Method for manufacturing outer ring of hub unit bearing

Abstract

To provide a method for manufacturing an outer ring of a hub unit bearing having three rows at low manufacturing cost.SOLUTION: A first negative gap is an axial negative gap between an outermost row and an innermost row in a case of assuming that a hub unit bearing is assembled with a hub disposed on a radially inner side of an outer ring 2 after completion of a grinding finishing process, and with a ball of the same gage disposed between three-row outer ring raceway 5a, 5b, 5c and three-row inner ring raceway. The difference between the first negative gap and a second negative gap, which is an axial negative gap between an intermediate row and one row, is made smaller than the difference between the first negative gap and the second negative gap in a case of assuming that a hub unit bearing is assembled with a hub disposed on the radially inner side of an outer ring 2 after completion of a super finishing process, and with a ball of the same gage disposed between three-row outer ring raceway 5a, 5b, 5c and three-row inner ring raceway.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing an outer ring of a hub unit bearing for rotatably supporting an automobile wheel relative to a suspension system. [Background technology]

[0002] An automobile wheel is rotatably supported by a suspension device by a hub unit bearing. The hub unit bearing comprises an outer ring having multiple rows of outer ring raceways on its inner circumferential surface, a hub having multiple rows of inner ring raceways on its outer circumferential surface, and multiple rolling elements arranged to roll freely between the multiple rows of outer ring raceways and the multiple rows of inner ring raceways. The outer ring is supported and fixed to the suspension device. A wheel of the wheel and a braking rotor are joined and fixed to the hub.

[0003] With respect to the hub unit bearing, the axially outer side is the outer side in the width direction of the vehicle when assembled to the vehicle, and the axially inner side is the center side in the width direction of the vehicle when assembled to the vehicle.

[0004] The number of rows of rolling elements that make up a hub unit bearing is normally two, but it has long been known, for example as disclosed in JP 2009-525446 A, to have three rows of rolling elements in hub unit bearings that use balls as the rolling elements.

[0005] In the conventional hub unit bearing described in JP 2009-525446 A, the balls in the outermost row, which is the row located furthest outward in the axial direction, and the balls in the innermost row, which is the row located furthest inward in the axial direction, are given a back-to-back contact angle with each other, and the balls in the middle row are given a back-to-back contact angle with respect to the balls in the innermost row. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2009-525446 [Non-Patent Document 1] "NSK Technical Report", NSK Ltd., 2020 edition (first edition 1991) Summary of the Invention [Problem to be solved by the invention]

[0007] The outer ring is usually made by forging and cutting a metal material to form the outer shape, heat treating the parts that will form the outer ring raceways of each row to form a hardened layer, grinding and finishing using a formed grindstone shaped with a diamond wheel (dresser), and then applying a super-finishing process. The hub, like the outer ring, is made by forging and cutting a metal material to form the outer shape, heat treating the parts that will form the inner ring raceways of each row to form a hardened layer, grinding and finishing using a formed grindstone, and then applying a super-finishing process.

[0008] In the outer rings and hubs manufactured in this manner, the radius of curvature (groove R) and axial position of the outer ring raceway and inner ring raceway of each row are guaranteed to be sufficiently precise by the grinding finish process using a formed grinding wheel, whereas the groove bottom diameter of the outer ring raceway and inner ring raceway of each row is prone to dimensional errors due to variations in the amount of material removed in the super-finishing process, which is affected by the roughness of the machined surface.

[0009] Therefore, after superfinishing the outer and inner raceways of each row, the groove bottom diameters of the outer and inner raceways of each row are measured, and then, based on the measurement results, an appropriate ball gauge is selected for each row, and the balls of that gauge are assembled between the outer and inner raceways of each row to apply an appropriate preload to the balls of each row.

[0010] The gauge is the dimensional difference between the average diameter of the lot and the nominal diameter, as specified in JIS (Japanese Industrial Standards) B 1501:2009 Rolling Bearings. The gauge spacing varies depending on the grade. Generally, the grade of balls for hub unit bearings is G20, and for G20, the cage spacing is 2 μm.

[0011] In a hub unit bearing with three rows, unless the preload applied to the outermost row balls and the innermost row balls is greater than the preload applied to the middle row balls, the bearing load cannot be shared in a balanced manner among the rows, and it may be difficult to ensure sufficient life and / or rigidity. Specifically, the middle row may share an excessive bearing load, resulting in a short life, or the effective distance between the points of application may be the distance between the points of application between the middle row and the innermost row (when a back-to-back contact angle is applied between the middle row balls and the innermost row balls) or the distance between the points of application between the middle row and the outermost row (when a back-to-back contact angle is applied between the middle row balls and the outermost row balls), rather than the distance between the points of application between the outermost row and the innermost row, i.e., the distance between the points of application may be short, resulting in a decrease in moment rigidity.

[0012] For this reason, in a hub unit bearing with three rows, it is necessary to select an appropriate ball gauge for each row so that the preload applied to the outermost row of balls and the preload applied to the innermost row of balls are greater than the preload applied to the middle rows of balls.

[0013] In this regard, in a hub unit bearing with two rows, the deviation and variation from the target value of the groove bottom diameter of the outer ring raceway and inner ring raceway of each row is small, so when applying an appropriate preload to the balls in each row, balls with a gauge of 0 or close to it can be assembled as the balls in each row.

[0014] In contrast, in a hub unit bearing with three rows, the deviation and variation of the groove bottom diameter of the inner and outer raceways of each row from the target value is greater in the outer raceway of the middle row than in the remaining outer and inner raceways.For this reason, when applying an appropriate preload to the balls in each row, while balls with a gauge of 0 or close to it can be assembled in the outermost and innermost rows, it may be necessary to assemble balls with a gauge far from 0 gauge in the middle row.

[0015] As a result, when manufacturing a hub unit bearing with three rows, a larger number of ball gauges must be prepared, which increases the size of the ball hopper that houses the balls for each gauge, resulting in an increase in the manufacturing costs of the hub unit bearing.

[0016] An object of the present disclosure is to provide a manufacturing method capable of reducing manufacturing costs for an outer ring of a hub unit bearing having three rows. [Means for solving the problem]

[0017] The inventors of the present disclosure conducted extensive research into the reasons why, when manufacturing a hub unit bearing with three rows, the deviation and variation in the groove bottom diameters of the outer ring raceways and inner ring raceways of each row from the target values ​​is greater in the outer ring raceways of the middle row than in the remaining outer ring raceways and inner ring raceways when super-finishing is performed on the outer ring raceways and inner ring raceways of each row.

