Steering shaft mounting system with angular roller bearings and adjusted rollers for increasing friction in steer-by-wire steering systems

Abstract

The invention relates to a steering shaft mounting system (1) for a steer-by-wire steering system of a motor vehicle, comprising at least one first steering shaft bearing for supporting a steering shaft, wherein the first steering shaft bearing is designed as an angular roller bearing and has a plurality of rollers (12) guided in a cage (11). The longitudinal axis (13) of at least one roller does not intersect the axis of rotation (14) of the steering shaft bearing, so that, in the event of a movement of the steering shaft in rolling contact, sliding friction occurs in addition to the rolling friction. The invention further relates to a steering direction changing device having an electric motor which, during operation, is coupled, so as to generate movement, to a steering shaft which is mounted via a steering shaft mounting system according to the invention.

Description

[0001] Steering shaft bearing with swashplate bearing and angled rollers for increased friction in steer-by-wire steering systems

[0002] The invention relates to a steering shaft bearing for a steer-by-wire steering system of a motor vehicle, such as a vehicle powered by an internal combustion engine, a hybrid vehicle or a fully electric vehicle, with at least one first steering shaft bearing for supporting a steering shaft, wherein the first steering shaft bearing is designed as a roller bearing.

[0003] So-called force-feedback actuators, as part of a steer-by-wire system for vehicles, must simulate the feedback forces (force feedback) mechanically transmitted in a conventional steering system. When changing the direction of rotation at the steering wheel, especially when driving straight ahead, where the driver stabilizes the direction of travel with slight steering corrections in the changing direction of rotation, steering systems without mechanical transmission of the steering forces result in a steering feel that is perceived as spongy and lacking resistance.

[0004] The reason for this is that the control loop must first detect the change in steering direction via the sensors and react accordingly. As described, the time or steering angle required for the force feedback to build up is perceived at the steering wheel as too light or too vague.

[0005] The basic idea is to improve this unpleasant and unusual steering feel by deliberately and consistently increasing friction, thereby partially solving the problem. However, in some implementation variations, the increase in friction is too small.

[0006] From DE 102018 131 204 B3, a friction device for a feedback actuator is known in connection with steer-by-wire steering systems, in which a housing body is rotatably mounted to a shaft via at least two bearings. At least one of the bearings is designed as an axial roller bearing with rollers whose main axes of extension are skew to the longitudinal axis of the shaft, so that in addition to rolling friction, sliding friction is generated during operation. An angular contact ball bearing is provided as a further bearing.

[0007] From DE 102022 132038 A1, a steering shaft bearing arrangement for a motor vehicle is known, in which the steering shaft is supported in a steering column tube via a rolling bearing arrangement and comprises at least one angular contact roller bearing with an inner and outer ring and rollers guided by a cage. The roller axes are aligned star-shaped around the axis of rotation, i.e., the longitudinal axes of the rollers intersect the axis of rotation.

[0008] The object of the present invention is to eliminate or at least mitigate the disadvantages known from the prior art.

[0009] According to the invention, the problem is solved by a steering shaft bearing according to claim 1.

[0010] For this purpose, it is provided that a first steering shaft bearing is designed as a roller bearing and has a plurality of rollers guided in a cage, at least one of which is arranged such that its longitudinal axis does not intersect an axis of rotation of the first steering shaft bearing, wherein the first steering shaft bearing is designed as an angular contact roller bearing.

[0011] This allows the sliding friction component compared to the rolling friction component to be precisely predetermined, resulting in a particularly good haptic experience for the user.

