Improved asymmetric hub bearing unit

Abstract

A hub bearing unit includes a hub rotatable about a central axis and having outer and inner inner raceways. An outer ring is disposed around the hub and connectable to a vehicle, the outer ring having outer and inner outer raceways. An outer set of rolling elements is disposed between the outer inner and outer raceways, traversing an outer pitch circle and having an outer contact angle. An inner set of rolling elements is disposed between the inner inner and outer raceways, traversing an inner pitch circle and having an inner contact angle. The outer pitch circle has a diameter at least five millimeters larger than the diameter of the inner pitch circle. The outer contact angle is at least thirty-four degrees, and the inner contact angle has a value within the range of forty-five percent and seventy percent of the outer contact angle.

Description

Background of the invention

[0001] The present invention relates to bearings, in particular to hub bearing units.

[0002] Wheel hub bearing assemblies are well known in the bearing and automotive industries and are used to rotatably couple wheels to vehicles such as passenger cars and trucks. A hub bearing assembly typically comprises a cylindrical hub connectable to an axle, an outer race disposed around the hub, and one or more rows or sets of rolling elements disposed between the hub and the outer race. In certain arrangements, the hub is rotatable about a central axis and includes a radial flange configured to receive a wheel, and the outer race is fixedly connected to the vehicle, either to a steering knuckle or a suspension member. In other arrangements, the hub is attached to a fixed shaft, and the outer race rotates about a central axis through the shaft and has a flange configured to receive a wheel.

[0003] With any basic structure, the hub bearing unit typically comprises two sets or rows of rolling elements, which can be balls, cylindrical rollers, tapered rollers, or any other suitable type of rolling element. When designing a wheel hub bearing unit for a specific application, consideration must be given to minimizing friction, providing sufficient structural rigidity to reliably support all expected loads, and reducing the mass and space requirements for installation in a vehicle. Wheel bearing units, in particular, are typically designed to provide adequate stiffness to the suspension system while minimizing friction and drag.These two requirements are typically contradictory, as a hub unit design that increases stiffness often results in an increase in friction, and conversely, a design that reduces friction usually results in a decrease in stiffness. Most hub bearing unit designs inherently represent a compromise between the two factors.

[0004] Traditionally, the balance between these factors has been achieved by sizing the two rows of rolling elements so that the pitch diameter of one row is slightly larger than that of the other, known as an asymmetric arrangement, and there is a small difference between the contact angles of each row. In such balanced designs, small changes to the internal contact angle have a significant impact on friction; that is, when the internal contact angle is increased to increase stiffness, friction within the hub bearing unit increases significantly. To mitigate the effect of increased friction, manufacturers often resort to additional raceway surface treatment and / or increased raceway lubrication, both of which increase the cost of the hub bearing unit.An alternative or additional solution is to provide low resistance seals to reduce the frictional effects of the seals, but such seals may result in a decrease in sealing performance. Summary of the invention

[0005] The present invention is a hub bearing assembly for rotatably coupling a wheel to a vehicle, the wheel being rotatable about a central axis. The hub bearing assembly includes a hub rotatable about the central axis and having an inner axial end and an outer axial end, a flange extending radially outward from a remainder of the hub at least generally adjacent the outer end and configured to secure the wheel to the hub, an outer inner race, and an inner inner race axially spaced from the outer inner race. An outer ring is disposed around the hub and configured to be connected to the vehicle, the outer ring having an outer outer race and an inner outer race axially spaced from the outer outer race.An outer set of rolling elements, preferably balls, is arranged between the outer inner raceway and the outer outer raceway to traverse an outer pitch circle having a pitch circle diameter. Each rolling element of the outer set of rolling elements contacts the outer inner raceway at an inner contact point and contacts the outer outer raceway at an outer contact point. A line extending through the inner and outer contact points defines an outer contact angle with a line perpendicular to the central axis.

