WO2024245664A1 - Steering gear for a steer-by-wire steering system of a motor vehicle - Google Patents

Abstract

The invention relates to a steering gear (1) for a steer-by-wire steering system of a motor vehicle, comprising: a drive unit (20) having an electric machine and the conversion gear (14) coupled to the electric machine, which is designed for axially moving the steering rod (12); at least one anti-rotation device (22) connected to the steering rod (12) in a rotationally fixed manner; and, a guide rod (24) arranged parallel to the steering rod (12) in the housing (10), wherein the anti-rotation device (22) is connected to the steering rod (12) at a first end portion (22a) and bears against the guide rod (24) at a second end portion (22b) arranged opposite to the first end portion (22a), in such a way that a torque applied to the steering rod (12) can be supported on the guide rod (24) by the anti-rotation device (22).

Description

Description

title

The invention relates to a steering gear for a steer-by-wire steering system of a motor vehicle.

State of the art

In an electromechanical power steering system with a ball screw drive, the rotational fixation of the steering rod is usually achieved via a non-circular contour on the steering rod. The negative form of this contour is shown in the steering housing. This is also where the torque is supported. The lever arm for the torque support is limited by the diameter of the steering rod.

The support is usually flat. This results in sliding friction when the handlebar is lifted. Sliding friction is a functionally undesirable effect. In a classic steering system with a mechanical connection to the steering wheel, this has a negative impact on the steering feel. In a steer-by-wire application, control is also made more difficult.

Forces acting radially on the steering rod are usually absorbed at several bearing points, such as a steering pinion and a toothing on the rack, a spring-loaded pressure piece, a ball screw and/or an optional support bearing.

The use of steering systems for steer-by-wire vehicles also results in new functional requirements for the steering gear. For example, a steering gear with a ball screw no longer requires a steering pinion that converts the manual torque into a translational force. This allows the handlebar to be secured against rotation and stored in a different way.

The axial space required for gearing is no longer needed when using a pure ball screw spindle. Steer-by-wire systems also require a larger axial stroke > ±100mm. The lengths of the steering rods, however, remain unchanged. This leads to the problem that the sequentially switched functions of ball screw drive, anti-twist device and bearing are difficult to accommodate on the steering rod axis.

DE 19937376 A1 discloses a rack and pinion steering system, in particular for motor vehicles, with a bearing housing that supports the rack and a pinion meshing therewith in a displaceable or rotatable manner, a tie rod carrier connected to the rack in a frame-like manner, which has a frame member parallel to the rack and side parts connected thereto in a U-shape and extending transversely to the rack axis in a common plane, tie rods arranged on the side parts, offset from the rack axis and guides which are arranged on the bearing housing at its ends adjacent to the side parts and are designed as a rotation lock against rotation of the rack about its axis relative to the bearing housing.

It is therefore the object of the invention to provide a steering gear for a steer-by-wire steering system of a motor vehicle, which enables an anti-twisting device and torque support of the steering rod that is optimized for steer-by-wire steering systems.

This object is solved by the subject matter of patent claim 1.

disclosure of the invention

The present invention provides a steering gear for a steer-by-wire steering system of a motor vehicle. The steering gear comprises a housing and a steering rod which is arranged at least in sections in a housing interior, which is mounted via a conversion gear and can be connected to a tie rod at each of the axial end sections.

Furthermore, the steering gear comprises a drive unit having an electric machine and the conversion gear coupled to the electric machine, which drive unit is designed to move the steering rod axially.

In addition, the steering gear comprises at least one anti-twisting device connected to the handlebar in a rotationally fixed manner, and a guide rod arranged parallel to the handlebar in the housing, wherein the anti-twisting device is connected to the handlebar at a first end section and rests against the guide rod at a second end section arranged opposite the first end section in such a way that a torque applied to the handlebar can be supported by the anti-twisting device on the guide rod.

One idea of the present invention is to enable an effective rotation limitation of the handlebar by providing a guide rod arranged parallel to the handlebar in the housing, to which the anti-twist device can be attached. Furthermore, significantly more torque can be supported via the long lever arm of the anti-twist device.

The handlebar now only has a spindle area and a cylindrical shaft. This simplifies production and increases the precision of the components. Because the handlebar no longer has any local cross-sectional cuts, the strength of the handlebar is increased. This means that the handlebar can now be made as a tube or the diameter can be reduced.

