Wheel bearing device

Abstract

Wheel bearing device comprising: an outer element (5) which is formed in one piece on its inner circumference with double-row outer walking path surfaces (5a, 5a); an inner element (3) which is formed on its outer perimeters with double-row inner walking path surfaces (1a, 2a) which are opposite the double-row outer walking path surfaces (5a, 5a); and double-row rolling elements (4, 4) which are arranged to roll in a space between the inner running path surfaces (1a, 2a) of the inner element (3) and the outer running path surfaces (5a, 5a) of the outer element (5); a wheel mounting flange (6 or 6') for attaching a wheel over a brake disc, which is attached to a rotating side of one of the outer element (5) or the inner element (3); and Hub bolts (6a) for fastening the wheel, which is secured to the wheel mounting flange (6 or 6') along its periphery at a uniform distance, wherein weight reduction openings (13, 15 or 16) are formed between hub bolts (6a) of the wheel mounting flange (6 or 6'); characterized in that: that an annular groove (7a) enclosing a region in which the hub bolts (6a) are fastened is formed on the outer side surface (7) of the wheel mounting flange (6 or 6'), and that a diameter of a circumcircle (ø A or ø C) circumscribing the weight reduction openings (13, 15 or 16) is dimensioned larger than an outer diameter (ø B) of the annular groove (7a), or the weight reduction openings (13, 15 or 16) are open to an outer circumferential surface of the wheel mounting flange (6 or 6').

Description

Field of invention

[0001] The invention relates generally to a wheel bearing device that can rotatably support a wheel of a vehicle, such as a motor vehicle, and in particular to a wheel bearing device that enables a reduction in the weight of the wheel bearing device and a suppression of brake judder by refining the accuracy of a flatness deviation of a wheel mounting flange, thus increasing the reliability of the wheel bearing device. background

[0002] Disc brakes have become widely popular due to their superior braking performance. However, a problem exists: disc brakes, especially at low speeds, tend to generate vibrations and thus unpleasant noises when braking, as a brake disc is sandwiched between the brake pads. This phenomenon is known as brake judder and has recently been recognized as a new technological issue requiring investigation and improvement due to the need for both high performance and smooth vehicle operation.

[0003] Although no theoretical mechanism causing brake judder has yet been found, it is assumed that one factor is the accuracy of the flatness deviation of a brake pad sliding surface. The accuracy of the flatness deviation is ultimately revealed as the flatness deviation of a side face of the brake disc due to an accumulation of not only the flatness deviation of the brake disc itself, but also of the wheel mounting flange to which the brake disc is attached, the axial deflection of rolling bearings, the accuracy of inner or outer raceway surfaces, and the mounting accuracy of rolling bearings.

[0004] In recent years, measures have been taken with regard to the flatness deviation accuracy of the side surface of the brake disc described above, satisfying conflicting demands for a reduction in the size and weight of the wheel bearing device to improve fuel consumption and for an increase in the stiffness of the wheel bearing device to improve the driving stability of a vehicle.

[0005] An example of a well-known wheel bearing device is in Fig. Figure 7 shows this wheel bearing assembly comprising an inner element 50, an outer element 60, and double-row rolling elements 70, 70. The inner element 50 has a wheel hub 51 and an inner ring 52, which is press-fitted to a section 53 formed on the wheel hub 51. An inner raceway surface 51a is formed on the outer circumference of the wheel hub 51, and the other inner raceway surface 52a is formed on the outer circumference of the inner ring 52. The wheel hub 51 is integrally formed at its outer end with a wheel mounting flange 54 for attaching a wheel (not shown), and hub bolts 55 are attached to the wheel mounting flange 54 at uniform intervals along its periphery.

[0006] On the other hand, the outer element 60 is formed on its outer circumference with a body mounting flange 61, which is designed to be attached to a (not shown) body of a vehicle, and furthermore on its inner circumference with double-row outer running surface 60a, 60a. The double-row rolling elements (balls) 70, 70 are housed in cages 71, 71 so as to roll between the inner and outer running surface 51a, 52a and 60a, 60a.

[0007] Seals 62, 63 are attached to both ends of the outer element 60 to seal annular spaces between the outer element 60 and the inner element 50, thus preventing leakage of lubricating grease trapped in the bearing and the ingress of rainwater or dust from the outside into the bearing.

[0008] An annular groove 56 is formed on the outer side surface 54a of the wheel mounting flange 54, and bolt holes 57 are formed in the annular groove 56 at uniform intervals along the annular groove 56. The hub bolts 55 are secured in the bolt holes by pressing knurled areas 55a of the hub bolts 55 into the bolt holes 57, and a wheel is designed to be secured to the wheel mounting flange 54 via the (not shown) brake disc by tightening (not shown) nuts onto the hub bolts 55.

