Wheel bearing device and power transmission structure

Abstract

To provide a wheel bearing device and a power transmission structure that prevents the generation of stick slip sound for a long time, even by the strong torque of an EV motor.SOLUTION: A stem portion 62 is projected out from a bottom portion 61a of a mouth portion 61 of an outside joint member of a constant velocity universal joint. The stem portion is made to be a male spline shaft 65 fitted with a female spline hole of a hub ring. An outer diameter of a mouth side root portion of the male spline shaft is made to be larger than the minimum diameter satisfying torque transmission capacity, and the other part of the male spline shaft is made to be smaller than the outer diameter of the mouth side root portion and satisfy the torque transmission capacity.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wheel bearing device that supports the wheels of a vehicle such as an automobile, and more specifically to a wheel bearing device that includes a wheel bearing and a constant velocity universal joint and supports drive wheels (the front wheels of FF vehicles, the rear wheels of FR or RR vehicles, and all wheels of 4WD vehicles) mounted on an independent suspension so that they can rotate freely relative to the suspension. [Background technology]

[0002] A power transmission device that transmits engine power of a vehicle such as an automobile to the wheels must transmit power from the engine to the wheels, and must also tolerate radial and axial displacements and moment displacements from the wheels that occur when the vehicle bounces or turns while traveling on rough roads. For this reason, for example, one end of a drive shaft interposed between the engine side and the driving wheels side is connected to a differential via a sliding type constant velocity joint, and the other end is connected to the driving wheels via a wheel bearing device that includes a fixed type constant velocity joint.

[0003] Various structures have been proposed for this wheel bearing device, and for example, the one shown in FIG. 6 is known. This wheel bearing device comprises an outer member 1 which has a vehicle body mounting flange 1b integrally formed on its outer periphery for mounting to a vehicle body and double row outer raceway surfaces 1a, 1a integrally formed on its inner periphery, a hub ring 2 which has a wheel mounting flange 4 integrally formed at one end for mounting a wheel (not shown) and which has an inner raceway surface 2a on its outer periphery facing one of the double row outer raceway surfaces 1a, 1a and a cylindrical small diameter step 2b extending in the axial direction from this inner raceway surface 2a, and an inner ring 3 which is press-fitted into the small diameter step 2b of the hub ring 2 and has an inner raceway surface 2a on its outer periphery facing the other of the double row outer raceway surfaces 1a, 1a, double row balls 7, 7 which are rollably accommodated between the raceway surfaces of the inner member 5 and the outer member 1 via cages 6, 6, and seals 8, 9 which are fitted to an opening of an annular space formed between the outer member 1 and the inner member 5.

[0004] The inner ring 3 is fixed in the axial direction to the hub wheel 2 by a crimped portion 10 formed by plastically deforming the end of the small diameter step portion 2b of the hub wheel 2 radially outward, and a constant velocity universal joint 11 is connected to the hub wheel 2. An outer joint member 12 of this constant velocity universal joint 11 integrally has a shoulder portion 13 forming the bottom of the cup-shaped mouth portion, and a stem portion 14 extending in the axial direction from this shoulder portion 13 and fitted into the hub wheel 2 via serrations (splines) 14a so as to be able to transmit torque, and the hub wheel 2 and the outer joint member 12 are connected axially detachably via a fixing nut 15, with the shoulder portion 13 abutting the crimped portion 10.

[0005] It is known that torque is applied to the wheels of such vehicles from the engine via the sliding type constant velocity joint 11, causing torsion in the drive shaft. As a result, a relative difference occurs between the crimped portion 10 of the hub wheel 2 and the shoulder portion 13 of the outer joint member 12 due to torsion. The axial force caused by the tightening of the nut 15 causes the contact surfaces of the crimped portion 10 and the shoulder portion 13 to move together due to frictional resistance, but when the engine is rotating at a low speed, for example when the vehicle starts, a larger torque is applied and a large torsion occurs in the drive shaft, and the contact surfaces of the outer joint member 12 and the inner member 5 cannot withstand the frictional resistance, causing a sudden slip and a stick-slip noise.

