JP5600527B2 - Rolling bearing unit for wheel support - Google Patents

Description

  The present invention relates to a wheel-supporting rolling bearing unit for rotatably supporting a wheel with respect to a suspension device of an automobile, and more particularly to a wheel-supporting rolling bearing unit that hardly causes rusting.

  For rolling bearing units (also referred to as hub bearings) for supporting automobile wheels, the first example is a configuration in which the inner ring is a stationary bearing ring and the hub is a rotating bearing ring, and the outer ring is a stationary bearing ring, and the hub rotates. A second example of a configuration that uses a side raceway is known (see Patent Document 1).

  First, a first example of a conventional structure of a wheel support rolling bearing unit will be described with reference to FIG. FIG. 5 is a cross-sectional view showing a first example of a conventional structure of a wheel bearing rolling bearing unit. A wheel 1 constituting a wheel is rotatably supported at an end portion of an axle 3 constituting a suspension device by a wheel bearing rolling bearing unit 2 as shown in FIG. That is, an inner ring 5 which is a stationary side bearing ring constituting the wheel bearing rolling bearing unit 2 is externally fitted to an axle 4 fixed to an end portion of the axle 3 and fixed by a nut 6. On the other hand, the wheel 1 is coupled and fixed to a hub 7, which is a rotating raceway wheel constituting the wheel support rolling bearing unit 2, by a plurality of studs 8 and nuts 9. Double-row outer ring rolling surfaces 10a and 10b, each of which is a rotation-side rolling surface, are formed on the inner peripheral surface of the hub 7, and a mounting flange 11 is formed on the outer peripheral surface. The wheel 1 is coupled and fixed to one side surface (outer side surface in the illustrated example) of each of the mounting flanges 11 by a stud 8 and a nut 9 together with a drum 12 for constituting a braking device. In the present specification, “outside” in the axial direction means the outside in the width direction when assembled to the vehicle, and “inside” means the center in the width direction.

  Between each outer ring rolling surface 10a, 10b and each inner ring rolling surface 13a, 13b formed on the outer peripheral surface of each inner ring 5 is a stationary side rolling surface, each ball 14 is a rolling element. Are provided so as to be able to roll while being held by the cage 15. By combining the components in this way, a double-row angular ball bearing, which is a rear combination, is configured, and the hub 7 can be rotated around each inner ring 5, and the radial load and thrust load can be supported. I support it. In addition, seal rings 16a and 16b are provided between the inner peripheral surfaces of both ends of the hub 7 and the outer peripheral surfaces of the end portions of the inner rings 5, respectively, so that the space provided with the balls 14 and the internal space 17 are blocked. ing. Further, the outer end opening of the hub 7 is closed by a cap 18.

  When the wheel bearing rolling bearing unit 2 is used, as shown in FIG. 5, the axle 4 with the inner ring 5 fitted and fixed is fixed to the axle 3, and a tire (not shown) is attached to the mounting flange 11 of the hub 7. The combined wheel 1 and drum 12 are fixed. A drum brake for braking is configured by combining the drum 12 and a wheel cylinder and a shoe (not shown) supported by a backing plate 19 fixed to the end of the axle 3. During braking, a pair of shoes provided on the inner diameter side of the drum 12 are pressed against the inner peripheral surface of the drum 12. Grease is enclosed in the internal space 17 to lubricate the rolling contact portions between the outer ring rolling surfaces 10a and 10b, the inner ring rolling surfaces 13a and 13b, and the rolling surfaces of the balls 14. I am doing so.