[0018] In a hub unit bearing with three rows, the groove bottom diameter of the outer ring raceway of the middle row is smaller than the groove bottom diameter of the outer ring raceway of the outermost row and the groove bottom diameter of the outer ring raceway of the innermost row.

[0019] When manufacturing a hub that constitutes a hub unit bearing having three rows, and performing grinding finishing on the inner raceways of each row using a formed grindstone, the formed grindstone is disposed radially outside the hub, so that the formed grindstone is not restricted by its outer diameter, and it is possible to use a formed grindstone with a large outer diameter, for example, a maximum outer diameter of about 455 mm to 610 mm when new. Therefore, even if there is a difference between the groove bottom diameters of the three rows of inner raceways (ground parts), for example, a difference of about 5 mm to 15 mm between the maximum groove bottom diameter and the minimum groove bottom diameter, the ratio of the outer diameters of the three rows of processed parts (grinding parts) that grind the three rows of inner raceways (ground parts) on the outer circumferential surface of the formed grindstone can be made close to "1:1:1". In other words, the ratio of the peripheral speeds of the three rows of processed parts can be made close to "1:1:1". For this reason, when the grain size of the abrasive grains constituting the three rows of processed portions is the same, it is possible to finish the three rows of inner ring raceways to approximately the same surface roughness.

[0020] On the other hand, when manufacturing an outer ring constituting a hub unit bearing having three rows, and simultaneously grinding and finishing the outer ring raceways of each row using a formed grindstone, the formed grindstone must be inserted from one axial side of the outer ring to the other axial side and positioned radially inside the outer ring, so a formed grindstone with a large outer diameter cannot be used. Specifically, the maximum outer diameter of the formed grindstone when new must be equal to or smaller than the inner diameter of the intermediate small diameter outer ring groove shoulder, which is the minimum inner diameter of the outer ring. For this reason, the ratio of the outer diameters of the three-row processed parts (grinding parts), which are the parts that grind the three-row outer ring raceways (ground parts) on the outer peripheral surface of the formed grindstone, becomes far from "1:1:1", and specifically, the outer diameter of the processed part of the middle row becomes smaller than the outer diameter of the processed part of the outermost row and the outer diameter of the processed part of the innermost row. More specifically, the outer diameter of the processing part of the outermost row and the outer diameter of the processing part of the innermost row are about 60 mm to 90 mm, while the outer diameter of the processing part of the middle row is about 45 mm to 75 mm. Therefore, the peripheral speed of the processing part of the middle row is slower than the peripheral speed of the processing part of the outermost row and the peripheral speed of the processing part of the innermost row. For this reason, when the grain size of the abrasive grains constituting the three rows of processing parts is the same, the surface roughness of the outer ring raceway of the middle row is likely to be worse than the surface roughness of the outer ring raceway of the outermost row and the outer ring raceway of the innermost row.

[0021] On the other hand, in the superfinishing process performed after the grinding finish process, a grindstone with a finer grain size (larger grit size) than the formed grindstone used in the grinding finish process is used, and the processed part (superfinished part (outer ring raceway, inner ring raceway)) of the workpiece (outer ring, hub) rotating around its own central axis is pressed with a predetermined pressure while the grindstone is oscillated along the raceway surface to improve the surface roughness of the processed part. In such a superfinishing process, the sharpness of the grindstone changes depending on the respective surface conditions of the processed part of the grindstone and the processed part of the workpiece. Specifically, if the surface roughness of the processed part is poor, the sharpness of the grindstone improves and the amount of the processed part is increased, whereas if the surface roughness of the processed part is good, the sharpness of the grindstone deteriorates and the amount of the processed part is reduced.

[0022] Therefore, for the three rows of inner raceways, which can have approximately the same surface roughness after grinding finish, the amount of material removed by superfinishing can be approximately the same.In contrast, the amount of material removed by superfinishing of the middle row of outer raceways, which have a relatively poor surface roughness after grinding finish, is greater than the amount of material removed by superfinishing of the outermost row of outer raceways and the innermost row of outer raceways, which have a relatively good surface roughness after grinding finish.

[0023] In view of these circumstances, it was discovered that, at the stage where the outer ring raceway and the inner ring raceway of each row are subjected to superfinishing, the deviation and variation of the groove bottom diameters of the outer ring raceway and the inner ring raceway of each row from the target value is likely to be larger in the outer ring raceway of the middle row than in the remaining outer ring raceway and the inner ring raceway. The present disclosure has been completed based on this discovery.

[0024] A hub unit bearing incorporating an outer ring that is the subject of the manufacturing method of the outer ring of a hub unit bearing according to one aspect of the present disclosure is as follows: an outer ring having three rows of outer ring raceways on its inner circumferential surface; A hub having three rows of inner ring raceways on its outer circumferential surface; a plurality of balls are arranged in each row between the three rows of outer ring raceways and the three rows of inner ring raceways; Equipped with Among the balls, a contact angle and a preload are applied to the outermost row balls arranged in the outermost row, which is the row located farthest outward in the axial direction, and the innermost row balls arranged in the innermost row, which is the row located farthest in the axial direction, such that they are back-to-back combination type, Among the balls, balls in an intermediate row that is a row located between the outermost row and the innermost row in the axial direction are given a contact angle and a preload that form a back-to-back type in relation to the balls in the outermost row or the balls in the innermost row, A first negative gap which is an axial negative gap between the outermost row and the innermost row is larger than a second negative gap which is an axial negative gap between the intermediate row and one of the rows.

[0025] The negative axial clearance refers to a negative internal clearance in the axial direction. For example, in a configuration in which two rows of balls are given a back-to-back contact angle, if the internal clearance in the axial direction between the two rows is increased by "δ" μm (δ: positive value) from a state in which the internal clearance in the axial direction between the two rows is zero, or the inter-row distance of the inner raceway of the two rows is decreased by "δ" μm, thereby applying preload to the two rows of balls, the negative axial clearance between the two rows will be "δ" μm.

[0026] As described above, when the first negative gap, which is the axial negative gap between the outermost row and the innermost row, is larger than the second negative gap, which is the axial negative gap between the intermediate row and one of the rows, the preload applied to the balls in the outermost row and the preload applied to the balls in the innermost row are larger than the preload applied to the balls in the intermediate row.

[0027] A manufacturing method for the outer ring of a hub unit bearing according to one embodiment of the present disclosure includes a grinding finishing process in which the three rows of outer ring raceways are simultaneously ground using a formed grinding wheel, and a superfinishing process in which the three rows of outer ring raceways are superfinished after the grinding finishing process is completed.

