Actuator of a steer-by-wire steering system of a motor vehicle and method for improving the smooth running of an actuator of a steer-by-wire steering system

Abstract

Actuator of a steer-by-wire steering system of a motor vehicle, comprising a housing (42), a spindle (44, 444, 544) with an external thread (43a) and a rotatably and stationary mounted spindle nut (43, 443, 543) with an internal thread (43a, 443a), which within the housing (42) form a spindle drive (41, 441, 541) with a drive thread for axially displacing the spindle (44, 444, 544) for steering the wheels (5, 6) of an axle, wherein the spindle (44, 444, 544) is connected at at least one end (44l, 44r) to a bearing sleeve (50, 60, 450, 460, 550, 560) in a rotationally fixed manner, and the spindle (44, 444, 544) is slidably mounted relative to the housing (42) by means of the bearing sleeve (50, 60, 450, 460, 550, 560), wherein the bearing sleeve (50, 60, 450, 460, 550, 560) is coupled at least indirectly to at least one wheel carrier (7). The invention is characterized in that an axially compressible element (70, 465, 470, 560, 560) is arranged between the bearing sleeve (50, 60, 450, 460, 550, 560) and the spindle nut (44, 444, 544), which surrounds the spindle (44, 444, 544) and is arranged to slide at least partially relative to the spindle, so that during large to maximum possible displacements of the spindle (44, 444, 544), the compressible element (70, 465, 470, 565, 570) comes into contact with the spindle (43) and the bearing sleeve (50), so that the compressible element (70, 465, 470, 565, 570) is compressed and thus the force level in the threaded rod is reduced. It can be changed.

Description

[0001] The invention relates to an actuator of a steer-by-wire steering device of a motor vehicle and to a method for assembling an actuator according to the preambles of the independent claims.

[0002] DE 10 2014 206 934 A1 discloses an actuator with a stationary spindle nut and a spindle that can be axially displaced relative to the spindle. At least one end of the spindle, which is used as a steering rod in an actuator in a steer-by-wire steering system, is connected to a wheel carrier by means of a bearing sleeve and a joint. The linear displacement of the spindle can thus change the steering angle of a wheel rotatably mounted on the wheel carrier. The actuator of the steer-by-wire steering system, which can be actuated by a steering handle such as a steering wheel or operates independently of it, is controlled via signal paths, i.e., without mechanical coupling. Such a steering system must overcome the frictional resistance of the wheels relative to the road surface during a steering maneuver.Particularly at very low speeds when maneuvering or parking until the vehicle comes to a standstill, comparatively high steering forces are required, which place a significant load on the actuator. Alternating static and sliding friction can cause the actuator's spindle drive to experience resonance vibrations on the one hand, and can also reach high temperatures on the other, which can ultimately lead to damage to the actuator and thus to the steer-by-wire steering system. This occurs particularly at large wheel steering angles in the range of the actuator's maximum travel range, i.e., at maximum displacement.

[0003] The chassis of a motor vehicle is subject to high lateral forces, which the aforementioned actuator must be able to support in order for the steering to guide the wheel. These high forces cause high friction in the moving thread of the actuator's spindle drive. There is high surface pressure between the thread flanks of the spindle and spindle nut, and even when optimized lubricants are used, high friction still occurs. The static friction and sliding friction that occur between the thread partners at the contact surfaces of the adjacent thread flanks can lead to a so-called stick-slip effect. This is the alternating sticking and sliding of the thread flanks, which can lead to fluctuating torques between the spindle nut and the spindle. This can, for example, cause the spindle to vibrate torsional vibrations.Continuous or temporary excitation over a minimum period of time can cause a resonance frequency of the spindle or other components in the actuator to be reached. Thus, under unfavorable conditions, the excitation can even emit airborne sound to such an extent that it can be acoustically perceived.

