JP2008064268A - Rolling bearing unit for wheel support - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize structure which can enhance rigidity of moment by making the pitch circle diameter of an outside train larger than that of an inside train and furthermore can fully assure rolling fatigue life of a plurality of outer ring tracks 13a, 13b provided in the inner peripheral surface of an outer ring 3a. <P>SOLUTION: Heat treatment hardened layers 17a, 17b, 17c are formed on a portion which contains both of the outer ring tracks 13a, 13b in two positions in the axial direction of the inner peripheral surface of the outer ring 3a and a space portion 16 between these outer ring tracks 13a, 13b at a halfway part in the axial direction of the inner peripheral surface of the outer ring 3a. The heat treatment hardened layers 17a, 17b, 17c on these portions are integrated and are continuous with one another. By this configuration, the rolling bearing unit can transmit a force generated radially inwardly on an unhardened part 18 of the space portion 16 to the heat treatment hardened layers 17a, 17b of the outer ring tracks 13a, 13b, thereby enhancing the rolling fatigue life of both of these outer ring tracks 13a, 13b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of a rolling bearing unit for supporting a wheel used for rotatably supporting a rotating member for braking such as a wheel and a brake disk of an automobile with respect to a suspension device.

  The wheel of the automobile and the rotating member for braking are rotatably supported with respect to the suspension device by the wheel bearing rolling bearing unit. A large moment is applied to such a wheel-supporting rolling bearing unit when the automobile is turning. Therefore, in order to ensure stability during turning, it is necessary to ensure a large moment rigidity. For this reason, conventionally, as a rolling bearing unit for supporting a wheel, a structure in which rolling elements are arranged in a double row and a preload and a combined contact angle of the back surface are given to the rolling elements in both rows is generally used. ing. Furthermore, in recent years, in order to ensure a larger moment rigidity while preventing an increase in size, for example, as described in Patent Documents 1 to 5, the pitch circle diameters and the rolling element diameters of both rolling elements are made different. A proposed structure has been proposed.

  FIG. 5 shows the structure described in Patent Document 4 among them. The wheel support rolling bearing unit 1 includes a hub 2, an outer ring 3, and a plurality of balls 4, 4 each of which is a rolling element. Of these, the hub 2 is formed by combining a hub body 5 and an inner ring 6. Further, the hub 2 is an outer end in the axial direction of the outer peripheral surface (outside with respect to the axial direction means the outer side in the width direction of the vehicle when assembled to the automobile, the left side of each figure. The right side of each figure is said to be inward with respect to the axial direction. The same throughout the present specification.) The mounting flange 7 for supporting the wheel and the rotating rotating member for braking is also provided at the intermediate portion and the inner end portion. Double row inner ring raceways 8a and 8b are formed respectively. Of these inner ring raceways 8a and 8b, the diameter of the inner ring raceway 8a on the outer side in the axial direction is larger than the diameter of the inner ring raceway 8b on the inner side. A base end portion of a plurality of studs 9 is fixed to the mounting flange 7 so that a braking rotator such as a disk or a wheel constituting a wheel can be supported and fixed to the mounting flange 7. .

  In order to make the diameters of the inner ring raceways 8a and 8b different, in the structure shown in FIG. 5, the outer circumferential surface of the hub body 5 is slightly closer to the inner side in the axial direction than the outer ring raceway 8a. An outer peripheral surface side inclined step portion 10 that is inclined in a direction in which the outer diameter decreases toward the inner side in the axial direction is formed in the portion. Further, a small-diameter step portion 11 is formed at the inner end portion in the axial direction of the hub body 5 which is closer to the inner side in the axial direction than the inclined step portion 10 on the outer peripheral surface side. The small-diameter step portion 11 is formed with the inner ring raceway 8b formed on the outer peripheral surface of the inner ring raceway 8b. The inner ring 6 is externally fitted, and the caulking portion 12 is formed on the inner end portion in the axial direction of the hub body 5. The inner ring 6 is coupled and fixed to the hub body 5. The inner ring raceways 8a and 8b have a circular cross-sectional shape (bus shape), and the outer diameter decreases as they approach each other (as they approach the center in the axial direction of the hub 2).

