Hub unit bearing and manufacturing method thereof

Abstract

To materialize structure in which the formation range of a coating film covering the surface of an axial outer portion of a pilot section can be regulated with high accuracy.SOLUTION: A pilot section 9 has an outer-diameter side small diameter surface portion 10 provided on the outer periphery of an axial outer portion, an outer-diameter side small diameter surface portion 11 provided on the outer periphery of an axial inner portion, an outer-diameter side difference-in-level surface portion 12 which connects the outer-diameter side small diameter surface portion 10 to the outer-diameter side large diameter surface portion 11, an outer-diameter side ridge portion 28 provided in a connection portion in which the outer-diameter side large diameter surface portion 11 is connected to the outer large-diameter side difference-in-level surface portion 12, an inner-diameter side large diameter surface portion 13 provided in the inner periphery of an axial outer portion, an inner-diameter side difference-in-level surface portion 14 folded toward a diametral inner side from an end portion of the inner-diameter side of an inner-diameter large diameter surface portion 13, and an inner-diameter side ridge portion 29 provided on a connection portion in which the inner-diameter side difference-in-level surface portion 14 is connected to a portion located on an axial inner side than the inner-diameter side difference-in-level surface portion 14 out of the inner periphery of the pilot section 9. Further, out of the pilot section 9, at least the outer-diameter side small diameter surface portion 10 and the inner-diameter side large diameter surface portion 13 are covered with a coating film 16.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a hub unit bearing for rotatably supporting a wheel and a braking rotor of an automobile relative to a suspension system. [Background technology]

[0002] The wheels and braking rotors of an automobile are rotatably supported by a suspension system through a hub unit bearing. The hub unit bearing comprises an outer ring having a double row outer ring raceway on its inner circumferential surface, a hub having a double row inner ring raceway on its outer circumferential surface, and a plurality of rolling elements arranged to roll freely between the double row outer ring raceway and the double row inner ring raceway.

[0003] The outer ring is supported and fixed to a knuckle that constitutes a suspension system, and does not rotate even during use.

[0004] The hub supports and fixes a wheel constituting a wheel set and a braking rotor such as a disk or drum, and rotates together with the wheel and the braking rotor. The hub has a rotating flange protruding radially outward at an axially intermediate portion in order to support and fix the wheel and the braking rotor, and has a cylindrical pilot portion protruding axially outward at an axially outer end portion. In addition, when the hub unit bearing is for a driving wheel, the hub has an engagement hole that passes axially through the center portion. A shaft portion of a joint outer ring constituting a constant velocity joint is engaged with the engagement hole to enable torque transmission.

[0005] In addition, "outside" in the axial direction refers to the side that is on the outer side in the width direction of the vehicle body when the hub unit bearing is assembled to an automobile, and conversely, the side that is on the central side in the width direction of the vehicle body when the hub unit bearing is assembled to an automobile is referred to as "inside" in the axial direction.

[0006] The rotating flange has a plurality of mounting holes disposed in a circumferential direction and penetrating in an axial direction. The mounting holes are, for example, press-fit holes into which studs are press-fitted from the axially inner side.

[0007] The pilot portion has a wheel fitting surface portion, on an axially outer portion of its outer peripheral surface, for fitting the wheel thereon, and a brake fitting surface portion, on an axially inner portion of its outer peripheral surface, for fitting the braking rotor thereon.

[0008] The braking rotor has a central hole formed in the center that fits onto the brake mating surface with a clearance fit to prevent rattle, and the stud is inserted into a through hole formed in the circumferential direction at the radially intermediate portion. The wheel has a central hole formed in the center that fits onto the wheel mating surface with a clearance fit, and the stud is inserted into a through hole formed in the circumferential direction at the radially intermediate portion. In this state, a hub nut is screwed onto the tip of the stud and further tightened, thereby supporting and fixing the wheel and the braking rotor to the hub. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2011-25732 A Summary of the Invention [Problem to be solved by the invention]

[0010] The braking rotor is fitted onto a brake mating surface portion provided on an axially inner portion of the outer circumferential surface of the pilot portion with a clearance fit to prevent rattle, thereby centering the braking rotor with respect to the hub.