[0006] Furthermore, an inner set of rolling elements, which are also preferably balls, is arranged between the inner inner race and the inner outer race to traverse an inner pitch circle having an inner pitch circle diameter, wherein the outer pitch circle diameter is at least five millimeters larger than the inner pitch circle diameter. Each rolling element of the outer set of rolling elements contacts the inner inner race at an inner contact point and contacts the inner outer race at an outer contact point. A line extending through the inner and outer contact points defines an inner contact angle with a line perpendicular to the central axis. To optimize the performance of the hub bearing unit, the outer contact angle has a value of at least thirty-four degrees and the inner contact angle has a value within a range of forty-five percent and seventy-five percent of the outer contact angle value.

[0007] Furthermore, each line extending through the inner contact point and the outer contact point of each rolling element of the outer set of rolling elements intersects the center axis at an outer center of pressure. The outer center of pressure is axially spaced from the outer pitch circle by an outer center of pressure spacing distance. Each line extending through the inner contact point and the outer contact point of each rolling element of the inner set of rolling elements intersects the center axis at an inner center of pressure. The inner center of pressure is axially spaced from the inner pitch circle by an inner center of pressure spacing distance. For further optimization of the bearing unit, the inner center of pressure spacing distance has a value within a range of fifty percent to seventy percent of the value of the outer center of pressure spacing distance.

[0008] The outer pressure center is preferably axially spaced from the outer axial end of the flange by a distance no greater than one and a half millimeters (1.5 mm). The inner pressure center is preferably axially spaced from the inner axial end of the outer ring by a distance no greater than three millimeters (3 mm). Short description of the different views of the figures

[0009] The foregoing summary and detailed description of the preferred embodiments of the present invention will be better understood when read in conjunction with the accompanying figures. For the purpose of illustrating the invention, the figures are schematic, showing embodiments that are presently preferred. It should be understood, however, that the present invention is not limited to the precise arrangements and instrumentalities shown. In the figures: Fig. 1 is an axial cross-sectional view of a hub bearing unit of the present invention; Fig. 2 is an axial cross-sectional view of a hub of the hub bearing unit; Fig. 3 is an axial cross-sectional view of an outer ring of the hub bearing unit; Fig. 4 is an axial cross-sectional view of an upper portion of the hub bearing unit; Fig. Figure 5 is a fragmentary, enlarged axial cross-sectional view of a portion of Fig. 4, which shows the outer raceways of the hub bearing unit; and Fig. 6 is a fragmentary, enlarged axial cross-sectional view of another section of Fig. 4, which shows the inner raceways of the hub bearing unit. Detailed description of the invention

[0010] Certain terminology is used in the following description for convenience only and is not limiting. The words "inside," "inboard," and "outside," "outboard" respectively denote directions toward and away from a particular centerline or geometric center of a described component, the specific meaning being readily apparent from the context. Furthermore, each of the words "connected" and "coupled" as used herein is intended to include direct connections between two elements without other elements disposed therebetween and indirect connections between elements where one or more other elements are disposed therebetween. The terminology includes the words specifically mentioned above, derivatives thereof, and words of similar meaning.

[0011] Now with reference to the figures in detail, in which the same numbers are used to identify the same components throughout, Fig. 1-6, a hub bearing unit 10 is shown for rotatably coupling a wheel 1 to a vehicle 2, in particular a steering knuckle or a suspension element 3, wherein the wheel 1 is rotatable about a central axis AC. The wheel hub bearing unit 10 basically comprises a hub 12 rotatable about the central axis AC, an outer ring 14 disposed around the hub 12, an outer set 16 of rolling elements 18, and an inner set 20 of rolling elements 22, each disposed therebetween and rotatably coupling the hub 12 and the outer ring 14. The hub 12 and the outer ring 14 are configured, i.e., constructed, assembled, etc., and the rolling elements 18, 22 are sized to position the rolling elements 18, 22 at locations that optimize the performance of the hub bearing unit 10, as discussed in detail below.

