JP2010013039A - Rolling bearing unit for wheel support and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve such a structure that damages, such as cracks, hardly occur in a stepped part 18 of an outward flange part 10 of a hub body 7, and to provide a method of manufacturing the same. <P>SOLUTION: A quench hardening layer 17 is formed in a part from an inner ring race 9a close to the outward flange part 10 to an inner part of the outward flange part 10 in the radial direction among an outer peripheral surface of the hub body 7. A position of boundary between the quench hardening layer 17 and the other part is set at a position deviated from the stepped part 18. The boundary where residual stresses occur and strength is reduced due to recrystallization caused by heat treatment for quenching is deviated from the stepped part 18 where the stresses are concentrated, so that the above problems are solved. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a wheel bearing rolling bearing unit for rotatably supporting a wheel with respect to a suspension device and an improvement of a manufacturing method thereof.

  In order to rotatably support the wheel with respect to the suspension device, for example, a rolling bearing unit 1 for supporting the wheel as shown in FIG. 5 is used. In the rolling bearing unit 1, a hub 3 is rotatably supported via a plurality of rolling elements 4 and 4 on the inner diameter side of an outer ring 2. Of these, the outer ring 2 has a double-row outer ring raceway 5, 5 on the inner peripheral surface, and an outer flange-like attachment portion 6 for fixing the outer ring 2 to the knuckle constituting the suspension device on the outer peripheral surface. Are provided. The hub 3 is formed by combining a hub body 7 and an inner ring 8, and has double-row inner ring raceways 9a and 9b on the outer peripheral surface. Of these, the hub body 7 is close to the outer end in the axial direction of the outer peripheral surface (outside with respect to the axial direction means the outer side in the width direction in the assembled state to the suspension device, the left side in FIGS. The outward flange portion 10 for supporting and fixing the wheel is fixed to the axially inner end portion (the inner side with respect to the axial direction means the center side in the width direction in the assembled state to the suspension device. Small diameter step portions 11 are provided on the right and left sides of 1 and 5, the upper side in FIG. 4, and the lower side in FIG. 6, respectively. The inner ring 8 is coupled to the hub body 7 by a caulking portion 12 formed by plastically deforming the axially inner end portion of the hub body 7 radially outward in a state of being externally fitted to the small diameter step portion 11. It is fixed. When such a rolling bearing unit 1 is used, the mounting portion 6 is coupled and fixed to the suspension device, and the wheel is supported and fixed to the outward flange portion 10 so that the wheel can be rotated with respect to the suspension device. To support.

  In order to manufacture the hub body 7 constituting the rolling bearing unit 1 as described above, it is considered that the hub body 7 is manufactured by cold forging for the purpose of improving the material yield and reducing the cost of machining. As a method for manufacturing such a hub body 7 by cold forging, for example, a method described in Patent Document 1 is known. FIG. 6 shows an example of a method for manufacturing a hub body by cold forging described in Patent Document 1. In this manufacturing method by cold forging, first, the columnar material 13 shown in FIG. The material 13 is preliminarily softened and annealed to facilitate plastic deformation even at room temperature. Such a material 13 is subjected to a forward extrusion process to obtain a stepped first intermediate material 14 as shown in FIG. And this 1st intermediate material 14 is made into the 2nd intermediate material 15 as shown to (C) by the cold forging process (extrusion process) using a floating die. Next, the second intermediate material 15 is subjected to a stepping process for forming a stepped portion or the like for providing an axially-shaped angular inner ring raceway 9a (see FIG. 5), and the third intermediate material 15 as shown in FIG. The intermediate material 16 is used. Further, the third intermediate material 16 is subjected to a side extrusion process and a process for forming the inner ring raceway 9a to obtain a hub body 7 as shown in FIG.

