Bearing unit

A bearing unit includes an outer ring member having an outer periphery on which a flange portion is formed, the flange portion being fitted to a vehicle body side; an inner ring member that is rotatably inserted in the outer ring member; and rolling elements in double rows, which are rollably arranged between the outer ring member and the inner ring member, wherein bolts are press-fitted in bolt holes formed in a peripheral edge portion of a wheel fitting flange that is formed on an outer periphery of the inner ring member, and a recessed portion is formed in an outer peripheral surface of the wheel fitting flange.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2012-187574 filed on Aug. 28, 2012 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a bearing unit, and in particular to a bearing unit in which a wheel fitting flange is formed on an outer periphery of an inner ring member.

2. Description of Related Art

Conventionally, various kinds of bearing units for supporting a wheel of a vehicle with respect to a suspension in a vehicle body so that the wheel is rotatable have been proposed. For example, as shown inFIG. 3, such a bearing unit includes an outer ring member2, an inner ring member3and balls4. A flange portion1, which is fitted to a vehicle body side, is formed on an outer periphery of the outer ring member2. The inner ring member3is rotatably inserted in the outer ring member2. The balls4are rolling elements in double rows, which are reliably arranged between the outer ring member2and the inner ring member3. The bearing unit shown inFIG. 3is a bearing unit for an axle on a drive wheel side of a vehicle. The inner ring member3includes a hub spindle5and an inner ring component member6that is a member separate from the hub spindle5. The inner ring component member6is fitted to an outer periphery of a vehicle inner side end portion (left side end portion inFIG. 3) of the hub spindle5. A wheel fitting flange7for fitting a wheel to the bearing unit is formed on an outer periphery of a vehicle outer side end portion of the hub spindle5. Bolt holes8are formed at predetermined intervals in a peripheral edge portion of the wheel fitting flange7. A wheel10and a brake rotor11, which are vehicle side component parts, are fitted to fitting bolts9that are press-fitted in the bolt holes8. The wheel10and the brake rotor11are fastened together by nuts13.

The brake rotor11is combined with a brake system that brakes the rotation of the wheel10so as to decelerate the running vehicle. The brake system brakes the rotation of the wheel10by pressing brake shoes (not shown), which are secured to the vehicle body side, to the brake rotor11so that frictional force is generated. In this case, in order to uniformly generate the frictional force during braking so as to allow the brake system to appropriately exhibit its performance, it is necessary to make clearances between the brake rotor11and the brake shoes uniform. For example, if the clearances are not uniform, the frictional force varies during one revolution of the brake rotor11, and such variation is transmitted in the form of vibration, to the wheel10and the vehicle body. As a result, the phenomenon called brake judder occurs.

The braking judder not only causes the occupants to feel discomfort, but also lowers the braking performance and adversely affects the drivability of the vehicle. Thus, in order to suppress the braking judder, it has been demanded to improve the runout accuracy of the brake rotor11after the brake rotor11is installed in the vehicle.

As a measure for improving the runout accuracy of the brake rotor11, it may be considered to improve the accuracy of the brake rotor11itself. In addition to the above-mentioned measure, there have been measures that are focused on an improvement in flatness of the wheel fitting flange7having a surface to which the brake rotor11is fitted.

The fitting bolts9are fitted in the bolt holes8by interference fit, and an interference is set to approximately 0.1 to 0.5 mm (the interference varies depending upon specifications of the bearing unit). Thus, press-fitting of the fitting bolts9into the bolt holes8may deteriorate the degree of flatness of the surface of the wheel fitting flange7. Specifically, by press-fitting the fitting bolts9in the bolt holes8, a bulging portion12may be formed on a surface7aof the wheel fitting flange7on a side opposite to a surface on which heads9aof the fitting bolts9abut, as exaggeratedly shown inFIG. 4. A bulging height of the bulging portion12may reach a value in a range from 25 to 30 μm. As a result, when the brake rotor11is fitted, a fitted surface of the brake rotor11abuts on the bulging portion12, and accordingly, the runout accuracy of the brake rotor11is lowered. Moreover, as exaggeratedly shown by a long dashed double-short dashed line inFIG. 4, an outer peripheral edge of the wheel fitting flange7may be deformed (warped) toward the above-mentioned fitted surface (toward the wheel). In the case where such deformation occurs in the wheel fitting flange7as well, since the fitted surface of the brake rotor11abuts on a deformed portion14that is deformed as described above, when the brake rotor11is fitted, the runout accuracy of the brake rotor11is lowered.