  The outer ring 3 is provided with double-row outer ring raceways 13a and 13b on the inner peripheral surface and a coupling flange 14 on the outer peripheral surface for coupling and fixing the outer ring 3 to a suspension device. Of the two outer ring raceways 13a and 13b, the diameter of the outer ring raceway 13a on the outer side in the axial direction is larger than the diameter of the outer ring raceway 13b on the inner side. For this reason, in the structure shown in FIG. 5, the inner diameter becomes smaller toward the inner side in the axial direction at a portion closer to the inner side in the axial direction than the outer outer ring raceway 13 a on the inner peripheral surface in the axial direction of the outer ring 3. An inner peripheral surface side inclined step portion 15 that is inclined in the direction is formed. Both the outer ring raceways 13a and 13b have a circular cross-sectional shape (bus shape), and the inner diameter decreases as they approach each other (as they approach the center in the axial direction of the hub 2).

A plurality of balls 4, 4 are provided between the inner ring raceways 8a, 8b and the outer ring raceways 13a, 13b, respectively, so that they can roll. In this state, a contact angle of a back combination type (DB type) is given to each of the balls 4 and 4 arranged in a double row together with a preload. The pitch circle diameters of the balls 4 and 4 in both rows differ from each other in accordance with the difference in diameter between the inner ring raceways 8a and 8b and the outer ring raceways 13a and 13b. That is, the pitch circle diameter PCD _OUT of each ball 4, 4 (outer row) in the axially outer row is larger than the pitch circle diameter PCD _IN of each ball 4, 4 (inner row) in the axially inner row ( PCD _OUT > PCD _IN ). In the illustrated example, balls 4 and 4 are used as rolling elements. However, in the case of a rolling bearing unit for automobiles that is heavy in weight, a tapered roller may be used as the rolling element.

The structure of the rolling bearing unit for supporting a wheel described in Patent Documents 1 to 5 in which the pitch circle diameters of the rolling elements in both rows are made different is as described above. In the case of such a structure, the moment circle rigidity can be increased as much as the pitch circle diameter PCD _OUT of the outer row can be increased to improve the running stability during turning and the durability of the wheel bearing rolling bearing unit. Is easy to design. On the other hand, since it is not necessary to increase the pitch circle diameter PCD _IN of the inner row, it is not necessary to increase the diameter of a part of the suspension device (knuckle mounting hole). Therefore, the traveling stability and the durability can be improved without particularly increasing the size of the suspension device.

  However, in order to sufficiently ensure the durability of such a wheel support rolling bearing unit, a general wheel support rolling bearing unit (the pitch circle diameter of the outer row is equal to the pitch circle diameter of the inner row) As in the case of the above, it is important to ensure the rolling fatigue life of the outer ring raceways 13a and 13b. However, in the case of a wheel bearing rolling bearing unit in which the pitch circle diameters of both rows of rolling elements are different as shown in FIG. 5, the rolling of the outer ring raceways 13a and 13b is performed for the following reason. It may be difficult to secure the fatigue life as compared with the above-described general wheel bearing rolling bearing unit. The reason will be described below.

  In order to ensure the rolling fatigue life of the outer ring raceways 13a and 13b, it is preferable to leave compressive stress in these outer ring raceways 13a and 13b. Residual compressive stress suppresses the occurrence of peeling and the like to prevent the occurrence of damage such as early separation on the outer ring raceways 13a and 13b, and from the aspect of ensuring the rolling fatigue life of both outer ring raceways 13a and 13b. It is valid. On the other hand, in order to leave compressive stress in both the outer ring raceways 13a, 13b, the periphery of the hardened hardening layer provided in the both outer ring raceways 13a, 13b (the quench hardened layer and the outer peripheral surface of the outer ring 3) It is preferable to leave an unquenched uncured part in the intermediate part).