[0028] The formed grindstone has three rows of processed portions, which are portions where the three rows of outer ring raceways are subjected to grinding finish processing, and the grain sizes of the abrasive grains that constitute these three rows of processed portions are the same.

[0029] In the grinding finishing process, assuming that the hub is placed radially inside the outer ring after the grinding finishing process is completed, and balls of the same gauge are placed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing, the grinding finishing process is performed on the three rows of outer ring raceways so that the first negative gap is larger than the second negative gap.

[0030] In the superfinishing process, assuming that the hub is placed radially inside the outer ring after completion of the superfinishing process, and balls of the same gauge are placed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing, the superfinishing process is applied to the three rows of outer ring raceways so that the first negative gap is larger than the second negative gap.

[0031] The difference between the first negative gap and the second negative gap when it is assumed that the hub is placed radially inside the outer ring after the grinding finish process is completed, and balls of the same gauge are placed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing is made smaller than the difference between the first negative gap and the second negative gap when it is assumed that the hub is placed radially inside the outer ring after the superfinishing process is completed, and balls of the same gauge are placed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing.

[0032] Specifically, the difference between the first negative gap and the second negative gap when it is assumed that the hub is placed radially inside the outer ring after the grinding finishing process is completed, and balls of the same gauge are placed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing can be made smaller by 10 μm or more and 20 μm or less, preferably 12 μm or more and 18 μm or less, than the difference between the first negative gap and the second negative gap when it is assumed that the hub is placed radially inside the outer ring after the superfinishing process is completed, and balls of the same gauge are placed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing. Effect of the Invention

[0033] According to the manufacturing method of the outer ring of the hub unit bearing of one aspect of the present disclosure, manufacturing costs can be easily reduced. [Brief description of the drawings]

[0034] [Figure 1]FIG. 1 is a half cross-sectional view of a hub unit bearing incorporating an outer ring that is the manufacturing target of a first example of an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a half sectional view showing how three rows of outer ring raceways are subjected to a finishing grinding process using a formed grindstone in the manufacturing method of the first example. [Diagram 3] FIG. 3 is a half cross-sectional view of a hub unit bearing incorporating an outer ring that is the manufacturing target of the second example of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] [Example 1] A first example of an embodiment of the present disclosure will be described with reference to FIGS. 1 and 2. FIG.

[0036] The manufacturing method of the outer ring of a hub unit bearing according to the present disclosure is intended to manufacture an outer ring of a hub unit bearing having three rows. The hub unit bearing including the outer ring to be manufactured may be for a driving wheel or a driven wheel, but in this example, a case will be described in which the manufacturing method of the present disclosure is applied to the outer ring of a hub unit bearing for a driving wheel.

[0037] (Structure of hub unit bearing) As shown in FIG. 1, a hub unit bearing 1 of this example includes an outer ring 2, a hub 3, and a plurality of balls 4a, 4b, and 4c.

[0038] In the following description of the hub unit bearing 1, the axially outer side is the left side in FIG. 1, which is the outer side in the width direction of the vehicle when assembled to the vehicle, and the axially inner side is the right side in FIG. 1, which is the center side in the width direction of the vehicle when assembled to the vehicle.

[0039] The outer ring 2 is made of a hard metal such as medium carbon steel or bearing steel, and has three rows of outer ring raceways 5a, 5b, and 5c on its inner circumferential surface.

[0040] The outer ring 2 has a stationary flange 6 protruding radially outward from an axially intermediate portion. The stationary flange 6 is a portion used for connecting and fixing the outer ring 2 to a knuckle of a suspension device.

[0041] The hub 3 is made of a hard metal such as medium carbon steel or bearing steel, and has three rows of inner ring raceways 7a, 7b, and 7c on its outer circumferential surface. The hub 3 is disposed coaxially with the outer ring 2 and radially inside the outer ring 2.

[0042] The hub 3 has a rotating flange 8 that protrudes radially outward at a portion located axially outward from the outer ring 2. The rotating flange 8 is a portion used for connecting and fixing a wheel and a rotating braking member to the hub 3.

[0043] Since the hub unit bearing 1 of this example is for a driving wheel, the hub 3 has a spline hole 9 that penetrates the center in the axial direction. A tip end of a drive shaft that is rotated and driven by an engine or electric motor as a drive source is spline-engaged with the spline hole 9. Note that when the manufacturing method of the present disclosure is applied to a hub unit for a driven wheel, the hub that constitutes the hub unit bearing can also have a solid structure.

[0044] The balls 4a, 4b, 4c are made of hard metal such as bearing steel or ceramics, and are arranged between three rows of outer ring raceways 5a, 5b, 5c and three rows of inner ring raceways 7a, 7b, 7c, with multiple balls in each row being held by retainers 10a, 10b, 10c so that they can roll freely.

[0045] The outermost row balls 4a, which are arranged in the outermost row, which is the row located farthest outward in the axial direction, and the innermost row balls 4c, which are arranged in the innermost row, which is the row located farthest in the axial direction, are given a contact angle and preload that form a back-to-back combination type with respect to each other, as shown by the dashed line in Fig. 1. In this example, the middle row ball 4b, which is arranged in the middle row, which is the row located between the outermost row and the innermost row in the axial direction, is given a contact angle and preload that form a back-to-back combination type with respect to the outermost row ball 4a, as shown by the dashed line in Fig. 1.

[0046] That is, each row of outer ring raceways 5a, 5b, 5c and each row of inner ring raceways 7a, 7b, 7c are angular and have a cross-sectional shape that is approximately a quarter circle arc.

[0047] The outer ring 2 has an outer small diameter outer ring groove shoulder 22, which has a smaller inner diameter than the portion adjacent to the axially outer side of the outer ring raceway 5a of the outermost row, on its inner circumferential surface. The outer ring 2 has an inner small diameter outer ring groove shoulder 23, which has a smaller inner diameter than the portion adjacent to the axially inner side of the outer ring raceway 5c of the innermost row, on its inner circumferential surface, on its axially outer side of the outer ring raceway 5c of the innermost row. The outer ring 2 has an intermediate small diameter outer ring groove shoulder 24, which has a smaller inner diameter than the portion adjacent to the axially inner side of the outer ring raceway 5b, on its inner circumferential surface, on its axially outer side of the outer ring raceway 5b of the intermediate row.