[0009] The outer surface 54a of the wheel mounting flange 54 is finished after the hub bolts 55 have been pressed in, for example by grinding. This ensures that deformations around the bolt opening 57 or waviness of the side surface 54a, which are caused by forming the bolt openings 57 in the annular groove 56 and pressing in the hub bolts 55, occur predominantly within the annular groove 56, and that the effects on the accuracy of the flatness deviation of the side surface 54a caused by pressing in the hub bolts 55 are essentially suppressed to zero (see, for example, patent document 1 below).

[0010] A wheel bearing assembly is known, for example, from JP 2010-089664 A. Another wheel bearing assembly is known from US 7 614 796 B2. A wheel bearing assembly is also known from JP 2007-126087 A. Prior art document (patent document)

[0011] Patent Document 1: JP 2003-154801 A; Patent Document 2: JP 2010-089664 A; Patent Document 3: US 7,614,796 B2; Patent Document 4: JP 2007-126087 A Description of the invention Problems to be solved by the invention

[0012] However, the wheel bearing device remains state-of-the-art if, as in Fig. Figure 8(a) shows that circular openings (weight reduction openings) 80 are formed between the hub bolts 55. Dirty water and the like, which has penetrated through the weight reduction openings 80, often collects in a space between the outer surface 54a of the wheel mounting flange 54 and a side surface 81a of the brake disc 81, so that rust spots form on the contact surfaces between them. As a consequence, the accuracy of the flatness deviation of the side surface 54a of the wheel mounting flange 54 deteriorates, so that there is a risk of brake judder and that the brake disc 81 becomes permanently bonded to the wheel mounting flange 54 via rust spots, thus making it more difficult to remove the brake disc 81 from the wheel mounting flange 54.

[0013] The present invention was achieved by focusing on a structure capable of readily draining away dirty water and the like that which has entered the weight reduction openings of the wheel mounting flange, thereby preventing dirty water and the like from remaining in a space between the wheel mounting flange and the brake disc, and it is an object of the present invention to create a wheel bearing device whose own weight can be reduced and whose reliability is increased by refining the accuracy of the flatness deviation of the wheel mounting flange, so that the formation of brake judder is suppressed. Means of solving the problems

[0014] To achieve the aforementioned objectives, according to claim 1 of the present invention, a wheel bearing device is provided comprising: an outer element integrally formed on its inner circumference with double-row outer running surface surfaces; an inner element formed on its outer circumferences with double-row inner running surface surfaces opposite the double-row outer running surface surfaces; and double-row rolling elements that are arranged to roll in a space between the inner running surface surfaces of the inner element and the outer running surface surfaces of the outer element; a wheel mounting flange for attaching a wheel over a brake disc that is mounted on a rotating side of either the outer element or the inner element; and hub bolts for securing the wheel, which is secured to the wheel mounting flange at a uniform distance along its periphery;characterized in that an annular groove enclosing a region in which the hub bolts are fastened is formed on the outer side surface of the wheel mounting flange; that weight reduction openings are formed between hub bolts of the wheel mounting flange; and that a diameter of a circumscribed area around the weight reduction openings is dimensioned larger than an outer diameter of the annular groove, or the weight reduction openings are open towards an outer circumferential surface of the wheel mounting flange.

[0015] According to the present invention according to claim 1, the wheel bearing device has a wheel mounting flange for attaching a wheel over a brake disc which is mounted on a rotating side of one of the outer elements or the inner element, and hub bolts for attaching the wheel which is secured to the wheel mounting flange at a uniform distance along its periphery, and is characterized in that an annular groove which encloses a region in which the hub bolts are attached is formed on the outer side surface of the wheel mounting flange, and that weight reduction openings are formed between hub bolts of the wheel mounting flange;and that a diameter of a circumscribed area around the weight reduction openings is dimensioned larger than an outer diameter of the annular groove, or that the weight reduction openings are open towards an outer circumferential surface of the wheel mounting flange, it is possible to provide a wheel bearing device that is able to easily drain away dirty water and the like that has entered the weight reduction openings of the wheel mounting flange, preventing the dirty water and the like from remaining in a space between the outer surface of the wheel mounting flange and the side surface of the brake disc, and also enables a reduction in weight and an increase in reliability by refining the accuracy of the flatness deviation of the wheel mounting flange, thus suppressing the formation of brake judder.