  That is, when a hardened layer is formed on both the outer ring raceways 13a and 13b by heat treatment such as induction hardening, the metal structure of the hardened layer expands albeit slightly due to martensitic transformation. In this case, if there is an uncured portion (which does not expand due to martensite transformation) in the peripheral portion of the cured layer, the cured layer is suppressed by the uncured portion, and residual compressive stress is generated inside. This residual compressive stress works advantageously from the aspect of securing the rolling fatigue life as described above, but the magnitude of the residual compressive stress increases as the thickness of the non-hardened portion around the hardened layer increases. .

However, in the case of a rolling bearing unit for supporting a wheel in which the pitch circle diameters of the rolling elements in both rows are different as shown in FIG. 5, the shape of the outer ring 3 is unique. , 13b can be increased in thickness in the radial direction (the thickness of the portion in between is increased). On the other hand, the thickness in the radial direction is ensured in the portion where the outer ring raceways 13a and 13b are provided. Things can be difficult. That is, the outer diameter of the outer ring 3 is smaller at the portion near the inner end in the axial direction because the portion near the inner end in the axial direction of the outer ring 3 needs to be fitted and fixed in the support hole of the knuckle that constitutes the suspension device. Yes. In contrast, with respect to the inner diameter of the outer ring 3, on necessary to increase the pitch circle diameter PCD _OUT of the outboard row is larger in the axial direction outer end portion close. On the other hand, the extent to which the inner diameter of the outer ring 3 near the inner end of the outer ring 3 is reduced and the extent of the outer diameter of the outer ring 3 closer to the outer end in the axial direction are limited by other conditions such as weight reduction. ing. Accordingly, in the case of a wheel bearing rolling bearing unit in which the pitch circle diameters of the rolling elements in both rows are different, the thickness of the portion where the outer ring raceways 13a and 13b are provided at both ends in the axial direction of the outer ring 3 is provided. It may be difficult to secure the thickness as compared with a general rolling bearing unit for supporting a wheel.

  As a result, in the case of a wheel bearing rolling bearing unit in which the pitch circle diameters of the rolling elements in both rows are different, the thickness of the non-hardened portion existing in the peripheral portions of the outer ring raceways 13a and 13b is ensured. Things can be difficult. The rolling fatigue life of both the outer ring raceways 13a and 13b is ensured by forming a heat treatment hardened layer on both the outer ring raceways 13a and 13b. However, the heat treatment hardened layer is simply formed on the heat treated hardened layer. If sufficient residual compressive stress is not generated, it is difficult to ensure a sufficient rolling fatigue life. None of Patent Documents 1 to 5 describe such a point. Patent Document 6 discloses a structure in which the pitch circle diameters of the rolling elements in both rows are equal, a structure in which the heat treatment hardened layers formed on both outer ring raceway portions are independent, and a structure in which the heat treatment hardened layers formed on both outer ring raceway portions are continuous. Is described. However, even with the technique described in Patent Document 6, it is possible to generate sufficient residual compressive stress in the heat-treated hardened layer of the outer ring raceway portions of both rows with a structure in which the pitch circle diameters of both rows of rolling elements are different. It is not a suggestion.

JP 2003-232343 A JP 2004-108449 A JP 2004-345439 A JP 2006-137365 A International Publication WO2005 / 065077 Japanese Utility Model Publication No. 3-22124

  In consideration of the above-described circumstances, the wheel bearing rolling bearing unit of the present invention can increase the moment rigidity by making the pitch circle diameter of the outer row larger than the pitch circle diameter of the inner row. A structure that is located between the double row outer ring raceways provided on the inner peripheral surface, and that can effectively secure the rolling fatigue life of both outer ring raceways by effectively using the part that can sufficiently secure the thickness dimension in the radial direction. Invented to realize the above.

