JP2009106995A - Method for manufacturing rolling bearing unit for supporting wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a rolling bearing unit for supporting a wheel having high fatigue strength and long service life. <P>SOLUTION: A hub-ring 2 in the rolling bearing unit 1 for supporting the wheel is obtained by forming step by step into a prescribed shape by applying hot-forging in the plurality of processes in order to a steel blank. In the plurality of hot-forgings, the hot-forging at the last process is performed while controlling the working temperature of the based part S of a flange 10 for fitting the wheel, an introduced von-Mises strain quantity and a hot-forging parameter P<SB>F</SB>. Further, a cooling process after hot-forging in the plurality of processes is performed while controlling the cooling speed according to the hot-forging parameter P<SB>F</SB>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a wheel-supporting rolling bearing unit that rotatably supports a wheel of an automobile or the like with respect to a suspension device.

  A wheel bearing rolling bearing unit that rotatably supports a wheel of an automobile or the like with respect to a suspension device generally has the following structure. That is, an inner member having a double-row raceway surface on the outer peripheral surface, an outer member having a double-row raceway surface on the inner peripheral surface, and between the raceway surface of the inner member and the raceway surface of the outer member A plurality of rolling elements which are arranged to be freely rollable, the inner member being a rotating wheel and the outer member being a fixed wheel (non-rotating wheel).

Further, a flange for attaching a wheel is provided on the outer peripheral surface of the inner member, and a flange for attaching a suspension device is provided on the outer peripheral surface of the outer member. Such a wheel-supporting rolling bearing unit has a structure in which the aforementioned flange is integrated with the inner member and the outer member.
The inner member and the outer member constituting the wheel support rolling bearing unit are made of, for example, medium carbon steel for machine structural carbon steel such as S53C as follows. In other words, a steel material is subjected to multiple steps of hot forging in order and formed into a predetermined shape in stages, then cooled, and if necessary, turning, grinding, drilling, etc. An inner member and an outer member having a composite ferrite-pearlite structure are obtained.

When driving the wheel-supporting rolling bearing unit, stress is applied to the inner member and the outer member, so that high fatigue strength is required for the inner member and the outer member. In particular, since a high bending stress or torsional stress is applied to the base portion of the flange to which the wheel or the suspension device is attached, a particularly high fatigue strength is required.
Therefore, the hot forging in the final step among the hot forgings in a plurality of steps is performed at a predetermined strain in a temperature range (approximately 750 to 850 ° C. in the case of S53C) within a temperature range of 100 ° C. higher than the A ₁ point to the A ₃ point. Patent Document 1 proposes a method for increasing the fatigue strength by making the crystal grain size fine (10 μm or less) by performing the above-described process.
JP 2007-23321 A JP 2007-24273 A Japanese Patent Laid-Open No. 2004-1000094

However, in steel materials with a carbon content of 0.4 to 0.6% by mass, if the crystal grain size is made fine, soft pro-eutectoid ferrite increases, leading to a decrease in hardness, and in turn a decrease in fatigue strength. There was a case. In order to prevent this, it is necessary to increase the cooling rate after hot forging. However, if the crystal grain size becomes excessively fine as described above, the cooling rate that can be realized in the production process (cooling and The cooling rate by cooling with a fan or the like) cannot sufficiently suppress the increase in pro-eutectoid ferrite, and the hardness may be reduced.
Accordingly, it is an object of the present invention to solve the above-described problems of the prior art and to provide a method for manufacturing a wheel support rolling bearing unit having high fatigue strength and a long service life.

  In order to solve the above problems, the present invention has the following configuration. That is, the method for manufacturing a wheel-supporting rolling bearing unit according to claim 1 of the present invention includes an inner member having a raceway surface on an outer peripheral surface and a raceway surface facing the raceway surface of the inner member. A wheel support comprising: an outer member arranged outward of the direction member; and a plurality of rolling elements arranged to roll freely between the raceway surface of the inner member and the raceway surface of the outer member. When manufacturing a rolling bearing unit for use, a plurality of steps of hot forging are sequentially applied to a steel material to form a predetermined shape in stages, thereby obtaining at least one of the inner member and the outer member. The hot forging of the final step among the hot forging of the plurality of steps is performed so as to satisfy the following conditions A, B, and C, and the cooling step after the hot forging of the plurality of steps is performed. It is characterized in that the following condition D is satisfied.

