Patent Application
20150267750
The disclosure of Japanese Patent Application No. 2014-059877 filed on Mar. 24, 2014 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a wheel bearing device with reduced abnormal noise during rotation.
2. Description of the Related Art
A hub unit 100 as illustrated in
The cause of the generation of the abnormal noise is considered to be that balls 105 override a shoulder 106, and thereby the indentations are generated in portions close to the shoulder 106 of the raceway surface 107. Thus, a structure is proposed that inhibits the balls from overriding the shoulder by setting the ratio of the height of the shoulder 106 to the diameter of the balls 105 to equal to or more than 0.25 to less than 0.50 (refer to Japanese Patent Application Publication No. 2012-31937 (JP 2012-31937 A)). Overriding the shoulder refers to a phenomenon in which a ball makes an elastic contact with a raceway surface, and a contact area elliptically spreading around the point of the contact (hereinafter, simply called a “contact area”) extends beyond the raceway surface.
Even in a bearing device in which the height of the shoulder is set to the extent described in JP 2012-31937 A, it has been observed that, in some cases, the abnormal noise still occurs depending on the amount of the impact load applied to the wheel. This is because the balls override the shoulder if an excessive thrust load is imposed on the wheel bearing device.
It is an object of the present invention to prevent the generation of the abnormal noise of the wheel bearing device by completely preventing the generation of indentations caused by balls overriding the shoulder when an excessive thrust load is applied.
A wheel bearing device according to an aspect of the present invention is constitutionally characterized by including a fixed member having double row fixed raceway surfaces around its axis line, a rotary member having double row rotary raceway surfaces coaxial with and facing the fixed raceway surfaces, and double ball rows in each of which a plurality of balls are rollably disposed between the double row fixed-side raceway surfaces and the double row rotary raceway surfaces facing each other. In the wheel bearing device, in the rotary raceway surface associated with the ball row on a vehicle outer side, a generatrix on a contact angle side has a circular arc shape, and a shoulder on the vehicle outer side of the rotary raceway surface has a height larger than a curvature radius of the circular arc.
The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
A hub unit 5 that is a first embodiment of the present invention will be described with reference to
The hub unit 5 includes an outer ring 6 (fixed member), a rotary member 3, a plurality of balls 7, 8, and cages 9, 10. The outer ring 6 is fixed to the vehicle. The rotary member 3 is rotatably supported coaxially with the outer ring 6. The balls 7, 8 are rollably disposed between the outer ring 6 and the rotary member 3. The cages 9, 10 hold the balls 7, 8 so that the balls 7, 8 are arranged at predetermined intervals in the circumferential direction.
The outer ring 6 is made of carbon steel such as S55C. The outer ring 6 is integrally provided at the outer periphery thereof with a flange 17. Bolt holes 18 are formed through the flange 17 in the axis line direction. Bolts (not illustrated) are inserted into the bolt holes 18, and screw-tightened to a vehicle body so that the hub unit 5 is fixed to the vehicle.
A pair of outer raceway surfaces 11, 12 is provided at the inner periphery of the outer ring 6. The outer raceway surfaces 11, 12 are shaped by a turning process, and then, are quench-hardened by induction heat treatment to a hardness of approximately 60 HRC. Thereafter, the outer raceway surfaces 11, 12 are precisely finished by grinding and super finishing processes. The sectional shapes in the axis line direction of the outer raceway surfaces 11, 12 are circular arc shapes, and have curvature radiuses slightly larger than the radiuses of the balls 7, 8, respectively.
Each of the outer raceway surfaces 11, 12 has, on both sides thereof in the axial direction, cylindrical surfaces continuous with the raceway surface. Each of the cylindrical surfaces is hereinafter called a “shoulder”. Regarding also each inner raceway surface to be described below, the “shoulder” refers to a similar cylindrical surface. Shoulders 13, 14, 15, 16 are provided on both sides in respective axial directions of the outer raceway surfaces. Each of the shoulders 13, 14, 15, 16 has a cylindrical shape coaxial with the outer raceway surfaces 11, 12. At the outer raceway surface 11, the height of the shoulder 13 on the inner side is smaller than the height of the shoulder 14 on the outer side. At the outer raceway surface 12, the height of the shoulder 16 on the outer side is smaller than the height of the shoulder 15 on the inner side. The height of the shoulder at the outer raceway surface refers to a dimension in a direction orthogonal to the axis line of the outer ring 6 from the groove bottom (position where the diameter is largest) of the raceway surface.
The rotary member 3 is composed of a hub shaft 21 and an inner ring 4 pressed onto a shaft end on the inner side of the hub shaft 21.