  Prior to coupling and fixing the inner ring 8, the hub body 7 manufactured in this way is quenched as shown in FIG. 1 for explaining the embodiment of the present invention. A hardened layer 17 is formed. That is, the hardened hardened layer 17 is formed in the outer peripheral surface of the hub body 7 from the small diameter step portion 11 to the inner ring raceway 9a to the end portion closer to the inner diameter of the outward flange portion 10 in the axial direction. . Of the quenched and hardened layer 17, the small-diameter step 11 portion is plastically deformed regardless of the impact load applied from the inner ring 8 (see FIG. 5) fitted and fixed to the small-diameter step portion 11. Provided to prevent this from happening. The inner ring raceway 9a is provided to ensure the rolling fatigue life of the inner ring raceway 9a regardless of the load applied from the rolling elements 4, 4 (see FIG. 5). Further, the proximal end portion of the outward flange portion 10 is prevented from being plastically deformed at the end portion on the inner diameter side in the axial direction of the outward flange portion 10 regardless of the moment applied to the outward flange portion 10 from the wheel. Provided for this purpose. Further, a portion between the small diameter step portion 11 and the inner ring raceway 9a is provided to prevent the intermediate portion in the axial direction of the hub body 7 from being plastically deformed by the moment or the like.

  By the way, the thickness dimension (wall thickness) in the axial direction of the outward flange portion 10 is large at the radially inner end portion and is also small at the intermediate portion or the outer end portion. Then, the radially inner end portion and the intermediate portion or the outer end portion having different thickness dimensions are continuously provided by the step portion 18 provided over the entire circumference in the portion near the inner diameter of the axial inner side surface of the flange portion 10. ing. As shown in FIG. 2 which will be described later, the stepped portion 18 has a circular arc shape and is continuous in a tangential direction with a radially intermediate portion of the axially inner side surface. The line representing) is continuous (angular) in a non-differentiable state. The reason why the thickness of the outward flange portion 10 is made different according to the radial position as described above by forming the step portion 18 as described above on the axially inner side surface of the outward flange portion 10 is as follows. This is to ensure the strength and rigidity of the base end portion (radially inner end portion) of the outward flange portion 10 while suppressing an increase in the weight of the hub body 7 including the outward flange portion 10.

  Conventionally, no particular consideration has been given to the position of the stepped portion 18 as described above and the position of the outer diameter side edge of the quenched and hardened layer 17 as described above. And in the case of the rolling bearing unit for wheel support provided with the hub main body which was generally used by the warm forging and hot forging conventionally used, there was no problem in particular. On the other hand, as described in Patent Document 1, when the hub body 7 is manufactured by cold forging, the position of the outer diameter side edge of the hardened hardened layer 17 is set to the position of the step portion 18. The inventors have found that the durability of the rolling bearing unit including the hub body 7 cannot always be sufficiently secured unless it is restricted by the relationship. This point will be described with reference to FIG.

  As a problem peculiar to the hub main body 7 made by cold forging, it has been found that a decrease in strength is caused at the peripheral portion of the hardened hardened layer 17 due to recrystallization of the metal structure. That is, although the interface portion between the region subjected to induction hardening to form the quench hardened layer 17 and the region outside this region (region not subjected to heat treatment such as induction hardening) is small, There is a region where the hardness decreases due to recrystallization. Further, the peripheral edge portion of the hardened and hardened layer 17 corresponds to the boundary between the region where the induction hardening is performed and the region outside the region, and the residual due to the difference in thermal deformation between the two regions. Stress is generated. For this reason, the peripheral part of the said hardening hardening layer 17 becomes weak in intensity | strength. On the other hand, the stepped portion 18 is a portion where stress based on the moment applied from the wheel to the outward flange portion 10 tends to concentrate when the rolling bearing unit 1 for supporting a wheel is used. For this reason, as shown in FIG. 7, when the peripheral portion of the hardened hardened layer 17 is present in the stepped portion 18, the outward flange portion is used under severe use conditions such as forcing the wheel to step on the road step. 10, damage such as cracks may occur in the stepped portion 18.

JP 2007-152413 A

  In view of the circumstances as described above, the present invention has been invented to realize a structure in which a stepped portion of an outward flange portion of a hub body is unlikely to be damaged such as a crack and a manufacturing method thereof.

Of the rolling bearing unit for supporting a wheel and the manufacturing method thereof according to the present invention, the rolling bearing unit for supporting a wheel described in claim 1 is, for example, an outer ring similar to the rolling bearing unit for supporting a wheel shown in FIG. And a hub, a plurality of rolling elements, an outward flange portion, and a step portion.
Of these, the outer ring is provided with double-row outer ring raceways on the inner peripheral surface. The outer ring is integrally formed by plastically deforming a material made of carbon steel for machine structure (so-called medium carbon steel or high carbon steel) by forging. The outer ring machining means is not particularly limited. Cold forging may be used in the same manner as the hub body described below, and warm or hot forging may be used. In any case, a hardened hardened layer is provided by induction hardening or the like in the portion where the outer ring raceways are formed on the inner peripheral surface of the outer ring.

