The shaft body 33 is located radially inward of the outer member 11. The flange 34 has an annular shape and is provided so as to extend radially outward from a portion 331 of the shaft body 33 on the vehicle outer side. The inner ring 32 is fixed to a portion 332 of the shaft body 33 on the vehicle inner side.

[0025] The flange 34 has a plurality of bolt holes 50. Hub bolts 35 are attached to the bolt holes 50. The plurality of bolt holes 50 are provided at equal intervals in the circumferential direction. The plurality of bolt holes 50 (the plurality of hub bolts 35) are arranged along a circle centered on the central axis C. The wheel 7 is attached to a flange 34 with a hub bolt 35, and the wheel 7 is fixed to the flange 34 by tightening a nut (not shown) onto the hub bolt 35. The hub bolt 35 is attached by being press-fit into the bolt hole 50, but the hub bolt 35 can be removed from the flange 34, for example, to replace the hub bolt 35.

[0026] The hub bolt 35 has, in order from the vehicle inner side, a head portion 41, a mating shaft portion 42, a non-mating shaft portion 43, and a male thread portion 44. The nut is tightened onto the male thread portion 44. As described above, the inner member 12 has the flange located on the vehicle outer side, and the plurality of hub bolts 35 for fixing the wheel 7 to the flange . The inner member 12 has inner raceway grooves 36, 37 on its outer periphery. Specifically, the inner shaft 31 has a first inner raceway groove 36 on its outer periphery. The inner ring 32 has a second inner raceway groove 37 on its outer periphery.

[0027] On the vehicle outer side, a plurality of balls 13 are provided between the first outer raceway groove 21 and the first inner raceway groove 36. The balls 13 on the vehicle outer side contact the first outer raceway groove 21 and the first inner raceway groove 36 at a contact angle. On the vehicle inner side, a plurality of balls 13 are provided between the second outer raceway groove 22 and the second inner raceway groove 37. The balls 13 on the vehicle inner side contact the second outer raceway groove 22 and the second inner raceway groove 37 at a contact angle.

[0028] When the bearing device 10 (inner member 12) rotates, the balls 13 on the vehicle outer side roll and contact the first outer raceway groove 21 and the first inner raceway groove 36, and the balls 13 on the vehicle inner side roll and contact the second outer raceway groove 22 and the second inner raceway groove 37.

[0029] An annular space is provided between the outer member 11 and the inner member 12. Seals 16 and 17 are provided on both axial sides of the annular space. The seals 16 and 17 prevent the grease applied to the annular space from leaking out. Lubrication of each part of the bearing device 10 is performed by the base oil of the grease.

[0030] FIG. 2 is an enlarged cross-sectional view showing a portion of the bearing device 10 shown in FIG. 1 on the vehicle outer side. The hub bolt 35 will be further described. The hub bolt 35 is attached to the bolt hole 50 by press-fitting the hub bolt 35 into the fitting hole portion 52 of the bolt hole 50.

[0031] The head 41 has a disk shape, and its outer diameter is larger than the inner diameter of the bolt hole 50. The head 41 contacts the inner side surface 341 of the flange 34. When the hub bolt 35 is attached to the bolt hole 50 and the head 41 contacts the side surface 341, the hub bolt 35 is attached to the flange 34, and this state is called the "attached state." In the attached state, the wheel 7 is fixed to the flange 34.

[0032] The fitting shaft portion 42 is a portion that is continuous with the head portion 41 and has a smaller diameter than the head portion 41. The fitting shaft portion 42 is a portion that is press-fitted into the fitting hole portion 52 and is in close contact with the fitting hole portion 52. The fitting shaft portion 42 has a plurality of ridges on its outer circumferential surface.