The wheel-supporting rolling bearing unit of the present invention includes an outer ring, a hub, and a plurality of rolling elements as in the conventional structure shown in FIG.
Out of these, the outer ring is made of carbon steel and has a double row outer ring raceway on the inner peripheral surface.
The hub has a mounting flange for supporting and fixing the wheel at the axially outer end portion of the outer peripheral surface, and double row inner ring raceways at the intermediate and inner end portions in the axial direction.
Each of the rolling elements is provided with a preload and a back contact type contact angle between each of the inner ring raceways and the outer ring raceways for each row.
The pitch circle diameter of the outer row in the axial direction is larger than the pitch circle diameter of the inner row.
In particular, in the rolling bearing unit for supporting a wheel of the present invention, the outer ring raceways are arranged between the outer ring raceway portions and the axially intermediate portion of the outer circumference of the outer race. A heat-treated and hardened layer is formed between the intermediate portions. And the heat-treatment hardening layer of these each part forms the heat treatment hardening layer continuously (it is not divided | segmented by the non-hardening layer) continuously.

When the rolling bearing unit for supporting a wheel according to the present invention as described above is implemented, preferably, the heat treatment hardened layer between the outer ring raceways is formed as the outer ring in both rows as described in claim 2. It exists only in the radially inner portion of the virtual conical cylindrical surface having a tangent common to the cross-sectional shape of the track as a generating line.
Alternatively, as described in claim 3, the cross-sectional shape of the portion between the outer ring raceways in the inner peripheral surface of the outer ring is a shape in which straight lines or smooth curves are continuous.

  According to the rolling bearing unit for supporting a wheel of the present invention configured as described above, the outer ring has a structure that can increase the moment stiffness by making the pitch circle diameter of the outer row larger than the pitch circle diameter of the inner row. By effectively using the portion between the double row outer ring raceways provided on the inner peripheral surface of the outer circumferential raceway, sufficient residual compressive stress is generated in the heat treatment hardened layer formed on both outer ring raceway portions, A sufficient rolling fatigue life can be secured. The reason will be described below.

  When a hardened layer is formed on the inner peripheral surface portion of the outer ring by heat treatment such as induction hardening, as described above, the metal structure of the hardened layer portion expands albeit slightly due to martensitic transformation. And when a non-hardened part exists in the surrounding part of this hardened layer, this hardened layer will be suppressed by this non-hardened part, and a residual compressive stress will generate | occur | produce inside. As described above, in order to generate a sufficient residual compressive stress in the heat-treated hardened layer formed on both outer ring raceway portions, it is only necessary to have a non-hardened portion having a sufficient thickness around the outer ring. However, for the reasons described above, it may be difficult to ensure the thickness of the uncured portion in the surrounding portion.

  On the other hand, in the case of a rolling bearing unit for supporting a wheel that gives a contact angle of the rear combination type to rolling elements arranged in a double row, the thickness of the portion between the outer ring raceways in the axial direction intermediate part of the outer ring It can be made larger than the thickness of the outer ring raceway. Therefore, if a heat treatment hardened layer is formed not only on the outer ring raceway portions but also on the inner peripheral surface of the intermediate portion, the residual compressive stress generated in the outer ring raceway portions can be increased using the intermediate portion. That is, when the heat treatment cured layer is formed on the inner peripheral surface of the intermediate portion, the peripheral portion of the heat treatment hardened layer is also pushed to the outer diameter side with respect to the intermediate portion, and as a reaction, the peripheral portion is radially inward from the peripheral portion. Adds the right power. The force directed inward in the radial direction is transmitted not only to the heat treatment hardened layer formed on the inner peripheral surface of the intermediate portion but also to the heat treatment hardened layer formed on both outer ring raceway portions. As a result, the residual compressive stress of these outer ring raceway portions is generated by that amount (the residual compressive stress generated by the heat-treated hardened layer formed on each outer ring raceway portion is caused by the radially inward force transmitted from the above-mentioned portion. As the residual compressive stress is added, the rolling fatigue life of both outer ring raceways is improved. The thickness of the heat-treated hardened layer is from the inner peripheral surface of the outer ring (for the outer ring raceway, the portion that is in rolling contact with the rolling surface of the rolling element) to a depth at which a predetermined hardness value is set. (For example, the distance until the higher hardness of the surface portion gradually decreases to Hv500).

