Bearing unit for wheel and manufacturing method thereof

Abstract: A bearing unit for a wheel has a rotary ring (16) whose raceway surface is hardened by a thermal process. In this bearing unit, the side surface of a fitting flange (13) for fixedly joining a rotary body for braking and a wheel, is formed by working in a predetermined configuration after the raceway surface of the rotary ring has been subjected to the thermal process. The raceway surface of the rotary ring is worked in a predetermined configuration and dimensions on the basis of the side surface of said fitting flange. This bearing unit can restrain disagreeable noises and vibration from being caused upon braking.

Description: The present invention relates to an improvement of a method of manufacturing a bearing unit for a wheel. US 5,494,358 discloses a method of manufacturing a bearing unit for a wheel, said bearing unit comprising: a static ring having a plurality of static raceway surfaces and supported by a suspension structure in use; a rotary raceway ring having a plurality of rotary raceway surfaces; a plurality of rolling members interposed between the static raceway surfaces and the corresponding rotary raceway surfaces; and a fitting flange, having an internal surface and an external surface, and being provided on an outer peripheral surface of said rotary ring, wherein, in use, a rotary braking body is fixedly joined to the external surface by a plurality of studs disposed on the same circumference as each other of the fitting flange, said method comprising: a step of working the external surface of said fitting flange in a predetermined configuration and a step of hardening an outer peripheral surface of an intermediate portion of said rotary ring by a hardening process. A wheel 1 constituting a travelling wheel of an automobile and a rotor 2 constituting a disk brake classified as a braking device, or rotary braking body, are rotatably supported by a knuckle 3 as a component of a suspension on the basis of, for example, a structure shown in FIG. 4. To be more specific, a circular support hole 4 is formed in the knuckle 3. An outer ring 6 defined as a static ring constituting a bearing unit 5 for a wheel, to which the present invention is applied, is fixed to within the support hole 4a by use of a plurality of bolts 7. On the other hand, the wheel 1 and the rotor 2 are fixedly joined through a plurality of studs 9 and a plurality of nuts 10 to a hub 8 as a component of the wheel bearing unit 5. Outer ring double raceways 11a, 11b each serving as a static-side raceway surface are formed in an inner peripheral surface of the outer ring 6, and a joint flange 12 is provided on an outer peripheral surface thereof. The thus configured outer ring 6 is fixed to the knuckle 3 by joining the joint flange 12 to the knuckle 3 with the bolts 7. By contrast, a fitting flange 13 is provided at a portion of the hub 8 and protrudes from an aperture of an outer side end (the term "outer or external" implies an outside portion in a widthwise direction when assembled to the automobile, i.e., the left side in each drawing. In contrast, the term "inner or internal" implies a central portion in the widthwise direction when assembled to the automobile, viz., the right side in each of the components.) of the outer ring 6. The wheel 1 and the rotor 2 are fixedly joined through the studs 9 and the nuts 10 to one single surface (an external surface in the illustrated example) of the fitting flange. Further, an inner ring raceway 14a is formed in a portion, facing to the more external raceway 11a of the outer ring double raceways 11a, 11b, of the outer peripheral surface of the intermediate portion of the hub 8. Moreover, the inner ring 16 is fixedly fitted onto a small-diameter stepped portion 15 provided at an inner side end of the hub 8. Then, the inner ring raceway 14b formed in the outer peripheral surface of the inner ring 16 is disposed facing to the more internal raceway 11b of the outer ring double raceways 11a, 11b. Balls 17, 17 each defined as a rolling member are provided in a rollable manner by pluralities between the outer ring raceways 11a, 11b and the inner ring raceways 14a, 14b in a state of being held by retainers 18, 18. Based on this construction, a double-row angular ball bearing with a back face combination is structured, the hub 8 is rotatably supported in the outer ring 6, and a radial load and a thrust load are supported in a sustainable manner. Note that seal rings 19a, 19b are provided between inner peripheral surfaces of two side ends of the outer ring 6, an outer peripheral surface of an intermediate portion of the hub 8 and an outer peripheral surface of an inner side end of the inner ring 16, thus