JP2003156054A - Axle unit for driving wheel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that the service life of a bearing unit is shortened unless a hardened layer of a bearing part, in particular, of a raceway surface of an outer ring is adequately set in the bearing unit for driving a wheel with a constant velocity joint and a hub unit integrated with each other in a disassembling manner. SOLUTION: A constant velocity joint 23 is spline-coupled with a hub 10, the hub 10 is supported at a hub outer ring 5 by a bearing device having rolling elements 18 and 19, and the hub outer ring 5 is fixed to a suspension by a knuckle 2 at a flange 4 part. This hub outer ring 5 is formed of steel, and when hardening a raceway surface 37 of the outer ring, the maximum hardness of a hardened layer is set to be >=Hv 700, and the effective hardening depth is set in a range of 12-25% of the diameter of the rolling elements. In addition, in the hub outer ring 5, a hardening-affected part of the raceway surface of the outer ring is prevented from overlapping a part of an inner diameter surface between raceway surfaces of the outer rings.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axle unit called a so-called hub unit in which a constant velocity joint and a hub unit are integrated so as to be disassembled. In particular, a drive wheel supported by an independent suspension type suspension is suspended. The present invention relates to a wheel drive axle unit that is rotatably supported by an apparatus and is used for rotationally driving the drive wheels.

[0002]

2. Description of the Related Art An axle unit to which the present invention is applied is a so-called hub unit in which a constant velocity joint and a hub unit are integrated in a disassembleable manner.
All front wheels of F cars (front engine front wheel drive cars), FR cars (front engine rear wheel drive cars) and RR cars (rear engine rear wheel drive cars), 4WD cars (four wheel drive cars) Drive wheels supported by an independent suspension type suspension,
It is an axle unit that is rotatably supported with respect to a suspension device and is also used for rotationally driving the drive wheels.

As described above, in order to rotatably support the wheel with respect to the suspension device, various axle units in which an outer ring and an inner ring are rotatably combined via rolling elements are used.
In addition, the wheel drive axle unit that supports the drive wheels on an independent suspension type and drives the drive wheels in rotation is combined with a constant velocity joint to provide relative displacement between the differential gear and the drive wheels and to the wheels. Regardless of the steered angle, it is necessary to ensure that the rotation of the drive shaft is smoothly transmitted to the shaft with a constant speed. Conventionally, as a wheel drive axle unit called a so-called fourth-generation hub unit, which can be configured in a relatively small size and light weight in combination with such a constant velocity joint, it has been conventionally disclosed in Japanese Patent Laid-Open No. 7-3177.
No. 54, or the one described in US Pat. No. 5,674,011 is known.

[0004]

However, these publications and the like do not consider the material and heat treatment of the inner peripheral surface of the outer ring of the axle unit, and in order to actually use these devices, each member There was no index for practical use, such as what kind of material was used and how heat treatment should be performed.

Therefore, the inventors of the present invention have conducted earnest researches on the heat treatment for the inner peripheral surface of the outer ring used in the axle unit, and as a result, when forming a quench-hardened layer on the outer ring raceway surface as the heat treatment, this bearing is used. It was found that the life of the unit greatly affects the material of the hub outer ring, the hardness of quenching, and the depth of the hardened layer. Therefore, further research was conducted on how to set these to improve the fatigue life of the hub outer ring.

Therefore, an object of the present invention is to provide an axle unit incorporating a hub outer ring having an excellent fatigue life by appropriately setting the material, the hardness of quenching, and the depth of the hardened layer.

[0007]

In order to solve the above-mentioned problems, the present invention according to claim 1 has a mounting flange for mounting on a vehicle body on an outer peripheral surface and a double row outer ring raceway on an inner peripheral surface, An axle having an outer ring that does not rotate during use, an inner ring that has an inner ring raceway on its outer peripheral surface and rotates with the wheel, and a plurality of rolling elements that are rotatably provided between the inner ring raceway and the outer ring raceway. In the unit, the maximum hardness of the quench-hardened layer on the outer raceway surface is Hv700 or more, and the quench-hardening effective hardening depth is within the range of 12 to 25% of the rolling element diameter. It was done.