[0012] With particular reference to Fig. 2, the hub 12 comprises a generally cylindrical body having an outer axial end 24a, an opposite inner axial end 24b, and an annular flange 26 extending radially outward from the body 24 at least generally adjacent the outer end 24a. The hub flange 26 is adapted to secure the wheel 1 to the hub 12, preferably by means of a plurality of fasteners 4 extending through holes 27 in the flange 26, and has an outer axial end 26a and an inner axial end 26b. The hub body 24 further has an outer inner race 28 and an inner inner race 30 axially spaced from the outer inner race 28.The cylindrical hub body 24 preferably includes or is formed from a main body portion 32 that includes the annular flange 26 and has an outer peripheral surface 33, and an annular ring 34 disposed around the main body portion 32 adjacent the inner axial end 24b. Specifically, the outer inner race 28 is formed in the outer peripheral surface 33 of the main body portion 32, and the annular ring 34 has an outer peripheral surface 35A that includes the inner inner race 30 and an inner peripheral surface 35B disposed around a portion of the outer surface 33 of the main body portion 32.

[0013] The outer inner raceway 28 is preferably formed from a first concave, annular groove 29 extending radially inward from the outer peripheral surface 33B of the hub main body portion 32. Similarly, the inner inner raceway 30 is preferably formed from a second concave, annular groove 31 extending radially inward from the inner peripheral surface 35B of the annular ring 34. With such concave, annular grooves 29, 31, the inner raceways 28, 30 are adapted to receive the rolling elements 18, 22, each formed as a ball 19, 23, as described below. However, one or both of the inner raceways 28, 30 could alternatively be formed as a flat, annular groove for cylindrical or needle rollers, as frustoconical, annular grooves for tapered rollers, or in any other suitable manner for a specific application (no alternatives shown).In addition, each concave annular groove 29, 31 of the hub 12 preferably has a respective radial portion 29a, 31a, wherein the radial portion 29a of the outer concave annular groove 29 faces the inner end 24b of the hub body and the radial portion 31a of the inner concave annular groove faces the outer end 24a of the hub body, for the reasons discussed below.

[0014] Now with reference to Fig. 3, the outer ring 14 is adapted to be connected to the vehicle 2 and comprises a generally circular, cylindrical body 40 having an outer axial end 40a, an opposite inner axial end 40b, an inner peripheral surface 42A, and an opposite outer peripheral surface 42B. The outer ring body 40 preferably has at least one and preferably a plurality of flanges 44 (only one shown), each extending radially outwardly from the outer peripheral surface 42B, each outer ring flange 44 being adapted to engage a steering knuckle or a suspension member 3 ( Fig. 1) to be connected using threaded connections (none shown).

[0015] Further, the outer ring body 40 has an outer outer race 46 and an inner outer race 48 axially spaced from the outer outer race 46, each outer race 46, 48 formed on the inner circumferential surface 42A of the body. When the outer ring 14 is disposed around the hub 12, the outer end 40a of the ring is disposed adjacent the hub flange 26, the outer end 40b of the outer ring 14 is disposed adjacent the inner end 24b of the hub, the outer outer race 46 is disposed around the inner inner race 28, and the outer outer race 48 is disposed around the inner inner race 30.

[0016] The outer outer raceway 46 is preferably formed from a first concave, annular groove 47 extending radially from the inner peripheral surface 42A of the outer ring cylindrical body 40. Similarly, the inner outer raceway 48 is preferably formed from a second concave, annular groove 49 extending radially from the outer peripheral surface 42B of the body 40 and axially spaced from the first groove 47. As discussed above with the hub 12, the concave, annular grooves 47, 49 of the outer raceways 46, 48 are each configured to receive rolling elements 18, 22, each formed as balls 19, 23. However, one or both of the outer raceways 46, 48 may alternatively be configured to receive cylindrical rollers, tapered rollers, etc., and mate with a similar inner raceway 28, 30.Furthermore, each concave annular groove 47, 49 of the outer ring 14 preferably has a respective radial portion 47a, 49a and is formed such that the radial portion 47a of the outer concave annular groove 47 is directed toward the outer end 40a of the outer ring, and the radial portion 49a of the inner concave annular groove 49 is directed toward the inner end 40b of the outer ring. As such, the rolling elements 18, 22 are generally arranged in an O-arrangement when mounted on the outer raceway pairs 28 / 46 and the inner raceway pairs 30 / 48, as is well known in the art of angular contact bearings.