[0016] According to claim 2, it is preferred that the outer surface of the wheel mounting flange is designed as a machined surface, which is machined after the hub bolts have been pressed in. This makes it possible to achieve the surface finishing process even by means of a simple turning operation, thus reducing manufacturing costs. Additionally, it is possible to suppress brake judder by refining the accuracy of the flatness deviation of the wheel mounting flange, thereby reducing the influence on the flatness deviation caused by the pressing in of the hub bolts.

[0017] According to claim 3, it is also preferred that each of the weight-reduction openings of the wheel mounting flange is designed as a conically tapered opening that gradually widens towards the inside. This facilitates the drainage of dirty water and the like from the weight-reduction openings, preventing the dirty water and the like from remaining in a space between the wheel mounting flange and the brake disc.

[0018] According to claim 4, it is preferred that radially extending drainage grooves are formed by machining a section of each weight reduction opening of the wheel mounting flange. This allows dirty water and the like to be easily drained from the weight reduction openings via the drainage grooves, even though the weight reduction openings are formed in a region of the annular groove, thus preventing dirty water and the like from remaining in a space between the wheel mounting flange and the brake disc.

[0019] According to claim 5, it is preferred that a radially extending reinforcing rib is formed as a structural component on the inner surface of the wheel mounting flange in an area where the hub bolt is secured. This makes it possible to reduce the weight of the wheel mounting flange while maintaining its strength and stiffness.

[0020] According to claim 6, it is also preferred that machined areas are formed on the outer circumference of the wheel mounting flange between bolt holes into which the hub bolts are pressed, maintaining a distance near the bolt holes, and that each of the machined areas is formed with a circular arc shape such that the deepest parts of the machined areas are positioned near a pitch circle diameter of the bolt holes. This makes it possible to reduce the weight and size of the wheel mounting flange while maintaining its strength and stiffness, and also to suppress the formation of brake judder by refining the accuracy of the flatness deviation of the wheel mounting flange through a reduction in the deformation of the wheel mounting flange attributable to its heat treatment.

[0021] According to claim 7, it is preferred that the diameter of the deepest areas of the cut-out sections is smaller than the outer diameter of the annular groove. This allows the weight-reduction openings to be open towards the outer circumference of the wheel mounting flange. Accordingly, it is possible to easily drain away dirty water and the like that which has penetrated the weight-reduction openings of the wheel mounting flange through the deepest areas of the machined sections, thus preventing dirty water and the like from remaining in a space between the wheel mounting flange and the brake disc. Furthermore, this reduces the dead weight and increases reliability by refining the accuracy of the flatness deviation of the wheel mounting flange, thereby suppressing brake judder. Effects of the invention

[0022] According to the wheel bearing device of the present invention, it comprises an outer element which is integrally formed on its inner circumference with double-row outer running surface surfaces; an inner element which is formed on its outer circumferences with double-row inner running surface surfaces which are opposite the double-row outer running surface surfaces; and double-row rolling elements which are provided to roll in a space between the inner running surface surfaces of the inner element and the outer running surface surfaces of the outer element; a wheel mounting flange for attaching a wheel over a brake disc which is attached to a rotating side of one of the outer element or the inner element;and hub bolts for fastening the wheel, which is secured to the wheel mounting flange at a uniform distance along its periphery, and is characterized in that an annular groove enclosing a region in which the hub bolts are fastened is formed on the outer side surface of the wheel mounting flange, and that weight reduction openings are formed between hub bolts of the wheel mounting flange;and that a diameter of a circumscribed area around the weight reduction openings is dimensioned larger than an outer diameter of the annular groove, or that the weight reduction openings are open towards an outer circumferential surface of the wheel mounting flange, it is possible to provide a wheel bearing device that is able to easily drain away dirty water and the like that has entered the weight reduction openings of the wheel mounting flange, preventing dirty water and the like from remaining in a space between the wheel mounting flange and the brake disc, and whose own weight can be reduced and whose reliability can be increased by refining the accuracy of the flatness deviation of the wheel mounting flange, so that the formation of brake judder is suppressed. Brief description of the drawings [ Fig. 1] A longitudinal section view of a first embodiment of the wheel bearing device of the present invention; [ Fig. 2] A side view of a wheel hub according to Fig. 1; [ Fig. 3] A partially enlarged view showing a weight reduction opening after Fig. 1 shows; [ Fig. 4(a)] A side view showing a modification according to Fig. 1 shows; [ Fig. 4(b)] A partially enlarged view showing a weight reduction opening after Fig. 4(a) shows; [ Fig. 5(a)] A side view showing a further modification according to Fig. 1 shows; [ Fig. 5(b)] A partially enlarged view showing a weight reduction opening after Fig. 5(a) shows; [ Fig. 6(a)] A side view showing a second embodiment of the wheel bearing device of the present invention; [ Fig. 6(b)] A longitudinal section view according to Fig. 6(a); [ Fig. 6(c)] A partially enlarged view showing a weight reduction opening after Fig. 6(b) shows; [ Fig. 7(a)] A side view of a wheel bearing device from the prior art; [ Fig. 7(b)] A longitudinal section view according to Fig. 7(a); [ Fig. 8(a)] A side view of a wheel bearing device in which weight reduction openings are provided in a wheel mounting flange according to Fig. 7(a) are trained; and [ Fig. 8(b)] A partially enlarged view showing a weight reduction opening after Fig. 8(a) shows. Preferred method of implementing the invention