  Next, a second example of a conventional structure of a wheel support rolling bearing unit will be described with reference to FIG. FIG. 6 is a sectional view showing a second example of a conventional structure of a wheel bearing rolling bearing unit. In the case of the wheel-supporting rolling bearing unit 2a shown in FIG. 6, a hub 7a that is a rotating side race ring is provided on the inner diameter side of an outer ring 20 that is a stationary side race ring, and a plurality of balls 14 each of which is a rolling element. Therefore, it is supported rotatably. For this purpose, double-row outer ring rolling surfaces 10a and 10b, each of which is a stationary rolling surface, are provided on the inner peripheral surface of the outer ring 20, and first, each of which is a rotary rolling surface on the outer peripheral surface of the hub 7a. Second inner ring rolling surfaces 21 and 22 are respectively provided. The hub 7 a is a combination of the hub body 23 and the inner ring 24. Of these, the mounting flange 11a for supporting the wheel on the outer end portion of the outer peripheral surface of the hub body 23, the first inner ring rolling surface 21 in the middle portion, and the first inner ring rolling surface 21 in the middle portion. Small-diameter step portions 25 each having a smaller diameter than the portion where the inner ring rolling surface 21 is formed are provided. And the inner ring | wheel 24 which provided the 2nd inner ring | wheel rolling surface 22 which is circular cross-section in an outer peripheral surface is externally fitted to this small diameter step part 25. Further, the inner end surface of the inner ring 24 is held down by a caulking portion 26 formed by plastically deforming the inner end portion of the hub body 23 radially outward, and the inner ring 24 is fixed to the hub body 23.

  Seal rings 16c and 16d are provided between the inner peripheral surface of both ends of the outer ring 20 and the outer peripheral surface of the intermediate part of the hub body 23 and the inner peripheral part of the inner ring 24, respectively. Between the inner space 17a provided with the balls 14 and the outer space. Grease is sealed in the internal space 17a to lubricate the rolling contact portions between the outer ring rolling surfaces 10a and 10b, the inner ring rolling surfaces 21 and 22, and the rolling surfaces of the balls 14. I have to.

  When the grease-filled rolling bearing is used as a wheel support bearing, the lubricating oil film of the lubricating grease is likely to break due to severe use conditions such as high speed and high load. When the lubricating oil film breaks, metal contact occurs, causing a problem that heat generation and frictional wear increase. For this reason, it is necessary to improve lubricity and load resistance under high speed and high load, and to prevent metal contact due to breakage of the lubricating oil film. The extreme pressure agent-containing grease is used to reduce the problems. In lubrication of the rolling bearing portion, in order to prevent the lubricating film of the lubricating grease from breaking, grease containing an extreme pressure agent (EP agent) is used to reduce the breaking of the lubricating oil film. For example, a lubricant composition for a rolling bearing comprising an organic bismuth compound has been proposed (see Patent Document 2). Further, a grease composition containing molybdenum dithiocarbamate and polysulfide for the purpose of reducing wear has been proposed (see Patent Document 3).

JP 2001-221243 A JP-A-8-41478 Japanese Patent Laid-Open No. 10-324885

  However, the rolling bearing unit for wheel support is basically used outdoors, and is used not only in sunny weather but also in extremely bad conditions such as rainy weather, bad roads, and coastal conditions. The Intrusion of rain or the like into the bearing unit is suppressed by a seal, but it is not perfect. Therefore, there is no denying the concern that moisture such as rain will enter the bearing unit during long-term use. When moisture enters, rust is generated inside the wheel bearing rolling bearing unit, which may make continuous use difficult.

  In addition, since the wheel-supporting rolling bearing unit is used at a high speed and under a high load, it may be difficult to use due to seizure only with a countermeasure using a conventional extreme pressure agent-containing grease. In particular, when moisture enters, the oil film is easily interrupted, and when the oil film is interrupted, metal contact occurs, so that the risk of seizure increases. In addition, molybdenum compounds and the like contained in extreme pressure agents are PRTR-regulated substances, and reduction of the usage amount is desired from the viewpoint of environmental protection.

  The present invention has been made to cope with such problems, and can suppress the generation of rust even when moisture enters the inside, and has excellent seizure resistance, and can be used for a long time. An object of the present invention is to provide a wheel bearing rolling bearing unit that can withstand.

  The rolling bearing unit for supporting a wheel of the present invention includes a stationary bearing ring that is supported and fixed to a suspension device in use, a rotating bearing ring that supports and fixes a wheel in use, the stationary bearing ring, and the rotating side. A plurality of rolling elements provided between a stationary-side rolling surface and a rotating-side rolling surface existing on circumferential surfaces facing each other with the raceway, and each rolling surface, each rolling element, and A rolling bearing unit for supporting a wheel that lubricates a surface in contact with rolling with grease, wherein the stationary side race ring, the rotation side race ring, and the rolling element are each a metal member, and the metal member At least one member is a member in which a coating treatment is performed with a plant-derived polyhydric alcohol compound on at least the surface of the member that comes into contact with rolling.