The hub shaft 21 is made of carbon steel such as S55C. An angular inner raceway surface 22 is provided at the outer periphery of the hub shaft 21 coaxially with an axis line 84 of the hub shaft 21. The sectional shape in the axis line direction of the inner raceway surface 22 is a circular arc shape. A shoulder 24 is provided on the outer side of the inner raceway surface 22. The shoulder 24 has a cylindrical shape coaxial with the inner raceway surface 22. The height of the shoulder 24 is set larger than the radius of the balls 8. The height of the shoulder at the inner raceway surface refers to a radial dimension from the groove bottom (position where the diameter is smallest) of the inner raceway surface 22 to the outer periphery of the shoulder 24.
The inner raceway surface 22 is provided, on the inner side thereof, with a shaft portion 25 coaxial with the axis line 84 of the hub shaft 21. The shaft portion 25 has a cylindrical shape, and has an outside diameter dimension approximately equal to the minimum diameter of the inner raceway surface 22. A part of the shaft portion 25 forms a shoulder on the inner side of the inner raceway surface 22.
An inner ring fitting portion 26 having a diameter smaller than that of the shaft portion 25 is provided at the inner-side end of the shaft portion 25 coaxially with the shaft portion 25. The shaft portion 25 continues to the inner ring fitting portion 26 via a stepped portion 27 that is a flat surface orthogonal to the axis line 84.
A disc-like flange 2 is provided at an end on the outer side of the hub shaft 21. A portion where the shoulder 24 continues to the flange 2 is provided with a corner rounded portion 75 having a circular arc-like section in the axis line direction so as to ensure strength against a bending load applied to the flange 2. The flange 2 is provided with a plurality of bolts 28 for mounting thereon a wheel (not illustrated). A cylindrically shaped wheel mounting portion 29 is coaxially provided on the outer side face of the flange 2. A concave portion 30 is provided on the radial inner side of the wheel mounting portion 29.
The hub unit 5 is assembled to the vehicle, and then, the wheel is fit onto the wheel mounting portion 29. The wheel is then tightened with the bolts 28 so as to be fastened to the flange 2.
The inner ring 4 is made of bearing steel. An inner raceway surface 31 is provided at the outer periphery of the inner ring 4. Shoulders 32, 33 are provided on both sides in the axial direction of the inner raceway surface 31. The height of the shoulder 33 on the inner side is larger than the height of the shoulder 32 on the outer side. The sectional shape in the axis line direction of the inner raceway surface 31 is a circular arc shape. The curvature radius of the inner raceway surface 31 is slightly larger than the radius of the balls 7. The inner ring 4 is quench-hardened so that the whole thereof is hardened to a hardness of approximately 60 HRC. Thereafter, the inner raceway surface 31 is precisely finished by grinding and super-finishing.
The overall structure of the hub unit 5 will be described with reference to
As illustrated in
Thereafter, the inner ring 4 is pressed onto the inner ring fitting portion 26. Thereafter, the inner-side end of the hub shaft 21 is clinched to prevent the inner ring 4 from coming off. Thus, the assembly of the hub unit 5 is completed.
The shape of the inner raceway surface 22 will be described in detail with reference to
A portion of the inner raceway surface 22 on the outside diameter side of the hub shaft 21 continues to the shoulder 24 via a corner 43. Forming the corner 43 at an acute angle is liable to cause problems of, for example, chipping the corner. However, as will be described later, in order to prevent the balls 8 from overriding the shoulder, the area of the inner raceway surface 22 needs to be set as large as possible. Given these factors, the size of a chamfer at the corner 43 is set to approximately 0.2 mm.
Thus, the inner raceway surface 22 is provided between a point tangent to the shaft portion 25 and the corner 43 such that the inner raceway surface 22 is formed of one circular arc that curves toward the outer side. The corner 43 is formed at one end in the axial direction of the shoulder 24, and the radial dimension from a groove bottom portion (point R) is equal to or larger than the curvature radius of the circular arc. Accordingly, a central angle θk for the circular arc (a central angle of a sector formed by both ends of the circular arc and a center of curvature O) is 90 degrees or larger.
The inner raceway surface 22 and the surface of the shoulder 24 are quench-hardened by the induction heat treatment to a hardness of approximately 60 HRC, and then are ground. As illustrated in
Thereafter, the inner raceway surface 22 is precisely finished by super-finishing. The super-finishing process of the inner raceway surface 22 is performed using a super-finishing grinding wheel that has a center of oscillation in the same position as the center of curvature O of the circular arc forming the inner raceway surface 22. The inner raceway surface 22 is formed of one circular arc, so that the whole area of the inner raceway surface 22 can be precisely finished by oscillating the super-finishing grinding wheel along the generatrix of the inner raceway surface 22.
