JP6167836B2 - Wheel support hub unit - Google Patents

Description

  The present invention relates to an improvement of a hub unit for supporting a wheel used for rotatably supporting a rotating member for braking such as a wheel and a brake disk of an automobile with respect to a suspension device.

  The wheel of the automobile and the rotating member for braking are rotatably supported by the suspension device by the wheel supporting hub unit. Since a large moment is applied to such a wheel support hub unit when the automobile turns, it is necessary to ensure a large moment rigidity in order to ensure stability during turning. For this reason, conventionally, as a wheel support hub unit, a structure in which rolling elements are arranged in a double row, and a preload and a combined contact angle on the back surface are provided to the rolling elements in both rows is generally used. ing. FIG. 3 shows one described in Patent Document 1 as an example of such a wheel support hub unit. The wheel support hub unit 1 includes a hub 2, an outer ring 3, a plurality of first balls 4a and 4a, and a plurality of second balls 4b and 4b.

  The hub 2 is formed by combining a hub body 5 and an inner ring 6. Of these, the hub body 5 is an outer end in the axial direction of the outer peripheral surface (outside with respect to the axial direction means the outside in the width direction of the vehicle when assembled to the automobile, and the left side of each figure. The right side of each figure that is the side is said to be inward with respect to the axial direction, which is the same throughout the present specification and claims.) The mounting flange 7 is located at the near side, and the outer inner ring raceway 8 is also located at the middle in the axial direction. Directly formed. A small-diameter step portion 9 is formed on the outer peripheral surface of the hub body 5 near the inner end in the axial direction. Further, in the outer peripheral surface of the hub main body 5, the portion closer to the inner end in the axial direction of the small-diameter step portion 9 from the inner surface in the axial direction of the portion closer to the base end of the mounting flange 7 (the portion indicated by the oblique grid in FIG. 3) Further, the hub side hardened layer 10 is formed.

  The inner ring 6 has an inner ring raceway 11 formed on the outer peripheral surface. Such an inner ring 6 is externally fixed to the small-diameter step portion 9 by an interference fit, and an axial inner end surface of the inner ring 6 is formed by a caulking portion 12 formed at an axial inner end portion of the hub body 5. It is suppressed. A base end portion of a plurality of studs 13 is fixed to the mounting flange 7, and a braking rotating body such as a disk rotor and a brake drum and a wheel constituting a wheel can be supported and fixed to the mounting flange 7. Like.

  The outer ring 3 is formed with an outer outer ring raceway 14 and an inner outer ring raceway 15 each having a circular cross section (bus shape) at positions spaced apart in the axial direction of the inner peripheral surface. A coupling flange 16 for coupling and fixing the outer ring 3 to a suspension device is provided on the outer peripheral surface of the outer ring 3. Further, in order to ensure the rolling fatigue life of the outer and inner outer ring raceways 14 and 15, the outer outer race 3 has an outer outer race track 14 portion (of the portion indicated by the oblique grid in FIG. 3). An outer hardened layer 17 is formed on the left side portion, and an inner hardened layer 18 is formed on the inner outer ring raceway 15 portion (the right side portion of the portion indicated by the oblique lattice in FIG. 3) by induction hardening. The thickness dimensions of the outer and inner hardened layers 17 and 18 (the dimensions in the curvature radius direction of the outer and inner outer ring raceways 14 and 15) are substantially equal over the entire length.

Each of the first balls 4 a and 4 a is provided between the outer inner ring raceway 8 and the outer outer ring raceway 14 so as to freely roll, and constitutes an outer ball train 19.
Each of the second balls 4 b and 4 b is provided between the inner inner ring raceway 11 and the inner outer ring raceway 15 so as to freely roll, and constitutes an inner ball train 20.
In this state, the outer contact angle θ _o is given to the first balls 4 a and 4 a constituting the outer ball row 19, and the inner contact with the second balls 4 b and 4 b constituting the inner ball row 20. By providing the angle θ _i , a back combination type (DB type) contact angle is given to each of the balls 4a and 4b constituting the outer and inner ball arrays 19 and 20 together with a preload.

