Method for manufacturing joint member

Abstract

This method for manufacturing a joint member (30) comprises: a molding step for molding an intermediate molded body, that will become the joint member (30), into a shape having a first inner raceway surface (33) and an outer guide groove (32); and a curing treatment step for curing both the first inner raceway surface (33) and the outer guide groove (32) of the intermediate molded body molded in the molding step. The curing treatment is a treatment for forming a non-cured layer (t3) between a cured layer (t1) on the first inner raceway surface (33) side and a cured layer (t2) on the outer guide groove (32) side by heating either the first inner raceway surface (33) or the outer guide groove (32) while cooling the other of the first inner raceway surface and the outer guide groove.

Description

Method for manufacturing joint member

[0001] The present disclosure relates to a method for manufacturing a joint member.

[0002] Patent Document 1 below discloses a conventional bearing device for a drive wheel. This bearing device for a drive wheel is a rolling bearing device for rotatably supporting a drive wheel, and has a structure in which a rolling bearing and a constant velocity universal joint are integrated. The rolling bearing is composed of an outer ring, a hub ring corresponding to an inner ring, a drive shaft integrated with the inner ring, rolling elements, etc., and the constant velocity universal joint is composed of a drive shaft integrated with an outer coupling member, an inner coupling member, balls, etc.

[0003] JP 2009-292275 A

[0004] In vehicles powered by electric motors or internal combustion engines, there is a demand for longer driving range and improved electricity and fuel economy. Therefore, there is a demand for lighter drive wheel bearing devices. The drive wheel bearing device of Cited Document 1 has a structure in which an inner ring raceway is provided on an outer joint member (hereinafter referred to as "joint member") of a constant velocity joint of a drive shaft, thereby eliminating the need for an inner ring, which is effective in reducing weight. However, further weight reduction is desired in the design of this type of drive wheel bearing device.

[0005] To reduce the weight of a bearing device for a driving wheel, it is effective to reduce the axial dimension of the joint member by, for example, providing a raceway surface on the outer surface of the joint member that guides the rolling elements in the circumferential direction and providing a guide groove on the inner surface of the joint member that guides the balls in the axial direction. In other words, reducing the weight of the joint member itself is effective. However, when this structure is adopted, the distance between the raceway surface and the guide groove of the joint member may become short. To manufacture the joint member, the raceway surface and the guide groove formed in the intermediate molded body must be hardened by heat treatment. However, if the distance between the guide groove and the raceway surface is short, the hardened layers formed by heat treatment on each may connect, resulting in no unhardened layer being formed between them. This may result in cracks occurring in the intermediate molded body during heat treatment. Therefore, when a structure that reduces the axial dimension of the joint member is adopted, a technology to prevent cracks from occurring during heat treatment is required.

[0006] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a manufacturing method that can manufacture a joint member while suppressing the occurrence of cracks during heat treatment.

[0007] One aspect of the present disclosure is a method for manufacturing a joint member including a cylindrical portion having a bottom and a connecting portion connected to a hub to which a wheel is attached so as to be able to transmit torque, wherein a first inner raceway surface that guides a plurality of first rolling elements in a circumferential direction is provided on a radial outer surface of the cylindrical portion, and an outer guide groove that guides a plurality of third rolling elements along an axial direction is provided on an inner radial surface of the cylindrical portion, the method comprising: a molding step of molding an intermediate formed body before it becomes the joint member into a shape having the first inner raceway surface and the outer guide groove; and a hardening step of hardening both the first inner raceway surface and the outer guide groove of the intermediate formed body formed in the molding step, wherein the hardening step is a process of heating either the first inner raceway surface or the outer guide groove while cooling the other, thereby forming an unhardened layer between the hardened layer on the first inner raceway surface side and the hardened layer on the outer guide groove side.

[0008] The joint member manufactured in the above-described manner has a structure in which the first inner raceway is disposed radially outward of the outer guide groove so as to overlap at least a portion of the outer guide groove, or the first inner raceway is disposed on a line perpendicular to a tangent to the outer guide groove, which is effective in reducing the axial dimension of the joint member and thereby reducing its weight.

[0009] When manufacturing a joint member having this structure, a hardening process is performed after the molding process, in which one of the first inner raceway surface and the outer guide groove is heated while the other is cooled, thereby forming an unhardened layer between the hardened layer on the first inner raceway surface side and the hardened layer on the outer guide groove side. This hardening process can reduce variations in the thickness of each hardened layer, and even when the first inner raceway surface and the outer guide groove are close to each other, it is possible to provide an unhardened layer between the two hardened layers that is less likely to crack.

[0010] According to the above-described aspect, it is possible to provide a manufacturing method that can manufacture a joint member while suppressing the occurrence of cracks during heat treatment.

[0011] Note that the symbols in parentheses in the claims indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present disclosure.