The hub is provided with double-row inner ring raceways on the outer peripheral surface, and is formed by coupling and fixing the hub body and the inner ring. Of these, the hub main body is integrally formed by plastically deforming a material made of carbon steel for machine structure of about S50C to S58C (generally S53C or S55C, JIS G 4051) by cold forging. On the other hand, the inner ring is integrally formed of a high carbon chrome bearing steel such as SUJ1 to SUJ5 (generally SUJ2, JIS G 4805), and the whole is quenched (so-called submerged).
A plurality of rolling elements are provided for each row between the outer ring raceways and the inner ring raceways.
The outward flange portion is for supporting and fixing the wheel to the hub, and is provided on the outer peripheral surface of the end portion of the hub body.
Further, the step portion is formed over the entire circumference in the radial intermediate portion of the side surface facing the axial end surface of the outer ring, of the both side surfaces in the axial direction of the outward flange portion, and has a circular cross-sectional shape. It is an arc shape, and the thick part on the inner diameter side and the thin part on the outer diameter side are made continuous.
Further, a hardened hardening layer is provided by induction hardening at least on an outer ring surface of the hub body from an inner ring raceway near the outward flange portion to a portion near the inner diameter portion of the outward flange portion. Yes.

In particular, in the wheel support rolling bearing unit according to the first aspect, the boundary between the hardened hardening layer and the other portion does not exist in the stepped portion.
That is, as shown in FIG. 3A described later, the boundary is positioned on the inner diameter side (lower side in FIG. 3) than the stepped portion, or as shown in FIG. The boundary is positioned on the outer diameter side (upper side in FIG. 3) than the stepped portion. In other words, the boundary is moved to the inner diameter side or the outer diameter side from the stepped portion as compared with the state shown in FIG.

Further, the invention of the manufacturing method of the wheel supporting rolling bearing unit according to claim 2 is the same as that described above in order to manufacture the wheel supporting rolling bearing unit according to claim 1, so that the material made of carbon steel can be used at room temperature. A step of performing cold forging to sequentially plastically deform.
In particular, in the method for manufacturing a wheel-supporting rolling bearing unit according to claim 2, the material is subjected to a softening annealing process before the first plastic working is performed on the material. Then, a hardened and hardened layer is formed by induction hardening on the hub body made through the respective steps.
In order to shift the boundary between this hardened layer and other parts from the stepped portion, the output, shape, and shape of the induction hardening coil (high frequency heating coil) for forming this hardened layer The installation position is restricted in consideration of the dimensions. That is, when forming the quench hardening layer, the step portion is not heated at all by the coil, or conversely, the entire step portion is heated. In other words, the step portion is not partially heated.

  According to the present invention configured as described above, it is possible to realize a wheel support rolling bearing unit that is low in cost and has excellent durability. That is, as described above, the hub body is made by cold forging for cost reduction, and when a hardened hardening layer is formed by induction hardening at a necessary portion of the hub main body, the peripheral portion of the hardened hardening layer is formed. The strength decreases due to recrystallization of the metal structure. Even in this case, since the peripheral edge portion is out of the step portion of the outward flange portion, the stress generated in the hub body is likely to be concentrated based on the moment applied to the outward flange portion. Damage can be less likely to occur.

  The features of the wheel-supporting rolling bearing unit and the manufacturing method thereof according to the present invention will be described with reference to FIG. 1. Even when the hub body 7 is manufactured by cold forging, the outward flange portion provided on the outer peripheral surface of the hub body 7 In order to make it difficult for damage such as cracks to occur in the stepped portion 18 on the side surface of the tenth surface, the position of the peripheral portion of the hardened hardened layer 17 is set at a position away from the stepped portion 18. With respect to the other portions, including the structure shown in FIG. 5 described above, the outward flange portion 10 and the outer ring raceway 9a in which the step portion 18 is formed near the inner diameter portion of the inner surface in the axial direction are provided on the outer peripheral surface. This is the same as the conventionally known rolling bearing unit 1 for supporting various types of wheels provided with the hub body 7.

