JP2014151703A - Wheel bearing device, and manufacturing method of wheel bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wheel bearing device in which heat treatment of an inner shaft whose inner peripheral surface is formed with a gear can be carried out adequately, and strength degradation and lifetime deterioration can be suppressed as the whole device.SOLUTION: A wheel bearing device comprises an inner shaft 2 formed with a small diameter part 6 to which an inner wheel member is externally fitted. On an inner peripheral surface of the inner shaft 2, a gear 10 is formed. A difference between a radius of an outer peripheral surface 6a of the small diameter part 6 in the inner shaft 2 and the outmost radius of a group of the tooth bottoms 10a of the gear 10 formed on the inner peripheral surface of the inner shaft 2 is set to 2.5 mm or more. On the outer peripheral surface 6a and the gear 10, hardened layers L2, L3 are formed by induction hardening. An unhardened layer is provided between the second hardened layer L2 formed on the outer peripheral surface 6a of the inner shaft 2 and the third hardened layer L3 formed on the gear 10, to secure fracture toughness of the inner shaft 2.

Description

  The present invention relates to a wheel bearing device for supporting a wheel of a vehicle, and more particularly to a wheel bearing device used for an in-wheel motor and a manufacturing method thereof.

  Wheel bearing devices for supporting wheels are used in vehicles such as automobiles. As shown in FIG. 6, the wheel bearing device includes an inner shaft 101 having a flange 100 to which a vehicle brake rotor and wheels are attached, an outer ring 102 fixed to the vehicle side and disposed concentrically with the inner shaft 101, What is provided with a plurality of balls 103 arranged in a double row between the inner shaft 101 and the outer ring 102 so as to freely roll, and a cage 104 that holds the plurality of balls 103 at a predetermined interval in the circumferential direction. is there.

  An inner ring raceway 101 a on which the balls 103 roll is formed on the outer peripheral surface of the inner shaft 101. A small-diameter portion 106 to which the inner ring member 105 is fitted is formed on the outer peripheral surface of the inner shaft. In the inner ring raceway 101 a, wear occurs due to rolling of the balls 103, and in the small diameter portion 6, a load acts repeatedly through the balls 103. For this reason, a hardened layer is formed on the inner ring raceway 101a and the small-diameter portion 106 by induction hardening in order to increase wear resistance and fatigue strength (see, for example, Patent Document 1).

JP 2005-214229 A

By the way, in recent years, the spread of electric vehicles using an electric motor as a drive source is expanding. In such an electric vehicle, an in-wheel motor that directly drives a wheel (wheel) may be used.
An in-wheel motor has an electric motor disposed inside or in the vicinity of the wheel, and the wheel is directly driven by the electric motor. The wheel bearing device is also applied to a wheel driven by an in-wheel motor.

In-wheel motors include a direct drive system that transmits the rotational force of the electric motor to the wheel without using a reduction mechanism, and a gear reduction system that transmits the rotational force of the electric motor to the wheel through a reduction mechanism.
Among these, in the gear reduction method, it is necessary to arrange a speed reduction mechanism in a limited narrow space between the electric motor and the wheel. For this reason, the planetary gear mechanism including the sun gear connected to the output shaft of the electric motor may be provided on the inner peripheral side of the inner shaft of the wheel bearing device.
In this case, an internal gear that meshes with the planetary gear disposed in the inner peripheral space of the inner shaft is formed on the inner peripheral surface of the inner shaft. The internal gear needs to be induction-hardened to ensure its strength.

  However, the outer diameter of the inner shaft is limited because the outer ring is disposed on the outer peripheral side or the inner ring raceway is formed on the outer peripheral surface thereof. Therefore, when the internal gear is formed on the inner peripheral surface, it is difficult to freely set the radial thickness dimension of the inner shaft, for example, it is necessary to set the radial thickness dimension of the inner shaft to be thin.

When the radial dimension of the inner shaft is set to be relatively thin, the diffusion path of the applied heat can be achieved by simultaneously quenching the outer peripheral surface and the inner gear on the inner peripheral surface by induction hardening. Is limited, and heat remains in the heated portion. For this reason, there exists a possibility that an inner shaft may be hardened over the whole area of a thickness direction, and may harden | cure. If it is cured over the entire region in the thickness direction, the toughness of the entire inner shaft is lowered, and the impact resistance is lowered.
On the other hand, if the quenching of the outer peripheral surface and the quenching of the inner gear of the inner peripheral surface are performed separately, the heat retention is improved, but the hardened layer obtained by performing the quenching first is the There is a possibility that the hardness of the hardened layer of the portion that has been tempered by heating and previously quenched is reduced. In this case, the necessary hardness may not be obtained for the tempered cured layer.