[0012] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 1 is an axial cross-sectional view of the bearing device for a driving wheel of embodiment 1, FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1, FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1, FIG. 4 is a cross-sectional view showing a contact state between an outer guide groove provided on the inner surface of the cylindrical part of the outer joint member in FIG. 1 and a first ball, FIG. 5 is a partial cross-sectional view for explaining a first lightweight structure of the bearing device for a driving wheel of embodiment 1, FIG. 6 is a partial cross-sectional view for explaining a second lightweight structure of the bearing device for a driving wheel of embodiment 1, FIG. 7 is a partial cross-sectional view for explaining a third lightweight structure and a fourth lightweight structure of the bearing device for a driving wheel of embodiment 1, FIG. 8 is a partial cross-sectional view for explaining a fifth lightweight structure of the bearing device for a driving wheel of embodiment 1, FIG. 9 is a partial cross-sectional view for explaining a sixth lightweight structure and a seventh lightweight structure of the bearing device for a driving wheel of embodiment 1, and FIG. 14 is a cross-sectional view showing a part of a circumferential cross section of the cylindrical portion of the outer joint member in FIG. 11 or 13 ; FIG. 15 is a cross-sectional view showing a part of a circumferential cross section of the cylindrical portion of the outer joint member in FIG. 13 ; FIG. 16 is a flowchart of a method for manufacturing the outer joint member; FIG. 17 is a cross-sectional view of the outer joint member after a molding step; FIG. 18 is a cross-sectional view showing a first step of a hardening treatment of the outer joint member;

[0013] Hereinafter, an embodiment of the above aspect will be described with reference to the drawings.

[0014] In the drawings used to explain this embodiment, unless otherwise specified, the axial direction of the drive wheel bearing device and its components is designated as the X direction, the radial direction is designated as the Y direction, the circumferential direction is designated as the Z direction, and the direction around the axis is designated as the D direction.

[0015] (Embodiment 1) 1. Overall configuration of driving wheel bearing device 1 As shown in Figure 1, a driving wheel bearing device 1 of embodiment 1 (hereinafter simply referred to as "bearing device") has a structure in which a constant velocity universal joint (constant velocity joint) 1a and a rolling bearing 1b are integrated. This bearing device 1 is mounted on a vehicle powered by an electric motor or an internal combustion engine.

[0016] The constant velocity universal joint 1a is composed of multiple components including an outer joint member 30, an inner joint member 41, multiple third balls 50 which are multiple third rolling elements, and a cage 51. The constant velocity universal joint 1a is a joint of a fixed joint center type, in which the multiple third balls 50 serve as torque transmission members. The rolling bearing 1b is composed of multiple components including an outer ring 10, a hub 20, the outer joint member 30, multiple first balls 60 which are multiple first rolling elements, and multiple second balls 70 which are multiple second rolling elements.

[0017] The outer ring 10 is formed in a substantially cylindrical shape. An inner peripheral surface of the outer ring 10 is provided with annular raceway surfaces 11, 12 formed in two rows spaced apart in the axial direction X. The raceway surface 11 is a raceway surface for a plurality of first balls 60. The raceway surface 12 is a raceway surface for a plurality of second balls 70. The outer ring 10 is fixed to a vehicle body member 2 with bolts (not shown). The vehicle body member 2 is, for example, a member called a "knuckle."

[0018] The hub 20 is formed in an annular shape. The connecting portion 35 of the outer joint member 30 is inserted into the inner periphery of the hub 20. A plurality of bolts 22 are fixed to the hub 20, and the wheels 3, which serve as drive wheels, are attached to the hub 20 via the plurality of bolts 22.

[0019] 2. Structure of the Outer Joint Member 30 The outer joint member 30 is a member called the outer race of the constant velocity universal joint 1a. The outer joint member 30 has a cylindrical portion (joint portion) 31 with a bottom and a connecting portion 35 that is connected to the hub 20 so as to be able to transmit torque. The cylindrical portion 31 and the connecting portion 35 are integrated.

[0020] The cylindrical portion 31 of the outer joint member 30 is formed in a cup shape with a bottom surface. The cylindrical portion 31 and the hub 20 are fitted together at a fitting portion 36 by press-fitting in the axial direction X. At this time, a gap sufficient to position the hub 20 and the outer joint member 30 may be formed in the fitting portion 36. The cylindrical portion 31 has an internal space 31a and an abutment surface 31b that abuts against the hub 20 in the axial direction X. The abutment surface 31b is formed at an intermediate position between a first inner raceway surface 33 provided on the cylindrical portion 31 and a second inner raceway surface 21 provided on the hub 20. In other words, the first inner raceway surface 33 is disposed closer to the shaft 40 than the abutment surface 31b, and the second inner raceway surface 21 is disposed closer to the wheel 3 than the abutment surface 31b, with the abutment surface 31b separated therefrom. Therefore, the first ball 60 is disposed on one side in the axial direction X with respect to an imaginary plane (not shown) passing through the abutment surface 31b, and the second ball 70 is disposed on the other side in the axial direction X. The abutment surface 31b is disposed so as to overlap with the internal space 31a in the radial direction Y, i.e., so as to be located within the range of the internal space 31a in the axial direction X. Arranging the abutment surface 31b in this manner is effective in reducing the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X.