According to a second aspect of the present invention, there is provided the axle unit according to the first aspect, characterized in that, in the outer ring, the quenching affected portions of the outer ring raceways do not overlap.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. A wheel drive axle unit to which the present invention is applied has an overall structure as shown in, for example, FIG. 1A. In this axle unit 1, a flange 4 fixed to a knuckle 2 with a bolt 3 is provided on the outer periphery. The hub outer ring 5 is provided, and two rows of outer ring races, an outer outer raceway 6 and an inner outer raceway 7, are formed on the inner peripheral surface of the hub outer race 5.
A hub 10 is rotatably supported inside a hub outer ring 5 by a bearing device, and a wheel is attached to the outer periphery of the hub 10 by bolts 1.
1, an outer inner ring raceway 13 is formed at a position facing the outer outer ring raceway 6, and an inner ring 15 having an inner inner ring raceway 14 is press-fitted at a position facing the inner outer ring raceway 7. Then, the end of the shaft supporting portion 16 of the hub 10 is fixed by caulking.

A plurality of outer rolling elements 17 are provided between the outer outer raceway 6 and the outer inner raceway 13, and a plurality of inner rolling elements 18 are provided between the inner outer raceway 7 and the inner inner raceway 14. The outer rolling elements 17 and the inner rolling elements 18 are held by a retainer 19 and are rotatably arranged on each track. Further, an outer seal 20 and an inner seal 21 are provided between the opposing surfaces of the hub outer ring 5 and the hub 10 to prevent water and various foreign substances from entering the bearing portion from the outside.

A female spline 22 is formed on the inner surface of the central opening of the hub 10, and a male spline 26 formed on the outer periphery of a shaft 25 projecting from a constant velocity joint outer ring 24 of a constant velocity joint 23 is engaged with the female spline 22. The constant velocity joint 23 and the hub 10 are firmly fixed by screwing the nut 27 into the screw formed at the end portion of the hub 25, and the end face 28 of the constant velocity joint outer ring 24 allows the shaft support portion 1 of the hub 10 to be fixed.
By pressing the end portion of 6, the appropriate preload is applied to each rolling element.

In the constant velocity joint 23, outer engagement grooves 30 are formed at a plurality of positions in the circumferential direction on the inner peripheral surface of the outer ring 24 for constant velocity joint, respectively, in a direction perpendicular to the circumferential direction. Further, the inner ring 31 for a constant velocity joint has a female spline 32 formed in the center thereof, and an inner engagement groove 33 facing the outer engagement groove 30 is formed on the outer peripheral surface thereof in a direction perpendicular to the circumferential direction. Is formed. Between the inner engagement grooves 33 and the outer engagement grooves 30, the balls 3
4 is held by a retainer 35 so as to be rollable along the groove.

In a state where the vehicle is mounted on a suspension system, a male spline portion provided at an outer end portion of a drive shaft (not shown) is spline-engaged with a female spline 32 provided at a central portion of the constant velocity joint inner ring 31. . The inner end of the drive shaft is fixedly coupled to the center of the trunnion of the tripod type constant velocity joint provided on the output shaft of a differential gear (not shown).

Therefore, when the vehicle is running, the drive shaft that engages with the female spline 32 of the constant velocity joint 23 is repeatedly subjected to a load in the axial direction, that is, a thrust load, due to the resistance of the tripod type constant velocity joint as it rotates. This acts as a thrust force on the bearing device between the hub outer ring 5 and the inner ring portion provided on the hub 10 side. Further, a radial force for supporting the vehicle body with wheels acts on the bearing device, and a thrust force also acts from the wheel side when the vehicle is running. Therefore, a large radial load and thrust load constantly act on this bearing device, and the bearing device must be able to withstand this load sufficiently.

In the present invention, in the wheel drive axle unit 1 as described above, particularly the bearing acting portion of the hub outer ring 5 is devised, and the hub outer ring 5 shown in FIG. 1 (a) is taken out. The enlarged one is shown in FIG. The hub outer ring 5 is provided with the flange 4 fixed to the knuckle 2 with the bolt 3 as described above, and the female screw 9 with which the bolt 3 is screwed is formed on the flange 4, and the inner peripheral surface of the hub outer ring 5 is formed. An outer outer ring raceway 6 and an inner outer ring raceway 7 are formed in the outer ring. The portion where these trajectories are formed is collectively referred to as the inner peripheral raceway surface 37. In addition, an inter-orbit inner diameter surface 8 is provided between each orbit.

This hub outer ring 5 is made of steel, and when it is manufactured, it is molded into the shape of the hub outer ring 5 as a whole.
The outer ring outer raceway 6 and the outer ring inner raceway 7 are subjected to a quenching treatment as described in detail later to form a quench hardened layer 38,
After that, the female screw 9 is formed and each raceway surface is machined to a predetermined size.