The following describes a contact state between the ball and the raceway surface when the wheel collides with a curb, with reference to
When the wheel 1 collides with the curb, a load Q is imposed on an outer peripheral portion of the wheel 1 in the direction indicated by a white arrow in
When the wheel 1 collides with the curb, the magnitude of the load Q imposed on the wheel 1 greatly differs depending on, for example, the speed at the time of the collision. If an excessively large load is imposed, problems of, for example, deformation of components (such as a knuckle) other than the hub unit occur. To substantially continue to use the parts after the collision with the curb, it is appropriate to set the maximum of the load Q imposed on the wheel 1 to a value six times a vehicle weight (hereinafter, this value of the load is expressed as “6G”). The following description will be made assuming that the value of the load Q imposed during the collision with the curb is 6G.
The contact area increases as the force pressing the ball to the inner raceway surface increases. When the wheel 1 collides with the curb and the large thrust load Fa is imposed, a central angle φ of a sector formed by the center of curvature O and both ends of the contact area E1 (hereinafter, simply called a “central angle”) is larger than the amount of a central angle during normal running of the vehicle. In addition, the thrust load Fa is displaced the inner raceway surface 22 to the inner side relative to the outer raceway surface 12, so that the angle θ of the contact between the ball 8 and the inner raceway surface 22 is larger than the contact angle during the normal running of the vehicle.
Thus, during the collision with the curb, both the contact angle and the central angle are larger than those during the normal running of the vehicle. In some cases, this phenomenon makes the radial dimension from the groove bottom portion (point R) on the inner raceway surface 22 to the position of an end S1 at the radial outside of the contact area E1 larger than the curvature radius of the circular arc. When the height of the shoulder 24 is smaller than the radial dimension from groove bottom portion (point R) to the end S1, the contact area E1 extends beyond the inner raceway surface 22, so that the ball 8 comes in contact with the edge (in the position of the corner 43) of the inner raceway surface 22. The contact at the edge produces a surface pressure higher than that of contact between planes, so that an indentation is generated at a portion of the inner raceway surface 22 near the shoulder 24, and an indentation is also generated on the surface of the ball 8.
The indentation generated on the inner raceway surface has little influence on generation of abnormal noise. The reason for this is as follows: when the thrust load Fa is imposed an the hub shaft 21, the indentation is generated in a position where the contact angle is larger than that during the normal running. Thus, when the normal running is restored, the contact angle returns to the original small value, so that the contact area E1 between the ball 8 and the inner raceway surface 22 moves away from the position of generation of the indentation.
However, after the indentation is generated on the surface of the ball 8 and then the normal running is restored, the indentation inevitably passes through the contact points between the ball 8 and the inner and the outer raceway surfaces 22 and 12 when the hub shaft rotates and thereby the ball 8 rolls. This results in generation of abnormal noise, and that is why the indentation needs to be surely prevented from occurring on the surface of the ball 8.
In the hub unit 5 of the first embodiment, the height of the shoulder 24 on the vehicle outer side of the inner raceway surface 22 is larger than the curvature radius of the circular arc forming the inner raceway surface 22. This allows the inner raceway surface 22 continuing to the shoulder 24 to be fainted so that the radial dimension from the groove bottom portion (point R) to an end at the radial outside of the inner raceway surface 22 is larger than the curvature radius of the circular arc. As a result, the position of the end at the radial outside of the inner raceway surface 22 can be set radially outside the end S1 of the contact area E1. This setting prevents the contact area E1 from extending beyond the end at the radial outside of the inner raceway surface 22. With this configuration, the edge of the inner raceway surface 22 is prevented from coming in contact with the ball 8. As a result, no indentations are generated at the portion of the inner raceway surface 22 near the shoulder 24 or on the surface of the ball 8.
In addition, the inner raceway surface 22 in the first embodiment is formed of one circular arc up to the corner 43 on the outer side of the center of curvature O in the axis line direction. This causes the contact area between the ball 8 and the inner raceway surface 22 to be always formed at the circular arc portion of the inner raceway surface 22. This makes the axis length of the contact ellipse longer and thereby the contact area larger, so that the contact pressure between the ball 8 and the inner raceway surface 22 can be reduced. Thus, the generation of the indentation of the inner raceway surface 22 can surely be prevented.
As has been described above, when the wheel collides with the curb, the hub unit 5 of the first embodiment can surely prevent the generation of abnormal noise by preventing the indentations from occurring due to the ball overriding the shoulder.
A second embodiment of the present invention will be described. The shape of an inner raceway surface in the second embodiment will be described in detail with reference to
As illustrated in
Thus, the height of a shoulder 73 on the vehicle outer side of the inner raceway surface 70 is larger than the curvature radius of the circular arc portion 71.