[0033] The non-fitting shaft portion 43 is a portion that continues from the fitting shaft portion 42 and has a smaller diameter than the fitting shaft portion 42. The non-fitting shaft portion 43 shown in FIG. 2 has a tapered surface that gradually reduces in diameter toward the bolt tip side, which is the opposite side from the head 41. The outer diameter of the non-fitting shaft portion 43 is smaller than the inner diameter of the fitting hole portion 52, and a gap is provided between the non-fitting shaft portion 43 and the fitting hole portion 52, so the non-fitting shaft portion 43 does not come into tight contact with the fitting hole portion 52. The male threaded portion 44 is a portion that is continuous with the non-fitted shaft portion 43, and is provided with a male thread on its outer periphery.

[0034] The bolt holes 50 will now be described. The bolt hole 50 has a fitting hole portion 52 that comes into close contact with the fitting shaft portion 42. The fitting hole portion 52 is a cylindrical hole whose center is on a straight line C1 that is parallel to the central axis C (see FIG. 1). The bolt hole 50 further has a first chamfered portion 53 and a second chamfered portion 54. The first chamfered portion 53 is located on the vehicle inner side of the fitting hole portion 52. The second chamfered portion 54 is located on the vehicle outer side of the fitting hole portion 52. The bolt hole 50 has a shape that expands toward the vehicle inner side at the end on the vehicle inner side due to the first chamfered portion 53. The bolt hole 50 has a shape that expands toward the vehicle outer side at the end on the vehicle outer side due to the second chamfered portion 54.

[0035] When the installed hub bolt 35 is pulled out of the bolt hole 50 toward the vehicle inner side, for example for replacement, if the fitting shaft portion 42 passes over the fitting hole portion 52 toward the vehicle inner side, the first chamfered portion 53 and the second chamfered portion 54 allow the hub bolt 35 to tilt. As will be explained later (see FIG. 5), tilting the hub bolt 35 allows the entire hub bolt 35 to be pulled out of the bolt hole 50.

[0036] The outer member 11 has, from its end 60 on the vehicle outer side, a first outer peripheral surface 61, a stepped surface 62, and a second outer peripheral surface 63. The first outer peripheral surface 61 corresponds to the end of the stepped surface 62 on the vehicle outer side. The first outer peripheral surface 61 is the surface of the outer peripheral surface of the outer member 11 closest to the vehicle outer side, and has a cylindrical shape centered on the central axis C (see FIG. 1). The stepped surface 62 is a surface that is continuous with the first outer peripheral surface 61, and expands in diameter toward the vehicle inner side. In the embodiment shown in Fig. 2, the stepped surface 62 is an inclined surface that gradually expands in diameter.

[0037] The second outer peripheral surface 63 is a surface that is continuous with the stepped surface 62 and has a cylindrical shape centered on the central axis C. The second outer peripheral surface 63 has a larger outer diameter than the first outer peripheral surface 61. The second outer peripheral surface 63 is located radially outward of the first outer race groove 21. A bottom 211 of the first outer race groove 21 is located radially inward of a portion 631 of the second outer peripheral surface 63. The bottom 211 is the radially outermost portion of the first outer race groove 21.

[0038] The first outer peripheral surface 61 and the step surface 62 are machined surfaces that have been machined. The machining is cutting (turning), and the first outer peripheral surface 61 and the step surface 62 are cut surfaces (turned surfaces). FIG. 3 is a cross-sectional view showing the vehicle outer side end 111 (hereinafter referred to as the "vehicle outer side end 111") of the outer member 11 (secondary outer member W2) before the machining (cutting) is performed. For the sake of explanation, FIG. 3 shows a case in which the secondary outer member W2 is assumed to be combined with a plurality of balls 13 and an inner member 12. In FIG. 3, the first outer peripheral surface 61 and the step surface 62 obtained after the machining are shown by imaginary two-dot chain lines. The first outer peripheral surface 61 and the step surface 62 are formed by cutting the vehicle outer side end 111.

[0039] The outer member 11 (secondary outer member W2) before the machining has, at the vehicle outer side end 111, a pre-machining outer peripheral surface 64 having the same outer diameter as the second outer peripheral surface 63, and a pre-machining inclined surface 65 whose diameter decreases toward the vehicle outer side. The pre-machining outer peripheral surface 64 and the pre-machining inclined surface 65 are turned to obtain the step surface 62 and the first outer peripheral surface 61.