By the way, when the vehicle travels, two kinds of shear stresses called so-called dynamic shear stress and static shear stress are generated under the outer layer of the outer ring raceway based on the moment applied to the wheel support hub unit.
Among them, the dynamic shear stress is generated at a shallow position from the surface layer portion of the outer ring raceway, and is a stress having a small absolute value but a large amplitude, which affects the rolling fatigue life.
On the other hand, the static shear stress occurs at a position deeper than the position where the maximum value of the dynamic shear stress (dynamic maximum shear stress) is generated, and is a stress having a large absolute value but a small amplitude. Although it has little effect on the service life, it is known to cause indentation on the outer ring raceway surface.
Conventionally, the load capacity of the wheel supporting hub unit has been set in a region where the dynamic shear stress based on the moment generated during normal driving of the vehicle is dominant over the durability (rolling fatigue life) of the bearing.
On the other hand, in recent years, with the spread of tires with a low flatness ratio, for example, when a wheel support hub unit gets over a hump (step) in a street or a parking lot, the tire is applied to the parking stop of the parking lot or climbs on a curb In some cases, the impact load is often input because the tire rim directly hits the object. Based on this impact load, the maximum value of the static shear stress (static maximum shear stress) is instantaneously generated in the outer layer of the outer ring raceway, which causes indentation. In this way, when an indentation is generated on the outer ring raceway, it not only causes abnormal noise but also may cause separation of the indentation starting point in the bearing.

In the case of the wheel support hub unit 1 as described above, the moment is distributed to the outer ball array 19 and the inner ball array 20 according to the positional relationship between the tire installation point and the wheel support hub unit 1, and each of these ball arrays. 19 and 20 are supported by the first and second balls 4a and 4b.
On the other hand, most of the impact loads are supported by the second balls 4b and 4b constituting the inner ball array 20 because the vertical component is large.
Therefore, in order to improve the durability of the outer outer ring raceway 14, it is sufficient to define the thickness of the outer hardened layer 17 in consideration of the depth at which the dynamic maximum shear stress is generated. In order to improve the durability of the outer ring raceway 15, it is necessary to define the thickness of the inner hardened layer 18 in consideration of the depth at which the static maximum shear stress is generated.
According to Hertz's elastic contact theory, the depth position from the surface layer of the outer ring raceway where the static maximum shear stress occurs is about 1.5 times the depth position where the dynamic maximum shear stress occurs. It is known to be deep.

  However, in the case of the wheel supporting hub unit 1 described in Patent Document 1, the outer and inner hardened layers 17 and 18 are substantially symmetrical with respect to a virtual plane orthogonal to the central axis of the outer ring 3. The thicknesses of the hardened layers 17 and 18 are substantially equal to each other, and the maximum value of each stress generated in the outer and inner outer ring raceways 14 and 15 (dynamic maximum shear stress or static maximum shear). It is not specified in consideration of the depth of stress. In the case of a structure in which the thickness dimension of each of the outer and inner hardened layers is substantially equal over the entire length, it is conceivable that the thickness dimension is defined according to the depth at which the static maximum shear stress is generated. However, in this case, the thickness of the outer hardened layer where static maximum shear stress hardly occurs is unnecessarily large, and it is difficult to secure the thickness of the non-hardened portion existing on the outer diameter side of the outer hardened layer. Become. This non-hardened portion suppresses the outer hardened layer portion that has been transformed into martensite and expanded after induction quenching from the outer diameter side, causes residual compressive stress in the outer hardened layer portion, and causes metal fatigue in the outer hardened layer. It has the role of generating and making it difficult. Therefore, as a result of difficulty in securing the thickness dimension of the non-cured portion, the rolling fatigue life of the outer cured layer portion may be reduced.

