Axial force controlling method and bearing apparatus

The present invention relates to an axial force controlling method for controlling an axial force applied to a rolling bearing in a bearing apparatus having a shaft body, the rolling bearing being mounted to the shaft body such that the rolling bearing fits an outside of the shaft body, and the bearing apparatus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an axial force controlling method for controlling an axial force applied to a rolling bearing in a bearing apparatus having a shaft body, the rolling bearing being mounted to the shaft body such that the rolling bearing fits an outside of the shaft body, and the bearing apparatus.

2. Description of the Related Art

An unpublished axial force controlling method of the present inventors will be described by reference toFIGS. 5 to 7.

A bearing apparatus shown inFIG. 5is a hub unit for a driving wheel of a vehicle. The hub unit has a hub wheel10as a shaft body and an angular ball bearing12which is mounted to a shaft portion11of the hub wheel10such that the ball bearing12fits an outside of the shaft portion11and which is an example of a rolling bearing of an inclined contact type. A free end of the shaft portion11is caused to bulge and deformed outward in a diameter direction by rolling caulking to form a caulked portion13. The bearing12has an inner ring12a, an outer ring12b, a plurality of balls12c, and two snap cages12d. In the bearing12, necessary preload is applied to the inner ring12aby the caulked portion13and the bearing12is prevented from dropping off from the hub wheel10.

Such a hub unit is mounted between a drive shaft14and a shaft case15of the vehicle. In other words, the shaft portion11of the hub wheel10is spline-fitted with the drive shaft14and connected to the drive shaft14by a nut16and an outer ring12bof the bearing12is connected to the shaft case15by a bolt17.

In the shaft portion11of the hub wheel10, a caulking jig20as shown inFIG. 7is held against a cylindrical portion11ato be caulked on a free end side of the shaft portion111as shown by a phantom line inFIG. 6before caulking. Then, by rolling the caulking jig20about a one-dot dashed line O at a constant angle a, the cylindrical portion11ato be caulked is caused to bulge and deformed radially outward, thereby forming the caulked portion13held against an outer end face of the inner ring12a.

In the above bearing apparatus, because the caulked portion13is held against the outer end face of the inner ring12ain order to bring the balls12cinto compressed states between the inner ring12aand the outer ring12b, a force for detaching the caulked portion13from the inner ring12ain an axial direction acts on the caulked portion13on the contrary. As a result, an axially inward reaction force (hereafter defined as an axial force) for resisting the above force is generated from the caulked portion13.

It is known that control for properly maintaining the axial force is necessary for ensuring a rolling property of the balls12c.

In the prior-art axial force controlling method, the axial force is controlled by merely caulking the caulked portion13firmly, adjusting a thickness of the caulked portion13, or adjusting applied pressure in caulking. However, it is not easy to properly control the axial force by this method.

The present inventors have studied the axial force earnestly and as a result, found the following point. There is a caulking starting point on an inner periphery side of the cylindrical portion11ato be caulked of the shaft portion11in caulking the cylindrical portion11aon the outer end face of the inner ring12aand outward in the radial direction by using the caulking jig20.

When an end edge on the inner periphery side of a chamfered portion formed at an inner peripheral shoulder portion of the inner ring12awas defined as a point A, the caulking starting point was defined as a point B, and a relationship between relative positions of both the points A and B was changed, it was found—that the axial force applied to the outer end face of the inner ring12afrom the caulked portion13varied.

SUMMARY OF THE INVENTION

Therefore, it is a main object of the present invention to provide an axial force controlling method for properly and easily control an axial force and a bearing apparatus according to the method.

Other objects, features, and advantages of the invention will become apparent from the following descriptions.

In an axial force controlling method of the present invention for controlling an axial force applied to a rolling bearing in a bearing apparatus having the rolling bearing and a shaft body, the rolling bearing being mounted to the shaft body such that the rolling bearing fits an outside of the shaft body, the rolling bearing being prevented from dropping off by holding a caulked portion against an outer end face of an inner ring of the rolling bearing, and the caulked portion being formed by bending a cylindrical portion to be caulked on a free end side of the shaft body outward in a diameter direction, the method comprises the following steps for controlling the axial force applied to the rolling bearing through the caulked portion: a first step of setting a position (first position) of an end edge on an inner periphery side of a chamfered portion formed at an inner peripheral shoulder portion of the inner ring; and a second step of setting a relationship between relative positions on an axial direction of the first position and a position (second position) of a caulking starting point on an inner periphery side of the cylindrical portion to be caulked, thereby controlling the axial force through the caulked portion.