[0048] The hub 3 has an outer large diameter hub groove shoulder 25, located on a portion of its outer peripheral surface adjacent to the axially outer side of the outermost row inner ring raceway 7a, which has a larger outer diameter than a portion adjacent to the axially inner side of the inner ring raceway 7a. The hub 3 has an inner large diameter hub groove shoulder 26, located on a portion of its outer peripheral surface adjacent to the axially inner side of the innermost row inner ring raceway 7c, which has a larger outer diameter than a portion adjacent to the axially outer side of the inner ring raceway 7c. The hub 3 has an intermediate large diameter hub groove shoulder 27, located on a portion of its outer peripheral surface adjacent to the axially inner side of the intermediate row inner ring raceway 7b, which has a larger outer diameter than a portion adjacent to the axially outer side of the inner ring raceway 7b.

[0049] In this example, the radius of curvature of the intermediate row outer ring raceway 5b is smaller than the radius of curvature of the outermost row outer ring raceway 5a and is smaller than the radius of curvature of the innermost row outer ring raceway 5c. In this example, the radius of curvature of the outermost row outer ring raceway 5a is larger than the radius of curvature of the innermost row outer ring raceway 5c.

[0050] The groove bottom diameter of the intermediate row outer ring raceway 5b is smaller than the groove bottom diameter of the outermost row outer ring raceway 5a and smaller than the groove bottom diameter of the innermost row outer ring raceway 5c. Specifically, the groove bottom diameter of the intermediate row outer ring raceway 5b is smaller than the groove bottom diameter of the outermost row outer ring raceway 5a and the groove bottom diameter of the innermost row outer ring raceway 5c by 10 mm to 20 mm, preferably 12 mm to 18 mm. In this example, the groove bottom diameter of the outermost row outer ring raceway 5a is approximately equal to the groove bottom diameter of the innermost row outer ring raceway 5c. However, the groove bottom diameter of the outermost row outer ring raceway can also be larger or smaller than the groove bottom diameter of the innermost row outer ring raceway.

[0051] The radius of curvature of the outermost row inner raceway 7a is slightly smaller than the radius of curvature of the outermost row outer raceway 5a. The radius of curvature of the middle row inner raceway 7b is slightly smaller than the radius of curvature of the middle row outer raceway 5b. The radius of curvature of the innermost row inner raceway 7c is slightly smaller than the radius of curvature of the innermost row outer raceway 5c.

[0052] The groove bottom diameter of the inner ring raceway 7b of the intermediate row is smaller than the groove bottom diameter of the inner ring raceway 7c of the innermost row. Specifically, the groove bottom diameter of the inner ring raceway 7b of the intermediate row is smaller than the groove bottom diameter of the outer ring raceway 5c of the innermost row by 2 mm to 10 mm, preferably 4 mm to 8 mm. In this example, the groove bottom diameter of the inner ring raceway 7a of the outermost row is approximately equal to the groove bottom diameter of the inner ring raceway 7b of the intermediate row. However, the groove bottom diameter of the inner ring raceway 7a of the outermost row can also be larger or smaller than the groove bottom diameter of the inner ring raceway 7b of the intermediate row.

[0053] In this example, in accordance with the relationship between the radii of curvature of the outer raceways 5a, 5b, 5c of each row and the relationship between the radii of curvature of the inner raceways 7a, 7b, 7c of each row, the diameter (ball diameter) of the intermediate row balls 4b is smaller than the diameter of the outermost row balls 4a and smaller than the diameter of the innermost row balls 4c. The diameter of the outermost row balls 4a is larger than the diameter of the innermost row balls 4c.

[0054] In the hub unit bearing 1 of this example, the shape and dimensions of each component are regulated so that the first negative gap, which is the axial negative gap between the outermost and innermost rows, is larger than the second negative gap, which is the axial negative gap between the intermediate and outermost rows, i.e., so that the preload applied to the outermost row balls 4a and the innermost row balls 4c is larger than the preload applied to the intermediate row balls 4b. This allows the bearing load to be shared in a balanced manner by each row, making it easier to ensure sufficient life and rigidity.

[0055] Specifically, it prevents the intermediate row from sharing an excessively large bearing load, resulting in a short lifespan. Also, the effective distance between the points of application is set to the distance between the outermost and innermost rows (longer distance between the points of application) rather than the distance between the points of application between the intermediate row and the outermost row (shorter distance between the points of application), making it easier to ensure moment rigidity.

[0056] In this example, the hub 3 is formed by combining an inner ring 11 and a hub wheel 12 .

[0057] The inner ring 11 has, on its outer circumferential surface, an intermediate row inner ring raceway 7b and an innermost row inner ring raceway 7c.

[0058] The hub ring 12 has an outermost row of inner ring raceways 7a and a rotation flange 8 on its outer circumferential surface, and also has a spline hole 9 in the center.

[0059] The hub ring 12 has a small diameter step 13 at a portion located axially inward of the inner ring raceway 7b of the middle row, the small diameter step 13 having an outer diameter smaller than a portion adjacent to it on the axially outer side, onto which the inner ring 11 is fitted. Furthermore, the hub ring 12 has a step surface 14 at the axially outer end of the small diameter step 13, which faces axially inward.

[0060] The hub 3 is constructed by externally fitting the inner ring 11 onto the small diameter step 13 of the hub ring 12 by press fitting, and by abutting the axially outer end face of the inner ring 11 against the step face 14 of the hub ring 12, thereby connecting and fixing the inner ring 11 to the hub ring 12. In the hub unit bearing 1 of this example, the hub 3 is constructed by connecting and fixing the inner ring 11 to the hub ring 12, so that a predetermined amount of preload is applied to each row of balls 4a, 4b, 4c.

[0061] When implementing the present disclosure, a structure can be adopted for the hub unit bearing in which the axially inner end face of the inner ring is pressed down by a crimping portion formed on the axially inner end of the hub wheel, or by a nut screwed onto the axially inner end of the hub wheel.

[0062] The hub unit bearing 1 of this example further includes sealing devices 16a, 16b that close openings on both axial sides of the rolling element installation space 15 that exist between the inner circumferential surface of the outer ring 2 and the outer circumferential surface of the hub 3. This prevents external foreign matter from entering the rolling element installation space 15 through the openings and prevents grease from leaking from the rolling element installation space 15 to the outside.

[0063] In this example, sealing device 16a that closes the axially outer opening of rolling element installation space 15 is composed of a seal ring fitted and fixed to an outer seal fitting surface 17 provided on the inner peripheral surface of the axially outer end of outer ring 2. Sealing device 16b that closes the axially inner opening of rolling element installation space 15 is composed of a combination seal ring that combines a seal ring fitted and fixed to an inner seal fitting surface 18 provided on the inner peripheral surface of the axially inner end of outer ring 2 with a slinger fitted and fixed to the outer peripheral surface of the axially inner end of inner ring 11.