[0023] A preferred embodiment of the present invention is a wheel bearing device comprising: an outer element which is integrally formed on its outer circumference with a body mounting flange for attachment to a steering knuckle which forms a suspension device and which is also integrally formed on its inner circumference with double-row outer running surface surfaces;an inner element comprising a wheel hub and an inner ring, wherein the wheel hub is integrally formed at one end with a wheel mounting flange and on its outer circumference with an inner running surface opposite one of the double-row outer running surfaces and having a cylindrical section extending axially from the inner running surface, wherein the inner ring is press-fitted to the cylindrical section of the wheel hub and has on its outer circumference an inner running surface opposite the other of the double-row outer running surfaces; double-row rolling elements which are provided to roll in a space between the inner running surfaces of the inner element and the outer running surfaces of the outer element;and hub bolts for fastening a wheel, which are attached to the wheel mounting flange at uniform intervals along its periphery, characterized in that an annular groove enclosing a region in which the hub bolts are installed is formed on the outer side surface of the wheel mounting flange, that the outer surface of the wheel mounting flange is formed as a machined surface which is machined after the hub bolts have been pressed in, weight reduction openings are formed between hub bolts of the wheel mounting flange; and that a diameter of a circumcircle that describes the weight reduction openings is dimensioned larger than an outer diameter of the annular groove. First embodiment

[0024] Embodiments of the present invention are described with reference to the accompanying drawings. Fig. Figure 1 shows a longitudinal section view of a first embodiment of the wheel bearing device of the present invention; Fig. 2 shows a side view of a wheel hub according to Fig. 1; Fig. Figure 3 illustrates a weight reduction opening in a partially enlarged view. Fig. 1; Fig. 4(a) illustrates a modification according to in a side view Fig. 1; Fig. Figure 4(b) shows a partially enlarged view of a weight reduction opening after Fig. 4(a); Fig. 5(a) illustrates in a side view a further modification according to Fig. 1; and Fig. Figure 5(b) shows a side view of a weight reduction opening after Fig. 5(a). In the description of this specification, an outer surface of a bearing device is defined as when it is attached to a vehicle (in Fig. 1(b) on the left side) is referred to as the ‘outside’, and an inside of a bearing device when it is attached to a vehicle (in Fig. 1(b) on the right side) is referred to as the “inside”.

[0025] The in Fig. 1 The wheel bearing device shown is of a so-called “third generation” design for a drive wheel and contains an inner element 3 with a wheel hub 1 and an inner ring 2 which is press-fitted to the wheel hub 1, and an outer element 5 which is attached to the inner element 3 via a double row of rolling elements (balls) 4, 4.

[0026] The wheel hub 1 is integrally formed at its outer end with a wheel mounting flange 6 for attaching a wheel over a brake disc or brake drum (not shown). Its outer circumference features an inner running surface 1a and a cylindrical section 1b extending axially from the inner running surface 1a. A toothed (or keyed) groove 1c for transmitting torque is formed on the inner circumference of the wheel hub 1. Hub bolts 6a are secured to the wheel mounting flange 6 at evenly spaced positions along its circumference.

[0027] The inner ring 2, on the other hand, is formed on its outer circumference with an inner running surface 2a and is attached to the outer circumference of the cylindrical area 1b of the wheel hub 1 by means of a predetermined engagement via a press fit and is axially secured to the cylindrical section 1b by a sealed section 1d, which is formed under a predetermined bearing preload by a radially outwardly directed plastic deformation of one end of the cylindrical area 1b.

