Bearing apparatus and producing method thereof

A bearing apparatus includes a hollow shaft provided around an outer peripheral surface with a bearing fitting region, and a rolling bearing having an inner ring fitted around the bearing fitting region of the hollow shaft. A shaft end of the hollow shaft is bent outwardly in a diametrical direction, thereby being caulked on an outer end surface of the inner ring. The bearing fitting region has a hardened layer in a region from a first position corresponding to an inner end surface of the inner ring of the rolling bearing to a second position before a position corresponding to an outer end surface of the inner ring, and has a non-hardened layer in another region from the outer end surface corresponding position of the inner ring to the shaft end. The second position representative of a caulked side end portion of the hardened layer is defined based on a predetermined relational expression.

BACKGROUND OF THE INVENTION

The present invention relates to a bearing apparatus and a producing method thereof, and more particularly, to a bearing apparatus and a producing method thereof which are preferably used for a hub unit for a vehicle such as an automobile.

A hub unit for a vehicle will be explained. The hub wheel has a hollow shaft. An inner ring of a rolling bearing is mounted to an outer periphery of the hollow shaft by press-fit. A shaft end of the hollow shaft is caulked on the outer end surface of the inner ring by bending the shaft end outwardly in a diametrical direction. The bearing is prevented from slipping off from the hollow shaft by this caulked portion. A pre-load is applied to the inner ring of the bearing by this caulking.

A load is applied to the hollow shaft by the pressure-fit of the inner ring of the bearing. The hollow shaft is formed around its outer periphery with a hardened layer due to heat by quenching or the like in order that the hollow shaft has the structure that can bear the load. On the other hand, the shaft end of the hollow shaft remains in a stage of being caulked on the outer end surface of the inner ring, i.e., the shaft end is not hardened.

A range of the hardened layer formed on the outer periphery of the hollow shaft is limited to a certain degree.

However, in the range where the hardened layer is formed, a position of the caulked side end portion in the axial direction is not clearly defined. Thus, when it is processed to be hardened, the position of the caulked side end portion of the hardened layer in its add is prone to be an incorrect position closer to an outer end or to inner end in the axial direction from the limited range.

If the position of the end portion in the axial direction of the hardened layer is positioned incorrectly with respect to the hollow shaft, a gap may be generated between an inner peripheral surface of the inner ring and an outer peripheral surface of the hollow shaft caulked on the outer end surface thereof in some cases. This gap deteriorates creep resistance.

Therefore, a caulking auxiliary jig is previously inserted on the side of the inner periphery of the hollow shaft before caulking, thereby preventing the gap from being generated. Further, after the caulking, the inner periphery of the hollow shaft is again worked. Such a gap-preventing operation of the hollow shaft increases the number of producing steps and cost of the hub unit.

SUMMARY OF THE INVENTION

Thus, it is a main object of the present invention to provide a bearing apparatus of a hub unit, and the like, for a vehicle, capable of appropriately managing a position of an end portion, in the axial direction, of a hardened layer formed on an outer periphery of a hollow shaft.

Other objects, features and merits of the present invention will be apparent from the following description.

The present invention is, in sum, described as follows. A bearing apparatus of the present invention includes a hollow shaft provided around its outer peripheral surface with a bearing fitting region, and a rolling bearing having an inner ring fitted around the bearing fitting region of the hollow shaft. A shaft end of the hollow shaft is bent outwardly in a diametrical direction, thereby being caulked on an outer end surface of the inner ring of the rolling bearing.

The bearing fitting region has a hardened layer in its region from an inner end surface corresponding position of the inner ring of the rolling bearing to a portion before an outer end surface corresponding position. The bearing fitting region further has a non-hardened layer in its region from the portion before the outer end surface corresponding position of the inner ring to the shaft end of the hollow shaft.

A position of a caulked side end portion of the hardened layer is defined based on the following relational expression (1):
((A−C−D)Y/E)≦X<(A−C)  (1)
wherein A represents a width in the axial direction of the inner ring, C represents a chamfering length in the axial direction in the outer end surface of the caulked side of the inner ring, D represents a chamfering length in the axial direction in an outer end surface of the inner ring, E represents a thickness of the hollow shaft, X represents a distance from a position of the chamfering length D to the caulked side end portion of the hardened layer, and Y (<E) represents a hardening treatment depth.