[0006] Conventional methods for preventing such stick-slip noise include adjusting the friction coefficient of the contact surface between the inner member and the shoulder portion of the outer joint member (Patent Document 1), and interposing (clamping) a plate formed with a low-friction resin coating layer between the inner member and the shoulder portion of the outer joint member. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-149183 A [Patent Document 2] JP 2013-082351 A Summary of the Invention [Problem to be solved by the invention]

[0008] The above-mentioned Patent Documents 1 and 2 disclose a technology for suppressing stick-slip on the contact surface that accompanies torque transmission. However, due to changes over time that occur with vehicle use, such as wear on the contact surface and peeling of the coating, it is difficult to maintain the effect (function of suppressing stick-slip) for a long period of time.

[0009] In recent years, improvements in motors and batteries have led to the emergence of engine-less electric vehicles (hereinafter simply referred to as EVs) in the automobile market. The defining feature of EVs is that they are quiet, from zero start (starting from a stopped state) to high speed operation.

[0010] For this reason, even the slightest noise is noticeable, compared to conventional internal combustion engine vehicles. Furthermore, the characteristics of EV motors are such that they generate maximum torque immediately after starting, and are used as regenerative brakes when the vehicle decelerates, so the contact surface is subjected to a greater load than in gasoline engine vehicles. For this reason, an axle module (power transmission structure) that can effectively prevent stick-slip noise was needed for EVs.

[0011] Furthermore, stick-slip noise at the contact surfaces is a high-frequency sound, a so-called metallic sound, that propagates through the vehicle body and can be heard, so it is difficult to address it with sound-proofing materials like road noise from tires, for example, and it is necessary to take measures at the source.

[0012] Therefore, in this application, we focus on the occurrence and increase of rattle at the spline mating portion of the wheel bearing device and the constant velocity universal joint, which is the source of stick-slip, and improve the mating method (diameter dimension, twist angle of the male spline, etc.) and strength (heat treatment of the female spline) of the said portion to prevent the occurrence of stick-slip noise at the contact surface, and to ensure that the strong torque of the EV motor can be tolerated for a long period of time. The present invention provides a wheel bearing device and power transmission structure (an axle module: comprising a pair of constant velocity universal joints, an intermediate shaft connecting the pair, and a wheel bearing device connected to the constant velocity universal joint) that is constructed so as not to generate stick-slip noise. [Means for solving the problem]

[0013] The bearing device for a wheel of the present invention comprises an outer member having a double row outer raceway surface formed on its inner circumference, an inner member having a double row raceway surface formed on its outer circumference facing the outer raceway surface, and double row rolling elements interposed between raceway surfaces of the outer member and the inner member, the inner member having a hub ring, and a stem portion of a constant velocity universal joint being integrally connected to the hub ring via a spline connection, The stem portion protrudes from the bottom of the mouth portion of the outer joint member of the constant velocity universal joint, and this stem portion has a male spline shaft that fits into the female spline hole of the hub wheel, and the outer diameter of the male spline shaft at the mouth side root portion is made larger than the minimum diameter that satisfies the torque transmission capacity, and the other portions of the male spline shaft are made smaller in diameter than the outer diameter of the mouth side root portion so as to satisfy the torque transmission capacity.

[0014] According to the wheel bearing device of the present invention, the diameter of the spline fit between the stem of the constant velocity universal joint and the hub wheel can be made larger on the base side, thereby preventing deformation and wear on the base side.

[0015] It is preferable to impart a twist angle to the spline convex teeth of the male spline shaft at the base on the mouth side. By imparting a twist angle to the spline convex teeth of the male spline shaft of the constant velocity universal joint in a direction in which the contact of the spline convex teeth is released from the twist of the male spline shaft accompanying the torque transmission when the torque transmission direction when the vehicle moves forward is defined as the forward rotation of the male spline shaft, the contact pressure can be reduced and deformation and wear of the female spline of the hub wheel can be suppressed.

[0016] The generatrix of the spline teeth at the base of the mouse side of the male spline shaft may be arc-shaped. Even if the generatrix is ​​arc-shaped, the contact of the spline teeth can be set to be released from the twist of the male spline shaft caused by torque transmission when the vehicle starts, and the contact pressure can be reduced, thereby suppressing deformation and wear of the female splines of the hub wheel.

[0017] The generatrix shape of the spline convex teeth at the base of the mouth side of the male spline shaft may be wavy. By making it wavy in this way, the number of contact points between the spline convex teeth of the male spline shaft and the spline concave teeth of the female spline hole increases, dispersing the load. Therefore, when the vehicle starts moving, the contact of the spline convex teeth can be set to be released from the twist of the male spline shaft caused by torque transmission, and the contact pressure can be reduced, thereby suppressing deformation and wear of the female splines of the hub wheel.

