CA2707533A1

CA2707533A1 - Wheel bearing for a motor vehicle

Info

Publication number: CA2707533A1
Application number: CA2707533A
Authority: CA
Inventors: Thomas Wolf
Original assignee: Ab Skf; Thomas Wolf
Current assignee: SKF AB
Priority date: 2007-09-21
Filing date: 2008-09-12
Publication date: 2009-04-02
Anticipated expiration: 2028-09-12
Also published as: WO2009040001A1; CA2707533C; DE102007045248A1; DE102007045248B4

Abstract

The invention relates to a wheel bearing (1) for a motor vehicle, particularly for a commercial vehicle, having a wheel bearing unit (2), which supports a wheel hub (3) on an steering knuckle (8) by means of rolling bearings (4, 5, 6, 7) acting axially and radially. In order to reduce the rolling friction to a minimum during the operation of the motor vehicle, the invention provides for the wheel hub (3) to be equipped directly or indirectly with two cylindrical raceways (9, 10) for cylinder rollers (11, 12), and with two raceways (15, 16) for balls (17, 18), placed on the front side in at least one radially extending annular section (13, 14), and for the steering knuckle (8) to be equipped directly or indirectly with two cylindrical raceways (19, 20) for the cylinder rollers (11, 12), and with two raceways (23, 24) for the balls (17, 18), placed on the front side in two radially extending annular sections (21, 22), wherein the cylinder rollers (11, 12) are disposed between the cylindrical raceways (9, 10, 19, 20), and the balls (17, 18) are disposed between the raceways (15, 16, 23, 24).

Description

Description Wheel bearing for a motor vehicle The invention relates to a wheel bearing for a motor vehicle, in particular for a commercial vehicle, with a wheel bearing unit which supports a wheel hub on a steering knuckle by means of a rolling bearing acting axially and radially.

Tapered rolling bearings which are generally fitted in an 0 arrangement are customary for supporting in particular commercial and trailer axles. In this case, two tapered roller bearings are positioned in as play-free a manner as possible or with a slight prestress in order to support the wheel hub on the steering knuckle.
The two tapered roller bearings therefore serve as a combined radial and axial bearing.
It has also been known to use multi-row angular-contact ball bearings to support a wheel hub, with up to four rows of bearings being arranged next to one another. It is therefore endeavored to reduce the friction moment or the loss of power of the bearing in relation to the abovementioned solution with two tapered roller bearings and thus to arrive at a reduction in the fuel consumption.

Even the abovementioned bearing arrangements with a plurality of angular-contact ball bearings still have a not inconsiderable bearing friction resulting in corresponding fuel consumption. There is consequently the requirement to develop the wheel bearing unit, which has to support the wheel hub radially and axially on the steering knuckle, in such a manner that an even smaller loss of power during operation can be achieved.

Therefore, the invention is based on the object of developing a wheel bearing for a motor vehicle of the type mentioned at the beginning in such a manner that a further reduced bearing friction can be obtained during operation, as a result of which the fuel consumption and therefore also the exhaust emission output can be reduced. At the same time, the rigidity of the bearing is to be improved.

The achievement of said object by means of the invention is characterized in that the wheel hub is provided directly or indirectly with two cylindrical raceways for cylinder rollers and with two raceways for balls, said raceways being placed on the end side of at least one radially extending annular section, and that the steering knuckle is provided directly or indirectly with two cylindrical raceways for the cylinder rollers and with two raceways for the balls, said raceways being placed on the end side of radially extending annular sections, the cylinder rollers being arranged between the cylindrical raceways and the balls being arranged between the raceways.

The two cylinder roller bearings are preferably arranged lying axially on the outside and enclose the two ball bearings.

The rolling bearing is advantageously formed symmetrically with respect to a center plane which is perpendicular to the axis of rotation of the steering knuckle.

The two cylinder roller bearings may be designed to be identical in size. The two ball bearings may also be designed to be identical in size.

