JP2010007798A - Rolling bearing unit for supporting wheel and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing unit for supporting a wheel which has excellent strength and a long life. <P>SOLUTION: A hub ring 2 of the rolling bearing unit 1 for supporting the wheel is provided by induction hardening after a steel element is treated by hot forging, molded in a predetermined shape and cooled. Hot forging is executed while controlling a heating temperature of the element on starting the hot forging, a processing temperature of a non-heat treated section which is used with a surface state just as it is treated by the hot forging, a quantity of von Mises torsion introduced for the non-heat treated section and a hot forging parameter P<SB>F</SB>. A cooling process after the hot forging is executed while controlling a cooling speed. In the non-heat treated section, an old austenite grain size measured by a method specified in the Japanese Industrial Standards JIS G0551 is arranged to be 6 or more and 9 or less and a decarburization depth is 0.3 mm or less by the hot horging or the cooling process. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

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

  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 hot forging in multiple steps in order and formed into a predetermined shape in stages and 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 bearing rolling bearing unit, stress is applied to the inner member and the outer member, so that the inner member and the outer member are required to have high strength. In addition, in the past, parts that were not loaded with high stress were often used in a surface state that had been subjected to the hot forging without being quenched from the viewpoint of cost. Since the thickness and weight have been reduced for the purpose of increasing the thickness, there is a case where high stress may be applied to such a portion, and thus high strength is required even in such a portion.

For example, in order to reduce the weight, a recess may be formed at one axial end of the inner member, but the ratio b / a between the axial length a of the inner member and the axial length b of the recess is If it is 0.2 or more, the possibility that a relatively large load is applied to one end in the axial direction in which the concave portion is formed in the inner member is increased.
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 of increasing the strength by making the crystal grain size fine (10 μm or less) by performing so as to add.
JP 2007-23321 A JP 2007-24273 A Japanese Patent Laid-Open No. 2004-1000094

However, in steel materials having a carbon content of 0.4 to 0.6% by mass used for a wheel bearing rolling bearing unit, the hardness increases because soft pro-eutectoid ferrite increases when the crystal grain size is made fine. In some cases, the strength was lowered. 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 (Cooling rate by cooling with a fan or the like), the increase in pro-eutectoid ferrite could not be sufficiently suppressed, and the hardness could be lowered.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a wheel bearing rolling bearing unit having a high strength and a long service life, and a method for manufacturing the same, in order to solve the above-described problems of the prior art.

  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, the inner member and the outer member are formed by subjecting a steel material to hot forging and forming it into a predetermined shape, and then subjecting at least the raceway surface to induction hardening and curing. A cooling step of obtaining at least one of the members and performing the hot forging so as to satisfy the following conditions A, B, C, and D and performing between the hot forging and the induction hardening. To satisfy the following condition E And wherein the door.

Condition A) The temperature of the steel material during the hot forging is set to 1200 ° C. or less.
Condition B) Of the inner member or the outer member, the non-tempered portion used in the surface state where the induction hardening is not performed and the hot forging is performed is 900 ° C. or higher and 1100 ° C. or lower. Hot forging at the processing temperature of
Condition C) A von Mises strain of 0.3 or more and 1.5 or less is introduced into the non-tempered portion by the hot forging.
Condition D) [the processing temperature] -150 × [the von Mises strain] becomes hot forging parameters P _F defined by the formula is 1000 or less.
Condition E) The cooling rate of the cooling step is 0.25 ° 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. The ratio b / a between the axial length a of the inner member and the axial length b of the recess is 0.2 or more, and the recess is formed in the inner member. The one axial direction end part is equivalent to the said non-tempered site | part.

  Furthermore, the rolling bearing unit for supporting a wheel according to claim 3 according to 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-supporting rolling bearing comprising: an outer member arranged outward; and a plurality of rolling elements arranged to roll between the raceway surface of the inner member and the raceway surface of the outer member. In the unit, the prior austenite grain size measured by the method defined in Japanese Industrial Standard JIS G0551 is manufactured by the method for manufacturing a wheel-supporting rolling bearing unit according to claim 1, The number is 6 or more and 9 or less, and the decarburization depth is 0.3 mm or less.