[0021] A plurality of outer guide grooves 32 that guide the plurality of third balls 50 along the axial direction X are provided on the inner surface in the radial direction Y of the cylindrical portion 31 of the outer joint member 30. The plurality of outer guide grooves 32 are formed at equal intervals in the circumferential direction Z of the cylindrical portion 31. A first inner raceway surface 33 is provided on the outer surface in the radial direction Y of the cylindrical portion 31 of the outer joint member 30 so as to overlap with the internal space 31 a in order to guide the plurality of first balls 60 in the circumferential direction Z. The first inner raceway surface 33 is formed in an annular shape in the circumferential direction Z of the cylindrical portion 31.

[0022] The connecting portion 35 of the outer joint member 30 engages with the hub 20 by so-called "spline fitting (a structure in which the convex teeth of a spline shaft fit into the grooves of a spline hole)" and is fastened to the hub 20 by the bolt 23. That is, a male thread provided on a shaft portion 23b extending from a head 23a of the bolt 23 is screwed into a female thread provided in a recess 35a of the connecting portion 35.

[0023] 3. Structure of the Inner Joint Member 41 The inner joint member 41 is formed in an annular shape and is fixed to the outer periphery of the shaft 40 connected to the vehicle's drive source (electric motor or internal combustion engine). The inner joint member 41 is housed in the internal space 31a of the cylindrical portion 31 of the outer joint member 30. The inner joint member 41 is tiltable relative to the outer joint member 30 around a predetermined joint center point P. In this embodiment, the angle between the central axis L1 of the outer joint member 30 and the central axis L2 of the inner joint member 41 is the joint angle. Note that FIG. 1 shows a state in which the joint angle is zero degrees.

[0024] 4. Structure of the Third Balls 50 The third balls 50 are spherical bodies of the same shape. The third balls 50 are housed in the internal space 31a of the cylindrical portion 31 of the outer joint member 30. The third balls 50 function to connect the cylindrical portion 31 of the outer joint member 30 and the inner joint member 41 so as to enable torque transmission. One third ball 50 is guided by one outer guide groove 32. The number of outer guide grooves 32 and third balls 50 is six or eight.

[0025] 5. Structure of the First Balls 60 As shown in Figures 1 and 2, the multiple first balls 60 are spherical bodies of the same shape. The multiple first balls 60 are provided between the raceway surface 11 of the outer ring 10 and the first inner raceway surface 33 of the outer joint member 30. The multiple first balls 60 have the function of supporting the outer ring 10 and the outer joint member 30 so that they can rotate relatively in the direction D around the axis (see Figure 1). The number of first balls 60 is not limited to that shown in Figure 2 and can be set to any appropriate number.

[0026] 6. Structure of the Second Balls 70 As shown in FIGS. 1 and 3 , the second balls 70 are spherical bodies of the same shape. The second balls 70 are disposed between the raceway surface 12 of the outer ring 10 and the second inner raceway surface 21 of the hub 20. The second balls 70 support the outer ring 10 and the hub 20 so that they can rotate relative to each other in the direction D about the axis (see FIG. 1 ). The second inner raceway surface 21 is disposed on the outer surface of the hub 20 in the radial direction Y so as to overlap with the internal space 31 a of the cylindrical portion 31 in order to guide the second balls 70 in the circumferential direction Z. The second inner raceway surface 21 is formed in an annular shape in the circumferential direction Z of the hub 20. The number of second balls 70 is not limited to that shown in FIG. 2 and may be any number.

[0027] The first ball 60 and the second ball 70 may be cylindrical rollers, needles, or conical tapered rollers, instead of spheres.

[0028] 4, each third ball 50 contacts the outer guide groove 32 at two contact positions 32a in the circumferential direction. A groove bottom 32b between the two contact positions 32a of the outer guide groove 32 forms a minute gap between the third ball 50 and the outer guide groove 32. The surface between two adjacent outer guide grooves 32 is formed by the joint inner spherical surface 34.

[0029] 5 , the cage 51 is formed in a cylindrical shape to hold the plurality of third balls 50. The outer and inner peripheral surfaces of the cage 51 are spherical, and the cage 51 is disposed between the joint inner spherical surface 34 provided on the cylindrical portion 31 of the outer joint member 30 and the joint outer spherical surface 42 provided on the inner joint member 41.

[0030] 8. Lightweight Structure of Bearing Device 1 for Drive Wheel Next, the lightweight structure characteristic of the bearing device 1 of this embodiment will be described with reference to Figures 5 to 15. The bearing device 1 does not have a separate member (such as a member called an "inner ring" or "hub inner ring") between the outer joint member 30 and the first balls 60, which is advantageous for reducing weight. The bearing device 1 of this embodiment is equipped with the following first to eighth lightweight structures to further reduce weight.