The cylindrical raceways of the two cylinder roller bearings are preferably incorporated directly into the material of the wheel hub. The raceways for balls of the two ball bearings may likewise be incorporated into at least one radially extending annular section directly into the material of the wheel hub. Other solutions, for example with outer rings pressed into a cast hub, are likewise possible.

The bearing rings which are placed onto the steering knuckle may be of L-shaped design in radial section and have both a cylindrical raceway of the two cylinder roller bearings and a raceway for balls of the two ball bearings. In this case, it has proven worthwhile if the cylindrical raceway of the two cylinder roller bearings of the bearing rings is bounded on both sides by a respective restraining flange. In this case, the two bearing rings may be held at a defined axial distance by means of a spacer sleeve.

Another development makes provision for the two axial ends of the spacer sleeve to be pushed into grooves in the two inner bearing rings, there being a radial press fit between the spacer sleeve and the bearing ring. The effect thereby advantageously achieved is that a transport and installation aid is produced without further components or elements, since the entire bearing unit is then captive owing to the frictional holding action of the press fit.

The wheel hub, as a part which is of single-piece design, may have the two cylindrical raceways of the two cylinder roller bearings and the two raceways for balls of the two ball bearings.

The wheel bearing unit is preferably designed as a prestressed unit which is lubricated to last its working life. It may be prestressed by means of an axle nut screwed onto the steering knuckle.

The wheel bearing unit may be sealed off from the surroundings by means of at least one sealing element.
To simplify the transport and/or installation operation, a sleeve may also be provided, the outside diameter of which corresponds to the inner bore in the wheel bearing unit and which is temporarily located in the preassembled wheel bearing unit. In this case, the sleeve is preferably composed of plastic. It may be arranged in the wheel bearing unit with a press fit.

According to the present invention, the radial and axial forces acting on the wheel and the resulting tilting moments are therefore absorbed by two cylinder roller bearings and two axial ball bearings which form a self-retaining bearing unit. The proposed refinement permits a very low-friction transmission of force between the wheel hub and the steering knuckle and therefore a noticeable reduction in the frictional losses during operation of the vehicle. At the same time, an increase in bearing rigidity is made possible by the separate absorption of the radial and axial forces.

In the case of the customary support by means of tapered rolling bearings, because of the structural characteristics of the tapered rolling bearing, an axial force which is induced in both bearings is in action even when the vehicle is travelling straight ahead, i.e. during a pure radial force, said axial force again being partially supported on the restraining guide flange of the two inner rings via the roller end sides and being effective as sliding friction. The comparatively high sliding friction between the roller end sides and the restraining guide flange of the inner ring is particularly apparent in the low speed range.

In contrast thereto, the proposed solution operates in all driving states with a pure rolling friction at a consistently low level. Consequently, a lower frictional moment and accordingly a lower steady-state temperature are produced for comparable operating forces, and this ultimately also has a positive influence on the duration of use of the grease. As a result of the lower operating temperatures, there is a higher kinematic viscosity of the lubricant and therefore also, as a prerequisite for a long duration of use of the bearings, reliable lubrication.

A sufficiently high moment rigidity of the bearing unit, which is of importance particularly in combination with disk brakes, is ensured by the two sets of cylinder roller bearings with the design-induced pressure angle (a = 00) and a sufficiently large distance therebetween.

Previously known bearing arrangements for wheel bearings generally revolve with a frictional moment of up to 5 Nm, that is to say, in the case of a semitrailer having three axles, i.e. six wheels hubs, a total frictional moment of approx. 30 Nm is calculated.
With the proposed solution, said value can be significantly reduced.

Finally, the installation of the unit is significantly simplified, since a wheel bearing basically does not need to be positioned. The installation is restricted to pushing the bearing unit onto the steering knuckle and bracing the inner rings and the spacer sleeve with a defined tightening moment by means of the axle nut.

After installation on the steering knuckle and tightening of the axle nut, the bearing unit is minimally prestressed via the two axial ball bearings.
A slight axial prestress merely ensures that the balls are acted upon with a minimal load in all load states in order to avoid slippage.