cutting off a space accommodating the balls 17, 17 from the outside space. Further, in the illustrated example, the wheel bearing unit 5 is structured for a drive wheel (corresponding to a rear wheel of a FR car and an RR car, a front wheel of an FF car, and whole wheels of a 4WD car), and hence a central portion of the hub 8 is formed with a spline hole 20. Then, a spline shaft 22 of a constant velocity joint 21 is inserted into the spline hole 20. When using the roll bearing unit 5 for the wheel described above, as shown in FIG. 4, the outer ring 6 is fixed to the knuckle 3, and the rotor 2 and the wheel 1 assembled with an unillustrated tire are fixed to the fitting flange 13 of the hub 8. Further, the rotor 2 of those components is combined with an unillustrated support and an unillustrated caliper which are fixed to the knuckle 3, thus constituting a disk brake for braking. When braking, a pair of pads provided with the rotor being interposed therebetween are pressed against the two side surfaces of the rotor 2. It is a known fact that vibrations called judder followed by disagreeable or annoying noises often occur when braking the wheels of the automobile. One of a variety of known causes of those vibrations may be non-uniform friction between the side surface of the rotor 2 and the lining of the pad, however, deflections of the rotor 2 are also known as another large cause. More specifically, the side surface of the rotor 2 should be . fundamentally right-angled to a rotational center of the rotor 2, however, a perfect perpendicularity is hard to obtain due to an inevitable manufacturing error. As a result, the side surface of the rotor 2 inevitably deflects more or less in directions of the rotational axis (right and left directions in FIG. 4) when the automobile travels. If such deflections (displacement quantities in the right and left directions in FIG. 4) increase, and if the linings of the pair of pads are pressed against the two side surfaces of the rotor 2 for braking, the judder occurs. Then, the contact between both surfaces of the rotor 2 and the respective linings of the pad becomes non-uniformed, wherein a partial abrasion of the linings is caused. It is of much importance for restraining the judder occurred by such causes to decrease (axial) deflections of the side surface of the rotor 2 (to enhance the perpendicularity of the side surface to the central axis of rotation). Then, it is required that a perpendicularity of a fitting surface (one side surface of the fitting flange 13) of the fitting flange 13 to the rotational center of the hub 8 and a surface accuracy of the fitting surface itself be enhanced for restraining those deflections. Many factors exert influence upon the perpendicularity and the surface accuracy. However, the factors having an especially large influence on perpendicularity may be the relationchip between the fitting surface and the raceway surface (between the outer ring raceways 11a, 11b and the inner ring raceways 14a, 14b). Thermal process deformation influences surface accuracy. It is desirable, therefore, to provide an accurate positional relationship between the one side surface of the fitting flange 13, the inner ring raceway 14a and the small-diameter stepped portion 15, and to provide accurate configurations and dimensions of those components. If the accuracy of the configurations and the dimensions of the inner ring raceway 14a and of the small-diameter stepped portion 15 are enhanced in relation to the fitting surface, the perpendicularity of the fitting surface to the rotational center of the hub 8 can be enhanced. Moreover, if removing the thermal process deformation out of the fitting surface, the surface accuracy of this fitting surface can also be enhanced. A technology for preventing the deflection of the fitting flange 13 which might conduce to the deflection of the rotor 2 may be what is disclosed in, e.g., Japanese Patent Application Laid-Open Publication No.10-217001. The prior art disclosed in this Publication does not, however, deal with anything about thermally processing the respective components, wherein the costs wastefully increase because of precisely finishing the surface which is not essentially needed as a reference surface. While on the other hand, the inner ring raceway 14a and the small-diameter stepped portion 15 are hardened over their surfaces and therefore required to undergo a thermal process such as high-frequency hardening. Then, the configurations and dimensions of the inner ring raceway 14a and the small-diameter stepped portion 15 might more or less change subsequent to the thermal process, and hence, according to the prior art disclosed in the above Publication, it is difficult to