Hub unit bearing and method for manufacturing the same

Abstract

The present invention provides a hub unit bearing that prevents creep of the inner ring relative to the hub ring while preventing unnecessary increases in manufacturing costs. [Solution] The hub 3 includes an inner ring 13 and a hub wheel 14. The inner ring 13 has at least the innermost axial inner ring raceway 8b among multiple rows of inner ring raceways 8a, 8b on its outer circumferential surface. The hub wheel 14 has a fitting shaft portion 15 into which the inner ring 13 is press-fitted. The outer circumferential surface of the fitting shaft portion 15 and / or the inner circumferential surface of the inner ring 13 are composed of machined surfaces 18, 19 that have the function of improving the frictional force against the mating surface.

Description

[Technical Field]

[0001] This disclosure relates to a hub unit bearing for rotatably supporting an automobile wheel with respect to a suspension system, and a method for manufacturing the same. [Background technology]

[0002] A hub unit bearing for rotatably supporting an automobile wheel relative to a suspension system comprises an outer ring having double rows of outer ring raceways on its inner circumference, a hub having double rows of inner ring raceways on its outer circumference, and a plurality of rolling elements positioned between the double rows of outer ring raceways and the double rows of inner ring raceways. The outer ring is supported and fixed to the suspension system. The hub is coupled and fixed to the axially outer end to the wheel and the braking rotating body of the vehicle.

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

[0004] In hub unit bearings, a common structure is one in which the hub is composed of multiple parts, including an inner ring having an axially inner inner ring raceway among two rows of inner ring raceways on its outer circumference, and a hub ring having a fitting shaft portion into which the inner ring is press-fitted.

[0005] In a hub unit bearing of this structure, if an excessive turning load is applied when the vehicle turns, the inner ring may creep (rotate relative to) the hub ring. To prevent such creep, it is conceivable to increase the interference fit between the inner surface of the inner ring and the outer surface of the fitting shaft of the hub ring. However, increasing the interference fit increases the circumferential stress on the inner ring, which may reduce the durability of the inner ring.

[0006] Japanese Patent Publication No. 2023-58824 describes a hub unit structure that, when press-fitting the inner ring onto the fitting shaft portion of the hub ring, engages the inner circumferential surface of the inner ring with the outer circumferential surface of the fitting shaft portion by causing a protrusion constituting a spline or serration formed on one of the circumferential surfaces of the inner ring or the outer circumferential surface of the fitting shaft portion to bite into the other circumferential surface, thereby engaging the inner circumferential surface of the inner ring with the outer circumferential surface of the fitting shaft portion. This structure effectively prevents creep of the inner ring relative to the hub ring compared to a structure in which the inner ring and the hub ring are simply joined by press-fitting of their cylindrical surfaces. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-58824 [Overview of the project] [Problems that the invention aims to solve]

[0008] In the conventional structure described in Japanese Patent Publication No. 2023-58824, it is necessary to form splines or serrations on one of the circumferential surfaces, either the inner surface of the inner ring or the outer surface of the fitting shaft, by rolling or broaching, which may lead to increased manufacturing costs. Furthermore, the load required to engage the protrusions constituting the splines or serrations formed on one of the circumferential surfaces with the other surface becomes large, which may lead to larger assembly equipment and thus increase manufacturing costs.

[0009] The present disclosure aims to provide a hub unit bearing that can prevent creep of the inner ring relative to the hub ring while preventing an unnecessary increase in manufacturing costs. [Means for solving the problem]

[0010] A hub unit bearing according to one aspect of this disclosure is An outer ring having multiple rows of outer ring raceways on its inner circumference, A hub having multiple rows of inner ring tracks on its outer surface, The system comprises multiple rolling elements positioned between the multiple rows of outer ring raceways and the multiple rows of inner ring raceways.

[0011] The hub includes an inner ring and a hub ring.

[0012] The inner ring has, on its outer surface, at least the innermost axially-oriented inner ring raceway among the multiple rows of inner ring raceways.

[0013] The hub wheel has a fitting shaft portion into which the inner ring is press-fitted.

[0014] The outer circumferential surface of the fitting shaft and / or the inner circumferential surface of the inner ring are configured with a machined surface that has the function of improving the frictional force against the mating surface.

[0015] In a hub unit bearing according to one aspect of the present disclosure, the machined surface may be configured as a ground surface having grinding marks inclined with respect to the circumferential direction.

[0016] In a hub unit bearing according to one aspect of the present disclosure, the outer circumferential surface of the fitting shaft and the inner circumferential surface of the inner ring can each be formed by the ground surface. Furthermore, the ground surface constituting the outer circumferential surface of the fitting shaft may be configured to include grinding marks inclined to one axial side with respect to the circumferential direction, and the ground surface constituting the inner circumferential surface of the inner ring may be configured to include grinding marks inclined to the other axial side with respect to the circumferential direction.