[0012] The invention achieves a greater increase in frictional torque compared to the prior art, the magnitude of which is independent of the steering direction or is the same for both steering directions. Furthermore, the use of an angular contact roller bearing avoids the disadvantage of an axial roller bearing regarding the lack of radial guidance and centering of the shaft. This eliminates the need for additional radial bearings and minimizes the number of bearings. Even with a conventional roller arrangement, differential slippage already exists between the rollers and the raceways in an angular contact roller bearing. However, the bearing friction torque is now increased by the fact that at least one roller is arranged parallel to the axis of rotation, meaning its longitudinal axis does not intersect the axis of rotation of the bearing. As a result, the roller tends to leave its circular raceway, a tendency prevented by the cage.The resulting constraint forces increase the bearing friction torque in the desired way.

[0013] In angular contact bearings, line contact is typically achieved kinematically by the rollers' longitudinal axes intersecting the axis of rotation. If the rollers are oriented as described in the application (the longitudinal axis does not intersect the axis of rotation), the line contact transitions into a near-point contact situation (generally two contact areas on the outer ring, typically one on the inner ring). This intentionally generates additional sliding components and thus a higher frictional torque.

[0014] Established bearing practice avoids this type of configuration in angular contact roller bearings due to the expected loss of load-bearing capacity compared to line contact. However, in the relevant application here as a steering shaft bearing in a steer-by-wire system, this deviation from the ideal geometry can be deliberately used at typical load levels to generate a defined sliding friction component and a reproducible frictional torque.

[0015] In a preferred embodiment, all rollers are arranged such that their longitudinal axes do not intersect the axis of rotation of the first steering shaft bearing. This maximizes the generated frictional torque.

[0016] In a preferred embodiment, the angular contact roller bearing has a cage in which the longitudinal axes of the rollers are alternately inclined in opposite directions. The rollers, arranged successively in the circumferential direction, are positioned such that their longitudinal axes alternately run spaced apart on opposite sides of the axis of rotation. This alternating orientation of the roller longitudinal axes on opposite sides of the circumferential axis of rotation helps to largely compensate for direction-dependent frictional torque components and to achieve a friction characteristic that is independent of the steering direction.

[0017] Additionally or alternatively, at least one roller can be arranged parallel to its reference position on the running circle in the circumferential direction; this affects the pitch or the angular distribution measured from the axis of rotation. In one embodiment, the parallel displacements of the rollers of a pair are opposite in direction (one clockwise, the other counterclockwise).

[0018] Preferably, the pressure angle α is in the range greater than 0° and less than 90°, preferably between 40° and 80°. Regardless of this, at least one roller is additionally oriented such that its longitudinal axis is inclined and / or shifted parallel in the circumferential direction, thereby selectively increasing the sliding friction component in the rolling contact.

[0019] In this context, the pressure angle α denotes the typical contact angle in angular contact bearings between the resulting load line in the rolling contact and the radial plane; α is greater than 0° and less than 90° and defines the combined absorption of radial and axial forces. This clarification is for the sake of clarity and is not intended to be restrictive.

[0020] The degree of friction torque increase can be customized by adjusting various characteristics, such as the axial roller offset, the roller longitudinal axis inclination, the axial bearing preload, and the contact angle. The friction-enhancing bearing can be positioned at any point in the steering torque transmission system.

[0021] During the design process, the desired increase in frictional torque is weighed against permissible contact pressures and service life requirements; the loads and preloads typical for hand-wheel actuators allow the targeted use of the described sliding components without impairing the functional reliability of the steering shaft bearing.

[0022] Preferably, the steering shaft bearing is used in an operating unit for influencing the direction of travel of a motor vehicle, comprising a steering shaft rotatably mounted via a rolling bearing arrangement within a connection structure, at the distal end of which a steering means can be coupled, wherein an actuation of the steering means representing a steering direction causes a rotation of the steering shaft and the rolling bearing arrangement has at least one first angular contact roller bearing with a first inner ring, a first outer ring and a first group of rollers which are guided by a cage.