As described above, when the toughness of the inner shaft is reduced, the strength of the entire bearing device is reduced. Further, if the required hardness of the hardened layer is not obtained, the life of the bearing device is reduced.
That is, it is difficult to appropriately heat-treat the inner shaft on which the gear is formed on the inner peripheral surface, and if the heat treatment is not properly performed, the strength and life of the entire apparatus are reduced.

  This invention is made | formed in view of such a situation, can heat-process the inner shaft in which the gearwheel is formed in the internal peripheral surface appropriately, and can suppress the intensity | strength fall and lifetime fall as the whole apparatus. It aims at providing the manufacturing method of the bearing device for wheels, and the bearing device for wheels.

  The present invention includes a cylindrical inner shaft to which a wheel is attached at one end in the axial direction, an outer ring concentrically arranged on the outer periphery of the inner shaft in a state where a double row rolling element is interposed, and the double row rolling. A wheel bearing comprising: an inner ring member formed on an outer periphery of a raceway of a row of rolling elements located on the other axial end side of the moving body and externally fitted to the outer peripheral surface of the other end portion of the inner shaft. In the device, an inner gear is formed on an inner peripheral surface of the inner shaft, and a radius of the outer peripheral surface of the other end portion of the inner shaft on which the inner ring member is fitted and formed on an inner peripheral surface of the inner shaft. The difference from the outermost radius of the tooth bottom of the inner gear being set is 2.5 mm or more, the outer peripheral surface of the other end of the inner shaft on which the inner ring member is fitted, and the inner periphery of the inner shaft A hardened layer is formed on the internal gear formed on the surface by induction hardening, a hardened layer formed on the outer peripheral surface of the other end of the inner shaft, and Between the serial inner teeth bottom formed cured layer of the gear, is characterized in that uncured layer for securing the toughness of the inner shaft.

In the wheel bearing device having the above-described configuration, the inner shaft is secured between the hardened layer formed on the outer peripheral surface of the other end portion of the inner shaft and the hardened layer formed on the tooth bottom of the internal gear. An uncured layer is provided. For this reason, the fall of the toughness of an inner shaft can be suppressed.
Moreover, in the said wheel bearing apparatus, hardening is performed so that an unhardened layer exists between the hardened layer of the other end part outer peripheral surface of an inner shaft, and the hardened layer of the bottom of an internal gear. Therefore, it is suppressed that the influence of the heating by quenching at the time of forming the hardened layer on the one peripheral surface side reaches the hardened layer on the other peripheral surface side. As a result, the required surface hardness can be ensured in both cured layers.
As described above, according to the present invention, the inner shaft can be appropriately heat-treated. As a result, it is possible to suppress a decrease in the toughness of the inner shaft and ensure the necessary surface hardness, and it is possible to suppress a decrease in strength and a decrease in life of the entire apparatus.

  According to the wheel bearing device of the present invention, it is possible to appropriately perform the heat treatment of the inner shaft on which the gear is formed on the inner peripheral surface, and it is possible to suppress the strength reduction and the life reduction of the entire device.

It is sectional drawing of the wheel bearing apparatus which concerns on one Embodiment of this invention. It is the flowchart which showed a part of manufacturing process of the inner shaft. It is sectional drawing of the inner axis | shaft in which induction hardening was performed from the outer peripheral surface side and the inner peripheral surface side, and has shown the profile of the hardened layer formed in the inner shaft. It is a graph which shows an example of the result of having measured the cross-sectional hardness distribution on the IV-IV line in FIG. It is the graph which showed the influence which the dimension T has with respect to the surface hardness of the outer peripheral surface in a small diameter part. It is sectional drawing of the conventional wheel bearing apparatus.

  Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a wheel bearing device 1 according to an embodiment. The wheel bearing device 1 is a bearing device that rotatably supports a drive wheel (wheel, not shown) driven by an in-wheel motor (not shown) used in an electric vehicle such as an electric vehicle with respect to a vehicle body. It is used.

