Technical Field The invention relates to a bearing arrangement, comprising a driven shaft element which is supported by at least two roller bearings, wherein the roller bearings are arranged at an axial distance along an axis and wherein an actuator element is arranged by which the axial pre-load between the two roller bearings can be influenced.

Background A bearing arrangement of this kind is shown for example in US 3,762,783. Here a shaft is supported by two roller bearings relatively to a housing. An expansion or actuator element being a coiled spring is engaged to preload the roller bearings. The pre-load effect can be influenced by a respective dimensioning of the coiled spring.

In some applications it is desired that the axial pre-load of a bearing arrangement, i. e. the axial load between two cooperating roller bearings, is adjusted in dependence on a torque which is transferred through the shaft element. Specifically, it is desired that the preload is interactively and automatically adapted depending on the transferred torque.

The pre-known solution does not allow an interactive adaption of the torque. To the contrary, after the selection of the coiled spring which is employed the pre-loading effect cannot be modified.

Summary of the invention

According to the invention, a design is proposed for a bearing arrangement which comprises a driven shaft element. The shaft element is supported by at least two roller bearings which are arranged at an axial distance. Furthermore, an actuator element is employed by which the axial pre-load between the two roller bearings can be influenced.

It is an o bj e c t of the invention to propose a design for such a bearing arrangement which allows an automatic adjustment of the axial pre-load between the two bearings in dependence on the torque which is transferred through the shaft element. This should be done in an easy way which allows a cost-effective realization.

A s o l u t i o n according to the invention is characterized in that the actuator element comprises a first axial end section and a second axial end section, wherein a plurality of beam elements extend between the first and second axial end sections, wherein the beam elements are arranged along an outer circumferential surface of the actuator element and wherein the beam elements are running along a helical curve or straight line between the first and second axial end sections.

Preferably, the first axial end section of the actuator element is rotationally connected to the shaft element, wherein the second axial end section of the actuator element is rotationally connected to an input shaft.

The actuator element has preferably a generally hollow-cylindrical or conical base geometry. The first and/or second axial end sections are preferably designed as ring-shaped sections.

The beam elements can be designed and arranged so that hollow sections exist between two adjacent beam elements - seen in circumferential direction. An alternative suggests that a filler material is arranged between the beam elements. The filler material can be for example rubber material.

At least one of the beam elements can be equipped with a sensor element for measurement of the stain in the beam element. Here, preferably a strain gauge is employed.

At least one damping element can be arranged between two adjacent beam elements to prevent oscillations or vibrations. The actuator element is preferably arranged coaxially to the shaft element. Furthermore, the actuator element and the shaft element can be arranged in series. An end stop can be arranged at one axial end section of the actuator element forming a support for axial forces from the actuator element. The axial end section can comprise a sliding surface. It is also possible that a thrust bearing is arranged between the axial end section of the actuator element and the end stop. The thrust bearing element can be an axial sliding bearing or an axial roller bearing.

The actuator element can be arranged between the two roller bearings. In this case the shaft element can be split at a location between the two roller bearings. Alternatively, the actuator element can be arranged adjacent to one of the roller bearing and extending in a direction remote from the other roller bearing.

The roller bearings are preferably taper roller bearings or angular contact ball bearings.

The beam elements consist preferably of metal, especially of steel. An alternative proposes that the beam elements consist of a fiber material, especially of a carbon composite material. Generally, the actuator element can consist of a variety of materials including plastic.

The bearing arrangement can be for example a part of a pinion gear unit, especially of a pinion gear unit being part of a power train of an automotive. Of course, also other applications can be equipped according to the invention, e. g. windmills. 0

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Brief description of the drawings

The drawings show embodiments of the bearing arrangement according to the invention.

Fig. 1 shows a perspective view, partially broken, of a bearing arrangement with a driven shaft and an actuator element for adjusting the pre-load of the bearing arrangement, Fig. 2 shows a cross section through a bearing arrangement according to Fig.

