JP5314877B2 - Wheel bearing device - Google Patents

Description

  The present invention relates to a wheel bearing device for rotatably supporting a wheel of an automobile or the like, and more particularly to a wheel bearing device with improved sealing performance.

  2. Description of the Related Art Conventionally, a wheel bearing device for supporting a wheel of an automobile or the like is such that a hub wheel for mounting a wheel is rotatably supported via a rolling bearing, and there are a drive wheel and a driven wheel. For structural reasons, an inner ring rotation method is generally used for driving wheels, and an inner ring rotation method and an outer ring rotation method are generally used for driven wheels. As the wheel bearing device, a double-row angular ball bearing having a desired bearing rigidity, exhibiting durability against misalignment, and having a small rotational torque from the viewpoint of improving fuel efficiency is often used. On the other hand, double row tapered roller bearings are used in vehicles such as off-road cars and trucks that have a heavy vehicle body weight.

  Since these wheel bearing devices are arranged at sites where muddy water or the like is likely to be applied, a seal device is mounted, and the space between the outer member and the inner member is sealed. Generally, in a sealing device, a sealing member having a sealing lip is attached to an outer member serving as a stationary member, and the sealing lip is slidably contacted with an outer peripheral surface of the inner member. In particular, in a vehicle that is driven in a poor environment such as an off-road car or a pickup truck, various means for further improving the sealing performance are taken.

  An example of such a wheel bearing device is shown in FIG. The wheel bearing device includes a knuckle 51 fixed to a chassis, an axle 52 extending through the knuckle 51, and fitted around the axle 52, and fastened to a wheel (not shown) via bolts 53. A hub wheel 54, a wheel bearing 55 that is fixed to the knuckle 51 and rotatably supports the hub wheel 54 and the axle 52, and a clutch 56 that is controlled by air pressure to engage and disengage the axle 52 and the hub wheel 54. It has.

  An annular chamber (vacuum chamber) 57 is formed between the knuckle 51 and the axle 52 and communicates with a clutch 56 provided in a sealed chamber 58 on the outer side. Here, when the annular chamber 57 is lower than the atmospheric pressure, the clutch 56 receives a negative pressure and is engaged, but when the annular chamber 57 is at the atmospheric pressure, the clutch 56 is disengaged. The annular chamber 57 communicates with a vacuum pump (not shown) through a vacuum passage 59 extending obliquely through the knuckle 51. The present invention is also applied to a mechanism that electrically implements a similar engagement mechanism.

  The wheel bearing 55 is integrally provided with a vehicle body mounting flange 60b to be attached to the knuckle 51 on the outer periphery, and an outer member 60 in which tapered double-row outer rolling surfaces 60a and 60a are formed on the inner periphery. , Inner rings 61 and 62 each having tapered inner rolling surfaces 61a and 62a facing the outer circumferential surfaces of the double row outer rolling surfaces 60a and 60a, respectively, and the double row cones accommodated between the rolling surfaces. It consists of a double row tapered roller bearing provided with rollers 63, 63 and cages 64, 64 for holding these double rows of tapered rollers 63, 63 in a rollable manner.

  The hub wheel 54 integrally has a wheel mounting flange 65 for mounting a wheel (not shown) at one end, and a cylindrical small-diameter stepped portion 54a extending in the axial direction from the wheel mounting flange 65 is formed on the outer periphery. Yes. The wheel bearing 55 is press-fitted into the small diameter step portion 54 a of the hub wheel 54 and is fixed in the axial direction by a fixing nut 66. A sliding bearing 67 for allowing relative rotation is attached between the axle 52 and the hub wheel 54.

  Seals 68 and 69 are attached to both ends of the wheel bearing 55 to seal the opening of the annular space formed between the outer member 60 and the inner rings 61 and 62, and from the annular chamber 57 and the surrounding environment. Isolated. The seal 68 includes an outer case 70 press-fitted into the outer member 60 and an inner case 71 press-fitted into the inner ring 61. Seal lips 70 a and 71 a are integrally joined to the inner edge of the outer case 70 and the outer edge of the inner case 71, respectively, and are in sliding contact with the inner case 71 and the outer case 70. These seal lips 70 a and 71 a are configured to bend in the presence of a differential pressure between the inside of the wheel bearing 55 and the annular chamber 57 and discharge the inside of the wheel bearing 55 to the annular chamber 57. Therefore, the inside of the wheel bearing 55 receives substantially the same pressure as the annular chamber 57 when the annular chamber 57 is exhausted.