  Furthermore, the rolling bearing unit for wheel support according to claim 4 according to the present invention is the rolling bearing unit for wheel support according to claim 3, wherein a recess is formed at one axial end of the inner member. A ratio b / a between the axial length a of the inner member and the axial length b of the recess is 0.2 or more, and one end in the axial direction where the recess is formed in the inner member Corresponds to the non-tempered part.

  According to the method for manufacturing a wheel-supporting rolling bearing unit of the present invention, it is possible to easily manufacture a wheel-supporting rolling bearing unit having high strength and a long service life. Moreover, the wheel-supporting rolling bearing unit of the present invention has high strength and a long life.

  DESCRIPTION OF EMBODIMENTS Embodiments of a wheel bearing rolling bearing unit and a method for manufacturing the same 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 a wheel bearing rolling bearing unit. 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, a seal device 7 is provided between the inner peripheral surface of the outer end side portion of the outer ring 4 and the outer peripheral surface of the intermediate portion of the hub wheel 2. Further, a concave portion 15 is formed at one axial end portion (outer end portion U) of the hub wheel 2 for weight reduction.
Further, 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 so as to protrude radially outward. A suspension device mounting flange 13 is provided on the outer peripheral surface of the outer ring 4 so as to protrude radially outward 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 a suspension device (not shown), 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. And these multiple processes of hot forging are performed so as to satisfy the following conditions A, B, C, and D.
Condition A) When starting hot forging, the steel material is first heated, and the heating temperature is set to 1200 ° C. or lower. And it controls so that the temperature of the steel raw material in hot forging does not exceed 1200 degreeC. Of course, the heating temperature is the same as or higher than the processing temperature at the time of hot forging described later.

Condition B) The outer peripheral surface including the first inner raceway surface 20a of the hub wheel 2 is subjected to induction hardening after hot forging. The flange 10 is not subjected to induction hardening and is used in an uncured surface state that has been subjected to hot forging. Such an unheated part, that is, the outer end side portion U, the wheel mounting flange 10 and the like are hot forged at a processing temperature of 900 ° C. or higher and 1100 ° C. or lower.
Condition C) By this hot forging, a von Mises strain of 0.3 or more and 1.5 or less is introduced into the non-tempered portion.
Condition D) [the 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 E.
Condition E) The cooling rate in the cooling step is 0.25 ° C./s or more and 3 ° C./s or less.
When this cooling step is completed, induction hardening is performed on the outer peripheral surface to form the first inner raceway surface 20a. Then, turning, grinding, drilling and the like are performed as necessary to complete the hub wheel 2.

Since the hub wheel 2 manufactured in this way was hot forged and cooled while the temperature, strain amount, and cooling rate were controlled, the non-heat treated part was specified in Japanese Industrial Standard JIS G0551. The prior austenite grain size measured by the above method is 6 or more and 9 or less in grain size number. And the said non-tempered site | part has the excellent ductility and intensity | strength, since the increase of the soft pro-eutectoid ferrite is suppressed and it has a suitable ferrite-pearlite structure | tissue.
Further, since the temperature of the steel material during hot forging was controlled so as not to exceed 1200 ° C., the decarburization phenomenon, which is an inevitable phenomenon in hot forging, was suppressed, and the decarburization depth was 0.3 mm. It is as follows. As a result, strength reduction due to the decarburization phenomenon is suppressed.

  Each portion of the hub wheel 2 is subjected to stress when the wheel bearing rolling bearing unit 1 is driven, but is not used in a surface state that is not quenched and hot forged. The tempered portion is not so high in strength that it cannot withstand stress and may be damaged. However, the hub wheel 2 manufactured as described above has high strength even if it is a non-tempered part that is used in a surface state that is not quenched and subjected to hot forging after hot forging. is there. Therefore, the wheel-supporting rolling bearing unit 1 has high strength and long life. In addition, since it is not necessary to perform high-cost quenching throughout the manufacturing, the wheel bearing rolling bearing unit 1 is inexpensive.