  The wheel bearing device 1 includes a cylindrical inner shaft 2, an outer ring 3 that is concentrically disposed on the outer peripheral side of the inner shaft 2, and a double row that is freely rollable between the inner shaft 2 and the outer ring 3. Are provided with a plurality of balls 4 as rolling elements and a pair of cages 5 that respectively hold the double-row balls 4 in the circumferential direction, thereby constituting a double-row angular ball bearing.

The outer ring 3 is a cylindrical member formed using, for example, carbon steel for machine structure or alloy steel for machine structure having a carbon content of 0.4 wt% or more such as S50C or SCM440.
On the outer peripheral surface of the outer ring 3, a fixing member 3c for fixing the driving wheel so as to be integrally rotatable is projected. That is, the outer ring 3 is an axle to which the drive wheel is attached and constitutes a rotating wheel of the wheel bearing device 1.
First and second outer ring raceways 3a and 3b on which the double-row balls 4 roll are formed on the inner peripheral surface of the outer ring 3.

Similarly to the outer ring 3, the inner shaft 2 is a cylinder along the axial direction formed using, for example, carbon steel for machine structure or carbon steel for machine structure having a carbon content of 0.4 wt% or more such as S50C or SCM440. Shaped member.
A flange 2c for fixing the wheel bearing device 1 to a knuckle or the like on the vehicle side is formed at one axial end portion of the inner ring 2. That is, the inner ring 2 constitutes a fixed wheel that is fixed to the vehicle body side.
A first inner ring raceway 2a is formed on the outer peripheral surface of the inner shaft 2 so as to face the first outer ring raceway 3a. A small-diameter portion 6 having a smaller diameter than the first inner ring raceway 2a is formed at the other end portion of the inner shaft 2. An annular inner ring member 7 in which a second inner ring raceway 2 b facing the second outer ring raceway 3 b is formed on the outer peripheral surface is fitted on the small diameter portion 6.
The inner ring member 7 is press-fitted and fixed in a state where the end surface 7 a is in contact with the step surface 8 connecting the outer peripheral surface of the inner shaft 2 and the small diameter portion 6.

  Between the first inner ring raceway 2a and the first outer ring raceway 3a, and between the second inner ring raceway 2b and the second outer ring raceway 3b located on the other end side in the axial direction from the first inner ring raceway 2a. Each of the above-mentioned plurality of balls 4 is arranged to roll freely.

  In the first inner ring raceway 2 a formed on the outer peripheral surface side of the inner shaft 2, wear occurs due to rolling of the balls 4, and a repeated load acts on the small diameter portion 6 via the balls 4. Therefore, a hardened layer by induction hardening is formed on the outer peripheral surface of the first inner ring raceway 2a and the outer peripheral surface of the small-diameter portion 6 for the purpose of enhancing wear resistance and fatigue strength.

  With the above configuration, the wheel bearing device 1 supports the drive wheel fixed to the outer ring 3 rotatably with respect to the vehicle body by fixing the inner shaft 2 to the vehicle body side.

  A gear 10 is formed on the inner peripheral surface of the inner shaft 2. The gear 10 is for transmitting the rotational force of the in-wheel motor to the drive wheels. On the inner peripheral side of the inner shaft 2, a sun gear (not shown) driven by a rotational force output from an electric motor included in the in-wheel motor, and a plurality of planets meshing with both the sun gear and the gear 10. A gear (not shown) is arranged. That is, a planetary gear mechanism for reducing the rotational force of the electric motor is provided on the inner peripheral side of the inner shaft 2. The gear 10 constitutes an internal gear of this planetary gear mechanism.

  The rotational force output by the electric motor is decelerated by the planetary gear mechanism, and is transmitted to a transmission shaft that protrudes outward from the other axial end of the inner shaft 2 and is coupled to the drive wheel so as to be integrally rotatable. As a result, the drive wheels are driven by the rotational force of the electric motor.

Moreover, also about the gearwheel 10 currently formed in the inner peripheral surface side of the inner shaft 2, the hardened layer by induction hardening is formed in the tooth | gear part surface in order to improve abrasion resistance and fatigue strength.
That is, the inner shaft 2 is subjected to induction hardening from the outer peripheral surface side and the inner peripheral surface side.