[0028] An outer surface (surface to which a brake disc is attached) 7 of the wheel mounting flange 6 is primarily machined, for example by turning, and additionally formed with an annular groove (circumferential groove) 7a having a predetermined width. Bolt holes 8 are formed in the annular groove 7a at uniformly spaced positions centered along the groove width. Secondarily, the side surface 7 is machined, for example by turning, after knurled sections 9 of the hub bolts 6a have been pressed into the bolt holes 8. The second machining operation can be performed by another machining operation, for example by a milling machine or a grinding machine.

[0029] The wheel hub 1 is made of a medium-carbon steel, such as S53C, which has 0.40–0.80 wt% carbon, and is hardened by high-frequency induction hardening to achieve a surface hardness of 50–64 HRC over the inner raceway surface 1a and a region extending from an inner base 6b of the wheel mounting flange 6, which forms a sealing web section of a seal 10, to the cylindrical section 1b. The riveted section 1d is not hardened and retains its hardness after forging. This not only improves the sliding friction properties of the base section 6b of the wheel mounting flange 6 but also provides sufficient mechanical strength against a rotating bending load applied to the wheel mounting flange 6.In addition, it is possible to improve the friction wear property of the cylindrical area 1b, on which the inner ring 2 is press-fitted, and to carry out the mortising process of the mortised section 1d without causing microcracks.

[0030] The inner ring 2, on the other hand, is made of high-carbon chromium steel, such as SUJ2, and is immersion-hardened to its core to achieve a hardness of 58–64 HRC. The rolling elements (balls) 4 are made of high-carbon chromium steel, such as SUJ2, and are immersion-hardened to their cores to achieve a hardness of 62–67 HRC.

[0031] The outer element 5 is formed on its outer circumference with a body mounting flange 5b, which is designed to be attached to a (not shown) axle stub that forms part of the suspension and is also formed on its inner circumference with double-row outer running surface surfaces 5a, 5a, which are opposite the inner running surface surfaces 1a, 2a of the inner element 3. The double-row rolling elements 4, 4 are embedded in cages 12 so as to roll between the inner and outer running surface surfaces 1a, 2a and 5a, 5a.

[0032] The outer element 5 is made of a medium-carbon steel, such as S53C, which has 0.40–0.80% carbon by weight. At least the outer raceway surfaces 5a, 5a are hardened by high-frequency induction hardening to achieve a surface hardness of 58–64 HRC. Seals 10, 11 are arranged at annular side openings formed between the outer element 5 and the inner element 3 to prevent grease from escaping the bearing and rainwater or dust from entering the bearing.

[0033] Although a wheel bearing device formed by a double-row angular contact ball bearing using balls as rolling elements 4 is shown here, the present invention is not limited to such a bearing, and a double-row tapered roller bearing using tapered rollers as rolling elements 4 can also be used. Although the bearing shown here is of the third generation design, the present invention can furthermore be applied to bearings of the second generation design, in which a pair of inner rings are press-fitted to the cylindrical section, or to bearings of the fourth generation design, in which inner raceway surfaces are formed directly on the outer circumferences of a wheel hub or an outer joint element of a (not shown) constant velocity joint.

[0034] As in Fig. As shown in Figure 2, in an area where the hub bolt 6a is secured, a reinforcing rib 21 is formed as a structural component on the inner surface of the wheel mounting flange 6. Each reinforcing rib 21 has a width that essentially corresponds to a forming part of each bolt opening 8 and extends radially outwards from the annular base body 6b of the wheel mounting flange 6 (see Figure 2). Fig. 1).

[0035] If the width of the annular groove 7a, which is formed on the outer surface 7 of the wheel mounting flange 6, is larger, it is preferred at one point that the side surface 7 can be machined by secondary machining after the hub bolts 6a have been pressed in. However, there is a risk that the contact area between the side surface of the brake disc and the side surface 7 of the wheel mounting flange would be reduced, and the strength and stiffness of the wheel mounting flange 6 would be reduced, and the wheel mounting flange would therefore be deformed by tightening the nuts.In this embodiment, it was found that the contact area between the brake disc and the wheel mounting flange 6 is not significantly reduced if the distance from the outer diameter of each hub bolt 6a to the annular groove 7a is at least 1 mm, and that deformation of the wheel mounting flange during wheel fastening with nuts can be avoided, thus minimizing any deterioration in the flatness deviation of the brake disc's side surface. If, in this case, a distance of more than 1 mm from the outer diameter of each hub bolt 6a is maintained, the applicability of a machining operation using a "bite" without mutual interference between the bit and the hub bolts 6a is not impaired.

[0036] As described above, the deformation of the outer surface 7, which would be caused by pressing in hub bolts 6a, is minimized by forming the annular groove 7a on the side surface 7 of the wheel mounting flange 6. Furthermore, if the secondary machining is performed on the outer surface 7 where the brake disc makes contact, the flatness deviation caused by pressing in hub bolts 6a is significantly reduced, and the formation of brake judder is thus suppressed by refining the accuracy of the flatness deviation of the wheel mounting flange 6.

