JP5105859B2 - 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 in particular, a wheel bearing device that solves the problems of strength, durability, high accuracy, and low cost and extends the life of the bearing. It is about.

  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. In this double row angular contact ball bearing, a plurality of balls are interposed between a fixed ring and a rotating ring, and a predetermined contact angle is given to the balls so as to contact the fixed ring and the rotating ring.

  The wheel bearing device shown in FIG. 3 is a typical example of this. This wheel bearing device includes an inner member 51, an outer member 60, and double rows of balls 70, 70. A constant velocity universal joint 80 is detachably fastened to the inner member 51 in the axial direction. Yes. The inner member 51 includes a hub wheel 52 and a separate inner ring 53. The hub wheel 52 has a wheel mounting flange 54 for mounting the wheel W via the brake rotor R at one end, and the other end. A small-diameter step portion 55 into which the inner ring 53 is press-fitted is formed. Inner rolling surfaces 52 a and 53 a are formed on the outer circumferences of the hub wheel 52 and the inner ring 53. A hub bolt 56 for fixing the wheel W at a circumferentially equidistant position is implanted in the wheel mounting flange 54 of the hub wheel 52.

  The outer member 60 has a vehicle body mounting flange 60b for mounting on the knuckle N on the outer periphery, and double row rolling surfaces 60a, 60a facing the inner rolling surfaces 52a, 53a are formed on the inner periphery. Yes. Between these rolling surfaces 60a, 52a and 60a, 53a, double rows of balls 70, 70 are accommodated so as to roll freely via a retainer 71, and the wheels W are rotatably supported on the vehicle body. In addition, seals 72 and 73 are attached to the end of the outer member 60 to prevent leakage of lubricating grease sealed inside the bearing and prevent rainwater and dust from entering the bearing. is doing.

  The constant velocity universal joint 80 includes an outer joint member 81, an inner ring (not shown), a cage, and a torque transmission ball. The outer joint member 81 integrally includes a cup-shaped mouth portion 82, a shoulder portion 83 that forms the bottom portion of the mouth portion 82, and a shaft portion 84 that extends in the axial direction from the shoulder portion 83. A serration 84a serving as a torque transmission means is provided around the outer periphery. Then, in a state where the end face of the inner ring 53 is abutted against the shoulder 83 of the outer joint member 81, the inner ring 53 is tightened by a fixing nut 85 screwed to the tip of the shaft portion 84, and the inner member 51 and the outer joint member 81 are Is detachably fastened.

Here, of the inner member 51 and the outer member 60, the inner member 51 that rotates with the wheel W during traveling, that is, the carbon steel in which the hub wheel 52 and the inner ring 53 contain carbon 0.60 to 0.80 wt%. The inner rolling surfaces 52a and 53a are formed with a predetermined hardened layer by induction hardening. Thereby, the workability of the inner member 51 is ensured and the rolling fatigue life is improved.
JP 2001-200314 A

  In such a conventional wheel bearing device, a moment load is applied to the inner member 51 via the wheel mounting flange 54 during operation. The inner rolling surfaces 52a and 53a are subjected to a compressive stress from the balls 70 and 70 in addition to the bending stress associated with the moment load, and the bending stress is applied to the inside of the metal material constituting the inner member 51. Together with the tensile stress due to the shear stress, the shear stress due to the compressive stress acts simultaneously. Therefore, it is difficult to ensure sufficient durability unless measures are taken against these tensile stress and shear stress.

  Further, in this type of wheel bearing device, when the vehicle collides with a curb or the like, there is a possibility that indentations may be generated on each rolling surface via the ball 70. This indentation not only generates abnormal noise, but also may not provide a desired rolling fatigue life.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a wheel bearing device that improves impact resistance and extends the life of the bearing.

In order to achieve the object, the invention according to claim 1 of the present invention includes an outer member having a double row outer raceway formed on the inner periphery, and a wheel mounting flange for mounting a wheel on one end. An inner member having an integrally formed hub wheel and having an inner rolling surface facing the outer rolling surface of the double row on the outer periphery, and both rolling of the inner member and the outer member In a wheel bearing device including a double row of rolling element rows accommodated in a freely rolling manner between the faces, a pitch circle diameter of an outer side rolling element row of the double row rolling element rows is an inner side rolling element. A diameter larger than the pitch circle diameter of the moving body row is set, and at least the outer member and the hub wheel are formed of medium-high carbon steel containing carbon of 0.40 to 0.80 wt%, and each rolling surface is a surface. 5 times the hardened layer of the maximum shear stress hardness in the range of 58~64HRC is formed, Furthermore, the child A minimum 2mm is the effective case depth in al cured layer was set at the seventh or the grain size number of austenite crystal grains of the metal structure so as to withstand the load of the corresponding 0.8G when the vehicle turning.