  Further, even in the process of manufacturing the hub body 7 by cold forging, basically a conventionally known method such as the method described in Patent Document 1 as shown in FIG. Build by. For example, the temperature condition is set as follows. First, the raw material 13 shown in FIG. 6A is held for 0.1 hr or more in a state of being heated to 740 to 860 ° C. above the A1 transformation point. Then, after cooling to 720-680 degreeC at 20-70 degreeC / hr, after hold | maintaining about 1-5 hours, it cools at 10-100 degreeC / hr to 620-680 degreeC. Furthermore, it cools at 10-150 degreeC / hr to 500-560 degreeC. By performing the soft annealing process under such conditions, the metal structure constituting the material 13 becomes a structure that is easily plastically deformed, in which spheroidized cementite, acicular cementite, and ferrite are combined.

  Therefore, by subjecting the material 13 that has been easily plastically deformed in this way to cold forging, the first intermediate material 14 shown in FIG. 6B and the second intermediate material shown in FIG. The hub body 7 shown in (E) is obtained through the material 15 and the third intermediate material 16 shown in (D). Then, after the shape of the hub body 7 is adjusted by turning, a hardened hardened layer 17 (see FIG. 1) is formed on a predetermined portion of the hub body 7 by induction hardening, and then the hub is ground by grinding. The shape and dimensions of the outer peripheral surface of the main body 7 are finished, and a predetermined portion including the inner ring raceway 9a in the outer peripheral surface is defined as a smooth surface. During the induction hardening process, as described above, a region where the hardness is reduced by recrystallization (strength reduction region) appears at the peripheral portion of the quenched and hardened layer 17 although it is minute. In the case of the present invention, such a strength-decreasing region is located in a portion that is out of the stepped portion 18. For this reason, as described above, the durability of the outward flange portion 10 in the hub body 7 can be improved.

  Hereinafter, experiments conducted by the present inventors in order to confirm the effects of the present invention will be described. In the experiment, a billet made of S55C (carbon content = 0.55 wt%) defined in JIS G 4051 and having an outer diameter of 60 mm was subjected to the above-described softening annealing treatment, and then the billet is shown in FIG. The hub main body 7 having a predetermined shape was obtained by performing a cold forging process including the steps described above. Then, a hardened hardened layer 17 was formed on the outer peripheral surface of the hub body 7 on the portion extending from the inner ring raceway 9a near the outward flange portion 10 to the inner diameter portion of the outward flange portion 10. At this time, the installation position of the high-frequency heating coil was regulated, and five types of samples (hub main body 7) were obtained in which the outer peripheral edge positions of the quenched and hardened layer 17 were different from each other. FIG. 2 shows the position of the outer peripheral edge of the quenched and hardened layer 17. There are five types of outer peripheral edge positions on the outer diameter side (a position and b position) and the inner diameter side (d position and e position) across the radial center position (c position in FIG. 2) of the stepped portion 18. A total of 5 locations were set, each at 2 locations. The radial distance (pitch) between positions adjacent in the radial direction was 2.0 mm. In addition, two types of curvature, 8.0 mm and 10.0 mm, are prepared for the radius of curvature of the cross-sectional shape (bus shape) of the step portion 18, and the above step portion is provided for a total of 10 types of samples. An intensity of 18 was measured.

  This intensity measurement was performed as shown in FIG. That is, the ten types of hub main bodies 7 (samples) were combined with other components such as the inner ring 8, the outer ring 2, the rolling elements 4, 4, and the like to form the rolling bearing unit 1. In a state where the outer ring 2 of the rolling bearing unit 1 is held and fixed to the jig 19, the axially inner side surface of the outward flange portion 10 provided on the outer peripheral surface of the hub body 7 is indicated by a thick arrow in FIG. The axial load was input to the outer flange portion 10 (the stepped portion 18), and the magnitude of the axial load that resulted in damage (cracking) was taken as the breaking load for the sample. In order to compare the magnitude of the breaking load, the magnitude of the breaking load of each of the 10 types of samples is set to 1, and the magnitudes of the breaking loads of the other samples have the same radius of curvature. It was expressed as a ratio to the magnitude of the fracture load of the comparative example. The results of experiments conducted under such conditions are shown in Table 1 below.