[0017] With reference to Fig. 1-5, the outer set 16 of rolling elements 18 is arranged between the outer inner raceway 28 and the outer outer raceway 46 and is circumferentially spaced about the central axis AC. The outer rolling elements 18 are rotatable simultaneously along the outer raceways 28, 46 as the hub 12 rotates about the central axis AC to traverse a theoretical outer pitch circle CPO extending through the center of all rolling elements 18, the pitch circle CPO having an outer pitch diameter DPO, as shown in Fig. 1. With the preferred rolling elements 18 being balls 19, each outer concave annular groove 29, 47 has a radius of curvature RCO ( Fig. 2 and Fig. 3) and each ball 19 of the outer set 16 has a diameter DPO ( Fig. 5) and are each dimensioned relatively so that a ratio between the radius of curvature RCO of each groove 29, 47 and the diameter DPO of each ball 19 is between 0.5175 and 0.539.

[0018] How best in Fig. 4 and Fig. 5, the outer raceways 28, 46 are configured such that each rolling element 18 of the outer set 16 contacts the outer inner raceway 28 at an inner contact point OCI and simultaneously contacts the outer outer raceway 46 at an outer contact point OCO. Each line LO extending through the inner and outer contact points OCI, OCO of an outer rolling element 18 defines an outer contact angle αO with each line LPO perpendicular to the central axis AC. Each line LO extending through the inner and outer contact points OCI, OCO of each outer rolling element 18 also intersects the central axis AC at an outer center of pressure PCO. Furthermore, the outer center of pressure PCO is axially spaced from the outer pitch circle CPO by an outer center of pressure spacing distance SDO.

[0019] With reference to Fig. 1-4 and 6, the inner set 20 of rolling elements 22 is disposed between the inner inner raceway 30 and the outer outer raceway 48 and is circumferentially spaced about the central axis AC. The inner rolling elements 22 are inherently simultaneously rotatable along the inner raceways 30, 48 as the hub 12 rotates about the central axis AC to traverse a theoretical inner pitch circle CPI extending through the center of all rolling elements 22, wherein the inner pitch circle CPI has an inner pitch diameter DPI. With the preferred rolling elements 22 being balls 23, each inner, concave, annular groove 31, 49 has a radius of curvature RCI ( Fig. 2 and Fig. 3) and each ball 23 of the inner rolling element set 20 has a diameter DPI ( Fig. 6) and are each dimensioned such that the ratio between the radius of curvature RCI of each groove 31, 49 and the diameter DPI of each ball 23 is between 0.5175 and 0.539. Preferably, each ball 19 and each ball 23 has a specific size so that the diameters DBO and DBI are equal, but alternatively, the balls 19 and 23 may be unequal or have different sizes.

[0020] How best in Fig. 4 and 5, the inner raceways 30, 48 are configured such that each rolling element 22 of the inner set 20 contacts the inner inner raceway 30 at an inner contact point ICI and simultaneously contacts the inner outer raceway 48 at an outer contact point ICO. Each line LI extending through the inner and outer contact points ICI, ICO of an inner rolling element 22 defines an inner contact angle αI with each line LPI perpendicular to the central axis AC. Each line Li extending through the inner and outer contact points ICI, ICOO of each inner rolling element 22 also intersects the central axis AC at an inner center of pressure PCI. Furthermore, the inner center of pressure PCI is axially spaced from the inner pitch circle CPI by an inner center of pressure spacing distance SDI.

[0021] Having described the basic structure, certain features of the hub bearing assembly 10 of the present invention that enhance its performance will now be discussed. To specifically enhance the performance of the wheel hub bearing assembly 10, the hub 12 and outer race 14 are formed or manufactured such that the rolling elements 18, 22 are positioned in a manner determined to best balance tradeoffs between friction on the rolling elements 18, 22 and the stiffness, mass, and fatigue life of the hub bearing assembly 10.