  Further, in Patent Document 2, a hardened layer that is continuous in the axial direction is formed on the outer and inner outer ring raceway portions and between the outer and inner outer ring raceways on the inner peripheral surface of the outer ring. An invention related to a wheel supporting hub unit is described. According to such an invention, the compressive force generated in the non-hardened layer portion existing on the outer diameter side of the portion between the outer and inner outer ring raceways is applied to the outer side and inner side of the outer and inner outer ring raceways. By transmitting to the hardened layer, it is possible to ensure the residual compressive stress of the outer and inner hardened layer portions. However, even in such an invention, the thickness of each outer and inner hardened layer is defined according to the depth of the stress (dynamic maximum shear stress or static maximum shear stress) generated in each outer and inner outer ring raceway. Not done.

JP 2005-214229 A JP 2008-64268 A

  In view of the circumstances as described above, the present invention is based on the maximum value of the stress (dynamic maximum shear stress or static maximum shear) generated based on the force or load (moment or impact load) applied to each of the outer and inner outer ring raceways. By defining the thickness dimension of the outer hardened layer and the inner hardened layer based on the depth at which stress is generated, the durability of the outer and inner outer ring raceways can be improved individually and on each track. The invention was invented to realize a wheel support hub unit structure that can be properly achieved.

The wheel support hub unit of the present invention includes an outer ring, a hub, and a plurality of first and second balls.
Among these, the outer ring has an outer outer ring raceway and an inner outer ring raceway, each of which has an arc shape on the inner peripheral surface.
Further, the hub has a mounting flange for supporting and fixing the wheel on the outer peripheral surface of the outer peripheral portion near the outer end in the axial direction, the outer ring race in the middle in the axial direction, and the inner ring race in the inner end in the axial direction. Have each.
Each of the first balls is provided between the outer inner ring raceway and the outer outer ring raceway so as to freely roll, and constitutes an outer ball train.
Each of the second balls is provided between the inner inner ring raceway and the inner outer ring raceway so as to roll freely, and constitutes an inner ball train.
In addition, the outer contact angle θ _o is given to each first ball constituting the outer ball row, and the inner contact angle θ _i is given to each second ball constituting the inner ball row. The contact angle of the back combination type is given to each ball constituting each outer and inner ball row together with the preload.
Further, of the inner peripheral surface of the outer ring, an outer hardened layer continuous in the circumferential direction with the outer outer ring raceway portion, and an inner hardened layer continuous in the circumferential direction with the inner outer ring raceway portion, the outer and inner sides in the axial direction. An intermediate cured layer that is continuous in the circumferential direction is formed between the cured layers in a state of being continuous in the axial direction.

In particular, in the wheel support hub unit of the present invention, the thickness dimension T _i of the inner hardened layer in the inner contact angle θ _i direction is equal to the thickness dimension of the outer hardened layer in the outer contact angle θ _o direction. Greater than T _o (T _i > T _o ).
Moreover, the thickness dimension in the radius direction of curvature of the outer outer ring raceway in the portion corresponding to the range of θ _o ± 10 degrees in the outer hardened layer increases toward the inner side in the axial direction.
Furthermore, the thickness dimension in the radius direction of curvature of the inner outer ring raceway of the portion corresponding to the range of θ _i ± 10 degrees in the inner hardened layer increases as it goes inward in the axial direction of the inner outer ring raceway. .

When the wheel support hub unit of the present invention as described above is implemented, for example, as in the invention described in claim 2, the hub is formed in a hub body and a portion near the inner end in the axial direction of the hub body. And an inner ring that is externally fitted and fixed to the small diameter step portion.
Further, the hub main body is formed by directly forming the mounting flange on the outer peripheral surface near the outer end in the axial direction, and the outer inner ring raceway in the intermediate portion in the axial direction.
Further, a hub-side hardened layer is formed on at least the outer inner ring raceway portion of the outer peripheral surface of the hub body.
Then, the thickness dimension of the inner cured layer in the inner contact angle θ _i direction and the thickness dimension of the outer cured layer in the outer contact angle θ _o direction are set as the outer contact angle θ of the hub-side cured layer. The thickness is larger than the thickness dimension in the _o direction.
Further, when the invention described in claim 2 as described above is carried out, for example, as in the invention described in claim 3, the carbon concentration of the metal material constituting the outer ring is set to the metal constituting the hub body. Make it higher than the carbon concentration of the material.

