JP2022153034A - hub unit bearing - Google Patents

Abstract

To provide a hub unit bearing capable of uniformly approaching an effective hardening layer depth in a curvature direction of a raceway surface, for a hardening layer formed at an axially outside part of an outer ring raceway on an axially outer side.SOLUTION: An outer ring 2 has double-row outer ring raceways 5a, 5b on its inner peripheral surface. A hardened layer is formed on each of the outer ring raceways 5a, 5b. The outer ring 2 has a shoulder part (small shoulder part) 23a at a location adjacent to the axially outside of the outer ring raceway 5a on the axially outside of the inner peripheral surface, and on the outer peripheral surface, a gutter groove 27 is arranged over the entire circumference so that a groove bottom part 28 overlaps the shoulder part (small shoulder part) 23a in a radial direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a hub unit bearing for rotatably supporting a vehicle wheel with respect to a suspension system.

5 and 6 show an example of a conventional structure of a hub unit bearing described in Japanese Patent Laying-Open No. 2015-227673 (Patent Document 1). A hub unit bearing 100 includes an outer ring 101, a hub 102, and a plurality of balls 103a and 103b, each of which is a rolling element. Regarding the hub unit bearing 100, the axially outer side is the left side in FIGS. It is the right side of FIGS. 5 and 6, which is the center side in the width direction.

The outer ring 101 has double-row outer ring raceways 104a and 104b on its inner peripheral surface, and a stationary flange 113 projecting radially outward from its axial intermediate portion. Each of the outer ring raceways 104a, 104b has an arcuate cross-sectional shape. The outer ring 101 is supported and fixed to the suspension system by means of support bolts screwed into support holes 114 axially penetrating through the stationary flange 113, so that the outer ring 101 does not rotate even when the wheel rotates.

The hub 102 is arranged on the inner diameter side of the outer ring 101, and has double-row inner ring raceways 105a and 105b on the outer peripheral surface and a rotary flange 106 on the axially outer side. Each of the inner ring raceways 105a and 105b has an arcuate cross-sectional shape. The hub 102 rotates integrally with the wheel and the braking rotator supported and fixed to the rotary flange 106 in the state of use.

A plurality of balls 103a and 103b are arranged for each row between the double-row outer ring raceways 104a and 104b and the double-row inner ring raceways 105a and 105b with a back-to-back combination contact angle, Allows rotation of the hub 102 with respect to the outer ring 101 .

Openings on both sides in the axial direction of the rolling element installation space 107 existing between the inner peripheral surface of the outer ring 101 and the outer peripheral surface of the hub 102 are closed by the seal ring 108 and the combination seal ring 109 . As a result, grease for lubrication existing in the rolling element installation space 107 leaks into the external space through the openings on both sides in the axial direction of the rolling element installation space 107, or foreign matter such as muddy water enters the rolling element installation space 107 from the external space. to prevent intrusion.

By the way, the method of manufacturing the outer ring that constitutes the hub unit bearing usually includes a process of hot forging a metal material to form a rough shape of the outer ring, and a finishing process such as cutting and grinding of the inner peripheral surface. A step of forming a double-row outer ring raceway by machining, and a step of forming a hardened layer on each of the double-row outer ring raceways by induction hardening treatment to ensure rolling contact fatigue life. A step of performing hot forging on the outer peripheral surface of the axially outer portion of the outer ring that is not subjected to finishing after hot forging, that is, on the outer peripheral surface of the portion located axially outside the stationary flange. is provided with a draft angle for extracting the mold toward the outside in the axial direction. Therefore, water such as muddy water adhering to the outer peripheral surface of the axially outer portion of the outer ring travels along the outer peripheral surface and reaches the seal sliding contact portion of the seal ring that closes the axially outer opening of the rolling element installation space. It may reduce the sealing performance of the seal ring.

To address this problem, in the illustrated hub unit bearing 100, a weir portion 110 projecting radially outward from the outer peripheral surface of the outer ring 101 is formed at the radially outer end portion of the seal ring 108 over the entire circumference, and A gutter groove 111 is formed along the entire circumference on the outer peripheral surface of the axially outer end portion of the outer ring 101 adjacent to the axially inner side of the weir portion 110 . In the illustrated example, the gutter groove 111 is arranged axially outside the shoulder portion 112 that is present on the inner peripheral surface of the outer ring 101 adjacent to the axially outer side of the outer ring raceway 104a on the axially outer side. . Here, the shoulder portion 112 is a portion having a smaller diameter than the groove bottom portion of the outer ring raceway 104a on the axially outer side. By adopting such a configuration, of the outer peripheral surface of the axially outer portion of the outer ring 101, which is the portion positioned axially outwardly of the stationary flange 113, the portion positioned axially inwardly of the gutter groove 111 is reduced. Moisture that is transmitted and moves axially outward is guided downward by the gutter groove 111 to prevent the moisture from reaching the seal sliding contact portion of the seal ring 108 .