[0017] In a hub unit bearing according to one aspect of the present disclosure, at least one of the ground surfaces constituting the outer circumferential surface of the fitting shaft portion and the ground surface constituting the inner circumferential surface of the inner ring may be configured to include grinding marks inclined axially to one side with respect to the circumferential direction and grinding marks inclined axially to the other side with respect to the circumferential direction.

[0018] In the hub unit bearing according to one aspect of the present disclosure, the processed surface can be constituted by a shot peened surface.

[0019] A method for manufacturing a hub unit bearing according to one aspect of the present disclosure is a method for manufacturing a hub unit bearing according to one aspect of the present disclosure, in which the processed surface is constituted by the grinding surface, and while rotating the surface to be processed, which is the outer peripheral surface of the fitting shaft portion or the inner peripheral surface of the inner ring, about its central axis, pressing a grinding wheel against the surface to be processed, and feeding the grinding wheel axially with respect to the surface to be processed, a step of forming the grinding marks inclined with respect to the circumferential direction on the surface to be processed is provided.

[0020] The present disclosure can be implemented by appropriately combining the configurations of the above-described aspects within a range where no contradiction occurs.

Advantages of the Invention

[0021] According to the hub unit bearing according to one aspect of the present disclosure, it is possible to prevent the creep of the inner ring with respect to the hub ring while preventing the manufacturing cost from increasing unnecessarily.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a cross-sectional view of a hub unit bearing according to a first example of an embodiment of the present disclosure. [Figure 2] FIG. 2 is an exploded perspective view showing a hub constituting the hub unit bearing according to the first example, cut along a virtual plane including its central axis. [Figure 3] FIG. 3 is a cross-sectional view showing a state in which a wide range of the outer peripheral surface of a hub ring constituting the hub unit bearing according to the first example is being subjected to grinding. [Figure 4] FIG. 4 is a cross-sectional view showing a state in which grinding marks are being formed on the outer peripheral surface of a hub ring constituting the hub unit bearing according to the first example. [Figure 5] FIG. 5 is a cross-sectional view showing a state in which grinding marks are being formed on the inner peripheral surface of an inner ring constituting the hub unit bearing according to the first example. [Figure 6] Figure 6 is a diagram corresponding to Figure 2, relating to a second example of the embodiment of the present disclosure. [Figure 7] Figure 7 is a diagram corresponding to Figure 2, relating to a third example of the embodiment of this disclosure. [Modes for carrying out the invention]

[0023] [Example 1] A first example of a hub unit bearing according to the embodiments of this disclosure and a method for manufacturing the same will be described with reference to Figures 1 to 5.

[0024] <Structure of hub unit bearings> The hub unit bearing 1 comprises an outer ring 2, a hub 3, and a plurality of rolling elements 4a, 4b. Regarding the hub unit bearing 1, the axial outer side is the left side of Figure 1, corresponding to the outer side in the width direction of the vehicle when assembled to the vehicle, and the axial inner side is the right side of Figure 1, corresponding to the center side in the width direction of the vehicle when assembled to the vehicle.

[0025] The outer ring 2 has a hollow shape and is made of a hard metal such as medium carbon steel. The outer ring 2 has multiple rows of outer ring raceways 5a and 5b on its inner circumferential surface. In this example, the multiple rows of outer ring raceways 5a and 5b are composed of double rows, i.e., two rows of outer ring raceways 5a and 5b.

[0026] Each of the outer ring raceways 5a and 5b has a generatrix shape corresponding to the shape of the multiple rolling elements 4a and 4b. When the multiple rolling elements 4a and 4b are composed of balls, each of the outer ring raceways 5a and 5b has an arc-shaped generatrix, and when the multiple rolling elements 4a and 4b are composed of cone-shaped rollers, the outer ring raceways 5a and 5b have a linear generatrix shape inclined with respect to the central axis of the outer ring 2. In this example, since the multiple rolling elements 4a and 4b are composed of balls, each of the outer ring raceways 5a and 5b has an arc-shaped generatrix.

[0027] In this example, the outer ring 2 has, as an optional component, a stationary flange 6 projecting radially outward from its axial middle section. The stationary flange 6 has multiple flange-side support holes 7 that penetrate axially at multiple locations in the circumferential direction of its radial middle section. The outer ring 2 is supported and fixed to the knuckle by inserting support bolts (not shown) into one of the support holes, either the flange-side support hole 7 or the knuckle-side support hole provided in the suspension device's knuckle, and screwing them into the other.

[0028] The hub 3 is positioned radially inward of the outer ring 2 and coaxially with the outer ring 2. The hub 3 has multiple rows of inner ring raceways 8a and 8b on its outer circumferential surface. In this example, the multiple rows of inner ring raceways 8a and 8b are composed of double rows, i.e., two rows of inner ring raceways 8a and 8b.