Condition A) Of the inner member or the outer member, a high load portion that is subjected to high stress when the wheel bearing rolling bearing unit is driven is hot forged at a processing temperature of 900 ° C. or higher and 1100 ° C. or lower.
Condition B) A von Mises strain of 0.3 or more and 1.5 or less is introduced into the high load portion by the hot forging in the final step.

Condition C) [the processing temperature] -150 × [the von Mises strain] becomes hot forging parameters P _F defined by the formula is 1000 or less.
If the condition D) the hot forging parameters P _F is 850 exceed 1,000 or less, the cooling rate of the cooling step is at 3 ° C. / s or less 0.25 ° C. / s or higher, the hot forging parameters P _F is When it is 850 or less, the cooling rate of the cooling step is 0.5 ° C./s or more and 3 ° C./s or less.

According to a second aspect of the present invention, there is provided a method for manufacturing a wheel-supporting rolling bearing unit according to the first aspect of the present invention. In the method for manufacturing a wheel-supporting rolling bearing unit according to the first aspect, in the high load part, the Japanese Industrial Standard JIS G0551. The prior austenite grain size measured by the method specified in 1) is 6 to 9 in grain size number.
Furthermore, the manufacturing method of the rolling bearing unit for wheel support of Claim 3 which concerns on this invention is a manufacturing method of the rolling bearing unit for wheel support of Claim 1 or Claim 2 in the said inner member and the said outer side. At least one of the members is provided with a flange to which a wheel or a suspension device is attached, and the high load portion is a base portion of the flange.

  The method for producing a wheel-supporting rolling bearing unit of the present invention can produce a wheel-supporting rolling bearing unit having high fatigue strength and a long service life.

  An embodiment of a method for manufacturing a wheel bearing rolling bearing unit according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing the structure of an embodiment of a wheel bearing rolling bearing unit according to the present invention. In this embodiment, in a state where the wheel bearing rolling bearing unit is attached to a vehicle such as an automobile, the portion facing the width direction outside of the vehicle is referred to as an outer end side portion, and the portion facing the width direction center side Is referred to as an inner end portion. That is, in FIG. 1, the left side is the outer end side, and the right side is the inner end side.

  The wheel support rolling bearing unit 1 of FIG. 1 includes a hub wheel 2, an inner ring 3, an outer ring 4, two rows of rolling elements 5 and 5, and cages 6 and 6 that hold the rolling elements 5. ing. A cylindrical portion 11 having a small outer diameter is formed on the inner end side portion of the hub wheel 2, and the inner ring 3 is press-fitted into the cylindrical portion 11. And the front-end | tip part of the cylindrical part 11 which protrudes in the inner end side rather than the inner ring | wheel 3 is caulked and spread radially outward, and the inner ring | wheel 3 and the hub ring 2 are being fixed integrally. However, the inner ring 3 and the hub ring 2 may be integrally fixed with a nut. In this case, the necessary preload can be applied to the inner ring 3 by the nut. A substantially cylindrical outer ring 4 is disposed concentrically outside the hub ring 2 and the inner ring 3. In addition, what fixed the inner ring | wheel 3 and the hub ring | wheel 2 integrally is corresponded to the inner member which is the structural requirements of this invention, and the outer ring | wheel 4 is equivalent to the outer member which is the structural requirements of this invention.

