Bearing device for wheel

Abstract

The objective of the present invention is to set mechanical properties such as rolling fatigue life and rigidity within appropriate ranges, and also reduce torque and weight. An outer diameter a at an inner side end of an outer ring (2) and an axial distance b between a flange surface (3k) of a hub flange (3b) and an inner side end surface (4b) of an inner ring (4) satisfy the relationship: (a / b) > 1.2, and a pitch circle diameter PCDo of balls 7 constituting an outer-side ball row (6) and a pitch circle diameter PCDi of balls 7 constituting an inner-side ball row satisfy the relationship: PCDo < PCDi.

Description

Wheel bearing device

[0001] The present invention relates to a wheel bearing device.

[0002] 2. Description of the Related Art Conventionally, wheel bearing devices that rotatably support wheels in suspension systems for vehicles such as automobiles have been known.

[0003] In recent years, fuel regulations have been imposed on vehicles that use wheel bearing devices due to social backgrounds such as energy conservation and decarbonization, and the trend toward electrification is progressing. Electric vehicles, which are expected to become more popular in the future and use on-board batteries as their main power source, tend to be heavier than gasoline-powered vehicles, and their axle loads tend to increase.

[0004] Generally, as the axle load increases, the rotational torque of a wheel support bearing device increases, and from the perspective of strength, the wheel support bearing device must be made larger. For example, wheel support bearing devices used in electric vehicles tend to be narrower and larger in diameter, with the outer diameter at the axial end of the outer ring being larger than the axial distance between the flange surface of the hub flange of the hub wheel and the axial end face of the inner ring fitted to the hub wheel. As a result, wheel support bearing devices used in electric vehicles are heavier than wheel support bearing devices used in gasoline-powered vehicles. Therefore, wheel support bearing devices used in electric vehicles are required to have lower torque and lighter weight.

[0005] In Patent Document 1, the pitch circle diameter of the rolling elements in the inner rolling element row is made larger than the pitch circle diameter of the rolling elements in the outer rolling element row, and the diameter of the rolling elements in the inner rolling element row is made larger than the diameter of the rolling elements in the outer rolling element row, and the radius of curvature of the raceway surface on the groove bottom side and shoulder side of the raceway surface between the outer ring and the inner ring is made larger than the radius of curvature of the raceway surface around the contact area of ​​the rolling elements on the raceway surface.

[0006] With this configuration, the occurrence of edge loads on the rolling surfaces of the rolling elements is suppressed while ensuring rolling fatigue life and moment rigidity, thereby improving the durability of the wheel bearing device. However, Patent Document 1 does not disclose specific values ​​for the diameter of the rolling elements, the number of rolling elements, the contact angle of the rolling elements with respect to the raceway surface, etc., and depending on these values, it may be difficult to obtain sufficient rolling fatigue life and moment rigidity.

[0007] Patent document 1 also describes a wheel bearing device in which the pitch circle diameter of the rolling elements in the outer rolling element row is larger than the pitch circle diameter of the rolling elements in the inner rolling element row.

[0008] In wheel bearing devices used in gasoline vehicles, the outer diameter at the axial end of the inner ring is often smaller than or equal to the axial distance between the flange surface of the hub flange of the hub ring and the axial end face of the inner ring that is fitted to the hub ring, and in order to ensure sufficient rolling fatigue life and rigidity in a limited space, a structure such as that described in Patent Document 1, in which the pitch circle diameter of the outer rolling element is larger than the pitch circle diameter of the inner rolling element, is more appropriate.

[0009] On the other hand, in wheel bearing devices for electric vehicles, which are becoming increasingly narrower and larger in diameter as axle loads increase, it is possible to form the pitch circle diameter of the inner rolling element larger, so if the pitch circle diameter of the outer rolling element is formed larger than or equal to the pitch circle diameter of the inner rolling element, the rolling fatigue life and mechanical properties such as rigidity of the outer side may be improved more than necessary.

[0010] Furthermore, as the width and diameter of a wheel bearing device become narrower and larger, the axial distance from the flange surface of the hub flange to the center position of the wheel attached to the flange surface tends to increase, and in addition, the axle load of an electric vehicle is large, so the moment load and rotational torque generated in the wheel bearing device tend to increase. Furthermore, as the axle load increases, it is necessary to increase the pitch circle diameter, diameter, and number of rolling elements of the wheel bearing device, which tends to increase the weight of the wheel bearing device.