[0037] Although the present invention has been described with reference to an embodiment in which the primary machining of the outer surface 7 of the wheel mounting flange 6 is carried out prior to pressing in the hub bolts 6a, and the secondary machining is subsequently carried out after pressing in the hub bolts 6a, the present invention is not limited to such an embodiment. For example, it is possible to carry out a primary machining operation comprising a rough turning operation and a semi-finished turning operation prior to pressing in the hub bolts 6a, and subsequently to carry out a secondary machining operation (a heat treatment turning operation) after pressing in the hub bolts 6a.Furthermore, it is possible to dispense with the turning process before pressing in the hub bolts 6a, while maintaining a forged surface condition, and to carry out the secondary machining (a heat treatment turning process) after pressing in the hub bolts 6a.

[0038] Circular openings (weight reduction openings) 13 are formed by forging between hub bolts 6a of the wheel mounting flange 6 at uniform intervals along its periphery. The weight reduction openings 13 extend beyond the outer diameter of the annular groove 7a. That is, if the diameter of a circle circumscribing the weight reduction openings 13 is defined as "A" and the outer diameter of the annular groove 7a is defined as "B", then A > B is set. Accordingly, such an arrangement of the weight reduction openings 13 and the annular groove 7a, as shown in an enlarged view according to Fig. 3 shows the dirty water and the like that has entered the weight reduction openings 13, as indicated by an arrow in Fig. Figure 3 shows that the fluid can be easily discharged through the weight reduction openings 13 without remaining in a space between the side surface 7 of the wheel mounting flange 6 and the side surface 14a of the brake disc 14. This makes it possible to create a wheel bearing device with reduced weight and increased reliability by refining the accuracy of the flatness deviation of the wheel mounting flange 6, thereby suppressing brake judder.

[0039] Fig. Figure 4 shows modified circular openings, i.e., weight reduction openings 15, of the type described above. Similar to the weight reduction openings 13 of the first embodiment, the diameter “A” of a circle circumscribing the weight reduction openings 15 is as shown in Figure 4. Fig. 4(a) shown, larger than the outer diameter “B” of the annular groove 7a. In this modification, an inner circumferential surface of each of the weight reduction openings 15 tapers conically at an inclined angle θ, while, as in Fig. 4 (b) shown, gradually widens towards the inside of the wheel mounting flange 6. Accordingly, it is possible to more easily drain dirty water and the like from the weight reduction openings 15, preventing the dirty water and the like from remaining in a space between the side surface 7 of the wheel mounting flange 6 and the side surface 14a of the brake disc 14.

[0040] Fig. Figure 5 shows a further modification of the previously described weight reduction openings 13. The weight reduction openings 16 of this modification are designed such that, as in Fig. 5 (a) shown, are arranged at radially inner points of the outer diameter of the annular groove 7a. That is, the diameter “C” of a circle circumscribing the weight reduction openings 16 is smaller than the outer diameter “B” of the annular groove 7a (C < B). In addition, radially extending discharge grooves 17 are formed by machining a section of each weight reduction opening 16 of the wheel mounting flange 6' to make the discharge grooves 17 open to the outer circumferential surface of the wheel mounting flange 6'. This makes it possible to drain dirty water and the like from the weight reduction openings 16 through the drainage grooves 17 even when the weight reduction openings 16 are formed within an area of ​​the annular groove 7a, preventing the dirty water and the like from remaining in a space between the outer surface 7 of the wheel mounting flange 6' and the side surface 14a of the brake disc 14. Second embodiment

[0041] Fig. 6(a) illustrates in a side view a second embodiment of the wheel bearing device of the present invention; Fig. 6(b) shows a longitudinal section view according to Fig. 6(a); and Fig. Figure 6(c) illustrates a weight reduction opening according to a partially enlarged view. Fig. 6(b). The second embodiment differs from the first embodiment essentially only in the arrangement of the wheel mounting flange, and therefore the same reference numerals are used here as for the first embodiment, and descriptions thereof are omitted.

[0042] The in Fig. 6(b) The wheel bearing device shown is of the so-called “third generation” design for a drive wheel and includes an inner element 19 with a wheel hub 18 and an inner ring 2 which is press-fitted to the wheel hub 18, and an outer element 5 which is attached to the inner element 19 via a double row of rolling elements (balls) 4, 4.

