Active wheel hub bearing

Abstract

A rolling bearing of a wheel hub group for motor vehicles, equipped with a stationary radially outer ring and with respective radially outer raceways, a pair of rotatable radially inner rings equipped with respective radially inner raceways, and two rows of rolling bodies positioned between the corresponding inner and outer raceways. The rolling bearing is also equipped with a piezoelectric actuator housed in a seat of the radially outer ring, in a symmetrical position relative to the raceways, and capable of varying the strain behavior of the radially outer ring.

Claims

1. A rolling bearing of a wheel hub group for motor vehicles comprising: a radially outer stationary ring having corresponded radially outer raceways, wherein the radially outer stationary ring is a one-piece member; a pair of radially inner rotatable rings having correspondent radially inner raceways; two rows of rolling bodies accommodated between the radially inner raceways of the pair of radially inner rotatable rings and the radially outer raceways of the radially outer stationary ring, wherein the rolling bearing comprises a piezoelectric element accommodated in a seat provided within the radially outer stationary ring in a symmetrical position with respect to the radially outer raceways, and the piezoelectric element is configured to modify strain behavior of the radially outer stationary ring and the radially outer raceways based on subjecting axial surfaces of the seat to a pressure differential, the pressure differential being achieved based on change in length of the piezoelectric element upon application of voltage to the piezoelectric element.

2. The rolling bearing according to claim 1, wherein the piezoelectric element is further configured to, apply a variable pressure on axial surfaces of the seat of the radially outer stationary ring, and modify the strain behavior of the radially outer stationary ring and the radially outer raceways based on the application of the variable pressure.

3. The rolling bearing according to claim 1, wherein the piezoelectric element is electrically connected to a control unit by means of a wiring harness passing through a hole of the radially outer stationary ring.

4. The rolling bearing of a wheel hub group for motor vehicles of claim 1, wherein the radially outer stationary ring defines a through hole extending from the seat.

5. The rolling bearing of a wheel hub group for motor vehicles of claim 4, further comprising a wiring harness coupled to the piezoelectric element and extending through the through hole.

6. The rolling bearing of a wheel hub group for motor vehicles of claim 5, wherein the through hole extends from the seat in a radial direction.

7. A system for active control of a rolling bearing of a wheel hub group for motor vehicles comprising: a control unit, a wiring harness, a rolling bearing comprising, a radially outer stationary ring having corresponded radially outer raceways, wherein the radially outer stationary ring is a one-piece member, a pair of radially inner rotatable rings having correspondent radially inner raceways, two rows of rolling bodies accommodated between the radially inner raceways and the radially outer raceways, wherein the rolling bearing comprises a piezoelectric element accommodated in a seat provided within the radially outer stationary ring in a symmetrical position with respect to the radially outer raceways, the piezoelectric element is configured to modify strain behavior of the radially outer stationary ring and the radially outer raceways based on subjecting axial surfaces of the seat to a pressure differential, the pressure differential being achieved based on change in length of the piezoelectric element upon application of voltage to the piezoelectric element.

8. The rolling bearing of a wheel hub group for motor vehicles of claim 7, wherein the radially outer stationary ring defines a through hole extending from the seat.

9. The rolling bearing of a wheel hub group for motor vehicles of claim 8, wherein the wiring harness is coupled to the piezoelectric element and extends through the through hole.

10. The rolling bearing of a wheel hub group for motor vehicles of claim 9, wherein the through hole extends from the seat in a radial direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the attached drawings, which show some non-limiting examples of embodiment, in which:

(2) FIG. 1, in partial axisymmetric section, shows a detail of an assembled wheel hub group,

(3) FIG. 2 is a sketch of an example of the bearing unit according to one embodiment of the present invention, and

(4) FIG. 3 is a detail of FIG. 2.

DETAILED DESCRIPTION

(5) With reference now to FIG. 1, a wheel hub group is indicated as a whole by 10. The figure shows a detail of an example of configuration. As stated in the introduction, the invention is applicable not only to the configuration described below but more generally to any wheel hub group for motor vehicles.

(6) The group 10 comprises a hub 20, which is rotatable, and a bearing unit 30. The hub 20, as shown in FIG. 1, is configured so that it also acts as an inner raceway of the bearing. On the other hand, as shown in FIG. 2, it is also possible to use a pair of radially inner rings 34, 35, and according to this configuration the hub does not act as a raceway. In the remainder of the present description, reference will be made explicitly to the latter configuration, comprising two radially inner rings. Additionally, throughout the present description and in the claims, any terms and expressions indicating positions and orientations such as radial and axial are to be interpreted as relating to the central axis of rotation X of the bearing unit 30. However, expressions such as axially outer and axially inner relate to the assembled condition, and, in this particular case, preferably relate to one side of a wheel and to a side opposed to this side of the wheel, respectively.

(7) Also, with reference to FIG. 2, the bearing unit 30 according to one embodiment of the present invention comprises a stationary radially outer ring 31, provided with respective radially outer raceways 31, a pair of rotatable radially inner rings 34, 35, provided with respective radially inner raceways 34 and 35, and two rows of rolling bodies 32, 33, which in this case are balls. The axially outer row of rolling bodies 32 is interposed between the radially outer ring 31 and the radially inner ring 35, in an axially outer position, while the axially inner row of rolling bodies 33 is interposed between the radially outer ring 31 and the radially inner ring 34, in an axially inner position. To simplify the graphic representation, the references 32, 33 will be given both to the individual balls and to the rows of balls. Also for simplicity, the term ball may be used by way of example in the present description and in the attached drawings in place of the more generic term rolling bodies (and the same reference numerals are also used). It is to be understood in all cases that the balls may be replaced by any other rolling bodies (such as rollers, tapered rollers, needle rollers, or the like).