[0011] Japanese Patent Application Laid-Open No. 2014-29202

[0012] For this reason, in a wheel bearing device with a narrower width and larger diameter, if the pitch circle diameter of the outer rolling element is made larger than or equal to the pitch circle diameter of the inner rolling element, mechanical properties such as rolling fatigue life and rigidity will become excessive, while it will be difficult to satisfy environmental performance requirements such as low torque and weight reduction.

[0013] The present invention has been made in consideration of the above circumstances, and provides a wheel bearing device in which the pitch circle diameter of the inner rolling element is made larger than the pitch circle diameter of the outer rolling element, and mechanical properties such as rolling fatigue life and rigidity can be set within appropriate ranges, while also achieving low torque and weight reduction.

[0014] That is, the wheel bearing device includes an outer member having a first outer raceway surface formed at one axial end thereof and a second outer raceway surface formed at the other axial end thereof relative to the first outer raceway surface, a hub ring having a hub flange for mounting a wheel at one axial end thereof and having a first inner raceway surface formed opposite to the first outer raceway surface, and an inner ring fitted to the other axial end thereof with respect to the hub ring and having a second inner raceway surface formed opposite to the second outer raceway surface, and a first rolling element accommodated so as to be freely rollable between the second outer raceway surface and the second inner raceway surface, and a second rolling element accommodated so as to be freely rollable between the second outer raceway surface and the second inner raceway surface, wherein an outer diameter a at the other axial end of the outer member and an axial distance b between the flange surface of the hub flange and the other axial end side surface of the inner ring satisfy the relationship (a / b) > 1.2, and a pitch circle diameter PCDo of the first rolling element and a pitch circle diameter PCDi of the second rolling element satisfy the relationship PCDo < PCDi.

[0015] According to the present invention, it is possible to set mechanical properties such as rolling fatigue life and rigidity within appropriate ranges while achieving low torque and light weight.

[0016] Fig. 1 is a side cross-sectional view showing a bearing device for a wheel. Fig. 2 is an enlarged side cross-sectional view showing an outer ring, a hub ring, and an inner ring that accommodate an inner ball row and an outer ball row. Fig. 3 is a side cross-sectional view. Fig. 4 is a side cross-sectional view showing a bearing device for a wheel according to a second embodiment. Fig. 5 is a side cross-sectional view showing a bearing device for a wheel according to a third embodiment. Fig. 6 is a side cross-sectional view showing bolt holes in a hub flange according to the second embodiment.

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0018] [Wheel Bearing Apparatus] A wheel bearing apparatus 1 shown in FIG. 1 is one embodiment of a wheel bearing apparatus according to the present invention, and supports a wheel rotatably in a suspension system of a vehicle such as an automobile.

[0019] In the following description, the axial direction refers to the direction along the rotation axis X of the wheel support bearing device 1. The radial direction refers to the direction perpendicular to the rotation axis X. Furthermore, the outer side refers to one axial end side, which is the wheel side of the wheel support bearing device 1 when attached to the vehicle body, and the inner side refers to the other axial end side, which is the vehicle body side of the wheel support bearing device 1 when attached to the vehicle body.

[0020] The wheel bearing device 1 has a configuration known as the third generation, and includes an outer ring 2 as an outer member, a hub ring 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.

[0021] 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.

[0022] An inner-side outer raceway surface 2c and an outer-side outer raceway surface 2d are formed on the inner peripheral surface of the outer ring 2. The outer-side outer raceway surface 2d is an example of a first outer raceway surface, and the inner-side outer raceway surface 2c is an example of a second outer raceway surface. A vehicle body mounting flange 2e for mounting the outer ring 2 to a vehicle body member is integrally formed on the outer peripheral surface of the outer ring 2. The inner end of the outer ring 2 is a pilot portion that is fitted into the vehicle body member.

[0023] A small-diameter step 3a, which is smaller in diameter than the outer end, is formed at the inner end of the outer peripheral surface 3j of the hub wheel 3. A hub flange 3b, for mounting a wheel, is integrally formed at the outer end of the hub wheel 3.