[0043] The wheel hub 18 is integrally formed at its outer end with a wheel mounting flange 20 for attaching a wheel over a brake disc (not shown) and has an inner running surface 1a and a cylindrical section 1b extending axially from the inner running surface 1a on its outer circumference. A toothed section 1c for torque transmission is formed on the inner circumference of the wheel hub 18, and hub bolts 6a are secured to the wheel mounting flange 20 at evenly spaced positions along its circumference.

[0044] As in Fig. As shown in Figure 6(a), a reinforcing rib 21 is formed as a structural component on the inner surface of the wheel mounting flange 20 in an area where the hub bolt 6a is secured. Each reinforcing rib 21 has a width that substantially corresponds to a forming part of each bolt opening 8 and extends radially outwards from the annular base body 6b of the wheel mounting flange 20.

[0045] Additionally, cutouts 22 are formed on the outer circumference of the wheel mounting flange 20 between bolt holes 8. These cutouts all have a circular arc shape, with a distance maintained near the bolt holes 8. The circular arc of each cutout 22 is arranged such that its deepest areas 22a are located near a pitch circle diameter PCDb of the bolt holes 8. That is, the cutouts 22 are located radially outside the pitch circle diameter PCDb of the bolt holes 8 and are smoothly extended to the outer circumference of the wheel mounting flange 20. The center of curvature of each cutout is located on an extension of a straight line passing through the center of the wheel hub 18 and a central point between adjacent bolt holes 8, and the radius of curvature R1 is set to R1 = 0.7 ~ 1.5 PCDb.This makes it possible to reduce the weight and size of the wheel hub 18 while maintaining its strength and stiffness, and also to suppress the formation of brake judder by refining the accuracy of a flatness deviation of the wheel mounting flange 20 by reducing a deformation of the wheel mounting flange 20 which is due to its heat treatment.

[0046] In this case, if the radius of curvature R1 is dimensioned with R1 < 0.7 PCDb, the plastic flow of forged material would be restricted, and the accuracy would be correspondingly degraded by the formation of a depression or similar feature. Conversely, the weight reduction effect achieved by the cut-out areas 22 could not be expected if the radius of curvature R1 is dimensioned with R1 > 1.5 PCDb.

[0047] Generally, such a wheel hub is formed by hot forging. In the case of the wheel mounting flange, which has the shape of a flower and whose material between the bolt holes 8 is insufficient, it is usually necessary to extrude excess forged material between tools (a punch and / or die) as burrs to improve the forging accuracy when the wheel hub is formed by a so-called closed forging process, in which upsetting parts of the wheel hub are restricted. However, since the machined areas 22 are positioned outside the PCDb of the bolt holes, and sufficient material is present between the bolt holes 8, it is possible, in the case of the wheel hub 18 of this embodiment, to carry out the forging process efficiently and accurately without blocking a plastic flow of material.Since the closed forging process allows corner areas, stepped areas and chamfered areas of material to be perfectly formed and thus the removal of burrs can be kept to a minimum, it is possible to reduce manufacturing costs by reducing the number of manufacturing steps.

[0048] The annular groove 23a is formed on the outer side surface 23 of the wheel mounting flange 20, similar to the embodiment described above. The annular groove 23a has a discontinuous shape, since the wheel mounting flange 20 has a flower-like shape instead of the circular shape of the preceding wheel mounting flange 6. The bolt holes 8 are formed at a uniform distance along the annular groove 23a, centered on both the width of the groove and the hub bolts 6a. Secondary machining of the side surface 23 is carried out by turning after the hub bolts 6a have been pressed into the bolt holes 8.

[0049] The weight-reduction openings (circular openings) 24 are formed by forging at uniform intervals along the circumference of the wheel mounting flange 20 between the hub bolts 6a. The weight-reduction openings 24 are arranged radially within the outer diameter of the annular groove 23a. That is, the diameter D of the deepest areas 22a of the cut-out areas 22 is smaller than the outer diameter B of the annular groove 23a (D < B). As shown in Fig.As shown in Figure 6(c), this allows dirty water and the like, which has entered the weight reduction openings 24 of the wheel mounting flange 20, to be easily drained through the deepest areas 22a of the cut-out areas 22, preventing the dirty water and the like from remaining in a space between the outer surface 23 of the wheel mounting flange 20 and the side surface 14a of the brake disc 14, and also reduces its own weight and increases reliability by refining the accuracy of a flatness deviation of the wheel mounting flange 20, thus suppressing the formation of brake judder.