[0018] It is preferable that the inner periphery of the inboard opening of the female spline hole of the hub wheel is a heat-hardened treatment. The inboard opening of the female spline hole is a portion that is prone to deformation and wear when a torque load is applied, so if a hardened treatment is formed in such a portion, deformation and wear can be effectively prevented.

[0019] The first power transmission structure of the present invention is a power transmission structure comprising a pair of left and right drive shafts, each drive shaft comprising a pair of constant velocity universal joints and an intermediate shaft connecting these constant velocity universal joints, the axial lengths of the intermediate shafts of the left and right drive shafts are different, the constant velocity universal joint arranged on the wheel side is connected to the wheel bearing device, and the twist directions of the spline convex teeth at the mouse side base portion of the left and right constant velocity universal joints are different.

[0020] The second power transmission structure of the present invention is a power transmission structure comprising a pair of left and right drive shafts, each drive shaft comprising a pair of constant velocity universal joints and an intermediate shaft connecting these constant velocity universal joints, the axial lengths of the intermediate shafts of the left and right drive shafts are different, the constant velocity universal joint arranged on the wheel side is connected to the wheel bearing device, and the arc shapes of the spline convex teeth at the mouse side base portions of the left and right constant velocity universal joints are symmetrical.

[0021] The third power transmission structure of the present invention is a power transmission structure comprising a pair of left and right drive shafts, each drive shaft comprising a pair of constant velocity universal joints and an intermediate shaft connecting these constant velocity universal joints, the axial lengths of the intermediate shafts of the left and right drive shafts being different, a constant velocity universal joint arranged on the wheel side being connected to the wheel bearing device, and at least one of the following is adopted: a torsion angle is imparted to the spline convex teeth, the generatrix shape of the spline convex teeth is an arc, or the generatrix shape of the spline convex teeth is a wave-shaped, and the spline convex teeth shapes at the mouse side root portions of the left and right constant velocity universal joints are different. Effect of the Invention

[0022] In the present invention, even when sudden torque transmission occurs (such as when an electric vehicle starts) in the spline engagement between the hub wheel and the stem portion of the constant velocity universal joint, the area where the contact pressure increases can be strengthened, suppressing the occurrence of rattle at the engagement portion and mitigating stick-slip noise that occurs between the inner member (hub wheel) and the outer joint member of the constant velocity universal joint over a long period of time. [Brief description of the drawings]

[0023] [Figure 1] 4 is a side view showing a stem portion of an outer joint member of a constant velocity universal joint connected to a hub wheel of the wheel bearing device according to the present invention. FIG. [Diagram 2] 1 is a cross-sectional view of a wheel bearing device according to the present invention. [Diagram 3] 1 is a simplified diagram of a power transmission structure (axle module) of the present invention. [Figure 4] 1 shows a male spline shaft and a female spline hole, where (a) is a cross-sectional view of a large diameter portion and (b) is a cross-sectional view of a small diameter portion. [Diagram 5] 1A is a simplified diagram showing the relationship between the spline convex teeth of a male spline shaft and the spline concave teeth of a female spline hole, where (a) is a simplified diagram when a twist angle is applied to the spline convex teeth, (b) is a simplified diagram when the generatrix shape of the spline convex teeth is arc-shaped, and (c) is a simplified diagram when the generatrix shape of the spline convex teeth is wavy. [Figure 6] FIG. 1 is a cross-sectional view of a conventional wheel bearing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of the present invention will be described with reference to Fig. 1 to Fig. 5. Fig. 3 shows a power transmission structure of the present invention, which includes a pair of drive shafts 51A, 52B, each of which includes a pair of constant velocity universal joints 53A, 54A and 53B, 54B, and intermediate shafts 55A, 55B connecting the pair of constant velocity universal joints 53A, 54A and 53B, 54B.