The proposed arrangement is furthermore distinguished by a lower degree of wear.

A lower generation of heat advantageously also results in less ageing of the lubricant and a longer duration of use of the bearing.
The proposed wheel bearing can be used in all commercial vehicle axles (truck and trailer axles).

An exemplary embodiment of the invention is illustrated in the drawing. The single figure shows the radial section through a wheel bearing of a truck or trailer.
A wheel bearing 1 for a truck can be seen in the figure. The wheel (not illustrated) is supported by a wheel bearing unit 2 which consists of four rolling bearings 4, 5, 6 and 7. A wheel hub 3 is mounted relative to a steering knuckle 8 of the wheel axle by the wheel bearing unit 2. In this case - as in the exemplary embodiment - the steering knuckle 8 may have a minimally stepped stem, which is advantageous for the installation of the wheel bearing unit.

The four rolling bearings 4, 5, 6 and 7 are two cylinder roller bearings 4 and 7 and two axial ball bearings 5 and 6.

The cylinder roller bearings 4, 7 have cylindrical raceways 9 and 10 of an outer ring which, in the present case, is formed by the wheel hub 3 itself. The cylindrical raceways 19 and 20 are formed by bearing rings (inner rings) 27 and 28 which are placed onto the steering knuckle 8. Cylinder rollers 11 and 12 are arranged between the cylindrical raceways 9, 10, 19, 20.

The two axial ball bearings 5 and 6 are positioned axially between the two cylinder roller bearings 4 and 7. The balls 17, 18 are arranged between in each case two annular or disk-shaped components which have the corresponding raceways for the balls. For this purpose, the wheel hub 3 has one or two radially extending annular sections 13, 14 into which raceways 15, 16 are incorporated, in each case on the end side. The bearing rings 27 and 28 have an L-shaped contour in radial section, thus producing radially extending annular sections 21 and 22 into which respective raceways 23 and 24 are incorporated.

As can be seen, the entire wheel bearing unit 2 with its four bearings 4, 5, 6, 7 is designed symmetrically with respect to a center plane 26 which is perpendicular to the axis of rotation 25 of the steering knuckle 8.

The cylinder rollers 11, 12 transmit pure radial forces. For the axial guidance of the cylinder rollers, the inner rings 27, 28 have restraining flanges 29 and on either side of the bearing ring 27 and restraining flanges 31 and 32 on either side of the bearing ring 28. On the corresponding outer ring, the cylindrical raceway 9, 10 is not bounded by restraining 30 flanges.

A spacer sleeve 33 keeps the two bearing rings 27, 28 at a defined distance when an axle nut 34 is screwed onto the steering knuckle 8 during the installation of the wheel bearing unit. The width of the spacer sleeve should preferably be selected such that, after the axle nut is tightened, the two axial ball bearings 5, 6 are slightly prestresed.

In addition, the spacer sleeve 33 may also serve as a frictional connecting element between the two inner rings 27 and 28. In this case, the sleeve sits with an overlap over the outside diameter thereof, i.e. with a press fit, in grooves 37 which are provided in the inner rings 27 and 28. This produces a captive unit, which has a noticeably positive effect on transport and installation.

A sealing element 35 in the form of a radial shaft seal ensures sealing off from the surroundings. The wheel bearing unit may optionally be sealed off on both sides. The radial shaft sealing ring for sealing off from the inside of the wheel should therefore be understood here as being by way of example.

The cylinder roller bearing on the inside of the wheel may be of stronger design, because of the generally higher radial force acting there, than the cylinder roller bearing arranged on the outside of the wheel;
however, this is in no way compulsory.

For economical reasons, the use of identical sets of rollers is preferred for the respectively identical bearings 4 and 7 and 5 and 6.