With this defining expression, appropriate hardening treatment can be carried out by applying concrete numerical values to the respective length in the axial direction of the inner ring and the thickness of the hollow shaft. Further, it is possible to reduce the number of steps and time of the producing operation of the bearing apparatus, such as a hub unit, and to enhance the productivity.

In the present invention, preferably, the hollow shaft is a hub wheel, the rolling bearing is a double row angular contact ball bearing with vertex of contact angles outside of bearing or a double row tapered roller bearing with vertex of contact angles outside of bearing.

These and other objects, as well as advantages, of the invention will become clear by the following description of preferred embodiments of the invention with reference to the accompanying drawings, wherein like components are indicated by the same numerals.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A hub unit for a driving wheel of a vehicle as a bearing apparatus according to a preferred embodiment of the present invention will be explained with reference toFIGS. 1 to 3.

A hub unit10includes a hub wheel11and a bearing12.

The hub wheel11includes a flange13and a hollow shaft14. A wheel (not shown) is mounted to the flange13. The hollow shaft14has a bearing fitting region comprising a large-diameter outer peripheral surface and a small-diameter outer peripheral surface. The bearing12is fixed to the bearing fitting region.

A shaft end14aof the hollow shaft14is bent outwardly in a diametrical direction from a state shown inFIG. 1by rolling caulking and is plastically deformed. With this operation, the shaft end14ais caulked on an outer end surface of an inner ring15of an angular contact ball bearing12as shown inFIG. 2.

The bearing12is a double row angular contact ball bearing with vertex of contact angles outside of bearing as one example of an inclined rolling bearing. The bearing12includes an inner ring (first inner ring)15having a single orbit which is fitted around the small-diameter outer peripheral surface of the bearing fitting region of the hollow shaft14, a single outer ring16having two rows of orbit grooves, a plurality of balls17arranged in two rows, and two cages18.

The large-diameter outer peripheral surface of the bearing fitting region of the hollow shaft14of the hub wheel11is one inner ring (second inner ring) of the bearing12. An inner ring of a common single raw angular contact ball bearing is used as the inner ring15as it is.

The outer ring16is provided around its outer periphery with a flange19.

The caulking operation of the hub unit10will be explained.

The shaft end14aof the hollow shaft14is caulked on the outer end surface of the inner ring15from a state shown inFIG. 1to a state shown inFIG. 2. Thereafter, the hub unit10is mounted between a drive shaft20and a knuckle (or carrier)21of the vehicle. That is, the hollow shaft14of the hub wheel11is spline-fitted into the drive shaft20and coupled by a nut22. The flange19of the outer ring16of the bearing12is non-rotatably coupled to the knuckle (or carrier)21by means of a bolt23.

Features of the present embodiment will be explained with reference toFIG. 3.

The outer end surface of the inner ring15of the bearing12has an inner peripheral angle portion15a.The inner peripheral angle portion15ais roundly chamfered, e.g., from a center O through ¼ circumference of radius of curvature C. An inner end surface in the inner ring15of the bearing12has an inner peripheral angle portion15b.The inner peripheral angle portion15bis roundly chamfered, e.g., from the center O through ¼ circumference of radius of curvature C.

The inner peripheral angle portion15ahas a chamfering-start point15c.The chamfering-start point15cis a bending-start point when the shaft end14aof the hollow shaft14is bent outwardly in a diametrical direction around the outer end surface of the inner ring15. The inner peripheral angle portion15bof the inner ring15has a chamfering-start point15d.

In the bearing fitting region of the hollow shaft14, hardened layers24aand24bare formed from the large-diameter outer peripheral surface to the small-diameter outer peripheral surface thereof as shown with cross hatchings in the drawings.

The hardened layer24bformed on the small-diameter outer peripheral surface into which the inner ring15of the bearing12is fitted is hardened through a required depth from its surface by thermal treatment such as quenching in a region from a position (first corresponding position) corresponding to an inner end surface of the inner ring15to a portion before a position (second corresponding position) corresponding to an outer end surface.