[0031] 8-1. First Lightweight Structure As shown in FIG. 5 , the first lightweight structure is a structure in which, in the outer joint member 30, the first inner raceway surface 33 is disposed radially outward of the outer guide groove 32 so as to overlap at least a portion of the outer guide groove 32. For convenience of explanation, in FIG. 5 , the region in which the outer guide groove 32 extends along the axial direction X is shown as hatched region A, and the region in which the first inner raceway surface 33 extends along the arcuate surface is shown as hatched region B. In this embodiment, region A in which the outer guide groove 32 extends along the axial direction X and region B in which the first inner raceway surface 33 extends along the arcuate surface completely overlap in the radial direction Y. Alternatively, region B may partially overlap region A in the radial direction Y.

[0032] According to the first lightweight structure, it is possible to realize a narrower structure in which the outer guide groove 32 and the first inner raceway surface 33 are closer to each other in the axial direction X than in the conventional structure. In this case, it is possible to shorten the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X. This makes it possible to reduce the weight of the bearing device 1.

[0033] 6, the second lightweight structure is a structure in which, in the outer joint member 30, the first inner raceway surface 33 is disposed on a vertical line L4 that is perpendicular to the tangent line L3 of the outer guide groove 32. The tangent line L3 is typically a tangent line to the groove bottom 32b (see FIG. 4) of the outer guide groove 32. Furthermore, this tangent line L3 may be a tangent line to the locus of the contact position 32a (see FIG. 4) of the outer guide groove 32, or may be a tangent line to the locus of the center of the third ball 50.

[0034] According to the second lightweight structure, as in the case of the first lightweight structure, the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X can be shortened, thereby making it possible to reduce the weight of the bearing device 1.

[0035] 7, the third lightweight structure is a structure in which the angle θa between the imaginary line L5 and the central axis L1 of the outer joint member 30 is set to 60 to 80 degrees. The imaginary line L5 is a line that imaginarily connects the joint center point P of the inner joint member 41 and the center Q2 of the first ball 60.

[0036] According to the third lightweight structure, as in the case of the first lightweight structure, the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X can be shortened, thereby making it possible to reduce the weight of the bearing device 1. In particular, the greater the angle θa is set to, the greater the effect of reducing the weight of the bearing device 1.

[0037] 7, the fourth lightweight structure is a structure in which the angle θb between the imaginary line L6 and the central axis L1 of the outer joint member 30 is set to 35 to 75 degrees when the joint angle of the outer joint member 30 is zero degrees (the state shown in FIG. 1). The imaginary line L6 is a line that imaginarily connects the center Q1 of the third ball 50 and the center Q2 of the first ball 60.

[0038] According to the fourth lightweight structure, as in the case of the first lightweight structure, the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X can be shortened, thereby making it possible to reduce the weight of the bearing device 1. In particular, the effect of reducing the weight of the bearing device 1 increases as the angle θb is set larger.

[0039] 8-5. Fifth Lightweight Structure As shown in FIG. 8 , the fifth lightweight structure is a structure in which, in a steady state where the joint angle is within the normal range, the third ball 50 contacts the tubular portion 31 of the outer joint member 30 in a contact area C, and the contact area C is located on a vertical line L8 that is perpendicular to a tangent line L7 of the first inner raceway surface 33. The steady state here refers to when the vehicle is stopped or traveling straight. The tangent line L7 is a tangent line at the point of contact between the first inner raceway surface 33 and the third ball 50. For ease of explanation, the contact area C is shown as a hatched area in FIG. 8 .

[0040] According to the fifth lightweight structure, as in the case of the first lightweight structure, the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X can be shortened, making it possible to reduce the weight of the bearing device 1.

[0041] 9, the sixth lightweight structure is a structure in which the angle θc between an imaginary line L9 and the central axis L1 of the outer joint member 30 is set to 40 to 60 degrees. The imaginary line L9 is a line that imaginarily connects the joint center point P of the inner joint member 41 and the center Q3 of the second ball 70.

[0042] According to the sixth lightweight structure, as in the case of the first lightweight structure, the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X can be shortened, thereby making it possible to reduce the weight of the bearing device 1. In particular, the greater the angle θc is set to, the greater the effect of reducing the weight of the bearing device 1.

[0043] 9, the seventh lightweight structure is a structure in which the angle θd between an imaginary line L10 and the central axis L1 of the outer joint member 30 is set to 15 to 55 degrees when the joint angle is zero degrees (the state shown in FIG. 1). The imaginary line L10 is a line that imaginarily connects the center Q1 of the third ball 50 and the center Q3 of the second ball 70.