As described above, in the wheel bearing device having the first to fourth generation structures including the double row rolling element rows, the pitch circle diameter of the outer side rolling element row of the double row rolling element rows is set to the inner side rolling element. The diameter is set larger than the pitch circle diameter of the moving body row, and at least the outer member and the hub wheel are formed of medium-high carbon steel containing carbon of 0.40 to 0.80 wt%, and each rolling surface has surface hardness. A hardened layer 5 times the maximum shear stress is formed in the range of 58 to 64 HRC, the effective hardened layer depth in these hardened layers is 2 mm minimum, and the austenite crystal grain size number of the metal structure is set to 7 or more Since it can withstand a load equivalent to 0.8G when turning the vehicle , the bearing space is effectively utilized to increase the bearing rigidity of the outer side portion compared to the inner side, thereby extending the life of the bearing. Bearing member is predetermined Since a predetermined hardened layer by induction hardening or the like to steel is formed, it is possible to further prolong the life of the bearing while ensuring the withstand voltage trace resistance.

  Preferably, as in the invention described in claim 2, the rolling element rows of the double row rolling element rows are the same, and the number of rolling elements of the outer side rolling element row is equal to that of the inner side rolling element row. If the number is set larger than the number of moving bodies, the bearing life can be further ensured while achieving high rigidity.

  Further, as in the invention according to claim 3, the outer member and the hub ring are composed of Si of 0.5 to 1.0 wt%, Mn of 0.1 to 2.0 wt%, and Cr of 0.4 to 0.4. 1.0 wt%, O is contained in 0.003 wt% or less, and the balance is formed of medium and high carbon steel having Fe and inevitable impurities, while ensuring workability and improving hardenability to increase rolling fatigue life. Can be improved.

  Further, as in the invention described in claim 4, if 0.01 to 0.15 wt% of V is added to the outer member and the hub ring, the growth of austenite crystal grains during the heat treatment is suppressed and the fineness is reduced. In addition, carbides with high hardness are formed in the steel, and wear resistance and rolling fatigue life can be improved.

  Further, as in the invention described in claim 5, the inner member integrally has a wheel mounting flange at one end, and one inner rolling surface facing the double row outer rolling surface on the outer periphery. And a hub wheel formed with a small-diameter step portion extending in the axial direction from the inner rolling surface, and the other inner side which is press-fitted into the small-diameter step portion of the hub wheel and faces the outer rolling surface of the double row on the outer periphery. The inner ring is formed with an inner ring formed with a rolling surface, and the inner ring is fixed in the axial direction by a caulking portion formed by plastically deforming an end portion of the small diameter step portion in the radial direction. A mortar-shaped recess is formed at the end on the mounting flange side, and the depth of the recess is at least near the groove bottom of the inner rolling surface of the hub wheel, and the end on the outer side of the hub wheel is If it is formed to have a substantially uniform thickness corresponding to the recess, the rigidity of the device is secured. Together, it is possible to reduce the weight and compact.

The wheel bearing device according to the present invention has an outer member having a double row outer raceway formed on the inner periphery and a hub wheel integrally formed with a wheel mounting flange for mounting the wheel at one end. And an inner member in which an inner rolling surface facing the outer rolling surface of the double row is formed on the outer periphery, and the inner member and the outer member are rotatably accommodated between both rolling surfaces. In the wheel bearing device including the double row rolling element row, the pitch circle diameter of the outer side rolling element row of the double row rolling element row is larger than the pitch circle diameter of the inner side rolling element row. The outer member and the hub wheel are formed of medium-high carbon steel containing carbon of 0.40 to 0.80 wt%, and each rolling surface has a surface hardness in the range of 58 to 64 HRC. 5 times the hardened layer of the maximum shear stress is formed, more effectively cured in the curing layer In minimum 2mm depth, so is set to the seventh or the grain size number of austenite crystal grains of the metal structure in the to withstand the load of the corresponding 0.8G when the vehicle turns, the inner leverage effectively bearing space Compared to the side, the bearing rigidity of the outer side part is increased to extend the life of the bearing, and the bearing member is formed with a predetermined hardened layer by induction hardening etc. on a predetermined steel material, ensuring resistance to pressure marks. In addition, the life of the bearing can be further increased.

