JP7691827B2 - Wheel bearing device - Google Patents

Description

The present invention relates to a wheel bearing device.

In wheel bearing devices that are double-row angular contact ball bearings, the hardness of the rolling elements is usually set higher than that of the raceway surface so that the elastic fatigue limit of the rolling elements is higher than that of the raceway surface in order to ensure the strength of the rolling elements that receive localized loads. As a result, when an excessive load is input, such as when the vehicle makes a sharp turn or drives over a curb, the rolling elements may ride up onto the shoulder of the raceway surface, causing the area of the contact ellipse to protrude from the raceway surface, resulting in a stress spike in which the contact surface pressure rises suddenly, and causing an indentation on the shoulder of the raceway surface. The indentation can cause abnormal noise and lead to early peeling of the raceway surface due to stress concentration, reducing the reliability of the wheel bearing device.

As a countermeasure to this problem, for example, Patent Document 1 discloses a technology for increasing the shoulder height of the raceway surface. This prevents the rolling elements from climbing up onto the shoulder of the raceway surface.

JP 2015-224655 A

However, with the increasing power and size of vehicles, lower profile tires, and the increasing number of vehicles driven with low tire pressure due to poor maintenance caused by the widespread use of self-service gas stations, there are increasing cases where the amount of tire deflection alone is not enough to absorb the impact load from the road surface to the wheel, not only in unforeseen circumstances such as running over a curb, but also during normal vehicle driving. In this case, an excessive load beyond what was expected is applied directly from the wheel to the bearing device. If an excessive load is applied and exceeds the elastic limit of the raceway surface, an indentation will occur on the raceway surface, which may lead to abnormal noise and early peeling of the raceway surface due to the indentation, leading to failure of the bearing device.

One possible way to prevent the occurrence of indentations on the raceway surface due to excessive loads is to enlarge the bearing device itself to a size that corresponds to the excessive load. However, this would go against the current trend toward lighter vehicles and more fuel-efficient vehicles, and would be difficult to adopt due to vehicle layout constraints.

The present invention aims to provide a wheel bearing device that improves reliability by suppressing the occurrence of indentations on the raceway surface without increasing the size.

The wheel bearing device of the present invention comprises an outer member having a double-row outer raceway surface on its inner circumference, an inner member having a double-row inner raceway surface facing the double-row outer raceway surface, and a double-row rolling row having a plurality of rolling elements housed in a rollable manner between the raceway surfaces of the outer member and the inner member, and is characterized in that in at least one of the rolling rows, the rolling elements are composed of hollow balls and solid balls.

The wheel bearing device of the present invention is characterized in that it comprises an outer member having a double-row outer raceway surface on its inner circumference, an inner member having a double-row inner raceway surface facing the double-row outer raceway surface, and a double-row rolling row having a plurality of rolling elements housed in a rollable manner between the raceway surfaces of the outer member and the inner member, and in at least one of the rolling rows, the rolling elements are composed of hollow balls.

According to the present invention, by using hollow balls as rolling elements in wheel bearing devices, which have the same surface hardness as solid balls but can reduce the apparent Young's modulus, it is possible to effectively suppress the occurrence of indentations on the raceway surface without increasing the size, thereby improving reliability.

1 is a cross-sectional view of a wheel bearing device according to an embodiment; FIG. 2 is a cross-sectional view of a ball in an inner ball row. 1A and 1B are diagrams for explaining the sizes of a hollow ball and a solid ball, where FIG. 1A is a cross-sectional view of a hollow ball and FIG. 1B is a cross-sectional view of a solid ball. FIG. 11 is a cross-sectional view of a ball in an inner ball row in another example.

[Overall configuration of wheel bearing device]
The overall configuration of the wheel support bearing device 1 will be described with reference to Fig. 1. In the following description, the inner side refers to the vehicle body side of the wheel support bearing device 1 when it is attached to the vehicle body, and the outer side refers to the wheel side of the wheel support bearing device 1 when it is attached to the vehicle body. The axial direction refers to the direction along the rotation axis A of the wheel support bearing device 1.

The wheel bearing device 1 shown in Figure 1 supports a wheel for free rotation in the suspension of a vehicle such as an automobile. The wheel bearing device 1 has a configuration called the third generation, and includes an outer ring 2 as an outer member, a hub wheel 3 and an inner ring 4 as inner members, two rolling rows of inner ball rows 5 and outer ball rows 6, an inner seal member 9 and an outer seal member 10.

The outer ring 2 supports the hub wheel 3 and the inner ring 4. An inner side opening 2a is formed at the inner side end of the outer ring 2, into which an inner side seal member 9 can be fitted. An outer side opening 2b is formed at the outer side end of the outer ring 2, into which an outer side seal member 10 can be fitted. An inner side outer raceway surface 2c and an outer side outer raceway surface 2d are formed in the circumferential direction on the inner peripheral surface of the outer ring 2. A vehicle body mounting flange 2e is integrally formed on the outer peripheral surface of the outer ring 2 for mounting the outer ring 2 to a vehicle body member. A bolt hole 2g is formed in the vehicle body mounting flange 2e, into which a fastening member (here, a bolt) is inserted to fasten the vehicle body member and the outer ring 2.