[0024] The hub flange 3b has a plurality of bolt holes 3e formed therein. Hub bolts 3f for fastening the hub wheel 3 to a wheel or brake component are press-fitted into the bolt holes 3e. The hub flange 3b has a flange surface 3k facing the outer side. The hub wheel 3 has a through hole 3i that passes through in the axial direction, and a constant velocity universal joint can be fitted into the through hole 3i so that it can rotate integrally with the hub wheel 3.

[0025] An outer inner raceway surface 3c is provided on the outer peripheral surface 3j of the hub ring 3 so as to face the outer outer raceway surface 2d on the outer ring 2. In other words, the inner raceway surface 3c is formed by the hub ring 3 on the outer side of the inner member. The inner raceway surface 3c of the hub ring 3 is an example of a first inner raceway surface. In the hub ring 3, a lip sliding surface 3d with which the outer seal member 10 slides is formed on the base side of the hub flange 3b.

[0026] The inner seal member 9 is fitted into the inner opening end of the annular space S formed by the outer ring 2 and the hub wheel 3, closing the inner opening end. The outer seal member 10 is fitted into the outer opening end of the annular space S formed by the outer ring 2 and the hub wheel 3, closing the outer opening end.

[0027] An inner ring 4 is provided on the small diameter step 3a of the hub ring 3. The inner ring 4 is fixed to the small diameter step 3a of the hub ring 3 by press fitting and crimping. The inner ring 4 applies preload to the inner ball row 5 and outer ball row 6, which are the rolling rows. The inner ring 4 has an inner end face 4b at its inner end. A crimped portion 3h is formed at the inner end of the hub ring 3 by crimping onto the inner end face 4b of the inner ring 4. The inner ring 4, which is fitted onto the small diameter step 3a of the hub ring 3, has a fitting surface 4c that fits onto the hub ring 3, and the fitting surface 4c is the inner circumferential surface of the inner ring 4.

[0028] An inner-side inner raceway surface 4a is provided on the outer peripheral surface of the inner ring 4 so as to face the inner-side outer raceway surface 2c of the outer ring 2. In other words, the inner raceway surface 4a is formed on the inner side of the inner member by the inner ring 4. The inner raceway surface 4a of the inner ring 4 is an example of a second inner raceway surface.

[0029] The inner ball row 5 and outer ball row 6, which are rolling rows, are formed by a plurality of balls 7, which are rolling elements, being held in a cage 8. The inner ball row 5 is rollably sandwiched between the inner raceway surface 4a of the inner ring 4 and the inner-side outer raceway surface 2c 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-side outer raceway surface 2d of the outer ring 2.

[0030] 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. The balls 7 of the outer ball row 6 are an example of first rolling elements, and the balls 7 of the inner ball row 5 are an example of second rolling elements.

[0031] In the wheel bearing device 1, a double-row angular contact ball bearing is formed by the outer ring 2, hub ring 3, inner ring 4, inner ball row 5, and outer ball row 6. Note that the wheel bearing device 1 may be formed as a double-row tapered roller bearing instead of the double-row angular contact ball bearing.

[0032] 1, the outer diameter of the inner end of the outer ring 2 is a. The axial distance between the flange surface 3k of the hub flange 3b and the inner end face 4b of the inner ring 4 is b. The outer diameter a and the axial distance b satisfy the relationship (a / b) > 1.2.

[0033] In other words, the outer diameter a at the inner end of the outer ring 2 is set to be larger than 1.2 times the axial distance b between the flange surface 3k and the inner end face 4b of the inner ring 4, and the wheel bearing device 1 is configured to have a narrow width and large diameter. In this embodiment, (a / b) is set to 1.46, which satisfies the relationship (a / b) > 1.2.

[0034] The pitch circle diameter of the balls 7 in the inner ball row 5 is PCDi, and the pitch circle diameter of the balls 7 in the outer ball row 6 is PCDo. The pitch circle diameter PCDi of the inner ball row 5 is the diameter of a circle that is centered on the rotational axis X and passes through the center Ci of a ball 7 in the inner ball row 5. The pitch circle diameter PCDo of the outer ball row 6 is the diameter of a circle that is centered on the rotational axis X and passes through the center Co of a ball 7 in the outer ball row 6.