[0025] Fixed type constant velocity universal joints are used for the constant velocity universal joints 53A and 53B, and sliding type constant velocity universal joints are used for the constant velocity universal joints 54A and 54B. The fixed type constant velocity universal joint is mainly composed of an outer joint member 60, an inner joint member (not shown) disposed inside the outer joint member 60, a plurality of torque transmission members (not shown) that are interposed between the outer joint member 60 and the inner joint member to transmit torque, and a cage (not shown) that is interposed between the outer joint member 60 and the inner joint member to hold balls as torque transmission members. The inner joint member is spline-fitted by press-fitting an end of an intermediate shaft into the inner diameter of a hole thereof, and is connected to the shaft 55 (55A, 55B) so as to be able to transmit torque.

[0026] The outer joint member 60 is composed of a mouth portion 61 and a shaft portion (also called a stem portion) 62. The mouth portion 61 is cup-shaped with an open end, and has a plurality of tracks extending in the axial direction on its inner spherical surface. The grooves are formed at equal intervals in the circumferential direction. The track grooves extend to the open end of the mouth portion. The inner joint member has a plurality of track grooves formed on its outer spherical surface, the track grooves extending in the axial direction, at equal intervals in the circumferential direction.

[0027] The opening of the mouth portion 61 is closed by a boot 63. The boot 63 is composed of a large diameter portion 63a, a small diameter portion 63b, and a bellows portion 63c connecting the large diameter portion 63a and the small diameter portion 63b. The large diameter portion 63a is fitted onto the opening of the mouth portion 61, and in this state is fastened by a boot band 64. The small diameter portion 63b is fitted onto the boot mounting portion of the shaft 55, and in this state is fastened by the boot band 64.

[0028] The sliding type constant velocity universal joint includes an outer joint member 70, an inner joint member, balls as torque transmission members interposed between the outer joint member 70 and the inner joint member, and a cage having pockets for holding the balls. The outer joint member is spline-fitted by press-fitting the ends of intermediate shafts 55 (55A, 55B) into the inner diameter of a hole thereof, thereby connecting the outer joint member to the shafts so as to be able to transmit torque.

[0029] The outer joint member 70 consists of a mouth portion 71 and a shaft portion (also called a stem portion) 72. A plurality of axially extending track grooves are formed on its inner diameter surface at equal intervals in the circumferential direction, while the inner joint member has a plurality of axially extending track grooves formed on its outer diameter surface at equal intervals in the circumferential direction.

[0030] The opening of the mouth portion 71 is closed by a boot 73. The boot 73 is composed of a large diameter portion 73a, a small diameter portion 73b, and a bellows portion 73c that connects the large diameter portion 73a and the small diameter portion 73b. The large diameter portion is fitted onto the opening of the mouth portion, and in this state is fastened by a boot band 74. The small diameter portion 73b is fitted onto the boot mounting portion of the shaft 55, and in this state is fastened by the boot band 74.

[0031] Meanwhile, fixed type constant velocity universal joints only allow angular displacement, while sliding type constant velocity universal joints allow not only angular displacement but also axial displacement (plunging). Fixed type constant velocity universal joints include a Barfield type constant velocity universal joint (BJ) in which the groove bottom of the track groove is made up of only an arcuate portion, and an undercut free type constant velocity universal joint (UJ) in which the groove bottom of the track groove is made up of an arcuate portion and a straight portion. Sliding type constant velocity universal joints include a tripod type constant velocity universal joint, a double offset type constant velocity universal joint, a cross groove type constant velocity universal joint, and the like. These various types of constant velocity universal joints can be used in the present invention.

[0032] A stem portion 72 of an outer joint member 70 of the sliding type constant velocity universal joints 54A, 54B is connected to a power section 75 including a motor, a reducer, and a differential. Then, the outer joint members 60, 60 of the fixed type constant velocity universal joints 53A, 53B are connected to a wheel bearing device.

[0033] As shown in Fig. 2, the wheel bearing device has a so-called third generation configuration, mainly consisting of an outer member 22, a hub ring 23, an inner ring 24, balls 25 as rolling elements, and a cage 26. In the following explanation, the side that is closer to the outside of the vehicle when assembled to the vehicle is called the outer side (left side in Fig. 2), and the side that is closer to the center is called the inner side (right side in Fig. 2).

[0034] The inner member 21 is composed of a hub ring 23 and an inner ring 24. An inner raceway surface 29 that faces one (the outer side) of the double row outer raceway surfaces 27, 27 of the outer member 22 is formed directly on the outer periphery of the hub ring 23, and a wheel mounting flange (not shown) for mounting a wheel (not shown) is formed integrally with the end of the outer side.