  In particular, as described in claim 2, the heat treatment hardened layer between the two outer ring raceways is a radially inner portion of a virtual conical cylindrical surface having a tangent line common to the cross-sectional shape of the two outer ring raceways as a generating line. In the heat treatment hardened layer formed on the outer ring raceway portions, the radially inwardly generated force generated in the intermediate portion is effectively applied to the portions that are in rolling contact with the rolling elements. Can communicate. That is, in the case of a rolling bearing unit for supporting a wheel that is a subject of the present invention, a contact angle of a back combination type is given to each of the rolling elements, and each of these rolling elements is the above-mentioned among the both outer ring raceways. Rolling contact with the part near the gap. In order to transmit the radially inward force generated in the non-hardened part of the intermediate part to the part near the intermediate part of the outer ring raceway, the unhardened part (residual compressive stress is generated) It is preferable to provide the portion as far as possible in the radially inner portion. In other words, if the heat-treated cured layer in the intermediate portion exists to the outside in the radial direction with respect to the virtual conical cylindrical surface, the heat-cured layer is blocked by the heat-cured cured layer and is generated in the non-cured portion. The force directed in the direction is less likely to be transmitted to a portion closer to the portion between the outer ring raceways.

  However, the thickness of the heat-cured layer provided on the inner peripheral surface portion of the intermediate portion is sufficiently large to generate a radially inward force on the uncured portion of the intermediate portion (for example, It is a condition that it is about 1 to 2 mm in the case of a rolling bearing unit for supporting a wheel for a general passenger car. If these things are considered, the said objective can be achieved in a high dimension by providing the heat treatment hardening layer of the said intermediate part only in the radial direction inner side rather than the said virtual conical cylinder surface. It should be noted that excessively increasing the thickness of the heat-treated cured layer formed in the intermediate portion (to the extent that it reaches the outside in the radial direction from the virtual conical cylinder surface) ensures the thickness of the uncured portion in the intermediate portion. This is also undesirable from the viewpoint of preventing the formation of coarse crystal grains due to overheating at the boundary surface (groove shoulder) between this surface and the outer ring raceway. For this reason, the appearance of the coarse crystal grains is not preferable from the standpoint of maintaining the quality, for example, causing a decrease in durability due to the embrittlement of the groove shoulder.

  Further, when carrying out the present invention, as described in claim 3, the cross-sectional shape of the portion between the outer ring raceways in the inner peripheral surface of the outer ring is made continuous with a straight line or a smooth curve. If the shape is adopted, the heat transfer length between the two outer ring raceways can be shortened, and the heat radiation area between the two outer ring raceways can be narrowed to easily heat both the outer ring raceways and the intermediate portion simultaneously and uniformly. . A uniform heat-treated hardened layer can be easily formed on both the outer ring raceways and the intermediate portions.