A range of the hollow shaft14from its portion before the second corresponding position to the shaft end14aof the hollow shaft14is non-hardened layer. With this layer, it is possible to caulk the shaft end14awith respect to the outer end surface of the inner ring15outwardly in a diametrical direction.

Here, the portion before the second corresponding position is defined as a position (X) of the caulked side end portion of a hardened layer24.

The position (X) of the caulked portion is defined between the bending-start point15cand a position which is determined by a thickness (E) of the hollow shaft14and a fitting region length (A−C−D) of the hollow shaft14into the inner ring15in the small-diameter outer peripheral surface with respect to at least predetermined hardening treatment depth (Y).

The definition of the position (X) of the caulked side end portion of a hardened layer24bwill be explained in detail.

A length in the axial direction of the inner ring15of the angular contact ball bearing12is defined as (A), a chamfering length in the axial direction of the outer end surface of the inner ring15is defined as (C), a chamfering length in the axial direction of the inner end surface of the inner ring15is defined as (D), an axial thickness of the hollow shaft14is defined as (E), a distance from the position of the chamfering length (D) in the inner ring15to the caulked side end portion of the hardened layer24bis defined as (X), and a hardening treating depth is defined as (Y). However, when the inner peripheral surface of the hollow shaft14is formed with female spline as in this embodiment, the axial thickness (E) is a thickness from the outer periphery of the hollow shaft14to the bottom of the tooth of the female spline.

The position (X) of the caulked side end portion of the hardened layer24bis defined in a range shown with the following expression (1).
((A−C−D)Y/E)≦X<(A−C)  (1)

In the expression (1), the left side term (A−C−D) Y/E is based on a condition that the fitting region length between the hollow shaft14and the inner ring15when the hollow shaft14is caulked and deformed is defined as (A−C−D), the axial thickness of the hollow shaft14is defined as (E)mm, the position of the caulked terminal end of the hardened layer24bis defined as (X) mm, and the hardening treatment depth of the hardened layer24bis defined as (Y) mm. In this case, according to experiments and calculations by the present inventors, an expression (A−C−D):E=X:Y is established. From this expression, the relation (A−C−D) Y/E is established.

In Table 1, “Result of test” shows the result after changing the value of X by each size (A, C, D, E, and Y) of the bearing shown in “Desk checking.” X(min) represents the minimum value of X, and X(max) represents the maximum value of X. The bearings (1) and (2) are only different in size, and they are employed in the test in order to obtain the relational expression (1) that satisfies in the cases of bearings with different sizes.

That is, when the hardened layer24bis formed on the hollow shaft14, if the length in the axial direction of the hollow shaft14is long, the treatment width of the hardened layer24bin the axial direction becomes long correspondingly. If the shaft thickness (E) of the hollow shaft14is increased, the load bearing capacity from the inner ring15is increased and thus, the thickness (Y) of the hardened layer24bmay be shallow correspondingly.

Therefore, from the left side term (A−C−D) Y/E of the above expression (1), the position (X) of the caulked side end portion of the hardened layer24bis proportional to the hardening treatment depth (Y) and the fitting region length (A−C−D) between the hollow shaft14and the inner ring15, and is inversely proportional to the shaft thickness (E) of the hollow shaft14.

From the above reasons, it is possible to harden the hollow shaft14by defining the position (X) of the caulked side end portion of the hardened layer24bin the region of the expression (1).

The hollow shaft14of the hub wheel11has low load bearing capacity of the inner ring15. Therefore, the position (X) of the caulked side end portion of the hardened layer24bis important. Thus, the hollow shaft14by defining the position (X) of the caulked side end portion of the hardened layer24bis defined as a position defined based on the length in the axial direction and axial thickness of the hollow shaft14which is caulked and deformed in shortest. With this design, it is possible to optimize the caulking load of the shaft end of the hollow shaft14with respect to the outer end surface of the inner ring15, and to optimize the load bearing capacity of the inner ring15.

From the above reasons, in the small-diameter outer peripheral surface of the hollow shaft14, the range from the position (X) to the shaft end is non-hardened layer. Therefore, at the time of caulking, no gap is generated between the small-diameter outer peripheral surface and the inner peripheral surface of the inner ring15in that range, and the hollow shaft14is caulked with respect to the outer peripheral surface of the inner ring15. The range from the first corresponding position to the position (X) is formed as the hardened layer24. Therefore, no gap is generated between the small-diameter outer peripheral surface and the inner peripheral surface of the inner ring15in that range, and the hollow shaft14is caulked with respect to the outer peripheral surface of the inner ring15. As a result, the hub unit10has excellent creep resistance.