[0044] According to the seventh lightweight structure, as in the case of the first lightweight structure, the dimension of the connecting portion 35 of the outer joint member 30 in the axial direction X can be shortened, thereby making it possible to reduce the weight of the bearing device 1. In particular, the effect of reducing the weight of the bearing device 1 increases as the angle θd is set larger.

[0045] The eighth lightweight structure is a structure for reducing the weight of the bearing device 1 by reducing the thickness of the cylindrical portion 31 of the outer joint member 30 in the radial direction Y. For the eighth lightweight structure, see Figures 10 to 15.

[0046] 10 and 11 show the state of the bearing device 1 when the wheel 3 is the right front wheel and the vehicle is traveling straight. This state is a steady state in which the joint angle α is within the normal range (for example, a value of approximately 6 degrees), and the inner joint member 41 is located, for example, in the first position R1. The same applies when the vehicle is stopped. In contrast, FIGS. 12 and 13 show the state of the bearing device 1 when the wheel 3 is the right front wheel and the vehicle is turning left. This state is a variable state in which the joint angle α exceeds the normal range (for example, a value of approximately 25 degrees at most), and the inner joint member 41 is located, for example, in the second position R2.

[0047] 11 and 13, the eighth lightweight structure satisfies the condition that the inner contact direction Ea and the outer contact direction Eb do not coincide with each other in a cross section including the central axes L1, L2 of the outer joint member 30 and the inner joint member 41. That is, the inner contact direction Ea and the outer contact direction Eb do not coincide with each other not only in three dimensions but also when viewed two-dimensionally in the cross section.

[0048] The inner contact direction Ea is the contact direction of the first ball 60 on the first inner raceway surface 33 of the cylindrical portion 31 of the outer joint member 30. The first ball 60 contacts the first inner raceway surface 33 at a contact position 33a (the region shown by the substantially elliptical cross section in FIGS. 11 and 13 ) at a contact angle β (the angle with respect to an imaginary line in the radial direction Y) and inputs a load in the inner contact direction Ea to the first inner raceway surface 33. The contact angle β is, for example, approximately 40 degrees when traveling straight (see FIG. 11 ) and approximately 52 degrees when turning left (see FIG. 13 ). At this time, stress is generated in the first inner raceway surface 33 of the cylindrical portion 31 in response to the load input from the first ball 60. The inner contact direction Ea can also be referred to as the load input direction from the first ball 60.

[0049] The outer contact direction Eb is the contact direction of the third ball 50 in the outer guide groove 32 of the tubular portion 31 of the outer joint member 30. When the joint angle is α, the center of the third ball 50 is located on a line passing through the joint center point P and tilted by α / 2, which is ½ of the joint angle α, from a plane passing through the joint center point P and perpendicular to the central axis L1. The third ball 50 contacts the outer guide groove 32 at a contact angle γ (angle with respect to a virtual line in the radial direction Y) greater than α / 2 at a contact position 32a (a region indicated by a substantially elliptical cross section in FIGS. 11 and 13 ), and inputs a load in the outer contact direction Eb to the outer guide groove 32. At this time, stress is generated in the outer guide groove 32 of the tubular portion 31 in response to the load input from the third ball 50. The outer contact direction Eb can also be referred to as the load input direction from the third ball 50.

[0050] Here, if the inner contact direction Ea and the outer contact direction Eb coincide, it is expected that local stress concentration will occur in the portion of the tubular portion 31 of the outer joint member 30 where the inner contact direction Ea and the outer contact direction Eb coincide. If measures were taken to increase the thickness of the tubular portion 31 so that it could withstand this stress concentration, this could result in an increase in the weight of the bearing device 1. Therefore, in the eighth lightweight structure, the inner contact direction Ea and the outer contact direction Eb are made to not coincide with each other, thereby suppressing the occurrence of the above-mentioned stress concentration in the tubular portion 31 of the outer joint member 30. This allows the thickness of the tubular portion 31 to be reduced, thereby enabling the weight of the bearing device 1 to be reduced.

[0051] 11 and 13 , when an extension line extending from the center of a first ball 60 in the inner contact direction Ea is defined as a first extension line M1, a plurality of first extension lines M1 are formed corresponding to the number of first balls 60. Here, the first extension line M1 is a line linearly connecting the center of the first ball 60 and the contact position 33a of the first ball 60 on the first inner raceway surface 33. Furthermore, when an extension line extending from the center of a third ball 50 in the outer contact direction Eb is defined as a third extension line M3, a plurality of third extension lines M3 are formed corresponding to the number of third balls 50. Here, the third extension line M3 is a line linearly connecting the center of the third ball 50 and the contact position 32a of the third ball 50 on the outer guide groove 32.

[0052] The eighth lightweight structure is preferably a structure that satisfies the following conditions: if the multiple first extension lines M1 include one that passes through the contact position 32a of the third ball 50 in the outer guide groove 32, the third extension line M3 for the third ball 50 at that contact position 32a does not pass through the contact position 33a of the first ball 60 on the first inner raceway surface 33; and if the multiple third extension lines M3 include one that passes through the contact position 33a of the first ball 60 on the first inner raceway surface 33, the first extension line M1 for the first ball 60 at that contact position 33a does not pass through the contact position 32a of the third ball 50 in the outer guide groove 32.