As described above, in the case of the present invention, the thickness dimension T _i in the inner contact angle θ _i direction of the inner hardened layer formed on the inner outer ring raceway portion is set to the outer contact angle θ _o of the outer hardened layer formed on the outer outer ring raceway portion. It is set to be larger than in the direction of the thickness dimension T _o. Therefore, the durability of the outer outer ring raceway against the dynamic shear stress generated based on the moment during turning is improved, and the inner outer ring raceway against the static shear load generated based on the instantaneous impact load is improved. Durability can be improved.

As described above, the reason why the thickness dimensions of the outer and inner hardened layers formed on the outer and inner outer ring raceway portions are individually defined is as follows.
Since the outer outer ring raceway mainly supports moment during turning, the durability of the outer outer ring raceway (thickness dimension of the outer hardened layer) takes into account the dynamic shear stress generated based on this moment. Is preferably defined. That is, the maximum value of the dynamic shear stress is repeatedly generated at a shallow position from the surface layer portion of the outer outer ring raceway. For this reason, when ensuring the durability against the dynamic shear stress, it is not necessary to increase the thickness of the outer hardened layer so much. In this way, if the thickness dimension of the outer hardened layer is not increased more than necessary, a large non-hardened portion existing radially outward from the outer hardened layer is ensured, and the residual compression of the outer hardened layer portion is ensured. Stress can be secured.

  On the other hand, the inner outer ring raceway mainly supports the impact load applied instantaneously. Therefore, the durability of the inner outer ring raceway (thickness dimension of the inner hardened layer) is a static shear generated based on this impact load. It is preferable to define in consideration of stress. The maximum value of the static shear stress is generated at a position deeper than the maximum value of the dynamic shear stress from the surface layer portion of the inner outer ring raceway. For this reason, when ensuring durability against static shear stress, it is necessary to make the thickness dimension of the inner hardened layer larger than the thickness dimension of the outer hardened layer defined in consideration of dynamic shear stress.

In the present invention, the thickness of the outer hardened layer corresponding to the range of θ _o ± 10 degrees in the radius direction of curvature of the outer outer ring raceway is increased toward the inner side in the axial direction. At the same time, the thickness of the inner hardened layer corresponding to the range of θ _i ± 10 degrees in the radius direction of curvature of the inner outer ring raceway is increased toward the inner side in the axial direction. For this reason, when a large moment load is applied and the contact angle of the outer ball train is displaced in the direction of increasing, or when an impact load is applied and the contact angle of each ball of the inner ball train is displaced in the direction of decreasing. In addition, the thickness dimension of each of the outer and inner hardened layers at the contact angle position after displacement can be appropriately ensured. As a result, it is possible to sufficiently ensure the durability of the outer and inner outer ring raceways without increasing the thickness of the outer and inner hardened layers over the entire length (full width in the axial direction). it can. In addition, since the thickness dimension of the outer and inner hardened layers does not increase, the outer and inner hardened layers are secured on the outer diameter side of the outer and inner hardened layers. It becomes easy to ensure the residual compressive stress of the layer portion.

Sectional drawing of the hub unit for wheel support which shows an example of embodiment of this invention. Similarly, the X section enlarged view of FIG. Sectional drawing of the hub unit for wheel support which shows an example of the conventional structure.

[Example of Embodiment]
1 and 2 show an example of an embodiment of the present invention. The feature of this example is that the structure of the hardened layer 21 (the portion indicated by the oblique lattice in FIGS. 1 and 2) formed on the inner peripheral surface of the outer ring 3a constituting the wheel supporting hub unit 1a is devised. . The structure other than this characteristic portion is substantially the same as the structure of the conventional wheel supporting hub unit 1 shown in FIG. Accordingly, the same reference numerals are given to the equivalent parts, and overlapping explanations are omitted or omitted, and the following description will focus on the characteristic parts of this example.

  In the outer ring 3a constituting the wheel supporting hub unit 1a of the present example, each cross-sectional shape (bus shape) is an arc shape at a position spaced apart in the axial direction of the inner peripheral surface as in the conventional structure described above. An outer outer ring raceway 14a and an inner outer ring raceway 15a are formed. A coupling flange 16 for coupling and fixing the outer ring 3a to a suspension device is provided on the outer peripheral surface of the outer ring 3a.

