JP2006029543A - Wheel supporting bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wheel supporting bearing device with a hub wheel or an outer ring whose crack is suppressed when manufactured by press molding of a steel plate. <P>SOLUTION: The wheel supporting bearing device comprises the hub wheel 2 to be rotated integrally with a wheel, a number of rolling elements 7 for rolling in an inner ring raceway groove 6 formed in the hub wheel 2 with the rotation of the hub wheel 2, and the outer ring 8 for rotatably supporting the hub wheel 2 via the rolling elements 7. At least one bearing member out of the hub wheel 2 and the outer ring 8 contains 0.45-0.75 mass% carbon. It is formed by press molding of a steel plate which has a plate thickness of 5 mm or more and which is subjected to softening annealing before press molding. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wheel support bearing device that rotatably supports a wheel or the like of an automobile with respect to a suspension device.

BACKGROUND ART A wheel support bearing device that rotatably supports a wheel of an automobile with respect to a suspension device is generally a hub wheel that rotates integrally with the wheel and an inner ring raceway groove formed on the outer peripheral surface of the hub wheel. This structure includes a large number of rolling elements that roll with the rotation of the motor and an outer ring that rotatably supports the hub wheel via the rolling elements.
In such a wheel support bearing device, conventionally, a hub wheel or an outer ring is formed by hot forging a high carbon steel material (for example, S50 to S55C equivalent material, SAE1070, etc.) and then cutting it into a predetermined shape. Therefore, there is a problem that it takes a lot of labor and time to manufacture the hub wheel and the outer ring.

Then, the technology which manufactures the hub wheel and outer ring | wheel of the wheel support bearing apparatus by using a carbon steel plate as a raw material of a hub wheel and an outer ring | wheel, and press-molding this steel plate to a defined shape is known (patent documents 1-1). 4).
JP 2003-25803 A Japanese Patent No. 3352226 JP-A-9-151950 JP 7-317777 A

However, when manufacturing the hub wheel and outer ring of the wheel support bearing device by press forming of a steel plate, if the material punched from the rolled steel plate is used as it is as the material of the hub wheel and outer ring, the part with a small forming amount is good There was a possibility that cracking would occur in the portion where the molding amount was large.
The present invention has been made paying attention to such problems, and provides a wheel support bearing device capable of suppressing the occurrence of cracking during press forming of a steel plate used as a material for a hub wheel or an outer ring. It is intended to provide.

  In order to achieve the above object, the invention of claim 1 is directed to a hub wheel that rotates integrally with a wheel, and an inner ring raceway groove formed in the hub wheel that rolls along with the rotation of the hub wheel. A wheel support bearing device comprising a rolling element and an outer ring that rotatably supports the hub wheel via the rolling element, wherein at least one bearing member of the hub wheel and the outer ring is 0.45. It is formed by press-forming a steel sheet containing 5% by mass to 0.75% by mass of carbon and having a thickness of 5 mm or more, and softening annealing is performed on the steel sheet before press-forming the steel sheet. Features.

The invention of claim 2 is characterized in that, in the wheel support bearing device of claim 1, the steel sheet is softened and annealed so that the area ratio of the pearlite structure at the time of press forming the steel sheet is 60% or less. To do.
According to a third aspect of the present invention, in the wheel support bearing device according to the first or second aspect, the steel sheet is softened and annealed so that the hardness of the steel sheet during press forming is Hv 200 or less. .
According to a fourth aspect of the present invention, in the wheel support bearing device according to the first or second aspect, the steel sheet is softened and annealed so that the hardness of the steel sheet during press forming is Hv180 or less. .

  According to the present invention, by applying softening annealing to a steel plate used as a material for a hub wheel or an outer ring of a wheel support bearing device before press forming, the hardness of the steel plate is lower than that without softening annealing. descend. Therefore, the formability of the steel plate used as the material for the hub wheel and the outer ring is improved, and the occurrence of cracking can be suppressed when the hub wheel and the outer ring of the wheel support bearing device are manufactured by press forming of the steel plate.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a wheel support bearing device according to an embodiment of the present invention. As shown in the figure, a wheel support bearing device 1 according to an embodiment of the present invention includes a cylindrical hub wheel 2 that rotates integrally with a wheel (not shown), and one end of the hub wheel 2. The part is formed with a wheel mounting flange 4 for mounting the wheel to the hub wheel 2 with bolts 3.