[0053] 14 , for example, in this structure, one of the three first extension lines M1 passes through the contact position 32a of the third ball 50 in the outer guide groove 32, but a third extension line M3 for the third ball 50 at that contact position 32a does not pass through any of the contact positions 33a of the first balls 60 in the first inner raceway surface 33. Furthermore, one third extension line M3 passes through the contact position 33a of the first ball 60 in the first inner raceway surface 33, but the first extension line M1 for the first ball 60 at that contact position 33a does not pass through any of the contact positions 32a of the third balls 50 in the outer guide groove 32.

[0054] Furthermore, the eighth lightweight structure is preferably a structure that satisfies the condition that, during a turn in which the joint angle α exceeds the normal range (see Figures 12 and 13), the first extension line M1 of the first ball 60 that has the greatest input load on the first inner raceway surface among the multiple first balls 60 does not pass through the contact position 32a in the outer guide groove 32 of any of the multiple third balls 50.

[0055] 15 , for example, with the upper side of the drawing being the upper side of the vehicle, the first ball 60 at the first position S1, which is the highest of the three first balls 60, receives the largest load F from the vehicle compared to the first balls 60 at the second position S2 or the third position S3, which are lower than the first position S1. Therefore, the first ball 60 at the first position S1 receives the largest input load on the first inner raceway surface 33 among the three first balls 60. At this time, the first extension line M1 of the first ball 60 at the first position S1 does not pass through the contact positions 32 a in the outer guide grooves 32 of any of the multiple third balls 50.

[0056] 16, the outer joint member 30 is manufactured by sequentially performing a molding step S101, a hardening step S102, and a post-treatment step S103. If necessary, another step may be added to these steps, or at least one step may be divided into a plurality of steps.

[0057] The forming step S101 is a step of forming an intermediate formed body, which will not yet become the outer joint member 30, into a shape having the first inner raceway surface 33 and the outer guide groove 32. Although not particularly shown, a known forging device is used in this forming step S101. As the material of the intermediate formed body, for example, carbon steel for mechanical structures (S55C) can be used.

[0058] 17 , the hardening step S102 is a step of hardening both the first inner raceway surface 33 and the outer guide groove 32 of the intermediate compact W formed in the molding step S101. This hardening step S102 is a step of heating one of the first inner raceway surface 33 and the outer guide groove 32 of the intermediate compact W while cooling the other. This hardening step S102 includes a first step S102a and a second step S102b, which will be described later.

[0059] The post-treatment step S103 is a step of performing post-treatment on the intermediate molded body W that has been subjected to the hardening treatment step S102. This post-treatment step S103 includes known treatments such as tempering, machining, threading, and painting.

[0060] In this embodiment, in order to reduce the weight of the outer joint member 30 and thereby the bearing device 1, a structure is adopted in which the dimension of the outer joint member 30 in the axial direction X is reduced. As a result, as shown in FIG. 17 , the distance d between the first inner raceway surface 33 and the outer guide groove 32 of the intermediate formed body W is shortened. That is, among the various portions of the intermediate formed body W, the thickness of the portion between the first inner raceway surface 33 and the outer guide groove 32 is reduced. If the distance d between the first inner raceway surface 33 and the outer guide groove 32 is short, there is a risk of cracks occurring in the intermediate formed body W during heat treatment. Therefore, in this embodiment, a hardening treatment step S102 is performed, which is effective in addressing this problem.

[0061] As shown in Figure 18, the first step S102a of the hardening treatment process S102 is a step of cooling the outer guide groove 32 while heating the first inner raceway surface 33 of the intermediate formed body W, and then cooling the first inner raceway surface 33 immediately after the heating is completed. In the first step S2a, as an example, an induction hardening device 80, a cooling device 90, and a cooling device 91 (see Figure 19) are used. The induction hardening device 80 is used to heat the first inner raceway surface 33 from the outside. The cooling device 90 is used to cool the outer guide groove 32 from the inside. The cooling device 91 is used to cool the first inner raceway surface 33 from the outside immediately after the heating by the induction hardening device 80 is completed.

[0062] The induction hardening device 80 has a heating unit 80a that is provided so as to surround from the outside the first inner raceway surface 33 that extends in the circumferential direction Z (see FIG. 6 ). The heating unit 80a has a known structure and has a function of heating the first inner raceway surface 33 by generating an eddy current in the first inner raceway surface 33 using a coil that generates a magnetic force m when a high-frequency induction current is passed through it. With this induction hardening device 80, the first inner raceway surface 33 of the intermediate formed body W is selectively heated from the outside.