[0004] In the aforementioned spindle drive, the stick-slip effect causes a torsional vibration, also known as a torsional vibration. In contrast to translational vibration, torsional vibration occurs around the rotational degree of freedom of a system. In both cases, it is a mechanical vibration.

[0005] It is an object of the invention to further develop an actuator of a steer-by-wire steering system of a motor vehicle such that the actuator is acoustically inconspicuous, so that resonance vibrations are minimized as far as possible and the service life of the steer-by-wire steering system is not impaired.

[0006] The problem is solved by an actuator of a steer-by-wire steering system of a motor vehicle according to claim 1. Preferred developments are specified in the subclaims.

[0007] An actuator for a steer-by-wire steering system of a motor vehicle comprises a housing in which a spindle and a rotatably and stationary spindle nut are mounted. Within the housing, the spindle and spindle nut form a spindle drive for axially displacing the spindle relative to the spindle nut or the housing. For this purpose, the spindle has an external thread which engages with the internal thread of the spindle nut and which forms a movement thread. If the spindle nut is rotationally driven, e.g., by an electric motor, preferably indirectly by a gear, preferably a slip-free belt drive, the movement thread causes the spindle to be displaced axially along its longitudinal axis relative to the spindle nut or the housing. At least one end of the spindle is connected, preferably screwed, to a bearing sleeve in a rotationally fixed manner.The bearing sleeve is radially supported relative to the housing and mounted for axial displacement, preferably by means of a bearing bush that is preferably pressed into the housing, such that the spindle is radially guided relative to the housing by means of the bearing sleeve and mounted for axial displacement. The bearing sleeve is at least indirectly coupled to at least one wheel carrier. For this purpose, the end of the bearing sleeve is preferably connected to a joint, preferably a ball or ball sleeve joint. The joint is coupled either directly to a wheel carrier or indirectly to the wheel carrier with the interposition of tie rods and possibly further joints (steering linkage). By axially displacing the spindle along its longitudinal axis, the wheel steering angle of a wheel rotatably arranged on a wheel carrier, which is connected to at least one end of the spindle, can be changed.The advantage of using bearing sleeves is that identical spindles can be used for different axial extensions of the steering actuator due to different vehicle track widths. To adapt the actuator or spindle drive to different vehicle track widths, at least one bearing sleeve is used at the end(s) of the spindle. This design, in keeping with the principle of commonality, allows for cost-effective mass production of the complex spindle, thus resulting in a cost-effective spindle drive or actuator.

[0008] The invention is characterized in that an axially compressible, preferably compressible, element is arranged between the bearing sleeve and the spindle nut, which element engages around the spindle and is arranged at least partially so as to slide relative to the spindle. For large to maximum wheel steering angles, it is necessary for the spindle to be displaced very far, up to the maximum possible. In order to achieve a large to maximum wheel steering angle when maneuvering a motor vehicle (e.g. when parking) at a very low speed of less than or equal to 10 km / h, the spindle must be displaced far, up to the maximum possible, relative to the spindle nut. The larger the wheel steering angle to be set, the closer the bearing sleeve, with its end facing the spindle nut, approaches the spindle nut. As the displacement of the spindle increases, the surface pressure of the thread flanks in the moving thread increases. This is due, among other things, toThis is due to the fact that at the low speeds mentioned, there is a high level of static friction between the tires and the road surface. Furthermore, the bearings and steering linkage between the actuator and the wheel carrier are increasingly preloaded as the wheel steering angle increases. In other words, the force level in the spindle drive or motion thread increases the larger the wheel steering angle and the lower the speed. This leads to an intensification of the so-called stick-slip effect. Due to the alternating static and sliding friction between the flanks of the external thread of the spindle and the internal thread of the spindle nut, torsional vibrations of the spindle occur, which are undesirable.