[0035] The pitch circle diameter PCDo of the outer ball row 6 and the pitch circle diameter PCDi of the inner ball row 5 satisfy the relationship PCDo<PCDi. In other words, the pitch circle diameter PCDi of the inner ball row 5 is larger than the pitch circle diameter PCDo of the outer ball row 6.

[0036] In this way, in the wheel bearing device 1, the pitch circle diameter PCDi of the inner ball row 5 is made larger than the pitch circle diameter PCDo of the outer ball row 6, and the outer diameter a at the inner end of the outer ring 2 is made larger than 1.2 times the axial distance b between the flange surface 3j and the inner end face 4b of the inner ring 4, thereby achieving low torque and weight reduction, which are environmental performance, while setting mechanical properties such as rolling fatigue life and rigidity within appropriate ranges.

[0037] 2, the radius of curvature of the outer raceway 2d on the outer side of the outer ring 2 is Roo, the radius of curvature of the outer raceway 2c on the inner side of the outer ring 2 is Rio, the radius of curvature of the inner raceway 3c of the hub ring 3 is Roi, and the radius of curvature of the inner raceway 4a of the inner ring 4 is Rii. Furthermore, the diameter of the balls 7 in the outer ball row 6 is Do, and the diameter of the balls 7 in the inner ball row 5 is Di.

[0038] The radius of curvature Roi of the outer-side inner raceway surface 3c is set to 51% to 53% of the diameter Do of the balls 7 in the outer-side ball row 6. The radius of curvature Rii of the inner-side inner raceway surface 4a is set to 51% to 53% of the diameter Di of the balls 7 in the inner-side ball row 5.

[0039] The radius of curvature Roo of the outer raceway surface 2d is set to 52% to 54% of the diameter Do of the balls 7 in the outer ball row 6. The radius of curvature Rio of the inner raceway surface 2c is set to 52% to 54% of the diameter Di of the balls 7 in the inner ball row 5.

[0040] By setting the radius of curvature of each raceway surface to a value within this range, it is possible to reduce the rolling fatigue life of each raceway surface.

[0041] Furthermore, it is preferable that the radius of curvature Rii of the inner-side inner raceway surface 4 a, the radius of curvature Rio of the inner-side outer raceway surface 2 c, the radius of curvature Roi of the outer-side inner raceway surface 3 c, and the radius of curvature Roo of the outer-side outer raceway surface 2 d satisfy the relationship Rii<Rio or Roi<Roo within a predetermined numerical range.

[0042] Setting the radius of curvature in this manner makes it possible to further reduce the rotational torque of the wheel bearing device 1. Specifically, since the circumferential lengths of the raceways are greater for the outer raceway surfaces 2c and 2d than for the inner raceway surfaces 4a and 3c, and torque is likely to be greater, by setting the radius of curvature Rii < radius of curvature Rio or the radius of curvature Roi < radius of curvature Roo, the sliding surfaces of the balls 7 on the outer raceway surfaces 2c and 2d can be made smaller than the sliding surfaces of the balls 7 on the inner raceway surfaces 4a and 3c, making it possible to reduce the rotational torque.

[0043] Furthermore, it is preferable that the radius of curvature Rii of the inner-side inner raceway surface 4a, the radius of curvature Rio of the inner-side outer raceway surface 2c, the radius of curvature Roi of the outer-side inner raceway surface 3c, and the radius of curvature Roo of the outer-side outer raceway surface 2d be within a predetermined numerical range, satisfying the relationships Roi≦radius of curvature Rii and Roo≦radius of curvature Rio.

[0044] Setting the diameters in this manner makes it possible to prevent the rolling life of the outer ball row 6 from being excessively shortened relative to the inner ball row 5. Specifically, when the pitch circle diameter PCDo<pitch circle diameter PCDi and 0.35 mm<(Di-Do)<0.80 mm are set, and the radius of curvature Roi>radius of curvature Rii and the radius of curvature Roo>radius of curvature Rio are set, the contact surface pressure of the outer ball row 6, which has a smaller ball diameter, against the outer inner raceway surface 3c and outer raceway surface 2d is likely to be excessively high relative to the contact surface pressure of the inner ball row 5, which has a larger ball diameter, against the inner inner raceway surface 4a and outer raceway surface 2c, and there is a risk that the life of the outer ball row 6 will be excessively shortened relative to the life of the inner ball row 5.