1 ,

Fig. 3 shows a perspective view of an actuator element according to the embodiment according to Fig. 1 ,

Fig. 4 shows a perspective view of an actuator element, equipped with a strain gauge to detect the strain in the actuator element,

Fig. 5 shows a perspective view of an actuator element, equipped with a damping element which is shown only schematically,

Fig. 6 shows a perspective view of an actuator element according to another embodiment, Fig. 7a till

Fig. 7d show schematically different bearing arrangements with an actuator element, wherein the rolling bearings of the embodiment are arrangement in X-configuration and Fig. 8a till

Fig. 8d show schematically different bearing arrangements with an actuator element, wherein the rolling bearings of the embodiment are arrangement in O-configuration.

Detailed description of the invention In Fig. 1 a bearing arrangement 1 is shown by which a driven shaft element 2 (which is an output shaft) is supported. For this support function two roller bearings 3 and 4 are arranged which are positioned in an axial distance a along an axis A (axial direction). The two roller bearings 3, 4 are designed as angular contact ball bearings in an O-configuration in the present case. The two outer rings of the two bearings 3, 4 are supported by a bush 16. The outer rings of the roller bearings 3, 4 can be arranged with press fit in the bush 16.

The shaft element 2 is connected with its right end region 26 with an actuator element 5 which is adapted to change its length in response to an applied torque; insofar the actuator element 5 could also be called an expansion (or contraction) element. From the right end side of the actuator element 6 a torque T is applied via a flange 25 which is connected with an input shaft 24 onto the actuator element 5 which torque is transferred through the whole axial extension of the shaft element 2 from its end region 26 to its left end side. There, a (not depicted) pinion can be arranged by which the torque is transferred into a bevel gear or the like.

The actuator element 5 comprises two ring-shaped end sections 6 and 7, namely a first axial end section 6 and a second axial end section 7. The two end sections 6, 7 are connected to each other by a plurality of beam elements 8, i. e. the beam elements 8 extend between the first and second axial end sections 6, 7. The beam elements 8 are arranged along an outer circumferential surface 9; in the present case the outer circumferential surface has a cylindrical shape. The beam elements 8 are running along a helical curve 10 between the two axial end sections 6, 7. The beam elements 8 are arranged with a spacing in circumferential direction C, i. e. hollow sections 1 1 exist between two adjacent beam elements 8. That means that the torque T is transferred from the input shaft 24 into the second axial end section 7 of the actuator element 5, through the actuator element 5 to the first axial end section 6 of it and from there into the shaft element 2 which acts as an output shaft. For transferring the torque from the input shaft 24 into the actuator element 5 a respective flange 25 can be employed. In other words: The whole shaft of the depicted arrangement is split into an input shaft 24 and an output shaft 2, wherein the input shaft 24 and the output shaft 2 are connected via the actuator 5.

In the embodiment shown in Fig. 1 the actuator element 5 has three beam elements 8. Due to the fact that the beam elements 8 run along a helical curve 10 it is observed that a torsional deformation between the two end sections 6, 7 leads to a change in the axial distance between the two end sections 6, 7. The right end section, i. e. the second axial end section 7 is axially supported by an end stop 15, i. e. the second axial end section 7 cannot be displaced to the right. Thus, a torsional deformation due to the torque T presses the first axial end section 6 to the left side, so that it presses axially onto the inner ring of the roller bearing 4. By doing so, the pre-load in the bearing arrangement 1 is increased. Thus, the actuator element 5 acts as an actuator so that the input torque T on the actuator 5 is converted to a bearing pre-load.

Fig. 2 shows this situation again. The torque application T is done in the second axial end section 7 of the actuator element 5. A sliding surface 17 of the end stop 15 supports the second axial end section 7 of the actuator element 5. The shaft element 2 has in its axial extension along the actuator element 5 a sliding contact denoted with 18. A sliding contact is also provided at 19 between the shaft element 2 and the inner ring of the roller bearing 4. At 20 a sliding contact or a fixed contact can be provided between the shaft element 2 and the inner ring of the roller bearing 3. The bush 16 is arranged with a fixed contact 21 in a housing (not depicted). The contact area located on the inside of the first axial end section 6 is equipped with torque transfer means 23 which allows an axial sliding between the actuator element 5 and the shaft element 2 which is established for example by splines. Thus, the contact point or contact area at the reference numeral 23 is an axially sliding contact which allows torque transfer from the actuator element 5 to the output shaft 2.