[0035] A cylindrical small diameter step 30 is formed on the outer periphery of the hub ring 23, extending axially from the inner raceway surface 29 to the inner side, and the inner ring 24 is press-fitted into this small diameter step 30 with a predetermined interference. An inner raceway surface 29 is formed on the outer periphery of the inner ring 24, which faces the other (inner side) of the double row outer raceway surfaces 27, 27 of the outer member 22. A plurality of balls 25, 25 are fitted between the outer raceway surfaces 27, 27 of the outer member 22 and the inner raceway surfaces 29, 29 of the inner member 21, and the balls 25 are accommodated in a cage 26 at predetermined intervals in the circumferential direction.

[0036] A pilot 23a having a short cylindrical shape extending toward the outer side is provided on the outer end face of the hub wheel 23. This pilot 23a guides the inner diameter surface (inner circumference) of a rotor of a disc brake (not shown). The opening of the annular space formed between the outer member 22 and the inner member 21 is sealed by a pair of sealing devices 31, 32.

[0037] 1, the outer joint member 60 of the constant velocity universal joint 53 has a shoulder portion 61a forming the bottom of a cup-shaped mouth portion 61, and a stem portion 62 extending in the axial direction from the shoulder portion 61a. The stem portion 62 has a male spline shaft 65 and a threaded portion 66 (see FIG. 3) formed from the male spline shaft 65.

[0038] 2, a female spline hole 67 is provided in the hub wheel 23, and a male spline shaft 65 of the stem portion 62 of the outer joint member 60 is fitted (inserted) into this female spline hole 67, and a nut member is screwed onto the threaded portion 66 of the stem portion 62 protruding from the female spline hole 67. In this way, the hub wheel 23 and the outer joint member of the constant velocity universal joint are integrated together.

[0039] In this case, as shown in Figures 4(a) and (b), the male spline shaft 65 has spline convex teeth 68a and spline concave teeth 68b formed alternately along the circumferential direction on its outer diameter surface, and the outer diameter of the mouse side base portion is made larger than the minimum diameter that satisfies the torque transmission capacity, while the other portions of the male spline shaft 65 have diameters smaller than the outer diameter of the mouse side base portion to satisfy the torque transmission capacity. That is, as shown in Figure 1, the male spline shaft 65 has a large diameter portion 65a at the mouse side base portion, and a small diameter portion 65b on the threaded portion side of this large diameter portion 65a.

[0040] The outer diameter of the base part on the mouse side, that is, the outer diameter of the large diameter part 65a, is the diameter of a circle drawn by the center of the tip surface of the tooth tip of the spline convex tooth 68a, and the diameter (outer diameter) of the small diameter part 65b is also the diameter of a circle drawn by the center of the tip surface of the tooth tip of the spline convex tooth 68a. That is, when the outer diameter of the large diameter part 65a is D1 (see FIG. 4(a)) and the outer diameter of the small diameter part 65b is D2 (see FIG. 4(b)), D1>D2 is set, and if D1 is, for example, about 32.2 mm to 24.4 mm, D1-D2 is set, for example, to about 1 mm to 2 mm.

[0041] In addition, when the overall length of the male spline shaft 65 is L, the length of the large diameter portion 65a is L1, and the length of the small diameter portion 65b is L2, L = L1 + L2, and L1:L2 = approximately 1:2. The cross-sectional shape of the spline convex teeth 68a of the male spline shaft 65 is trapezoidal in the illustrated example, but it may be a mountain shape with a convex arc-shaped apex.

[0042] 4(a) and (b), the female spline hole 67 has spline convex teeth 69a and spline concave teeth 69b formed alternately along the circumferential direction on the inner diameter surface of the shaft hole of the hub wheel 23, and has a large diameter portion 67a formed on the inboard side corresponding to the male spline shaft 65, and a small diameter portion 67b on the outboard side from this large diameter portion 67a. When the outer diameter of the large diameter portion 67a is D3 and the outer diameter of the small diameter portion 67b is D4, D3>D4 is set, for example, to about 1 mm to 2 mm.

[0043] Furthermore, when the overall length of the female spline hole 67 is L5, the length of the large diameter portion 67a is L3, and the length of the small diameter portion 67b is L4, L5 = L3 + L4 is obtained, and L3:L4 = approximately 1:2. The cross-sectional shape of the spline convex teeth 69a of the female spline hole 67 is trapezoidal in the illustrated example, but it may be a mountain shape with a convex arc-shaped apex.