sufficiently enhance the accuracy of each components in the way described above. Besides, the invention disclosed in the Publication given above takes a structure of fixing a couple of inner rings each separated from the hub to the outer peripheral surface of this hub, and therefore an error, etc. between the end surface of each inner ring and the inner ring raceway might be added as an error of the positional relationship between the fitting surface of the fitting flange and the inner ring raceway. Furthermore, a contact portion between the hub and the inner ring is not worked based on the fitting surface of the fitting flange, so that the positional relationship between the fitting surface and the inner ring raceway is hard to sufficiently enhance. Moreover, the bearing unit 5 for the wheel and the rotor 2 have hitherto been selectively combined in order to make offsets of the deflection of the fitting flange 13 and the deflection of the rotor 2 based on the configuration error of the rotor 2 itself. In this case, however, the selecting operation for the combination becomes laborious, resulting in an increase in cost. It is desirable, under such circumstances, to improve a method of manufacturing a bearing unit for a wheel. Therefore, the present invention provides a method of manufacturing a bearing unit for a wheel, said bearing unit comprising: a static ring having a plurality of static raceway surfaces and supported by a suspension structure in use; a rotary raceway ring having a plurality of rotary raceway surfaces; a plurality of rolling members interposed between the static raceway surfaces and the corresponding rotary raceway surfaces; and a fitting flange, having an internal surface and an external surface, and being provided on an outer peripheral surface of said rotary ring, wherein, in use, a rotary braking body is fixedly joined to the external surface by a plurality of studs disposed on the same circumference as each other of the fitting flange, said method comprising: a step of working the external surface of said fitting flange in a predetermined configuration after an outer peripheral surface of an intermediate portion of said rotary ring has been hardened by a hardening process. Preferably, the method further comprises a step of working a said rotary raceway surface of the intermediate portion of said rotary ring in the axial direction in a predetermined configuration and dimensions using the external surface as a reference surface. Three embodiments of the invention are described in detail in relation to the drawings. However, some aspects of the embodiments are discussed in the following paragraphs. In a bearing unit manufactured according to an embodiment, the side surface of the fitting flange for fixedly joining the rotary body for braking and the wheel, is worked in a predetermined configuration after the rotary-side raceway surface has been subjected to the thermal process, and the rotary-side raceway surface is worked in a predetermined configuration and dimensions using the side surface of the fitting flange as a reference surface. Hardening of the rotary-side raceway surface of a rotary ring by a thermal process is followed by a step of working a side surface of a fitting flange in a predetermined configuration and a step of subsequently working the rotary-side raceway surface in a predetermined configuration and dimensions by using the side surface of the fitting flange as a fiducial, or reference, surface. The methods embodying the invention are capable of making normal a relationship between the rotary-side raceway surface and the side surface of the fitting flange irrespective of deformations of the respective components which are subsequent to a thermal process. As a result, it is feasible to restraining deflections of the rotary body for braking which is fixed to the fitting flange by enhancing a perpendicularity of the side surface of the fitting flange to the rotational center of the rotary ring. The rotary-side raceway surface may be worked in a predetermined configuration and dimensions on the basis of the braked surface of the rotary body for braking in a state where the rotary body for braking is fixedly joined to the one single surface of the fitting flange. In order that the present invention may be well understood, three embodiments thereof, which are given by way of example only, will now be described with reference to the accompanying drawings, in which: FIG. 1 is a sectional view showing a bearing unit for explaining a method of a first embodiment of the present invention: FIG. 2 is a sectional view showing a state of working an outer peripheral surface of a hub in the first embodiment; FIG. 3 is a sectional view showing a state of