In the present invention, regarding the quench-hardened layer 38 portion of the double-row inner peripheral raceway surface 37, the maximum hardness of the quench-hardened layer and how the quench-hardened layer depth is set to prolong the life. This is what was examined.

Generally, the tensile strength (kgf / mm ² ) of steel is about 1/3 times the Vickers hardness (Hv), and the shear strength (kgf / mm ² ) is the tensile strength (kgf / mm ^2). ) Is about 1/2 times. From this, the shear strength can be shown as 1/6 times the Vickers hardness. In other words, it can be considered that the value obtained by multiplying the shear strength by 6 is the Vickers hardness.

It is now considered that the rolling element rolls on the induction hardened raceway surface under a load perpendicular to the raceway surface. The hardness in the depth direction of the raceway surface and the shear stress applied by the rolling of the rolling elements are schematically shown in FIG. Here, the solid line shows the hardness measured from the rolling surface in the depth direction, and the broken line shows the value obtained by multiplying the shear stress by 6 and converting it into Vickers hardness. In FIG. 2, when the solid line shows a larger value in the vertical axis direction than the broken line, it indicates that the orbit is damaged at that depth. In FIG. 2, the solid line A shows a larger value than the broken line at any place, so there is no damage to the rolling material. On the other hand, the solid line B and the solid line C have a portion below the broken line due to insufficient hardness near the surface or insufficient hardened layer depth, and the rolling material will be damaged.

When the phenomenon of FIG. 2 is applied to the hub outer ring of the axle unit, the shear stress in the depth direction from the outer ring raceway is greatly affected by the rolling element (ball) diameter, etc., but these are set as design guidelines. Therefore, the broken line in FIG. 2 can be determined as a fixed value. That is, in order to provide a bearing ring that will not be damaged at any point in the rolling surface depth direction,
It is only necessary to be able to define the surface hardness and the effective hardened layer depth required for the outer ring raceway surface.

According to the present invention, the maximum hardness of the quench hardened layer is Hv.
When it is 700 or more and the quench hardened layer depth is 12 to 25% of the diameter of the rolling element, the condition shown by the solid line A in FIG. 2 is satisfied, and the race ring is formed by the shear stress generated under the outer ring raceway surface. It was devised to find out that it would not be damaged.

Further, when induction-hardening the raceway surface of the hub outer ring, by appropriately arranging the position of the induction heating coil, the quench-hardened layers formed around the raceway surface are independent from each other on the plurality of raceway surfaces. Since it is possible to prevent abnormal occurrence of retained austenite caused by overheating that occurs from the shoulder portion of the hub outer ring to the inner peripheral surface of the raceway surface, it is possible to obtain appropriate hardness below the raceway surface. FIG. 3 shows a cross-sectional view of the hub outer ring. FIG. 3A shows the case where the quench-hardened layers are independent.
(B) shows a case where the quench-hardened layers are overlapped with each other on the inner diameter surface 8 between the raceways.

By using steel with an appropriate alloying element as the material for the hub outer ring, proper mechanical properties can be obtained.

Table 1 collectively shows the experimental results of the present invention. Here, SUJ2 (JIS
G4805) was adopted. All of the data shown in Table 1 are so-called hubs II that incorporate rolling elements with a diameter of 12.0 mm.
It was obtained by an experiment using I.

[Table 1] Hv-surf: Vickers hardness just under the outer ring surface of the hub outer ring η: Hardness exploration index (hardened effective hardened layer depth ÷ rolling element diameter × 100) γR: retained austenite amount

The column of "overlapping of hardened layers" in the table shows whether or not the quench-hardened layers applied to the raceway surfaces of the double rows are overlapped at the portion of the inner diameter surface 8 between the raceways.
The case where the hardened layers do not overlap in the portion of the inter-raceway inner diameter surface 8 as shown in (a) is marked with a circle, and the case where they overlap as shown in FIG. In addition, "life" in the table indicates whether or not the rolling life satisfies the regulation. When the rolling life is satisfied, "○" is indicated, and when not satisfied, "x" is indicated.

Here, a method of determining the rolling life will be described with reference to FIG. First, rolling life evaluation device 4
I will explain about 0. The evaluated hub outer ring is assembled as a hub unit 41 by pairing with the hub inner ring and the like.
The hub unit 41 is attached to the rotary shaft attachment portion 42. The hub unit 41 includes a radial load actuator 43, a first link 44 and a second link 45.
From the radial load applied via the thrust load actuator 46 to the first link 44 and the second link 4
Thrust loads applied via 5 are applied respectively.
The hub outer ring rotates in a state where a radial load and a thrust load are applied. Regarding the rotation of the hub outer ring, the rotation of the drive motor 47 is the rotation of the motor side pulley 48, the transmission belt 4
9, spindle shaft side pulley 50, support spindle 5
First, it is performed by being transmitted through the rotary shaft mounting portion 42.

