JP2010089522A - Method for manufacturing rolling bearing unit for supporting wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain a manufacturing method capable of suppressing a value of remained tensile stress generated on an inner diameter side portion existing at an inner side in a radial direction smaller than that of a cured layer with formation of the cured layer on an outer peripheral surface of an intermediate part of a hub body 9 by high frequency quenching. <P>SOLUTION: A recession hole 17 is formed on a bottom part of a recession part 12 provided on an outer end surface in an axial direction of the hub body 9 after the cured layer is formed. A part of a stress line of the remained tensile stress existing at an inner diameter side portion of the cured layer is cut by formation of the recession hole 17 and a value of the remained tensile stress applied to the inner diameter side portion can be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in a method of manufacturing a wheel-supporting rolling bearing unit for rotatably supporting a wheel with respect to a suspension device of an automobile, and relates to a wheel-supporting rolling bearing unit that is lightweight and has sufficient durability. The realization of the resulting manufacturing method is intended.

  In order to rotatably support the wheel with respect to the automobile suspension system, a wheel bearing rolling bearing unit 1 as shown in FIG. 4 is used. In this wheel support rolling bearing unit 1, a hub 3 is rotatably supported via a plurality of rolling elements 4, 4 on the inner diameter side of an outer ring 2. Out of these, the outer ring 2 is made of medium carbon steel, and has double-row outer ring raceways 5 and 5 on the inner peripheral surface and a stationary flange 6 on the outer peripheral surface. Such an outer ring 2 does not rotate when the stationary flange 6 is coupled and fixed to the knuckle constituting the suspension device when used. The hub 3 has double-row inner ring raceways 7 and 7 and a rotation side flange 8 on the outer peripheral surface, and rotates together with the wheel when in use. Each of the rolling elements 4 and 4 is made of bearing steel or ceramic and is provided between the outer ring raceways 5 and 5 and the inner ring raceways 7 and 7 so as to be freely rollable in both rows. ing. In addition, the rotating flange 8 supports and fixes a braking rotator such as a wheel and a disc rotor in use.

  The hub 3 is formed by connecting and fixing a hub body 9 and an inner ring 10. Of these, the hub main body 9 is made of medium carbon steel, and is a portion near the outer end in the axial direction (outside with respect to the axial direction means the side that is the outer side in the width direction of the vehicle body when assembled to the suspension device. The same applies to the entire claims.) The rotation-side flange 8 is directly attached to the outer peripheral surface of the inner ring raceway and the inner ring raceway 7 on the outer side in the axial direction of the double-row inner ring raceways 7 and 7 is directly Forming. A cylindrical portion 11 called a pilot portion is provided at the outer end of the hub body 9 in the axial direction for positioning the wheel and the braking rotator. A recess 12 is formed at the center of the axially outer end surface of the hub body 9 at the axially outer end of the hub body 9 including the inner diameter side of the cylindrical part 11.

  On the other hand, the inner ring 10 is made of bearing steel and has an outer circumferential surface on the inner side in the axial direction of the double-row inner ring raceways 7 and 7. The inner ring raceway 7 is formed, which is the same in the entire specification and claims. Such an inner ring 10 is caulked 14 formed at the inner end in the axial direction of the hub body 9 in a state where the inner ring 10 is externally fitted and fixed to a small-diameter step 13 formed near the inner end of the hub body 9 in the axial direction. The hub body 9 is coupled and fixed to the hub body 9. A structure in which a nut is screwed to a male screw portion provided at an axially inner end portion of the hub body 9 in order to connect and fix the inner ring 10 to the hub body 9 is also widely known.

  In any structure, a part of the hub 3 is quenched and hardened. First, the entire inner ring 10 is cured by so-called submerged quenching in which the entire inner ring 10 is heated and immersed in quenching oil. On the other hand, with respect to the hub main body 9, the hardened layer 15 is formed in the portion shown by the oblique lattice in FIG. 5 by quenching and hardening by high-frequency heat treatment. This hardened layer 15 is a portion closer to the outer diameter of the intermediate portion of the hub body 9 (surface layer portion including the outer peripheral surface), and from the proximal end portion on the inner side in the axial direction of the rotation side flange 8, the small diameter step portion 13. It is formed in the part hung on the outer half in the axial direction. By forming the hardened layer 15 in such a portion, the moment rigidity of the rotation side flange 8 is ensured, the rolling fatigue life of the inner ring raceway 7 on the outer side in the axial direction is ensured, and the fretting wear of the small diameter step portion 13 is achieved. And to secure the bending rigidity of the hub body 9 as a whole. The concave portion 12 opened on the outer end surface in the axial direction of the hub body 9 contributes to weight reduction of the hub body 9.