Further, a hardened layer 21 is formed by induction hardening over the inner peripheral surface of the outer ring 3a from the outer outer ring raceway 14a to the inner outer ring raceway 15a. Such a hardened layer 21 includes an outer hardened layer 17a, an inner hardened layer 18a, and an intermediate hardened layer 22.
Of these, the outer hardened layer 17a is formed over the entire circumference of the outer peripheral raceway 14a portion of the inner peripheral surface of the outer ring 3a. The inner hardened layer 18a is formed over the entire circumference of the inner peripheral surface of the outer ring 3a on the inner outer ring raceway 15a. Further, the intermediate hardened layer 22 is formed by placing the outer and inner hardened layers 17a and 18a between the outer and inner hardened layers 17a and 18a in the axial direction on the inner peripheral surface of the outer ring 3a. It is formed over the entire circumference in a state of being continuous in the axial direction.

In the case of this example as well, the outer contact angle θ _o is given to the first balls 4 a, 4 a constituting the outer ball row 19, and the second balls 4 b, 4 b constituting the inner ball row 20. By applying an inner contact angle θ _i to the ball 4 a, 4 b constituting the outer and inner ball rows 19, 20, a contact angle (initial contact angle) of a rear combination type (DB type) together with a preload. Is granted.

And in this embodiment, the inner contact angle theta _i direction about the thickness T _i of the inner cured layer 18a _(thickness of the position indicated by the chain line alpha ₁ in Fig. 1-2), the outer hardened layer is made larger than the outer contact angle theta _o direction thickness _{T o} of 17a (thickness dimension of the position indicated by the chain line beta ₁ in FIG. _{1~2) (T o <T i} ). As described above, according to Hertz's elastic contact theory, the depth position from the surface layer of the outer ring raceway where the static maximum shear stress based on the impact load is generated is approximately the contact ellipse between the outer ring raceway and the ball. The depth position where the dynamic maximum shear stress based on the moment occurs is 0.6 times the short radius, and the depth position where the outer ring raceway and the ball contact the ellipse is 0.4 times the short radius. The depth position where the static maximum shear stress is generated is approximately 1.5 times deeper than the depth position where the dynamic maximum shear stress is generated. From such a viewpoint, it is preferable that T _i ≈1.5T _o .

In addition, the thickness dimension of the outer outer ring raceway 14a in the radius direction of curvature of the portion corresponding to the range of θ _o ± 10 degrees in the outer hardened layer 17a is increased toward the inner side in the axial direction. That is, the thickness dimension in the radius direction of curvature of the outer outer ring raceway 14a at a portion corresponding to a position of θ _o −10 degrees (position indicated by a one-dot chain line β2 in FIGS. 1 and ₂ ) in the outer hardened layer 17a. If a and T _o2, the portion corresponding to the position of theta _o +10 degrees (the position shown in Figure 1-2 the dashed line beta _3), the thickness dimension about a curvature radius direction of the inner ring raceway 14a and the T _o3 In addition, the relationship of T _o2 <T _o <T _o3 is satisfied.
When the contact angle θ of each ball changes due to an increase in moment, the load supported by each ball is proportional to 1 / cos θ.
Considering that the initial contact angle (inner contact angle θ _i , outer contact angle θ _o ) of the wheel support hub unit is generally 30 to 40 degrees, each of the balls when the contact angle changes by 10 degrees The change in the load supported by the ball is 8-19%, and the size of the contact ellipse (long radius and short radius) is proportional to the 1/3 power of the load supported by the ball as described above. _{considering, T} o _/ T _o2 is in the range of _{1.08~1.12, T} o3 / T _o is in the range of 1.13 to 1.19.