[0029] Each of the inner ring raceways 8a and 8b has a generatrix shape corresponding to the shape of the multiple rolling elements 4a and 4b. When the multiple rolling elements 4a and 4b are composed of balls, each of the inner ring raceways 8a and 8b has an arc-shaped generatrix, and when the multiple rolling elements 4a and 4b are composed of cone-shaped rollers, the inner ring raceways 8a and 8b have a linear generatrix shape inclined with respect to the central axis of the outer ring 2. In this example, since the multiple rolling elements 4a and 4b are composed of balls, each of the inner ring raceways 8a and 8b has an arc-shaped generatrix.

[0030] In this example, the hub 3 has a rotating flange 9 that protrudes radially outward on the portion that protrudes axially outward from the outer ring 2, and a cylindrical pilot portion 10 at the axially outward end.

[0031] The rotating flange 9 has mounting holes 11 that penetrate axially at multiple locations in the circumferential direction in the radially intermediate portion. Each of the mounting holes 11 is either a press-fit hole or a threaded hole.

[0032] If each of the mounting holes 11 is a press-fit hole, a stud is press-fitted into each of the mounting holes 11 from the axially inward side. Braking rotating bodies such as brake discs and wheel hubs are connected and fixed to the rotating flange 9 by inserting a pilot portion 10 through a central hole provided in the center of each, and inserting studs through through holes provided at multiple locations in the circumferential direction in the radial middle of each, and screwing hub nuts onto the tips of the studs.

[0033] If each of the mounting holes 11 is a threaded hole, the braking rotating body such as a brake disc and the wheel of the wheel are connected and fixed to the rotating flange 9 by inserting the pilot portion 10 through the central hole provided in the center of each and screwing hub bolts, which are inserted through the through holes provided at multiple locations in the circumferential direction in the radial middle of each, into the mounting holes 11 from the axial outside.

[0034] In this example, each of the mounting holes 11 is a press-fit hole, and a stud is press-fitted into each of the mounting holes.

[0035] In this example, the hub unit bearing 1 is a hub unit bearing for a drive wheel, and therefore the hub 3 has a spline hole 12 in its radial center that penetrates the hub 3 axially. The tip of the drive shaft, which is driven by an engine or electric motor, is spline-engaged into the spline hole 12. When the vehicle is running, the hub 3 is rotated by the drive shaft, and the wheel and braking rotating body, which are coupled and fixed to the rotation flange 9 of the hub 3, are rotated.

[0036] Furthermore, when a hub unit bearing according to one aspect of this disclosure is applied to a hub unit bearing for a driven wheel, the hub can be constructed to be solid.

[0037] The hub 3 comprises an inner ring 13 and a hub ring 14.

[0038] The inner ring 13 is constructed in a cylindrical shape from a hard metal such as bearing steel.

[0039] The inner ring 13 has at least the innermost inner ring raceway 8b in the axial direction among multiple rows of inner ring raceways 8a and 8b on its outer circumferential surface. In this example, the inner ring 13 has the innermost inner ring raceway 8b in the axial direction among two rows of inner ring raceways 8a and 8b on its outer circumferential surface in the axial middle section.

[0040] The hub wheel 14 has a fitting shaft portion 15 into which the inner ring 13 is press-fitted.

[0041] The hub wheel 14 has at least the outermost inner ring raceway 8a of multiple rows of inner ring raceways 8a, 8b on its outer circumferential surface. In this example, the hub wheel 14 has the outermost inner ring raceway 8a of double rows of inner ring raceways 8a, 8b on its outer circumferential surface in the axial middle section.

[0042] In this example, the hub wheel 14 has a rotating flange 9 in a portion located axially outward from the inner ring raceway 8a on the axial side, and a pilot portion 10 at the axially outward end.

[0043] In this example, the hub wheel 14 has a fitting shaft portion 15 located axially inward of the axially outer inner ring raceway 8a, having an outer diameter smaller than the outer diameter of the portion adjacent to it axially outward. In this example, the hub wheel 14 has a stepped surface 16 that connects the portion of its outer circumferential surface adjacent to the axially inward side of the axially outer inner ring raceway 8a with the outer circumferential surface of the fitting shaft portion 15, and that faces axially inward.

[0044] In this example, the inner ring 13 is joined and fixed to the hub ring 14 by abutting its axially outer end face against the stepped surface 16 of the hub ring 14 and by press-fitting it onto the fitting shaft portion 15 of the hub ring 14, i.e., by a press fit.

[0045] The hub ring and the inner ring can also be joined and fixed together by clamping the inner ring from both axial sides between the stepped surface of the hub ring and a crimping portion provided at the axially inner end of the hub ring, or by clamping the inner ring from both axial sides between the stepped surface of the hub ring and a nut screwed onto the axially inner end of the hub ring.