working the outer peripheral surface of the hub in a second embodiment; FIG. 4 is a sectional view showing one example of assembling a bearing unit for a wheel; FIG. 5 is a sectional view showing a state of working the outer peripheral surface of the hub in a third embodiment of the present invention; and FIG. 6 is a view taken along the arrow line A in FIG. 5. FIGS. 1 and 2 show a first embodiment of the present invention. An outer peripheral surface of an outer ring 6 defined as a static ring is provided with a joint flange 12 for fixedly joining the outer ring 6 to a knuckle, or suspension structure, 3 (FIG. 4). Outer ring double raceways 11a, 11b each serving as a static-side raceway surface are formed in an inner peripheral surface of the outer ring 6 which is defined as a static-side peripheral surface. A portion 6a, indicated by lattice-hatching in an upper half part in FIG. 1 and embracing the outer ring raceways 11a, 11b, of the inner peripheral surface of an intermediate portion of the outer ring 6, is hardened over its entire periphery by high-frequency hardening. Further, areas, facing to the outer ring raceways 11a, 11b, of outer peripheral surfaces of a hub 8 and an inner ring 16 which correspond to a rotary ring, are provided with inner ring raceways 14a, 14b each serving as a rotary-side raceway surface. To be more specific, the inner ring raceway 14a is formed directly in an outer peripheral surface of an intermediate portion of the hub 8, and the inner ring 16 having the inner ring raceway 14b formed in its outer peripheral surface is fixedly fitted on a small-diameter stepped portion 15 formed at an inner side end of this hub 8. The inner ring 16 is composed of a hard metal like bearing steel such as SUJ2, and hardened to its core by the hardening process. Further, a fitting flange 13 for fixing a wheel 1 constituting a traveling wheel and a rotor 2 (FIG. 4) classified as a rotary body for braking or a drum, is provided at a portion closer to the outer side end of the intermediate portion of the hub 8 and protruding from an aperture of an outer side end of the outer ring 6. Fitting holes 23 are respectively formed on the same circumference, concentric with a rotational center of the hub 8, in a plurality of positions in the circumferential direction of the fitting flange 13. Proximal ends of studs 24 are individually fixedly fitted in these fitting holes 23. Each of the studs 24 includes a collar 25 provided on a proximal end surface thereof and a serrated portion 26 formed, closer to the proximal end, on the outer peripheral surface of the intermediate portion. The thus configured stud 24 is inserted outward from inward (from right to left in FIG. 1) into the fitting hole 23, and the serrated portion 26 is fitted by pressing into the fitting hole 23. Then, the collar 25 is made to impinge upon an inside surface of the fitting flange 13. Note that a widthwise central position of the serrated portion 26 which is indicated by a chain line α in FIG. 1 is set more inward than a thicknesswise central position of the fitting flange 13 which is indicated by a chain line β in FIG. 1 in a state where the stud 24 is fixed to the fitting flange 13 in the way described above. The following is an elucidation of the reason why so. In this embodiment, an external surface 27 (a left side surface in FIGS. 1 and 2) of the fitting flange 13 is set as a fitting surface to which the wheel 1 and the rotor 2 should be fitted. Accordingly, there must be a necessity for preventing a decline of configuration accuracy of the external surface 27 to the greatest possible degree. While on the other hand, when the serrated portion 26 of the stud 24 is press-fitted into the fitting hole 23, the fitting flange 13 might deform to some extent in the vicinity of the fitting hole 23. This deformation might extend to the external surface 27, and, if the external surface 27 deforms in a convex-direction, a deflection of the rotor 2 fixedly joined to this external surface 27 tends to become large. Such being the case, the fitted portion between the fitting hole 23 and the serrated portion 26 is set inward as much as possible , thereby preventing the external surface 27 from deforming in the convex-direction due to the deformation of the flange 13. As a matter of course, a width W 26 of the serrated portion 26 is set well smaller than a thickness T 13 of the fitting flange 13 (W 26 << T 13 ) within a range where a sufficient fitting strength can be ensured. In the illustrated embodiment, at the side end of the fitting hole 23, a chamfered large-diameter portion is formed in an aperture on the side of the external surface 27 by a counterboring work or lathe work. Hence, the convex-directional