[0009] It has been shown that when using an axially compressible, preferably sleeve-like, element, when this element comes into contact at least indirectly between the spindle nut and the bearing sleeve during large to maximum possible displacements of the spindle, the element is compressed axially, i.e. in the axial direction, between the aforementioned components, so that the force level in the movement thread can be changed. This reduces or minimizes torsional excitation. The compressible element is designed with regard to its axial extent such that the compression increases continuously from the initial contact between the spindle nut and the bearing sleeve up to a maximum displacement of the spindle. The maximum displacement corresponds to a maximum wheel angle - at the latter, maximum compression occurs. This results in an increase in compression and thus a change in the force level in the movement thread depending on the wheel steering angle.In addition to changing the force level, it has surprisingly been shown that the compressible element also has a damping effect. In other words, the vibration-damping effect also increases with increasing compression. In other words, the tendency to vibrate is reduced and any vibrations are dampened.

[0010] For the large wheel steering angles considered here, 75 to 95% of the maximum displacement of the steering rod, or in this case, the spindle in the spindle drive, can be assumed. The maximum displacement of the spindle or steering rod results in the setting of a maximum wheel steering angle.

[0011] The approach presented here is based on the realization that in certain situations increased force is required for steering or, in other words, for turning the respective wheel to a desired wheel steering angle. The situation considered here assumes a very low speed of the vehicle from a standstill to parking and / or maneuvering. At a complete standstill, the speed is 0 km / h. When parking and / or maneuvering, a speed of less than or equal to approximately 1 km / h is assumed. In a speed range from 0 to approximately 1 km / h, particularly high forces are required to turn the desired wheel steering angle. The lower the speed, the greater the expected steering forces that must be managed by the steer-by-wire steering actuator.This is because the entire weight of the vehicle is exerted on the tires mounted on the wheels. The contact between the tire and the road surface is determined by the tire contact patch. The size of a tire's contact patch depends primarily on the wheel load and tire pressure, because the internal pressure of the tire bears the majority of the wheel load. But tire width, tire diameter and sidewall stiffness also play a role. When the wheel is not rotating, more force is required to steer, i.e. to turn the wheel around its vertical axis, than when the wheel is rolling due to the vehicle's movement. This is because the friction between the tire and the road surface must be overcome when the tire is steered. As the rolling motion increases, less force is required to steer.It is clear that, in addition to the vehicle's mass, the ambient temperature and tire temperature also have an influence, as they directly affect the friction between the tire and the road surface. The following additional parameters are not exhaustive: tire compound, tire type, tire friction coefficient, road surface, and road surface conditions (dry, wet, slippery, etc.).

[0012] The tire of a wheel is usually made of rubber – an elastic material. When a force is applied to the wheel from the actuator of a steer-by-wire steering system, a preload is created due to the static or sliding friction between the tire and the road surface. The tire is essentially pulled up against the road surface and thus preloaded. Further preload is created between the actuator and the wheel carrier by bearings inserted between them, as well as possibly by links, such as a steering linkage, depending on the chassis design.

[0013] If, in the aforementioned low speed range, the steer-by-wire steering system steers from a large to the maximum possible wheel steering angle or vice versa, the preloads are initially reduced briefly and then preloads arise again. This preload increases the lower the vehicle speed or when it is reduced from rolling to a standstill. When parking and / or maneuvering, this is more or less constantly changing. When steering from the previously set to a larger wheel steering angle or vice versa, the direction of force in the steer-by-wire steering actuator changes. This leads to a load change within a gearbox or spindle drive of the actuator, which in turn leads to a changed stick-slip behavior. This can cause vibrations and high thermal loads within the actuator or its motion thread.This behavior needs to be reduced or minimized.

[0014] Large wheel steering angles here refer to wheel steering angles that range from two-thirds of the maximum possible wheel steering angle up to the maximum design-specific wheel steering angle of the respective axle. When maneuvering or parking, the wheel steering angles frequently change. Utilizing large, preferably the largest possible, wheel steering angles makes it easier to enter a parking space, for example, or to maneuver with a trailer. It is particularly advantageous if the rear axle of the vehicle is steerable in addition to the front axle.