A body mounting flange for mounting to the knuckle on the outer periphery is integrated, an outer member with a double row outer raceway formed on the inner periphery, and a wheel mounting flange for mounting the wheel on one end is integrated. A hub wheel having one inner rolling surface facing the outer rolling surface of the double row on the outer periphery, a small diameter step portion extending in the axial direction from the inner rolling surface, and a small diameter of the hub wheel An inner member consisting of an inner ring that is press-fitted into a stepped portion and has the other inner rolling surface facing the outer rolling surface of the double row on the outer periphery, and both rolling of the inner member and the outer member The inner ring is fixed in the axial direction by a caulking portion formed by plastically deforming an end portion of the small-diameter step portion radially outward. In the wheel bearing device according to the present invention, the outer side ball row of the double row ball row is picked up. The circle diameter is set to be larger than the pitch circle diameter of the inner side ball row, the ball diameters of the double row ball row are the same, and the number of balls in the outer side ball row is the same as the inner side ball row. The outer member and the hub ring are made of medium-high carbon steel containing carbon of 0.40 to 0.80 wt%, and each rolling surface is surface hardened by induction hardening. A hardened layer 5 times the maximum shear stress is formed in the range of 58 to 64 HRC, the effective hardened layer depth in these hardened layers is 2 mm minimum, and the austenite crystal grain size number of the metal structure is set to 7 or more As a result, the vehicle can withstand a load equivalent to 0.8G when the vehicle turns.

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 a graph showing the relationship between austenite grain size and impact value. In the following description, the side closer to the outer side of the vehicle in a state assembled to the vehicle is referred to as the outer side (left side in the drawing), and the side closer to the center is referred to as the inner side (right side in the drawing).

  This wheel bearing device is for a driven wheel referred to as a third generation, and is a double row rolling element housed in a freely rollable manner between the inner member 1 and the outer member 2, and both members 1 and 2. (Balls) 3, 3 rows. The inner member 1 includes a hub ring 4 and an inner ring 5 press-fitted into the hub ring 4 through a predetermined shimiro.

  The hub wheel 4 integrally has a wheel mounting flange 6 for mounting a wheel (not shown) at an end portion on the outer side, and has one (outer side) inner rolling surface 4a on the outer periphery and the inner rolling surface. A small-diameter step portion 4b is formed through a shaft-like portion 7 extending in the axial direction from the surface 4a. Hub bolts 6a are implanted in the wheel mounting flange 6 in a circumferentially equal distribution, and circular holes 6b are formed between the hub bolts 6a. The circular hole 6b can not only contribute to weight reduction, but also a fastening jig such as a wrench can be inserted from the circular hole 6b in the assembly / disassembly process of the apparatus, and the work can be simplified.

  The inner ring 5 is formed with the other (inner side) inner raceway surface 5a on the outer periphery and is press-fitted into the small-diameter stepped portion 4b of the hub wheel 4 to form a back-to-back type double row angular contact ball bearing. The end portion of 4b is fixed in the axial direction by a caulking portion 4c formed by plastic deformation. The inner ring 5 and the rolling element 3 are made of high carbon chrome steel such as SUJ2, and are hardened in the range of 58 to 64 HRC to the core part by quenching.

  The hub wheel 4 is made of medium and high carbon steel containing 0.40 to 0.80 wt% of carbon, such as S53C, and the inner raceway surface 4a and the base portion 6c on the inner side of the wheel mounting flange 6 to the small diameter step portion 4b. Thus, a predetermined hardened layer 8 having a surface hardness in the range of 58 to 64 HRC is formed by induction hardening (indicated by cross-hatching in the upper half of the figure). The caulking portion 4c is kept in the surface hardness after forging. Thereby, it has sufficient mechanical strength with respect to the rotational bending load applied to the wheel mounting flange 6, the fretting resistance of the small-diameter step portion 4b serving as the fitting portion of the inner ring 5 is improved, and the minute There is no occurrence of cracks and the like, and the plastic working of the caulking portion 4c can be performed smoothly.