JP 2015-227673 A

The effective hardened layer depth in forming hardened layers by induction hardening on the outer ring raceways 104a and 104b increases as the thickness of the outer ring raceways 104a and 104b of the outer ring 101, that is, the heat capacity decreases.

Therefore, when the outer ring 101 is provided with the gutter grooves 111 on the outer peripheral surface of the axially outer portion, if the axial position of the gutter grooves 111 with respect to the outer ring raceway 104a on the axially outer side is not appropriate, the outer ring raceway 104a will have more troughs than the groove bottoms. The thickness of the axially outer portion of the outer ring raceway 104a, which is the portion located on the axially outer side, becomes uneven in the curvature direction of the raceway surface. The depth of the hardened layer may become non-uniform in the direction of curvature of the raceway surface.

In this case, for example, as in the illustrated example, if the gutter groove 111 is arranged axially outside of the shoulder portion 112, the thickness of the axially outside portion of the outer ring raceway 104a increases toward the axially outside. so it gets bigger. As a result, the effective hardening layer depth of the hardening layer formed on the axially outer portion of the outer ring raceway 104a becomes smaller toward the axial outer side, and in particular at the axially outer end of the hardening layer, sufficient compression is achieved. It may become impossible to apply stress.

On the other hand, when the groove bottom of the groove 111 is arranged at an axial position where the groove bottom of the groove 111 radially overlaps with the axially outer portion of the outer ring raceway 104a, the thickness of the groove bottom of the groove 111 is is smaller than the surrounding area. As a result, the effective hardened layer depth of the hardened layer formed on the axially outer portion of the outer ring raceway 104 a becomes particularly deep at the axial position where the groove bottom of the groove 111 exists, and the hardened layer approaches the groove 111 . It is possible that the hardened layer reaches the gutter groove 111 and the part corresponding to the gutter groove 111 is broken, that is, it is easy to break along the circumferential direction. have a nature.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hub unit bearing in which the effective hardened layer depth of the hardened layer formed on the axially outer portion of the outer ring raceway on the axially outer side can be made uniformly close to the curvature direction of the raceway surface. and

A hub unit bearing according to one aspect of the present invention comprises an outer ring having a double-row outer ring raceway on its inner peripheral surface and a hardened layer formed on each of the outer ring raceways, and a double-row inner ring raceway on its outer peripheral surface. and a plurality of rolling elements for each row between the double-row outer ring raceway and the double-row inner ring raceway and arranged with a back-to-back contact angle. .
An axially outer ring raceway of the double-row outer ring raceway and an axially-outer inner ring raceway of the double-row inner ring raceway each have an arcuate cross-sectional shape.
The rolling elements of the axially outer row are constituted by balls.
The outer ring has a shoulder portion having a smaller diameter than a groove bottom portion of the outer ring raceway at a portion of the inner peripheral surface adjacent to the axially outer side of the outer ring raceway, and has a groove bottom portion on the outer peripheral surface. has a gutter groove arranged so as to radially overlap with the shoulder portion over the entire circumference.

In one aspect of the present invention, in an imaginary plane including the central axis of the outer ring, the axially inner portion of the inner surface of the gutter groove is parallel to a tangent line to the axially outer edge portion of the axially outer outer ring raceway. It has a linear shape.

In one aspect of the present invention, the gutter has an axially symmetrical shape centering on the groove bottom of the gutter.

According to the hub unit bearing of one aspect of the present invention, the effective hardened layer depth of the hardened layer formed on the axially outer portion of the outer ring raceway on the axially outer side can be made uniformly close to the curvature direction of the raceway surface. .

FIG. 1 is a cross-sectional view of a hub unit bearing according to a first embodiment of the invention. 2 is an enlarged view of the axially outer portion of the outer ring in FIG. 1. FIG. FIGS. 3A and 3B are cross-sectional views of gutter grooves showing modifications of the first example. FIG. 4 is a diagram corresponding to FIG. 2 regarding the second example of the embodiment of the invention. FIG. 5 is a sectional view showing an example of a conventional structure of a hub unit bearing. FIG. 6 is an enlarged view of the upper left part of FIG.