The wheel support bearing device 1 includes a bearing portion 5 that rotatably supports a wheel via a hub wheel 2, and the bearing portion 5 is formed in two rows of inner ring raceways formed on the outer peripheral surface of the hub wheel 2. A plurality of spherical rolling elements 7 that roll the groove 6 with the rotation of the hub wheel 2, and an outer ring 8 that rotatably supports the hub wheel 2 via the rolling element 7. An outer ring raceway groove 9 is formed on the inner peripheral surface of the outer ring 8 so as to face the inner ring raceway groove 6.
The hub wheel 2 and the outer ring 8 are formed by press-molding a steel plate (carbon content: 0.45 to 0.75 mass%) having a thickness of 5 mm or more, and used as a material for the hub wheel 2 and the outer ring 8. The steel sheet is softened and annealed before press forming.

FIG. 2 is a diagram showing a manufacturing process when the hub wheel of the wheel supporting bearing device is manufactured from a steel plate, and the operation of the present invention will be described below with reference to FIG.
In FIG. 2, reference numeral 10 indicates a hub wheel material 10 obtained by punching a rolled steel plate. When a hub wheel of a wheel support bearing device is manufactured from the hub wheel material 10, first, the hub wheel material 10. 2 is pressed into a predetermined shape in the deep drawing step of FIG. 2B, and then the through hole 11 is pierced in the center of the hub wheel material 10 in the piercing step of FIG. Next, the hub wheel material 10 is press-molded into a finished product shape in the deep drawing process of FIG. 2D, and then the hub wheel material 10 is pierced with bolt holes 12 in the piercing process of FIG. A hub wheel of a supporting bearing device is manufactured.

  The above-described process is a general method used when manufacturing a hub wheel or an outer ring of a wheel support bearing device from a rolled steel plate. From the material obtained by punching the rolled steel plate, the hub wheel of the wheel support bearing device or When the outer ring is manufactured by press molding, the formability of the material, particularly deep drawability, is important. Further, a portion requiring strength such as a root of a flange includes a thickness process for increasing the thickness, and the workability is increased, so that good press formability is required.

  However, if the raw material obtained by punching a rolled steel sheet is used as it is (as it is hot-rolled), it depends on the cooling rate in the manufacturing process of the steel sheet, but the metal structure of the material is different from the ferrite structure. It becomes a mixed phase of pearlite structure, and the hardness of the material is about Hv220 to Hv300. For this reason, it becomes too hard to press-mold the material, and if the material is press-molded in such a state, the deformation resistance and processing stress at the time of press-molding become extremely large, and the material cannot be molded into a predetermined product shape. Cracks may occur.

  In the present invention, when the hub wheel and outer ring of the wheel support bearing device are manufactured by press forming, the material obtained by punching the rolled steel sheet is not used as it is, and soft annealing is performed before press forming. By applying to the material, the hardness of the material is lower than the state during hot rolling, so that the press formability of the material is improved and the occurrence of cracks during press forming can be suppressed.

As for the hardness of the material obtained by annealing, sufficient press formability can be obtained if it is Hv 200 or less, but the lower the hardness of the material, the smaller the deformation resistance at the time of press molding, and the easier it is to form the material. Therefore, the hardness of the material obtained by annealing is preferably Hv180 or less.
When manufacturing hub wheels and outer rings for wheel support bearing devices by press molding, the hardness of the steel sheet, which is the hub wheel material and outer ring material, is increased, and the factor that reduces formability is the pearlite structure of the steel sheet. An example is plate-like cementite (carbide). In the present invention, by annealing the steel plate before press forming, the plate-like cementite constituting the pearlite structure is divided and changed from a plate shape to a spherical shape, so that the hardness of the steel plate is reduced. Can do.

  Here, the steel sheet can be most softened by subjecting the steel sheet to spheroidizing annealing in which cementite is completely spheroidized (spheroidization rate: 100%). The steel plate to be made is hypoeutectoid steel having a carbon content of 0.45 to 0.75 mass%. For this reason, like hypereutectoid steel represented by bearing steel, it is difficult to spheroidize all cementite constituting the pearlite structure by annealing, and the pearlite structure tends to remain. However, even in the case where the pearlite structure remains, the basic constituent phase is changed to ferrite structure and spheroidized cementite, and the area ratio of the remaining pearlite structure is set to 60% or less, thereby improving the formability of the steel sheet, particularly deep drawability be able to.