  In particular, if the concave portion 15 of the outer end portion U is enlarged for weight reduction, the stress applied to the portion U increases, and the axial length a of the hub wheel 2 and the axial length of the concave portion 15 (hub If the ratio b / a of the axial distance (b) between the outer end of the wheel 2 and the bottom of the recess 15 is 0.2 or more, a high stress can be applied to the portion U having insufficient strength. However, if hot forging and cooling satisfying the above conditions are performed, the non-heat treated part has high strength, so it can withstand high stress and can be reduced in weight.

  The present invention can be applied to various wheel bearing rolling bearing units. For example, a so-called first generation wheel support rolling bearing unit, a wheel mounting flange or a suspension device mounting flange provided integrally with the outer ring, where the wheel mounting flange is provided separately from the hub wheel and 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 the same three steps as described above to form a hub wheel shape, and then cooled. Conditions for hot forging in the second step, which is a step for forming a recess mainly in the outer end side portion (heating temperature of the material, processing temperature in the outer end side portion, von Mises strain, and hot forging parameter P _F ) Table 1 shows the cooling rate of the cooling step.
The heating temperature and the processing temperature were determined by measuring the workpiece surface temperature using a radiation thermometer. Further, the von Mises strain was adjusted by changing the shape dimension during 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 obtained hot forged product was shot blasted to remove the oxidized scale on the surface, and then 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 axial distance between the raceways of the double row of this rolling bearing unit for wheel support is 59 mm, the number of balls as rolling elements is 12 per row, the axial length a of the hub wheel and the axial length of the recess. The ratio b / a with b is 0.3.

An axial load of 3500 N and a radial load of 4000 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 300 min ⁻¹ to repeatedly apply stress. did. And it continued rotation for 100 hours and observed the presence or absence of the damage (cracking) of the outer end side part in which the recess was formed. The results are shown in Table 1. In Table 1, “◯” indicates that there was no damage even after 100 hours of rotation, “Δ” indicates that cracks were confirmed after 100 hours of rotation, and “×” indicates that It shows that it was damaged in less than 100 hours and could not continue to rotate.

  Table 1 also shows the prior austenite grain size (old austenite grain size measured by the method defined in Japanese Industrial Standard JIS G0551) and the decarburization depth of the outer end side portion. The method for measuring the prior austenite grain size is as follows. The hub wheel is broken in a plane parallel to the axial direction, the cross section is polished, and then etched with a nital etchant, so that a portion 1.0 mm inside from the outermost surface of the outer side of the hub wheel (that is, decarburization occurs) The austenite crystal grain size was measured for the unexposed portion. The numerical values shown in Table 1 are particle size numbers. Moreover, the measuring method of decarburization depth is as follows. Etching was performed in the same manner as in the case of the prior austenite grain size, and the cross section was observed with a metallographic microscope. And the depth from the outermost surface where the change accompanying decarburization is not seen in a metal structure was made into the decarburization depth.

In order to increase the fatigue strength of the non-quenched part (non-tempered part), it is effective to make the crystal grains fine. 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 diligent investigations, the present inventor conducted hot forging so as to satisfy the above-mentioned conditions A, B, C, and D (Examples 1 to 8). -It has discovered that it has a pearlite structure | tissue and can make a prior-austenite crystal grain size 6 or more and 9 or less by a particle size number, and high fatigue strength is obtained. For this reason, Examples 1 to 8 had excellent fatigue strength without being damaged in the outer end side portion of the hub wheel even after rotating for 100 hours under the above-described conditions.

When the processing temperature is less than 900 ° C. as in Comparative Example 3, the crystal grains become excessively fine, so that the pro-eutectoid ferrite increases and the hardness decreases. Therefore, the fatigue strength was insufficient. Further, when the processing temperature was over 1100 ° C. as in Comparative Example 1, the crystal grains did not become fine even when sufficient von Mises strain was applied, so that sufficient fatigue strength could not be obtained.
Furthermore, if the von Mises strain is less than 0.3 as in Comparative Example 4, the crystal cannot be sufficiently recrystallized, so even if the processing temperature is appropriate, the crystal grains do not become fine and high fatigue strength cannot be obtained. It was. Furthermore, if the von Mises strain is more than 1.5, processing heat is generated and the crystal grains become larger, or the load on the mold may increase when the processing temperature is low. It is not preferable.