[0045] In this way, if the life of the outer ball row 6 is excessively reduced compared to the inner ball row 5, it may become impossible to optimize the mechanical properties of the outer ball row 6 and the inner ball row 5, so it is preferable to set the radius of curvature Roi≦radius of curvature Rii and the radius of curvature Roo≦radius of curvature Rio.

[0046] Furthermore, in order to optimize the mechanical properties and environmental performance, it is preferable to satisfy the relationship: radius of curvature Rii<radius of curvature Rio, or radius of curvature Roi<radius of curvature Roo, and also satisfy the relationship: radius of curvature Roi≦radius of curvature Rii, and radius of curvature Roo≦radius of curvature Rio.

[0047] 2, the balls 7 in the inner ball row 5 are in contact with the inner raceway surface 4a at contact point 41, and the contact angle of the balls 7 in the inner ball row 5 with the inner raceway surface 4a is αi. The balls 7 in the inner ball row 5 are in contact with the outer raceway surface 2c at contact point 21, and the contact angle of the balls 7 in the inner ball row 5 with the outer raceway surface 2c is αi.

[0048] The contact angle αi is the inclination angle of a straight line Li passing through the center Ci of the ball 7 in the inner ball row 5 and the contact point 41 and the contact point 21 relative to the radial direction.

[0049] The balls 7 in the outer ball row 6 are in contact with the inner raceway surface 3c at contact point 31, and the contact angle of the balls 7 in the outer ball row 6 with the inner raceway surface 3c is αo. The balls 7 in the outer ball row 6 are in contact with the outer raceway surface 2d at contact point 22, and the contact angle of the balls 7 in the outer ball row 6 with the outer raceway surface 2d is αo.

[0050] The contact angle αo is the angle of inclination of a straight line Lo passing through the center Co of the ball 7 in the outer ball row 6 and the contact point 31 and the contact point 22 relative to the radial direction.

[0051] The contact angle αi of the balls 7 in the inner ball row 5 with the inner raceway surface 4a and the outer raceway surface 2c and the contact angle αo of the balls 7 in the outer ball row 6 with the inner raceway surface 3c and the outer raceway surface 2d satisfy the relationship αo ≧ αi. In this embodiment, the contact angle αo is set to 40°, and the contact angle αi is set to 35°, satisfying the relationship αo ≧ αi. The contact angle αo can be set to a range of 35° to 45°.

[0052] In the wheel bearing device 1, the load on the outer raceway surface is greater than the load on the inner raceway surface, so the outer raceway surface is at a disadvantage in terms of rolling fatigue life compared to the inner raceway surface.

[0053] However, by setting the contact angle αo with the outer-side inner raceway surface 3 c and outer raceway surface 2 d to be equal to or larger than the contact angle αi with the inner-side inner raceway surface 4 a and outer raceway surface 2 c, it is possible to prevent the rolling fatigue life of the outer-side inner raceway surface 3 c and outer raceway surface 2 d from being shorter than the rolling fatigue life of the inner-side inner raceway surface 4 a and outer raceway surface 2 c.

[0054] The diameter Di of the balls 7 in the inner ball row 5 is larger than the diameter Do of the balls 7 in the outer ball row 6 (Di > Do), and the diameter Di of the inner balls 7 and the diameter Do of the outer balls 7 satisfy the relationship 0.35 mm < (Di - Do) < 0.80 mm. Furthermore, the number Zi of the balls 7 in the inner ball row 5 and the number Zo of the balls 7 in the outer ball row 6 are set to the same number (Zi = Zo).

[0055] In a wheel bearing device 1 in which the pitch circle diameter PCDi of the inner ball row 5 is formed larger than the pitch circle diameter PCDo of the outer ball row 6, by setting the number Zi of the inner balls 7 and the number Zo of the outer balls 7 to be the same, and further configuring the diameter Di of the inner balls 7 and the diameter Do of the outer balls 7 to satisfy the relationship 0.35 mm < (Di - Do) < 0.80 mm, it is possible to prevent the mechanical properties of the outer side, such as rolling fatigue life and rigidity, from becoming excessive compared to the inner side, and it is possible to set the mechanical properties of the outer and inner sides within appropriate ranges.