Further, the thickness dimension in the radius direction of curvature of the inner outer ring raceway 15a of the inner hardened layer 18a corresponding to the range of θ _i ± 10 degrees is directed inward in the axial direction of the inner outer ring raceway 15a. It is getting bigger. That is, the thickness dimension of the inner hardened layer 18a in the radius direction of curvature of the inner outer ring raceway 15a at a portion corresponding to a position of θ _i −10 degrees (position indicated by a one-dot chain line α2 in FIGS. 1 and ₂ ). If a and T _i2, the portion corresponding to the position of theta _i +10 degrees (the position shown in Figure 1-2 the dashed line alpha _3), the thickness dimension about a curvature radius direction of the inner ring raceway 15a and the T _i3 In addition, the relationship of T _i3 <T _i <T _i2 is satisfied.
When the contact angle θ of each ball changes due to an increase in radial load, the load supported by each ball is proportional to the third power of cos θ.
The initial contact angle (inner contact angle θ _i , outer contact angle θ _o ) of the wheel supporting hub unit is generally 30 to 40 degrees, and the size of the contact ellipse (long radius and short radius) is T _i2 / T _i is in the range of 1.04 to 1.06, and T _i / T _i3 is in the range of 1.06 to 1.08, considering that the ball is proportional to the 1/3 power of the load supported by the ball. It becomes.
As described above, since the thickness dimension of the outer cured layer 17a and the thickness dimension of the inner cured layer 18a are T _i ≈1.5T _o , the above dimensions are, for example, T _o2 <T _o It is also possible to regulate the relationship such as <T _o3 <T _i3 <T _i <T _i2 .

  In the case of this example, the hub 2a constituting the wheel supporting hub unit 1a is configured by combining the hub main body 5a and the inner ring 6a as in the conventional structure described above. Of these, the hub main body 5a is directly formed with a mounting flange 7a on the outer circumferential surface of the outer peripheral surface near the outer end in the axial direction, and with an outer inner ring raceway 8a on the intermediate portion in the axial direction. A small-diameter step portion 9a is formed on the outer peripheral surface of the hub body 5a near the inner end in the axial direction. Further, in the outer peripheral surface of the hub main body 5a, the hub-side hardened layer 10a (FIGS. 1 and 2) extends from the axially inner surface of the portion near the proximal end of the mounting flange 7a to the axially intermediate portion of the small-diameter step portion 9a. (Parts indicated by diagonal lattices) are formed.

  The inner ring 6a has an inner ring raceway 11a formed on the outer peripheral surface. Such an inner ring 6a is fitted and fixed to the small-diameter step 9a by an interference fit, and an inner end surface in the axial direction of the inner ring 6a is formed by a caulking portion 12a formed at an inner end portion in the axial direction of the hub body 5a. It is suppressed. The inner ring 6a is soaked soaked in quenching oil in a heated state.

And in this embodiment, the inner contact angle theta _i direction thickness T _i of the inner cured layer 18a of the outer ring _3a, and the outer contact angle theta _o direction thickness of the outer hardened layer 17a of the outer ring 3a the T _o, is made larger than the outer contact angle theta _o direction thickness T _h of the hub-side hardened layer 10a. In other words, the thickness dimension _{T i, T o, T h} satisfy _the relation of _{T h <T o <T i} .

Thus, the outer contact angle theta _o direction thickness T _h of the hub-side cured layer 10a, reasons smaller than the thickness T _i, T _o, and is as follows.
The hub body 5a has an advantageous structure for supporting moment and load because the outer inner ring raceway 8a is formed on the outer peripheral surface of a hollow or solid shaft member. Since the portion corresponding to the outer inner ring raceway 8a is thick, it is easy to generate a compressive stress in the outer inner ring raceway 8a. Also the thickness T _h of this result the hub-side hardened layer 10a without so large, easy to secure the durability. Accordingly, it is suppressed to a small thickness dimension T _h about the hub-side hardened layer 10a.
Further, the short radius of the contact ellipse at the contact portion between the outer inner ring raceway 8a and each of the balls 4a, 4a is small, and the depth at which the dynamic maximum shear stress is generated (about 0.4 times the short radius of the contact ellipse). Depth) and the depth at which static maximum shear stress is generated (the depth of about 0.6 times the short radius of the contact ellipse) is shallow, so the thickness dimension of the hub-side hardened layer 10a is made so large. Even if it is not, the durability against both stresses can be ensured.
In this example, the carbon concentration of the metal material constituting the outer ring 3a is set higher than the carbon concentration of the metal material constituting the hub body 5a. Specifically, for example, the hub body 5a is made of carbon steel for machine structure (for example, S53C to S55C), and the outer ring 3a is medium carbon steel (for example, SAE1070 or the like) having a carbon content of 0.6 to 0.7%. ).