Examples of the soft annealing conditions for spheroidizing cementite include the following (a) to (d).
(A) After heating the steel plate for about 1 to 2 hours at a temperature 20-30 ° C. higher than the Ac1 transformation point, the steel plate is cooled at a cooling rate of 20 ° C./hour, and then the steel plate is heated to a temperature of 550-600 ° C. Allow to cool.
(B) After heating the steel plate at a temperature 20-30 ° C. higher than the Ac1 transformation point, the steel plate is cooled to a temperature 20-30 ° C. lower than the Ac1 transformation point. And after repeating this 3 times or more, a steel plate is cooled.
(C) After heating the steel plate at a temperature immediately above the Ac1 transformation point (760 to 780 ° C.), the steel plate is cooled to a temperature of 700 ° C., and then the steel plate is held at a temperature of 700 ° C. for 2 to 10 hours and then air-cooled. To do.
(D) After quenching the steel plate at a temperature of 800 to 900 ° C., the steel plate is tempered under the conditions of tempering temperature: 680 to 700 ° C. and tempering time: 5 to 40 hours.

The Ac1 transformation point is expressed by the following equation, and changes depending on the contents of Mn, Ni, and Cr contained in the steel plate.
Ac1 = 723-10.7 * Mn% -16.9 * Ni% + 29.1 * Si% + 16.9 * Cr% (° C.)
Also, if the Hv is 200 or less and the area ratio of the pearlite structure is 60% or less, good formability can be obtained, and therefore the annealing conditions are not limited to the above-described conditions.

  In order to confirm the effect of the present invention, the present inventor uses a steel plate equivalent to S55C (plate thickness: 9 mm, hardness before annealing: Hv232, Ac1 transformation point: 725 ° C.) as a hub wheel material of a wheel support bearing device. The hub wheel material was annealed under the following annealing conditions 1-8. Then, after measuring the hardness of the hub wheel material after annealing and the area ratio of the pearlite structure, the hub wheel material is deep drawn into a product shape, and the surface state of the hub wheel material is visually observed after deep drawing. The incidence of cracking was investigated. In addition, the area ratio of the pearlite structure | tissue which remains after annealing was measured from the microscope picture expanded 500 times. Moreover, about the incidence rate of a crack, the hub wheel raw material was deep-drawn 10 times in each condition of annealing conditions 1-8, and the incidence rate of the crack was calculated | required.

<Annealing condition 1>
After holding at 770 ° C. for 1 to 2 hours, cooling to 700 ° C. at 30 ° C./hour, then holding at 700 ° C. for 2 hours and then allowing to cool.
<Annealing condition 2>
After holding at 770 ° C. for 1 to 2 hours, cooling to 700 ° C. at 30 ° C./hour, then holding at 720 ° C. for 4 hours and allowing to cool.
<Annealing condition 3>
After holding at 760 ° C. for 2 to 5 hours, cooling to 720 ° C. at 20 ° C./hour, holding at 720 ° C. for 4 hours, cooling to 680 ° C. at 10 ° C./hour, and then allowing to cool.
<Annealing condition 4>
After holding at 760 ° C. for 30 minutes, cooling to 720 ° C. at 10 ° C./hour, then holding at 720 ° C. for 30 minutes, repeating this three times as one cycle, and allowing to cool.

<Annealing condition 5> (The holding temperature of condition 4 was lowered to 700 ° C.)
After holding at 760 ° C. for 30 minutes, cooling to 700 ° C. at 10 ° C./hour, then holding at 720 ° C. for 30 minutes, repeating this three times as one cycle, and allowing to cool.
<Annealing condition 6>
After holding at 760 ° C. for 2 hours, it is cooled to 580 ° C. at 20 ° C./hour and then allowed to cool.
<Annealing condition 7>
After holding at 700 ° C. for 10 hours, it is allowed to cool.
<Annealing condition 8>
After holding at 800 to 950 ° C. for 30 minutes, oil cooling, then tempering at 700 ° C. for 20 to 40 hours, and then allowing to cool.
Table 1 shows the hardness after annealing of the hub wheel material, the pearlite structure area ratio, and the occurrence rate of cracks when the hub wheel material is annealed under the above annealing conditions 1 to 8.

  In Table 1, when Examples 1 to 5 and Comparative Example 4 are compared, since Comparative Example 4 is formed by deep drawing the hub wheel material while being hot-rolled, cracks occur during deep drawing. You can see that On the other hand, in Examples 1-5, since it anneal-treats to the steel plate before deep-drawing a hub wheel raw material, it turns out that a crack does not generate | occur | produce at the time of deep drawing.

  Moreover, when Examples 1-5 are compared with Comparative Example 1, since Comparative Example 1 anneals the hub wheel material under annealing condition 4, the hardness after annealing is high as Hv203, and the remaining pearlite structure It can be seen that the area ratio is as high as 61%. On the other hand, in Examples 1-5, since the hub wheel material was annealed under any one of annealing conditions 1, 2, 3, 5, and 8, compared with Comparative Example 1, It can be seen that the hardness is as high as Hv 200 or less and the area ratio of the remaining pearlite structure is as low as 60% or less.