[0040] The second outer peripheral surface 63 is not machined. In other words, the second outer peripheral surface 63 is a non-machined surface. As will be explained later, the outer member 11 (secondary outer member W2) is formed through forging, and then heat treated and machined. Because the second outer peripheral surface 63 is not machined, it remains a forged surface and has a larger surface roughness (Ra: arithmetic mean roughness) than the first outer peripheral surface 61 and the second outer peripheral surface 62.

[0041] As shown in FIG. 2, a plurality of hub bolts 35 are attached to the flange 34 . The outer diameter D1 of the first outer peripheral surface 61 is smaller than the diameter d1 of the inscribed circle K1 of the head 41 of the plurality of hub bolts 35 (D1 <d1)。 The outer diameter D2 of the second outer peripheral surface 63 is larger than the diameter d1 of the inscribed circle K1 (D2>d1).

[0042] 2 shows the installed state of the hub bolt 35. To remove the hub bolt 35 from the installed state, the hub bolt 35 is pulled out toward the vehicle inner side against the fitting force between the fitting shaft portion 42 and the fitting hole portion 52. When pulling out the hub bolt 35, the hub bolt 35 can only move linearly along the line C1 while the fitting shaft portion 42 is fitted in the fitting hole portion 52. When this happens, it is possible that the head 41 of the hub bolt 35 will come into contact with the stepped surface 62.

[0043] The head 41 has a convex arc surface portion 411 on the outer periphery. The head 41 comes into contact (point contact) with the step surface 62 at this portion 411. A point on the head 41 (convex arc surface portion 411) that can come into contact with the step surface 62 is referred to as a "first contact point P1." A point on the step surface 62 that the head 41 (first contact point P1) can come into contact with is referred to as a "second contact point P2."

[0044] In the case of the bearing device 10 of this embodiment, a first dimension L1 defined below is equal to or less than a second dimension L2 defined below (L1≦L2).

[0045] First dimension L1: The axial dimension of the portion where the fitting hole portion 52 and the fitting shaft portion 42 are actually tightly fitted together Second dimension L2: The dimension of the distance until the head 41 contacts the step surface 62 when the hub bolt 35 fitted in the bolt hole 50 is pulled out

[0046] In the embodiment shown in FIG. 2, the first dimension L1 is the dimension in the axial direction from the vehicle inner side end 521 of the fitting hole portion 52 to the vehicle outer side end 421 of the fitting shaft portion . The second dimension L2 is the distance between the first contact point P1 and the second contact point P2, and can be said to be the extraction dimension, which is the distance until the head 41 contacts the step surface 62 when the hub bolt 35 is extracted in an installed state.

[0047] When the hub bolt 35 is removed from the bolt hole 50, as described above, the first dimension L1 is equal to or less than the second dimension L2, so the mating shaft portion 42 comes out of the mating hole portion 52, as shown in Figure 4. Because the non-mating shaft portion 43 has a small diameter, it is possible to tilt the hub bolt 35, as shown in Figure 5, and then the hub bolt 35 can be completely removed from the bolt hole 50.

[0048] As shown in Figure 1, the bearing device 10 of this embodiment has a first rolling element row F1 of a plurality of balls 13 located on the vehicle outer side, and a second rolling element row F2 of a plurality of balls 13 located on the vehicle inner side, as the plurality of balls 13. The pitch circle diameter D5 of the plurality of balls 13 located on the vehicle outer side is larger than the pitch circle diameter D6 of the plurality of balls 13 located on the vehicle inner side (D5 > D6). In this embodiment, the diameter of the balls 13 located on the vehicle inner side is the same as the diameter of the balls 13 located on the vehicle outer side.