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

A hub unit bearing 1 of this example is for a drive wheel, and includes an outer ring 2, a hub 3, and balls 4a and 4b, each of which is a rolling element. However, the present invention can also be applied to hub unit bearings for driven wheels. Regarding the hub unit bearing 1, the axially outer side is the left side in FIGS. It is the right side of FIGS. 1 and 2, which is the center side in the width direction.

The outer ring 2 is made of hard metal such as medium carbon steel. The outer ring 2 has double-row outer ring raceways 5a and 5b on its inner peripheral surface. Each of the outer ring raceways 5a, 5b has an arcuate cross-sectional shape.

The inner peripheral surface of the outer ring 2 has a small shoulder portion 23a, which is a shoulder in the present invention, adjacent to the axially outer side of the axially outer outer ring raceway 5a, and is adjacent to the axially inner side of the axially outer outer ring raceway 5a. It has a large shoulder portion 24a at the place where it does. The small shoulder portion 23a has a smaller diameter than the groove bottom portion 25a, which is the radially outermost portion of the outer ring raceway 5a on the axially outer side, and is formed of a cylindrical surface. The large shoulder portion 24a has a smaller diameter than the groove bottom portion 25a and a smaller diameter than the small shoulder portion 23a, and is formed of a cylindrical surface. The outer ring 2 has a cylindrical seal fitting surface 26 with a larger diameter than the small shoulder portion 23a on the inner peripheral surface of the axially outer end located axially outside the small shoulder portion 23a.

The inner peripheral surface of the outer ring 2 has a small shoulder portion 23b at a location adjacent to the axially inner side of the axially inner outer ring raceway 5b, and a large shoulder portion 24b at a location adjacent to the axially outer side of the axially inner outer ring raceway 5a. have Each of the small shoulder portion 23b and the large shoulder portion 24b has a smaller diameter than the groove bottom portion 25b, which is the radially outermost portion of the axially inner outer ring raceway 5b, and is formed of a cylindrical surface. there is The large shoulder portion 24b has a smaller diameter than the small shoulder portion 23b. In this example, the two large shoulders 24a and 24b exist within the same imaginary cylindrical plane and are formed continuously with each other.

Hardened layers 32a, 32b are formed on the double-row outer ring raceways 5a, 5b by induction hardening treatment in order to ensure rolling contact fatigue life.

The outer ring 2 has a stationary flange 6 projecting radially outward at an axially intermediate portion. The stationary flange 6 has axially penetrating support holes 7 at a plurality of locations in the circumferential direction of the radially intermediate portion.

In this example, the outer ring 2 has a gutter groove 27 over the entire circumference on the outer peripheral surface of the axially outer portion, which is a portion located axially outside the stationary flange 6 . The gutter groove 27 is arranged so that the groove bottom portion 28, which is the most radially inner portion, overlaps the small shoulder portion 23a in the radial direction.

In this example, in the virtual plane containing the central axis of the outer ring 2, that is, in the paper plane of FIGS. It has a linear shape parallel to the tangential line L to the axial outer edge of the track 5a. The tangent line L is a straight line extending radially outward as it extends axially inward.

Specifically, in this example, the inner surface of the gutter groove 27 is composed of a bottom surface 29 including a groove bottom portion 28 and two side surfaces 30 and 31 sandwiching the bottom surface 29 from both sides in the axial direction. In this example, the bottom surface 29 and the axially outer side surface 30 have arcuate cross-sectional shapes that are continuous with each other. The groove bottom 28 exists in the axial center of the bottom surface 29 . In this example, the side surface 31 on the inner side in the axial direction has a linear cross-sectional shape that is inclined in the direction toward the outer side in the radial direction as it goes inward in the axial direction. That is, the axially inner side surface 31 is configured by a conical surface.

In particular, in this example, in a virtual plane including the central axis of the outer ring 2, the axially inner side surface 31 corresponding to the axially inner portion of the inner surface of the gutter groove 27 has a linear shape parallel to the tangent line L, that is, It has a linear cross-sectional shape. That is, the inclination angle of the axially inner side surface 31 with respect to the central axis of the outer ring 2 is the same as the inclination angle of the tangent line L with respect to the central axis of the outer ring 2 .