[0015] The term stick-slip effect is derived from the two English words "stick" (stick) and "slip." In physics and engineering, the stick-slip effect describes a generally undesirable, jerky sliding (stationary-sliding-stationary-sliding) of solid bodies moving against each other. In the case of a spindle, a torsional vibration is caused by the spindle nut, although the spindle itself does not rotate.

[0016] To change the spindle's vibration behavior, it could be manufactured with a larger mass, e.g., with a larger diameter. While this would change its resonant frequency, it would require more material, increasing its weight, and requiring additional machining, such as machining, during production, which would make the spindle more expensive. Increasing the spindle's diameter would also require adjusting the dimensions of the spindle bearings relative to the housing, as well as the spindle nut. Furthermore, problems could arise during spindle assembly.

[0017] Advantageously, the invention can cost-effectively change the force level and thus the vibration behavior by adding the compressible element without otherwise changing the existing actuator of a steer-by-wire steering device.

[0018] Preferably, the compressible element is connected at a first end at least indirectly, preferably at the front, to the spindle nut or the bearing sleeve, preferably in a form-fitting and / or force-fitting manner, e.g. by means of a screw connection, preferably by means of a fine thread, and / or in a material-fitting manner, preferably by means of gluing.

[0019] In a preferred embodiment, the compressible element is connected to the spindle nut or bearing sleeve at its first end via a plain bearing, preferably in the form of a radial bearing. This prevents the spindle nut from becoming jammed, thus preventing the spindle nut from jamming directly with the compressible element or indirectly with the bearing sleeve as soon as the compressible element comes into contact between the spindle nut and the bearing sleeve.

[0020] Preferably, the compressible element, with its second end facing away from the first end, is slidably mounted on the spindle by means of a plain bearing, preferably an axial / radial bearing. This also counteracts any jamming and simultaneously ensures a simple radial guidance of the compressible element, allowing it to slide concentrically with the spindle.

[0021] In a further preferred embodiment, the compressible element is made of at least one elastic material, preferably an elastomer, most preferably a microcellular or compact polyurethane elastomer. Due to its amplitude-selective damping, this polyurethane elastomer offers good vibration reduction at small amplitudes and high frequencies. The microcellular and compact polyurethane elastomers are capable of absorbing very large amounts of kinetic energy. Due to their high volume compressibility, the compressible element can be designed to reduce installation space and component weight by up to 30%. The compressible element can therefore be advantageously integrated into the limited space available in the actuator without modification.

[0022] The compressible element preferably has the shape of a hollow cylinder or a truncated cone. The hollow cylinder can have a very small height and thus the shape of a disc (circular disc with a central hole). When designed as a truncated cone, the compressible element can be given a desired spring characteristic due to the changing diameter along its axial extent. This can be adapted to the steering ratio.

[0023] Preferably, the axial / radial bearing connected to the second end of the compressible element is in the form of a sliding disk or a sliding bush, preferably made of PTFE or of a metal body or plastic body coated with PTFE.

[0024] Further preferably, the spindle nut is additionally guided radially relative to the spindle by means of the at least one axial / radial bearing. This can achieve a concentric rotational behavior of the spindle nut relative to the spindle, which can contribute to increased smoothness.

[0025] In a further embodiment, the axial / radial bearing has, at least at one end, preferably a radially inwardly projecting sealing lip, so that when connected, preferably at the end face, to the spindle nut, a seal is created against the spindle, so that lubricant for the moving thread is kept within the boundaries of the spindle nut. It is essential for the service life of the spindle drive that the lubricant introduced into the spindle drive during assembly, which is intended for the service life of the spindle drive or actuator, is also available in the moving thread within the axial extent of the spindle nut. A seal that would otherwise be additionally inserted on the end face of the spindle nut can thus be omitted.