[0011] In contrast, the wheel is fitted onto the wheel fitting surface provided on the axially outer side of the outer circumferential surface of the pilot portion with a slight clearance fit. The wheel is supported and fixed to the hub by inserting the stud into the through hole provided in the circumferential direction of the radially middle portion and screwing and further tightening a hub nut onto the tip of the stud, thereby centering the wheel with respect to the hub.

[0012] In other words, the wheel fitting surface is a portion for temporarily holding the wheel when supporting and fixing the wheel to the hub. After the hub nut is fastened to the tip of the stud, there is a slight radial gap (radial dimension of about 0.1 mm) between the wheel fitting surface and the inner circumferential surface of the center hole of the wheel.

[0013] For this reason, as the vehicle travels, moisture (foreign matter) such as rainwater or muddy water splashed up from the road surface may enter the radial gap between the wheel fitting surface portion and the inner circumferential surface of the center hole of the wheel, causing rust on the wheel fitting surface portion and damaging the aesthetic appearance. Therefore, it is conceivable to prevent the occurrence of rust by covering the wheel fitting surface portion and the portion of the inner circumferential surface of the pilot portion that is located radially inward of the wheel fitting surface portion with a paint film.

[0014] However, in a hub unit bearing for a driving wheel, when painting to cover the surface of the pilot portion with a paint film, if paint adheres to the seating surface present around the axially outer opening of the engagement hole, the following problem may occur: That is, if paint adheres to the seating surface, the end face of the nut screwed onto the tip of the shaft portion of the joint outer ring cannot be brought into contact with the seating surface, and the axial force of the shaft portion cannot be sufficiently secured, which may cause the nut to become loose.

[0015] Japanese Patent Application Laid-Open Publication No. 2011-25732 (Patent Document 1) discloses a method for forming a coating film on the surface of a pilot portion of a hub by immersing an elastic member having countless air bubbles in a paint tank containing ultraviolet-curing paint and pressing the pilot portion of a hub against the elastic member while rotating the pilot portion.

[0016] However, in the painting method described in JP 2011-25732 A, it is difficult to press the hub evenly, and because wear occurs in the elastic member, it is difficult to precisely regulate the range in which the paint film is formed. Furthermore, if the axially outer side of the hub is turned upward before the paint dries in order to check the range in which the paint film is formed, the paint adhering to the inner peripheral surface of the pilot portion may reach the seating surface (causing dripping) along the inner peripheral surface of the hub. Therefore, in the painting method described in JP 2011-25732 A, it is necessary to hold the hub with the axially outer side turned downward and suspended in the air until the paint dries, which requires dedicated equipment.

[0017] In view of the above-mentioned circumstances, an object of the present invention is to realize a hub unit bearing structure that can precisely regulate the formation area of ​​a coating film that covers the surface of the axially outer portion of the pilot portion. [Means for solving the problem]

[0018] The hub unit bearing of the present invention comprises an outer ring, a hub, and a plurality of rolling elements.

[0019] The outer ring has a double row outer ring raceway on its inner circumferential surface. The outer ring is supported and fixed to a knuckle that constitutes a suspension device during use and does not rotate.

[0020] The hub has a double row inner ring raceway on its outer circumferential surface, a cylindrical pilot portion on its axially outer end, and an engagement hole at its center that penetrates in the axial direction. The hub supports a wheel that constitutes a wheel and a braking rotor such as a disk or drum during use, and rotates together with the wheel and the braking rotor.

[0021] The plurality of rolling elements are disposed so as to roll freely between the double row outer ring raceways and the double row inner ring raceways.

[0022] In the hub unit bearing of the present invention, the pilot portion has an outer diameter side small diameter surface portion, an outer diameter side large diameter surface portion, an outer diameter side step surface portion, an outer diameter side ridge portion, an inner diameter side large diameter surface portion, an inner diameter side step surface portion, and an inner diameter side ridge portion.

[0023] The outer diameter side small diameter surface portion is provided on the outer peripheral surface of the axially outer portion of the pilot portion.