An end in the direction toward the outer periphery of the inner raceway surface 70 (that is, an end on the outer periphery side of the linear portion 72) continues to the shoulder 73 having a cylindrical shape. A corner 74 where the linear portion 72 continues to the shoulder 73 is slightly chamfered. This is because a sharp corner on the corner 74, if formed, is liable to cause problems of, for example, chipping of the sharp corner. However, in order to prevent the ball 8 from overriding the shoulder, the area of the inner raceway surface 70 needs to be ensured, so that the size of the chamfer at the corner 74 is set to approximately 0.2 mm. A portion where the shoulder 73 continues to the flange 2 provided on the outer side thereof is provided with a corner rounded portion 75 having a circular arc-like section in the axis line direction so as to ensure strength against a bending load applied to the flange 2.
A method for processing the inner raceway surface will be described with reference to
The second embodiment is advantageous over the first embodiment in that the inner raceway surface 70 can be more efficiently ground. This advantage will first be described. To facilitate understanding, with reference to
As illustrated in
When the height of the shoulder 24 is larger than the curvature radius of the circular arc portion forming the inner raceway surface 22, the inner raceway surface 22 is formed so that the position in the axis line direction of the corner 43 where the inner raceway surface 22 continues to the shoulder 24 overlaps the position in the axis line direction of the grinding wheel 85. As a result, rotating the hub shaft 21 about the axis line 84 causes the corner 43 to interfere with the grinding wheel 85 at T1 and T2 in
Employing the shape of the inner raceway surface 22 according to the second embodiment can avoid the interference described above. In the second embodiment, the linear portion 72 is provided so as to extend in the direction orthogonal to the axis line 76, so that the corner 74 where the inner raceway surface 70 continues to the shoulder 73 does not overlap the grinding wheel 77 in the axis line direction. As a result, the corner 74 does not interfere with the grinding wheel 77, so that the processing efficiency in the process of grinding the inner raceway surface can be markedly improved.
With reference to
When the wheel 1 collides with the curb and the thrust load Fa is imposed on the hub shaft 87, the contact area E2 is larger than the contact area during the normal running of the vehicle. In addition, when the thrust load Fa is imposed on the hub shaft 87, the inner raceway surface 70 is displaced to the inner side relative to the outer raceway surface 12, so that the angle θ between the ball 8 and the inner raceway surface 70 is larger than the contact angle during the normal running of the vehicle. Thus, in some cases, the collision with the curb makes the radial dimension from the groove bottom portion (point A) on the inner raceway surface 70 to the position of an end S2 at the radial outside of the contact area E2 larger than the curvature radius of the circular arc. As a result, the contact area E2 is formed to extend from the circular arc portion 71 to the linear portion 72.
In the hub unit of the second embodiment, the height of the shoulder 73 on the vehicle outer side of the inner raceway surface 70 is larger than the curvature radius of the circular arc forming the inner raceway surface 70. This dimensional relationship allows the inner raceway surface 70 to be formed so that the radial dimension from the groove bottom portion (point A) to the position of an end at the radial outside of the inner raceway surface 70 is larger than the curvature radius of the circular arc. As a result, the dimension from the groove bottom portion (point A) to the position of the end at the radial outside of the inner raceway surface 70 can be set larger than the dimension from the groove bottom portion (point A) to the end S2 of the contact area E2. This setting prevents the contact area E2 from extending beyond the end at the radial outside of the inner raceway surface 70. With the configuration, the edge of the inner raceway surface 70 is prevented from coming in contact with the ball 8. As a result, no indentations are generated at a portion of the inner raceway surface 70 near the shoulder 73 or on the surface of the ball 8.
The linear portion 72 is a tangent line to the circular arc portion 71, so that the generatrix of the inner raceway surface 70 has a smoothly changing curvature radius. Thus, what is called a stress concentration does not occur at the joint between the linear portion 72 and the circular arc portion 71, so that the contact pressure is uniformed, thus allowing the maximum surface pressure to be kept low. Thus, the generation of the indentation on the raceway surface can surely be prevented.
The direction in which the linear portion 72 extends is not limited to the direction orthogonal to the axis line 76. The scope of the present invention includes slightly tilting the linear portion 72 toward the outer side in order to surely avoid interference between the grinding wheel 77 and the corner 74.
When tilting the linear portion 72 as described above, increasing the tilt angle increases the area of a portion of the contact area E2 formed in the linear portion 72. In the linear portion 72, the axis length of the contact ellipse forming the contact area decreases, so that the contact area decreases and the contact pressure increases. To prevent occurrence of problems, such as flaking, on the inner raceway surface 70, the tilt angle (angle formed by the axis line 76 and the linear portion 72) is preferably set to 70 degrees or larger.
As has been described above, when the wheel collides with the curb, the hub unit of the second embodiment can surely prevent the generation of abnormal noise by preventing the indentations due to the balls overriding the shoulder.
With the present invention, it is possible to completely prevent balls from overriding the shoulder, thereby preventing generation of abnormal noise of a wheel bearing device, when an excessive thrust load is applied.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-059877 | Mar 2014 | JP | national |