[0064] In this example, the inner diameter of the outer seal fitting surface 17 is larger than the groove bottom diameter of the outermost row of outer ring raceways 5a. The inner diameter of the inner seal fitting surface 18 is larger than the groove bottom diameter of the innermost row of outer ring raceways 5c. The inner diameter of the inner seal fitting surface 18 is larger than the inner diameter of the outer seal fitting surface 17.

[0065] (Manufacturing method of outer ring) The manufacturing method of the outer ring 2 that constitutes the hub unit bearing 1 of this example includes a grinding finishing process in which the three rows of outer ring raceways 5a, 5b, 5c are simultaneously ground and finished using a formed grindstone 19, and after completion of the grinding finishing process, a superfinishing process in which each of the three rows of outer ring raceways 5a, 5b, 5c is superfinished.

[0066] That is, when manufacturing the outer ring 2 that constitutes the hub unit bearing 1 of this example, a material made of hard metal such as medium carbon steel is forged to obtain an outer ring intermediate having the rough shape of the outer ring 2. The outer ring intermediate is then sequentially subjected to cutting to adjust the shape, heat treatment to impart the required hardness and other mechanical properties, and finishing to achieve the final shape and surface roughness, thereby obtaining the outer ring 2.

[0067] The manufacturing method of the outer ring 2 of the hub unit bearing 1 of this embodiment includes the grinding finishing step and the super-finishing step as the finishing steps.

[0068] In this embodiment, the grinding process for the three rows of outer ring raceways 5a, 5b, 5c is carried out as shown in FIG.

[0069] That is, the outer peripheral surface of the outer ring 2 is rotatably supported at multiple points in the circumferential direction by the tips of shoes (not shown), thereby positioning the outer ring 2 in the radial direction. Then, by rotating a magnetic chuck (not shown) that is magnetically attracted to an end face on one axial side (axially outer or axially inner) of the outer ring 2, the outer ring 2 is rotated about its own central axis O.

[0070] In this state, the shaped grinding wheel 19 inserted radially inside the outer ring 2 from the other axial side (axially inside or axially outside) is rotated about its own central axis α (or β) while the outer peripheral surface of the shaped grinding wheel 19 is pressed against a circumferential portion of the workpiece, including the three rows of outer ring raceways 5a, 5b, 5c, on the inner peripheral surface of the outer ring 2, to perform grinding finishing on the workpiece.

[0071] The formed grindstone 19 has three rows of processing parts 20a, 20b, and 20c on its outer circumferential surface, which are used to perform grinding finish processing on the three rows of outer ring raceways 5a, 5b, and 5c. The grain size of the abrasive grains constituting the three rows of processing parts 20a, 20b, and 20c is the same for each other.

[0072] When implementing the present disclosure, the grain size of the abrasive grains constituting the three rows of processing portions 20a, 20b, and 20c can be appropriately determined depending on the target surface roughness value of the processed portion after finishing, but can preferably be #100 to #150.

[0073] In this example, the processed portions of the inner peripheral surface of the outer ring 2 that are ground and finished by the formed grindstone 19 include the outer seal fitting surface 17 and the inner seal fitting surface 18. For this reason, the outer peripheral surface of the formed grindstone 19 further includes two rows of processed portions 21a, 21b, which are portions where the outer seal fitting surface 17 and the inner seal fitting surface 18 are ground and finished.

[0074] In this example, the formed grindstone 19 is made as a single piece, and the grain size is uniform throughout.

[0075] In addition, when the formed grinding wheel 19 wears with use, the generatrix shape of the processing parts 20a, 20b, 20c, 21a, and 21b provided on the outer circumferential surface of the formed grinding wheel 19 is appropriately adjusted by a diamond wheel to a shape that matches the generatrix shape of the processed part after completion. In Fig. 2, the central axis of the formed grinding wheel 19 when it is new is indicated by a dashed line α, and the central axis of the formed grinding wheel 19 immediately before replacement, whose outer diameter has become smaller due to wear or being cut by the diamond wheel, is indicated by a dashed line β.

[0076] In this example, the super-finishing process for the three rows of outer ring raceways 5a, 5b, 5c is carried out as follows.

[0077] That is, in the super-finishing process, a grinding wheel having a finer grit size (larger number) than the formed grinding wheel 19 used in the grinding finishing process is used, and the processed portion (super-finished portion) of the grinding wheel is pressed with a predetermined pressure against each row of outer ring raceways 5a, 5b, 5c of the outer ring 2 rotating around its own central axis O while the grinding wheel is oscillated, thereby improving the surface roughness of each row of outer ring raceways 5a, 5b, 5c.

[0078] When implementing the present disclosure, the grit size of the grindstone used in the superfinishing process can be appropriately determined depending on the target surface roughness value after finishing of the workpiece, but can be preferably #1000 to #2000, and more preferably #1200 to #1500.

[0079] In particular, in the manufacturing method of the outer ring 2 of this example, in the grinding finishing process, a hub 3 (hub 3 in which the groove bottom diameters of the three rows of inner ring raceways 7a, 7b, 7c have the same deviation (including 0) from the design value) is placed radially inside the outer ring 2 after the grinding finishing process is completed, and balls 4a, 4b, 4c of the same gauge (for example, 0 gauge) are placed between the three rows of outer ring raceways 5a, 5b, 5c and the three rows of inner ring raceways 7a, 7b, 7c to complete the hub unit bearing 1, and grinding finishing is performed on the three rows of outer ring raceways 5a, 5b, 5c so that the first negative gap is larger than the second negative gap.

[0080] In addition, in the super-finishing process, assuming that a hub 3 (hub 3 in which the groove bottom diameters of three rows of inner ring raceways 7a, 7b, 7c have the same deviation (including 0) from the design value) is placed radially inside the outer ring 2 after the super-finishing process is completed, and balls 4a, 4b, 4c of the same gauge (for example, 0 gauge) are placed between the three rows of outer ring raceways 5a, 5b, 5c and the three rows of inner ring raceways 7a, 7b, 7c to complete the hub unit bearing 1, super-finishing is performed on the three rows of outer ring raceways 5a, 5b, 5c so that the first negative gap is larger than the second negative gap.