[0046] In the hub unit bearing 1 of this example, the hub ring 14 is integrally constructed from a hard metal such as medium carbon steel. However, for example, when implementing a hub unit bearing according to one aspect of this disclosure, the hub ring can also be constructed by combining a hub spindle having a rotating flange and a pilot portion with another inner ring having an inner ring raceway that is axially outward on its outer circumferential surface.

[0047] In any case, in the hub unit bearing 1 of this disclosure, the outer circumferential surface of the fitting shaft portion 15 of the hub ring 14 and / or the inner circumferential surface of the inner ring 13 are configured with machined surfaces 18 and 19 that have the function of improving the frictional force with respect to the mating surface. The machined surfaces 18 and 19 are not limited to these, but can be configured with a grinding surface having grinding marks inclined with respect to the circumferential direction, a shot peening surface, and the like. Grinding marks are fine lines formed on the surface of a metal member by the abrasive grains that make up the grinding wheel when the surface of the metal member is ground.

[0048] Thus, in the hub unit bearing 1 of this example, the outer circumferential surface of the fitting shaft portion 15 of the hub ring 14 and / or the inner circumferential surface of the inner ring 13 are configured with machined surfaces 18 and 19 that have the function of improving the frictional force with respect to the mating surface. Therefore, the frictional force of the fitting portion between the outer circumferential surface of the fitting shaft portion 15 and the inner circumferential surface of the inner ring 13 can be improved, that is, creep of the inner ring 13 relative to the hub ring 14 can be prevented.

[0049] Furthermore, unlike the conventional structure described in Japanese Patent Application Publication No. 2023-58824, the hub unit bearing 1 of this disclosure does not require the formation of splines or serrations, which are costly to process, on either the outer circumferential surface of the fitting shaft portion 15 of the hub ring 14 or the inner circumferential surface of the inner ring 13, thus keeping manufacturing costs low.

[0050] Furthermore, unlike the conventional structure described in Japanese Patent Application Publication No. 2023-58824, the hub unit bearing 1 of this disclosure does not require a heavy load-bearing process in which a protrusion constituting a spline or serration formed on one of the circumferential surfaces of the inner ring 13 or the outer circumferential surface of the fitting shaft portion 15 is made to bite into the other circumferential surface when joining the inner ring 13 and the hub ring 14. Therefore, manufacturing costs can be kept low in this respect as well.

[0051] In this example, both the outer circumferential surface of the fitting shaft portion 15 and the inner circumferential surface of the inner ring 13 are composed of machined surfaces 18 and 19. That is, the outer circumferential surface of the fitting shaft portion 15 is composed of machined surface 18, and the inner circumferential surface of the inner ring 13 is composed of machined surface 19. Each of the machined surfaces 18 and 19 is composed of a grinding surface having grinding marks 20 and 21 that are inclined with respect to the circumferential direction. Note that in Figure 2, the grinding marks 20 and 21 are depicted schematically.

[0052] The lower limit of the inclination angle (absolute value) of the grinding marks 20 and 21 with respect to the circumferential direction is not limited to this, but is preferably 20° or more, more preferably 30° or more, and even more preferably 35° or more. If the inclination angle (absolute value) of the grinding marks 20 and 21 with respect to the circumferential direction is less than 20°, it may not be possible to sufficiently improve the circumferential frictional force of the fitting portion between the outer surface of the fitting shaft portion 15 and the inner surface of the inner ring 13.

[0053] The upper limit of the inclination angle (absolute value) of the grinding marks 20 and 21 with respect to the circumferential direction is not limited to this, but is preferably 70° or less, more preferably 60° or less, and even more preferably 55° or less. If the inclination angle (absolute value) of the grinding marks 20 and 21 with respect to the circumferential direction is greater than 70°, the processing time required to form the grinding marks 20 and 21 will increase, which may increase manufacturing costs.

[0054] In this example, the outer circumferential surface of the fitting shaft portion 15 (excluding the corner radius portion located at the axially outer end) and the inner circumferential surface of the inner ring 13 (excluding the chamfered portions located at both ends in the axial direction) are each composed of machined surfaces 18 and 19 made of the grinding surface.

[0055] In this example, the machined surface 18 constituting the outer circumferential surface of the fitting shaft portion 15 is configured to include grinding marks 20 that are inclined to one side in the axial direction with respect to the circumferential direction (for example, inclined to one side in the axial direction (axially outward or inward) as it moves in the forward rotation direction, which is the rotation direction of the hub 3 when the vehicle is moving forward), and the machined surface 19 constituting the inner circumferential surface of the inner ring 13 is configured to include grinding marks 21 that are inclined to the other side in the axial direction with respect to the circumferential direction (for example, inclined to the other side in the axial direction (axially inward or outward) as it moves in the forward rotation direction).