In the case of steering knuckles without a step and with the inner rings having identical bore diameters, the provision of a sleeve 36 (shown in addition to the steering knuckle 8 in the figure) which is preferably composed of plastic and which permits very simple installation is particularly advantageous. The sleeve 36 which is pressed with its outside diameter D into the bore in the wheel bearing unit 2 keeps the bearing unit together during transportation. While the bearing unit 2 is being slid onto the steering knuckle 8, the sleeve 36 is pushed out of the bearing bore at the same time.

As an alternative, to assist in the handling during transportation and/or installation, use may be made of the abovementioned solution, according to which the spacer sleeve 33 sits with a moderate press fit in the grooves 37 in the inner rings 27, 28 such that the two inner rings are held together in the axial direction.
The bearing unit is lubricated with a use-optimized smooth movement grease.

During straight-ahead travel, a share of the wheel force acting at the tire contact point and corresponding to the axial position of the wheel pressure line is absorbed by the two cylinder roller bearings. The axial force resulting from the wheel camber is absorbed by one of the two axial ball bearings. Otherwise, the axial prestressing force applied during installation acts in both rows of balls.
During cornering, a share of the radial wheel contact force corresponding to the axial position of the wheel pressure line is absorbed by the two cylinder roller bearings and the tilting moment which is induced by the axial force and the dynamic tire radius is likewise supported via the two cylinder roller bearings. The axial force which is produced at the wheel hub by the centrifugal force acting on the vehicle is transmitted by the central housing disk to the respectively loaded axial ball bearing as a function of the direction of the force (wheel on the inside or outside of the corner) and conducted via the "shaft disk" of the respective inner ring into the steering knuckle.

For the installation of the wheel bearing unit, the procedure is as follows:

First of all, the wheel bearing unit is pushed over the end side of the outer inner ring of the cylinder roller bearing. The inner rings sit on the steering knuckle with a loose fit (recommended tolerance range: "f7").
The transport sleeve (sleeve 36) prevents separation of the bearing components. When the bearing unit is pushed on, the transport sleeve is pushed off.

The central axle nut 34 is then tightened with a previously specified tightening moment. In the process, the two inner rings 27, 28 and the intermediate sleeve (spacer sleeve) 33 are braced against each other. The bracing force at the same time secures the axle nut against release.
The radial play in the cylinder roller bearings is preset and is very close to zero; a change during installation is prevented by the loose fit of the inner rings.

List of designations 1 Wheel bearing 2 Wheel bearing unit 3 Wheel hub 4 Rolling bearing (cylinder roller bearing) 5 Rolling bearing (axial ball bearing) 6 Rolling bearing (axial ball bearing) 7 Rolling bearing (cylinder roller bearing) 8 Steering knuckle 9 Cylindrical raceway 10 Cylindrical raceway 11 Cylinder roller 12 Cylinder roller 13 Annular section 14 Annular section 15 Raceway 16 Raceway 17 Ball 18 Ball 19 Cylindrical raceway 20 Cylindrical raceway 21 Annular section 22 Annular section 23 Raceway 24 Raceway 25 Axis of rotation 26 Center plane 27 Bearing ring 28 Bearing ring 29 Restraining flange 30 Restraining flange 31 Restraining flange 32 Restraining flange 33 Spacer sleeve 34 Axle nut 35 Sealing element 36 Sleeve 37 Groove D Diameter

Claims

1. A wheel bearing (1) for a motor vehicle, in particular for a commercial vehicle, with a wheel bearing unit (2) which supports a wheel hub (3) on a steering knuckle (8) by means of a rolling bearing (4, 5, 6, 7) acting axially and radially, characterized in that the wheel hub (3) is provided directly or indirectly with two cylindrical raceways (9, 10) for cylinder rollers (11, 12) and with two raceways (15, 16) for balls (17, 18), said raceways being placed on the end side of at least one radially extending annular section (13, 14), and in that the steering knuckle (8) is provided directly or indirectly with two cylindrical raceways (19, 20) for the cylinder rollers (11, 12) and with two raceways (23, 24) for the balls (17, 18), said raceways being placed on the end side of radially extending annular sections (21, 22), the cylinder rollers (11, 12) being arranged between the cylindrical raceways (9, 10, 19, 20) and the balls (17, 18) being arranged between the raceways (15, 16, 23, 24).