[0049] Here, when an impact load acts on the bearing device 10, there is a possibility that an indentation will occur in the first outer raceway groove 21 (first inner raceway groove 36) due to the large load input from the balls 13. In the case of the bearing device 10 of this embodiment, the pitch circle diameter D5 of the plurality of balls 13 located on the vehicle outer side is large, which makes it possible to suppress the occurrence of an indentation in the first outer raceway groove 21 (first inner raceway groove 36).

[0050] When the pitch circle diameter D5 increases in this way, the outer diameter of the outer member 11 at the vehicle outer end 111 also increases. However, even in this case, with the above-described configuration of "L1≦L2" (see FIG. 2), when the hub bolt 35 is removed from the bolt hole 50, the head 41 of the hub bolt 35 does not interfere with part of the outer periphery of the outer member 11, preventing removal (see FIGS. 4 and 5), and the hub bolt 35 can be completely removed from the bolt hole 50.

[0051] Although not shown, the diameter of the ball 13 located on the vehicle outer side may be larger than the diameter of the ball 13 located on the vehicle inner side. In this case, the diameter of the pitch circle of the ball 13 may be the same on the vehicle outer side and the vehicle inner side, or, as shown in Figure 1, the diameter D5 of the pitch circle on the vehicle outer side may be larger than the diameter D6 of the pitch circle on the vehicle inner side. In other words, the circumscribing circle of the balls 13 located on the vehicle outer side may be larger than the circumscribing circle of the balls 13 located on the vehicle inner side. Such a bearing device 10 only needs to have a configuration that satisfies the relationship "L1≦L2" described above (see FIG. 2). This allows the hub bolt 35 to be completely removed from the bolt hole 50.

[0052] [Method for manufacturing outer member 11] A description will now be given of a method for manufacturing the outer member 11 of the bearing device 10 shown in Fig. 1. The manufacturing method includes a molding step, a heat treatment step, and a cutting step. The forming step is a step of plastically processing the primary outer member to form a cylindrical secondary outer member W2. Fig. 6 is a cross-sectional view of the secondary outer member W2 after the plastic processing. In the forming step, the primary outer member made of a metal material that can be plastically processed is forged to form the secondary outer member W2. The secondary outer member W2 has a cylindrical shape.

[0053] The heat treatment step is a step in which a tertiary outer member is obtained by heat treating a portion 21A including the first outer raceway groove 21 and a portion 22A including the second outer raceway groove 22 that the secondary outer member W2 has after the forming step and that come into contact with the balls 13. The heat treatment is quenching, and may be partial quenching.

[0054] After the molding step and before the heat treatment step, the first outer raceway groove 21 and the second outer raceway groove 22 that the secondary outer member W2 has and that come into contact with the balls 13 are subjected to cutting (turning) (first cutting step). By this processing, the groove shapes that will become the first outer raceway groove 21 and the second outer raceway groove 22 are obtained.

[0055] The cutting step is a step (second cutting step) for obtaining the outer member 11 by cutting (turning) the outer peripheral surface of the vehicle outer side end portion 111 of the tertiary outer member that has been subjected to the heat treatment. The molding, heat treatment and cutting steps will be further described below.

[0056] The manufacturing method of the outer member 11 further includes a polishing step. In the polishing step, the first outer raceway groove 21 and the second outer raceway groove 22 of the tertiary outer member that has been subjected to the heat treatment step are polished. The polishing step is preferably performed after the cutting step. In the polishing step, the surface cut in the cutting step (second cutting step) may be used as a reference surface.

[0057] Specifically, in the polishing step, a grindstone is brought into contact with the inner peripheral surface (portions that will become the first outer raceway groove 21 and the second outer raceway groove 22) of the outer member 11 that has been subjected to the heat treatment step and the cutting step. At this time, a shoe (support member) is brought into contact with the outer peripheral surface of the outer member 11 so as to receive the contact force (pressing force) of the grindstone against the outer member 11. The shoe is brought into contact with the surface (first outer peripheral surface 61) that was cut in the cutting step (second cutting step).