  Here, the outer diameter of the inner shaft 2 is limited because the outer ring 3 is disposed on the outer peripheral side or the first inner ring raceway 2a is formed on the outer peripheral surface. Further, the inner shaft 2 is also formed with a gear 10 constituting a planetary gear mechanism on the inner peripheral side. For this reason, the thickness dimension in the radial direction of the inner shaft 2 is limited by the dimension of the outer ring 3 and the dimension of the planetary gear mechanism, and is difficult to set freely. For this reason, the thickness dimension in the radial direction of the inner shaft is set to be relatively thin.

If induction hardening is performed simultaneously on both the outer peripheral surface and the inner peripheral surface of the inner shaft 2 having a relatively thin radial dimension as described above, the heat remains without any escape. May be cured over the entire region in the thickness direction.
For this reason, in this embodiment, when manufacturing the inner shaft 2, the outer peripheral surface side quenching and the inner peripheral surface side quenching are performed separately.

FIG. 2 is a flowchart showing a part of the manufacturing process of the inner shaft 2.
In order to manufacture the inner shaft 2, first, a rough product of the inner shaft 2 which is made cylindrical from a material is formed (step S <b> 1).
Next, the rough shape product is machined to form the first inner ring raceway 2a and the small diameter portion 6 (step S2).
Then, induction heating is performed by bringing the heating coil closer to the first inner ring raceway 2a and the small diameter portion 6 formed in step S2 from the outer peripheral side, and a hardened layer is formed on a necessary portion on the outer peripheral surface side of the inner shaft 2. Form (step S3).

  Thereafter, gear cutting for forming the gear 10 on the inner peripheral surface side is performed (step S4), the heating coil is approached from the inner peripheral side, induction hardening is performed, and a hardened layer is formed on the surface portion of the gear 10. (Step S5).

  In the present embodiment, after performing induction hardening on the outer peripheral surface side (step S3), gear cutting on the inner peripheral surface side is performed, so that the gear 10 formed in step S4 has at least induction hardening on the outer peripheral surface side. There is no distortion caused by heating. Thereby, the distortion amount of the gear 10 can be suppressed as small as possible.

FIG. 3 is a cross-sectional view of the inner shaft 2 subjected to induction hardening from the outer peripheral surface side and the inner peripheral surface side, and shows a profile of the hardened layer formed on the inner shaft 2.
As shown in FIG. 3, a first hardened layer L <b> 1 and a second hardened layer L <b> 2 are formed on the outer peripheral surface side of the inner shaft 2. The first hardened layer L1 is formed from the base end portion of the flange 2c to the first inner ring raceway 2a. The first hardened layer L1 is formed to improve the fatigue strength of the base end portion of the flange 2c and to improve the wear resistance of the first inner ring raceway 2a.

The second hardened layer L2 is formed from the step surface 8 to the outer peripheral surface of the small diameter portion 6. The second hardened layer L2 is formed for improving the fatigue strength of the small diameter portion 6.
A third hardened layer L <b> 3 is formed on the inner peripheral surface side of the inner shaft 2 along the tooth surface of the gear 10. The third hardened layer L3 is formed to improve the wear resistance and fatigue strength of the gear 10.
In addition, each hardening layer shown in FIG. 3 has shown the range which can distinguish the difference of a physical or chemical property with respect to the material | dough of the raw material which forms the inner shaft 2 by hardening. More specifically, the range in which it is determined that the cross-sectional hardness by quenching is increased with respect to the cross-sectional hardness of the material dough is shown as a hardened layer.

As shown in FIG. 3, the small diameter portion 6 overlaps the portion where the gear 10 is formed in the axial direction. Therefore, the dimension T between the outer peripheral surface 6a of the small-diameter portion 6 and the tooth bottom 10a of the gear 10 is the smallest compared to the radial thickness dimension in other portions.
This dimension T is determined by the radius of the outer peripheral surface 6a (the outer peripheral surface of the other end) of the small-diameter portion 6 in the inner shaft 2 and the outermost surface of the tooth bottom 10a of the gear 10 formed on the inner peripheral surface of the inner shaft 2. It is the difference from the radius.