[0026] According to a further aspect of the invention, a method for improving the smoothness of operation in an actuator of a steer-by-wire steering system, as described above, is provided. A compressible element is selected at least as a function of the vibration behavior of at least the spindle and the stick-slip behavior previously determined for the spindle used in the motion thread of the spindle drive, taking into account the expected longitudinal and / or transverse forces acting on the spindle. When selecting the compressible element, the available installation space is taken into account, in particular with regard to its radial extent. With regard to the axial extent of the compressible element, the transmission ratio of the steer-by-wire steering system is preferably taken into account. As described above, the effect of the compressible element only begins when it comes into contact between the spindle nut and the bearing sleeve.The effect of minimizing torsional vibrations should preferably occur at large to maximum wheel steering angles. For these wheel steering angles, a correspondingly large displacement of the spindle is required. With a linear transmission, the axial extension or length of the compressible element is designed so that it only comes into contact between the spindle nut and the bearing sleeve when the displacement falls within the aforementioned range (large wheel steering angles 75 to 95% up to the maximum wheel steering angle).

[0027] A steer-by-wire steering system is a steering device that is decoupled from the mechanical steering system with a steering handle, such as a steering wheel. The driver's steering movement via the steering handle is not transmitted to the wheel carriers or wheels purely mechanically, for example, via a linkage. Rather, a wheel steering angle is calculated for each wheel on an axle, e.g., in a control unit, which sends control signals to the actuator(s) of the steer-by-wire steering system and ultimately causes the wheel steering angle to change.

[0028] The invention is described below using preferred embodiments with reference to the drawing. In the drawing: Fig. 1 a rear wheel axle with an actuator of a steer-by-wire steering system according to the state of the art, Fig. 2 and Fig. 3 schematic detailed views according to the invention Fig. 4 and Fig. 5 schematic detailed views of various embodiments according to the invention

[0029] In the schematic representation according to Fig. 1 shows a vehicle axle 1 in plan view, represented here as a rear axle with a subframe 2, which is attached to a vehicle body (not shown) or forms this and is connected to the body of a motor vehicle. However, the invention is not limited to a rear axle. The wheels 5 and 6 are articulated to the subframe 2 by means of control arms 3, 4 as part of a wheel suspension. An actuator 10 of a steer-by-wire steering system 12 is arranged on the subframe 2. The actuator 10 is attached to the subframe 2 by its housing 22. In the present embodiment, the actuator 10 has a continuous steering rod 24 designed as a spindle, which is guided through the housing 22 of the actuator 10. The drive motor in the form of an electric motor 29 is arranged axially parallel to the steering rod 24, but can also be designed in a different way, e.g., as a hollow shaft motor.At the ends of the steering rod 24, tie rods 23, 25 are articulated via joints 27, 28, which are each articulated to a wheel carrier 7 of the wheels 5 and 6 at the end facing away from the actuator 10 (only the left wheel carrier is shown).

[0030] The axial displacement of the steering rod 24 in the form of a spindle 44 is achieved by a rotation / translation converter in the form of a spindle drive 41 with a spindle nut 43 and the spindle 44, which form a movement thread. This is in Fig. 2 and Fig. 3, which shows the spindle drive 41 of the actuator 10 of the steer-by-wire steering 12 from Fig. 1 in detail. When the electric motor 29 rotates (for clarity only in Fig. 1), the spindle nut 43, which is fixedly mounted in the housing 22, 42 and rotatably mounted, is set in rotation about its longitudinal axis s by means of a drive belt (not shown) without slippage. The spindle nut 43 has an internal thread 43a, which engages with the external thread 44a of the spindle 44 (corresponds to the steering rod 24) and forms the movement thread. Depending on the direction of rotation of the spindle nut 43, a linear displacement of the spindle 44, which is secured against rotation about the longitudinal axis s, takes place in one direction or the other along the longitudinal axis s, depending on the direction of rotation of the electric motor 29. The longitudinal axes of the spindle nut 43 and spindle 44 coincide here. The spindle nut 43 is fixed by means of a rolling bearing 45 and is rotatable relative to the Fig. 2 and 3 only schematically indicated housing 42. The spindle 44 is axially displaceable by means of the bearing sleeves 50, 60, which also ensure the radial guidance of the spindle. For this purpose, the spindle 44 is connected at its right end 44r to the left end 50l of a bearing sleeve 50 in a rotationally fixed manner to the spindle 44. The left end 44l of the spindle 44 is also rotationally fixedly connected to the right end 60r of the bearing sleeve 60. The bearing sleeves 50, 60 are each radially supported by means of plain bearings as bearing bushes 51, 61 in the housing 42 and are mounted in an axially sliding manner in the housing 42, which results in the aforementioned mounting of the spindle 44. At the left end 60l, the bearing sleeve 60 is fixedly connected to a joint fork 62. By means of this joint fork 62, for example, an articulated connection to the wheel carrier 7 is possible. Alternatively, a tie rod 23, 24 (see Fig. 1) be connected in an articulated manner. A joint fork 52 or a sleeve joint or ball joint is also arranged here on the bearing sleeve 50 and coupled to it on another wheel carrier, so that a double-acting actuator can steer both the left and right wheels of an axle simultaneously.