[0024] The outer diameter side large diameter surface portion is provided on an outer peripheral surface of an axially inner portion of the pilot portion, and has an outer diameter larger than the outer diameter of the outer diameter side small diameter surface portion.

[0025] The outer diameter side stepped surface portion connects an axially inner end portion of the outer diameter side small diameter surface portion and an axially outer end portion of the outer diameter side large diameter surface portion.

[0026] The outer diameter side ridge portion is provided at a connection portion between the outer diameter side large diameter surface portion and the outer diameter side step surface portion. Cage (Exists on the boundary death ) The curvature of the hub changes discontinuously in a cross section including the central axis of the hub. .

[0027] The inner diameter side large diameter surface portion is provided on an inner circumferential surface of an axially outer portion of the pilot portion.

[0028] The inner diameter side stepped surface portion is bent radially inward from an axially inner end portion of the inner diameter side large diameter surface portion.

[0029] The inner diameter side ridge portion is provided at a connection portion between the inner diameter side step surface portion and a portion of the inner circumferential surface of the pilot portion that is located axially more inward than the inner diameter side step surface portion. Cage (Exists on the boundary death ), The curvature of the hub changes discontinuously in a cross section including the central axis of the hub. .

[0030] Furthermore, the pilot portion covers at least the outer small diameter surface portion and the inner large diameter surface portion, Furthermore, a portion of the outer peripheral surface located axially inside the outer diameter side ridge portion and a portion of the inner peripheral surface located axially inside the inner diameter side ridge portion The part located axially inward and It has a coating that does not cover the

[0031] In one aspect of the hub unit bearing of the present invention, the outer diameter side small diameter surface portion constitutes a wheel fitting surface portion for externally fitting the wheel, and the outer diameter side large diameter surface portion constitutes a brake fitting surface portion for externally fitting the braking rotating body.

[0032] The method for manufacturing a hub unit bearing of the present invention includes the steps of: The hub is placed with the axially outer side facing upward, The method includes a step of forming the coating film on at least the outer diameter side small diameter surface portion and the inner diameter side large diameter surface portion of the surface of the pilot portion by spray painting. Effect of the Invention

[0033] According to the hub unit bearing of the present invention, the formation area of ​​the coating film which covers the surface of the axially outer portion of the pilot portion can be controlled with precision. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a cross-sectional view showing a hub unit bearing according to one embodiment. [Diagram 2] FIG. 2 is an enlarged view of the portion X in FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of a main part, showing an example of a method for forming a coating film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] An embodiment of the present invention will be described with reference to Figures 1 to 3. A hub unit bearing 1 of this example is for a drive wheel, and includes an outer ring 2, a hub 3, and a plurality of rolling elements 4a, 4b.

[0036] 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, 5b on its inner circumferential surface, and has a stationary flange 6 protruding radially outward at an axially intermediate portion. The stationary flange 6 has support holes 7 penetrating in the axial direction at multiple circumferential positions at the radially intermediate portion.

[0037] In this example, the support hole 7 is configured as a screw hole. The outer ring 2 is supported and fixed to the suspension by inserting a support bolt, which is inserted through a through hole provided in the knuckle of the suspension, into the support hole 7 of the stationary flange 6 from the inside in the axial direction, so that the outer ring 2 does not rotate even when the wheel rotates.

[0038] The hub 3 is disposed radially inside the outer ring 2 and coaxially with the outer ring 2. The hub 3 has double row inner ring raceways 8a, 8b on its outer peripheral surface, a cylindrical pilot portion 9 at its axially outer end, and an engagement hole 19 penetrating in the axial direction at its center.

[0039] Note that "outside" in the axial direction refers to the left side in Fig. 1 and Fig. 2 and the upper side in Fig. 3, which are the outer side of the vehicle body when the hub unit bearing 1 is installed in the vehicle. Conversely, the right side in Fig. 1 and Fig. 2 and the lower side in Fig. 3, which are the center side of the vehicle body when the hub unit bearing 1 is installed in the vehicle, are referred to as "inside" in the axial direction.