On the other hand, the seal 69 includes an outer case 72 press-fitted into the outer member 60 and an inner case 73 press-fitted into the inner ring 62, as shown in an enlarged view in FIG. A seal lip 72 a slidably contacting the inner case 73 and a side lip 72 b slidably contacting the side surface of the wheel mounting flange 65 are integrally joined to the end portion of the outer case 72. Further, a seal lip 73 a that is in sliding contact with the outer case 72 is integrally joined to the outer edge of the inner case 73. The seal 69 supports a pressure difference so that the inside of the wheel bearing 55 is maintained at a reduced pressure, and further prevents rainwater, dust, and the like from entering the bearing.
Special table 2001-510534 gazette

  In such a conventional wheel bearing device, in particular, in the seal 69 on the hub wheel 54 side, in addition to the seal lips 72a and 73a slidably contacted with the outer case 72 and the inner case 73, which are opposed to each other, the wheel mounting flange 65 is provided. Since the side lip 72b slidably contacted with the side surface is joined to the outer edge of the outer case 72, a strong sealing performance can be obtained. Here, in the configuration in which the side lip 72b is in direct sliding contact with the wheel mounting flange 65, the side lip 72b is worn on the sliding contact surface by turning, and it is difficult to maintain a stable sealing performance for a long period of time. Therefore, in order to improve the sealing performance, it is necessary to set the sliding contact surface to a desired surface roughness by grinding. However, grinding the wheel mounting flange 65 serving as the slidable contact surface increases the number of processing steps and causes an increase in cost.

  This invention is made | formed in view of such a situation, and aims at the improvement of the sealing performance of a seal | sticker, and it aims at providing the wheel bearing apparatus which can maintain bearing performance over a long period of time. .

In order to achieve such an object, the invention according to claim 1 of the present invention has a vehicle body mounting flange integrally attached to the suspension on the outer periphery, and a double row outer rolling surface integrally on the inner periphery. A formed outer member and a hub wheel integrally having a wheel mounting flange for mounting a wheel at one end and a small-diameter stepped portion formed on the outer periphery, and an inner ring or a constant speed fitted to the hub ring An inner member comprising an outer joint member of a universal joint and having a double-row inner rolling surface facing the double-row outer rolling surface on the outer periphery, and both the inner member and the outer member. A double-row rolling element accommodated between the running surfaces via a cage, and a seal attached to an opening in an annular space formed between the outer member and the inner member. In the wheel bearing device provided, a back is provided on the outer side of the outer seal among the seals. The back seal is provided with a side lip formed in a trumpet shape that extends in a radially outwardly inclined manner and has a tip that expands in diameter, and the side lip is formed on the wheel mounting flange. The annular projecting surface formed on the side surface on the inner side is slidably contacted , and the projecting surface is formed into a flat surface perpendicular to the rotation axis by grinding .

Thus, in the wheel bearing device including the seal mounted on the opening of the annular space formed by the outer member and the inner member, the backup seal is provided on the outer side of the outer seal among the seals. The back-up seal is integrally extended with a trumpet-shaped side lip that extends radially outwardly and has a tip that expands in diameter, and the side lip is formed on the inner side of the wheel mounting flange. Since the projecting surface is formed into a flat surface perpendicular to the rotation axis by grinding, the processing of the lip sliding surface is within the minimum necessary range. In addition to being limited, the processing itself is facilitated, and the number of processing steps can be reduced to reduce the cost. In addition, even if rainwater or muddy water is applied, it flows downward along the side lip, and rainwater or muddy water does not stay in the lip sliding contact area, and the base of the wheel mounting flange rusts and is strong and durable. A wheel bearing device capable of suppressing the reduction of the rotational speed of the backup seal, suppressing the rotational torque of the backup seal, improving the sealing performance of the seal, and maintaining the bearing performance over a long period of time. Can be provided.