[0044] According to the wheel bearing device of the present invention, the diameter of the spline fit between the stem portion 62 of the constant velocity universal joint 53 and the hub wheel 23 can be increased on the root side. This makes it possible to prevent deformation and wear on the root side. Even when sudden torque transmission occurs (such as when an EV starts moving) in the spline fit between the stem portion 62 of the constant velocity universal joint 53 and the hub wheel 23, it is possible to strengthen the portion where the contact surface pressure increases, suppressing the occurrence of rattle at the fit portion and mitigating stick-slip noise that occurs between the inner member 21 (hub wheel 23) and the outer joint member 60 of the constant velocity universal joint 53 over a long period of time.

[0045] ' In the above embodiment, the spline convex teeth 68a of the male spline shaft 65 extend along the axis of the stem portion 62, but as shown in Fig. 5(a), a torsion angle θ may be imparted to them. When a torsion angle θ is imparted in this manner, there are areas where the spline convex teeth 68a strongly contact the spline concave teeth 69b of the female spline hole 67 and areas where the spline concave teeth 69b are cushioned. This torsion angle θ is set, for example, to about 6' to 14'.

[0046] When the direction of torque transmission when the vehicle is moving forward is the positive rotation of the male spline shaft 65, by imparting a twist angle θ to the spline convex teeth 68a of the male spline shaft 65 in a direction in which the contact of the spline convex teeth 68a is released from the twist of the male spline shaft 65 associated with torque transmission when the vehicle starts, the contact pressure can be reduced and deformation and wear of the female spline hole 67 of the hub wheel 23 can be suppressed.

[0047] 5(b), the generatrix shape of the spline protruding teeth 68a of the male spline shaft 65 may be an arc shape. Even if the generatrix shape is an arc shape, the contact of the spline protruding teeth 68a can be set so as to be released from the twist of the male spline shaft 65 accompanying torque transmission when the vehicle starts, and the contact pressure can be reduced, thereby suppressing deformation and wear of the female spline hole of the hub wheel 23.

[0048] The generatrix shape of the spline convex teeth 68a at the base of the male spline shaft 65 on the mouse side may be wavy. Such a wavy shape increases the number of contact points between the spline convex teeth 68a of the male spline shaft 65 and the spline concave teeth 69b of the female spline hole 67, dispersing the load. As a result, when the vehicle starts moving, the contact of the spline convex teeth 68a can be set to be released from the twist of the male spline shaft 65 accompanying torque transmission, reducing the contact pressure and suppressing deformation and wear of the female spline hole 67 of the hub wheel 23. When the wave shape is used, the number of strong contact points on the rotational direction side can be three or more.

[0049] In addition, in the hub ring 23 of the present wheel bearing device, a hardening treatment portion 80 is formed at the inboard opening of the female spline hole 67. As the thermal hardening treatment, various heat treatments such as laser hardening, high-frequency hardening, and carburizing hardening can be used. Here, high-frequency hardening is a hardening method that applies the principle of placing the part required for hardening in a coil through which a high-frequency current flows, generating Joule heat by electromagnetic induction, and heating a conductive object. In addition, carburizing hardening is a method in which carbon is infiltrated / diffused from the surface of a low-carbon material, and then hardening is performed. Laser hardening is a hardening method in which a high-energy density laser beam is irradiated onto the surface of a part to harden it. Laser irradiation devices include carbon dioxide lasers, solid-state lasers (YAG lasers), and semiconductor lasers. The part that has been laser hardened expands in a convex shape and hardens.

[0050] In other words, since the inboard opening of the female spline hole 67 is a portion that is prone to deformation and wear when a torque load is applied, if the hardened treatment portion 80 is formed in such a portion, deformation and wear can be effectively prevented.

[0051] Incidentally, in an axle module such as that shown in Fig. 3, the lengths (axial lengths) of the intermediate shafts 55 of a pair (left and right) of drive shafts may differ (the torsional rigidities may differ), and for this reason, it is preferable to adjust the torsion angles θ of the male spline shafts 65 in the left and right fixed type constant velocity universal joints, respectively. Also, in an axle module such as that shown in Fig. 3, the spline convex teeth 68a of the left and right male spline shafts 65 may be of the same type or different types.