The hub wheel 3 rotatably supports the wheel and brake rotor (or brake drum) of a vehicle (not shown). The inner end of the outer circumferential surface of the hub wheel 3 is provided with a small diameter step 3a that extends in the axial direction. The outer end of the hub wheel 3 is integrally formed with a wheel mounting flange 3b for mounting a wheel. The wheel mounting flange 3b is formed with a bolt hole 3f into which a hub bolt is pressed to fasten the hub wheel 3 to the wheel or brake component.

The hub wheel 3 has an inner raceway surface 3c on the outer side that faces the outer raceway surface 2d on the outer side of the outer ring 2. A seal land 3d is formed on the base side of the wheel mounting flange 3b of the hub wheel 3, with which the lip of the outer seal member 10 slides.

The inner ring 4 is provided on the small diameter step 3a of the hub wheel 3. The inner ring 4 is fixed to the small diameter step 3a of the hub wheel 3 by press fitting and crimping. The inner ring 4 applies preload to the inner ball row 5 and the outer ball row 6. At the inner end of the hub wheel 3, a crimped portion 3h is formed by crimping the inner end face of the inner ring 4.

The inner raceway 4a is formed on the outer peripheral surface of the inner ring 4. In other words, the inner raceway 4a is formed by the inner ring 4 on the inner side of the hub ring 3. The inner raceway 4a faces the outer raceway 2c on the inner side of the outer ring 2. The outer peripheral surface at the inner end of the inner ring 4 is formed with a fitting surface 4b into which the inner side seal member 9 can be fitted.

The inner ball row 5 and the outer ball row 6, which are rolling rows, are formed by a plurality of balls 7, which are rolling bodies, held by a cage 8. The inner ball row 5 is rollably sandwiched between the inner raceway surface 4a of the inner ring 4 and the outer raceway surface 2c on the inner side of the outer ring 2. The outer ball row 6 is rollably sandwiched between the inner raceway surface 3c of the hub ring 3 and the outer raceway surface 2d on the outer side of the outer ring 2. In other words, the inner ball row 5 and the outer ball row 6 are housed in a rollable manner between the raceway surfaces of the outer member and the inner member.

In the wheel bearing device 1, a double-row angular ball bearing is formed by an outer ring 2, a hub ring 3, an inner ring 4, an inner ball row 5, and an outer ball row 6.

The inner seal member 9 and the outer seal member 10 are seal members that close the open ends of the annular space S formed by the outer member and the inner member. The inner seal member 9 is attached to the inner open end of the annular space S formed between the outer ring 2 and the inner ring 4. On the other hand, the outer seal member 10 is attached to the outer open end of the annular space S formed between the outer ring 2 and the hub wheel 3.

[Rolling elements]
2 is a cross-sectional view of the balls 7 in the inner ball row 5. In the inner ball row 5, the balls 7 are composed of hollow balls 71 and solid balls 72.

The hollow ball 71 and the solid ball 72 are made of bearing steel. The bearing steel is made of high carbon chromium bearing steel such as SUJ2, and is hardened by through hardening to a hardness of 62 to 67 HRC. The hollow ball 71 and the solid ball 72 may be made of ceramics, but steel is less expensive than ceramics. There are no particular limitations on the manufacturing method of the hollow ball 71, and it is also possible to use, for example, the manufacturing method described in JP 2011-58065 A, which uses high carbon chromium bearing steel that has been carburized rather than through hardening.

When the hollow balls 71 and solid balls 72 are made of the same material, the hollow balls 71 have the same surface hardness and a smaller apparent Young's modulus than the solid balls 72. In other words, when the hollow balls 71 and solid balls 72 are arranged between the raceway surfaces of the outer member and the inner member, the hollow balls 71 are more likely to elastically deform than the solid balls 72, and the contact ellipse with the raceway surfaces becomes larger. Therefore, compared to the conventional case in which all the balls 7 in the inner ball row 5 are made of solid balls 72, the contact surface pressure with the outer raceway surface 2c and the inner raceway surface 4a is lower by the amount of hollow balls 71 used, and the same effect as when the outer diameter of the balls 7 is increased can be achieved, that is, the life of the wheel bearing device 1 can be extended.

And by using hollow balls 71, which are more flexible than solid balls 72, it is possible to prevent surface pressure exceeding the elastic limit from acting on the outer raceway surface 2c and the inner raceway surface 4a, even when an excessive load is applied. This makes it possible to prevent indentations from occurring on the outer raceway surface 2c and the inner raceway surface 4a. As a result, it is possible to prevent abnormal noise and failure of the wheel bearing device 1 due to early peeling of the raceway surface caused by indentations, improving the reliability of the wheel bearing device 1.

Figure 3 is a diagram explaining the sizes of hollow ball 71 and solid ball 72, where (a) is a cross-sectional view of hollow ball 71 and (b) is a cross-sectional view of solid ball 72. In order to ensure that the load is evenly applied to hollow ball 71 and solid ball 72 when a preload is applied, the outer diameter D1 of hollow ball 71 is made larger than the outer diameter D3 of solid ball 72 within the same range as the outer diameter of a conventional ball. Furthermore, when an excessive load is applied, hollow ball 71 with a larger outer diameter receives the load first, so that hollow ball 71 acts like a buffer material and is likely to suppress indentations.