However, when carrying out the present invention, as in the first modification of the present example shown in FIG. , the angle of inclination of the tangent line L with respect to the central axis of the outer ring 2 may be larger. Alternatively, as in the second modification of this example shown in FIG. It can also be smaller than the inclination angle of L. 3(A) and 3(B), the auxiliary line S is a straight line parallel to the tangent line L. As shown in FIG.

The outer peripheral surface of the axially outer portion of the outer ring 2, which is the portion located axially outwardly of the stationary flange 6, is hot forged when manufacturing the outer ring 2, except for the portion where the gutter groove 27 is formed. A draft angle is provided for extracting the mold toward the outside in the axial direction in the process of (1). That is, the portion of the outer peripheral surface of the axially outer portion of the outer ring 2, excluding the portion where the gutter groove 27 is formed, is composed of an inclined surface 33 inclined in a direction in which the outer diameter decreases toward the axially outer side. It is The gutter groove 27 divides the inclined surface 33 into two in the axial direction.

The outer ring 2 is supported and fixed to the suspension system by means of support bolts screwed into support holes 7 of the stationary flange 6, so that it does not rotate even when the wheel rotates.

The hub 3 has double-row inner ring raceways 8 a and 8 b on its outer peripheral surface, and is arranged coaxially with the outer ring 2 radially inward of the outer ring 2 . Each of the inner ring raceways 8a, 8b has an arcuate cross-sectional shape. The hub 3 has a rotary flange 9 protruding radially outward at a portion located axially outside the axially outer end of the outer ring 2, and a cylindrical pilot portion 10 at the axially outer end. have The rotating flange 9 has mounting holes 11 extending axially through it at a plurality of locations in the circumferential direction of the radially intermediate portion. A stud 12 is press-fitted into each of the mounting holes 11 .

In this example, the hub 3 is formed by combining a hub ring 14 and an inner ring 15 . The axially outer inner ring raceway 8a is provided on the outer peripheral surface of the hub wheel 14 at the axially intermediate portion. The rotating flange 9 and the pilot portion 10 are provided on the axially outer portion of the hub wheel 14 . The inner ring raceway 8 a on the inner side in the axial direction is provided on the outer peripheral surface of the inner ring 15 . The inner ring 15 is externally fitted and fixed to the axially inner portion of the hub ring 14 . Since the hub unit bearing 1 of this example is for a drive wheel, the hub wheel 14 has a spline hole 16 in its radial center portion for spline engagement with a spline shaft portion constituting a drive shaft member.

In addition, the present invention provides a hub unit bearing having a crimped portion that presses down the axially inner surface of the inner ring at the axially inner end portion of the hub ring, and an inner ring raceway on the axially outer side that is fitted onto the hub ring. It can also be applied to a hub unit bearing provided on the outer peripheral surface of another inner ring.

The braking rotator and the wheel each have a central hole provided at its center, through which the pilot portion 10 is inserted, and studs 12 are inserted through through holes provided at a plurality of locations in the circumferential direction of their radial intermediate portions. By screwing a hub nut onto the distal end of the stud 12 while it is inserted, the stud 12 is coupled to the rotating flange 9 . The braking rotor and the wheel are coupled and fixed to the rotating flange by screwing a hub bolt inserted through a through hole provided in the braking rotor and a through hole provided in the wheel into the mounting hole. can also

A plurality of balls 4a, 4b are arranged for each row between the double-row outer ring raceways 5a, 5b and the double-row inner ring raceways 8a, 8b with a back-to-back contact angle and preload. and are rotatably held by retainers 13a and 13b in respective rows. Thereby, the hub 3 is rotatably supported radially inwardly of the outer ring 2 .

In this example, the rolling elements in the axially outer row are composed of balls 4a, and the rolling elements in the axially inner row are composed of balls 4b. However, when carrying out the present invention, the rolling elements in the axially inner row can also be composed of tapered rollers. In this case, each of the outer ring raceway and the inner ring raceway on the inner side in the axial direction is composed of a conical surface. In this example, the pitch diameter of the balls 4a in the axially outer row is the same as the pitch diameter of the balls 4b in the axially inner row. However, the present invention can also be applied to a different diameter PCD type hub unit bearing in which the pitch diameter of the rolling elements in the axially outer row and the pitch diameter of the rolling elements in the axially inner row are different from each other.