  1 to 3 show a first example of an embodiment of the present invention corresponding to all claims. The feature of the present invention is that the heat treatment hardened layers 17a, 17b, 17c are formed on the outer ring raceways 13a, 13b of the double row formed on the inner peripheral surface of the outer ring 3a and the portion 16 between these outer ring raceways 13a, 13b. It is in the point that it forms continuously (these heat treatment hardening layers 17a, 17b, and 17c are united). In the case of this example, the cross-sectional shape (bus shape) of the portion corresponding to the intermediate portion 16 on the inner circumferential surface in the axial direction of the outer ring 3a is a straight line. Therefore, the shape of the inner peripheral surface is a partial conical concave surface that is inclined in a direction in which the inner diameter increases toward the outer side in the axial direction. In addition, it is preferable that the angle of the bent part which exists in the continuous part of the both ends of the said intermediate part 16 and the edge part of the said both outer ring track 13a, 13b is made as large as possible (an obtuse angle). The reason for this is to prevent the above-described continuous portion from overheating and quenching of the heat-treated cured layers 17a, 17b, and 17c to generate coarse crystal grains as described above.

  In the illustrated example, the outer rows 4a and 4a have a diameter (for example, about 10.3 mm) smaller than the inner rows 4b and 4b (for example, about 11.1 mm). The number of balls 4a, 4a in the row (for example, 15) is made larger than the number of balls (4b, 4b) in the inner row (for example, 11). Accordingly, the curvature radii of the cross-sectional shapes (bus shape) of the inner ring raceway 8a and the outer ring raceway 13a in the outer row are made smaller than the curvature radii of the cross-sectional shapes of the inner ring raceway 8b and the outer ring raceway 13b in the inner row. The pitch circle diameter of the balls 4a and 4a in the outer row is set to 60 mm, for example, and the pitch circle diameter of the balls 4b and 4b in the inner row is set to 50 mm, for example. In short, the present invention is applied to a structure in which both the outer and inner rows of balls 4a and 4b have a pitch circle diameter of less than 6 times the diameter of the balls, and the outer ring raceways 13a and 13b of both rows are rolled. This is effective from the viewpoint of ensuring fatigue life. Conversely, in the case of a relatively large wheel-supporting rolling bearing unit that can increase the pitch circle diameter to more than six times the ball diameter, a sufficient thickness is provided around the outer ring raceways in both rows. Since it is easy to provide the uncured portion, it is possible to secure a rolling fatigue life even if not according to the present invention (although it is of course free to secure superior durability by applying the present invention). Design is relatively easy. Since the configuration and operation of the other parts are the same as those of the conventional structure shown in FIG. 5 described above, explanations of the equivalent parts will be omitted or simplified, and the following description will focus on the features of the present invention and this example.

  As shown in FIG. 2, the heat treatment hardened layers 17 a, 17 b, 17 b, 17 b, 17 b, and a portion including the double row outer ring raceways 13 a, 13 b and the intermediate portion 16, except for both axial ends of the inner peripheral surface of the outer ring 3 a 17c (portions indicated by oblique lattices) are formed over the entire circumference by induction hardening. These heat treatment hardened layers 17a, 17b, and 17c simultaneously heat both the outer ring raceways 13a and 13b and the intermediate portion 16 by an integrated high-frequency heating coil having an outer peripheral surface shape that follows the inner peripheral surface of the outer ring 3a. It is formed by high frequency heat treatment. For the purpose of explanation, the heat treatment cured layers 17a, 17b, and 17c are given a separate reference numeral, but the heat treatment cured layers 17a, 17b, and 17c are integrated with each other except that the thicknesses of the respective parts are different. Is homogeneous.

  Of the heat treatment hardened layers 17a, 17b, and 17c, the range in which the heat treatment hardened layers 17a and 17b of the outer ring raceways 13a and 13b are formed, regardless of the moment and the axial load applied to the wheel support rolling bearing unit, The range is regulated so that the contact ellipse existing at the rolling contact portion between the rolling surfaces of the balls 4a and 4b and the outer ring raceways 13a and 13b does not protrude from the heat-treated cured layers 17a and 17b. Yes. Further, the thickness of the heat-treated hardened layers 17a and 17b of both the outer ring raceways 13a and 13b is restricted from the viewpoint of ensuring the rolling fatigue life and pressure proof property of both the outer ring raceways 13a and 13b. The thicknesses Ta and Tb of the heat-treated hardened layers 17a and 17b in the outer ring raceways 13a and 13b are determined by Hertz's theory, which is widely known in the technical field of rolling bearings. In the case of the rolling bearing unit for supporting the wheel, it is set to about 2 to 3 mm.