The rolling life evaluation test is carried out with a radial load of 95.
It was carried out under conditions of 0 (kgf) and 1 million rotations with a thrust load of 550 (kgf). After the rolling life evaluation test was completed, the hub unit was disassembled, and if there was no damage such as Brinell impression or crack on the raceway surface of each hub outer ring, it was judged that the life was satisfied. That is, the mark ◯ in the “life” column of Table 1 indicates that the rolling life evaluation test satisfied the life.

In Table 1 above, No. Nos. 1 to 6 show series in which η is changed, and No. 7-9 is Hv
-shows a series with varying surf. In the series (No. 1 to 6) in which the hardening depth index η was changed,
No. of η = 10. No. 1 did not satisfy the life because the effective hardened layer depth with respect to the rolling element diameter was insufficient. η ≧
In Nos. 4 to 6 of No. 28, since the quench-hardened layers applied to the raceway surfaces of the double rows were overlapped with each other on the inner diameter surface portion between the raceways, thermal stability of retained austenite occurred due to overheating, and the life was not satisfied. No. of η = 12. No. 2 and η = 25. Sample No. 3 had a sufficient depth of the hardened layer, and there were no overlapping hardened layers, so that the life was satisfied.

No. of the series in which the Vickers hardness Hv-surf just below the raceway surface was changed. 7-9, Hv-sur
No. of f = 680. No. 7 did not satisfy the service life because the hardness near the surface was insufficient as indicated by the solid line B in FIG. H
No. with v-surf ≧ 700. 8 and No. No. 9 had a sufficient hardness not only on the surface but also at a deeper position, so that it satisfied the life.

In the above experimental example, the case of the so-called hub III type was shown, but the present invention does not limit the application to other types of hub units, and for example, the so-called hub II, the outer ring raceway. This is applicable as long as it is an axle unit having a plurality of wheels.

[0031]

Since the present invention is constructed and operates as described above, it is possible to provide a wheel drive axle unit that is small in size and light in weight and has excellent durability and reliability. It can also contribute to improvement of power performance and fuel efficiency performance.

[Brief description of drawings]

1 shows a wheel drive axle unit to which the present invention is applied, (a) is a cross-sectional view showing the entire configuration, and (b) is an enlarged cross-sectional view of a hub outer ring portion.

FIG. 2 is a schematic diagram of a relationship between hardness in the depth direction of a raceway surface and shear stress.

FIG. 3 is a cross-sectional view showing a state of a quench-hardened layer of an outer ring of a hub, (a) is a proper example, and (b) is an unfavorable case where quench-hardened layers of raceway portions on both sides of an inner diameter surface between raceways are overlapped It is sectional drawing which shows an example.

FIG. 4 is a schematic view of a rolling life evaluation device.

[Explanation of symbols]

1 axle unit 2 knuckles 4 flange 5 hub outer ring 6 outer ring raceway 7 Inner outer ring raceway 8 Inter-orbit inner diameter surface 10 hubs 12 flange 13 Outer inner ring raceway 14 Inner ring raceway 15 inner ring 17 Outer rolling element 18 Inner rolling element 19 cage 20 outer seal 21 Inner seal 23 constant velocity joint 24 constant velocity joint outer ring 25 axes 28 Edge 30 Outer engagement groove 31 Inner ring for constant velocity joint 32 female spline 33 inner engagement groove 34 balls 35 cage 37 outer ring raceway 38 Hardened layer

Claims (2)

[Claims] 1. An outer ring having a mounting flange for mounting on a vehicle body on an outer peripheral surface, a double row outer ring raceway on an inner peripheral surface, which does not rotate during use, and an inner ring having an inner raceway on an outer peripheral surface and rotating with a wheel. In an axle unit including a plurality of rolling elements rotatably provided between the inner ring raceway and the outer ring raceway, the maximum hardness of the quench-hardened layer on the outer ring raceway surface is Hv700.
Above, and the effective hardening depth of quenching is 12 of the rolling element diameter.
Axle unit characterized by being set within the range of up to 25%. 2. The axle unit according to claim 1, wherein, in the outer ring, quenching-affected parts of the outer ring raceways do not overlap with each other.