It is preferable that the second step is a step of positioning the second position on an axially outside with respect to the first position.

It is preferable that the second step is a step of axially aligning the second position with respect to the first position.

It is preferable that the second step is a step of positioning the second position on an axially inside with respect to the first position.

It is further preferable that the method includes a third step of setting a radial thickness of the cylindrical portion to be caulked.

It is further preferable that the method includes a fourth step of setting a hardness of the cylindrical portion to be caulked.

A bearing apparatus of the present invention comprises a rolling bearing and a shaft body, the rolling bearing being mounted to the shaft body such that the rolling bearing fits an outside of the shaft body and the shaft body having a cylindrical portion to be caulked on a free end side of the shaft body, wherein the cylindrical portion to be caulked of the shaft body is bent outward in a diameter direction onto an outer end face of an inner ring to form a caulked portion in a state in which a relationship between relative positions in an axial direction of a caulking starting point on an inner periphery side of the cylindrical portion and an end edge on an inner periphery side of a chamfered portion formed at an inner peripheral shoulder portion of the inner ring of the rolling bearing, and an axial force is applied to the rolling bearing through the caulked portion.

In all these figures, like components are indicated by the same numerals.

DETAILED DESCRIPTION OF THE INVENTION

An axial force controlling method according to a preferred embodiment of the present invention and a bearing apparatus according to the method will be described below by reference to the drawings. In this embodiment, a hub unit for a vehicle driving wheel is taken as an example of the bearing apparatus. Because a basic structure of the hub unit is shown inFIG. 5, a detailed description of it will be omitted.

By reference toFIGS. 1 to 3, the axial force controlling method of the preferred embodiment of the invention will be described. All ofFIGS. 1 to 3show a state before bending and caulking a cylindrical portion11ato be caulked of a shaft portion11outward in a diameter direction onto an outer end face of an inner ring12a. Illustration of a form after the caulking is omitted.

In these drawings, a character A designates a position on an axial direction of an end edge on an inner periphery side at a chamfered portion at an inner peripheral shoulder portion of the inner ring12aof a rolling bearing12as a first position. In the following description, this position will be referred to as an origin point position A. A character B designates a position of a caulking starting point on an inner periphery side of the cylindrical portion11ato be caulked as a second position.

The axial force controlling method of this embodiment includes a first step of setting the origin point position A and a second step of setting a relationship between relative positions in an axial direction of the origin point position A and the caulking starting position B as the steps for controlling an axial force applied to the rolling bearing12through the caulked portion13.

With regard to the above relationship between the relative positions, the caulking starting point position B is positioned on an axially outside with respect to the origin point position A inFIG. 1, the caulking starting point position B and the origin point position A are aligned with each other in the axial direction inFIG. 2, and the caulking starting point position A is positioned on an axially inside with respect to the origin point position A inFIG. 3.

Here, the axial direction is plotted in a one-dimensional coordinate, e.g., x, the origin point position A is defined as an origin point of the one-dimensional coordinate x, and the caulking starting point position B is defined as a coordinate point x on the one-dimensional coordinate. As a result, the coordinate point x of the caulking starting point position B is greater than 0 in the case ofFIG. 1, the coordinate point x of the caulking starting point position B is equal to 0 in the case ofFIG. 2, and the coordinate point x of the caulking starting point position B is less than 0 in the case ofFIG. 3.

Therefore, if a thickness of the cylindrical portion11ato be caulked in a diameter direction is defined as t, x/t>0 in the case ofFIG. 1, x/t=0 in the case ofFIG. 2, and x/t<0 in the case ofFIG. 3.

The present inventors measured the axial force according to the settings of the relationship between the relative positions of the origin point position A and the caulking starting point position B in the respective cases ofFIGS. 1 to 3by experiment and obtained results as shown inFIG. 4. A horizontal axis designates x/t and a vertical axis designates the axial force (kgf) respectively inFIG. 4.

In this experiment, hardness of the cylindrical portion11ato be caulked is varied among the case ofFIG. 1, the case ofFIG. 2, and the case ofFIG. 3to be low (16 to 18 HRC: hardness1, represented by a mark ⋄ inFIG. 4), middle (20 to 22 HRC: hardness2, represented by marks □ and ▪ inFIG. 4), and high (26 to 28 HRC: hardness3, represented by a mark Δ inFIG. 4).