[0056] Furthermore, the straight line Li passing through the center Ci of the ball 7 in the inner ball row 5 and the contact point 41 passes through the fitting surface 4c of the inner ring 4 with the hub wheel 3. If the straight line Li were to pass further inward than the fitting surface 4c of the inner ring 4, the hub wheel 3 would not be able to fully withstand the load from the inner ball 7, which could result in a decrease in the rigidity of the wheel bearing device.

[0057] However, as in the wheel bearing device 1, since the straight line Li passes through the mating surface 4c, the load from the inner ball 7 can be sufficiently absorbed by the hub wheel 3, making it possible to ensure the rigidity of the wheel bearing device 1.

[0058] In the wheel bearing device 1, the radius of curvature of the shoulder-side raceway surface 4aa located at the inner-side end of the inner-side inner raceway surface 4a can be formed to be larger than the radius of curvature of the inner raceway surface 4a near the contact point 41. The radius of curvature of the shoulder-side raceway surface 3ca located at the outer-side end of the outer-side inner raceway surface 3c can be formed to be larger than the radius of curvature of the inner raceway surface 3c near the contact point 31.

[0059] The radius of curvature of the shoulder-side raceway surface 2ca located at the outer end of the inner-side outer raceway surface 2c can be made larger than the radius of curvature of the outer raceway surface 2c near the contact point 21. The radius of curvature of the shoulder-side raceway surface 2da located at the inner end of the outer-side outer raceway surface 2d can be made larger than the radius of curvature of the outer raceway surface 2d near the contact point 22.

[0060] In this way, by making the radius of curvature of the raceway surface on the shoulder side of each raceway surface larger than the radius of curvature of each raceway surface near the point of contact with the ball 7, it is possible to suppress a decrease in durability due to edge load that occurs when the ball 7 rides over the shoulder.

[0061] 1 and 2, a wheel WH constituting a wheel is attached to the flange surface 3k of the hub flange 3b at the outer end of the hub wheel 3. The axial center position of the wheel WH is Wp. The wheel center distance, which is the axial distance between the flange surface 3k of the hub flange 3b and the axial center position Wp of the wheel WH attached to the flange surface 3k, is Wc.

[0062] Furthermore, a line Li passing through the center Ci of a ball 7 in the inner ball row 5 and the contact point 41 and a line Lo passing through the center Co of a ball 7 in the outer ball row 6 and the contact point 31 intersect at the span center SP. The span center SP is the span center between the ball 7 in the inner ball row 5 and the ball 7 in the outer ball row 6. The span center distance, which is the axial distance between the flange surface 3k of the hub flange 3b and the span center SP, is Bc.

[0063] In the wheel bearing device 1, the wheel center distance Wc, the span center distance Bc, the contact angle αi of the inner ball 7 with respect to the inner raceway surface 4a, and the contact angle αo of the outer ball 7 with respect to the inner raceway surface 3c satisfy the relationship (Bc - Wc) ≦ (-0.57 × (αo - αi) + 7.15 mm). In other words, the difference in axial position between the wheel center distance Wc and the span center distance Bc is configured to be within (-0.57 × (αo - αi) + 7.15 mm).

[0064] For example, when αo is set to 40° and αi is set to 35°, the above relationship becomes (Bc - Wc) ≦ 4.3 mm. However, in this embodiment, when αo = 40° and αi = 35°, the wheel center distance Wc and the span center distance Bc are set so that (Bc - Wc) = -0.4 mm, and (Bc - Wc) ≦ 4.3 mm is satisfied.

[0065] In this way, in a wheel bearing device 1 in which the inner pitch circle diameter PCDi is formed larger than the outer pitch circle diameter PCDo, if it is configured so that (Bc - Wc) ≦ (-0.57 × (αo - αi) + 7.15 mm), the span center SP will move to the inner side compared to, for example, a wheel bearing device in which the inner pitch circle diameter PCDi and the outer pitch circle diameter PCDo are formed to be the same diameter.

[0066] This reduces the moment load acting on the wheel support bearing device 1, and reduces the rotational torque of the wheel support bearing device 1 formed to have a narrow width and large diameter.