[0023] To explain the "parallel-shifted roller arrangement": In a conventional angular contact roller bearing, the roller axes (longitudinal axes of the rollers) typically intersect the axis of rotation of the steering shaft; the rollers are arranged in a star-shaped pattern around the circumference. In contrast, the arrangement according to the invention also includes the parallel shifting of at least one roller along its running circle relative to a reference position. The reference position is the position in which a reference roller is located or would be located.

[0024] To illustrate the "inclined arrangement of the roller": In conventional angular contact roller bearings, the rollers are arranged in a star shape around the axis of rotation. The previously described measures (incline and parallel displacement) can be combined.

[0025] It has proven advantageous to only use rollers whose longitudinal axes do not intersect the axis of rotation of the steering shaft bearing; this simplifies the design.

[0026] In a particular embodiment, the angular contact roller bearing comprises a plurality of rollers, wherein at least one friction-enhancing roller is arranged inclined and / or parallel displaced relative to an adjacent reference roller; the longitudinal axis of the reference roller intersects the axis of rotation of the first steering shaft bearing. In the circumferential direction, friction-enhancing rollers and reference rollers can be arranged alternately.

[0027] Preferably, a second steering shaft bearing is arranged axially offset from the first to prevent the steering shaft from tilting.

[0028] Furthermore, it is advantageous if the first and second steering shaft bearings surround the steering shaft and are arranged in a steering column tube (outer tube).

[0029] The invention also relates to a steering direction change device (hand-wheel actuator) with an electric motor which, in operation, is coupled to a steering shaft in a motion-generating manner and which is supported by the steering shaft bearing according to the invention.

[0030] The invention is explained in more detail below with the help of the figures. They show:

[0031] Fig. 1 shows a schematic representation of a steering shaft bearing according to the invention in a motor vehicle, namely a steer-by-wire steering system of the motor vehicle,

[0032] Fig. 2 shows a part of a steering direction change device according to the invention with the steering shaft bearing according to the invention,

[0033] Fig. 3 shows a first embodiment of a steering shaft bearing with rollers designed exclusively as friction-enhancing rollers, the longitudinal axes of which do not intersect the axis of rotation of the steering shaft and all run spaced apart on the same side of the axis of rotation.

[0034] Fig. 4 shows a further embodiment of a steering shaft bearing according to the invention, in which the rollers positioned in a cage are designed exclusively as friction-enhancing rollers and their longitudinal axes run alternately spaced apart in the circumferential direction on one or the opposite side of the axis of rotation of the steering shaft, respectively. Fig. 5 shows an embodiment of a steering shaft bearing in which the roller axes are inclined in alternating directions and additionally displaced parallel to the axis, wherein the parallel displacement of the rollers of a pair is carried out in opposite directions.

[0035] Fig. 6 shows another embodiment in which the roller axes are inclined in alternating directions and additionally shifted parallel to the axis, wherein the axial shift of the rollers of a pair is carried out in the same direction.

[0036] The figures are purely schematic and serve only to illustrate the invention. The same elements are identified by the same reference numerals. Features of the individual embodiments can be combined and interchanged.

[0037] Figure 1 shows a steering shaft bearing 1 according to the invention in a steer-by-wire steering system 2 in a motor vehicle 3. The steering shaft bearing 1 supports a steering shaft 4.

[0038] The steering shaft bearing is part of a steering direction change device 5, which can also be called a hand-wheel actuator.

[0039] This steering direction change device 5 is shown in more detail in Fig. 2. It comprises a steering column tube 6 (outer tube) in which a first steering shaft bearing 7 and a second steering shaft bearing 8 are arranged. The first steering shaft bearing 7 is mounted with a pressure angle α (reference numeral 9) and is designed as an angular contact roller bearing 10. The second steering shaft bearing 8 is designed as an angular contact ball bearing. The first steering shaft bearing 7 has, among other things, a cage 11, as shown in Figures 3 and 4. Other parts of the steering shaft bearing 1 are not shown in Figures 3 to 6; it is essential that a plurality of rollers 12 are provided. In the embodiments according to Figures 3, 4, 5 and 6, all rollers 12 are designed as friction-enhancing rollers. Each roller 12 has a longitudinal axis 13 that extends outside the axis of rotation 14 of the steering shaft 4. The rollers 12 of the embodiment according to Fig. 3 are distributed equidistantly over the cage 11.