  Preferably, as in the invention described in claim 2, if the protruding surface is hardened by induction hardening in a range of 50 to 64 HRC, the protruding surface is prevented from being worn and the sealing performance is improved. Can be made.

  Further, as in the invention described in claim 3, if the surface roughness of the projecting surface is regulated to 0.8 Ra or less by grinding, it is possible to suppress side lip wear and improve sealing performance. it can.

  Further, as in the invention described in claim 4, if the grinding is performed by the plunge cut method, no lead eyes are generated, and a pumping action is generated by sliding contact so that foreign matter does not enter and is sealed. Can be improved.

  Further, as in the invention described in claim 5, if a low friction coating made of low friction synthetic resin or ceramic is formed on the projecting surface, the sliding resistance without reducing the contact pressure of the side lip. Becomes smaller and the rotational torque becomes smaller. Further, the lip wear is further reduced by the low friction between the protruding surface and the side lip, and the heat generation at the lip sliding portion is suppressed, so that the durability of the backup seal is improved.

A wheel bearing device according to the present invention has an outer member integrally formed with a vehicle body mounting flange for mounting to a suspension device on the outer periphery, and an outer member formed integrally with a double row outer rolling surface on the inner periphery, and one end A hub ring integrally having a wheel mounting flange for mounting a wheel on the part, and a outer ring member of an inner ring or a constant velocity universal joint fitted to the hub ring, and a small-diameter stepped portion formed on the outer periphery, An inner member in which a double row inner rolling surface facing the outer rolling surface of the double row is formed on the outer periphery, and a cage is provided between both rolling surfaces of the inner member and the outer member. In a wheel bearing device comprising: a double row of rolling elements housed so as to be freely rollable; and a seal attached to an opening of an annular space formed between the outer member and the inner member; A backup seal is provided on the outer side of the outer seal. The backup seal integrally has a side lip formed in a trumpet shape that extends in a radially outward direction and has a tip that expands in diameter, and this side lip is formed on the inner side surface of the wheel mounting flange. Since the protruding surface is formed into a flat surface perpendicular to the rotation axis by grinding, the processing of the lip sliding surface is limited to the minimum necessary range, and the processing itself Not only becomes easy, but also the number of processing steps can be reduced and the cost can be reduced. In addition, even if rainwater or muddy water is applied, it flows downward along the side lip, and rainwater or muddy water does not stay in the lip sliding contact area, and the base of the wheel mounting flange rusts and is strong and durable. A wheel bearing device capable of suppressing the reduction of the rotational speed of the backup seal, suppressing the rotational torque of the backup seal, improving the sealing performance of the seal, and maintaining the bearing performance over a long period of time. Can be provided.

  A hub wheel having a wheel mounting flange for mounting a wheel at one end and a small diameter step portion extending in the axial direction from the wheel mounting flange is formed on the outer periphery, and the hub wheel is press-fitted into the small diameter step portion of the hub wheel. An outer member comprising a wheel bearing, the wheel bearing integrally including a vehicle body mounting flange to be attached to the suspension device on the outer periphery, and a double row outer rolling surface formed on the inner periphery; A pair of inner races formed on the outer periphery with an inner raceway facing the outer raceway of the double row, and a double row rolling element housed between the raceways via a cage between the raceways. A caulking portion that is formed by plastically deforming an end portion of the small-diameter step portion radially outward, including a seal attached to an opening portion of an annular space formed between the outer member and the inner ring. In the wheel bearing device, the inner ring is axially fixed to the hub ring by A side lip formed in a trumpet shape in which a backup seal is disposed on the outer side of the seal on the outer side of the seal, and this backup seal extends while inclining radially outward and the tip portion expands in diameter. The side lip is slidably contacted with an annular protruding surface formed on the inner side surface of the wheel mounting flange, and the protruding surface has a surface hardness of 50 to 64 HRC by induction hardening. The surface roughness is regulated to 0.8 Ra or less by grinding by plunge cutting.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing an embodiment of a wheel bearing device according to the present invention, and FIG. 2 is an enlarged view of a main part of FIG. In the following description, the side closer to the outer side of the vehicle when assembled to the vehicle is referred to as the outer side (left side in FIG. 1), and the side closer to the center is referred to as the inner side (right side in FIG. 1).