Advantageous embodiments and further developments emerge from the subclaims and from the description with reference to the figures. According to a preferred development, it is provided that the anti-twisting device has a force-fitting, form-fitting or material-fitting connection with the handlebar at the first end section and engages around the guide rod at the second end section.

The connection of the rotating rod to the guide rod by means of the twisted lock thus advantageously enables an effective rotation limitation of the handlebar due to the fact that the anti-rotation device moves with the handlebar as it moves and thus forms a lever arm which rests on the guide rod and thus prevents the handlebar from rotating.

According to a further preferred development, it is provided that the anti-twisting device at the first end section has a, in particular cylindrical, press fit with the handlebar, wherein the handlebar and the anti-twisting device are each made of steel.

The pressing force of the press fit on the handlebar is higher than the torque supported by the anti-twisting device on the guide rod.

According to a further preferred development, it is provided that the anti-twisting device is designed to provide a torque support of the torque applied to the handlebar by means of a first lever arm formed between the handlebar and the guide rod by the anti-twisting device.

The parallel main guide and torque support allow the axial installation space of the steering system to be significantly reduced. This is reflected in the fact that significantly more axial stroke can be achieved with the same steering rod length.

In previous applications in steering systems, the ball screw drive is subjected to transverse forces due to its design. However, transverse forces are unfavourable for a ball screw drive and can lead to premature damage. This can lead to undesirable effects such as discontinuities or snagging. The new additional main guide thus provides better protection for the KGT against transverse forces.

According to a further preferred development, it is provided that the anti-twisting device at the second end section has a rolling or sliding friction element, in particular a linear ball bearing, which can be displaced along the guide rod during a stroke of the handlebar connected to the anti-twisting device.

A cylindrical design of the main guide or guide rod and the torque support makes it easy to use a linear roller guide. This can be done using simple and proven standard parts. The play and friction remain almost constant over the service life. This is important for control and NVH behavior. Alternatively, the main guide can also be designed with inexpensive sliding friction elements.

By reducing friction (rolling friction instead of sliding friction), the steering force can now be detected much more accurately. This has a positive effect on the control system. The steering feel and the centering are improved. In particular, the transition from static friction to sliding friction (stick-slip effect) is significantly reduced.

According to a further preferred development, it is provided that the guide rod and the anti-twisting device that can be guided along the guide rod by the rolling or sliding friction element provide a bearing for the handlebar. The provision of the bearing by the rolling or sliding friction element that can be guided along the guide rod thus advantageously enables a reduction in other bearings for the handlebar.

According to a further preferred development, it is provided that the anti-twisting device has a rolling or sliding friction element, in particular a linear ball bearing, which is fixed to the housing at the second end section, wherein a first anti-twisting device and a second anti-twisting device are firmly connected to the guide rod at a fourth axial end cut of the guide rod.

This alternative design of the anti-twist device has increased stability and thus improved mounting of the handlebar due to the provision of two anti-twist devices.

According to a further preferred development, it is provided that when the handlebar is lifted, the guide rod which is firmly connected to the first anti-twist device and the second anti-twist device can be guided along the rolling or sliding friction element.

Due to the two anti-twisting devices that are attached to the guide rod at each axial end section, the guide rod can be designed with a lower rigidity or material thickness, since the torque support is transmitted to the guide rod via two different force introduction points.

According to a further preferred development, it is provided that a second lever arm formed between the anti-twisting device and the axial end sections of the handlebar is constant when the handlebar is subjected to a radial force, in particular via at least one of the tie rods, regardless of the stroke of the handlebar. The distance from the inner joint of the tie rod to the handlebar bearing point thus advantageously remains constant during a lifting movement.

According to a further preferred development, it is provided that the steering rod is mounted adjacent to the first axial end section by a first support bearing arranged in the housing of the steering gear and adjacent to the second axial end section by a second support bearing arranged in the housing of the steering gear.

The first and second support bearings thus advantageously enable additional moment support of the radial force applied to the handlebar due to, for example, road surface influences. According to a further preferred development, the support bearings have a radial play when the steering force applied to the handlebar by the drive unit via the conversion gear, in particular a ball screw drive, is up to 1/10 of a maximum support force that can be applied. The support bearings are therefore only used when the steering force applied to the handlebar exceeds 1/10 of the maximum support force that can be applied.