[0040] The pilot portion 9 has an outer diameter side small diameter surface portion 10, an outer diameter side large diameter surface portion 11, an outer diameter side stepped surface portion 12, an outer diameter side ridge portion 28, an inner diameter side large diameter surface portion 13, an inner diameter side stepped surface portion 14, and an inner diameter side ridge portion 29.

[0041] The outer diameter side small diameter surface portion 10 is provided on the outer peripheral surface of the axially outer portion of the pilot portion 9, and constitutes a wheel fitting surface portion for fitting a wheel 30 constituting a wheel. In this example, the outer diameter side small diameter surface portion 10 has a groove 15 recessed radially inward over the entire circumference at the axially intermediate portion. However, the groove 15 may be omitted.

[0042] The outer diameter large surface portion 11 is provided on the outer peripheral surface of the axially inner portion of the pilot portion 9, and constitutes a brake fitting surface portion for fitting a braking rotor 31 such as a drum or a disk. The outer diameter large surface portion 11 is a portion of the outer diameter small surface portion 10 that is axially out of the recessed groove 15. 10 Outside diameter D is larger than 11 The outer diameter D of the outer diameter side large diameter surface portion 11 11and the outer diameter D of the outer small diameter surface portion 10 10 Difference from (D 11 -D 10 ) is not particularly limited, and is determined by the rim diameter of the wheel 30 constituting the wheel and the outer diameter of the braking rotor 31. For example, in the case of a hub unit bearing for a passenger car, the difference (D 11 -D 10 ) can be 2 mm or more and 20 mm or less, and preferably 2 mm or more and 8 mm or less.

[0043] The outer diameter side step surface portion 12 connects the axially inner end of the outer diameter side small diameter surface portion 10 and the axially outer end of the outer diameter side large diameter surface portion 11. In this example, the outer diameter side step surface portion 12 is inclined in a direction in which the outer diameter increases toward the axially inner side and is configured as a conical convex surface facing axially outward. However, when implementing the hub unit bearing of the present invention, the outer diameter side step surface portion can also be configured as a concave curved surface having an arc-shaped cross-sectional shape.

[0044] The outer diameter side ridge portion 28 is provided at the connection between the outer diameter side large diameter surface portion 11 and the outer diameter side stepped surface portion 12. In other words, the outer diameter side large diameter surface portion 11 and the outer diameter side stepped surface portion 12 are not connected by a curved surface having an arc-shaped cross section, but the outer diameter side large diameter surface portion 11, which has a cylindrical surface shape, and the outer diameter side stepped surface portion 12, which has a conical convex surface shape, are directly connected by the non-differentiable (pointed) outer diameter side ridge portion 28.

[0045] The inclination angle θ of the generatrix of the outer diameter side step surface portion 12 with respect to the central axis O of the hub 3 is not particularly limited, but can be 20 degrees or more and 60 degrees or less, and is preferably 30 degrees or more and 45 degrees or less. In the illustrated example, the inclination angle θ is about 45 degrees. If the inclination angle θ is smaller than 20 degrees, as described later, after the coating film 16 is formed, the paint constituting the coating film 16 may reach the outer diameter side large diameter surface portion 11 along the outer diameter side step surface portion 12 with the axial outside of the hub unit bearing 1 facing upward. On the other hand, if the inclination angle θ is larger than 60 degrees, it becomes difficult to perform the work of fitting the braking rotor 31 onto the outer diameter side large diameter surface portion 11.

[0046] The inner diameter side large diameter surface portion 13 is provided on the inner peripheral surface of the axially outer portion of the pilot portion 9 .

[0047] The inner diameter side stepped surface portion 14 is bent radially inward from the axially inner end of the inner diameter side large diameter surface portion 13. In other words, the inner diameter side stepped surface portion 14 is provided on the inner peripheral surface of the pilot portion 9 on the axially inner side, and is located at the inner diameter d 13 and connects an axially outer end of inner diameter side small diameter surface portion 17 having a draft and an axially inner end of inner diameter side large diameter surface portion 13. In this example, inner diameter side stepped surface portion 14 is located radially inside a portion of outer diameter side small diameter surface portion 10 that is located inside groove 15 in the axial direction.