In order to suppress the lowering of the runout accuracy of the brake rotor11caused by the bulging portion12and the deformed portion14as described above, it has been proposed to remove the bulging portion12and the deformed portion14by performing a turning process. However, the turning process is laborious, and accordingly, the cost for the tuning process is caused. As a result, the cost for producing the bearing unit is increased. Further, a problem regarding the quality of the bearing unit may be caused due to adhesion of chips or the like.

Thus, a method for preventing deformation of the wheel fitting flange7without the necessity of machining the wheel fitting flange7after the fitting bolts9are press-fitted has been proposed (refer to, for example, Japanese Patent Application Publication 2007-232169 (JP 2007-232169 A)). In a bearing unit described in JP 2007-232169 A, recesses are formed by removing material at positions around bolt holes to a predetermined depth, in the wheel fitting flange. Accordingly, when the fitting bolts are press-fitted in the bolt holes, regions around the bolt holes are elastically deformed toward the recesses. Thus, it is described that the deformation of the wheel fitting flange can be prevented.

However, in the method described in JP 2007-232169 A, as shown in FIG. 1 to FIG. 3 in JP 2007-232169, it is necessary to subject the portions around the bolt holes to a fine cutting process that cannot be easily performed, and further, the cost for the cutting process is high. Moreover, in the method described in JP 2007-232169 A, since the recesses are formed, the strength of the wheel fitting flange is lowered.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a bearing unit in which deformation of a wheel fitting flange is suppressed during press-fitting of bolts, by using simple machining, and at low cost.

According to an aspect of the preset invention, there is provided a bearing unit including: an outer ring member having an outer periphery on which a flange portion is formed, the flange portion being fitted to a vehicle body side; an inner ring member that is rotatably inserted in the outer ring member; and rolling elements in double rows, which are rollably arranged between the outer ring member and the inner ring member, wherein bolts are press-fitted in bolt holes formed in a peripheral edge portion of a wheel fitting flange that is formed on an outer periphery of the inner ring member, and a recessed portion is formed in an outer peripheral surface of the wheel fitting flange.

DETAILED DESCRIPTION OF EMBODIMENTS

Detailed description will be hereinafter made as to a bearing unit according to an embodiment of the present invention with reference to the accompanying drawings.FIG. 1is a sectional view for illustrating a bearing unit H according to the embodiment of the present invention.FIG. 2is a sectional view for illustrating a vicinity of a fitting bolt in the bearing unit H shown inFIG. 1. It is to be noted that the bearing unit H shown inFIG. 1andFIG. 2has the same basic structure as that of the bearing unit shown inFIG. 3, and accordingly, the same reference numerals are assigned to constitutional elements of the bearing unit H, which are the same as those shown inFIG. 3.

The bearing unit H is a bearing unit for an axle on a drive wheel side in a vehicle. The bearing unit H includes an outer ring member2, an inner ring member3and balls4. A flange portion1, which is fitted to a vehicle body side, is formed on an outer periphery of the outer ring member2. The inner ring member3is rotatably inserted in the outer ring member2. The balls4are rolling elements in double rows, which are rollably arranged between the outer ring member2and inner ring member3.