  The member that has been subjected to the coating treatment has an iron oxide coating on at least a surface of the member that contacts the rolling. The iron oxide coating has a thickness of 0.05 μm to 2 μm.

  The grease contains a polyhydric alcohol compound derived from the plant, and the coating treatment is a treatment applied through the grease.

  The coating treatment is a treatment of immersing the metal member to be coated in a treatment solution in which the plant-derived polyhydric alcohol compound is dispersed or dissolved in water and / or an organic solvent. .

  The plant-derived polyhydric alcohol compound is chlorogenic acid or a derivative thereof. The plant-derived polyhydric alcohol compound is quinic acid or a derivative thereof. The plant-derived polyhydric alcohol compound is gallic acid or a derivative thereof.

  The plant-derived polyhydric alcohol compound is caffeic acid or a derivative thereof. The plant-derived polyhydric alcohol compound is ellagic acid or a derivative thereof.

  The plant-derived polyhydric alcohol compound is curcumin or a derivative thereof. The plant-derived polyhydric alcohol compound is quercetin or a derivative thereof.

  The rolling bearing unit for supporting a wheel according to the present invention includes a plant-derived multi-layered structure on at least one member of a stationary side race ring, a rotary side race ring, and a rolling element, which are metal members, on at least the rolling contact surface of the member. Since the coating treatment is performed with the monohydric alcohol compound, it is possible to suppress the occurrence of rust inside the bearing unit even when moisture enters. In addition, since the coating treatment is performed with the polyhydric alcohol compound and the iron oxide coating is formed, the seizure resistance is improved, and it is possible to use for a long time. Furthermore, since a plant-derived polyhydric alcohol compound is used for the surface treatment, a wheel bearing rolling bearing unit with a low environmental load is obtained.

It is sectional drawing which shows the 1st example of the structure of the rolling bearing unit for wheel support of this invention. It is sectional drawing which shows the 2nd example of the structure of the rolling bearing unit for wheel support of this invention. It is sectional drawing which shows the 3rd example of the structure of the rolling bearing unit for wheel support of this invention. It is sectional drawing which shows the 4th example of the structure of the rolling bearing unit for wheel support of this invention. It is sectional drawing which shows the 1st example of the conventional structure of the rolling bearing unit for wheel support. It is sectional drawing which shows the 2nd example of the conventional structure of the rolling bearing unit for wheel support.

  About the rolling bearing unit for wheel support, when the rust prevention test was done using what processed the surface of the component with the plant-derived polyhydric alcohol compound, it turned out that generation | occurrence | production of rust can be suppressed. This is because the action of the polyhydric alcohol compound derived from the plant causes an iron oxide film to be formed on the surface of a metal (carbon steel for machine structure or bearing steel), which inactivates the surface and has a rust prevention effect. It is like that. The present invention is based on such knowledge.

  Four examples of the structure of the rolling bearing unit for supporting a wheel of the present invention will be described below. The 1st example of a suitable structure as a rolling bearing unit for wheel support of this invention is shown in FIG. In the first example, on the inner diameter side of the outer ring 20 that is a stationary side race ring, a hub 7b that is a rotation side race ring is rotatably supported by a plurality of balls 14 each of which is a rolling element. The first example is a structure for supporting driven wheels (front wheels of FR and RR vehicles, rear wheels of FF vehicles), and the rotational torque of the hub 7b is increased by improving the structure shown in FIG. The structure can be further reduced. For this purpose, in the case of the first example, the inner end opening of the outer ring 20 is closed by the cap 18a, and the gap between the outer peripheral part of the outer ring 20 and the intermediate part of the hub body 23 is sealed. It is blocked by the ring 16c. Since the cap 18a is provided, the seal ring 16d between the inner peripheral surface of the inner end portion of the outer ring 20 and the outer peripheral surface of the inner ring 24 shown in FIG. 6 can be omitted. Intrusion of foreign matter such as rainwater into the internal space 17b where each ball 14 is installed is prevented by the seal ring 16c and the cap 18a. The structure of the other parts is the same as the conventional structure shown in FIG. When the rolling bearing unit for supporting a wheel according to the present invention is applied to a driven wheel, the seal ring between the inner peripheral surface of the inner end of the outer ring and the outer peripheral surface of the inner ring is omitted. It can be reduced from the product.