  The outer member 2 integrally has a vehicle body mounting flange 2c to be attached to a knuckle (not shown) on the outer periphery, and the outer side outer rolling facing the inner rolling surface 4a of the hub wheel 4 on the inner periphery. The surface 2a and the inner side outer rolling surface 2b facing the inner rolling surface 5a of the inner ring 5 are integrally formed. Double-row rolling elements 3 and 3 are accommodated between these rolling surfaces and are held by the cages 9 and 10 so as to roll freely. Seals 11 and 12 are attached to the opening of the annular space formed between the outer member 2 and the inner member 1, and leakage of grease sealed inside the bearing and rainwater from the outside. And dust are prevented from entering the bearing.

  The outer member 2 is made of medium and high carbon steel containing 0.40 to 0.80 wt% of carbon such as S53C, and the double row outer rolling surfaces 2a and 2b have a surface hardness in the range of 58 to 64HRC by induction hardening. A predetermined hardened layer 13 is formed (indicated by cross hatching in the upper half of the figure). In addition, although the double row angular contact ball bearing which used the ball for the rolling element 3 was illustrated here, not only this but the double row tapered roller bearing which uses the tapered roller for the rolling element 3 may be sufficient. In addition, the first generation and second generation, or the fourth generation structure may be used instead of the third generation structure on the driven wheel side.

  In the present embodiment, the pitch circle diameter PCDo of the three outer rolling elements is set to be larger than the pitch circle diameter PCDi of the inner three rolling elements. The sizes of the rolling elements 3 and 3 are the same, but due to the difference in the pitch circle diameters PCDo and PCDi, the number of rolling elements in the outer three rolling elements is greater than the number of rolling elements in the inner three rolling elements. There are also many settings. As a result, the bearing space can be effectively utilized to increase the bearing rigidity of the outer side portion compared to the inner side, and the life of the bearing can be extended.

  The outer shape of the hub wheel 4 is that the counter portion 15 from the groove bottom portion of the inner rolling surface 4a, the shaft portion 7 extending in the axial direction from the counter portion 15 via the arc-shaped step portion 7a, and the inner ring 5 protrude. It continues to the small diameter step part 4b through the shoulder part 7b fitted together. Further, a mortar-shaped recess 14 extending in the axial direction is formed at the outer side end of the hub wheel 4. The recess 14 is formed by forging, and the depth thereof is at least up to the vicinity of the groove bottom of the inner side rolling surface 4a on the outer side. The thickness of the outer side of the hub wheel 4 corresponding to the recess 14 Is formed to be substantially uniform.

  On the other hand, in the outer member 2, the outer side outer rolling surface 2a is formed with a larger diameter than the inner side outer rolling surface 2b due to the difference in pitch circle diameters PCDo and PCDi, and the outer side outer rolling surface 2b is formed. A shoulder portion 17 of the outer side rolling surface 2b on the inner side is formed from the running surface 2a via a cylindrical shoulder portion 16 and a tapered step portion 16a.

  In this type of wheel bearing device, the hub wheel 4 and the outer member 2 are usually designed to withstand a load corresponding to 0.8 G (acceleration) when the vehicle is turning. The maximum shear stress is generated at a depth of about 0.4 mm due to the contact with the rolling elements 3 on the rolling surface 4a and the double row outer rolling surfaces 2a, 2b. Therefore, in order to satisfy the desired rolling fatigue life, the hardened layers 8 and 13 at least about five times the maximum shear stress are required, so that the effective hardened layer depth is a minimum of 2 mm. Furthermore, in addition to this minimum depth, it is necessary to consider variations in the hardened layers 8 and 13 due to induction hardening. Accordingly, in order to satisfy the desired rolling fatigue life, the hub wheel 4 and the outer member 2 have at least about five times the maximum shear stress on the inner rolling surface 4a and the double-row outer rolling surfaces 2a, 2b. In addition to the hardened layers 8 and 13, that is, the minimum depth of 2 mm, the effective hardened layer depth is set to 3.5 mm in consideration of variations caused by induction hardening.

  Here, as described above, the hub wheel 4 and the outer member 2 contain C of 0.40 to 0.80 wt%, preferably 0.70 to 0.80 wt%. 0.5 to 1.0 wt%, Mn 0.1 to 2.0 wt%, Cr 0.4 to 1.0 wt%, O 0.003 wt% or less, the balance being Fe and inevitable impurities It is made of medium and high carbon steel. And the hardness of the depth position 0.1mm from the surface of the hardened layers 8 and 13 of each rolling surface is set to Hv670 or more, and the grain size number of the austenite crystal grain of the metal structure in these hardened layers 8 and 13 However, ASTM (American Society for Testing and Materials) grain size number is set to 7 or more.