In Fig. 3 some relevant geometrical data are denoted. The actuator element 5 has four beam elements 8 in the present case which run along a helical curve 10. The angle a of the orientation of the length axis of the beam element 8 and the axial direction A defines the actuation effect of the actuator element 5. The torsional deformation of the shaft will result in an axial deformation determined by the angle a. If the angle a is small, large axial forces can be obtained given a certain input torque. In the depicted embodiment the angle a is about 30°. A change in the direction of rotation between the two end sections 6, 7 changes the movement of the actuator element 5 from expansion to contraction and vice versa. It should be noted that the beam element 8 can be designed straight (as depicted) or can have any kind of a curve (e. g. S-shaped). Also the number of beam elements 8 can vary due to the specific demands of an application.

Further relevant parameters of the actuator element 5 are the width b of the beam elements 8 and their length L in axial direction.

In Fig. 4 it is shown that the beam elements 8 or at least one of them can be equipped with a sensor element 13, which is a strain gauge in the embodiment. By a sensor element 13 the actual strain in the beam element 8 can be detected, which is a direct indicator for the pre-load force which is applied onto the bearing arrangement. The application of strain gauges 13 on the beam elements 8 of the actuator allows thus to measure the amount of torque that is transferred. To prevent oscillations or vibrations a damping element 14 can be arranged between two or more beam elements 8 as shown in Fig. 5. This depiction is a schematic representation only. The damping element 14 can be a damping device but also a damping material which is brought between two beam elements 8, e. g. a damping material like rubber.

The actuator element 5 is a very stiff torsion spring. The open areas (hollow sections 1 1) between the beam elements 8 can thus be used for adding damping using a damper or damping materials like rubber. Hence, a very compact spring-damper system is feasible. In Fig. 6 another embodiment of an actuator element 5 is shown. Here, the beam elements 8 are again arranged under the mentioned angle, but here the beam elements 8 are formed by fiber material, e. g. carbon composite material. Between the single fibers a filler material 12 is placed which hold the plurality of beam elements 8 in position. The filler material 12 can be a soft material.

In Fig. 7a till 7d different conceptual designs are shown where two roller bearings 3, 4 in an X-configuration are employed. As can be seen, the actuator element 5 can be arranged at different locations: between the roller bearings or at one axial side of the bearing arrangement. One or two sleeve elements 22 guide the actuator element 5 or form an axial support for the same. In Fig. 8a till 8d different conceptual designs are shown similar to Fig. 7a till 7d where the two roller bearings 3, 4 are arranged in O-configuration.

For the design of the torque-activated actuator element 5 different embodiments with multiple variations are possible.

As said, the behavior of the actuator element (expansion or contraction element) 5 is strongly dependent on the angle a of the beam elements 8. The angle a can basically be between 0° and 90°. The amount of expansion or contraction is adjustable with this parameter significantly.

With an angle of 0° a low torque transfer is feasible with low expansion. With an angle of 90° a high torque transfer is feasible with low expansion. A middle angle, like e. g. 45°, leads to a middle torque transfer with high expansion. The angle a of the beam elements 8 can also vary over the length of the beams. Another relevant parameter is - as said - the length L of the beam element 8 as well as the number of beam elements 8.

Also the shape of the beam elements 8 is relevant. The cross-sectional area can vary over the length of the beam elements 8.

The material of the actuator element 5 can be ferrous metals or non-ferrous metals. Also ceramic and plastics can be used.

Another relevant parameter is the inner and the outer diameter of the actuator element 5. The diameters can be variable over the length of the actuator element 5 resulting for example in a conical shape.

The beam elements 8 in the actuator element 5 are mostly created by removing material from a hollow tube. In the case of a hollow tube made out of fiber material, it is possible to gain the same result by changing the orientation of the fibers to an angular position without removing any material.