  Next, the 2nd example of a suitable structure as a rolling bearing unit for wheel support of this invention is shown in FIG. The second example is also a structure for supporting driven wheels (front wheels of FR and RR vehicles, rear wheels of FF vehicles). In the case of the second example, a male threaded portion 27 is provided at the inner end of the hub body 23a constituting the hub 7c, and a nut 28 screwed onto the male threaded portion 27 is externally fitted to the small diameter step portion 25 of the hub body 23a. The inner end surface of the inner ring 24 is suppressed. In accordance with this, the shape of the cap 18b attached to the inner end opening of the outer ring 20 is expanded to prevent the male screw portion 27 and the nut 28 from interfering with each other. Other configurations are the same as those of the first example described above.

  Next, the 3rd example of a suitable structure as a rolling bearing unit for wheel support of this invention is shown in FIG. The third example is a structure for supporting driving wheels (rear wheels of FR and RR vehicles, front wheels of FF vehicles, and all wheels of 4WD vehicles). In the case of the third example, a spline hole 29 is formed in the center portion of the hub body 23b constituting the hub 7d which is a rotating side race ring, which is rotatably supported on the inner diameter side of the outer ring 20 which is a stationary side race ring. ing. A spline shaft (not shown) attached to the constant velocity joint is inserted into the spline hole 29 in the assembled state to the vehicle. In addition, when the rolling bearing unit for supporting a wheel of the present invention is applied to a drive wheel, a spline hole is formed in the central portion of the hub body having a hub which is a rotating raceway, so that the constant speed is formed in the spline hole. By connecting the spline shaft attached to the joint, the rotational torque of the constant velocity joint can be reliably transmitted to the hub. Further, the inner end surface of the inner ring 24 that is externally fitted to the small-diameter step portion 25 formed at the inner end portion of the hub main body 23b is crimped by a caulking portion 26 that is obtained by plastically deforming the inner end portion of the hub main body 23b radially outward. In this manner, the inner ring 24 is fixed to the hub body 23b to constitute the hub 7d. Then, seal rings 16c and 16d are provided between the inner peripheral surface of both ends of the outer ring 20 and the outer peripheral surface of the intermediate part of the hub main body 23b and the inner end part of the inner ring 24, respectively. The internal space 17b in which each ball 14 is provided between the outer peripheral surface of the hub 7b and the external space are blocked. Other configurations are the same as those in the first and second examples described above.

  Next, the 4th example of a suitable structure as a rolling bearing unit for wheel support of this invention is shown in FIG. The fourth example is also a structure for supporting driving wheels (rear wheels of FR and RR vehicles, front wheels of FF vehicles, and all wheels of 4WD vehicles). In the case of the fourth example, the inner end surface of the inner ring 24 that is externally fitted to the small diameter step portion 25 provided at the inner end portion of the hub main body 23c and forms the hub 7e together with the hub main body 23c is used as the inner end surface of the hub main body 23c. It protrudes inward rather than. The outer end surface of a constant velocity joint (not shown) hits the inner end surface of the inner ring 24 in the assembled state in the vehicle, and the inner ring 24 is prevented from falling off the small diameter step portion 25. Other configurations are the same as those of the third example described above.

  In these first to fourth examples, grease is sealed in the internal space 17b, and between the outer ring rolling surfaces 10a and 10b, the inner ring rolling surfaces 21 and 22, and the rolling surface of each ball 14. The rolling contact portion is lubricated.