  A raceway surface is formed on each of the axially intermediate portion of the outer peripheral surface of the hub wheel 2 and the outer peripheral surface of the inner ring 3. The raceway surface of the hub wheel 2 is the first inner raceway surface 20a, and the raceway surface of the inner ring 3 is the first. Two inner raceway surfaces 20b are provided. Further, a raceway surface facing both the inner raceway surfaces 20a and 20b is formed on the inner peripheral surface of the outer ring 4, and the raceway surface facing the first inner raceway surface 20a is the first outer raceway surface 21a and the second raceway surface. The track surface facing the second inner track surface 20b is a second outer track surface 21b. Further, a plurality of rolling elements 5 are freely rollable between the first inner raceway surface 20a and the first outer raceway surface 21a and between the second inner raceway surface 20b and the second outer raceway surface 21b. It is arranged in. In the illustrated example, balls are used as rolling elements, but rollers may be used depending on the application of the wheel bearing rolling bearing unit 1 or the like.

Further, between the inner peripheral surface of the inner end side portion of the outer ring 4 and the outer peripheral surface of the inner end side portion of the inner ring 3, and the outer periphery of the inner peripheral surface of the outer end side portion of the outer ring 4 and the intermediate portion of the hub ring 2. Sealing devices 7a and 7b are provided between the surfaces.
Furthermore, a wheel mounting flange 10 for fixing a wheel (not shown) is provided on the outer end side portion of the outer peripheral surface of the hub wheel 2. A suspension device mounting flange 13 is provided on the outer peripheral surface of the outer ring 4 at an end portion on the side away from the wheel mounting flange 10.

  In order to assemble such a wheel support rolling bearing unit 1 to a vehicle such as an automobile, the suspension device mounting flange 13 is fixed to the suspension device, and the wheel is fixed to the wheel mounting flange 10. As a result, the wheel is rotatably supported by the wheel support rolling bearing unit 1 with respect to the suspension device. That is, the inner ring 3 and the hub ring 2 are integrally fixed to be a rotating ring, and the outer ring 4 is a fixed ring (non-rotating ring).

In such a wheel support rolling bearing unit 1, the hub wheel 2, the inner ring 3, and the outer ring 4 are hot forged products formed by hot forging a steel material into a predetermined shape. A method for manufacturing a hot forged product will be described using the hub wheel 2 as an example. The hub wheel 2 has a complicated shape, and it is difficult to form it by one-step hot forging. Therefore, multiple steps of hot forging are sequentially applied to a cylindrical steel material, and the shape is changed step by step. Molded by
The number of hot forging steps is not particularly limited, but is usually 3 to 4 steps. For example, in the case of three steps, upsetting is performed in the first step, rough forming is performed in the second step, and finish forming is performed in the third step. Then, the hot forging of the final process (the third process in the above example) among the multiple processes of hot forging is performed so as to satisfy the following conditions A, B, and C.

Condition A) A stress is applied to each part of the hub wheel 2 when the wheel supporting rolling bearing unit 1 is driven, but a high load part (for example, the wheel mounting flange 10 of the wheel mounting flange 10) is subjected to a high stress. The base portion S (particularly the outer end side) is hot forged at a processing temperature of 900 ° C. or higher and 1100 ° C. or lower.
Condition B) A von Mises strain of 0.3 to 1.5 is introduced into the high-load portion (however, more preferably 0.5 to 1.5).
Condition C) [processing temperature] -150 × [von Mises strain] becomes hot forging parameters P _F defined by the formula is 1000 or less.

Next, after such hot forging, the hot forged product is cooled, and this cooling step is performed so as to satisfy the following condition D.
If the condition D) hot forging parameters P _F is 850 exceed 1000 or less, the cooling rate of the cooling step is at 3 ° C. / s or less 0.25 ° C. / s or higher, in the hot forging parameters P _F is 850 or less In some cases, the cooling rate of the cooling step is not less than 0.5 ° C./s and not more than 3 ° C./s.

  The hub wheel 2 manufactured in this manner has an increase in soft pro-eutectoid ferrite at a high load site and has an appropriate ferrite / pearlite structure, so that it has excellent fatigue strength and a long life. Furthermore, in a high load site | part, it is more preferable that the prior austenite crystal grain size measured by the method prescribed | regulated to Japanese Industrial Standard JISG0551 is 6-9.

  The conditions for the processing temperature, the von Mises strain, and the prior austenite grain size are conditions for a high load site, but it is more preferable that the same conditions are satisfied for all sites as well as the high load site. By doing so, an increase in soft pro-eutectoid ferrite is suppressed in all parts, and since it has an appropriate ferrite / pearlite structure, fatigue strength is very excellent and a longer life is achieved.