[0050] The present invention has been described with reference to preferred embodiments. Naturally, after studying the foregoing detailed description, the person skilled in the art will think of modifications and variations. It is intended that the present invention should encompass all such variations and modifications, provided they fall within the scope of the appended claims or their equivalent meanings. Applicability in industry

[0051] The present invention can be used in connection with a wheel bearing device of the second to fourth generation types, which is provided with a rotating wheel, for example a wheel hub and the like, which has a wheel mounting flange at one end. Reference symbol list 1.18 Wheel hub 1a, 2a inner walking path area 1b cylindrical section 1c gearing 1d crimped section 2 inner ring 3, 19 inner element 4 rolling element 5 outer element 5a outer walking path area 5b Body mounting flange 6, 6', 20 wheel mounting flange 6a Hub bolts 6b internal base of the wheel mounting flange 7, 23 outer surface of the wheel mounting flange 7a, 23a Ring groove 8 bolt opening 9 knurled section 10, 11 Seal 12 cage 13, 15, 16, 24 circular opening 14 brake disc 14a Side surface of the brake disc 17 Laxative 21 Reinforcing rib 22 machined part 22a deepest section 50 inner element 51 Wheel hub 51a, 52a inner walking path area 52 inner ring 53 cylindrical section 54 Wheel mounting flange 54a Side surface of the wheel mounting flange 55 hub bolts 55a Knurling 56 Ring groove 57 bolt opening 60 outer element 60a outer walking path area 61 Wheel mounting flange 62 Seal 63 Seal 70 balls 71 cage 80 Weight Reduction Opening 81 Brake disc 81a Side surface of the brake disc A, C Diameter of a circle that circumscribes a circular opening B Outer diameter of the ring groove D Outer diameter of the deepest section of the cut-out area PCDb rolling circle diameter of the bolt holes R1 Radius of curvature of the cut-out area θ inclined angle

Claims

[1] Wheel bearing device comprising: an outer element (5) which is formed in one piece on its inner circumference with double-row outer walking path surfaces (5a, 5a); an inner element (3) which is formed on its outer perimeters with double-row inner walking path surfaces (1a, 2a) which are opposite the double-row outer walking path surfaces (5a, 5a); and double-row rolling elements (4, 4) which are arranged to roll in a space between the inner running path surfaces (1a, 2a) of the inner element (3) and the outer running path surfaces (5a, 5a) of the outer element (5); a wheel mounting flange (6 or 6') for attaching a wheel over a brake disc, which is attached to a rotating side of one of the outer element (5) or the inner element (3); and Hub bolts (6a) for fastening the wheel, which is secured to the wheel mounting flange (6 or 6') along its periphery at a uniform distance, wherein weight reduction openings (13, 15 or 16) are formed between hub bolts (6a) of the wheel mounting flange (6 or 6'); characterized by : that an annular groove (7a) enclosing a region in which the hub bolts (6a) are fastened is formed on the outer side surface (7) of the wheel mounting flange (6 or 6'), and that a diameter of a circumcircle (ø A or ø C) circumscribing the weight reduction openings (13, 15 or 16) is dimensioned larger than an outer diameter (ø B) of the annular groove (7a), or the weight reduction openings (13, 15 or 16) are open to an outer circumferential surface of the wheel mounting flange (6 or 6'). [2] Wheel bearing device according to claim 1, wherein the outer surface (7) of the wheel mounting flange (6 or 6') is designed as a machined surface which is machined after the hub bolts (6a) have been pressed in. [3] Wheel bearing device according to claim 1, wherein each of the weight reduction openings (15) of the wheel mounting flange (6) is designed as a conically tapered opening (15) which gradually widens towards the inside. [4] Wheel bearing device according to claim 1, wherein radially extending discharge grooves (17) are formed by machining a section of each weight reduction opening (16) of the wheel mounting flange (6'). [5] Wheel bearing device according to any one of claims 1 to 4, wherein a radially extending reinforcing rib (21) is formed on the inner surface of the wheel mounting flange (6 or 6') as a structural component in an area in which the hub bolt (6a) is secured. [6] Wheel bearing device according to claim 1, wherein machined areas (22) are formed on the outer circumference of the wheel mounting flange (20) between bolt openings (8) into which the hub bolts (6a) are pressed, wherein a distance is maintained in the vicinity of the bolt openings (8), and all machined areas (22) are formed with a circular arc shape, such that the deepest areas (22a) of the machined areas (22) are positioned in the vicinity of a pitch circle diameter (PCDb) of the bolt openings (8). [7] Wheel bearing device according to claim 6, wherein a diameter (D) of the deepest areas (22a) of the machined areas (22) is smaller than an outer diameter (B) of the annular groove (23a) (D < B).

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