  In these first to fourth examples, the outer ring 20 that is a stationary side race ring, the hubs 7b to 7e (including the hub body) and the inner race 24 that are rotation side race rings, and the balls 14 that are rolling elements are metal members. In at least one of these members, at least the surface that is in rolling contact is coated with a plant-derived polyhydric alcohol compound described later. Rusting can be suppressed at the place where the treatment is performed and the iron oxide film is formed. As described above, the rolling contact surfaces are the outer ring rolling surfaces 10a and 10b, the inner ring rolling surfaces 21 and 22, and the rolling surfaces of the balls 14, and thus the above-described coating treatment is applied to these surfaces. Is done. In order to suppress rust and seizure, it is preferable that the surface of the cage 15 is also subjected to the coating treatment. Furthermore, in order to suppress the rust generation in the entire interior of the bearing unit, it is most preferable to perform the coating treatment on the entire surface related to the internal space 17b.

  The iron oxide film preferably has a thickness of 0.05 μm to 2 μm. If the film thickness is less than 0.05 μm, rusting cannot be suppressed over a long period of time due to the film peeling off in a short time. When the film thickness exceeds 2 μm, the processing time for film formation becomes too long.

  Members such as a stationary side race ring, a rotation side race ring, a rolling element, and a cage used in the wheel bearing rolling bearing unit of the present invention are made of a well-known bearing metal material. In the present invention, at least one metal member needs to be made of a metal material that can be coated with a plant-derived polyhydric alcohol compound. Specific examples of the bearing ring material include bearing steel (high carbon chromium bearing steel JIS G 4805), case-hardened steel (JIS G4104, etc.), high-speed steel (AMS 6490), stainless steel (JIS G4303), induction-hardened steel. Examples include steel (JIS G4051 etc.) and carbon steel for machine structure (S53C etc.). Examples of cage materials include cold rolled steel plates for punching cages (JIS G 3141, etc.), carbon steel for machined cages (JIS G4051), high strength brass castings for machined cages (JIS H 5102, etc.), and the like. It is done. Other bearing alloys can also be employed. Among these, it is preferable to use carbon steel for machine structure such as S53C which has good forgeability and is inexpensive as a material for the stationary side race ring (outer ring) and the rotation side race ring (hub). The carbon steel is generally used after high-frequency heat treatment to ensure the rolling fatigue strength of the bearing portion.

  The seal member may be made of a metal or a rubber molded body alone, or may be a composite of a rubber molded body and a metal plate, a plastic plate, a ceramic plate, or the like. From the viewpoint of durability and ease of fixing, a composite of a rubber molded body and a metal plate is preferable.

  In the rolling bearing unit for wheel support of the present invention, the coating treatment applied to the surface of the metal member may be a treatment in which an iron oxide coating is formed on the surface by the action of a plant-derived polyhydric alcohol compound, The coating method is not particularly limited. As a coating method, for example, a metal member to be coated is immersed in a treatment liquid in which a plant-derived polyhydric alcohol compound is dispersed or dissolved in water and / or an organic solvent, and an iron oxide coating is formed on the surface of the member. It is possible to adopt a method of forming In this method, it is preferable to carry out heating while accelerating the film formation.

  Further, an iron oxide film is formed on the surface of a metal member to be coated with a treatment liquid in which a plant-derived polyhydric alcohol compound is dispersed or dissolved in water or an organic solvent. You can also.

  Furthermore, the coating treatment may be a treatment applied through grease. That is, a plant-derived polyhydric alcohol compound is blended with grease sealed in the internal space of a wheel bearing rolling bearing unit, and iron oxide is produced by a reaction between the compound in the grease and a metal member during rotation of the bearing unit. A film can also be formed.

  The polyhydric alcohol compound that can be used in the present invention is derived from a plant described later. By applying a coating treatment using these compounds to each member, in addition to suppressing rust generation inside the bearing unit due to the formation of the iron oxide coating, it is possible to improve seizure resistance and to support a wheel with a low environmental load. It becomes a rolling bearing unit.

  Examples of plant-derived polyhydric alcohol compounds that can be used in the present invention include gallic acid, ellagic acid, chlorogenic acid, caffeic acid, quinic acid, curcumin, quercetin, pyrogallol, theaflavin, anthocyanin, rutin, lignan, catechin and the like. It is done. Polyhydric alcohol compounds obtained from plant-derived sesamin, isoflavones, coumarins and the like can also be used. Such polyhydric alcohol compounds may be used alone or in combination of two or more.