[0056] More specifically, in this example, the machined surface 18 constituting the outer circumferential surface of the fitting shaft portion 15 is composed of grinding marks 20 that are inclined axially to one side with respect to the circumferential direction, and the machined surface 19 constituting the inner circumferential surface of the inner ring 13 is composed of grinding marks 21 that are inclined axially to the other side with respect to the circumferential direction. In other words, the inclination direction with respect to the circumferential direction of the grinding marks 20 included in the machined surface 18 constituting the outer circumferential surface of the fitting shaft portion 15 and the inclination direction with respect to the circumferential direction of the grinding marks 21 included in the machined surface 19 constituting the inner circumferential surface of the inner ring 13 are opposite to each other.

[0057] In Figure 2, the grinding marks 20 on the front side of the outer circumferential surface of the fitting shaft portion 15 and the grinding marks 21 on the back side of the inner circumferential surface of the inner ring 13 appear at different circumferential positions (circumferential positions that are opposite to each other in the diametrical direction). Therefore, looking at Figure 2, one might mistakenly think that the inclination directions of both grinding marks 20 and 21 with respect to the circumferential direction are the same, but in reality, the inclination directions of both grinding marks 20 and 21 with respect to the circumferential direction are opposite to each other.

[0058] In other words, the grinding marks 20 of the machined surface 18 that constitutes the outer circumferential surface of the fitting shaft portion 15 and the grinding marks 21 of the machined surface 19 that constitutes the inner circumferential surface of the inner ring 13 are arranged to intersect each other when viewed from the radial direction. Therefore, in the structure of this example, the circumferential frictional force of the fitting portion between the outer circumferential surface of the fitting shaft portion 15 and the inner circumferential surface of the inner ring 13 can be effectively improved.

[0059] The inclination angles (absolute values) of the grinding marks 20 and 21 with respect to the circumference can be the same or different. In this example, the inclination angles (absolute values) of the grinding marks 20 and 21 with respect to the circumference are the same.

[0060] Multiple rolling elements 4a and 4b are arranged to roll freely between multiple rows of outer ring raceways 5a and 5b and multiple rows of inner ring raceways 8a and 8b, with multiple elements in each row. In this example, multiple rolling elements 4a and 4b are arranged to roll freely at equal intervals in the circumferential direction, held by retainers 17a and 17b, with multiple elements in each row between double-row outer ring raceways 5a and 5b and double-row inner ring raceways 8a and 8b. The rolling elements 4a and 4b arranged in double rows are given a back-to-back (DB) contact angle.

[0061] The rolling elements 4a and 4b are made of hard metals such as bearing steel, or ceramics.

[0062] Furthermore, the rolling elements 4a and 4b are composed of balls or tapered rollers. In this example, the rolling elements 4a and 4b are composed of balls.

[0063] The hub unit bearing 1 in this example has a so-called equal-diameter PCD type structure in which the pitch circle diameter of the axially outer rolling element 4a is equal to the pitch circle diameter of the axially inner rolling element 4b. However, one aspect of the hub unit bearing of this disclosure can also be applied to a so-called different-diameter PCD type hub unit bearing in which the pitch circle diameter of the axially outer rolling element is larger or smaller than the pitch circle diameter of the axially inner rolling element.

[0064] The hub unit bearing 1 in this example further includes sealing devices 23 and 24 that close the openings on both axial sides of the rolling element installation space 22 located between the inner circumferential surface of the outer ring 2 and the outer circumferential surface of the hub 3. This prevents leakage of grease sealed in the rolling element installation space 22 to the outside, and prevents foreign matter from entering the rolling element installation space 22 from the outside.

[0065] The sealing device 23 that closes the axially outer opening of the rolling element installation space 22 is not limited to this, but in this example, it is composed of a sealing ring that has at least one sealing lip that slides against the surface of the hub ring 14 and is supported and fixed to the axially outer end of the outer ring 2.

[0066] The sealing device 24 that closes the axially inner opening of the rolling element installation space 22 is not limited to this, but in this example it is composed of a combined sealing ring comprising a slinger externally fitted and fixed to the axially inner end of the inner ring 13, and a sealing ring having at least one sealing lip that slides against the surface of the slinger and internally fitted and fixed to the axially inner end of the outer ring 2.

[0067] <Manufacturing method for hub unit bearings> The manufacturing method of the hub unit bearing 1 in this example includes a step of forming grinding marks (20, 21) on the workpiece surface, which is the outer circumferential surface of the fitting shaft portion 15 or the inner circumferential surface of the inner ring 13, by pressing a grinding wheel against the workpiece surface while rotating it around its own central axis, and moving the grinding wheel axially relative to the workpiece surface. The manufacturing method of the hub 3, which is part of the manufacturing method of the hub unit bearing 1 in this example and includes this step, will be described in detail below.

[0068] In the manufacturing method of the hub 3 in this example, when manufacturing the hub ring 14, first, the outer shape of the hub ring 14 is formed by forging or cutting a metal material. Then, a continuous area of ​​the surface of the hub ring 14, from the radially inner end of the axially inner surface of the rotating flange 9 to the outer circumferential surface of the fitting shaft portion 15, is subjected to heat treatment.