  In addition, the austenite crystal grain should just be a grain boundary which can give and observe the process which reveals a grain boundary, such as an etching, with respect to the sample of the object member. In addition to the ASTM grain size number, it may be referred to as a prior austenite grain size number. The measurement is carried out by converting the average value of the particle size numbers in the ASTM measurement method and JIS standard (JIS G 0551 steel austenite grain size test method) into an average particle size.

  Thus, in the hardened layers 8 and 13, the hardness and austenite crystal grains are one of the factors that influence the properties of the steel material. The higher the hardness and the finer the austenite crystal grains, the higher the impact value. It is said to be. As shown in FIG. 2, the ASTM grain size 7 has an impact value that is 2.5 times higher than that of 4 even with the same surface hardness.

  In the present embodiment, since the hardness of the portion at a depth of 0.1 mm from the surface of the hardened layer 8, 13 of each rolling surface is set to Hv670 or more, it accompanies the compressive stress applied via each rolling element 3. The amount of elastic deformation of each rolling surface can be suppressed, and the shear stress applied to each rolling surface can be suppressed. Further, since the grain size number of the austenite crystal grains of the metal structure in these hardened layers 8 and 13 is set to 7 or more in the grain size number, the bending stress accompanying the moment load applied through the wheel mounting flange 6, Improves durability against tensile stress, relaxes stress concentration at the grain boundaries of austenite crystals, makes it difficult to open fatigue cracks, improves rolling fatigue life, and increases impact resistance It is possible to increase resistance to pressure marks.

  In the present embodiment, the heating temperature for hot forging is set to a predetermined temperature range in order to reduce the grain size of the austenite crystal. That is, the heating temperature at the time of induction hardening for forming the hardened layers 8 and 13 is set to 900 to 1100 ° C. This is because if the heating temperature exceeds 1100 ° C., the grain size of austenite crystal grains grows and becomes coarse, and if it is less than 900 ° C., the metal structure is not sufficiently softened and the workability is remarkably lowered.

  Mn, Si, Cr, S, and O are added as alloy elements other than C. Among these, Mn is 0.1 to 2 in order to improve the hardenability of the steel and form the predetermined hardened layer described above. 0.0 wt% is added. If it is less than 0.1 wt%, the thickness of the cured layer cannot be sufficiently secured by induction hardening, and if it exceeds 2.0 wt%, the workability is lowered, which is not preferable.

  Si has an effect of improving hardenability and strengthening martensite to improve rolling fatigue life, so 0.5 to 1.0 wt% is added. If it is less than 0.5 wt%, the effect of hardenability is not exhibited, and if it exceeds 1.0 wt%, not only the workability is lowered, but decarburization after forging is increased, which is not preferable.

  Cr, like Si, improves hardenability and strengthens martensite to improve the rolling fatigue life, so 0.4 to 1.0 wt% is added. If it is less than 0.4 wt%, the effect of hardenability is not exhibited, and if it exceeds 1.0 wt%, the workability is lowered, which is not preferable.

Since S forms non-metallic inclusions such as MnS in steel and may become a starting point of peeling in the hardened layer, it is preferably as small as possible, so is regulated to 0.03 wt% or less. Also in O, since non-metallic inclusions such as Al ₂ are formed in steel and adversely affect the rolling fatigue life, it is regulated to 0.003 wt% or less.

  Furthermore, here, an alloying element is added which suppresses the growth of austenite crystal grains and refines them. Specifically, 0.01 to 0.15 wt% of V is added. This V is effective in forming a hard carbide in steel and improving wear resistance and rolling fatigue life. If the V content exceeds 0.15 wt%, the workability decreases, and if it is less than 0.01 wt%, the effect of improving the life is not exhibited. In addition to this V, the same amount of Nb or Ti that acts similarly to V may be added.

  Thus, in this embodiment, the pitch circle diameter PCDo of the three outer rolling elements is set larger than the pitch circle diameter PCDi of the inner three rolling elements, and the pitch circle diameters PCDo, PCDi Due to the difference, the number of rolling elements in the outer three rolling elements is set to be larger than the number of rolling elements in the inner three rolling elements. The bearing rigidity is increased to increase the bearing life in a macro manner, and the bearing member is formed with a predetermined hardened layer by induction hardening or the like on a predetermined steel material. In addition, the life of the bearing can be extended.