In this example, an axially outer opening of a substantially cylindrical rolling element installation space 17 that exists between the inner peripheral surface of the outer ring 2 and the outer peripheral surface of the hub 3 and in which the balls 4a and 4b are arranged. is blocked by a seal ring 18 . As a result, grease for lubrication existing in the rolling element installation space 17 leaks into the external space through the opening portion on the axial outer side of the rolling element installation space 17, or foreign matter such as muddy water enters the rolling element installation space 17 from the external space. to prevent intrusion.

The seal ring 18 includes an annular core metal 19 made of a metal plate and a rubber sealing material 20 reinforced by the core metal 19 . The seal member 20 has a plurality of (three in the illustrated example) seal lips 21a, 21b, and 21c. The seal ring 18 is attached to the axially outer end portion of the outer ring 2 by press-fitting the core metal 19 into the seal fitting surface 26 of the outer ring 2 . In this state, the tip portions of the seal lips 21a, 21b, and 21c are brought into sliding contact with the surface of the hub wheel 14 over the entire circumference.

In this example, the axial inner opening of the rolling element installation space 17 is closed by the combined seal ring 22 . As a result, the lubricating grease existing in the rolling element installation space 17 leaks into the external space through the axially inner opening of the rolling element installation space 17, or foreign matter such as muddy water enters the rolling element installation space 17 from the external space. to prevent intrusion.

When manufacturing the outer ring 2 that constitutes the hub unit bearing 1 of this example, a metal material is subjected to hot forging to form a rough shape of the outer ring 2 . After that, finishing such as cutting and grinding is applied to the double-row outer ring raceway 5a, 5b, small shoulders 23a, 23b, large shoulders 24a, 24b, seal fitting surface 26, gutter groove 27, and A support hole 7 is formed. After that, hardened layers 32a and 32b are formed on the double-row outer ring raceways 5a and 5b by induction hardening, respectively. A draft angle ( An inclined surface 33) is provided. The gutter groove 27 is formed by cutting the axial intermediate portion of the inclined surface 33 after the hot forging process, and divides the inclined surface 33 into two in the axial direction.

When the hub unit bearing 1 of this embodiment is used, the gutter groove 27 drains water such as muddy water traveling axially outward along the portion of the inclined surface 33 of the outer ring 2 located axially inward of the gutter groove 27 . lead to As a result, the amount of water reaching the sliding contact portion between the front end portions of the plurality of seal lips 21a, 21b, 21c and the surface of the hub wheel 14 can be reduced.

According to the hub unit bearing 1 of the present embodiment, it is formed in the axially outer portion of the outer ring raceway 5a on the axially outer side, specifically, in the portion of the outer ring raceway 5a positioned axially outer than the groove bottom portion 25a. For the hardened layer, that is, the axially outer portion of the hardened layer 32a, the effective hardened layer depth can be made uniformly close to the curvature direction of the raceway surface.

That is, in this example, the gutter groove 27 provided on the outer peripheral surface of the axially outer portion of the outer ring 2 is arranged so that the groove bottom portion 28 overlaps the small shoulder portion 23a in the radial direction. Therefore, based on the presence of the gutter groove 27, the thickness of the axially outer portion of the outer ring raceway 5a on the axially outer side of the outer ring 2, that is, the heat capacity, can be made uniform in the curvature direction of the raceway surface. Therefore, the effective hardened layer depth of the hardened layer formed on the axially outer portion of the outer ring raceway 5a on the axially outer side can be uniformly approached in the curvature direction of the raceway surface. As a result, the hardened layer on the axially outer portion of the outer ring raceway 5a on the outer side in the axial direction comes too close to the gutter groove 27 and cracks occur in the gutter groove 27. The hardened layer reaches the gutter groove 27 and corresponds to the gutter groove 27. It is possible to prevent the occurrence of problems such as the portion where the hardened layer is likely to be broken, or the hardened layer being unable to apply a sufficient compressive stress.

In particular, in this example, in the virtual plane including the central axis of the outer ring 2, the axially inner side surface 31 corresponding to the axially inner portion of the gutter groove 27 is the axially outer edge of the axially outer outer ring raceway 5a. It has a linear shape parallel to the tangent line L to the part. Therefore, the thickness of the axially outer portion of the outer ring raceway 5a on the axially outer side of the outer ring 2, that is, the heat capacity, can be made uniform at a high level in the curvature direction of the raceway surface. Therefore, the effective hardened layer depth of the hardened layer formed on the axially outer portion of the outer ring raceway 5a on the axially outer side can be brought uniformly close to the curvature direction of the raceway surface at a high level. As a result, it is possible to prevent the above-described problems from occurring at a high level.