2. The wheel bearing as claimed in claim 1, characterized in that the two cylinder roller bearings (9, 11, 19; 10, 12, 20) are arranged lying axially on the outside and enclose the two ball bearings (15, 17, 23; 16, 18, 24).

3. The wheel bearing as claimed in claim 1 or 2, characterized in that the rolling bearing (4, 5, 6, 7) is formed symmetrically with respect to a center plane (26) which is perpendicular to the axis of rotation (25) of the steering knuckle (8).

4. The wheel bearing as claimed in one of claims 1 to 3, characterized in that the two cylinder roller bearings (9, 11, 19; 10, 12, 20) are designed to be the same size.

5. The wheel bearing as claimed in one of claims 1 to 4, characterized in that the two ball bearings (15, 17, 23; 16, 18, 24) are designed to be the same size.

6. The wheel bearing as claimed in one of claims 1 to 5, characterized in that the cylindrical raceways (9, 10) of the two cylinder roller bearings (9, 11, 19; 10, 12, 20) are incorporated directly into the material of the wheel hub (3).

7. The wheel mounting as claimed in one of claims 1 to 6, characterized in that the raceways (15, 16) for balls (17, 18) of the two ball bearings (15, 17, 23;
16, 18, 24) are incorporated into at least one radially extending annular section (13, 14) directly into the material of the wheel hub (3).

8. The wheel bearing as claimed in one of claims 1 to 7, characterized in that the bearing rings (27, 28) which are placed onto the steering knuckle (8) are of L-shape design in radial section and have both a cylindrical raceway (19, 20) of the two cylinder roller bearings (9, 11, 19; 10, 12, 20) and a raceway (23, 24) for balls (17, 18) of the two ball bearings (15, 17, 23; 16, 18, 24).

9. The wheel bearing as claimed in claim 8, characterized in that the cylindrical raceway (19, 20) of the two cylinder roller bearings (9, 11, 19; 10, 12, 20) of the bearing rings (27, 28) is bounded on both sides by a respective restraining flange (29, 30; 31, 32).

10. The wheel bearing as claimed in claim 8 or 9, characterized in that the two bearing rings (27, 28) are held at a defined axial distance by means of a spacer sleeve (33).

11. The wheel bearing as claimed in claim 10, characterized in that the two axial ends of the spacer sleeve (33) are pushed into grooves (38) in the two bearing rings (27, 28), there being a radial press fit between the spacer sleeve (33) and the bearing ring (27, 28).

12. The wheel bearing as claimed in one of claims 1 to 11, characterized in that the wheel hub (3), as a part of single-piece design, has the two cylindrical raceways (9, 10) of the two cylinder roller bearings (9, 11, 19; 10, 12, 20) and the two raceways (15, 16) for balls (17, 18) of the two ball bearings (15, 17, 23; 16, 18, 24).

13. The wheel bearing as claimed in one of claims 1 to 12, characterized in that the wheel bearing unit (2) is designed as a prestressed unit which is lubricated to last its working life.

14. The wheel bearing as claimed in claim 13, characterized in that the wheel bearing unit (2) is prestressed by means of an axle nut (34) screwed onto the steering knuckle (3).

15. The wheel bearing as claimed in one of claims 1 to 14, characterized in that the wheel bearing unit (2) is sealed off from the surroundings by means of at least one sealing element (35).

16. The wheel bearing as claimed in one of claims 1 to 15, characterized by a sleeve (36), the outside diameter (D) of which corresponds to the inner bore in the wheel bearing unit (2) and which is temporarily located in the preassembled wheel bearing unit (2).

17. The wheel bearing as claimed in claim 16, characterized in that the sleeve (36) is composed of plastic.

18. The wheel bearing as claimed in claim 16 or 17, characterized in that the sleeve (36) is arranged in the wheel bearing unit (2) with a press fit.