  From the experiment whose results are shown in Table 1, the load resistance of the outward flange portion 10 can be improved by shifting the edge (outer peripheral edge) of the hardened hardened layer 17 from the stepped portion 18 as in the present invention. It was confirmed that it improved (breaking strength increased). That is, in the case of Examples 1 to 8 where the edge of the quench hardened layer 17 is similarly deviated compared to Comparative Examples 1 and 2 in which the stepped portion 18 exists, the difference in curvature radius of the stepped portion 18 is concerned. It was confirmed that the strength was improved by 20% or more. In the case of Comparative Examples 1 and 2, as described above, the strength of the edge portion of the quenched and hardened layer 17 that is the boundary between the quenched portion and the non-quenched portion is based on the heat treatment for quenching. Since it decreased due to the generation of residual stress and recrystallization, it was inferior to the case of each example in terms of the load resistance. It should be noted that there was no significant difference between the displacement direction and displacement amount of the edge of the quenched hardened layer 17 from the stepped portion 18 and the load resistance.

  If the present invention is a wheel-supporting rolling bearing unit having a hub body provided with an inner ring raceway and an outward flange portion on the outer peripheral surface, the driven wheel (rear wheel of the FF vehicle, FR The present invention is not limited to the structure for the vehicle and the front wheel of the MR vehicle, but can also be implemented for a structure for driving wheels (front wheel of the FF vehicle, rear wheel of the FR vehicle and MR vehicle, all wheels of the 4WD vehicle). Further, the type of rolling element provided between the pair of outer ring raceways and the pair of inner ring raceways is not limited to the balls as shown in FIG. 5 but may be tapered rollers. Moreover, the kind of rolling element can also differ between both rows.

The half part sectional view of a hub main part for explaining the present invention. 1. The X section enlarged view of FIG. 1 for demonstrating the positional relationship of the outer periphery position of a hardening hardening layer, and a level | step difference part by the structure which belongs to this invention. FIG. 3 is a drawing-substituting photograph corresponding to the Y part of FIG. Sectional drawing for demonstrating the implementation state of the destructive experiment conducted in order to confirm the effect of this invention. Sectional drawing which shows one example of the rolling bearing unit for wheel support used as the object of this invention. The figure which shows one example of the manufacturing method of a hub main body in order of a process. The figure similar to FIG. 3 regarding the structure which remove | deviates from this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing unit 2 Outer ring 3 Hub 4 Rolling body 5 Outer ring raceway 6 Mounting part 7 Hub body 8 Inner ring 9a, 9b Inner ring raceway 10 Outward flange part 11 Small diameter step part 12 Caulking part 13 Material 14 First intermediate material 15 Second intermediate material 16 Third intermediate material 17 Hardened and hardened layer 18 Stepped portion 19 Jig

Claims (2)

  An outer ring having a double row outer ring raceway on the inner peripheral surface, a hub having a double row inner ring raceway provided on the outer peripheral surface, which is formed by coupling and fixing the hub body and the inner ring, both the inner ring raceways and the both outer ring raceways. And a plurality of rolling elements provided for each row, and the hub provided on the outer peripheral surface of the end of the hub body among the hubs protruding from the axial end surface of the outer ring. An inner diameter formed over the entire circumference of the outward flange portion for supporting and fixing the wheel, and the radially intermediate portion of the side surface facing the axial end surface of the outer ring among the axially opposite side surfaces of the outward flange portion. An inner ring raceway having a stepped portion having a circular cross-sectional shape, the outer circumferential surface of the hub main body being at least near the outward flange portion. Harden and harden the part of the outward flange from the part near the inner diameter The In the wheel support rolling bearing unit are provided, the boundary between the quench hardened layer and other parts, the wheel support rolling bearing unit, characterized in that does not exist in the step portion.   A method for manufacturing a wheel-supporting rolling bearing unit, comprising the step of performing cold forging in which a carbon steel material is sequentially plastically deformed at room temperature in order to manufacture the wheel-supporting rolling bearing unit according to claim 1. For wheel support, characterized in that before the first plastic working of the above material, this material is softened and annealed, and a hardened hardened layer is formed by induction hardening on the hub body made through each process. A method for manufacturing a rolling bearing unit.