If the wheel supporting hub unit 1a of the present embodiment as described above, the inner ring raceway 15a portion formed inner cured layer 18a, the inner contact angle theta _i direction thickness T _i, the outer ring raceway 14a the outer hardened layer 17a formed on the portion, is made larger than the outer contact angle theta _o direction thickness _{T o (T o <T i} ). For this reason, while improving the durability of the outer outer ring raceway 14a against dynamic shear stress generated based on the moment during turning, the inner side against the static shear load generated based on the impact load generated instantaneously. The durability of the outer ring raceway 15a can be improved.

As described above, the reason why the thickness dimensions of the outer and inner hardened layers 17a and 18a formed in the outer and inner outer ring raceways 14a and 15a are individually defined is as follows.
Since the outer outer ring raceway 14a mainly supports a moment during turning, the durability of the outer outer ring raceway 14a (thickness dimension of the outer hardened layer 17a) is the dynamic maximum shear stress generated based on this moment. Is preferably taken into consideration. The maximum value of the dynamic shear stress is repeatedly generated at a shallow position from the surface layer portion of the outer outer ring raceway 15a. For this reason, when ensuring the durability against the dynamic shear stress, it is not necessary to increase the thickness of the outer hardened layer 17a so much. Thus, if the thickness dimension of the outer hardened layer 17a is not increased more than necessary, a large non-hardened portion existing radially outward from the outer hardened layer is secured, and the outer hardened layer portion Residual compressive stress can be secured.

  On the other hand, since the inner outer ring raceway 15a mainly supports an impact load applied instantaneously, the durability of the inner outer ring raceway 15a (thickness dimension of the inner hardened layer 18a) is generated based on the impact load. It is preferable to define in consideration of the maximum value of the static shear stress. The maximum value of the static shear stress is generated at a position deeper than the maximum value of the dynamic shear stress from the surface layer portion of the inner outer ring raceway 15a. For this reason, when ensuring the durability against the static shear stress, the thickness of the inner hardened layer 18a is made larger than the thickness of the outer hardened layer 17a defined in consideration of the dynamic shear stress. There is a need.

In the case of this example, the thickness dimension in the radius direction of curvature of the outer outer ring raceway 14a in the portion corresponding to the range of θ _o ± 10 degrees in the outer hardened layer 17a is increased inward in the axial direction. In addition, the thickness of the inner hardened layer 18a corresponding to the range of θ _i ± 10 degrees in the radial direction of the curvature of the inner outer ring raceway 15a is set inward in the axial direction of the inner outer ring raceway 15a. The bigger it is For this reason, when an impact load is applied, the contact angles of the balls 4a, 4a of the outer ball array 19 are displaced in the direction of increasing, and the contact angles of the balls 4b, 4b of the inner ball array 20 are decreased. Even when displaced, the thicknesses of the outer and inner cured layers 17a and 18a are appropriately regulated by appropriately regulating the thicknesses of the outer and inner cured layers 17a and 18a at the contact angle positions after the displacement. It is possible to sufficiently ensure the durability of each of the outer and inner outer raceways 14a and 15a without increasing the overall length of the outer raceway. As a result, it is possible to secure a large uncured layer portion on the outer diameter side of each of the outer and inner cured layers 17a and 18a, and to ensure a large residual compressive stress in the outer and inner cured layers 17a and 18a.