Here, in the wheel bearing device 1 of the present embodiment, the dimension T is set to 2.5 mm.
In addition, the second hardened layer L2 formed on the outer peripheral surface 6a of the small-diameter portion 6 of the inner shaft 2 and the tooth bottom 10a portion of the third hardened layer L3 formed on the gear 10 are individually induction-hardened. In this case, the total value when the total hardened layer depths are summed is a value smaller than 2.5 mm by a predetermined amount. For this reason, there exists a range where both the hardened layers L2 and L3 do not reach between the second hardened layer L2 on the outer peripheral surface 6a of the small diameter portion 6 in the inner shaft 2 and the third hardened layer L3 of the gear 10. Yes. That is, an uncured layer S that maintains the hardness of the material before the heat treatment is provided in the radial cross section of the inner shaft 2 between both the cured layers L2 and L3. Accordingly, the entire radial direction of the inner shaft 2 is prevented from being hardened, and a decrease in toughness of the inner shaft 2 is suppressed.

Thus, in the radial cross section of the inner shaft 2, an uncured layer S for ensuring the toughness of the inner shaft 2 is formed between the two hardened layers L2, L3.
The total hardened layer depth refers to a distance from the surface of the hardened layer to a position where a difference in physical or chemical properties between the hardened layer and the material cloth forming the inner shaft 2 cannot be distinguished.

  As described with reference to FIG. 2, the inner shaft 2 of the present embodiment is formed on the inner peripheral surface side after first forming the outer peripheral surface side hardened layers (first hardened layer L1 and second hardened layer L2) by induction hardening. The hardened layer (third hardened layer L3) is formed by induction hardening.

In the inner shaft 2 of the present embodiment, the outer ring 3 is disposed on the outer peripheral side, and the planetary gear mechanism is disposed on the inner peripheral side, so that the setting of the radial thickness dimension is limited. For this reason, the thickness dimension of the inner shaft 2 must be set relatively thin.
For the inner shaft 2 set to be relatively thin, for example, if induction hardening on the outer peripheral surface side and induction hardening on the inner peripheral surface side are performed simultaneously, the diffusion path of the applied heat is limited, Heat remains in the heated part. For this reason, there exists a possibility that the inner shaft 2 may be quenched and cured over the entire thickness direction. If it hardens over the entire region in the thickness direction, the toughness of the inner shaft 2 as a whole is lowered, and the impact resistance is lowered.

  In this respect, in the present embodiment, as described above, after forming the outer peripheral surface side hardened layer (first hardened layer L1 and second hardened layer L2), the inner peripheral surface side hardened layer (third hardened layer). As L3) is formed, quenching on the outer peripheral surface side and quenching on the inner peripheral surface side are performed as separate processes, so that a heat diffusion path during heating can be secured and heat remains in the heated portion. Can be suppressed. As a result, it is possible to suppress the inner shaft 2 from being quenched and cured over the entire thickness direction.

  Furthermore, since the inner shaft 2 can be suppressed from being hardened and cured over the entire thickness direction, the uncured layer S is formed into the diameter of the inner shaft 2 when the both cured layers L2 and L3 are formed as described above. It can provide in a direction cross section, and can suppress the fall of toughness as a whole inner shaft 2, and impact resistance.

  On the other hand, the hardened layers (first hardened layer L1 and second hardened layer L2) obtained by first quenching are tempered by heating during subsequent quenching, and the hardened hardened layer that has been previously hardened is hardened. There is a risk of reducing the thickness. In this case, the necessary hardness may not be obtained for the tempered cured layer.

  On the other hand, in the wheel bearing device 1 of the present embodiment, the second hardened layer L2 and the third hardened layer L3 are obtained by adding up the total hardened layer depth when induction hardening is performed individually. Induction hardening is performed so that the total value at that time is a predetermined amount smaller than 2.5 mm. As a result, an uncured layer S that does not reach both of the hardened layers exists between the second hardened layer L2 on the outer peripheral surface 6a of the small-diameter portion 6 of the inner shaft 2 and the third hardened layer L3 of the gear 10. Quenching is carried out. Therefore, it is suppressed that the influence of the heating by hardening at the time of forming the hardened layer on the one peripheral surface side reaches the hardened layer on the other peripheral surface side. As a result, the required surface hardness can be ensured in both the hardened layers L2, L3.

  In addition, the quenching conditions of induction hardening for forming the second cured layer L2 and the quenching conditions of induction hardening for forming the third cured layer L3 are as described above while obtaining the surface hardness necessary for each cured layer. The total hardened layer depth is set to be obtained.