[0058] The molding step, the heat treatment step and the cutting step will be further explained. [Molding process] As described above, FIG. 3 shows the secondary outer member W2 after the forming process has been completed and before cutting (machining) is performed. In the forming step, the secondary outer member W2 is formed so that the pre-cutting dimension L3, defined below, is equal to or smaller than the first dimension L1, defined below (L3≦L1). The pre-cutting dimension L3 and the first dimension L1 are dimensions when it is assumed that the secondary outer member W2 is combined with a plurality of balls 13 and an inner member 12, as shown in FIG.

[0059] First dimension L1: The axial dimension of the portion where the fitting hole portion 52 and the fitting shaft portion 42 are actually tightly fitted together Pre-cutting dimension L3: When the hub bolt 35 fitted into the bolt hole 50 is extracted, the dimension of the extraction distance until the head 41 comes into contact with a part of the outer peripheral surface of the secondary outer member 11 (which becomes the outer member 11)

[0060] The first dimension L1 here is the same as the "first dimension L1" described with reference to FIG. At the stage where the forming process is carried out, the outer member 11 is not yet completed and has not yet been assembled with the inner member 12 and the balls 13. For this reason, the pre-cutting dimension L3 is the dimension of the extraction distance until the head 41 comes into contact with a part of the outer peripheral surface of the secondary outer member W2, assuming that the secondary outer member W2 that becomes the outer member 11 is combined with the inner member 12 and multiple balls 13 as shown in Figure 3 and that the hub bolt 35 is inserted into the bolt hole 50 of the inner member 12, when the hub bolt 35 is extracted.

[0061] According to the relationship L3≦L1, even if the hub bolt 35 is to be removed, the head 41 will come into contact with a portion of the outer peripheral surface of the secondary outer member W2, and the fitting shaft portion 42 will not be able to come out of the fitting hole portion 52, making it impossible to remove the hub bolt 35.

[0062] [Heat treatment process] In the heat treatment step, as described above, the portion 21A that will become the first outer raceway groove 21 and the portion 22A that will become the second outer raceway groove 22 of the secondary outer member W2 that has completed the molding step are subjected to heat treatment. After the molding step is completed and before the cutting step (second cutting step) is performed, the thickness of the portion 21A including the first outer raceway groove 21 around the first outer raceway groove 21 is greater than that after the cutting step, as shown in Fig. 3. In Fig. 3, the outer peripheral surface shape of the vehicle outer end portion 111 after the cutting step is shown by a two-dot chain line.

[0063] The secondary outer member W2 has, at the vehicle outer side end 111, a pre-machining outer peripheral surface 64 having the same outer diameter as the second outer peripheral surface 63, and a pre-machining inclined surface 65, so that the heat treatment is performed in a state where the thickness around the first outer raceway groove 21 is large.

[0064] [Cutting process (second cutting process)] In the cutting step, cutting is performed on the vehicle outer side end 111 of the outer peripheral surface of the tertiary outer member obtained after the heat treatment step. In the cutting step, the vehicle outer side end portion 111 is cut so that the post-cutting dimension L4, defined below, is larger than the first dimension L1 (L4>L1). The post-cutting dimension L4 and the first dimension L1 are dimensions when it is assumed that the tertiary outer member is combined with the plurality of balls 13 and the inner member 12.

[0065] Post-cutting dimension L4: The dimension of the extraction distance until the head 41 contacts the step surface 62 when the hub bolt 35 fitted in the bolt hole 50 is extracted.

[0066] 2, but at the stage where the cutting process is performed, the outer member 11 is not yet completed and has not yet been assembled with the inner member 12 and the plurality of balls 13. For this reason, the dimension L4 after cutting in the cutting process is the dimension when it is assumed that the outer member 11 obtained after the cutting process has been combined with the inner member 12 and the plurality of balls 13, and is the dimension of the extraction distance until the head 41 comes into contact with the step surface 62 obtained by cutting when the hub bolt 35 attached to the inner member 12 is extracted.