  In this example, the carbon concentration of the metal material constituting the outer ring 3a is set higher than the carbon concentration of the metal material constituting the hub body 5a. In this way, for example, even when the surface heating temperature at the time of heat treatment is the same heating temperature in the outer ring 3a and the hub body 5a, the outer ring 3a is hardened deeper. Further, the outer ring 3a having a higher carbon concentration has a higher martensite ratio, and the hardness of the outer and inner hardened layers 17a and 18a formed on the outer ring 3a is set to the hub side hardening formed on the hub body 5a. It is easy to make it higher than the hardness of the layer 10a. Furthermore, if a metal material having a large amount of carbon is used, the strength of the metal material is increased and the residual compressive stress can be increased. As a result, the outer and inner hardened layers 17a and 18a can be backed up to prevent internal origin breakage (for example, case crash).

DESCRIPTION OF SYMBOLS 1, 1a Wheel support hub unit 2, 2a Hub 3, 3a Outer ring 4a, 4b Ball 5, 5a Hub main body 6, 6a Inner ring 7, 7a Mounting flange 8, 8a Outer inner ring raceway 9, 9a Small diameter step part 10, 10a Hub Side hardened layer 11, 11a Inner inner ring raceway 12, 12a Caulking portion 13 Stud 14, 14a Outer outer ring raceway 15, 15a Inner outer ring raceway 16 Coupling flange 17, 17a Outer hardened layer 18, 18a Inner hardened layer 19 Outer ball array 20 Inner ball Row 21 Hardened layer 22 Intermediate hardened layer 23 Bottom 24 Axial inner edge 25 Bottom 26 Axial outer edge

Claims (3)

An outer ring having an outer outer ring raceway and an inner outer ring raceway, each of which has an arc shape on the inner peripheral surface;
A hub having a mounting flange for supporting and fixing the wheel on the outer peripheral surface of the outer peripheral surface near the outer end in the axial direction, an inner ring raceway in the middle in the axial direction, and an inner ring raceway in the inner end in the axial direction;
A plurality of first balls constituting an outer ball array, provided to be freely rollable between the outer outer ring raceway and the outer inner ring raceway;
A plurality of second balls constituting an inner ball array, which are provided between the inner outer ring raceway and the inner inner ring raceway so as to roll freely;
The outer contact angle θ _o is given to each first ball constituting the outer ball row, and the inner contact angle θ _i is given to each second ball constituting the inner ball row. A contact angle of the back combination type is given to each ball constituting each inner ball row,
Of the inner peripheral surface of the outer ring, an outer hardened layer is provided on the outer outer ring raceway portion, an inner hardened layer is provided on the inner outer ring raceway portion, and an intermediate hardened layer is provided between the outer and inner hardened layers in the axial direction. In the hub unit for supporting the wheel formed in a continuous state in the axial direction,
Wherein said inner contact angle theta _i direction thickness T _i of the inner hard layer, the larger than the outer contact angle theta _o direction of the outer hardened layer thickness T _o,
Of the outer hardened layer, the thickness dimension of the portion corresponding to the range of θ _o ± 10 degrees in the radius direction of curvature of the outer outer ring raceway is larger toward the inner side in the axial direction,
Of the inner hardened layer, the thickness dimension of the portion corresponding to the range of θ _i ± 10 degrees in the radius direction of curvature of the inner outer ring raceway is larger toward the inner side in the axial direction of the inner outer ring raceway. Wheel support hub unit. The hub is composed of a hub body and an inner ring that is externally fitted and fixed to a small-diameter step portion formed in the axially inner end portion of the hub body,
The hub main body is formed by directly forming the mounting flange at a portion near the outer peripheral end of the outer peripheral surface and the outer ring raceway at the intermediate portion in the axial direction.
Of the outer peripheral surface of the hub body, a hub side hardened layer is formed at least on the outer inner ring raceway portion,
The thickness dimension of the inner contact angle theta _i direction of the inner cured layer, and the thickness dimension of the outer contact angle theta _o direction of the outer hardened layer, the outer contact angle theta _o direction of the hub side cured layer The wheel supporting hub unit according to claim 1, wherein the wheel supporting hub unit is larger than a thickness dimension of the wheel supporting hub unit. The wheel support hub unit according to claim 2, wherein a carbon concentration of a metal material constituting the outer ring is higher than a carbon concentration of a metal material constituting the hub body.

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