[0022] First, the size of the outer inner and outer raceways 28, 46 and each outer rolling element 18 relative to the inner inner and outer raceways 30, 48 and to each inner rolling element 22 is determined such that the outer pitch diameter DPO is at least five millimeters (5 mm) larger, or at least seven and a half percent (7.5%) larger than the inner pitch diameter DPI. Such an asymmetrical structure of the two rolling element rows 16, 20 increases an axial distance DA ( Fig. 4) between the inner pressure center PCI and the outer pressure center PCO, regardless of the actual values ​​of the contact angles αO, αI.

[0023] To further maximize stiffness, the outer raceways 28, 46 and the outer rolling elements 18 are formed and sized such that the outer contact angle αO has a value of at least thirty-four degrees (34°). With such a relatively large value for the outer angle αO, the outer pressure center PCO is displaced away from the inner pressure center PCI, which increases the stiffness of the hub bearing unit 10. The outer pressure center PCO is preferably axially spaced from the outer axial end 26a of the flanges 26 by a distance dPO that is not greater than one and a half millimeters (1.5 mm), most preferably outward from the axial end 26a, as shown in Fig. 5 shown.

[0024] Then, to increase stiffness with minimal impact on or increase in friction within the hub bearing unit 10, the inner contact angle αI is adjusted or configured relative to the outer contact angle αO to ideally locate the inner center of pressure PCI. Specifically, the inner raceways 30, 48 and the inner rolling elements 22 are formed and sized such that the inner contact angle αI has a value within a range of forty-five percent (45%) to seventy-five percent (75%) of the value of the outer contact angle αO. With such relative sizing of the contact angles αO, αI, the inner center of pressure separation distance SDI has a value within a range of fifty percent (50%) and seventy percent (70%) of the value of the outer center of pressure separation distance SDO.Further, the inner center of pressure PCI is preferably axially spaced from the inner axial end 40b of the outer ring 14 by a distance dPI no greater than three millimeters (3 mm), most preferably outwardly from the axial end 40b, as shown in FIG. Fig. 6 shown.

[0025] With the above combination of the relative dimensions of the outer and inner pitch diameters DPO, DPI and the relative values ​​of the outer and inner contact angles αO, αI, the present hub bearing unit 10 has the desired amount of stiffness with a relatively low amount of friction compared to previous hub bearing units. In particular, the friction of the present hub bearing unit 10 is significantly lower and has a similar amount of stiffness compared to previous hub bearing units in which the rolling element preload was increased to increase stiffness.

[0026] Representative, non-limiting examples of the present invention have been described in detail above with reference to the accompanying figures. This detailed description is intended only to teach those skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention.

[0027] Furthermore, combinations of features and steps disclosed in the above detailed description may not be necessary to practice the invention in its broadest sense, and are instead taught only to particularly describe representative examples of the invention. Furthermore, various features of the representative example described above, as well as the various independent and dependent claims below, may be combined in ways not specifically and explicitly enumerated to provide additional useful embodiments of the present teachings.

[0028] All features disclosed in the description and / or claims are intended to be disclosed separately and independently of one another for the purpose of original written disclosure, as well as for the purpose of limiting the claimed subject matter, regardless of the combination of features in the embodiments and / or the claims. In addition, all ranges of values ​​or references to groups of units are intended to disclose every possible intermediate value or unit for the purpose of original written disclosure, as well as for the purpose of limiting the claimed subject matter. The invention is not limited to the embodiments described above and may be varied within the scope of the following claims.