[0052] Here, the same type means that all of them are given a torsion angle θ, all of them have a generating line shape on a circular arc, and all of them have a wave-shaped generating line shape. The different type means that the spline convex tooth shapes of the mouse side root parts of the left and right constant velocity universal joints are different.

[0053] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. In the above embodiment, balls are used as rolling elements serving as torque transmission means, but tapered rollers may be used. In addition, the wheel bearing device has evolved from a structure in which a double row rolling bearing is used alone, called the first generation, to a second generation having a vehicle body mounting flange integral with an outer member, and further to a third generation in which an inner rolling surface is formed integrally with one side of a double row rolling bearing on the outer periphery of a hub wheel having an integral wheel mounting flange, and even a fourth generation in which a constant velocity universal joint is integrated with a hub wheel and an inner rolling surface of the other side of a double row rolling bearing is formed integrally with the outer periphery of an outer joint member constituting the constant velocity universal joint. Therefore, the present wheel bearing device may be a first to fourth generation wheel bearing device.

[0054] The male spline shaft 65 can be formed by rolling (cold working) using a rolling rack, but the female spline hole 67 cannot be formed by normal broaching because it has a stepped portion. Therefore, it can be formed by vibration pressing. [Explanation of symbols]

[0055] 21 Inner member 22 Outer member 25 Ball 27 Outer raceway surface 28 Wheel mounting flange 29 Inner raceway surface 51A, 52B Drive shaft 53, 53A, 53B, 54A, 54B Constant velocity universal joint 55, 55A, 55B Intermediate shaft 60 Outer joint member 61 Mouse section 62 Stem 65 Male spline shaft 67 Female spline hole 67a Large diameter section 67b Small diameter section 68a spline convex teeth 80 Hardening Processing Section θ Twist angle

Claims

1. A wheel bearing device comprising an outer member having a double row outer raceway surface formed on its inner circumference, an inner member having a double row raceway surface formed on its outer circumference facing the outer raceway surface, and double row rolling elements interposed between raceway surfaces of the outer member and the inner member, the inner member having a hub ring, and a stem portion of a constant velocity universal joint being integrally connected to the hub ring via a spline connection, a wheel bearing device comprising: said stem portion protruding from a bottom of the mouth portion of the outer joint member of the constant velocity universal joint, said stem portion having a male spline shaft fitted into a female spline hole of a hub wheel, said male spline shaft having an outer diameter larger than the minimum diameter which satisfies the torque transmission capacity at a mouse side root portion and other portions of said male spline shaft having diameters smaller than the outer diameter of said mouse side root portion and which satisfy the torque transmission capacity, and a generatrix shape of the spline convex teeth at the mouse side root portion of said male spline shaft being wavy.

2. 2. The wheel bearing device according to claim 1, wherein an inner peripheral portion of an inboard side opening of the female spline hole of the hub wheel is heat-hardened.

3. A power transmission structure having a pair of left and right drive shafts, Each drive shaft is provided with a pair of constant velocity universal joints and an intermediate shaft connecting these constant velocity universal joints, the axial lengths of the intermediate shafts of the left and right drive shafts being different, and the constant velocity universal joints arranged on the wheel side are connected to a wheel bearing device, the wheel bearing device comprising an outer member having a double row outer raceway surface formed on its inner periphery, an inner member having a double row raceway surface formed on its outer periphery facing the outer raceway surface, and double row rolling elements interposed between the raceway surfaces of the outer member and the inner member, the inner member having a hub wheel, and a stem portion of a constant velocity universal joint is integrally connected to this hub wheel via a spline connection, the stem portion being a mouth of an outer joint member of the constant velocity universal joint, a male spline shaft protruding from the bottom of the left and right constant velocity joints and fitted into a female spline hole of the hub wheel, the stem portion being provided with an outer diameter of a mouse side root portion of the male spline shaft larger than the minimum diameter which satisfies the torque transmission capacity, and other portions of the male spline shaft being smaller than the outer diameter of the mouse side root portion so as to satisfy the torque transmission capacity, and at least one of the following is adopted: a torsion angle is imparted to the spline convex teeth, the generatrix shape of the spline convex teeth is made arcuate, or the generatrix shape of the spline convex teeth is made wavy, and the spline convex teeth shapes at the mouse side root portions of the left and right constant velocity joints are made different.

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