With the hardnesses1and3, the radial thickness t of the cylindrical portion11ato be caulked is maintained at a constant value, i.e., 5 mm to carry out measurement.

With the hardness2, two kinds of radial thicknesses t of the cylindrical portion11ato be caulked, i.e., 5 mm (□ inFIG. 4) and 7 mm (▪ inFIG. 4) are used to carry out the measurement.

The measurement will be described below by reference toFIG. 4.

(1) The Case of the Relationship Between the Relative Positions inFIG. 1(x/t>0):

To improve accuracy and reliability of the measurement of the axial force, conditions of the measurement of the axial force are as follows. (1) The position of the caulking starting point B is varied four times toward the outside in the axial direction. (2) The hardness of the cylindrical portion11ato be caulked is varied to be three kinds of hardnesses, i.e., the hardness1, the hardness2, and the hardness3at the respective positions of the caulking starting point B.

(3) With the hardness2, the radial thickness t of the cylindrical portion11ato be caulked is varied to be two kinds of thicknesses, i.e., 5 mm and 7 mm.

On the above conditions of the measurement, the axial force was measured at the respective caulking starting point positions B. These conditions of the measurement are similar in the following case.

The measurement results on the above conditions of the measurement are as shown inFIG. 4. InFIG. 4, variation of the axial force is between a measurement upper line L1and a measurement lower line L2and a downward slope toward the outside in the axial direction in an area between both the lines L1and L2is large.

According to the above results, with any hardnesses of the cylindrical portion11ato be caulked, the axial force varies to be smaller as the caulking starting point position B moves toward the outside in the axial direction. Therefore, because the axial force varies depending on the setting of the relationship between the relative positions in the axial direction of the origin point position A and the caulking starting point position B, it is possible to properly and easily control the axial force applied to the rolling bearing12through the caulked portion13.

Because the axial force varies also when the radial thickness—t of the cylindrical portion11ato be caulked is varied to be 5 mm and 7 mm with the hardness2, it is possible to further properly control the axial force by setting the radial thickness t of the cylindrical portion11aas the third step.

Because the axial force varies also when the hardness of the cylindrical portion11ato be caulked is varied to be the hardness1, the hardness2, and the hardness3with the same relationship between the relative positions, it is possible to further properly control the axial force by setting the hardness as the fourth step.

In this case of the hardness, the lower the hardness, the greater the axial force became. The reason for this is considered to be as follows. If the hardness of the cylindrical portion I1ato be caulked is smaller, the cylindrical portion I1acan be caulked easily and the inner ring12acan be pushed axially inward to a greater extent. As a result, the larger axial force is obtained. Therefore, in order to increase the axial force, it is preferable that the hardness of the cylindrical portion11ato be caulked is reduced.

Furthermore, the closer the caulking starting point position B to the origin point position A, the greater the axial force becomes.

(2) The Case of the Relationship Between the Relative Positions inFIG. 2(x/t=0):

The conditions of the measurement in the case of this relationship between the relative positions are similar to those in the above (1) except that the caulking starting point position B is aligned with the origin point position A.

In this case also, it is possible to control the axial force by setting the relationship between the relative positions in the axial direction of the origin point position A and the caulking starting point position B.

Similarly to the above (1), it is possible to control the axial force by setting the radial thickness t of the cylindrical portion11ato be caulked.

Similarly to the above (1), it is possible to control the axial force by setting the hardness. In other words, when a comparison was made between the hardness1, the hardness2, and the hardness3of the cylindrical portion11ato be caulked, the greatest axial force was obtained with the hardness1and the axial force with the hardness2was substantially equal to that with the hardness3or slightly greater than that with the hardness3on average. The reason for this is considered to be the same as that in the above (1).

(3) The Case of the Relationship Between the Relative Positions inFIG. 3(x/t<0):

The conditions of the measurement in the case of this relationship between the relative positions are similar to those in the above (1) except that the caulking starting point position B is on the axially inside.

In this case also, the axial force varies according to the setting of the relationship between the relative positions with any hardness. Therefore, it is possible to control the axial force by setting the relationship between the relative positions.

Similarly to the above (1), it is also possible to control the axial force by setting the radial thickness t of the cylindrical portion11ato be caulked.