[0069] Subsequently, grinding is performed on the surface of the hub wheel 14 to improve surface roughness, specifically in a continuous area from the radially inner end of the axially inner surface of the rotating flange 9 to the cylindrical shoulder adjacent to the axially outer side of the axially outer inner ring raceway 8a, and on the axially outer inner ring raceway 8a itself, which is the portion that the seal lip constituting the sealing device 23 slides against.

[0070] In this regard, in this example, the surface of the hub wheel 14 after the heat treatment is performed is simultaneously ground using a full-type grinding wheel 25 over a continuous area from the radially inner end of the axially inner surface of the rotating flange 9 to the outer circumferential surface of the fitting shaft portion 15. Specifically, as shown in Figure 3, the hub wheel 14 is ground along its own central axis O 14 It rotates around its central axis O, and the grinding wheel 25 is positioned on its own central axis O 25 While rotating around the center, the outer surface of the grinding wheel 25 is pressed against the continuous area on the surface of the hub wheel 14, which is the workpiece, thereby performing grinding on the workpiece.

[0071] In this example, grinding is then performed on the outer circumferential surface of the fitting shaft portion 15 (excluding the corner radius portion located at the axially outer end) to form grinding marks 20 (processed surface 18). However, when implementing this disclosure, after the heat treatment, grinding to form grinding marks 20 on the outer circumferential surface of the fitting shaft portion 15 can also be performed without grinding the outer circumferential surface of the fitting shaft portion 15 using a full-type grinding wheel 25.

[0072] In other words, in this example, after the heat treatment, the surface roughness of the outer circumferential surface of the fitting shaft portion 15 is improved by sequentially performing grinding using a full-type grinding wheel 25 and grinding to form grinding marks 20 on the outer circumferential surface of the fitting shaft portion 15. However, when implementing this disclosure, the surface roughness of the outer circumferential surface can also be improved by performing only grinding to form grinding marks 20 on the outer circumferential surface of the fitting shaft portion 15.

[0073] In this example, the grinding wheel 26 for forming grinding marks 20 on the outer circumferential surface of the fitting shaft portion 15 has an axial dimension smaller than the axial dimension of the outer circumferential surface of the fitting shaft portion 15, as shown in Figure 4, and has a cylindrical outer circumferential surface.

[0074] When forming grinding marks 20 on the outer surface of the fitting shaft portion 15 using the grinding wheel 26, the hub wheel 14 is positioned on its own central axis O 14 It rotates around the central axis O of the grinding wheel 26. 26 The central axis O of the hub wheel 14 14 With the grinding wheel 26 positioned parallel to its own central axis O 26 The wheel is rotated around the center. In this state, the outer surface of the grinding wheel 26 is pressed against the outer surface of the fitting shaft portion 15 of the hub wheel 14, and the grinding wheel 26 is moved axially relative to the hub wheel 14. This moves the grinding area on the outer surface of the fitting shaft portion 15 axially, thereby performing grinding on the outer surface. At this time, whether the grinding wheel 26 is moved inward or outward relative to the hub wheel 14 in the axial direction is determined according to the inclination direction of the grinding marks 20 with respect to the circumferential direction and the rotation direction of the hub wheel 14.

[0075] In this example, as shown in Figure 2, the grinding marks 20 are inclined in a direction that moves outward in the axial direction as you move forward in a clockwise direction when viewed from the axial inside. In this example, when grinding with the grinding wheel 26 to form such grinding marks 20, the hub wheel 14 is positioned along its central axis O 14 The grinding wheel 26 is rotated clockwise when viewed from the axial inner side, and is moved from the axial outer side to the axial inner side, as shown in Figure 4. This moves the grinding area on the outer surface of the fitting shaft portion 15 from the axial outer end to the axial inner end.

[0076] In this example, a grinding operation using the grinding wheel 26 as shown in Figure 4 is performed at least once. This forms a processed surface 18 on the outer circumferential surface of the fitting shaft portion 15, which has grinding marks 20 inclined to one side in the axial direction with respect to the circumferential direction.

[0077] In other words, generally, when grinding a cylindrical surface of a metal member using a grinding wheel, if the grinding wheel is not moved axially relative to the cylindrical surface of the metal member, as in grinding with a full-type grinding wheel 25 (see Figure 3), the direction of the grinding marks formed on the cylindrical surface after processing is circumferential. In contrast, if the grinding wheel is moved axially relative to the cylindrical surface of the metal member, as in grinding with a grinding wheel 26 (see Figure 4), the direction of the grinding marks formed on the cylindrical surface after processing is inclined relative to the circumferential direction. In this case, the inclination angle (absolute value) of the grinding marks with respect to the circumferential direction increases as the axial feed speed of the grinding wheel increases, and decreases as the axial feed speed of the grinding wheel decreases. Also, the inclination angle (absolute value) of the grinding marks with respect to the circumferential direction decreases as the peripheral speed of the cylindrical surface of the metal member increases, and increases as the peripheral speed of the cylindrical surface of the metal member decreases.