Claims

[1] Hub bearing unit for rotatably coupling a wheel to a vehicle, the wheel being rotatable about a central axis, the hub bearing unit comprising: - a hub rotatable about the central axis and having an outer axial end, an inner axial end, a flange extending radially outward from a remainder of the hub at least generally adjacent to the outer axial end and adapted to secure the wheel to the hub, an outer inner race and an inner inner race axially spaced from the outer inner race; - an outer ring disposed around the hub and adapted to be connected to the vehicle, the outer ring having an outer outer race and an inner outer race axially spaced from the outer outer race; - an outer set of rolling elements arranged between the outer inner raceway and the outer outer raceway to traverse an outer pitch circle having a pitch circle diameter, each rolling element of the outer set of rolling elements contacting the outer inner raceway at an inner contact point and contacting the outer outer raceway at an outer contact point, a line extending through the inner and outer contact points defining an outer contact angle with the line perpendicular to the central axis; and - an inner set of rolling elements arranged between the inner inner race and the inner outer race to traverse an inner pitch circle having an inner pitch circle diameter, the outer pitch circle diameter being at least five millimeters larger than the inner pitch circle diameter, and wherein each rolling element of the inner set of rolling elements contacts the inner inner race at an inner contact point and contacts the outer outer race at an outer contact point, a line extending through the inner and outer contact points defining an inner contact angle with the line perpendicular to the central axis; wherein the outer contact angle has a value of at least thirty-four degrees and the inner contact angle has a value within a range of forty-five percent and seventy percent of the value of the outer contact angle. [2] Hub bearing unit according to claim 1, wherein - each line extending through the inner contact point and the outer contact point of each rolling element of the outer set of rolling elements intersects the center axis at an outer center of pressure, the outer center of pressure being axially spaced from the outer pitch circle by an outer center of pressure spacing distance; and - each line extending through the inner contact point and the outer contact point of each rolling element of the inner set of rolling elements intersects the center axis at an inner center of pressure, the inner center of pressure being axially spaced from the inner pitch circle by an inner center of pressure spacing distance, the inner center of pressure spacing distance having a value within a range of fifty percent and seventy percent of a value of the outer center of pressure spacing distance. [3] Hub bearing unit according to claim 2, wherein: the flange of the hub has an outer axial end and an inner axial end, the outer center of pressure being axially spaced from the outer axial end of the flange by a distance not greater than one and a half millimeters (1.5 mm); and the inner pressure center is axially spaced from the inner axial end of the outer ring by a distance not greater than three millimeters (3 mm). [4] Hub bearing unit according to claim 1, wherein the value of the outer pitch circle diameter is at least seven and a half percent (7.5%) greater than the value of the inner pitch circle diameter. [5] Hub bearing unit according to claim 1, wherein each of the outer inner race and the inner inner race is formed as a concave annular groove extending radially outward from an outer peripheral surface of the hub; each of the outer outer raceway and the inner outer raceway is formed as a concave annular groove extending radially outward from an inner peripheral surface of the outer ring; and each rolling element of the outer set of rolling elements and each rolling element of the inner set of rolling elements is a sphere. [6] Hub bearing unit according to claim 5, wherein: each concave annular groove of the hub has a radial portion, the radial portion of the concave annular groove of the outer inner race being directed toward the inner end of the hub and the radial portion of the concave annular groove of the inner inner race being directed toward the outer end of the hub; and each concave annular groove of the outer ring has a radial portion, the radial portion of the concave annular groove of the outer outer race being directed toward the outer end of the hub and the radial portion of the concave annular groove of the inner outer race being directed toward the inner end of the hub. [7] Hub bearing unit according to claim 5, wherein: each of the concave, annular grooves of the outer inner race and the outer outer race has a radius of curvature and each ball of the outer set of rolling elements has a diameter, wherein a ratio between the radius of curvature of each concave, annular groove of the outer inner race and the outer outer race and the diameter of each ball is between 0.5175 and 0.539; and each of the concave, annular grooves of the inner inner race and the inner outer race has a radius of curvature and each ball of the outer set of rolling elements has a diameter, wherein a ratio between the radius of curvature of each concave, annular groove of the inner inner race and the inner outer race and the diameter of each ball is between 0.5175 and 0.

539. [8] A hub bearing unit according to claim 1, wherein the hub has a cylindrical main body portion including an annular flange and an annular ring disposed around the main body portion adjacent the inner axial end, the annular ring having an outer peripheral surface and a concave annular groove extending radially inward from the outer peripheral surface and being provided with an inner inner race. [9] The hub bearing unit of claim 1, wherein the outer ring has an outer peripheral surface and at least one flange extending radially outward from the outer peripheral surface, the at least one flange of the outer ring being adapted to be connected to a steering knuckle or a suspension component.

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