deformation of the external surface 27 due to the press-fitting of the serrated portion 26 can be prevented more surely. Further, though considered almost unnecessary, if the working on the external surface 27 is again performed after the press-fitting of the serrated portion 26, the distortion of the external surface 27 can be eliminated with a certainty. Moreover, as shown in FIGS. 5 and 6 according to a third embodiment, an annular channel 123 communicating with all the fitting holes 23 may be previously formed in the external surface 27, thereby preventing the external surface 27 from being deformed and distorted based on the press-fitting of the serrated portion 26. Further, the portion 8a, indicated by the lattice-hatching in the upper half part in FIG. 1, of the outer peripheral surface of the hub 8 is hardened over its entire periphery by the high-frequency hardening. Of this hardened portion 8a, the proximal end of the fitting flange 13 is hardened for preventing a plastic deformation of this proximal end irrespective of a large moment applied to the fitting flange 13 when travelling. In addition, the inner ring raceway 14a is hardened for preventing an impression from being formed in the inner ring raceway 14a regardless of a large surface pressure applied to a contact area between balls 17, 17 which will hereinafter be explained. Further, the small-diameter stepped portion 15 is hardened for preventing this small-diameter stepped portion 15 from being plastically deformed irrespective of a large radial load applied from the inner ring 16. Moreover, a portion between the small-diameter stepped portion 15 and the inner ring raceway 14a is hardened for preventing this in-between portion from being plastically deformed regardless of a large moment load and thrust load applied when travelling. A plurality of balls 17, 17 each defined as a rolling member are provided in a state of being held by retainers 18, 18 between the outer ring raceways 11a, 11b and the inner ring raceways 14a, 14b. With this configuration, the hub 8 is rotatably supported on the side of an inside diameter of the outer ring 6, and the traveling wheel including the wheel 1 and the rotor 2 can be rotatably supported with respect to the knuckle 3. Note that seal rings 19a, 19b are provided between the inner peripheral surfaces of two side ends of the outer ring 6, the outer peripheral surface of the intermediate portion of the hub 8 and the outer peripheral surface of the inner side end of the inner ring 16 so as to cut off the space accommodating the balls 17, 17 from the outside space, thereby preventing a leak of grease sealed in the above space and foreign matters from entering this space. In the thus constructed bearing unit 5 for the wheel, the external surface 27 of the fitting flange 13, for fixedly joining the wheel 1 and the rotor 2, is worked in the predetermined configuration after the outer peripheral surface 8a, indicated by the lattice-hatching in the upper half part in FIG. 1, of the intermediate portion of the hub 8 has been hardened by the high-frequency hardening process categorized as one type of thermal processes. That is, the lattice-hatching portion 8a undergoes the high-frequency thermal process and is thereby hardened. Then, the hub 8 comes to have a deformation based on the thermal process, and thereafter the outer periphery of the hub 8 as well as the external surface 27 are subjected to machining. . More in detail, the inner ring raceway 14a formed directly in the outer peripheral surface of intermediate portion of the hub 8 and the outer peripheral surface and the stepped surface of the small-diameter stepped portion 15 formed at the inner side end of the hub 8, are worked in predetermined configurations and predetermined dimensions using the external surface 27 as shown in FIG. 2 as a reference surface, before or after the external surface 27 of the fitting flange 13 has been worked as the flat surface by lathe turning or the like machining. Even before working the flange surface, the surfaces of the inner ring raceway 14a and of the stepped portion 15 can be worked at by far higher accuracy than in the prior art because of the flange surface serving as the basis or reference surface. More specifically, a backing plate 28 abuts on the external surface 27 and is joined to the fitting flange 13 by a magnetic attractive force, etc.. then, the hub 8 is rotated by rotating the backing plate 28. On this occasion, a rotational center of the hub 8 is an axis orthogonal to the external surface 27. Then, an unillustrated shoe is slid on the outer peripheral surface of the hub 8, and the inner ring raceway 14a and the outer peripheral surface and the stepped surface of the small-diameter