[0081] Furthermore, assuming that a hub 3 is disposed radially inside the outer ring 2 after the grinding finish process is completed, and balls 4a, 4b, and 4c of the same gauge are disposed between three rows of outer ring raceways 5a, 5b, and 5c and three rows of inner ring raceways 7a, 7b, and 7c to complete the hub unit bearing 1, the difference ΔG between the first negative gap and the second negative gap is 1 The difference ΔG between the first negative gap and the second negative gap when it is assumed that the hub 3 is disposed radially inside the outer ring 2 after the superfinishing process is completed, and balls 4a, 4b, and 4c of the same gauge are disposed between three rows of outer ring raceways 5a, 5b, and 5c and three rows of inner ring raceways 7a, 7b, and 7c to complete the hub unit bearing 1. 2 Make it smaller than (ΔG 1 <ΔG 2 Specifically, the above ΔG 1 The above ΔG 2 The thickness should be smaller by 2 μm or more and 10 μm or less, preferably by 4 μm or more and 8 μm or less.

[0082] Said ΔG 1 The above ΔG 2 The reason for making the value smaller than 1 will be explained below.

[0083] In the manufacturing method of the outer ring 2 of this example, when the outer ring raceways 5a, 5b, 5c of each row are simultaneously ground and finished using the shaped grindstone 19, the shaped grindstone 19 must be disposed radially inside the outer ring 2, and therefore the outer diameter φa of the processed portion 21b, which is the maximum outer diameter of the shaped grindstone 19, must be smaller than the inner diameter φb of the intermediate small diameter outer ring groove shoulder portion 24, which is the minimum inner diameter of the outer ring 2. Specifically, when the shaped grindstone 19 is new, the outer diameter φa of the processed portion 21b must be equal to or smaller than the inner diameter φb of the intermediate small diameter outer ring groove shoulder portion 24.

[0084] In this example, the groove bottom diameter of the middle row outer ring raceway 5b is smaller than the groove bottom diameter of the outermost row outer ring raceway 5a and the groove bottom diameter of the innermost row outer ring raceway 5c by 10 mm to 20 mm, preferably 12 mm to 18 mm. The three rows of processed portions 20a, 20b, 20c (grinding portions) of the formed grindstone 19 also have the same diameter difference as the three rows of outer ring raceways 5a, 5b, 5c, so the ratio of the outer diameters of the three rows of processed portions 20a, 20b, 20c (grinding portions) is about 1:(0.7-0.8):1.

[0085] Specifically, the outer diameter of the minimum diameter portion (the axially outer end portion) of the processed portion 20b of the middle row is about 2 / 3 of the outer diameter of the maximum diameter portion of the processed portion 20a of the outermost row and the outer diameter of the maximum diameter portion of the processed portion 20c of the innermost row when the formed grindstone 19 is new, and is about 1 / 2 of the outer diameter of the maximum diameter portion of the processed portion 20c just before the formed grindstone 19 is replaced.

[0086] In other words, the peripheral speed of the minimum diameter portion of the processing portion 20b in the middle row is about 2 / 3 of the peripheral speed of the maximum diameter portion of the processing portion 20a in the outermost row and the maximum diameter portion of the processing portion 20c in the innermost row when the forming wheel 19 is new, and is about 1 / 2 ... processing portion 20b in the state immediately before the forming wheel 19 is replaced.

[0087] On the other hand, when grinding the outer raceway of a hub unit bearing, the grain size of the abrasive grains constituting the formed grindstone is usually #100 to #150, and the surface roughness of the outer raceway is finished to about 0.25 μmRa to 0.32 μmRa. However, in grinding finish processing, if the peripheral speed of the grindstone is high (fast), the grindstone acts hard, resulting in surface properties similar to those when the abrasive grains are small, improving the surface roughness of the processed part, whereas if the peripheral speed of the grindstone is low (slow), the grindstone acts soft, resulting in surface properties similar to those when the abrasive grains are large, deteriorating the surface roughness of the processed part.

[0088] Therefore, in this example, when the circumferential speed of the minimum diameter portion of the processed portion 20b of the intermediate row is approximately 2 / 3 to 1 / 2 of the circumferential speed of the maximum diameter portion of the processed portion 20a of the outermost row and the maximum diameter portion of the processed portion 20c of the innermost row, if one attempts to finish the surface roughness of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c, which have a high circumferential speed of the processed portions 20a, 20c, to approximately 0.25 to 0.32 μmRa, the surface roughness of the outer ring raceway 5b of the intermediate row, which has a low circumferential speed of the processed portion 20b, will deteriorate to approximately 0.40 to 0.45 μmRa.

[0089] As a method for making the surface roughness of the three rows of outer ring raceways 5a, 5b, 5c that have been subjected to grinding finish processing using a formed grindstone approximately equal, a method can be considered in which the grindstones for each row are combined to form a formed grindstone, and the grain size of the grindstones for each row (grain size of the processed parts of the three rows) is made different. However, when making such a formed grindstone, it is difficult to provide spacers to prevent cracks from occurring at the boundaries between the grindstones for each row, and even if such spacers could be provided, the manufacturing costs of the formed grindstones increase, resulting in a problem of increased manufacturing costs for the hub unit bearings.

[0090] In addition, in the superfinishing process performed after the grinding finish process, if the surface roughness of the part to be processed is poor, the sharpness of the grindstone will be sharp, and the amount of the part to be processed will increase, whereas if the surface roughness of the part to be processed is good, the sharpness of the grindstone will be poor, and the amount of the part to be processed will decrease. Therefore, in order to make the surface properties of the three rows of outer ring raceways 5a, 5b, 5c approximately the same, the amount of the part to be processed by the superfinishing process of the middle row outer ring raceway 5b, which has a relatively poor surface roughness after the grinding finish process, will be greater than the amount of the part to be processed by the superfinishing process of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c, which have a relatively good surface roughness after the grinding finish process.

[0091] Specifically, when the surface roughness of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c is finished to the relatively good roughness of about 0.25 to 0.32 μmRa, and the surface roughness of the middle row outer ring raceway 5b is finished to the relatively poor roughness of about 0.40 to 0.45 μmRa, the amount of material removed by the superfinishing process of the middle row outer ring raceway 5b will be about 5 to 10 μm more in terms of axial internal clearance than the amount of material removed by the superfinishing process of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c.

[0092] In other words, the amount of cutting required for the superfinishing of the intermediate row outer ring raceway 5b is greater than the amount of cutting required for the superfinishing of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c by "an amount that reduces the axial negative gap (the second negative gap) between the outermost row and the intermediate row by approximately 5 to 10 μm," or in other words, by "an amount that increases the difference between the first negative gap and the second negative gap by approximately 5 to 10 μm."