  When the wheel supporting rolling bearing unit 1 including the hub body 9 as described above is used, a large force (load) is applied to the hub 3. In particular, during turning, a large moment is applied to the rotation side flange 8 from the contact portion (ground contact surface) between the wheel supported on and fixed to the rotation side flange 8 and the road surface. Such a moment is supported by a continuous portion 16 between the base end portion (inner diameter side end portion) of the rotation side flange 8 and the main body portion of the hub main body 9. The thickness of the continuous portion 16 is not only originally small due to the presence of the concave portion 12, but also based on the presence of the hardened layer 15, the thickness of an unquenched (so-called raw) portion that is easy to ensure toughness. Is small. For this reason, unless any measures are taken, it is impossible to achieve both weight reduction by increasing the volume of the concave portion 12 and securing the strength and rigidity of the continuous portion 16.

  For this reason, conventionally, it has been considered to improve the strength, rigidity and durability of the hub body by means such as those described in Patent Documents 1 to 4, for example. Of these, Patent Document 1 describes a technique for securing the strength of the hub body by subjecting the hub body to a tempering treatment. Further, Patent Document 2 discloses that a crack is caused by removing the decarburized layer on the inner surface of the recess to make the inner surface smooth, and further generating residual compressive stress on the inner surface by shot peening or turning, and starting from the inner surface. The technique which makes it hard to generate | occur | produce damages, such as this, is described. Patent Document 3 describes a technique for forming a protrusion projecting radially inwardly on the inner peripheral surface portion of the recess to improve the strength and rigidity of the peripheral portion of the recess. Further, in Patent Document 4, the inner surface portion of the recess is cooled at the end of the forging process for manufacturing the hub body, and a layer of a non-standard structure such as a fine ferrite / pearlite structure is formed on this portion. Techniques for improving the strength and fatigue life of the steel are described.

  In the case of the prior art described in Patent Documents 1 to 4 as described above, a certain effect can be obtained, but from the aspect of further reducing the weight while securing the durability of the hub body 9 while suppressing the cost. The inventors have found that there is room for improvement. That is, in the conventional techniques described in Patent Documents 1 to 4, cracks are likely to occur in the continuous portion 16 in the hub body 9 with the processing of the hardened layer 15 while suppressing costs. Cannot be prevented. That is, due to the study by the present inventors, a large residual tensile stress is generated in the inner diameter side portion existing on the radially inner side of the hardened layer 15 including the continuous portion 16 as the hardened layer 15 is processed, It was found that the cracks are likely to occur. This point will be described with reference to FIG.

  When the intermediate portion in the axial direction of the outer peripheral surface of the hub body 9 is induction-quenched and then rapidly cooled to form the hardened layer 15, the portion that should become the hardened layer 15 rapidly shrinks after thermal expansion. As a result, residual compressive stress is applied to the hardened layer 15 as shown in FIG. On the other hand, a residual tensile stress is applied to the inner diameter side portion of the hub body 9 that is present on the radially inner side of the hardened layer 15. That is, the inner diameter side portion rises in temperature with heat conduction during heating for induction hardening, while the temperature drop during the rapid cooling is delayed as compared with the portion to be the hardened layer 15. And when the said inner diameter side part shrink | contracts with a temperature fall, the said hardened layer 15 has already been formed, and this hardened layer 15 becomes resistance with respect to the said inner diameter side part thermally contracting. This inner diameter side portion is thermally contracted against the resistance caused by such a hardened layer 15, and as a result, residual tensile stress is applied to the inner diameter side portion. Of these stresses, the residual compressive stress acts as a force that suppresses crack damage, while the residual tensile stress acts as a force that promotes this damage.