Specifically, when the outer diameter D1 of the hollow ball 71 and the outer diameter D3 of the solid ball 72 are 5 to 15 mm, it is preferable that the outer diameter D1 of the hollow ball 71 is larger than the outer diameter D3 of the solid ball 72 by 10 μm to 30 μm. If the outer diameter D1 of the hollow ball 71 is larger than the outer diameter D3 of the solid ball 72 by less than 10 μm, the effect of making the outer diameter D1 of the hollow ball 71 larger than the outer diameter D3 of the solid ball 72 is small. On the other hand, if the outer diameter D1 of the hollow ball 71 is larger than the outer diameter D3 of the solid ball 72 by more than 30 μm, the contact ellipse of the hollow ball 71 with the raceway surface becomes larger, which increases the rotational torque due to increased spin slippage, etc., which is undesirable.

In the inner ball row 5 of this embodiment, 14 balls 7 are arranged, with seven hollow balls 71 and seven solid balls 72 arranged alternately. The number of balls 7 is not particularly limited. In the inner ball row 5, the proportion of hollow balls 71 is preferably 30% or more and 70% or less. If the proportion of hollow balls 71 is less than 30%, the effect of using hollow balls 71 is small. On the other hand, if the proportion of hollow balls 71 is 70% or more, the contact ellipse of the hollow balls 71 with the track surface becomes large, and the rotation torque increases due to increased spin slip, etc., which is not preferable. Therefore, if the proportion of hollow balls 71 is 70% or more, it is necessary to adjust the amount of deflection of the hollow balls 71 by reducing the inner diameter D2 of the hollow balls 71 or using a material with a large Young's modulus.

As shown in FIG. 4, in the inner ball row 5, the balls 7 may all be hollow balls 71. In this case, multiple types of hollow balls 71 with different outer diameters D1 and inner diameters D2 may be mixed.

In addition, by using the hollow balls 71, the weight of the wheel bearing device 1 can be reduced. For example, if D1/D2 = 1.28, the weight of the hollow balls 71 is approximately half the weight of the solid balls 72. Reducing the weight of the wheel bearing device 1 improves the fuel efficiency of the vehicle, and the driving stability is improved by reducing the so-called unsprung weight.

The configuration of the balls 7 in the outer ball row 6 is similar to that of the balls 7 in the inner ball row 5, and therefore a description thereof will be omitted. The inner ball row 5 and the outer ball row 6 may differ in the number of balls 7, the material of the balls 7, the pitch circle diameter, the outer diameter D1 of the hollow balls 71, the inner diameter D2 of the hollow balls 71, the outer diameter D3 of the solid balls 72, the proportion of hollow balls 71, and the like. In addition, it is sufficient that at least one of the inner ball row 5 or the outer ball row 6 includes hollow balls 71.

In this embodiment, the wheel bearing device 1 for a driven wheel is described, but the present invention can also be applied to a wheel bearing device for a driving wheel.

The wheel bearing device 1 of this embodiment has been described above as a wheel bearing device with a third-generation inner ring rotation structure in which the inner raceway surface 3c of the rolling elements is formed directly on the outer periphery of the hub wheel 3, but is not limited to this. For example, it may be a second-generation inner ring rotation structure in which a pair of inner rings are press-fitted into the hub wheel. It may also be a third-generation or second-generation outer ring rotation structure. It may also be a first-generation structure consisting of an outer ring and an inner ring. The above embodiment merely shows a typical form of the present invention, and various modifications can be made without departing from the gist of the present invention.

1 Wheel bearing device 2 Outer ring (outer member)
2c, 2d Outer raceway surface 3 Hub ring (inner member)
3c, 4a: inner raceway surface 4: inner ring (inner member)
5 Inner ball row (rolling row)
6 Outer ball row (rolling row)
7. Ball (rolling element)
71 Hollow ball 72 Solid ball

Claims (4)

an outer member having a double row outer raceway surface on an inner periphery thereof;
an inner member having a double row inner raceway surface facing the double row outer raceway surface;
a double row of rolling elements having a plurality of rolling elements rollably accommodated between the raceway surfaces of the outer member and the inner member,
In at least one of the rolling rows, the rolling elements are constituted by hollow balls and solid balls,
A wheel bearing device, characterized in that a ratio of the hollow balls in one rolling row and a ratio of the hollow balls in the other rolling row are different. The wheel bearing device according to claim 1, characterized in that in the rolling row composed of the hollow balls and the solid balls, the proportion of the hollow balls is 30% or more and 70% or less. The wheel bearing device according to claim 1 or 2, characterized in that in the rolling row composed of the hollow balls and the solid balls, the outer diameter of the hollow balls is larger than the outer diameter of the solid balls. The wheel bearing device according to claim 3, characterized in that in the rolling row composed of the hollow balls and the solid balls, the outer diameter of the hollow balls is greater than the outer diameter of the solid balls by a range of 10 μm to 30 μm.

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