  Among these, since it is easy to form an iron oxide film on the surface of a metal member during the coating treatment, gallic acid or a derivative thereof, ellagic acid or a derivative thereof, chlorogenic acid or a derivative thereof, caffeic acid or a derivative thereof, It is preferable to use quinic acid or a derivative thereof, curcumin or a derivative thereof, quercetin or a derivative thereof. Moreover, as shown in the below-mentioned Examples, chlorogenic acid, quinic acid, and gallic acid are particularly preferable, and then caffeic acid and ellagic acid are preferable because the bearing unit after coating is excellent in rust prevention.

Gallic acid used in the present invention is a polyhydric alcohol compound contained in fusinoki, tea leaves, etc., and has a structure represented by the following formula (1). Moreover, the ellagic acid used for this invention is a polyhydric alcohol compound contained in a red raspberry etc., and has a structure shown to following formula (2).

  Derivatives of gallic acid used in the present invention include gallic acid esters such as methyl gallate, ethyl gallate, propyl gallate, butyl gallate, pentyl gallate, hexyl gallate, heptyl gallate, octyl gallate, and gallic acid. Examples thereof include gallates such as bismuth. Moreover, the same derivative can be used also about ellagic acid.

Chlorogenic acid used in the present invention is a polyhydric alcohol compound contained in coffee beans and the like, and has a structure represented by the following formula (3).

Caffeic acid and quinic acid used in the present invention are polyhydric alcohol compounds obtained by hydrolysis of chlorogenic acid. Caffeic acid has a structure represented by the following formula (4), and quinic acid has a structure represented by the following formula (5). .

Curcumin used in the present invention is a polyhydric alcohol compound contained in turmeric and the like, and has a structure represented by the following formula (6).

Quercetin used in the present invention is a polyhydric alcohol compound contained in citrus fruits and has a structure represented by the following formula (7).

  All the polyhydric alcohol compounds used in the following examples used reagents manufactured by Tokyo Chemical Industry Co., Ltd.

Examples 1 to 7
The polyhydric alcohol compound shown in Table 1 was dissolved in an aqueous solution or an organic solvent, adjusted to 0.5 wt%, and used as a treatment liquid. At room temperature (25 ° C), the processing liquid is stirred for 4 hours while the rolling bearing unit for wheel support (material: S53C, SUJ2) is immersed in the processing liquid, and the surface including the inner space surface of the metal member of the bearing unit. An iron oxide film (film thickness: 0.08 μm) was formed on the entire surface. The obtained bearing unit was subjected to the following wet test, and the time required until rust generation was measured. The results are also shown in Table 1.

<Wetting test>
The time (hours, h) until rust is generated on the raceway surface (inner / outer ring rolling surface) of the bearing unit while maintaining the surface-treated bearing unit in a wet state with a temperature of 49 ° C and a relative humidity of 95% or more. investigated.

Comparative Example 1
A wet test was carried out without subjecting the wheel-supporting rolling bearing unit as in Example 1 to surface treatment, and the time required until rust generation was measured. The results are also shown in Table 1.

  As shown in Table 1, Examples 1 to 7 exhibited excellent rust prevention properties in which the time until rust generation in the wet test was 500 hours or more. This is considered to be because the generation of rust due to the iron oxide film formed from a specific polyhydric alcohol compound could be suppressed. In particular, when chlorogenic acid, quinic acid, and gallic acid were used, very excellent rust prevention property of 2000 hours or more was exhibited. On the other hand, in Comparative Example 1, the time until the occurrence of rust was significantly shorter than in Examples 1-7.