  FIG. 4 is a graph showing an example of the result of measuring the cross-sectional hardness distribution on the IV-IV line in FIG. The IV-IV line passes through the radially outermost portion of the tooth bottom 10a of the inner shaft 2. In the figure, the vertical axis indicates the cross-sectional hardness of the inner shaft 2, and the horizontal axis indicates the radial depth dimension (mm) from the outer peripheral surface 6 a of the small diameter portion 6.

  In the figure, the portion having a hardness H1 or less that can be regarded as the hardness of the material forming the inner shaft 2 has a radial depth dimension from the outer peripheral surface 6a of the small diameter portion 6 of about 1 mm to 1.8 mm. The range of the degree. This range corresponds to the uncured layer S shown in FIG. Outside the range of the uncured layer S corresponds to the second cured layer L2 and the third cured layer L3.

  Further, the cross-sectional hardness near the surface of the outer peripheral surface 6a of the small-diameter portion 6 and the cross-sectional hardness near the surface of the tooth bottom 10a of the gear 10 are values H2, which are predetermined as the required cross-sectional hardness on each surface. The value is larger than H3.

  As described above, the inner shaft 2 of the present embodiment is provided with the uncured layer S in the radial cross section of the inner shaft 2, thereby suppressing toughness and impact resistance as the entire inner shaft 2, and The required surface hardness of the inner shaft 2 is ensured.

  As described above, according to the wheel bearing device 1 of the present invention, the heat treatment of the inner shaft 2 is appropriately performed. As a result, a decrease in toughness of the inner shaft 2 can be suppressed and a necessary surface hardness can be secured, and a decrease in strength and a decrease in life of the entire apparatus 1 can be suppressed.

  In the present embodiment, the dimension T between the outer peripheral surface 6a of the small diameter portion 6 and the tooth bottom 10a of the gear 10 is set to 2.5 mm. It is possible to provide it in the radial cross section of the inner shaft 2. Therefore, the dimension T can be set in a range of 2.5 mm or more.

  However, the thickness dimension of the inner shaft 2 is limited to a settable value due to the presence of the outer ring 3 and the planetary gear mechanism as described above, and must be set relatively thin. Furthermore, it is desirable that the inner shaft 2 be as light as possible. For this reason, it is preferable to set the dimension T to 5 mm or less, and this makes it possible to reduce the weight without making the inner shaft 2 unnecessarily thick.

  Moreover, in the said embodiment, although the wheel bearing apparatus 1 which comprises a double row angular ball bearing was shown, it is applicable also to the wheel bearing apparatus which comprises a double row tapered roller bearing, for example.

Next, the test which verified about the influence which the dimension T between the outer peripheral surface 6a of the small diameter part 6 and the tooth bottom 10a of the gearwheel 10 has on the surface hardness of the outer peripheral surface 6a of the small diameter part 6 in the inner shaft 2 The results will be described.
As a test method, for the inner shaft 2 of the wheel bearing device 1 described in the above embodiment, the dimension T is set every 0.5 mm in a range of 1.5 mm to 5.5 mm in FIG. Formed according to the indicated process.
Note that S55C was used as the material used to form the inner shaft 2. The conditions of induction hardening when forming the second hardened layer L2 on the outer peripheral surface side of the inner shaft 2 and the conditions of induction hardening when forming the third hardened layer L3 on the inner peripheral surface side are shown in Table 1 below. It is as follows. Water was used as the coolant.

  The surface hardness (Rockwell hardness) of the 6 outer peripheral surfaces 6a of the small diameter portion in each inner shaft 2 obtained as described above was measured and compared.

  FIG. 5 is a graph showing the influence of the dimension T on the surface hardness of the outer peripheral surface 6 a of the small diameter portion 6. In the drawing, the vertical axis indicates the surface hardness of the outer peripheral surface 6a of the small diameter portion 6, and the horizontal axis indicates the dimension T from the outer peripheral surface 6a of the small diameter portion 6 to the tooth bottom 10a.

  In the figure, when the dimension T is 2.5 mm or more, the surface hardness of the outer peripheral surface 6a exceeds the hardness value required for the outer peripheral surface 6a. Further, when the dimension T is 2.5 mm or more, the hardness value is substantially constant. This is set so that the necessary hardness for the outer peripheral surface 6a is obtained as a condition of induction hardening, and a target hardness determined by the setting of induction hardening is obtained when the dimension T is 2.5 mm or more. .