[0067] [Method for manufacturing the outer member 11 of this embodiment] As described above, in the heat treatment process, the portion including the first outer raceway groove 21 is heat treated. Because the heat treatment is performed before cutting the vehicle outer end portion 111 (before the cutting process), the heat treatment can be performed while ensuring a sufficient thickness of the portion 21A including the first outer raceway groove 21 (see FIG. 3). This makes it possible to suppress cracks or distortion caused by the heat treatment.

[0068] In the cutting step after the heat treatment, the post-cutting dimension L4 becomes larger than the first dimension L1 (see FIG. 2). Therefore, even if the outer diameter of the outer side of the outer member 11 is increased for the heat treatment, the first outer peripheral surface 61 and the step surface 62 are obtained by subsequent cutting, and the outer diameter is reduced (see FIG. 3). Therefore, a configuration is obtained that allows the hub bolt 35 to be removed from the bolt hole 50 of the flange 34 (see FIGS. 4 and 5).

[0069] To enable the hub bolt 35 to be extracted in this manner, the portion 21A including the first outer raceway groove 21 is heat treated, and then the first outer peripheral surface 61 and the step surface 62 are machined to reduce the outer diameters of these surfaces (see Figure 2). In contrast, the second outer peripheral surface 63 of the outer member 11 is a non-machined surface, and its outer diameter is not reduced. The thickness of the portion 21A including the first outer raceway groove 21 is ensured.

[0070] A portion 631 of the second outer peripheral surface 63 is located radially outward of the bottom 211 of the first outer raceway groove 21. The second outer peripheral surface 63 is a non-machined surface, and its outer diameter is not reduced, so that the radial distance (thickness) between the bottom 211 of the first outer raceway groove 21 and the portion 631 of the second outer peripheral surface 63 is secured.

[0071] 〔others〕 In the above embodiment, the outer member 11 has, from its end on the vehicle outer side, a first outer peripheral surface 61, a step surface 62 that expands in diameter toward the vehicle inner side, and a second outer peripheral surface 63 that is located radially outward of the first outer raceway groove 21 and has an outer diameter larger than that of the first outer peripheral surface 61, but this is not limited to this. For example, the first outer peripheral surface 61 may not be provided, and a stepped surface 62 that expands in diameter toward the vehicle inner side may be provided at the vehicle outer side end of the outer member 11, i.e., a stepped surface 62 and a second outer peripheral surface 63 may be provided from the vehicle outer side end of the outer member 11. In this case, the second outer peripheral surface 63 has a larger outer diameter than the vehicle outer side end of the stepped surface 62, and the outer diameter of the vehicle outer side end of the stepped surface 62 is smaller than the diameter of the inscribed circle in the heads 41 of the multiple hub bolts 35.

[0072] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is not limited to the above-described embodiments, but includes all modifications within the scope of the claims and equivalents thereof. [Explanation of symbols]

[0073] 7 wheels 10 Wheel bearing device 11 Outer member 12 Inner member 13 Ball (rolling element) 21 First outer raceway groove 21A Outer raceway groove 22 Second outer raceway groove 22A Outer raceway groove 34 flange 35 Hub bolt 41 Head 42 mating shaft 43 Non-mating shaft 44 Male thread 50 bolt holes 52 Fitting hole 60 Vehicle outer edge 61 First outer peripheral surface 62 Step surface 63 Second outer peripheral surface 111 Vehicle outer end 421 Vehicle outer end 521 Vehicle inner side end D1 Outer diameter of the first outer surface D2 Outer diameter of the second outer surface K1 inscribed circle d1 diameter L1 First dimension L2 Second dimension L3 Dimension before cutting L4 Dimensions after cutting W2 Secondary outer member