  On the other hand, regarding the thickness Tc of the heat treatment hardened layer 17c in the intermediate portion 16, the heat treatment hardened layer 17c is processed into the uncured portion 18 around the heat treatment hardened layer 17c in the intermediate portion 16. Therefore, the force directed inward in the radial direction that is transmitted to the heat-treated and hardened layers 17a and 17b of both the outer ring raceways 13a and 13b is restricted from the aspect of increasing as much as possible. In consideration of these matters, the thickness Tc of the heat-treated cured layer 17c is appropriately about 1 to 2 mm in the case of a general rolling bearing unit for supporting a wheel for a passenger car as described above. At least the thickness Tc of the heat-treated hardened layer 17c is such that the heat-treated hardened layer 17c is radially outward from the virtual conical cylinder surface whose tangent line α is common to the cross-sectional shapes of the outer raceways 13a and 13b. Keep it to the extent that it does not reach.

  On the other hand, as shown in FIG. 3, the outer peripheral surface of the hub body 5, which is also made of carbon steel, is a heat treatment hardened layer 19 (indicated by a slanted lattice) in a portion extending from the inner side surface of the mounting flange 7 to the small diameter step portion 11. And the inner ring raceway 8a on the outer side in the axial direction are formed over the entire circumference in a state of being continuous in the axial direction. The quench hardened layer 19 is also formed by induction hardening. As shown in FIG. 1, an inner ring 6 made of bearing steel and hardened and hardened (so-called baked) is externally fitted to the small diameter step portion 11, and the caulking portion 12 is coupled and fixed to the hub body 5. is doing.

  The wheel support rolling bearing unit of the present example configured as described above has a pitch circle diameter of the outer row larger than that of the inner row for the reason explained in the above [Effects of the invention], and a moment With the structure capable of improving the rigidity, it is possible to sufficiently ensure the rolling fatigue life of the double row outer ring raceways 13a and 13b formed on the inner peripheral surface of the outer ring 3a. In summary, a heat-treated cured layer 17c is formed on the inner peripheral surface portion of the intermediate portion 16 having a sufficient thickness dimension, and the uncured portion 18 existing around the heat-treated cured layer 17c is sufficiently formed in the intermediate portion 16 in the intermediate portion. A large force directed radially inward is generated, and this force is applied radially inward from the uncured portion 18 as indicated by a plurality of arrows in FIG. That is, the force generated in the uncured portion 18 is pressed not only in the heat-treated hardened layer 17c in the intermediate portion 16 but also in the heat-treated hardened layers 17a and 17b in the outer ring raceways 13a and 13b. To do. As a result, residual compressive stress is also generated in the heat-treated hardened layers 17a and 17b of both the outer ring raceways 13a and 13b, and the rolling fatigue life of both the outer ring raceways 13a and 13b is improved.

  For this reason, even in the case of a wheel bearing rolling bearing unit that is relatively small and cannot sufficiently secure the thickness dimension of the uncured portion existing around the heat-treated cured layers 17a and 17b of the outer ring raceways 13a and 13b, It is possible to improve the durability of the wheel support portion of an automobile incorporating the wheel support rolling bearing unit. In particular, since the intermediate portion 16 is inclined in a direction in which the inner diameter increases toward the outer ring raceway 13a in the outer row, the component force of each arrow in FIG. 2 acts outward in the axial direction. As is clear from this, a large residual compressive stress can be generated in the heat-treated hardened layer 17a formed in the outer ring raceway 13a portion of the outer row. And the thickness regarding the radial direction of the outer ring raceway 13a part of this outer side row | line | column can be suppressed small, and it can be made easy to design for the rolling bearing unit for wheel support.