According to a further preferred development, it is provided that the support bearings provide an overload protection, in particular in the case of a transverse force acting on the handlebar, of the bearing of the handlebar provided by the guide rod and the anti-twisting device that can be guided on the guide rod by the rolling or sliding friction element. The overload protection thus advantageously supports transverse forces applied to the handlebar in such a way that overloading of the handlebar is prevented.

The described designs and further training courses can be combined as desired.

Further possible embodiments, further developments and implementations of the invention also include combinations of features of the invention described above or below with respect to the embodiments that are not explicitly mentioned.

Short description of the drawings

The accompanying drawings are intended to provide a further understanding of embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain principles and concepts of the invention.

Other embodiments and many of the above advantages will become apparent upon consideration of the drawings. The illustrated elements of the drawings are not necessarily shown to scale with respect to one another. They show:

Fig. 1 is a schematic representation of a steering gear for a steer-by-wire steering system of a motor vehicle according to a first embodiment of the invention; and

Fig. 2 is a schematic representation of the steering gear for the steer-by-wire steering system of the motor vehicle according to a second embodiment of the invention.

In the figures of the drawings, identical reference symbols designate identical or functionally identical elements, parts or components, unless otherwise stated.

Fig. 1 shows a steering gear 1 for a steer-by-wire steering system of a motor vehicle.

The steering gear 1 comprises a housing 10 and a steering rod 12 which is arranged at least in sections in a housing interior, which is mounted via a conversion gear 14 and can be connected at axial end sections to a respective tie rod 16a, 16b.

Furthermore, the steering gear 1 comprises a drive unit 20 having an electric machine (not shown in Fig. 1) and the conversion gear 14 coupled to the electric machine, which is designed to move the steering rod 12 axially.

In addition, the steering gear 1 comprises at least one anti-twisting device 22 connected to the handlebar 12 in a rotationally fixed manner, and a guide rod 24 arranged parallel to the handlebar 12 in the housing 10, wherein the anti-twisting device 22 is connected to the handlebar 12 at a first end section 22a and rests against the guide rod 24 at a second end section 22b arranged opposite the first end section 22a in such a way that a torque applied to the handlebar 12 can be supported by the anti-twisting device 22 on the guide rod 24. The anti-twisting device 22 has a force-fitting, form-fitting or material-fitting connection with the handlebar 12 at the first end section 22a, and the anti-twisting device 22 engages around the guide rod 24 at the second end section 22b.

Furthermore, the anti-twisting device 22 has a, in particular cylindrical, press fit with the handlebar 12 at the first end section 22a. The handlebar 12 and the anti-twisting device 22 are each made of steel.

The anti-twisting device 22 is designed to provide a torque support of the torque applied to the handlebar 12 by means of a first lever arm 26 formed between the handlebar 12 and the guide rod 24 by the anti-twisting device 22.

Furthermore, the anti-twisting device 22 has a rolling or sliding friction element 28, in particular a linear ball bearing, on the second end section 22b, which can be displaced along the guide rod 24 during a stroke of the handlebar 12 connected to the anti-twisting device 22.

The guide rod 24 and the anti-twisting device 22, which can be guided on the guide rod 24 by the rolling or sliding friction element 28, provide a bearing for the steering rod 12.

Fig. 2 shows a schematic representation of the steering gear for the steer-by-wire steering system of the motor vehicle according to a second embodiment of the invention.

The anti-twisting device 22 has a rolling or sliding friction element 28', in particular a linear ball bearing, which is fixedly connected to the housing at the second end section 22b.

Furthermore, a first anti-twisting device 30a is firmly connected to the guide rod 24 at a third axial end section 24a of the guide rod 24, and a second anti-twisting device 30b is firmly connected to the guide rod 24 at a fourth axial end section 24b of the guide rod 24. When the handlebar 12 is lifted, the guide rod 24, which is firmly connected to the first anti-twisting device 22 and the second anti-twisting device 22, can be guided along the rolling or sliding friction element 28.

The features of the invention described below are applicable to both the first embodiment and the second embodiment.

A second lever arm 32 formed between the anti-twisting device 22 and the axial end sections of the handlebar 12 when the handlebar 12 is subjected to a radial force, in particular via at least one of the tie rods 16a, 16b, is constant regardless of the stroke of the handlebar 12.

The steering rod 12 is supported adjacent to the first axial end portion by a first support bearing arranged in the housing 10 of the steering gear 1 and adjacent to the second axial end portion by a second support bearing arranged in the housing 10 of the steering gear 1.