  Further, the present invention can be applied to various wheel bearing rolling bearing units. For example, a wheel mounting flange is provided separately from a hub wheel or an outer ring, a so-called first-generation wheel support rolling bearing unit, a wheel mounting flange or a suspension device mounting flange is provided integrally with the outer ring, It is applied to a so-called third generation rolling bearing unit for wheel support in which a so-called second generation wheel supporting rolling bearing unit, a wheel mounting flange and a suspension mounting flange are provided integrally with either the inner ring or the outer ring, respectively. It is possible.

〔Example〕
Hereinafter, the present invention will be described more specifically with reference to examples. The cylindrical S53C material was hot forged in three steps to form a hub wheel shape, and then cooled. The conditions of the hot forging in the third process, which is the final process (processing temperature, von Mises strain, and hot forging parameter P _{F at} the root of the wheel mounting flange where high stress is applied) and the cooling rate of the cooling process are As shown in Table 1.
The processing temperature was determined by measuring the temperature of the workpiece surface using a radiation thermometer. Further, the von Mises strain was adjusted by changing the shape dimension at the time of hot forging, and was determined using a finite element method. Furthermore, the cooling rate was adjusted by the air volume and air speed of the air cooling fan.

  The resulting hot forged product was subjected to turning, induction hardening, tempering, grinding, and superfinishing to obtain a hub wheel. And using this hub wheel, the wheel support rolling bearing unit of the structure substantially the same as the above-mentioned wheel support rolling bearing unit 1 was manufactured. The distance between the double-row raceway surfaces of the wheel supporting rolling bearing unit is 25 mm, the thickness (axial width) of the wheel mounting flange is 10 mm, and the hub bolt has a bolt diameter of 14 mm.

An axial load of 3000 N and a radial load of 2000 N are input to the wheel mounting flange of the wheel support rolling bearing unit via hub bolts, and the wheel support rolling bearing unit is rotated at a rotational speed of 100 min ⁻¹ to repeatedly apply stress. did. Then, repeated stress at which fatigue failure does not occur in the hub wheel even when applied 10 ⁶ times was determined and used as fatigue strength. The results are shown in Table 1. In addition, the numerical value of the fatigue strength of Table 1 is shown as a relative value when the fatigue strength of Comparative Example 1 is 1. Moreover, the numerical value described in the column of former austenite crystal grain size (old austenite crystal grain size measured by the method specified in Japanese Industrial Standards JIS G0551) is a grain size number.

In order to increase the fatigue strength of the non-quenched portion, it is known that making the crystal grains fine is effective. The crystal grains of the non-quenched part (former austenite crystal grains in the ferrite-pearlite structure) are formed by recrystallization during hot forging, but the lower the processing temperature, the larger the strain introduced, Crystal grains can be made fine.
As a result of further earnest studies, the present inventor conducted the hot forging of the final process among the multiple processes of hot forging so as to satisfy the above-described conditions A, B, and C (implementation) Example 1-10, which is the hatched portion of the graph of FIG. 2), has an appropriate ferrite-pearlite structure, and the prior austenite grain size can be made from 6 to 9 in grain size number, and has high fatigue strength It was found that it can be obtained.

When the processing temperature is less than 900 ° C. as in Comparative Example 4, the crystal grains become excessively fine, so that the pro-eutectoid ferrite increases and the hardness decreases, and high fatigue strength cannot be obtained. Further, when the processing temperature is over 1100 ° C. as in Comparative Examples 1 and 2, the crystal grains do not become fine even when sufficient von Mises strain is applied, so that high fatigue strength cannot be obtained.
Furthermore, if the von Mises strain is less than 0.3 as in Comparative Example 5, the crystal cannot be sufficiently recrystallized, so that the crystal grains do not become fine even if the processing temperature is appropriate, and high fatigue strength cannot be obtained. . Furthermore, if the von Mises strain exceeds 1.5, processing heat generation may occur, and the crystal grains may be enlarged. Even when the processing temperature is low, the burden on the mold may increase, which is not preferable.