[0067] Furthermore, when the pitch circle diameter PCDo<pitch circle diameter PCDi and (Bc-Wc)≦(-0.57×(αo-αi)+7.15 mm) are configured to satisfy the relationships, it is preferable to simultaneously satisfy the relationships of number Zo=number Zi, 0.35 mm<(Di-Do)<0.80 mm, and αo≧αi. By configuring in this way, it is possible to efficiently achieve low torque and weight reduction while setting mechanical properties such as rolling fatigue life and rigidity within appropriate ranges.

[0068] 3, the outer ring 2 and hub ring 3 are shown by solid lines when the inner pitch circle diameter PCDi is larger than the outer pitch circle diameter PCDo, as in this embodiment, and the outer ring 2 and hub ring 3 are shown by two-dot chain lines when the inner pitch circle diameter PCDi and the outer pitch circle diameter PCDo are the same. Also, areas where the shapes of the outer ring 2 and hub ring 3 shown by the solid lines differ from the shapes of the outer ring 2 and hub ring 3 shown by the two-dot chain lines are lightly marked.

[0069] When the weight of the outer ring 2 and hub ring 3 in this embodiment, in which the pitch circle diameter PCDi is larger than the pitch circle diameter PCDo, is calculated using the weight of the outer ring 2 and hub ring 3 when the pitch circle diameter PCDi and the pitch circle diameter PCDo are formed to be the same size as the denominator, the weight of the outer ring 2 and hub ring 3 in this embodiment can be reduced by approximately 7% compared to the weight of the outer ring 2 and hub ring 3 when the pitch circle diameter PCDi and the pitch circle diameter PCDo are formed to be the same size.

[0070] The weight reduction rate of the outer ring 2 and the hub ring 3 is (PCDo ２ -PCDi ２ ), making the inner pitch circle diameter PCDi larger than the outer pitch circle diameter PCDo is effective in reducing weight in the wheel bearing device 1 of this embodiment, which is formed with a narrow width and large diameter and is subjected to a large axle load.

[0071] In addition, reducing the weight of the outer ring 2 and the hub ring 3 allows for a reduction in the amount of material and grinding required when producing the outer ring 2 and the hub ring 3, thereby making it possible to reduce the manufacturing cost of the wheel bearing device 1.

[0072] [Second embodiment of wheel bearing device] The wheel bearing device 1 is configured for use with a driving wheel in which the inner ring 4 is crimped to the hub wheel 3, but the wheel bearing device 1 can also be configured for use with a driven wheel, as in the wheel bearing device 1A shown in Fig. 4. The wheel bearing device 1A differs from the wheel bearing device 1 in that it includes a hub wheel 3A instead of the hub wheel 3.

[0073] The hub wheel 3A does not have a through hole 3i that penetrates in the axial direction, but instead has a recess 3m that is recessed in the axial direction from the outer side. Other configurations of the hub wheel 3A are the same as those of the hub wheel 3.

[0074] The wheel support bearing device 1A can have the same dimensional relationships as those described for the wheel support bearing device 1. This makes it possible for the wheel support bearing device 1A to achieve low torque and weight reduction while setting mechanical properties such as rolling fatigue life and rigidity within appropriate ranges.

[0075] [Third embodiment of wheel bearing device] The wheel bearing device 1 is configured to specifications for a drive wheel in which the inner ring 4 is crimped to the hub wheel 3, but it can also be configured to specifications for a drive wheel in which the inner ring 4 is not crimped to the hub wheel 3, as in the wheel bearing device 1B shown in Fig. 5. The wheel bearing device 1B differs from the wheel bearing device 1 in that it includes a hub wheel 3B instead of the hub wheel 3.

[0076] The hub wheel 3A differs from the hub wheel 3 in that it does not have a crimping portion 3h for crimping the inner ring 4. The rest of the configuration of the hub wheel 3B is the same as that of the hub wheel 3.

[0077] The wheel support bearing device 1B can have the same dimensional relationships as those described for the wheel support bearing device 1. This makes it possible for the wheel support bearing device 1B to achieve low torque and weight reduction while setting mechanical properties such as rolling fatigue life and rigidity within appropriate ranges.

[0078] [Second embodiment of bolt holes in hub flange] The bolt holes 3e formed in the hub flange 3b may be formed as tapped holes, such as bolt holes 3eA shown in Fig. 6. Wheel bolts are fastened from the outer side into the bolt holes 3eA formed as tapped holes.