In this example, with respect to the inner surface of gutter 27 , axially outer side surface 30 has an arcuate cross-sectional shape that is continuous with bottom surface 29 . Therefore, when the axially outer side surface 30 has a shape axially symmetrical with the axially inner side surface 31, that is, when it is configured by a conical surface axially symmetrical with the axially inner side surface 31. Compared to , the axial width dimension of the gutter groove 27 can be made smaller. Therefore, when the gutter grooves 27 are formed by turning, the cutting distance in the axial direction by the turning tool can be shortened, and the machining cost of the gutter grooves 27 can be reduced accordingly.

[Second example of embodiment]
A second example of the embodiment of the invention will be described with reference to FIG.

In this example, the gutter groove 27a provided on the outer peripheral surface of the axially outer portion of the outer ring 2 has an axially symmetrical shape centering on the groove bottom portion 28 of the gutter groove 27a. That is, in this example, with respect to the inner surface of the gutter 27a, the axially outer side surface 30a has a shape axially symmetrical with the axially inner side surface 31. As shown in FIG. That is, the axially outer side surface 30a is configured by a conical surface that is axially symmetrical with the axially inner side surface 31 .

In the structure of this example, the axial width dimension of the gutter groove 27a is larger than that of the first example of the embodiment. Longer axial cutting distance due to However, in the structure of this example, since the gutter groove 27a has a symmetrical shape in the axial direction with respect to the groove bottom 28, the axial position of the groove bottom 28 is easy to understand. Therefore, for example, in an inspection process at a factory, it is easy to confirm that the groove bottom 28 of the gutter 27a overlaps the small shoulder 23a in the radial direction, and to easily measure the dimensions and contour shape of the gutter 27a. can do
Other configurations and effects are the same as those of the first embodiment.

The present invention can be practiced by appropriately combining the structures of the above-described embodiments (including the modification of the first embodiment) as long as there is no contradiction.

Reference Signs List 1 hub unit bearing 2 outer ring 3 hub 4a, 4b balls 5a, 5b outer ring raceway 6 stationary flange 7 support hole 8a, 8b inner ring raceway 9 rotating flange 10 pilot portion 11 mounting hole 12 stud 13a, 13b retainer 14 hub ring 15 inner ring 16 Spline hole 17 Rolling element installation space 18 Seal ring 19 Core metal 20 Seal material 21a, 21b, 21c Seal lip 22 Combined seal ring 23a, 23b Shoulder (small shoulder)
24a, 24b large shoulder portion 25a, 25b groove bottom portion 26 seal fitting surface 27, 27a gutter groove 28 groove bottom portion 29 bottom surface 30, 30a side surface 31 side surface 32a, 32b hardened layer 33 inclined surface 100 hub unit bearing 101 outer ring 102 hub 103a, 103b ball 104a, 104b outer ring raceway 105a, 105b inner ring raceway 106 rotating flange 107 rolling element installation space 108 seal ring 109 combined seal ring 110 dam portion 111 gutter groove 112 shoulder portion 113 stationary flange 114 support hole

Claims (3)

an outer ring having double-row outer ring raceways on its inner peripheral surface, and a hardened layer being formed on each of the outer ring raceways;
a hub having a double-row inner ring raceway on its outer peripheral surface;
A plurality of rolling elements for each row are arranged between the double-row outer ring raceway and the double-row inner ring raceway and are provided with a back-to-back contact angle,
each of the axially outer outer ring raceway of the double-row outer ring raceway and the axially outer inner ring raceway of the double-row inner ring raceway has an arcuate cross-sectional shape,
the rolling elements of the axially outer row are constituted by balls,
The outer ring has a shoulder portion having a smaller diameter than a groove bottom portion of the outer ring raceway at a portion of the inner peripheral surface adjacent to the axially outer side of the outer ring raceway, and has a groove bottom portion on the outer peripheral surface. has a gutter groove arranged so as to radially overlap with the shoulder portion over the entire circumference,
hub unit bearings. In a virtual plane including the central axis of the outer ring, the axially inner portion of the inner surface of the gutter groove has a linear shape parallel to a tangent line to the axially outer edge portion of the axially outer outer ring raceway,
A hub unit bearing according to claim 1. The gutter groove has a shape symmetrical in the axial direction around the groove bottom of the gutter groove,
A hub unit bearing according to claim 1 or 2.

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