[0093] The hub unit bearing 1 of this example is a double-row angular contact ball bearing, and a predetermined relationship exists between the radial internal clearance and the axial internal clearance of a double-row angular contact ball bearing, and a known conversion method is known (for example, see equations (5) to (7) on page 102 of the "NSK Technical Report"). For this reason, using this known conversion method, the amount of change in the radial internal clearance (corresponding to the amount of material removed in the superfinishing process in the above explanation) can be converted into the amount of change in the axial internal clearance.

[0094] As can be seen from the above explanation, when manufacturing the outer ring 2 of this example, if the difference between the groove bottom diameters of the three rows of outer ring raceways 5a, 5b, 5c at the end of the grinding finish process is set to be the same as the target value of the difference between the groove bottom diameters of the three rows of outer ring raceways 5a, 5b, 5c after completion, the middle row outer ring raceway 5b will be ground more than the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c in the super-finishing process, so that the difference between the groove bottom diameters of the three rows of outer ring raceways 5a, 5b, 5c after completion will deviate significantly from the target value. Specifically, the difference between the groove bottom diameters of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c and the groove bottom diameter of the middle row outer ring raceway 5b will be smaller than the target value.

[0095] In view of this, in this example, the difference ΔG 1 The difference ΔG 2 Make it smaller than (ΔG 1 <ΔG 2 That is, taking into consideration that the amount of material to be removed in the superfinishing process of the intermediate row outer ring raceway 5b is greater than the amount of material to be removed in the superfinishing process of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c, the mutual differences between the groove bottom diameters of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c and the groove bottom diameter of the intermediate row outer ring raceway 5b are made greater at the end of the grinding finish process than at the end of the superfinishing process.

[0096] For example, when carrying out the manufacturing method of the outer ring 2 of this embodiment, as described above, if the amount of material removed by the superfinishing process of the intermediate row outer ring raceway 5b is about 5 to 10 μm more in terms of the internal clearance in the axial direction than the amount of material removed by the superfinishing process of the outermost row outer ring raceway 5a and the innermost row outer ring raceway 5c, the ΔG 1 The above ΔG 2 In other words, the difference between the groove bottom diameter of the outermost row outer ring raceway 5a and the groove bottom diameter of the innermost row outer ring raceway 5c and the groove bottom diameter of the middle row outer ring raceway 5b is made larger, converted into an axial internal clearance, by about 5 to 10 μm at the end of the grinding finish process than at the end of the superfinishing process.

[0097] In this way, at the end of the super-finishing process, the mutual differences between the groove bottom diameters of the outermost row outer ring raceways 5a and the innermost row outer ring raceways 5c and the groove bottom diameter of the intermediate row outer ring raceways 5b can be brought close to the target values.

[0098] As a result, at the end of the superfinishing process, the deviations and variations in the groove bottom diameters of the outer ring raceways 5a, 5b, 5c and the inner ring raceways 7a, 7b, 7c of each row from the target values ​​can be made substantially uniform.

[0099] When manufacturing the hub 3 that constitutes the hub unit bearing 1 of this example, as with the outer ring 2, for the inner ring 11 and hub ring 12, a material made of hard metal such as medium carbon steel or bearing steel is forged to obtain an intermediate body having the rough shape of the respective target parts (inner ring 11 or hub ring 12). Each intermediate body is then sequentially subjected to cutting to adjust the shape, heat treatment to impart the necessary hardness and other mechanical properties, and finishing to achieve the final shape and surface roughness, to obtain the respective target parts (inner ring 11 or hub ring 12).

[0100] In this example, the finishing process includes a grinding process in which grinding is performed on the inner raceway (7a, 7b or 7c) provided on the target part (inner race 11 or hub wheel 12), and a super-finishing process in which super-finishing is performed on the inner raceway (7a, 7b or 7c) after the grinding process.

[0101] When performing a grinding finish process on the middle row inner ring raceway 7b and the innermost row inner ring raceway 7c provided on the outer circumferential surface of the inner ring 11, a plurality of circumferential locations of the processed portion, including the middle row inner ring raceway 7b and the innermost row inner ring raceway 7c, on the outer circumferential surface of the inner ring 11 are rotatably supported by the tip ends of shoes (not shown), thereby radially positioning the inner ring 11. Then, by rotating a magnet chuck magnetically attracted to the axially inner end face of the inner ring 11, the inner ring 11 is rotated about its own central axis.

[0102] In this state, the formed grinding wheel arranged radially outside the inner ring 11 is rotated about its own central axis, while the outer circumferential surface of the formed grinding wheel is pressed against a portion of the processed part that is circumferentially removed from the portion supported by the tip of the shoe, and the processed part is subjected to grinding finishing. The generatrix shape of the outer circumferential surface of the formed grinding wheel is appropriately adjusted by a diamond wheel so as to match the generatrix shape of the processed part after completion.

[0103] When performing a grinding finish process on the outermost row of inner ring raceways 7a provided on the outer peripheral surface of hub ring 12, multiple circumferential locations of the processed portion, including the outermost row of inner ring raceways 7a, on the outer peripheral surface of hub ring 12 are rotatably supported by the tips of shoes (not shown), thereby radially positioning hub ring 12. Then, by rotating a magnet chuck magnetically attracted to the axially outer surface of rotation flange 8 of hub ring 12, hub ring 12 is rotated about its own central axis.

[0104] In this state, the formed grindstone arranged radially outward of the hub wheel 12 is rotated about its own central axis while the outer circumferential surface of the formed grindstone is pressed against a portion of the processed part that is circumferentially removed from the portion supported by the tip of the shoe, and grinding finish is applied to the processed part. The generatrix shape of the outer circumferential surface of the formed grindstone is appropriately adjusted by a diamond wheel so as to match the generatrix shape of the processed part after completion.

[0105] In this example, the shaped grindstones for grinding the middle row inner raceway 7b and the innermost row inner raceway 7c have the same grain size as the shaped grindstones for grinding the outermost row inner raceway 7a. When implementing this disclosure, the grain size can be the same as that of the shaped grindstones 19.

[0106] The superfinishing process for each row of inner raceways 7a, 7b, 7c is carried out in the same manner as the superfinishing process for each row of outer raceways 5a, 5b, 5c.

[0107] When implementing the present disclosure, the grit size of the grinding stones used to perform superfinishing on the inner ring raceways 7a, 7b, 7c of each row can be the same as the grit size of the grinding stones used to perform superfinishing on the outer ring raceways 5a, 5b, 5c of each row.