The actuation can be applied to any kind of pre-loaded bearings. Four types of integration within a bearing system exist.

1. For a bearing unit with rotating inner ring, the actuator element 5 can be positioned at one axial side of the bearing unit, as shown in Fig. 7c (for X-arrangement) and Fig 8c (for O-arrangement). The actuator element 5 is fitted on the rotating shaft outside the bearing unit.

In the case of X-arrangement: The bearing preload decreases when the actuator element 5 expands and increases when the actuator element 5 contracts. The actuator element 5 is therefore adapted to contract in response to an increase in applied torque in the arrangement shown in Fig. 7c. Suitably, the actuator element 5 exerts a high initial preload.

In the case of O-arrangement: The bearing preload increases when the actuator element 5 expands and decreases when the actuator element 5 contracts. The actuator element 5 in the arrangement shown in Fig. 8c is therefore adapted to expand in response to an increase in applied torque. For a bearing unit with rotating inner ring, the actuator element 5 can be positioned between the first and second bearings 3, 4 of the bearing unit, as shown in Fig. 7a (for X-arrangement) and Fig. 8a ( for O- arrangement).

The rotating shaft is split where the actuator element 5 is fitted in between the two bearing inner rings.

In the case of X-arrangement: The bearing preload increases when the actuator element 5 expands and decreases when the actuator element 5 contracts. Consequently, the actuator element 5 in the arrangement shown in Fig. 7a is adapted to expand in response to an increase in applied torque. In the case of O-arrangement: The bearing preload decreases when the actuator element 5 expands and increases when the actuator element 5 contracts. The actuator element 5 is therefore adapted to contract in response to an increase in applied torque in the arrangement shown in Fig. 8a.

For a bearing unit with rotating outer ring, the actuator element 5 can be positioned at one axial side of the bearing unit, as shown in Fig. 7d (for X-arrangement) and 8d (for O-arrangement). The actuator element 5 is fitted on the rotating shaft outside the bearing unit.

In the case of X-arrangement: The bearing preload increases when the actuator element 5 expands and decreases when the actuator element 5 contracts. Consequently, the actuator element 5 in the arrangement shown in Fig. 7d is adapted to expand in response to an increase in applied torque.

In the case of O-arrangement: The bearing preload decreases when the actuator element 5 expands and increases when the actuator element 5 contracts. In the arrangement of Fig. 8d, the actuator element 5 is therefore designed to contract in response to an increase in applied torque.

For a bearing unit with rotating outer ring, the actuator element 5 can be positioned between the first and second bearings 3, 4 of the bearing unit, as shown in Fig. 7b (for X-arrangement) and Fig. 8b (for O- arrangement). The rotating housing is split where the actuator element 5 is fitted in between the two bearing outer rings. In the case of X-arrangement: The bearing preload decreases when the actuator element 5 expands and increases when the actuator element 5 contracts. In the arrangement of Fig. 7b, the actuator element 5 is therefore adapted to contract in response to an increase in applied torque.

In the case of O-arrangement: The bearing preload increases when the actuator element 5 expands and decreases when the actuator element 5 contracts. The actuator element 5 is therefore adapted to expand in response to an increase in applied torque in the arrangement shown in Fig. 8b.

Reference Numerals:

1 Bearing arrangement

2 Driven shaft element

3 Roller bearing

4 Roller bearing

5 Actuator element (expansion and/or contraction element)

6 First axial end section

7 Second axial end section

8 Beam element

9 Outer circumferential surface

10 Helical curve / straight line

1 1 Hollow section

12 Filler material

13 Sensor element (strain gauge)

14 Damping element

15 End stop

16 Bush

17 Sliding surface (thrust bearing)

18 Sliding contact

19 Sliding contact

20 Sliding contact / fixed contact

21 Fixed contact

22 Sleeve element 23 Torque transfer means (axially sliding) (splines)

24 Input shaft

25 Flange

26 End region of the driven shaft element

a Distance

A Axial direction / Axis

C Circumferential direction

b Width

L Length (in axial direction)

a Angle

T Location of torque application