Furthermore, similarly to the above (1), it is also possible to control the axial force by setting the hardness.

In the variation of the axial force shown inFIG. 4, a downward slope toward the outside in the axial direction in the axial force area between the measurement upper line L1and the measurement lower line L2is large in the case of x/t>0 of the above (1) and a downward slope toward the inside in the axial direction in an axial force area between a measurement upper line L3and a measurement lower line L4is small in the case of x/t<0 of the above (3).

The reason for this is that deformed volume due to caulking of the cylindrical portion11ato be caulked becomes large in the case of the above (1) and as a result, the axial force reduces if the applied pressure is constant.

If the minimum axial force (required axial force) required to ensure the rolling property of the balls12cof the rolling bearing12is 2500 kgf, for example, x/t is in a range of −0.15 s x/t≦0.05 for the respective hardnesses,1,2, and3from the graph inFIG. 4. If the radial thickness t of the cylindrical portion11ato be caulked is equal to 5 mm, for example, −0.75≦x≦0.25, in other words, a maximum permissible position to which the caulking starting point B of the cylindrical portion11ato be caulked can move axially inward from the origin point position A is 0.75 mm inFIG. 3and the maximum permissible position to which the caulking starting point position B of the cylindrical portion11ato be caulked can move axially outward from the origin point position A is 0.25 mm inFIG. 1. Within this range, the required axial force of 2500 Kgf or more can be obtained.

As pieced together from the above measurement results, the closer the caulking starting point position B to the origin point position A, the greater the axial force becomes, but the caulking starting position B does not necessarily have to be aligned with the origin point position A if the above-described axial force required to ensure the rolling property of the balls12cis considered and the caulking starting position B may be separated axially outward or axially inward from the origin point position A. In this case, there are both axially outward and inward maximum permissible separated distances, it is necessary to set the caulking starting point position B within a range of the maximum separated distances to control the axial force.

In order to obtain a necessary axial force with high accuracy, it is preferable to properly separate the caulking starting point position B axially outward or inward from the origin point position A.

Furthermore, because the radial thickness of the cylindrical portion11ato be caulked is also related to the axial force, it is preferable to consider the radial thickness in addition to the axial position of the caulking starting point position B in controlling the axial force.

Moreover, because the hardness of the cylindrical portion11ato be caulked is related to the axial force, it is preferable to consider the hardness in addition to the axial position of the caulking starting point position B in controlling the axial force.

In the above manner, according to the axial force controlling method of the present embodiment, it is possible to easily control the axial force such that the proper axial force can be obtained basically by setting the relationship between the relative positions.

The bearing apparatus to which the present invention is applied is not limited to the hub wheel shown in the above-described embodiment. The invention can be applied to control of the axial force in every bearing apparatus having a rolling bearing and a shaft body, the rolling bearing being mounted to—he shaft body such that the rolling bearing fits an outside of the shaft body, the rolling bearing being prevented from dropping off by holding the caulked portion against the outer end face of the inner ring of the rolling bearing, the caulked portion being formed by bending the cylindrical portion to be caulked on the free end side of the shaft body outward in the diameter direction.

Although the above hardness has a range of 2 HRC, this is variation caused by a heat treatment and this amount of variation is generated even in a treatment of the same lot.

The smaller the hardness, the larger the axial force becomes from the above measurement results only. However, a lower limit of the hardness is 16 HRC.

By the above axial force controlling method, the bearing apparatus according to the embodiment has the rolling bearing12and the shaft body11, the rolling bearing12being mounted to the shaft body11such that the rolling bearing12fits the outside of the shaft body11, and the shaft body11having the cylindrical portion11ato be caulked on the free end side of the shaft body11. The cylindrical portion11ato be caulked of the shaft body11is bent outward in the diameter direction onto the outer end face of the inner ring12ato form the caulked portion13in a state in which the relationship between the relative positions in the axial direction of the caulking starting point position B on the inner periphery side of the cylindrical portion11aand the position A of the end edge on the inner periphery side of the chamfered portion formed at the inner peripheral shoulder portion of the inner ring of the rolling bearing is set. In this manner, in the case of this bearing apparatus, the axial force is applied to the rolling bearing12through the caulked portion13and it is possible to control the axial force applied to the rolling bearing12by setting the relationship between the relative positions.

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.