[0108] When manufacturing the hub unit bearing 1 of this example, after performing superfinishing on the outer raceways 5a, 5b, 5c and inner raceways 7a, 7b, 7c of each row, the groove bottom diameters of the outer raceways 5a, 5b, 5c and inner raceways 7a, 7b, 7c of each row are measured by, for example, placing the stylus of a measuring device against the groove bottoms of the outer raceways 5a, 5b, 5c and inner raceways 7a, 7b, 7c of each row. Then, depending on the measurement results, an appropriate gauge for the balls 4a, 4b, 4c is selected for each row, and the balls 4a, 4b, 4c of the gauge are assembled between the outer raceways 5a, 5b, 5c and inner raceways 7a, 7b, 7c of each row, thereby applying an appropriate preload to the balls 4a, 4b, 4c of each row.

[0109] In particular, in the manufacturing method of the outer ring 2 of this example, the deviation and variation of the groove bottom diameter of each row of the outer ring raceway 5a, 5b, 5c and the inner ring raceway 7a, 7b, 7c from the target value can be made almost the same at the end of the super-finishing process. Therefore, when applying an appropriate preload to each row of balls 4a, 4b, 4c, it is possible to assemble balls with a gauge of 0 or close to it not only in the outermost row and the innermost row but also in the middle row. Therefore, the number of types of gauges of the balls 4a, 4b, 4c that need to be prepared when manufacturing the hub unit bearing 1 can be reduced. As a result, the ball hopper that houses the balls 4a, 4b, 4c of each gauge can be made small, and the manufacturing cost of the hub unit bearing 1 can be reduced.

[0110] When implementing the present disclosure, in order to reduce the number of types of gauges of the balls 4a, 4b, and 4c to be assembled in each row, the difference ΔG 2 It is preferable to set the value in the range of 5 μm to 15 μm.

[0111] [Example 2] A second embodiment of the present disclosure will be described with reference to FIG.

[0112] In the hub unit bearing 1a of this embodiment, the middle row balls 4b are provided with a contact angle and preload that forms a back-to-back combination type in relation to the innermost row balls 4c, as shown by the dashed line in FIG.

[0113] For this reason, in this example, the outer ring 2a has an intermediate small diameter outer ring groove shoulder 24a on its inner circumferential surface adjacent to the axially inner side of the intermediate row outer ring raceway 5b, the inner diameter being smaller than that of the portion adjacent to the axially outer side of the outer ring raceway 5b. The hub 3a has an intermediate large diameter hub groove shoulder 27a on its outer circumferential surface adjacent to the axially outer side of the intermediate row inner ring raceway 7b, the outer diameter being larger than that of the portion adjacent to the axially inner side of the inner ring raceway 7b.

[0114] In this example, the hub 3a is formed by combining an inner ring 11a having an innermost row inner ring raceway 7c on its outer circumferential surface with a hub ring 12a having an outermost row inner ring raceway 7a and an intermediate row inner ring raceway 7b on its outer circumferential surface.

[0115] In this example, the diameter of the middle row balls 4b is smaller than the diameter of the outermost row balls 4a and smaller than the diameter of the innermost row balls 4c, and the diameter of the innermost row balls 4c is larger than the diameter of the outermost row balls 4a.

[0116] Other functions and effects relating to the structure and manufacturing method of the hub unit bearing 1a in the second example are similar to those in the first example. [Explanation of symbols]

[0117] 1, 1a Hub unit bearing 2, 2a Outer ring 3, 3a hub 4a, 4b, 4c balls 5a, 5b, 5c outer ring raceway 6 Stationary Flange 7a, 7b, 7c Inner raceway 8 Rotating flange 9 Spline hole 10a, 10b, 10c retainer 11, 11a Inner ring 12, 12a Hub wheel 13 Small diameter stepped section 14 Step surface 15 Rolling element installation space 16a, 16b Sealing device 17 Outer seal mating surface 18 Inner seal mating surface 19. Formed whetstone 20a, 20b, 20c processing section 21a, 21a processing section 22 Outside small diameter outer ring groove shoulder 23 Inner small diameter outer ring groove shoulder 24, 24a Intermediate small diameter outer ring groove shoulder 25 Outside large diameter hub groove shoulder 26 Inner large diameter hub groove shoulder 27, 27a Intermediate large diameter hub groove shoulder

Claims

[Claim 1] an outer ring having three rows of outer ring raceways on an inner circumferential surface; A hub having three rows of inner ring raceways on its outer circumferential surface; a plurality of balls are disposed in each row between the three rows of outer ring raceways and the three rows of inner ring raceways; Equipped with Among the balls, a contact angle and a preload are applied to the outermost row balls arranged in the outermost row, which is the row located farthest outward in the axial direction, and the innermost row balls arranged in the innermost row, which is the row located farthest in the axial direction, such that they are back-to-back combination type, Among the balls, balls in an intermediate row that is a row located between the outermost row and the innermost row in the axial direction are given a contact angle and a preload that form a back-to-back type in relation to balls in one of the outermost row and the innermost row, a first negative gap which is an axial negative gap between the outermost row and the innermost row is larger than a second negative gap which is an axial negative gap between the intermediate row and one of the rows; A manufacturing method of the outer ring constituting a hub unit bearing, comprising the steps of: a grinding finishing process for simultaneously grinding the three rows of outer ring raceways using a formed grindstone; a super-finishing step of subjecting the three rows of outer ring raceways to a super-finishing process after the grinding finishing step is completed; Equipped with The formed grindstone has three rows of processing portions, which are portions for grinding the three rows of outer ring raceways, and the grain sizes of the processing portions are the same. In the grinding finishing process, assuming that the hub is disposed radially inside the outer ring after the grinding finishing process is completed, and balls of the same gauge are disposed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing, the grinding finishing process is performed on the three rows of outer ring raceways so that the first negative gap is larger than the second negative gap, In the superfinishing step, assuming that the hub is disposed radially inside the outer ring after completion of the superfinishing step, and balls of the same gauge are disposed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing, the superfinishing process is performed on the three rows of outer ring raceways so that the first negative gap is larger than the second negative gap; a difference between the first negative gap and the second negative gap when it is assumed that the hub is disposed radially inside the outer ring after the grinding finish process is completed, and balls of the same gauge are disposed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing, is made smaller than a difference between the first negative gap and the second negative gap when it is assumed that the hub is disposed radially inside the outer ring after the superfinishing process is completed, and balls of the same gauge are disposed between the three rows of outer ring raceways and the three rows of inner ring raceways to assemble the hub unit bearing; A method for manufacturing the outer ring of a hub unit bearing.

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