(8) The rolling bodies of the rows 32, 33 are held in position by corresponding cages 39, 40.

(9) Returning to FIG. 1, the hub 20 forms at its axially inner end a rolled edge 22 which is configured to axially pre-load the inner ring 34, which is mounted on a radially outer surface 20 of the hub.

(10) For completeness of description, the hub 20 also has an axially outer flange portion. The flange portion has a plurality of axial fixing holes. These holes are the seats for the same number of fixing means (such as captive bolts), which connect, in a known way, an element of the wheel of the motor vehicle, for example the brake disc (also of a known type), to the hub 20. All these characteristics are known in themselves and are therefore not shown in the attached drawings.

(11) The components of the bearing unit 30, particularly the radially outer ring 31 and the raceways 31, the radially inner rings 34, 35 and the respective raceways 34, 35, as well as the rows 32, 33 of rolling bodies, are designed, as shown in FIG. 2, according to the current stands for bearings for wheel hub groups.

(12) With reference to FIGS. 2 and 3, according to an embodiment of the invention, the bearing unit 30 is provided with a piezoelectric actuator 50 housed in a seat 31a of the radially outer ring 31, in a symmetrical position relative to the raceways 31.

(13) The application of a voltage to the piezoelectric actuator 50 causes a change in the length of the actuator, in the direction indicated by the arrows in FIGS. 2 and 3. The elongation of the piezoelectric actuator subjects the axial surfaces 31b of the seat 31a of the radially outer ring 31 to a different pressure, thereby modifying the strain behaviour of the radially outer ring 31 and its raceways 31. As a result, the force transmitted between the raceways 31 and the rolling bodies 32, 33 is modified. The strain that is produced is a function of the specific driving conditions of the vehicle (straight or cornering).

(14) The piezoelectric actuator 50 is connected by means of a wiring harness 51, which passes through a hole 31c in the radially outer ring 31, to a control unit (of a type which is known and therefore not shown in the figures) configured to monitor the conditions of movement of the vehicle and particularly its lateral acceleration. The control unit can therefore control the piezoelectric actuator, by supplying feedback to it, preferably by closed loop control.

(15) The active internal geometry proposed by the present invention, with a radially outer ring capable of modifying its strain behavior and consequently the forces applied to the rolling bodies, provides real-time control of the key geometrical parameters, namely:

(16) the pre-loading of the bearing, that is to say the pre-loading between the races and the rolling bodies;

(17) the contact angle between the raceways and the rolling bodies in general, defined as the angle between the axis Y of axial symmetry between the radially inner rings 34, 35 and the axis Z passing through the points of contact P, P between the rolling bodies and the respective raceways (in FIG. 2, by way of example, the raceway 31, the ball 32 and raceway 35);

(18) the osculation, that is to say the ratio between the radius of curvature of the raceway and the diameter of the ball.

(19) Such active control reduces the friction of the internal geometry while simultaneously matching the behavior of the bearing, in terms of mechanical strength, to the various driving conditions.

(20) In particular, during straight driving, the bearing can operate in the low friction mode. This mode is taken to mean that the working curve, that is to say the contact curve, of the raceway 31 is as indicated by 31a in FIG. 3. Thus, the pre-loading between the races and the rolling bodies is reduced, decreasing the contact angle between the rolling bodies and the respective raceways, and increasing the osculation. In these driving conditions, the reduction of pre-loading and therefore of the overall load capacity of the bearing is acceptable, since it provides the advantage of a lower force on the bearing, minimizing friction losses and thus enabling fuel savings to be made.

(21) Conversely, during cornering, the bearing can operate in the high friction mode. This mode is taken to mean that the working curve, that is to say the contact curve, of the raceway 31 is as indicated by 31b in FIG. 3. Thus, the pre-loading between the races and the rolling bodies is increased, in the same way as the contact angle between the rolling bodies and the respective raceways is increased, and the osculation is reduced. In these driving conditions, which usually last for a shorter time than straight driving, the need to accept higher friction is acceptable, because there is also an increase in pre-loading and therefore in the overall load capacity of the bearing, which is highly advantageous for the stability of the vehicle.

(22) Evidently, the piezoelectric actuator may also be used as a sensor for monitoring the load capacity of the bearing. Thus a smart wheel hub group is provided.

(23) The proposed solution provides considerable advantages: the use of the piezoelectric element as an actuator considerably reduces the friction of the bearings, while maintaining the same service life and the same mechanical strength, in the operating conditions of the vehicle, during cornering for example, when this is required.

(24) Additionally, by using the piezoelectric element as a sensor the load conditions on the bearing can be constantly monitored.

(25) In addition to the embodiments of the invention as described above, it should be understood that there are numerous other variants. It should also be understood that the embodiments are described purely by way of example, and do not limit the object of the invention, or its applications, or its possible configurations. On the contrary, although the above description enables a person skilled in the art to implement the present invention at least according to an example of configuration thereof, it should be understood that numerous variations of the components described could be devised without thereby departing from the object of the invention as defined in the attached claims, whether interpreted literally and/or according to their legal equivalents.