[0048] The radial height of the inner diameter side step surface portion 14, i.e., the inner diameter d 13 and the inner diameter d of the axially outer end of the inner diameter side small diameter surface portion 17 17 Difference from (d 13 -d 17 ) is not particularly limited and is determined according to the diameter of the cap fitted to the wheel 30 constituting the wheel. For example, in the case of a hub unit bearing for a passenger car, the difference (d 13 -d 17 ) can be set to 1 mm or more and 5 mm or less, and preferably to 1 mm or more and 2 mm or less.

[0049] In this example, the inner diameter side step surface portion 14 is inclined in a direction such that the inner diameter becomes smaller toward the inside in the axial direction, and is configured as a conical concave surface facing axially outward. However, when implementing the hub unit bearing of the present invention, the inner diameter side step surface portion can also be configured as a flat surface that is perpendicular to the central axis of the hub and faces axially outward, or it can be configured as a concave curved surface having an arc-shaped cross section.

[0050] The inner diameter side ridge portion 29 is provided at the connection between the inner diameter side stepped surface portion 14 and the inner diameter side small diameter surface portion 17. In other words, the inner diameter side stepped surface portion 14 and the inner diameter side small diameter surface portion 17 are not connected by a curved surface having an arc-shaped cross section, but the conical concave inner diameter side stepped surface portion 14 and the conical concave or cylindrical inner diameter side small diameter surface portion 17 are directly connected by a non-differentiable (pointed) inner diameter side ridge portion 29.

[0051] The inclination angle φ of the generating line of the inner diameter side step surface portion 14 with respect to the central axis O of the hub 3 is not particularly limited, but can be 20 degrees or more and 90 degrees or less, and is preferably 30 degrees or more and 45 degrees or less. In the illustrated example, the inclination angle φ is set to about 30 degrees. If the inclination angle φ is set to be smaller than 20 degrees, as described later, after the coating film 16 is formed, with the axially outer side of the hub unit bearing 1 facing upward, the paint constituting the coating film 16 may run down the inner diameter side step surface portion 14 and reach the inner diameter side small diameter surface portion 17 and even the seat surface 18 described later.

[0052] The hub 3 has an engagement hole 19 at its center that penetrates in the axial direction. A shaft portion of a joint outer ring that constitutes a constant velocity joint is engaged with the engagement hole 19 to enable torque transmission. For example, the engagement hole 19 is configured as a spline hole having a female spline portion on its inner circumferential surface, in which recesses and protrusions are alternately arranged around the entire circumference, and a male spline portion provided on the outer circumferential surface of the shaft portion is spline-engaged with the female spline portion.

[0053] A nut is screwed onto the tip of the shaft portion that protrudes from the axially outer opening of engagement hole 19. As a result, hub 3 is sandwiched from both axial sides between the nut and the joint outer ring, and hub unit bearing 1 and the joint outer ring are joined together.

[0054] In this example, the hub 3 has a seat 18 for abutting the nut in a portion surrounding the axially outer opening of the engagement hole 19. The seat 18 has a hollow circular end face shape when viewed from the axial direction, and is composed of a flat surface perpendicular to the central axis O of the hub 3.

[0055] Pilot portion 9 has coating film 16 that covers at least outer diameter side small diameter surface portion 10 and inner diameter side large diameter surface portion 13, but does not cover outer diameter side large diameter surface portion 11 and a portion of the inner circumferential surface of pilot portion 9 that is located axially more inward than inner diameter side stepped surface portion 14. In this example, coating film 16 covers outer diameter side stepped surface portion 12, outer diameter side small diameter surface portion 10, axially outer end face 25 of pilot portion 9, inner diameter side large diameter surface portion 13, and inner diameter side stepped surface portion 14, as shown by the thick line in Figure 2, but does not cover outer diameter side large diameter surface portion 11 and inner diameter side small diameter surface portion 17.

[0056] The type of paint constituting the coating film 16 is not particularly limited as long as it has good adhesion to the metal material constituting the hub 3, is easy to form a coating film, and is corrosion resistant. For example, epoxy resin-based or acrylic resin-based paints can be used as the paint constituting the coating film 16.