[0063] The cooling device 90 is an injection nozzle extending in the axial direction X, and the outer peripheral surface of this injection nozzle is provided with a plurality of injection ports 90a for injecting the cooling liquid CL. The cooling device 90 is inserted into the internal space 31a so that the plurality of injection ports 90a face the outer guide grooves 32 of the intermediate formed body W, and injects the cooling liquid CL through the plurality of injection ports 90a. Note that liquids such as water or oil can be appropriately used as the cooling liquid CL. With this cooling device 90, the outer guide grooves 32 of the intermediate formed body W are selectively cooled from the inside.

[0064] 19 , the cooling device 91 is a cooling jacket provided so as to surround the first inner raceway surface 33 from the outside, and the inner circumferential surface of this cooling jacket is provided with a plurality of injection ports 91 a for injecting coolant CL. The cooling device 91, instead of the induction hardening device 80, injects the coolant CL through the plurality of injection ports 91 a, with the plurality of injection ports 91 a arranged so as to face the outer guide groove 32 of the intermediate formed body W. With this cooling device 91, the first inner raceway surface 33 is rapidly cooled immediately after heating is completed, and a hardened layer t1 (see FIG. 20 ) is formed in which the surface side of this first inner raceway surface 33 is hardened.

[0065] 19 , the second step S102b of the hardening treatment process S102 is a step of cooling the first inner raceway surface 33 while heating the outer guide groove 32 of the intermediate formed body W after the first step S102a is performed, and then cooling the outer guide groove 32 immediately after the end of heating. In the second step S102b, for example, an induction hardening device 81 for heating the outer guide groove 32 from the inside, and the cooling devices 91 and 90 (see FIG. 18 ) are used.

[0066] The induction hardening device 81 has a heating unit 81a disposed opposite the outer guide groove 32. Similar to the heating unit 80a of the induction hardening device 80, the heating unit 81a has a function of generating eddy currents in the outer guide groove 32 by utilizing a coil that generates a magnetic force m when a high-frequency induction current is passed through it, thereby heating the outer guide groove 32. With this induction hardening device 81, the outer guide groove 32 of the intermediate formed body W is selectively heated from the inside. Thereafter, the outer guide groove 32 is rapidly cooled by a cooling device 90 immediately after heating is completed, and a hardened layer t2 (see FIG. 20 ) is formed on the surface side of the outer guide groove 32.

[0067] As shown in Figure 20, according to the hardening treatment process S102, a hardened layer t1 is formed on the first inner raceway surface 33 side of the intermediate molded body W, a hardened layer t2 is formed on the outer guide groove 32 side, and a non-hardened layer t3 is formed between the hardened layer t1 and the hardened layer t2.

[0068] The non-hardened layer t3 may be a layer made only of the base material, a layer including a layer made of the base material and a low-hardness layer whose hardness is greater than that of the base material but less than that of the hardened layers t1 and t2, or a layer made only of the low-hardness layer. For example, if the Vickers hardness of the first inner raceway surface 33 and the outer guide groove 32 is 700 to 800 HV and the Vickers hardness of the base material is 200 to 250 HV, the target Vickers hardness of the hardened layers t1 and t2 can be preferably 500 HV or greater, and the target Vickers hardness of the non-hardened layer t3 can be preferably less than 500 HV. Vickers hardness is based on JIS Z2244 (2009).

[0069] In the hardening treatment step S102, it is preferable to harden both the first inner raceway surface 33 and the outer guide groove 32 so that the thickness d3 of the non-hardened layer t3 is greater than 0 mm and not greater than 2 mm. For example, when the distance d between the first inner raceway surface 33 and the outer guide groove 32 is approximately 8 mm, the target hardening depth can be set so that the thickness d1 of the hardened layer t1 and the thickness d2 of the hardened layer t2 are both approximately 3 mm, taking into account variations in the actual hardening depths achieved by the induction hardening devices 81 and 82. The target hardening depths can be changed, for example, by adjusting the output of the induction hardening devices 81 and 82.

[0070] 10. Effects According to the first embodiment described above, the following effects can be obtained.

[0071] The outer joint member 30 constituting the bearing device 1 of Embodiment 1 has a structure in which the first inner raceway surface 33 is disposed radially outward of the outer guide groove 32 so as to overlap at least a portion of the outer guide groove 32, or the first inner raceway surface 33 is disposed on a vertical line L4 perpendicular to a tangent line L3 of the outer guide groove 32. This structure is effective for reducing the dimension of the outer joint member 30 in the axial direction X and thereby achieving weight reduction. Furthermore, this structure can also be said to be a structure that satisfies the condition that the inner contact direction Ea of the first ball 60 on the first inner raceway surface 33 and the outer contact direction Eb of the third ball 50 on the outer guide groove 32 do not coincide with each other.