In this way, when residual tensile stress is applied to the inner diameter side portion and a stress in the tensile direction is applied to the portion in accordance with the moment, crack damage is caused in the hub body 9 starting from the inner diameter side portion. It tends to occur. FIG. 6 is a modified Goodman diagram showing a situation in which crack damage is likely to occur due to the residual tensile stress acting in this manner. In FIG. 6, a solid line α represents a Goodman line, and a broken line β represents a yield line. Assuming that the stress amplitude is a predetermined value (constant) and the average stress becomes a tensile stress starting from point a where the average stress is 0, the combination of this average stress and the stress amplitude is above the Goodman line α. Especially, as shown by point B in FIG. 6, there is a high possibility that the crack damage will occur beyond the yield point. In addition, crack damage due to such a cause becomes significant when the volume of the recess 12 is increased (the depth in the axial direction is increased) in order to further reduce the weight of the hub body 9.
The conventional techniques described in Patent Documents 1, 3, and 4 among the aforementioned Patent Documents 1 to 4 cannot suppress crack damage due to such a cause. On the other hand, the conventional technique described in Patent Document 2 can suppress crack damage due to such a cause, but for that purpose, it is necessary to newly add a shot peening or turning process, and the manufacturing cost is reduced. Cause the problem of rising.

JP 2005-3061 A JP 2005-145313 A JP 2006-143069 A JP 2007-38804 A

  In view of the circumstances as described above, the present invention can be implemented at a low cost, and as the hardened layer is formed on the outer peripheral surface of the intermediate portion of the hub body by induction hardening, the inner side in the radial direction of the hardened layer is formed. The present invention was invented to realize a method of manufacturing a wheel-supporting rolling bearing unit that can keep the value of the residual tensile stress generated in the existing inner diameter side portion small.

A wheel-supporting rolling bearing unit that is an object of the manufacturing method of the present invention includes an outer ring, a hub, and a plurality of rolling elements.
Among these, the outer ring has a double row outer ring raceway on the inner peripheral surface, and does not rotate during use.
The hub has a double-row inner ring raceway on the outer peripheral surface, and rotates together with the wheel when in use. The hub main body and the inner ring are coupled and fixed. Of these, the hub body directly forms the rotation side flange for supporting and fixing the wheel on the outer peripheral surface near the outer end in the axial direction, and the inner ring raceway on the outer side in the axial direction on the outer peripheral surface in the axial direction. A recess is formed in the central portion of the outer end surface in the axial direction. The inner ring is formed with an inner ring raceway on the outer peripheral surface on the inner side in the axial direction, and is fitted and fixed to a small-diameter step portion formed near the inner end in the axial direction of the hub body. A hardened layer is formed by induction hardening at least on the outer peripheral surface of the intermediate portion of the hub body including the inner ring raceway on the outer side in the axial direction.
Further, a plurality of rolling elements are provided between the outer ring raceways and the inner ring raceways so as to be freely rollable in both rows.

In order to manufacture such a wheel-supporting rolling bearing unit, the manufacturing method of the wheel-supporting rolling bearing unit of the present invention devises the processing process of the hub body. And the value of the residual tensile stress which generate | occur | produces in the internal diameter side part which exists in a radial inside rather than the said hardened layer is suppressed small.
For this reason, in the case of the invention of the method for manufacturing the wheel-supporting rolling bearing unit of the present invention, the concave hole is formed at the bottom of the concave portion after the hardened layer is formed. The concave hole is formed on the central axis of the hub body, and the size thereof is appropriately regulated in relation to the object of the present invention, while ensuring the strength and rigidity of the hub body. For example, in the case of a general passenger car hub body (the inner diameter of the opening of the recess is about 40 to 60 mm), the inner diameter is about 5 to 8 mm (for example, 6 to 7 mm), and the depth is 8 to 15 mm (for example, 10mm).