Furthermore, as in Comparative Example 2, even a fair processing temperature and von Mises strain, the hot forging parameters P _F is a 1000 exceeded, no sufficient fatigue strength grain does not become fine is obtained It was.
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. That is, by setting the cooling rate to 0.25 ° C./s or more, it is possible to suppress a decrease in hardness. On the other hand, when the cooling rate is higher than 3 ° C./s, martensitic transformation is locally generated, so that there is a possibility that cracking or the like may occur. Since the comparative example 5 had a slow cooling rate, the fatigue strength was insufficient. In addition, the cooling rate in this invention means the cooling rate until it falls to 550 degreeC after completion | finish of hot forging.

In hot forging, decarburization is an inevitable phenomenon, but since the hardness is reduced by decarburization, the fatigue strength is also reduced. In Comparative Examples 6 and 7, the heating temperature exceeded 1200 ° C. and the decarburization depth was large, so the fatigue strength was insufficient.
Although shot blasting was performed, this not only removed the oxide scale but also applied compressive residual stress to the surface of the hub wheel, so that hot forging was performed without being quenched after hot forging. This contributes to improving the strength of non-tempered parts that are used in the raw surface state. In Comparative Examples 6 and 7, the decarburization depth is large, and it is considered that the effect of shot blasting was not sufficiently obtained, so this is also considered to be a cause of insufficient fatigue strength.

It is a fragmentary sectional view which shows the structure of the rolling bearing unit for wheel support.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wheel support rolling bearing unit 2 Hub ring 3 Inner ring 4 Outer ring 5 Rolling body 10 Wheel mounting flange 13 Suspension apparatus mounting flange 15 Recess 20a First inner raceway surface 20b Second inner raceway surface 21a First outer raceway surface 21b First Two outer raceways a Hub length in the axial direction b Axial length in the recess U Outer end portion

Claims (4)

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,
After performing hot forging on a steel material and forming it into a predetermined shape, at least one of the inner member and the outer member is obtained by performing induction hardening on at least the raceway surface and curing,
The hot forging is performed so as to satisfy the following conditions A, B, C, and D, and the cooling process performed between the hot forging and the induction hardening satisfies the following condition E: A method for manufacturing a wheel-supporting rolling bearing unit, characterized in that:
Condition A) The temperature of the steel material during the hot forging is set to 1200 ° C. or less.
Condition B) Of the inner member or the outer member, the non-tempered portion used in the surface state where the induction hardening is not performed and the hot forging is performed is 900 ° C. or higher and 1100 ° C. or lower. Hot forging at a processing temperature of
Condition C) By the hot forging, a von Mises strain of 0.3 to 1.5 is introduced into the non-tempered portion.
Condition D) [the processing temperature] -150 × [the von Mises strain] becomes hot forging parameters P _F defined by the formula is 1000 or less.
Condition E) The cooling rate in the cooling step is 0.25 ° C./s or more and 3 ° C./s or less.   A concave portion is formed at one axial end portion of the inner member, and a ratio b / a between the axial length a of the inner member and the axial length b of the concave portion is 0.2 or more. 2. The method for manufacturing a wheel-supporting rolling bearing unit according to claim 1, wherein one end portion in the axial direction in which the concave portion is formed in the inner member corresponds to the non-heat treated portion. 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. A rolling bearing unit for supporting a wheel, comprising: a plurality of rolling elements that are freely rollable between the outer race member and the raceway surface of the outer member;
The prior austenite grain size measured by the method defined in Japanese Industrial Standard JIS G0551 in the non-heat treated portion is 6 in terms of the grain size number. A rolling bearing unit for supporting a wheel, wherein the rolling bearing unit is 9 or less and has a decarburization depth of 0.3 mm or less.   A concave portion is formed at one axial end portion of the inner member, and a ratio b / a between the axial length a of the inner member and the axial length b of the concave portion is 0.2 or more. The rolling bearing unit for supporting a wheel according to claim 3, wherein one end in the axial direction in which the concave portion is formed in the inner member corresponds to the non-heat treated portion.

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