[0072] When manufacturing the outer joint member 30 having this structure, in a hardening treatment step S102 after the molding step S101, one of the first inner raceway surface 33 and the outer guide groove 32 is heated while the other is cooled, thereby forming an unhardened layer t3 between the hardened layer t1 on the first inner raceway surface 33 side and the hardened layer t2 on the outer guide groove 32 side. This hardening treatment can prevent variations in the thickness of each hardened layer, and even when the distance d between the first inner raceway surface 33 and the outer guide groove 32 is short, the unhardened layer t3, which is less likely to crack, can be provided between the two hardened layers t1, t2.

[0073] As described above, according to the first embodiment, it is possible to manufacture a lightweight joint member 30 while suppressing the occurrence of cracks in the intermediate formed body W during heat treatment. Furthermore, the weight of the joint member 30 can be reduced, thereby reducing the weight of the bearing device 1. As a result, it is possible to extend the driving range of a vehicle equipped with the bearing device 1 and improve its electricity cost or fuel economy.

[0074] According to the first embodiment, in the hardening treatment step S102, cooling of both the first inner raceway surface 33 and the outer guide groove 32 is performed by spraying the cooling liquid CL, which enables the equipment required for cooling to be shared, thereby making it possible to keep equipment costs low.

[0075] According to the first embodiment, in the hardening treatment step S102, the thickness d3 of the non-hardened layer t3 is set to be greater than 0 mm and equal to or less than 2 mm, so that the non-hardened layer t3 is provided between the two hardened layers t1 and t2, and the distance between the first inner raceway surface 33 and the outer guide groove 32 can be minimized.

[0076] 11. Modifications Although the present disclosure has been described with reference to the above-described embodiments, it is understood that the present disclosure is not limited to such embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and embodiments, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0077] In the embodiment described above, in the hardening treatment step S102, the first step S102a is performed to heat the first inner raceway surface 33 before the outer guide groove 32, and then the second step S102b is performed to heat the outer guide groove 32. However, instead of this, the second step S102b may be performed before the first step S102a. In this case, the second step S102b in Fig. 16 corresponds to the "first step," and the first step S102a in Fig. 16 corresponds to the "second step."

[0078] In the above embodiment, the structures of the induction hardening devices 81 and 82 used for heating and the structures of the cooling devices 90 and 91 used for cooling are not limited to the above structures, and can be changed as necessary.

Claims

1. A manufacturing method (S101 to S103) of a joint member (30) including a bottomed cylindrical tubular portion (31) and a connecting portion (35) that is torque-transmissibly connected to a hub to which a wheel is attached. On an outer surface in the radial direction (Y) of the tubular portion, a first inner raceway surface (33) for guiding a plurality of first rolling elements (60) in the circumferential direction (Z) is provided. On an inner surface in the radial direction (Y) of the tubular portion, an outer guide groove (32) for guiding a plurality of third rolling elements (50) along the axial direction (X) is provided. A forming step (S101) of forming an intermediate molded body (W) before becoming the joint member into a shape having the first inner raceway surface and the outer guide groove. A hardening treatment step (S102) of hardening both the first inner raceway surface and the outer guide groove of the intermediate molded body formed in the forming step. The hardening treatment is a process of forming a non-hardened layer (t3) between a hardened layer (t1) on the first inner raceway surface side and a hardened layer (t2) on the outer guide groove side by heating one of the first inner raceway surface and the outer guide groove while cooling the other. A manufacturing method (S101 to S103) of a joint member.

2. The manufacturing method of a joint member according to claim 1, wherein the first inner raceway surface is arranged so as to overlap at least a part of the outer guide groove on the outer side in the radial direction (Y) of the outer guide groove, or the first inner raceway surface is arranged on a perpendicular line (L4) perpendicular to a tangent line (L3) of the outer guide groove.

3. The manufacturing method of a joint member according to claim 1 or 2, wherein the hardening treatment step includes a first step (S102a) of cooling the outer guide groove while heating the first inner raceway surface and then cooling the first inner raceway surface immediately after the heating of the first inner raceway surface is completed, and a second step (S102b) of cooling the first inner raceway surface while heating the outer guide groove after the first step and then cooling the outer guide groove immediately after the heating of the outer guide groove is completed.

4. The hardening treatment step includes a first step (S102a) of cooling the first inner raceway surface while heating the outer guide groove and then cooling the outer guide groove immediately after the heating of the outer guide groove is completed, and a second step (S102b) of cooling the outer guide groove while heating the first inner raceway surface after the first step and then cooling the first inner raceway surface immediately after the heating of the first inner raceway surface is completed. The method for manufacturing a joint member according to claim 1 or 2.

5. The method for manufacturing a joint member according to claim 1 or 2, wherein cooling of both the first inner raceway surface and the outer guide groove is performed by spraying a coolant (CL).

6. The method for manufacturing a joint member according to claim 1 or 2, wherein in the hardening treatment step, the thickness (d3) of the non-hardened layer is made greater than 0 [mm] and less than or equal to 2 [mm].

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