[0057] In Fig. 2, the thickness of the coating film 16 is exaggerated. In practice, the thickness of the coating film 16 can be 5 µm or more and 30 µm or less, and preferably 10 µm or more and 20 µm or less. Therefore, the outer diameter of the portion of the coating film 16 that covers the outer diameter side small diameter surface portion 10 is 10 µm or more and 10 µm or less. 11 The inner diameter of the portion of the coating film 16 that covers the inner large diameter surface portion 13 is smaller than the inner diameter d 17 Greater than.

[0058] The hub 3 has a rotation flange 20 that protrudes radially outward at a portion located axially outward of the axially outer end of the outer ring 2 and axially inward of the pilot portion 9 .

[0059] The rotating flange 20 has mounting holes 21 penetrating in the axial direction at multiple locations in the circumferential direction of a radially middle portion. In this example, the mounting holes 21 are configured as threaded holes having a female thread groove on the inner circumferential surface.

[0060] The braking rotor 31, such as a drum or disk, is fitted onto the outer diameter side large diameter surface portion 11 with a clearance fit that does not rattle. This allows the braking rotor 31 to be centered with respect to the hub 3. The wheel 30, which constitutes the wheel, is fitted onto the outer diameter side small diameter surface portion 10 with a clearance fit that has some rattle (having a radial gap with a radial dimension of about 0.1 mm).

[0061] With the braking rotor 31 fitted onto the outer diameter large diameter surface portion 11 and the wheel 30 fitted onto the outer diameter small diameter surface portion 10, hub bolts are inserted into through holes provided at multiple circumferential positions in the radially intermediate portion of the braking rotor 31 and through holes provided at multiple circumferential positions in the radially intermediate portion of the wheel 30, and then screwed into the mounting holes 21 and further tightened. This bonds and fixes the braking rotor 31 and the wheel 30 to the rotating flange 20, and also centers the wheel 30 relative to the hub 3.

[0062] The mounting hole 21 may be a press-fit hole such as a serrated hole. In this case, a stud is press-fitted into the mounting hole 21 from the inside in the axial direction, and a hub nut is screwed onto the tip of the stud while the stud is inserted into through-holes provided at multiple locations in the circumferential direction in the radially middle portions of the braking rotor 31 and the wheel 30. This bonds and fixes the braking rotor 31 and the wheel 30 to the rotating flange 20, and also centers the wheel 30 relative to the hub 3.

[0063] The hub 3 of this example is formed by combining an inner ring 22 and a hub ring 23 .

[0064] The inner ring 22 is made of a hard metal such as bearing steel, etc. The inner ring 22 has, on its outer circumferential surface, an inner ring raceway 8a on the axially inner side of the double row inner ring raceways 8a, 8b.

[0065] The hub ring 23 is made of a hard metal such as medium carbon steel. The hub ring 23 has the axially outer inner ring raceway 8b of the double row inner ring raceways 8a, 8b at the axially middle portion of the outer peripheral surface. The hub ring 23 has a rotation flange 20 that protrudes radially outward at a portion located axially outer than the axially outer inner ring raceway 8b, and has a cylindrical pilot portion 9 at the axially outer end.

[0066] Furthermore, the hub wheel 23 has a fitting tubular portion 24, located axially more inward than the axially outer inner ring raceway 8b, which has an outer diameter smaller than that of an adjacent axially outer portion and into which the inner ring 22 is fitted. The hub 3 in this example is constructed by fitting the inner ring 22 onto the fitting tubular portion 24 of the hub wheel 23 with an interference fit, and connecting and fixing the inner ring 22 and the hub wheel 23 together.

[0067] In addition, the hub wheel and the inner ring can also be joined by plastically deforming the axially inner end of the hub wheel protruding from the axially inner end of the inner ring toward the radially outward direction to form a crimped portion, or by screwing a nut onto the axially inner end of the hub wheel protruding from the axially inner end of the inner ring.

[0068] A plurality of rolling elements 4a, 4b are respectively arranged between double row outer ring raceways 5a, 5b and double row inner ring raceways 8a, 8b so as to be rollable while being held by cages 26a, 26b. This allows the hub 3 to be rotatably supported on the radially inner side of the outer ring 2. In this example, tapered rollers are used as the rolling elements 4a, 4b, but balls can also be used instead of tapered rollers.