[0031] It is from the Fig. 2 and Fig. 3 shows that upon axial displacement, i.e., displacement of the steering rod 24 or spindle 44 along the longitudinal axis s in one direction or the other, a change in the wheel steering angle 8, 9 of the wheels 5, 6 occurs because the tie rods 23, 25 represent a positive connection between the wheel 5, 6 or wheel carrier 7 and the actuator 10. To steer the wheels 5, 6, they are pivoted about their vertical axis via the wheel carrier 7 to the wheel suspension 3, 4. In other words, the actuator 10 is part of the steer-by-wire steering system 12, which enables its operation.

[0032] In Fig. 2 shows a neutral position of the spindle 43 and thus of the actuator 10. The internal thread 43a of the spindle nut 43 engages centrally in the external thread 44a of the spindle 44 when viewed in the axial direction. This neutral position corresponds to a wheel steering angle of 0°, which corresponds to straight-ahead travel. This is shown in Fig. 1 is shown analogously: the wheels 5, 6 have a wheel steering angle of 0°. Therefore, straight-ahead travel G is shown with an arrow in the direction of travel. For the neutral position, this results in a distance d1 between the right-hand end face 60rs of the bearing sleeve 60 and the opposite left-hand end face 43ls of the spindle nut 43. The same distance d1 also exists between the end face 43rs of the spindle nut 43 and the end face 50ls of the bearing sleeve 50. The distance on the right decreases when the spindle 44 is moved to the left. In order to achieve a large to maximum wheel steering angle 8, 9 when maneuvering (e.g. when parking) at a very low speed of less than or equal to 10 km / h, the spindle 44 must be moved far to the left to the maximum. The bearing sleeve 50 with its left end face 50ls approaches the spindle nut 43 or its right end face 43rs more and more, the larger the wheel steering angle 8, 9 to be set is. Fig. Figure 3 shows a state of maximum wheel steering angle, such that a minimum distance d2 has been established between the end faces 43rs of the spindle nut and the end face 50ls of the bearing sleeve 50. In this case, the compressible element 70 is maximally compressed.

[0033] The greater the displacement of the spindle 44 and the lower the vehicle speed or wheel speed, the greater the surface pressure of the thread flanks in the movement thread of the actuator 10. The reasons for this have already been explained above (see high friction of the tires against the road surface and increasing preload in the steering linkage or in bearings the greater the wheel steering angle to be set). Force is required to compress the compressible element 70. This changes the force level in the movement thread, which is also determined by the longitudinal and transverse forces F, Q acting on the spindle 44, which on the one hand changes the surface pressure on the thread flanks between the internal thread 43a of the spindle nut 43 and the external thread 44a of the spindle 44.In addition, the compressible element 70 can achieve damping from the moment it contacts the spindle nut 43 and the bearing sleeve 50, 60, which can reduce any incipient or existing vibration of the spindle 44. In the embodiment shown, an axial bearing in the form of a sliding disk 71 is arranged between the right-hand end face 43rs and the left-hand end face 70ls of the compressible element 70. The sliding disk ensures that there is no jamming between the compressible element 70 and the spindle nut 43 when the element 70 comes into contact with the spindle nut 43 while it is rotating. This also makes it easy to continue turning or loosen the spindle nut 43 after it has come to a standstill, even with maximum compression of the element 70.