[0079] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, which are merely examples, and it goes without saying that the present invention can be embodied in various other forms without departing from the spirit of the present invention. The scope of the present invention is indicated by the claims, and further includes the equivalent meanings set forth in the claims, and all modifications within the scope of the claims.

[0080] The present invention can be used in a wheel bearing device.

[0081] REFERENCE SIGNS LIST 1 Wheel bearing device 2 Outer ring 2c (inner side) outer raceway surface 2d (outer side) outer raceway surface 3 Hub ring 3a Small diameter step portion 3b Hub flange 3c Inner raceway surface 3k Flange surface 4 Inner ring 4a Inner raceway surface 4b Inner side end face 5 Inner side ball row 6 Outer side ball row 7 Ball a Outer diameter (at other axial end of outer ring) b Axial distance (between flange surface and inner side end face of inner ring) PCDi Pitch circle diameter (of ball in inner side ball row) PCDo Pitch circle diameter (of ball in outer side ball row)

Claims

1. A wheel bearing device comprising: an outer member having a first outer raceway formed at one axial end thereof and a second outer raceway formed further toward the other axial end than the first outer raceway; an inner member comprising: a hub wheel having a hub flange for mounting a wheel at one axial end thereof, a first inner raceway formed facing the first outer raceway; and an inner ring fitted to the other axial end of the hub wheel, the first inner raceway formed facing the second outer raceway; a first rolling element housed between the first outer raceway and the first inner raceway; and a second rolling element housed between the second outer raceway and the second inner raceway, wherein an outer diameter a at the other axial end of the outer member and an axial distance b between the flange surface of the hub flange and the other axial end side of the inner ring satisfy the relationship: (a / b) > 1.2; and a pitch circle diameter PCDo of the first rolling element and a pitch circle diameter PCDi of the second rolling element are A wheel bearing device characterized in that the relationship PCDo<PCDi is satisfied.

2. A wheel bearing device as described in claim 1, wherein the radius of curvature Roi of the first inner raceway surface is 51% to 53% of the diameter Do of the first rolling element, the radius of curvature Rii of the second inner raceway surface is 51% to 53% of the diameter Di of the second rolling element, the radius of curvature Roo of the first outer raceway surface is 52% to 54% of the diameter Do of the first rolling element, and the radius of curvature Rio of the second outer raceway surface is 52% to 54% of the diameter Di of the second rolling element.

3. A wheel bearing device as described in claim 2, wherein the number Zo of the first rolling elements accommodated between the first outer raceway surface and the first inner raceway surface is the same as the number Zi of the second rolling elements accommodated between the second outer raceway surface and the second inner raceway surface.

4. A wheel bearing device according to claim 2, wherein a diameter Do of the first rolling element and a diameter Di of the second rolling element satisfy the relationship: 0.35 mm < (Di - Do) < 0.80 mm.

5. A wheel bearing device as described in claim 2, wherein a contact angle αo of the first rolling element with respect to the first inner raceway surface and a contact angle αi of the second rolling element with respect to the second inner raceway surface satisfy the relationship αo ≧ αi.

6. A wheel bearing device as described in claim 1, wherein a straight line Li passing through the contact point with the second rolling body on the second inner raceway surface and the center of the second rolling body passes through the fitting surface of the inner ring with the hub wheel.

7. The number Zo of the first rolling elements housed between the first outer raceway surface and the first inner raceway surface is the same as the number Zi of the second rolling elements housed between the second outer raceway surface and the second inner raceway surface; a diameter Do of the first rolling element and a diameter Di of the second rolling element satisfy the relationship of 0.35 mm < (Di - Do) < 0.80 mm; a contact angle αo of the first rolling element with respect to the first inner raceway surface and a contact angle αi of the second rolling element with respect to the second inner raceway surface satisfy the relationship of αo ≧ αi; a wheel center distance Wc which is the axial distance between the flange surface and a central position in the axial direction of a wheel attached to the flange surface; a span center distance Bc which is the axial distance between the flange surface and the span center of the first rolling element and the second rolling element; a contact angle αo of the first rolling element with respect to the first inner raceway surface and a contact angle αi of the second rolling element with respect to the second inner raceway surface satisfy the relationship of The wheel bearing device according to claim 2, wherein the relationship: (Bc-Wc)≦(-0.57×(αo-αi)+7.15 mm) is satisfied.

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