[0069] The present invention can be applied to equal PCD type hub unit bearings in which the pitch diameter of the rolling elements in the axially inner row is equal to the pitch diameter of the rolling elements in the axially outer row, and can also be applied to different PCD type hub unit bearings in which the pitch diameter of the rolling elements in the axially inner row is larger or smaller than the pitch diameter of the rolling elements in the axially outer row.

[0070] A method for forming the coating film 16 when manufacturing the hub unit bearing 1 of this example will be described. In this example, the coating film 16 is formed by spray painting, which sprays atomized paint onto the portion of the surface of the pilot portion 9 where the coating film 16 is to be formed.

[0071] First, as shown in Fig. 3, the hub wheel 23 is placed with the axially outer side facing upward. Next, the nozzle 27 for spraying paint is brought into opposition to the portion of the surface of the pilot portion 9 where the coating film 16 is to be formed. Specifically, in this example, the nozzles of the pair of nozzles 27 are brought into opposition to the outer peripheral surface and the inner peripheral surface, respectively, at one circumferential position on the axially outer portion of the pilot portion 9.

[0072] Then, while rotating the hub 3, a mist of paint is sprayed from the outlets of the pair of nozzles 27, so that the paint is sprayed all around the surface of the pilot portion 9, onto the outer diameter side stepped surface portion 12, the outer diameter side small diameter surface portion 10, the axially outer end face 25, the inner diameter side large diameter surface portion 13, and the inner diameter side stepped surface portion 14. This forms a coating film 16 that covers the outer diameter side stepped surface portion 12, the outer diameter side small diameter surface portion 10, the axially outer end face 25 of the pilot portion 9, the inner diameter side large diameter surface portion 13, and the inner diameter side stepped surface portion 14.

[0073] In this example, the nozzles of the pair of nozzles 27 are arranged to face the outer peripheral surface and inner peripheral surface of the axially outer portion of the pilot section 9, respectively, and paint is sprayed from the nozzles of the pair of nozzles 27 while rotating the hub wheel 23 to form the coating film 16. However, when implementing the present invention, the nozzles of a plurality of nozzles may be arranged to face the outer peripheral surface and inner peripheral surface at a plurality of positions in the circumferential direction of the axially outer portion of the pilot section, respectively, and paint may be sprayed from the nozzle nozzles to paint a plurality of positions in the circumferential direction simultaneously, thereby forming a uniform coating film all around.

[0074] Furthermore, when forming the coating film 16 by spray painting, the areas where the coating film 16 should not be formed can be masked with a cover, tape, etc. Specifically, in this example, the axially outer side surface of the rotating flange 20, the seat surface 18, etc. can be masked.

[0075] It is preferable that the coating for forming the coating film 16 is carried out after the outer ring 2, the rolling elements 4a, 4b, and the inner ring 22 are assembled around the hub ring 23.

[0076] The hub unit bearing 1 of this embodiment has an outer ridge 28 on the outer peripheral surface of the pilot portion 9, and an inner ridge 29 on the inner peripheral surface of the pilot portion 9. Therefore, even when the hub 3 is placed with the axially outer side facing upward before the paint constituting the coating film 16 dries, the paint sprayed onto the outer step surface portion 12 and the outer small diameter surface portion 10, the axially outer end face 25, the inner large diameter surface portion 13 and the inner step surface portion 14 does not go over the outer ridge 28 and adhere to the outer large diameter surface portion 11 or the axially outer surface of the rotating flange 20 due to the surface tension of the paint, or does not go over the inner ridge 29 and adhere to the inner small diameter surface portion 17 or the seat surface 18 due to the surface tension of the paint (drip). Therefore, the part covered by the coating film 16 and the part not covered by it can be clearly distinguished. In short, the formation range of the coating film 16 can be precisely controlled.

[0077] Furthermore, with the hub unit bearing 1 of this embodiment, there is no need for special equipment to hold the hub with the axially outward side facing downward and suspended in the air until the paint dries, as is the case with the painting method described in JP 2011-25732 A. This makes it possible to reduce the manufacturing costs of the hub unit bearing 1.