[Second Example of Embodiment]
FIG. 4 shows a second example of an embodiment of the invention which also corresponds to all claims. In the case of this example, cylindrical surface portions 20a and 20b are formed between the ends of the outer ring raceways 13a and 13b in both rows and the both ends of the intermediate portion 16a, respectively. Of these cylindrical surface portions 20a and 20b, the presence of the cylindrical surface portion 20b provided adjacent to the inner row outer ring raceway 13b allows the angle of the bent portion of the continuous portion present at the end of the inner row outer ring raceway 13b to be determined. It can be made larger than in the case of the first example described above. And it can prevent that the said continuous part overheats at the time of quenching of each heat processing hardening layer 17a, 17b, 17c. As is clear from the above description, the cylindrical surface portion 20a provided adjacent to the outer ring raceway 13a in the outer row may be omitted from the viewpoint of preventing overheating. In short, the steep {bending angle is 90 degrees or less and the radius of curvature is extremely small (for example, 1 mm or less) in the portion of the inner peripheral surface of the outer ring 3a where the heat treatment hardened layers 17a, 17b, 17c are formed. The overheating is prevented without providing an inflection point. However, the outer cylindrical surface portion 20a is effective in terms of providing the shoulder height of the outer ring raceway 13a in the outer row and preventing the ball from rolling on the rolling surface. Other configurations and operations are the same as in the case of the first example of the above-described embodiment, and thus overlapping illustrations and descriptions are omitted.

Sectional drawing which shows the 1st example of embodiment of this invention. FIG. 4 is a partial cross-sectional view showing only the outer ring in order to explain the range of the heat-treated hardened layer in the outer ring raceway portion. FIG. 4 is a partial cross-sectional view showing only the hub body in order to explain the range of the heat-treated hardened layer of the inner ring raceway and the small-diameter stepped portion. The figure similar to FIG. 2 which shows the 2nd example of embodiment of this invention. Sectional drawing which shows an example of a conventional structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wheel support rolling bearing unit 2 Hub 3, 3a Outer ring 4, 4a, 4b Ball 5 Hub main body 6 Inner ring 7 Mounting flange 8a, 8b Inner ring track 9 Stud 10 Outer peripheral surface side inclined step part 11 Small diameter step part 12 Caulking part 13a, 13b Outer ring raceway 14 Coupling flange 15 Inner peripheral surface side inclined step portion 16, 16a Between portions 17a, 17b, 17c Heat-treated cured layer 18 Uncured portion 19 Heat-treated cured layer 20a, 20b Cylindrical surface portion

Claims (3)

  A carbon steel outer ring having a double-row outer ring raceway on the inner peripheral surface, and a mounting flange for supporting and fixing the wheel on the outer peripheral end in the axial direction on the outer peripheral surface, also in the intermediate and inner end portions in the axial direction. A hub having double-row inner ring raceways, and a rolling element provided with a contact angle of a back combination type between each of the inner ring raceways and the outer ring raceways. In the rolling bearing unit for supporting a wheel having a pitch circle diameter of the outer row in the axial direction larger than the pitch circle diameter of the row in the axial direction, the outer ring raceway of the inner race surface of the outer ring. A heat-treated and hardened layer is formed between the outer ring raceway and a portion between the outer ring raceways in the axially intermediate portion of the inner peripheral surface of the outer ring. Wheel-supporting rolling characterized by forming a layer Receiving unit.   The heat treatment hardened layer in a portion between both outer ring raceways is present only in a radially inner portion of a virtual conical cylindrical surface having a tangent common to the cross-sectional shape of both rows of outer ring raceways as a generating line. Rolling bearing unit for wheel support.   The wheel support according to any one of claims 1 to 2, wherein a cross-sectional shape of a portion between both outer ring raceways in the inner peripheral surface of the outer ring is a shape in which a straight line or a smooth curve is continuous. Rolling bearing unit for use.

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