Claims

1. A method for manufacturing an outer member of a wheel bearing device that is mounted on a vehicle to rotatably support a wheel, comprising: The wheel bearing device includes the outer member having a cylindrical shape, an inner member having a portion located radially inward of the outer member, and a plurality of rolling elements located between the outer member and the inner member, the inner member has a flange located on the vehicle outer side and a plurality of hub bolts for fixing the wheel to the flange, The hub bolt has, in order from the vehicle inner side, a head, a fitting shaft portion having a smaller diameter than the head, a non-fitting shaft portion having a smaller diameter than the fitting shaft portion, and a male thread portion, the flange has a bolt hole having a fitting hole portion that comes into close contact with the fitting shaft portion, the outer member has, on its inner circumference, a first outer raceway groove on a vehicle outer side and a second outer raceway groove on a vehicle inner side, and, on the vehicle outer side, a stepped surface whose diameter increases toward the vehicle inner side, and a second outer peripheral surface which is located radially outward of the first outer raceway groove and has an outer diameter larger than that of an end of the stepped surface on the vehicle outer side, an outer diameter of the step surface at the vehicle outer side end is smaller than a diameter of an inscribed circle of the heads of the plurality of hub bolts; The outer diameter of the second outer peripheral surface is larger than the diameter of the inscribed circle, The manufacturing method includes: a forming step of plastically processing the primary outer member to form a cylindrical secondary outer member; a heat treatment step of heat treating a portion of the secondary outer member that will become the outer raceway groove to obtain a tertiary outer member; a cutting step for cutting an end portion of an outer peripheral surface of the tertiary outer member on a vehicle outer side to obtain the outer member; and In the molding step, forming the secondary outer member so that a pre-cutting dimension, as defined below, is equal to or less than a first dimension, as defined below; In the cutting step, The outer end portion is cut so that a dimension after cutting defined below is larger than a first dimension defined below. Method for manufacturing the outer member. First dimension: The axial dimension of the portion where the fitting hole and the fitting shaft are actually tightly fitted together Pre-cutting dimension: The dimension of the extraction distance until the head of the hub bolt fitting into the bolt hole comes into contact with a part of the outer peripheral surface of the secondary outer member when the hub bolt is extracted. Dimension after cutting: The dimension of the distance that the head of the hub bolt that fits into the bolt hole can be pulled out until it comes into contact with the stepped surface.

2. A wheel bearing device mounted on a vehicle to rotatably support a wheel, the wheel bearing device comprising: a cylindrical outer member; an inner member having a portion located radially inward of the outer member; and a plurality of rolling elements located between the outer member and the inner member, the inner member has a flange located on the vehicle outer side and a plurality of hub bolts for fixing the wheel to the flange, The hub bolt has, in order from the vehicle inner side, a head, a fitting shaft portion having a smaller diameter than the head, a non-fitting shaft portion having a smaller diameter than the fitting shaft portion, and a male thread portion, the flange has a bolt hole having a fitting hole portion that comes into close contact with the fitting shaft portion, the outer member has, on its inner circumference, a first outer raceway groove on a vehicle outer side and a second outer raceway groove on a vehicle inner side, and, on the vehicle outer side, a stepped surface whose diameter increases toward the vehicle inner side, and a second outer peripheral surface which is located radially outward of the first outer raceway groove and has an outer diameter larger than that of an end of the stepped surface on the vehicle outer side, the step surface is a machined surface, the second outer peripheral surface is a non-machined surface, an outer diameter of the step surface at the vehicle outer side end is smaller than a diameter of an inscribed circle of the heads of the plurality of hub bolts; The outer diameter of the second outer peripheral surface is larger than the diameter of the inscribed circle, A first dimension, as defined below, is less than or equal to a second dimension, as defined below; Wheel bearing device. First dimension: The axial dimension of the portion where the fitting hole and the fitting shaft are actually tightly fitted together Second dimension: The dimension of the distance that the head of the hub bolt that fits into the bolt hole can be pulled out until it comes into contact with the stepped surface.

3. the plurality of rolling elements include a first row of rolling elements located on a vehicle outer side, and a second row of rolling elements located on a vehicle inner side, a circumscribing circle of the plurality of rolling elements located on the vehicle outer side is larger than a circumscribing circle of the plurality of rolling elements located on the vehicle inner side; 3. A wheel bearing device according to claim 2.

Images