  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 first 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 graph which shows the relationship between the crystal grain size of austenite, and an impact value. It is a longitudinal cross-sectional view which shows the conventional wheel bearing apparatus.

Explanation of symbols

1 ... Inner member 2 ... Outer member 3 ... Rolling element 4 ... ······································· Hub Wheels 4a, 5a ········ Inner Rolling Surface 4b ········ Small Step 4c 5 .... Inner ring 6 ... Wheel mounting flange 6a ... Hub bolt 6b ...・ Circular hole 6c ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Base 7 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Shaft-shaped part 7a, 7c ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Stepped part 7b, 16, 17 ...・ Shoulders 8, 13 ... Hardened layer 9, 10, ... Cage 11, 12, ... Seal 14 ...・ Recess 15 ・ ・ ・ ・ ・ ・ Counter 51 ・ ・ ・ ・ ・ ・ Inner member 52 ・ ・ ・ ・ ・ ・.... Hub wheels 52a, 53a ... Inner rolling surface 53 ... Inner ring 54 ... Wheel mounting flange 55 ... ... Small-diameter step 56 ... Hub bolt 60 ... Outer member 60a ... Outer rolling surface 60b ... ··· Body mounting flange 70 ··· Ball 71 ··· Cage 72, 73 ········ Seal 80 ···・ ・ ・ ・ Constant velocity universal joint 81 ・ ・ ・ ・ ・ ・ Outer joint member 82 ・ ・ ・ ・ ・ ・ Mouse part 83 ・ ・ ・ ・ ・ ・ Shoulder part 84 ... Shaft part 84a ... Serration 85 ... Fixing nut N ... Knuckle PCDi ... In -Side rolling element group pitch circle diameter PCDo ... Pitch circle diameter R of outer side rolling element group ... Brake rotor W ... ·····Wheel

Claims (5)

An outer member having a double row outer raceway formed on the inner periphery;
An inner member having a hub wheel integrally formed with a wheel mounting flange for mounting a wheel at one end, and an inner rolling surface facing the outer rolling surface of the double row on the outer periphery;
In the wheel bearing device comprising the inner member and a double row rolling element row that is slidably accommodated between both rolling surfaces of the outer member,
The pitch circle diameter of the outer rolling element row of the double row rolling element rows is set to be larger than the pitch circle diameter of the inner rolling element row, and at least the outer member and the hub ring are made of carbon. It is formed of medium to high carbon steel containing 0.40 to 0.80 wt%, and each of the rolling surfaces has a surface hardness of 58 to 64 HRC and a hardened layer 5 times the maximum shear stress is formed. The effective hardened layer depth at the minimum is 2 mm, and the grain size number of the austenite crystal grains of the metal structure is set to 7 or more so that it can withstand a load equivalent to 0.8 G when turning the vehicle . Bearing device.   The rolling element size of the said rolling element row | line | column of the said double row is the same, The rolling element number of the said outer side rolling element row | line | column is set more than the rolling element number of the said inner side rolling element row | line | column. Wheel bearing device.   The outer member and the hub wheel have a Si content of 0.5 to 1.0 wt%, a Mn content of 0.1 to 2.0 wt%, a Cr content of 0.4 to 1.0 wt%, and an O content of 0.003 wt% or less. The wheel bearing device according to claim 1 or 2, wherein the bearing device is formed of medium-high carbon steel containing Fe and inevitable impurities.   The wheel bearing device according to any one of claims 1 to 3, wherein 0.01 to 0.15 wt% of V is added to the outer member and the hub wheel. The inner member integrally has a wheel mounting flange at one end, one inner rolling surface facing the outer rolling surface of the double row on the outer periphery, and a small diameter extending in the axial direction from the inner rolling surface. A hub ring having a stepped portion and an inner ring press-fitted into a small-diameter stepped portion of the hub ring and having the other inner rolling surface facing the outer rolling surface of the double row on the outer periphery. Is fixed in the axial direction by a caulking portion formed by plastically deforming the end portion of the small-diameter stepped portion in the radial direction, and a mortar-shaped recess is formed at the end of the hub wheel on the wheel mounting flange side. The depth of the recess is at least near the groove bottom of the inner raceway surface of the hub wheel, and the outer end of the hub wheel has a substantially uniform thickness corresponding to the recess. The wheel bearing device according to any one of claims 1 to 4, wherein the wheel bearing device is formed as described above.

Images