The outer ring member2has outer ring raceway surfaces2ain double rows formed in an inner peripheral surface thereof. The inner ring member3has inner ring raceway surfaces3athat are formed in an outer peripheral surface thereof and opposed to the outer ring raceway surfaces2a. The balls4are arranged between the outer ring raceway surfaces2aand the inner ring raceway surfaces3a.

The inner ring member3includes a hub spindle5and an inner ring component member6that is a member separate from the hub spindle5, and that is fitted to an outer periphery of a vehicle inner side end portion (left side end portion inFIG. 1) of the hub spindle5. The hub spindle5is rotatably supported by the outer ring member2through the balls4in double rows.

The balls4are retained at predetermined circumferential intervals on the inner ring raceway surfaces3aby a cage20. Opposite end portions of an annular space defined between the inner ring member3and the outer ring member2are hermetically sealed by seal members21.

A wheel fitting flange7for fitting a wheel to the bearing unit H is formed on an outer periphery of a vehicle outer side end portion of the hub spindle5. Bolt holes8are formed at predetermined intervals in a peripheral edge portion of the wheel fitting flange7. A wheel10and a brake rotor11, which are wheel side component parts, are fitted to fitting bolts9that are press-fitted in the bolt holes8. The wheel10and the brake rotor11are fastened together by nuts13. Further, each of the fitting bolts9has an engagement portion9bin the vicinity of a head9athereof, and the engagement portion9bis formed so as to have a diameter larger than that of each of the bolt holes8. Accordingly, when the fitting bolt9is press-fitted in the corresponding bolt hole8, the engagement portion9bis caught into an inner peripheral surface of this bolt hole8, and thus, it is possible to prevent the fitting bolt9from being rotated together with the corresponding nut13when the nut13is tightened.

The feature of the present invention is that a recessed portion is formed in an outer peripheral surface of the wheel fitting flange7. As shown inFIG. 2, the recessed portion may be a circumferential groove22whose bottom portion has an arc-shaped section (in a plane containing the rotation axis of the bearing unit H). Further, the recessed portion may be a circumferential groove that has a section in another shape, for example, a circumferential groove that has a rectangular section or V-shaped section. Although a depth d of the circumferential groove22is not particularly limited, the depth d may be set to, for example, 1 to 2 mm. The recessed portion may be formed over the entire outer peripheral surface of the wheel fitting flange7, like the circumferential groove22in the embodiment. However, the recessed portion may be formed only in a portion outside each of the bolt holes8in a radial direction of the wheel fitting flange7, in the outer peripheral surface of the wheel fitting flange7.

Since the recessed portion is formed in the outer peripheral surface of the wheel fitting flange7having the peripheral edge portion that has the bolt holes8into which the fitting bolts9are press-fitted, a portion outside each of the bolt holes8can be made thin. Thus, a ridge of material, that is, deformation of the material in a portion around each of the bolt holes8, which is caused by press-fitting the corresponding fitting bolt9in the bolt hole8with a predetermined interference (for example, approximately 0.1 to 0.5 mm), can be absorbed by the thin portion. Thus, it is possible to suppress the formation of the above-mentioned bulging portion12or occurrence of deformation due to the press-fitting of the bolt. The recessed portion in the outer peripheral surface of the wheel fitting flange7can be formed more easily than the recesses in JP 2007-23169 A, and accordingly, the production cost can be reduced.

It is to be noted that the described embodiment is to be considered in all respects only as illustrative and not restrictive. The scope of the present invention should not be limited by the above-mentioned embodiment, and should be defined by the appended claims. All changes that come within the meaning and range of equivalency of the claims are to be embraced within the scope.

For example, although the balls are used as rolling elements in the above-mentioned embodiment, tapered rollers may be used as rolling elements. Further, although the bearing unit is used for the axle on the drive wheel side in the vehicle in the above-mentioned embodiment, the present invention may be applied to a bearing unit for an axle on a driven wheel side.

With the bearing unit according to the present invention, it is possible to suppress deformation of the wheel fitting flange during press-fitting of the fitting bolts, by using simple machining, and at low cost.