According to the method for manufacturing the wheel-supporting rolling bearing unit of the present invention having the above-described configuration, a hardened layer is formed on the outer peripheral surface of the intermediate portion of the hub body by induction hardening, and the inner diameter side of the hardened layer is formed. It is possible to reduce the value of the residual tensile stress generated in the inner diameter side portion. As a result, cracking damage to the hub body starting from the inner diameter side portion can be prevented.
That is, in the case of the method of manufacturing the wheel-supporting rolling bearing unit of the present invention, by forming a concave hole at the bottom of the concave portion, a part of the stress line of the residual tensile stress existing in the inner diameter side portion is cut, As a result, the value of the residual tensile stress acting on the inner diameter side portion can be reduced.
Further, in the case of the method of manufacturing the wheel-supporting rolling bearing unit of the present invention, in order to suppress the occurrence of crack damage of the hub body, the crack damage as in the prior art described in Patent Document 2 described above. It is not necessary to add a dedicated process to suppress the occurrence of For this reason, compared with the prior art described in this patent document 2, an increase in manufacturing cost can be suppressed.

  FIG. 1 shows an example of an embodiment of the present invention. In the case of this example, a hardened layer is formed by induction hardening at a portion near the outer diameter including the outer peripheral surface at the axially intermediate portion of the hub main body 9, and then the concave portion provided at the outer axial end portion of the hub main body 9. A concave hole 17 is formed at the bottom of 12. The concave hole 17 is formed by a cutting process using a drilling machine (with a drill blade). The concave hole 17 exists in the back half and has a constant inner diameter, and in the opening side half. It consists of the inclined surface part 19 whose internal diameter becomes large as it goes to. The size of the concave hole 17 is about 5 to 8 mm at the inner diameter R of the cylindrical surface portion 18 and 8 to 15 mm at the depth D of the portion excluding the mortar-like portion at the back end portion. The angle θ is about 50 to 70 degrees.

  By forming the concave hole 17 as described above at the bottom of the concave portion 12 after the hardened layer is formed, the stress line of the residual tensile stress existing in the inner diameter side portion of the hub body 9 including the continuous portion 16 is formed. A part is cut by the concave hole 17. As a result, the value of the residual tensile stress acting on the inner diameter side portion can be reduced, and cracking damage to the hub body 9 starting from the inner diameter side portion can be prevented.

  In addition, what was conventionally formed in the center part of the axial direction outer end surface of the hub main body 9 was known for the above-mentioned concave holes 17. However, in the conventional case, the operation of forming the concave hole 17 in the hub body 9 has been performed before the hardened layer is formed near the outer diameter of the intermediate portion of the hub body 9. For this reason, the residual tensile stress generated in the inner diameter side portion of the hub body 9 due to the formation of the hardened layer cannot be reduced based on the presence of the concave hole 17. On the other hand, in the case of this example, since the concave hole 17 is formed after the hardened layer is formed, as described above, the residual tensile stress generated by forming the hardened layer is reduced ( Open).

  Furthermore, in the case of the manufacturing method of the wheel-supporting rolling bearing unit of this example, in order to suppress the occurrence of crack damage of the hub body 9, this crack is caused as in the prior art described in Patent Document 2 described above. There is no need to add a dedicated process to reduce the occurrence of damage. That is, the concave holes 17 are respectively centered when the wheel supporting rolling bearing unit is assembled to the suspension device by the assembly robot in the automobile assembly plant, or when the wheel is assembled to the wheel supporting rolling bearing unit. It may be used as a hole for use. For this reason, only when the hub body 9 having the concave hole 17 is manufactured, the occurrence of crack damage can be suppressed only by changing the order of the steps of processing the concave hole 17. Compared to the described prior art, an increase in manufacturing cost can be suppressed.

  An experiment conducted for confirming the effect of the present invention will be described. In the experiment, three types of hub bodies 9 shown in FIGS. 2A to 2C, each of which is made of medium carbon steel, are formed with a hardened layer on the outer peripheral surface portion of the intermediate portion, and then the inner surface of the recess 12 is formed. Whether or not the concave hole 17 is formed in the central portion was determined in order to know the influence on the magnitude of the residual stress acting on the inner surface of the concave portion 12. In this experiment, the measurement position of the residual stress was set to the position indicated by the arrow in FIG. The three types of hub main bodies 9 are all for ordinary passenger cars, and the inner diameter of the opening of the cylindrical portion 11 surrounding the recess 12 is 48 mm. Further, the rotation-side flange 8 formed on the outer peripheral surface near the outer end in the axial direction has a cross shape as shown in FIG. In FIGS. 2A to 2C, the aspect ratio and the radius of curvature of the curved surface are drawn in accordance with the actual situation (according to the actual proportion). In addition, the size of each of the formed concave holes 17 is such that the inner diameter R of the cylindrical surface portion 18 is 6 mm, the opening angle θ of the inclined surface portion 19 is 60 degrees, and the distance from the bottom surface of the concave portion 12 to the back end of the cylindrical surface portion 18. L was 9 mm.