When the hub unit10is produced, it is unnecessary to previously insert the caulking auxiliary jig into the inner diameter side of the hollow shaft14to prevent a gap from being generated, and to work the inner diameter of the hollow shaft14.

For these reasons also, the structure of the hub unit10is suitable for mass production in which the number of steps and time of the production can be reduced.

In the above case, if the axial chamfering length of the inner peripheral angle portion of the outer end surface of the inner ring15is added to the correlation in the definition of the shortest position of the caulked side end portion of the hardened layer24b,it is possible to manage the position of the caulked side end portion of the hardened layer24bmore appropriately.

The present invention is not limited to the above embodiment, and various applications of modifications are possible.

(1) According to the present invention, as shown inFIG. 4, the above hardened layer24bcan also be applied to a hub unit in which the first inner ring15and the second inner ring15ehave a bearing12disposed adjacent thereto in its axial direction. In this case, both the first inner ring15and the second inner ring15eare fitted around the small-diameter outer peripheral surface of the hollow shaft14. The shaft end of the hollow shaft14is caulked on the outer end surface of the first inner ring15.

(2) In the invention, a double row tapered roller bearing with vertex of contact angles outside of bearing may be used. An inner ring in that case may comprise one inner ring and an inner ring and another inner ring which is integrally formed on an outer peripheral surface of the hollow shaft, or may comprise two inner rings adjacently disposed in the axial direction, like the double row angular contact ball bearing with vertex of contact angles outside of bearing. The above hardened layer24can also be applied to a hub unit having the tapered roller bearing with vertex of contact angles outside of bearing.

(3) The present invention is not limited to the hollow shaft14which is hollow in the axial direction, and as shown inFIG. 5, the hardened layer24bcan also be applied to a hub unit having a bottomed shaft14a.

(4) The present invention is not limited to the driving wheel of a vehicle, and the hardened layer24bcan also be applied to a hub unit for a follower wheel of the vehicle.

(5) An inner periphery of the hollow shaft14of the hub wheel11is formed with the female spline14bmeshing with male spline formed on an outer periphery of the drive shaft20for fitting the drive shaft20into the hollow shaft14.

In order to couple the hollow shaft14and the drive shaft20to each other with mechanically necessary strength, it is preferable that the spline14bis formed in the axial direction on the inner periphery of the hollow shaft14. With this design, an end of the spline14bis close to the caulked portion. According to this design, in a region close to the caulked portion, the male spline of the drive shaft20is prone to be deformed such as to be shrunk in the diametrical direction in such a degree that the male spline of the drive shaft20can not be fitted into the female spline easily when the caulked portion is caulked. This deformation could reach 50 mm in the diametrical direction in some cases. To avoid this deformation, the following first and second producing methods are proposed.

In the first producing method, the spline14bis subjected to a primary working such as spline broach with respect to the inner periphery of the hollow shaft14before caulking, and the spline14bon the inner periphery of the hollow shaft14after caulking is subjected to a secondary working such as the spline broach. In the case of the secondary working, a deformed portion of the spline14bformed by the primary working generated during the caulking working is subjected to correcting working such as plastically deformation so that the spline of the drive shaft20can be fitted.

In the second producing method, the inner periphery of the hollow shaft14is not formed with the spline14bbefore caulking, and the inner periphery of the hollow shaft14is formed with the spline14bby mechanical working such as spline broach after caulking.

With any of the methods, it is possible to enhance the shape precision of the spline14bformed on the inner periphery of the hollow shaft14after caulking. Therefore, it is possible to easily fit the spline formed on the outer periphery of the drive shaft20to the spline14b.

(6) In the present invention, a structure in which the first inner ring15and the second inner ring15eof the common single row angular contact ball bearing may be subjected to the spline broach as in the same manner as that of above (5) with respect to the spline14bto the inner periphery of the hollow shaft14as partially shown inFIG. 4.

While there has been described what is at present considered to be preferred embodiments of this invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of this invention.