Furthermore, when Examples 1-5 and Comparative Examples 2 and 3 are compared, since Comparative Examples 2 and 3 are annealing the hub wheel material under annealing conditions 6 or 7, the hardness after annealing is Hv200 or less. However, it can be seen that the area ratio of the remaining pearlite structure is higher than 60%. On the other hand, in Examples 1-5, since the hub wheel material was annealed under any one of annealing conditions 1, 2, 3, 5, and 8, compared with Comparative Example 1, It can be seen that the hardness is as high as Hv 200 or less and the area ratio of the remaining pearlite structure is as low as 60% or less.
Therefore, in order to set the material hardness after annealing of the hub wheel material to Hv 200 or less and the area ratio of the remaining pearlite structure to 60% or less, among annealing conditions 1 to 8, annealing conditions 1, 2, 3, 5 , 8, the hub wheel material may be annealed before press forming.

  Next, a steel plate equivalent to S55C (plate thickness: 9 mm, hardness before annealing: Hv232, Ac1 transformation point: 725 ° C.) was used as the hub wheel material of the wheel support bearing device, and annealing treatment was performed before press forming. The operation in this case will be described with reference to FIG. In FIG. 3, black circles indicate that cracking occurred during deep drawing, and ◯ indicates that cracking did not occur during deep drawing.

  As is apparent from FIG. 3, the pearlite structure that existed during hot rolling is divided by annealing the hub wheel material obtained by punching the rolled steel sheet before press forming, and is a hub wheel material. It can be seen that the steel sheet tends to soften. It can also be seen that the hardness of the hub wheel material does not change much before annealing when the area ratio of the pearlite structure after annealing of the hub wheel material is about 40%. It can be seen that the hardness of the wheel material tends to increase linearly. Further, it is understood that when the area ratio of the pearlite structure after annealing of the hub wheel material is more than 60% and the hardness of the hub wheel material is higher than Hv200, the formability is lowered and cracking is likely to occur. Even when the hardness of the hub wheel material after annealing is Hv 200 or less, as in Comparative Examples 2 and 3, when the area ratio of the remaining pearlite structure exceeds 60%, the formability is slightly lowered.

Therefore, in order to prevent cracking during press molding, the hub wheel material is pressed so that the hardness after annealing of the hub wheel material is Hv 200 or less and the area ratio of the remaining pearlite structure is 60% or less. What is necessary is just to anneal before forming.
As for the formability of the hub wheel material and the outer ring material, the smaller the initial hardness of the material, the smaller the deformation resistance during press molding, and the easier the press molding, so the hardness after annealing of the material is Hv 180 or less. It is desirable that Moreover, the limit which can soften the raw material whose carbon content is 0.45-0.75 mass% by softening annealing is about Hv130, and it is desirable to set the lower limit of hardness to Hv130.

It is sectional drawing in alignment with the axial direction of the wheel support bearing apparatus which concerns on one Embodiment of this invention. It is a figure which shows the manufacturing process in the case of manufacturing the hub wheel of the bearing apparatus for wheel support by press-molding a steel plate. It is a figure for demonstrating an effect | action at the time of annealing-processing the hub wheel raw material obtained by stamping a rolled steel plate before press molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wheel support bearing device 2 Hub wheel 3 Bolt 4 Wheel mounting flange 5 Bearing part 6 Inner ring raceway groove 7 Rolling element
8 Outer ring 9 Outer ring raceway groove 10 Hub wheel material

Claims (4)

A hub wheel that rotates integrally with the wheel, a number of rolling elements that roll along an inner ring raceway groove formed in the hub wheel as the hub wheel rotates, and the hub wheel is rotatable through the rolling element A wheel support bearing device comprising an outer ring supported by
Of the hub wheel and the outer ring, at least one bearing member is formed by pressing a steel plate containing 0.45 mass% to 0.75 mass% of carbon and having a plate thickness of 5 mm or more, and the steel plate A wheel support bearing device, wherein the steel plate is subjected to soft annealing before press forming.   The wheel support bearing device according to claim 1, wherein the steel plate is softened and annealed so that an area ratio of a pearlite structure at the time of press forming the steel plate is 60% or less.   3. The wheel support bearing device according to claim 1, wherein the steel plate is softened and annealed so that a hardness at the time of press forming of the steel plate is equal to or less than Hv200. 4.   The wheel support bearing device according to claim 1 or 2, wherein the steel plate is softened and annealed so that the hardness of the steel plate during press forming is Hv180 or less.

Images