Reference Example 1 to Reference Example 7
The polyhydric alcohol compound shown in Table 2 was dissolved in an aqueous solution or an organic solvent, adjusted to 0.5 wt%, and used as a treatment liquid. At room temperature (25 ° C.), 6204 bearings (bearing dimensions: inner diameter 20 mm, outer diameter 47 mm, width 14 mm, material: SUJ2) are immersed in the treatment solution for 4 hours, and the entire surface of the metal member of the rolling bearing is rotated. An iron oxide film was formed on. 0.7 g of grease (Kyodo Yushi Martemp SRL) was sealed in this bearing to obtain a rolling bearing test piece. The obtained rolling bearing test piece was subjected to the high temperature durability test described below, and the bearing life time was measured. The results are also shown in Table 2.

<High temperature durability test>
The rolling bearing test piece was rotated at a rotational speed of 10,000 rpm under a bearing outer ring outer diameter temperature of 150 ° C., a radial load of 67 N, and an axial load of 67 N, and the time (time, h) until seizure was measured as the bearing life time. .

Reference Comparative Example 1
Without applying surface treatment to the metal member, 0.7g of grease (Maltemp SRL manufactured by Kyodo Yushi Co., Ltd.) was sealed in a 6204 bearing (bearing dimensions: inner diameter 20 mm, outer diameter 47 mm, width 14 mm) to obtain a rolling bearing test piece. . The obtained rolling bearing test piece was subjected to the above high temperature durability test, and the bearing life time was measured. The results are also shown in Table 2.

  As shown in Table 2, Reference Examples 1 to 7 exhibited excellent high temperature durability with a lifetime of 120 hours or more in the high temperature durability test. This is considered to be because the iron oxide film formed of a specific polyhydric alcohol compound can suppress the oxidative deterioration of the grease and prevent seizure. On the other hand, in Comparative Example 1, the life was shorter than in Reference Examples 1-7.

  The wheel-supporting rolling bearing unit of the present invention can suppress the generation of rust even when moisture enters the inside, and has excellent seizure resistance, and can withstand long-term use. It can be suitably used as a rolling bearing unit for supporting a wheel that is used for a long period of time under an intruding environment.

DESCRIPTION OF SYMBOLS 1 Wheel 2 Rolling bearing unit for wheel support 3 Axle 4 Axle 5 Inner ring 6 Nut 7 Hub 8 Stud 9 Nut 10 Outer ring rolling surface 11 Mounting flange 12 Drum 13 Inner ring rolling surface 14 Ball 15 Cage 16 Seal ring 17 Internal space 18 Cap 19 Backing plate 20 Outer ring 21 Inner ring rolling surface 22 Inner ring rolling surface 23 Hub body 24 Inner ring 25 Small diameter step part 26 Caulking part 27 Male thread part 28 Nut 29 Spline hole

Claims (4)

Present on stationary surfaces that are supported and fixed to the suspension device in use, rotation-side bearing rings that support and fix the wheels in use, and opposite circumferential surfaces of the stationary-side and rotation-side bearing rings A wheel that includes a plurality of rolling elements provided between the stationary rolling surface and the rotating rolling surface, and that lubricates the surface where the rolling surface and the rolling element are in rolling contact with each other with grease. A rolling bearing unit for support,
The stationary side raceway, the rotation side raceway, and the rolling element are each a metal member, and at least one member of the metal member is derived from a plant on at least the surface of the member that is in rolling contact. Ri member der which provide Reinforced coating process preformed iron oxide film at a polyhydric alcohol compound,
Wheel support, wherein the plant-derived polyhydric alcohol compound is at least one selected from chlorogenic acid, quinic acid, gallic acid, caffeic acid, ellagic acid, curcumin, quercetin, and derivatives thereof Rolling bearing unit for use. The plant-derived polyhydric alcohol compound is at least one selected from the chlorogenic acid, the quinic acid, the gallic acid, the caffeic acid, the ellagic acid, the curcumin, and their derivatives. A rolling bearing unit for supporting a wheel according to claim 1. The coating treatment is a treatment of immersing the metal member to be coated in a treatment solution in which the plant-derived polyhydric alcohol compound is dispersed or dissolved in water and / or an organic solvent. The rolling bearing unit for wheel support according to claim 1 or 2 . Wherein the iron oxide coating is claim 1, claim 2 or claim 3 wheel support rolling bearing unit, wherein the film thickness is 0.05Myuemu～2myuemu.

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