Furthermore, as in Comparative Example 3, even a fair processing temperature and von Mises strain, the hot forging parameters P _F is a 1000 exceeded, grain can not be obtained a high fatigue strength does not become fine.
However, if the crystal grains are excessively fine, soft pro-eutectoid ferrite is increased, so that the hardness is lowered and the fatigue strength may be lowered. The amount of pro-eutectoid ferrite becomes smaller as the crystal grain becomes larger and the cooling rate in the cooling step after hot forging becomes faster.

When hot forging parameters P _F is 850 to 1,000 is less than 8 at prior austenite grain size grain size number, to suppress a decrease in hardness if the cooling rate between 0.25 ° C. / s or higher be able to. When hot forging parameters P _F is 850 or less, the cooling rate it is possible to suppress a decrease in hardness if 0.5 ° C. / s or higher.
When the cooling rate is higher than 3 ° C./s, martensitic transformation is locally generated, so that cracking or the like may occur.

Comparative Example 6, since hot forging parameters P _F is the slow cooling rate is 900, the fatigue strength is not improved. In Comparative Example 7, since hot forging parameters P _F is the slow cooling rate is 800, the fatigue strength is not improved.
In addition, in order to improve the fatigue strength of a non-hardened part, it is necessary to apply this invention to the root part of the flange which is a high load site | part at least.

It is sectional drawing which shows the structure of one Embodiment of the rolling bearing unit for wheel support which concerns on this invention. It is a graph which shows the conditions (working temperature and von Mises distortion) of the hot forging performed in manufacture of the hub wheel of an Example and a comparative example. It is a graph which shows the relationship between prior austenite grain size (grain number) and fatigue strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing unit for wheel support 2 Hub wheel 3 Inner ring 4 Outer ring 5 Rolling body 10 Wheel mounting flange 13 Suspension device mounting flange 20a First inner raceway surface 20b Second inner raceway surface 21a First outer raceway surface 21b Second outer race Track surface S Base part

Claims (3)

An inner member having a raceway surface on an outer peripheral surface; an outer member having a raceway surface facing the raceway surface of the inner member; and the raceway surface of the inner member. And a plurality of rolling elements arranged so as to be freely rollable between the outer member and the raceway surface of the outer member, when manufacturing a wheel support rolling bearing unit,
By sequentially performing hot forging of a plurality of steps on a steel material and forming it in a predetermined shape step by step, obtaining at least one of the inner member and the outer member,
Among the multiple processes of hot forging, the final process of hot forging is performed so as to satisfy the following conditions A, B and C, and the cooling process after the multiple processes of hot forging is as follows: A method for manufacturing a wheel-supporting rolling bearing unit, wherein the method is carried out so as to satisfy the condition D.
Condition A) Of the inner member or the outer member, a high load portion that is subjected to high stress when the wheel bearing rolling bearing unit is driven is hot forged at a processing temperature of 900 ° C. or higher and 1100 ° C. or lower.
Condition B) A von Mises strain of 0.3 or more and 1.5 or less is introduced into the high load portion by the hot forging in the final step.
Condition C) [the processing temperature] -150 × [the von Mises strain] becomes hot forging parameters P _F defined by the formula is 1000 or less.
If the condition D) the hot forging parameters P _F is 850 exceed 1,000 or less, the cooling rate of the cooling step is at 3 ° C. / s or less 0.25 ° C. / s or higher, the hot forging parameters P _F is When it is 850 or less, the cooling rate of the cooling step is 0.5 ° C./s or more and 3 ° C./s or less.   2. The wheel support rolling according to claim 1, wherein in the high-load portion, the prior austenite grain size measured by a method defined in Japanese Industrial Standard JIS G0551 is 6 to 9 in grain size number. Manufacturing method of bearing unit.   A flange to which a wheel or a suspension device is attached is provided on at least one of the inner member and the outer member, and the high load portion is a base portion of the flange. The manufacturing method of the rolling bearing unit for wheel support of Claim 2.

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