  This wheel bearing device is for a drive wheel called a second generation, and is composed of a hub wheel 1 and a wheel bearing 2, and the wheel bearing 2 is composed of an outer member 3, a double row rolling element ( A pair of inner rings 5 and 5 that are fitted through tapered rollers 4 and 4.

  The hub wheel 1 integrally has a wheel mounting flange 6 for mounting a wheel (not shown) at one end portion, and a small-diameter step portion 1b extending in the axial direction from the wheel mounting flange 6 to the outer periphery via a shoulder portion 1a. A serration (or spline) 1c for torque transmission is formed on the inner periphery. Hub bolts 6a are planted on the wheel mounting flange 6 at equal intervals in the circumferential direction. The wheel bearing 2 is formed by being press-fitted into the small-diameter step portion 1b through a predetermined shimiro until it abuts against the shoulder portion 1a of the hub wheel 1, and the end of the small-diameter step portion 1b is plastically deformed radially outward. It is fixed to the hub wheel 1 in the axial direction in a state where a predetermined bearing preload is applied by the crimped portion 1d.

  The hub wheel 1 is made of medium and high carbon steel containing 0.40 to 0.80 wt% of carbon such as S53C, and has a small diameter step from a base portion 6b formed in an arc shape on the inner side of the wheel mounting flange 6 via a shoulder portion 1a. The surface hardness is hardened to a range of 58 to 64 HRC by induction hardening over the portion 1b. Thereby, it has sufficient mechanical strength with respect to the rotational bending load applied to the wheel mounting flange 6, and the fretting resistance of the small-diameter step portion 1 b that becomes the fitting portion of the inner rings 5, 5 is improved.

  The outer member 3 of the wheel bearing 2 has a vehicle body mounting flange 3b integrally attached to a knuckle (not shown) on the outer periphery, and the outer side of the tapered double row that opens outward on the inner periphery. The rolling surfaces 3a and 3a are integrally formed. This outer member 3 is made of medium and high carbon steel containing 0.40 to 0.80 wt% of carbon such as S53C, and at least the double row outer rolling surfaces 3a and 3a have a surface hardness of 58 to 64 HRC by induction hardening. Hardened to range.

  On the other hand, on the outer periphery of the inner ring 5, the tapered inner rolling surface 5a facing the double row outer rolling surfaces 3a, 3a and the rolling element 4 are guided to the larger diameter side of the inner rolling surface 5a. A large collar 5b and a small collar 5c for preventing the rolling element 4 from falling off are formed on the small diameter side. The inner ring 5 and the rolling element 4 are made of high carbon chrome steel such as SUJ2, and are hardened in the range of 58 to 64 HRC up to the core part by quenching. And the double-row rolling elements 4 and 4 are accommodated between both rolling surfaces of the outer member 3 and a pair of inner ring | wheels 5 and 5, and are hold | maintained by the holder | retainers 7 and 7 so that rolling is possible. The wheel bearing 2 is constituted by a so-called back-to-back type double row tapered roller bearing in which the small ribs 5c of the inner ring 5 abut each other in a butted state.

  Further, seals 8 and 8 are attached to an opening of an annular space formed between the outer member 3 and the inner ring 5. These seals 8 and 8 prevent the grease sealed inside the bearing from leaking to the outside and preventing rainwater, dust, etc. from entering the bearing from the outside. As shown in FIG. 2 in an enlarged manner, the seal 8 constitutes a so-called pack seal comprising an annular seal plate 9 and a slinger 10 which are substantially L-shaped in cross section and arranged to face each other.

  The seal plate 9 includes a metal core 11 that is press-fitted into the inner periphery of the end of the outer member 3, and a seal member 12 that is integrally vulcanized and bonded to the metal core 11. The core 11 has a substantially L-shaped cross section by pressing from an austenitic stainless steel plate (JIS standard SUS304 type or the like) or a rust-proof cold rolled steel plate (JIS standard SPCC type or the like). Is formed. The seal member 12 is made of an elastic member such as synthetic rubber, and integrally includes a pair of side lips 12a and 12b and a radial lip 12c.