この表１に示した実験結果から明らかな通り、本発明の車輪支持用転がり軸受ユニットの製造方法によれば、ハブ本体９の中間部外周面に硬化層１５（図５参照）を形成するのに伴って、この硬化層１５の内径側に存在する内径側部分に発生した引っ張り応力を緩和できる。 The results of experiments conducted under such conditions are shown in Table 1 below. In Table 1, a residual stress value of “+” indicates that this residual stress is a tensile stress.

As is apparent from the experimental results shown in Table 1, according to the method for manufacturing the wheel-supporting rolling bearing unit of the present invention, the hardened layer 15 (see FIG. 5) is formed on the outer peripheral surface of the intermediate portion of the hub body 9. Accordingly, the tensile stress generated in the inner diameter side portion existing on the inner diameter side of the hardened layer 15 can be relaxed.

  The present invention can be applied to a case where the hub body is manufactured by cold forging, and a particularly remarkable effect can be obtained. The reason for this is that cold forging has a large processing resistance, and a large residual stress is likely to be generated inside the hub body produced by cold forging. That is, if a residual tensile stress generated along with the formation of a hardened layer is applied to a hub body that originally has a large residual stress, damage such as a crack is likely to occur. Therefore, when the present invention is applied to a hub body manufactured by such cold forging, it is possible to effectively prevent damage. However, even in the case of warm forging or hot forging, although there is a difference in degree, residual stress is generated inside the hub body to be produced, so it is effective to apply the present invention.

The fragmentary sectional view which shows the state which formed the concave hole after forming the hardening layer in the hub main body by induction hardening in the process of implementing the manufacturing method of this invention. Sectional drawing of three types of hub main bodies used for the experiment conducted in order to confirm the effect of this invention. The figure which looked at each hub main body shown in FIG. 2 from the right side of the figure. Sectional drawing which shows one example of the rolling bearing unit for wheel support used as the object of the manufacturing method of this invention. The half part sectional view for demonstrating the residual stress which generate | occur | produces in a hub main body accompanying hardened layer formation. The diagram for demonstrating the reason the durability of a hub main body falls with generation | occurrence | production of a residual tensile stress.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing unit for wheel support 2 Outer ring 3 Hub 4 Rolling body 5 Outer ring raceway 6 Stationary side flange 7 Inner ring raceway 8 Rotation side flange 9 Hub body 10 Inner ring 11 Cylindrical part 12 Recessed part 13 Small diameter step part 14 Caulking part 15 Hardening layer 16 Continuous Part 17 Recessed hole 18 Cylindrical surface part 19 Inclined surface part

Claims (1)

  An outer ring having double-row outer ring raceways on the inner peripheral surface and not rotating even when used, a hub having a double row inner ring raceway on the outer peripheral surface and rotating together with the wheels during use, both inner ring raceways and the both outer rings A plurality of rolling elements are provided in each row between the raceway, and the hub is configured such that the hub body and the inner ring are coupled and fixed. The hub body directly forms the rotation side flange for supporting and fixing the wheel on the outer peripheral surface near the outer end in the axial direction, and the inner ring raceway on the outer peripheral surface in the axial direction on the outer peripheral surface in the axial direction. A concave portion is formed in the central portion of the outer end surface, and the inner ring is formed by forming an inner ring raceway on the outer peripheral surface on the inner side in the axial direction, and a small-diameter step portion formed near the inner end in the axial direction of the hub body. The outer peripheral surface of this hub body is at least above the outer peripheral surface. A method for manufacturing a wheel-supporting rolling bearing unit in which a hardened layer is formed by induction hardening on a portion including an inner ring raceway on an outer side in the axial direction, wherein a concave hole is formed at the bottom of the concave portion, and the hardened layer is formed. A method for manufacturing a wheel-supporting rolling bearing unit, which is formed later.

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