[0034] In the further description of the figures, the same components with the same functions as in the Fig. 2 and Fig. 3 in the Fig. 4 and Fig. 5 with reference numerals increased by 400 or 500.

[0035] In the Fig. 4 and Fig. 5 shows two further embodiments of spindle drives 441, 541, which can be used in a double-acting actuator 10 for simultaneously steering left and right wheels 5, 6. Both embodiments show compressible elements 465, 470, 565, 570 arranged on both sides of the spindle nut 443, 543. In both Fig. 4, Fig. 5 shows the neutral position with a wheel steering angle of 0° (my compression) corresponding to straight-ahead driving.

[0036] In the execution according to Fig. 4, hollow cylindrical recesses 443h1, 443h2 are provided in the spindle nut 443, which connect to the internal thread 443a. A sliding bearing 468, 478 is connected to the right end face 465rs and the left end face 470ls of the compressible elements 465, 470, which are connected to the end faces 465rs, 470ls as shown in Fig. 4 are firmly connected. The plain bearings 468, 478 enable the compressible elements 465, 470 to slide radially relative to the spindle 444 as well as relative to the spindle nut 443. Until the compressible elements 465, 470 come into contact with the spindle nut 443, they can slide axially on the spindle 444. The hollow cylindrical recesses 443h1, 443h2 are used to ensure that the plain bearings 468, 478 engage axially therein on the end face of the spindle nut 443. This provides radial support for the spindle nut 443 with its inner contour in the region of its end faces, so that the spindle nut 443 is guided concentrically around the spindle 444. This results in improved smoothness of the spindle drive 441 and a concentric position of the spindle nut 443 relative to the spindle 444.As the elements 465, 470 approach the spindle nut 443, the bearings 468, 478, designed as bearing bushes, increasingly penetrate the spindle nut 443. A further advantage is that the otherwise conventional radially inwardly extending seals, which keep a lubricant within the boundaries of the spindle nut 443 for the moving thread, can be eliminated. In the illustrated design, the plain bearings 468, 478 seal the spindle nut 443 against the spindle 444.

[0037] In the execution according to Fig. 4, the compressible elements 465, 470 are each formed as a hollow cylindrical truncated cone. This allows for a variable spring characteristic curve from the initial contact of the compressible elements 465, 470 with the spindle nut 443 or the bearing sleeves 450, 460 at large wheel steering angles to a maximum compression at a maximum wheel steering angle.

[0038] This allows the necessary compression or the desired degree of damping on the spindle drive to be set depending on the large to maximum wheel steering angle to be set.