  On the other hand, the slinger 10 has a substantially L-shaped cross section by pressing from an austenitic stainless steel plate (JIS standard SUS304 type or the like) or a rust-proof cold rolled steel plate (JIS standard SPCC type or the like). The cylindrical portion 10a is press-fitted into the large collar 5b of the inner ring 5, and the upright plate portion 10b extends radially outward from the cylindrical portion 10a. The pair of side lips 12a and 12b are in sliding contact with the upright plate portion 10b, and the radial lip 12c is in sliding contact with the cylindrical portion 10a.

  In the present embodiment, a backup seal 13 is further disposed on the outer side of the outer seal 8. The backup seal 13 includes a metal core 14 that is press-fitted and fixed to the outer periphery of the outer end of the outer member 3, and a seal member 15 that is integrally vulcanized and bonded to the metal core 14. The core 14 has a substantially L-shaped cross section by pressing from an austenitic stainless steel plate (JIS standard SUS304, etc.) or a rust-proof cold rolled steel plate (JIS standard SPCC, etc.). Is formed.

  On the other hand, the seal member 15 includes a fixing portion 15a fixed to the outer edge of the core metal 14, and a side lip formed in a trumpet shape that extends from the fixing portion 15a so as to incline radially outward and whose tip portion has a diameter increased. 15b. The side lip 15b is in sliding contact with an annular projecting surface 16 formed on the inner side surface 6c of the wheel mounting flange 6, and prevents rainwater, dust, and the like from directly entering the outer side seal 8.

  In this way, a separate backup seal 13 is disposed on the outer side of the outer seal 8 attached to the wheel bearing 2, and the backup seal 13 is composed of a side lip 15b. Even if rainwater, muddy water, or the like is applied, it flows downward along the side lip 15b, and rainwater, muddy water, etc. do not stay in the narrow annular space between the hub wheel 1 and the wheel bearing 2. Therefore, the base 6b of the wheel mounting flange 6 can be prevented from rusting and the strength / durability is reduced, and the rotational torque of the backup seal 13 can be suppressed, and the sealing can be stably performed over a long period of time. Sex can be secured.

  Here, the annular projecting surface 16 is hardened by induction hardening after turning to a range of 50 to 64 HRC, and then set to a predetermined surface roughness by grinding. The grinding process is performed by a plunge cut method without a lead, and is considered from the viewpoint of wear and sealing performance of the side lip 15b, and the surface roughness of the protruding surface 16 is regulated to 0.8 Ra or less. Thereby, a sealing effect can be improved without causing a pumping action due to sliding contact and entering foreign matter. Here, Ra is one of the JIS roughness shape parameters (JIS B0601-1994), which means the arithmetic average roughness, which means the average value of the absolute value deviation from the average line.

  In the present embodiment, the projecting surface 16 serving as the slidable contact surface of the side lip 15b projects from the inner side surface 6c of the wheel mounting flange 6 and is formed in an annular shape, and therefore requires hardening processing and grinding by induction hardening. It is limited to the minimum range, and not only the processing itself becomes easy, but also the processing man-hours can be reduced and the cost can be reduced.

  The protruding surface 16 may be subjected to a low friction process. Examples of the low-friction treatment include polyamides such as PA (polyamide) 6 and PA12, low-friction synthetic resins such as polytetrafluoroethylene and polyethylene, DLC (diamond-like carbon) films, ceramic coatings, and the like. As a result, the sliding resistance is reduced without reducing the contact pressure of the side lip 15b, and the rotational torque is reduced. Furthermore, the lip wear is further reduced by the low friction between the projecting surface 16 and the side lip 15b, and the heat generation at the lip sliding portion is suppressed, and the durability of the backup seal 13 is improved.