[0078] Taking these points into consideration, in this example, the axial feed speed of the grinding wheel 26 and the peripheral speed of the outer surface of the fitting shaft portion 15 are adjusted so that the inclination angle (absolute value) of the grinding marks 20 with respect to the circumferential direction becomes the desired size.

[0079] The grinding operation using the grinding wheel 26, as shown in Figure 4, only needs to be performed at least once, and can be repeated multiple times if necessary. In this example, before the grinding operation using the grinding wheel 26 is performed, circumferential grinding marks are formed on the outer surface of the fitting shaft portion 15 by grinding with a full-type grinding wheel 25 (see Figure 3). These circumferential grinding marks can be completely removed by repeatedly performing the grinding operation with the grinding wheel 26. When implementing the structure in this example, the number of grinding operations using the grinding wheel 26 can be adjusted to leave the circumferential grinding marks or to completely remove them.

[0080] In the manufacturing method of the hub 3 in this example, when producing the inner ring 13, first, the outer shape of the inner ring 13 is formed by forging or cutting a metal material. Then, the inner ring 13 is subjected to heat treatment such as deep quenching, carburizing quenching, or carbonitriding quenching.

[0081] In this example, thereafter, a grinding process for forming the grinding marks 21 (machined surface 19) is performed on the inner peripheral surface of the inner ring 13 (excluding the chamfered portions existing at both ends in the axial direction). In this example, the grinding wheel 27 for forming the grinding marks 21 on the inner peripheral surface of the inner ring 13 has an axial dimension smaller than the axial dimension of the inner peripheral surface of the inner ring 13, an outer diameter smaller than the inner diameter of the inner ring 13, and a cylindrical outer peripheral surface as shown in FIG. 5.

[0082] When forming the grinding marks 21 on the inner peripheral surface of the inner ring 13 using the grinding wheel 27, the inner ring 13 is rotated about its own central axis O 13 and the central axis O 27 of the grinding wheel 27 is arranged parallel to the central axis O 13 of the inner ring 13, and the grinding wheel 27 is rotated about its own central axis O 27 In this state, while pressing the outer peripheral surface of the grinding wheel 27 against the inner peripheral surface of the inner ring 13, the grinding wheel 27 is fed axially with respect to the inner ring 13. Thereby, while moving the grinding portion of the inner peripheral surface of the inner ring 13 in the axial direction, the inner peripheral surface is subjected to a grinding process. At this time, whether the grinding wheel 27 is fed axially to the inner side or the outer side with respect to the inner ring 13 is determined according to the inclination direction of the grinding marks 21 in the circumferential direction and the rotation direction of the inner ring 13.

[0083] In this example, as shown in FIG. 2, the grinding marks 21 are inclined in a direction toward the inner side in the axial direction as going toward the front side in the clockwise direction when viewed from the inner side in the axial direction. In this example, in order to form such grinding marks 21, when performing grinding with the grinding wheel 27, the inner ring 13 is rotated counterclockwise about its own central axis O 13 and the grinding wheel 27 is fed from the outer side in the axial direction toward the inner side in the axial direction as shown in FIG. 5. Thereby, the grinding portion of the inner peripheral surface of the inner ring 13 is moved from the end portion on the outer side in the axial direction to the end portion on the inner side in the axial direction.

[0084] In this example, a grinding operation using the grinding wheel 27 as shown in Figure 5 is performed at least once. This forms a processed surface 19 on the inner circumferential surface of the inner ring 13, which has grinding marks 21 inclined to the other axial direction with respect to the circumferential direction.

[0085] In this example, the axial feed speed of the grinding wheel 27 and the peripheral speed of the inner surface of the inner ring 13 are adjusted so that the inclination angle (absolute value) of the grinding marks 21 with respect to the circumferential direction becomes a desired size.

[0086] [Example 2] A second example of the embodiment of this disclosure will be described with reference to Figure 6.

[0087] In the hub unit bearing of this example, the machined surface 18a, which is the outer circumferential surface of the fitting shaft portion 15a of the hub ring 14a, is composed of grinding marks 20 inclined axially to one side with respect to the circumferential direction and grinding marks 20a inclined axially to the other side with respect to the circumferential direction. Similarly, the machined surface 19a, which is the inner circumferential surface of the inner ring 13a, is composed of grinding marks 21a inclined axially to one side with respect to the circumferential direction and grinding marks 21 inclined axially to the other side with respect to the circumferential direction. In other words, the machined surface 18a has diagonal grinding marks 20, 20a, and the machined surface 19a also has diagonal grinding marks 21, 21a. Therefore, the frictional force acting between the outer circumferential surface of the fitting shaft portion 15a and the inner circumferential surface of the inner ring 13a can be effectively improved.