stepped portion 15 are, as indicated by broken lines in FIG. 2, machined in desired configuration as by cut working or precision lathe working while being positioned in the radial direction of the hub 8. The machining described above is performed in such a way that the axis orthogonal to the external surface 27 serves as the rotational center. Hence, the positional relationship between the external surface 27 on the one hand, and the inner ring raceway 14a formed directly in the outer peripheral surface of the intermediate portion of the hub 8 and the inner ring raceway 14b formed in the outer peripheral surface of the inner ring 16 (FIG. 1) fitted on the small-diameter stepped portion 15 on the other hand, becomes normal irrespective of the thermal deformation caused by the high-frequency hardening process described above. As a result, the deflection of the external surface 27 can be restrained down to a slight degree in a state where the wheel bearing unit 5 as illustrated in FIG. 1 is assembled. Next, a second embodiment of the present invention will be shown in FIG. 3. In accordance with the second embodiment, after the outer peripheral surface 8a has been hardened and after an external surface 27 of the fitting flange 13 provided on the outer peripheral surface of the hub 8 has been finished as a flat surface, in a state where the outer side end of the hub 8 is chucked by a chuck 30, the inner ring raceway 14a formed directly in the outer peripheral surface of the intermediate portion of the hub 8 and the outer peripheral surface and the stepped surface of the small-diameter stepped portion 15, are worked in predetermined configurations and dimensions. On this occasion, one single surface (a right end surface in FIG. 3) of the chuck 30 in the axial direction abuts on the external surface 27, and the external surface 27 is used as a fiducial, or reference, surface for working. Further, an inner peripheral surface of the chuck 30 is brought into contact with an outer peripheral surface of a cylindrical member 31 provided at the external side end of the hub 8, thereby restraining a displacement in the radial direction of the hub 8. In the second embodiment discussed above, it is feasible to regulate more strictly the radial positions of the inner ring raceway 14a formed directly in the outer peripheral surface of the intermediate portion of the hub 8 and of the outer peripheral surface of the small-diameter stepped portion 15 formed at the inner side end of the hub 8. As a result, vibrations of the car when traveling can be decreased by restraining the radial displacements of the wheel 1 and of the rotor 2 (FIG. 4). Other configurations and operations are the same as those in the first embodiment, and hence the repetitive explanations and illustrations of the same components are herein omitted. The wheel bearing unit manufacturing method according to the present embodiment restrains disagreeable noises and vibrations caused when braking without increasing particularly the costs.

Claims: A method of manufacturing a bearing unit for a wheel, said bearing unit comprising: a static ring (6) having a plurality of static raceway surfaces (11a, 11b) and supported by a suspension structure (3) in use; a rotary raceway ring (8) having a plurality of rotary raceway surfaces (14a, 14b); a plurality of rolling members (17) interposed between the static raceway surfaces and the corresponding rotary raceway surfaces; and a fitting flange (13), having an internal surface and an external surface (27), and being provided on an outer peripheral surface of said rotary ring, wherein, in use, a rotary braking body (2) is fixedly joined to the external surface by a plurality of studs (24) disposed on the same circumference as each other of the fitting flange, said method comprising: a step of working the external surface (27) of said fitting flange in a predetermined configuration after an outer peripheral surface of an intermediate portion (8a) of said rotary ring (8) has been hardened by a hardening process. A method of manufacturing a bearing unit for a wheel according to claim 1, further comprising a step of working a said rotary raceway surface (14a, 14b) of the intermediate portion (8a) of said rotary ring (8) in the axial direction in a predetermined configuration and dimensions using the external surface (27) as a reference surface.

Inventors: KANEKO TAKEYASU, KAWASE YASUNORI, MIYAZAKI HIROYA, NAKAMURA YUJI, KANEKO, TAKEYASU, KAWASE, YASUNORI, MIYAZAKI, HIROYA, NAKAMURA, YUJI, Kaneko, Takeyasu, c/o NSK Ltd., Kawase, Yasunori, c/o NSK Ltd., MIYAZAKI, HIROYA, C/O NSK LTD., Nakamura, Yuji, c/o NSK Ltd.
Applicants: NSK LTD
Application year: 2000
Main classification: B60B27
IPC codes: B60B27