  In addition, although the 2nd generation structure by the side of a drive wheel was illustrated here, the wheel bearing apparatus which concerns on this invention is not restricted to this, A 3rd or 4th generation structure may be sufficient. Moreover, the driven wheel side may be sufficient. Furthermore, in this embodiment, the double row tapered roller bearing using the tapered roller as the rolling element 4 is exemplified, but it is needless to say that the double row angular contact ball bearing using a ball as the rolling element may be used.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  The wheel bearing device according to the present invention can be applied to a wheel bearing device having a second to fourth generation structure regardless of whether it is for driving wheels or driven wheels.

It is a longitudinal section showing one embodiment of a wheel bearing device concerning the present invention. It is a principal part enlarged view of FIG. It is a longitudinal cross-sectional view which shows the conventional wheel bearing apparatus. It is a principal part enlarged view of FIG.

Explanation of symbols

1 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Hub wheel 1a ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Shoulder 1b ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・... Small diameter step 1c ... Serration 1d ... Casting part 2 ...・ ・ ・ ・ ・ ・ ・ ・ ・ Bearing bearing 3 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Outside member 3a ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Outward rolling Running surface 3b ······ Body mounting flange 4 ············ Rolling element 5 .... Inner ring 5a ... Inner rolling surface 5b ...・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Small 6 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Wheel mounting flange 6a ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・Hub bolt 6b ... Base 6c ... Side 7 on the inner side ...・ ・ ・ ・ ・ Cage 8 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Seal 9 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Seal plate 10 ・ ・ ・······· Slinger 10a ··························································・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Core metal 12, 15 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Seal members 12a, 12b, 15b ・ ・ ・ ・ ・ ・ Side lip 12c ・ ・ ・ ・ ・ ・... Radial lip 13 ... Backup seal 15a ... Fixing part 16 ...・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Projection surface 51 ・ ・ ・ ・ ・.... Knuckle 52 ... Axle 53 ... Bolt 54 ... ... hub wheel 54a ... small diameter step 55 ... wheel bearing 56 ............ Clutch 57 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ annular chamber 58 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・Sealed chamber 59 ... vacuum passage 60 ... outer member 60a ... ··· Outer rolling surface 60b ··················· Body mounting flanges 61 and 62・ ・ ・ ・ ・ Inner rolling surface 63 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Conical roller 64 ・ ・... Cage 65 ... Wheel mounting flange 66 ... Fixing nut 67 ... Slide bearing 68, 69 ... Seal 70, 72 ...・ Outer case 70a, 71a, 72a, 73a..Seal lip 71, 73 ........ Inner case 72b ........ Side lip

Claims (5)

An outer member integrally having a vehicle body mounting flange to be attached to the suspension device on the outer periphery, and an outer rolling surface of a double row integrally formed on the inner periphery;
It consists of a hub wheel that has a wheel mounting flange for mounting a wheel at one end and a small-diameter step on the outer periphery, and an outer ring member of an inner ring or constant velocity universal joint that is fitted to this hub ring. An inner member in which a double row inner rolling surface facing the double row outer rolling surface is formed on the outer periphery;
A double row rolling element housed between the rolling surfaces of the inner member and the outer member so as to be freely rollable via a cage;
In a wheel bearing device comprising a seal mounted in an opening of an annular space formed between the outer member and the inner member,
A backup seal is disposed on the outer side of the seal on the outer side of the seal, and this backup seal has a side lip formed in a trumpet shape that extends in a radially outward direction and whose tip portion expands in diameter. The side lip is in sliding contact with an annular projecting surface formed on the inner side surface of the wheel mounting flange, and the projecting surface is formed on a flat surface perpendicular to the rotation axis by grinding. A wheel bearing device characterized by comprising:   2. The wheel bearing device according to claim 1, wherein the protruding surface is hardened by induction hardening in a range of 50 to 64 HRC.   The wheel bearing device according to claim 1 or 2, wherein the projecting surface is regulated to a surface roughness of 0.8Ra or less by grinding.   The wheel bearing device according to claim 3, wherein the grinding is performed by a plunge cut method.   The wheel bearing device according to any one of claims 1 to 4, wherein a low-friction film made of low-friction synthetic resin or ceramic is formed on the protruding surface.

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