[0040] While in the embodiment according to Fig. 3 the longitudinal axes 13 of all rollers 12 are inclined in the same direction, the longitudinal axes 13 of the rollers 12 in the embodiment according to Fig. 4 are inclined in alternating directions. Reference numeral 15 represents an imaginary normal orientation of a longitudinal axis of a roller. An angle of inclination β (reference numeral 16) is established between the longitudinal axis 13 of a roller 12 and the imaginary normal orientation 15; an exemplary value for β can be 20°. The number of roller pairs 17 can vary and is not limited to a specific value; it is adapted to the respective bearing design and requirements. If the longitudinal axis of a roller 12 is arranged offset from the imaginary normal orientation 15, an offset 18 occurs. Reference numeral 19 visualizes the raceway diameter in Fig. 4.

[0041] Steering shaft bearing

[0042] Steer-by-wire steering

[0043] motor vehicle

[0044] steering shaft

[0045] Steering direction change device

[0046] Steering column tube (outer tube)

[0047] first steering shaft bearing

[0048] second steering shaft bearing

[0049] pressure angle a

[0050] Angular roller bearings

[0051] cage

[0052] role

[0053] Longitudinal axis of a roller

[0054] Axis of rotation of the steering shaft / axis of rotation of the first steering shaft bearing; imaginary normal orientation of a longitudinal axis of a roller; angle of inclination β

[0055] Role pair

[0056] Offset

[0057] Wheel diameter

Claims

Patent claims 1. Steering shaft bearing (1 ) for a steer-by-wire steering system (2) of a motor vehicle (3), comprising at least one first steering shaft bearing (7) for supporting a steering shaft (4), wherein the first steering shaft bearing (7) is designed as a roller bearing and has a plurality of rollers (12) guided in a cage (11), at least one of which is arranged such that its longitudinal axis (13) does not intersect an axis of rotation (14) of the first steering shaft bearing (7), characterized by the fact that the first steering shaft bearing (7) is designed as an angular contact roller bearing.

2. Steering shaft bearing (1) according to claim 1, characterized in that only such rollers (12) are present whose longitudinal axes (13) do not intersect the axis of rotation (14) of the first steering shaft bearing (7).

3. Steering shaft bearing (1) according to claim 2, characterized in that the rollers (12) arranged successively in the circumferential direction are arranged such that the longitudinal axes (13) run alternately spaced apart on opposite sides of the axis of rotation (14).

4. Steering shaft bearing (1 ) according to claim 1 , characterized in that a plurality of rollers (12) are provided, at least one of which is predetermined as a friction-enhancing roller (12) is arranged inclined at an angle and / or parallel displaced relative to an adjacent roller (12) predetermined as a reference roller, wherein the longitudinal axis (13) of the reference roller intersects the axis of rotation (14) of the first steering shaft bearing (7).

5. Steering shaft bearing (1) according to claim 4, characterized in that the circumferentially successive rollers (12) are arranged alternately as friction-enhancing rollers and as reference rollers.

6. Steering shaft bearing (1) according to any one of claims 1 to 5, characterized in that a second steering shaft bearing (8) is arranged axially offset from the first steering shaft bearing (7).

7. Steering shaft bearing (1) according to claim 6, characterized in that the steering shaft (4) is encompassed by a first steering shaft bearing (7) and a second steering shaft bearing (8) which are arranged in a steering column tube (6).

8. Steering direction change device (5) with an electric motor which is coupled to a steering shaft (4) in a motion-generating manner during operation, wherein the steering shaft (4) is mounted via a steering shaft bearing (1) according to one of the preceding claims.

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