[0088] In this example, when forming a processed surface 18a on the outer circumferential surface of the fitting shaft portion 15a, the grinding operation of the grinding wheel on the outer circumferential surface of the fitting shaft portion 15a is performed alternately, moving axially from the axially outer end to the axially inner end of the outer circumferential surface, and moving axially from the axially inner end to the axially outer end of the outer circumferential surface. This forms a processed surface 18a having a diagonal pattern of grinding marks 20, 20a.

[0089] Furthermore, when forming a processed surface 19a on the inner circumferential surface of the inner ring 13a, the grinding wheel is alternately moved axially from the axially outer end to the axially inner end of the inner circumferential surface of the inner ring 13a, and from the axially inner end to the axially outer end of the inner circumferential surface. This forms a processed surface 18a having a diagonal pattern of grinding marks 21, 21a.

[0090] The other configurations and effects of the second example are the same as those of the first example of the embodiment.

[0091] [Example 3] A third example of the embodiment of this disclosure will be described with reference to Figure 7.

[0092] In the hub unit bearing of this example, the machined surface 18b that constitutes the outer circumferential surface of the fitting shaft portion 15b of the hub ring 14b, and the machined surface 19b that constitutes the inner circumferential surface of the inner ring 13b, are each composed of shot-peened surfaces, which are formed by applying a shot-peening treatment instead of a ground surface. Therefore, the frictional force acting between the outer circumferential surface of the fitting shaft portion 15b and the inner circumferential surface of the inner ring 13b can be improved.

[0093] Other configurations and effects are the same as in the first example of the embodiment.

[0094] The present disclosure allows for the implementation of the configurations of each embodiment described above by combining them as appropriate, to the extent that no inconsistencies arise. For example, one of the outer circumferential surface of the fitting shaft portion of the hub ring and the inner circumferential surface of the inner ring may be configured with a ground surface, and the other with a shot peened surface. [Explanation of symbols]

[0095] 1 Hub unit bearing 2 Outer ring 3 Hubs 4a, 4b Rolling elements 5a, 5b Outer ring track 6. Stationary flange 7 Flange-side support holes 8a, 8b Inner ring track 9 Rotating flange 10 Pilot Section 11 mounting holes 12 spline holes 13, 13a, 13b inner ring 14, 14a, 14b hub wheels 15, 15a, 15b mating shaft part 16 Step surface 17a, 17b retainer 18, 18a, 18b Machined surfaces 19, 19a, 19b Machined surfaces 20, 20a grinding marks 21, 21a Grinding marks 22 Rolling element installation space 23. Sealing device 24. Sealing device 25 grinding wheels 26 Grinding Wheels 27 Grinding Wheel

Claims

1. An outer ring having multiple rows of outer ring raceways on its inner circumference, A hub having multiple rows of inner ring tracks on its outer surface, The system comprises a plurality of rolling elements positioned between the plurality of rows of outer ring raceways and the plurality of rows of inner ring raceways, The hub includes an inner ring and a hub ring. The inner ring has, on its outer surface, at least the innermost axially-inner inner ring raceway among the multiple rows of inner ring raceways, The hub ring has a fitting shaft portion into which the inner ring is press-fitted, The outer circumferential surface of the fitting shaft and / or the inner circumferential surface of the inner ring are configured with a machined surface that has the function of improving the frictional force against the mating surface. Hub unit bearing.

2. The hub unit bearing according to claim 1, wherein the processed surface is composed of a ground surface having grinding marks inclined with respect to the circumferential direction.

3. The outer circumferential surface of the fitting shaft and the inner circumferential surface of the inner ring are each formed by the ground surface, The grinding surface constituting the outer circumferential surface of the fitting shaft portion is configured to include grinding marks inclined to one side in the axial direction with respect to the circumferential direction, and the grinding surface constituting the inner circumferential surface of the inner ring is configured to include grinding marks inclined to the other side in the axial direction with respect to the circumferential direction. The hub unit bearing according to claim 2.

4. The hub unit bearing according to claim 3, wherein at least one of the ground surfaces constituting the outer circumferential surface of the fitting shaft portion and the ground surface constituting the inner circumferential surface of the inner ring is configured to include grinding marks inclined toward one axial side with respect to the circumferential direction and grinding marks inclined toward the other axial side with respect to the circumferential direction.

5. The hub unit bearing according to claim 1, wherein the processed surface is composed of a shot-peened surface.

6. A method for manufacturing a hub unit bearing according to any one of claims 2 to 4, The process includes a step of forming grinding marks on the workpiece surface, which is the outer circumferential surface of the fitting shaft or the inner circumferential surface of the inner ring, by rotating the workpiece surface, which is the outer circumferential surface of the fitting shaft, around its own central axis, while pressing the grinding wheel against the workpiece surface and moving the grinding wheel axially relative to the workpiece surface. A method for manufacturing a hub unit bearing.

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