On the other hand, when the dimension T is 1.5 mm and 2 mm, the surface hardness of the outer peripheral surface 6a is lower than the surface hardness value required for the outer peripheral surface 6a. This is because when the third hardened layer L3 on the inner peripheral surface side is formed by induction hardening after the formation of the second hardened layer L2 on the outer peripheral surface side, heat from the induction hardening is transmitted to the outer peripheral surface side, and the second hardened layer L2 has been tempered.
The second hardened layer L2 is tempered by heating by induction hardening for forming the third hardened layer L3, and the surface hardness is reduced to a value lower than the required surface hardness value.
That is, when the dimension T is 1.5 mm and 2 mm, since the radial thickness of the inner shaft 2 is small, the heat from the inner peripheral side is conducted to the outer peripheral surface, and the surface hardness of the second hardened layer L2 Is reduced.

  From this result, by setting the dimension T to 2.5 mm or more, the influence of heating by induction hardening when forming the hardened layer on the one peripheral surface side can be suppressed from reaching the hardened layer on the other peripheral surface side. It was revealed that the required surface hardness can be secured in both cured layers.

1: Wheel bearing device 2: Inner shaft 3: Outer ring 4: Ball (rolling element)
6: Small diameter portion 6a: Outer peripheral surface (outer peripheral surface of the other end) 7: Inner ring member 10: Gear (internal gear) 10a: Tooth bottom L2: Second hardened layer L3: Third hardened layer S: Unhardened layer

Claims (3)

A cylindrical inner shaft with wheels attached to one axial end;
An outer ring arranged concentrically on the outer periphery of the inner shaft with a double row of rolling elements interposed therebetween;
An inner ring member that is formed on the outer periphery of the row of rolling elements located on the other end side in the axial direction of the double row rolling elements and is fitted on the outer peripheral surface of the other end of the inner shaft. In the wheel bearing device provided,
An internal gear is formed on the inner peripheral surface of the inner shaft,
The difference between the radius of the outer peripheral surface of the other end of the inner shaft on which the inner ring member is fitted and the outermost radius of the tooth bottom of the internal gear formed on the inner peripheral surface of the inner shaft is 2.5 mm. Set to above,
A hardened layer is formed by induction hardening on the outer peripheral surface of the other end portion of the inner shaft on which the inner ring member is fitted, and the inner gear formed on the inner peripheral surface of the inner shaft.
An uncured layer is provided between the hardened layer formed on the outer peripheral surface of the other end of the inner shaft and the hardened layer formed on the tooth bottom of the internal gear to ensure the toughness of the inner shaft. A bearing device for a wheel, characterized in that   The difference between the radius of the outer peripheral surface of the other end portion of the inner shaft and the outermost radius of the tooth bottom of the internal gear formed on the inner peripheral surface of the inner shaft is set to 5 mm or less. Wheel bearing device. A cylindrical inner shaft with wheels attached to one axial end;
An outer ring arranged concentrically on the outer periphery of the inner shaft with a double row of rolling elements interposed therebetween;
An inner ring member that is formed on the outer periphery of the row of rolling elements located on the other end side in the axial direction of the double row rolling elements and is fitted on the outer peripheral surface of the other end of the inner shaft. Prepared,
In the method of manufacturing a wheel bearing device in which an internal gear is formed on the inner peripheral surface of the inner shaft,
A first step of forming an outer peripheral surface of the other end portion of the inner shaft on which the inner ring member is fitted, with respect to an outer peripheral surface of the rough shaped product of the inner shaft;
A second step of forming a hardened layer by induction hardening on the outer peripheral surface of the other end;
A third step of forming the internal gear with respect to the inner peripheral surface of the rough shaped product of the inner shaft;
A fourth step of forming a hardened layer by performing induction hardening on the internal gear,
The difference between the radius of the outer peripheral surface of the other end portion of the inner shaft formed by the first step and the outermost radius of the tooth bottom of the internal gear formed by the third step is set to 2.5 mm or more,
The toughness of the inner shaft is between the hardened layer formed on the outer peripheral surface of the other end of the inner shaft by the second step and the hardened layer formed on the tooth bottom of the internal gear by the fourth step. A method for manufacturing a wheel bearing device, characterized in that an uncured layer is provided for securing the wheel.

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