The support bearings 34a, 34b have a radial play of up to 1/10 of a maximum support force that can be applied when a steering force is applied to the steering rod 12 by the drive unit 20 via the conversion gear 14, in particular a ball screw drive.

Furthermore, the support bearings 34a, 34b provide overload protection, in particular in the event of a transverse force acting on the handlebar 12, for the bearing of the handlebar 12 provided by the guide rod 24 and the anti-twisting device 22 that can be guided on the guide rod 24 by the rolling or sliding friction element 28.

Claims

claims 1. Steering gear (1) for a steer-by-wire steering system of a motor vehicle, with: a housing (10) and a steering rod (12) which is arranged at least in sections in a housing interior and which is mounted via a conversion gear (14) and can be connected to a tie rod (16a, 16b) at axial end sections (12a, 12b); a drive unit (20) having an electric machine and the conversion gear (14) coupled to the electric machine, which drive unit is designed to move the steering rod (12) axially; at least one anti-twisting device (22) connected to the steering rod (12) in a rotationally fixed manner; and a guide rod (24) arranged parallel to the handlebar (12) in the housing (10), wherein the anti-twist device (22) is connected to the handlebar (12) at a first end section (22a) and rests against the guide rod (24) at a second end section (22b) arranged opposite the first end section (22a) in such a way that a torque applied to the handlebar (12) can be supported by the anti-twist device (22) on the guide rod (24). 2. Steering gear according to claim 1, wherein the anti-twisting device (22) has a force-fitting, form-fitting or material-fitting connection with the steering rod (12) at the first end section (22a) and engages around the guide rod (24) at the second end section (22b). 3. Steering gear according to claim 2, wherein the anti-twisting device (22) has a, in particular cylindrical, press fit with the handlebar (12) at the first end portion (22a), wherein the handlebar (12) and the anti-twisting device (22) are each made of steel. 4. Steering gear according to one of the preceding claims, wherein the anti-twisting device (22) is designed to provide a torque support of the torque applied to the handlebar (12) by a first lever arm (26) formed between the handlebar (12) and the guide rod (24) by the anti-twisting device (22). 5. Steering gear according to one of the preceding claims, wherein the anti-twisting device (22) has a rolling or sliding friction element (28), in particular a linear ball bearing, at the second end section (22b), which can be displaced along the guide rod (24) during a stroke of the steering rod (12) connected to the anti-twisting device (22). 6. Steering gear according to claim 5, wherein the guide rod (24) and the anti-twisting device (22) which can be guided on the guide rod (24) by the rolling or sliding friction element (28) provide a bearing for the steering rod (12). 7. Steering gear according to one of claims 1 to 4, wherein the anti-twisting device (22) has a rolling or sliding friction element (28'), in particular a linear ball bearing, which is connected to the housing at the second end section (22b), wherein a first anti-twisting device (30a) is connected to a third axial end section (24a) of the guide rod (24) and a second anti-twisting device (30b) is connected to the guide rod (24) at a fourth axial end section (24b) of the guide rod (24). 8. Steering gear according to claim 7, wherein during a stroke of the steering rod (12), the guide rod (24) firmly connected to the first anti-twist device (22) and the second anti-twist device (22) can be guided along the rolling or sliding friction element (28). 9. Steering gear according to one of the preceding claims, wherein a device between the anti-twist device (22) and the axial end sections of the steering rod (12) is provided with a The second lever arm (32) is designed for radial force and is constant regardless of the stroke of the handlebar (12). 10. Steering gear according to one of the preceding claims, wherein the steering rod (12) is mounted adjacent to the first axial end portion (12a) by a first support bearing (34a) arranged in the housing (10) of the steering gear (1) and adjacent to the second axial end portion (12b) by a second support bearing (34b) arranged in the housing (10) of the steering gear (1). 11. Steering gear according to claim 10, wherein the support bearings (34a, 34b) have a radial play of up to 1/10 of a maximum applicable support force when a steering force is applied to the steering rod (12) by the drive unit (20) via the conversion gear (14), in particular a ball screw drive. 12. Steering gear according to claim 10 or 11, wherein the support bearings (34a, 34b) provide an overload protection, in particular in the case of a transverse force acting on the steering rod (12), the bearing of the steering rod provided by the guide rod (24) and the anti-twisting device (22) which can be guided on the guide rod (24) by the rolling or sliding friction element (28). (12) .