[0078] Furthermore, in the method of forming the coating film 16 in this example, the hub 3 is placed with the axially outer side facing upward, and the surface of the pilot portion 9 is painted to form the coating film 16. Therefore, after painting is completed, it can be easily confirmed by visual inspection whether the coating film 16 has been properly formed.

[0079] In this example, the outer diameter side small diameter surface portion 10 constitutes a wheel fitting surface portion for fitting the wheel 30 thereon, and the outer diameter side large diameter surface portion 11 constitutes a brake fitting surface portion for fitting the braking rotor 31 thereon. However, when carrying out the present invention and forming a coating film only on the axially outer portion of the wheel fitting surface portion, an outer diameter side stepped surface portion can also be disposed in the axially middle portion of the wheel fitting surface portion.

[0080] In addition, in the method of forming the coating film 16 in this example, the coating film 16 is formed by spray coating, but the coating film can also be formed by brush coating, dip coating, or the like, as long as dripping can be prevented and the area in which the coating film is formed can be precisely controlled. [Explanation of symbols]

[0081] 1 Hub unit bearing 2 Outer ring 3. Hub 4a, 4b Rolling elements 5a, 5b Outer raceway 6 Stationary Flange 7 Support hole 8a, 8b Inner raceway 9 Pilot Division 10 Small diameter surface on outer diameter side 11 Large diameter surface on outer diameter side 12 Step surface on outer diameter side 13 Large diameter surface on inner diameter side 14 Inner diameter side step surface 15 Groove 16 Coating 17 Inner diameter side small diameter surface part 18 Seat 19 Engagement hole 20 Rotating flange 21 Mounting hole 22 Inner Circle 23 Hub wheel 24 Fitting cylinder part 25 End face 26a, 26b retainer 27 Nozzle 28 Outer diameter side ridge 29 Inner diameter side edge 30 Wheels 31 Braking rotor

Claims

1. an outer ring having a double row outer ring raceway on an inner circumferential surface; a hub having a double row inner ring raceway on its outer circumferential surface, a cylindrical pilot portion on its axially outer end, and an engagement hole penetrating in the axial direction at its center; A plurality of rolling elements are arranged to roll freely between the double row outer ring raceways and the double row inner ring raceways; Equipped with The pilot portion includes an outer diameter side small diameter surface portion provided on an outer peripheral surface of an axially outer portion, an outer diameter side large diameter surface portion provided on an outer peripheral surface of an axially inner portion and having an outer diameter larger than the outer diameter of the outer diameter side small diameter surface portion, an outer diameter side stepped surface portion connecting an axially inner end portion of the outer diameter side small diameter surface portion and an axially outer end portion of the outer diameter side large diameter surface portion, an outer diameter side ridge portion provided at a connection portion between the outer diameter side large diameter surface portion and the outer diameter side stepped surface portion and being a portion where a curvature changes discontinuously in a cross section including a central axis of the hub, an inner diameter side large diameter surface portion provided on an inner peripheral surface of an axially outer portion, and the hub has an inner diameter side stepped surface portion bent radially inward from an axially inner end of a radial surface portion, and an inner diameter side ridge portion provided at a connection portion between the inner diameter side stepped surface portion and a portion of the inner circumferential surface located axially more inward than the inner diameter side stepped surface portion, the inner diameter side ridge portion being a portion where a curvature changes discontinuously in a cross section including a central axis of the hub, and the hub has a coating film that covers at least the outer diameter side small diameter surface portion and the inner diameter side large diameter surface portion, but does not cover a portion of the outer circumferential surface located axially more inward than the outer diameter side ridge portion and a portion of the inner circumferential surface located axially more inward than the inner diameter side ridge portion; Hub unit bearing.

2. A method for manufacturing a hub unit bearing according to claim 1, comprising the steps of: forming the coating film by spray painting on at least the outer diameter side small diameter surface portion and the inner diameter side large diameter surface portion of the surface of the pilot portion while the hub is placed with the axial outer side facing upward. A manufacturing method for a hub unit bearing.

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