[0039] Fig.5 shows a further embodiment of a spindle drive 541 with a spindle 544, which engages with the spindle nut 543, wherein the compressible elements 565, 570 are arranged on the end faces 560rs, 550ls of the bearing sleeves 550, 560 facing the spindle nut, and are preferably firmly connected thereto in a materially bonded manner, preferably by gluing. In order to counteract the previously mentioned problem of jamming of the end faces of the spindle nut 543 with the compressible elements 565, 570, axially acting bearings in the form of sliding disks 566, 571 are arranged in the direction of the spindle nut 543, preferably firmly connected, preferably glued, to the compressible elements 565, 570, preferably in a materially bonded manner. The aforementioned advantages can also be achieved with this embodiment. Reference symbol 1 vehicle axle 2 subframes 3, 4 handlebars 5, 6 wheels 7 wheel carriers 8, 9 Wheel steering angle 10, 100 actuator 12 Steer-by-wire steering 22 housings 23 Tie rod 24 Steering rod, spindle 25 Tie rod 27, 28 joint 29 Electric motor 41 spindle drive 42 housings 43 Spindle nut 43ls left front side 43rs right front side 43a Thread, internal thread spindle nut 44 spindle 44r right end of the spindle 44l left end of the spindle 44a thread, external thread spindle 45 rolling bearings 49 Electric motor 50 bearing sleeve 50l left end of the bearing sleeve 50ls left front side 51 bearing bush 52 articulated fork 60 bearing sleeve 60r right end of the bearing sleeve 60rs right front side 61 bearing bush 62 articulated fork 70 compressible element 70ls left front side 71 plain bearing, sliding disc 441 spindle drive 443 spindle nut 443a Thread, internal thread 443h1 hollow cylindrical recess 443h2 hollow cylindrical recess 444 spindle 450 bearing sleeve 451 bearing bush 452 articulated fork 460 bearing sleeve 461 bearing bush 462 articulated fork 465 compressible element 465rs front side 468 plain bearings, bearing bushes, axial / radial bearings 470 compressible element 470ls front side 478 plain bearings, bearing bushes, axial / radial bearings 541 spindle drive 543 spindle nut 544 spindle 550 bearing sleeve 550ls front side 551 bearing bush 552 articulated fork 560 bearing sleeve 560rs front side 561 bearing bush 562 articulated fork 565 compressible element 566 plain bearing, sliding disc 570 compressible element 571 plain bearing, sliding disc d1 distance d2 distance F Longitudinal force Q shear force G Straight ahead s longitudinal axis QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 206 934 A1

[0002]

Claims

[1] Actuator of a steer-by-wire steering system of a motor vehicle, comprising a housing (42), a spindle (44, 444, 544) with an external thread (43a) and a rotatably and stationary spindle nut (43, 443, 543) with an internal thread (43a, 443a), which form a spindle drive (41, 441, 541) with a movement thread for axially displacing the spindle (44, 444, 544) for steering the wheels (5, 6) of an axle, wherein the spindle (44, 444, 544) is connected with at least one end (44l, 44r) in a rotationally fixed manner to a bearing sleeve (50, 60, 450, 460, 550, 560), and the spindle (44, 444, 544) is mounted displaceably relative to the housing (42) by means of the bearing sleeve (50, 60, 450, 460, 550, 560), wherein the bearing sleeve (50, 60, 450, 460, 550, 560) is coupled at least indirectly to at least one wheel carrier (7), characterized bythat an axially compressible element (70, 465, 470, 565, 570) is arranged between the bearing sleeve (50, 60, 450, 460, 550, 560) and the spindle nut (44, 444, 544), which element encompasses the spindle (44, 444, 544) and is arranged at least partially sliding relative to the spindle, so that in the case of large to maximum possible displacements of the spindle (44, 444, 544), the compressible element (70, 465, 470, 565, 570) comes at least indirectly into contact with the spindle (43) and the bearing sleeve (50), so that the compressible element (70, 465, 470, 565, 570) is compressed and thus the force level in the movement thread can be changed is. [2] Actuator of a steer-by-wire steering system of a motor vehicle according to claim 1, characterized bythat the compressible element (70, 465, 470, 565, 570) is connected at a first end at least indirectly, preferably at the front, to the spindle nut (43, 443, 543) or the bearing sleeve (50, 60, 450, 460, 550, 560), preferably in a form-fitting and / or force-fitting and / or material-fitting manner. [3] Actuator of a steer-by-wire steering system of a motor vehicle according to claim 2, characterized by that the compressible element (70, 465, 470, 565, 570) is connected at its first end by means of a sliding bearing (71, 468, 478, 566, 571), preferably to the spindle nut (43, 443, 543) or bearing sleeve (50, 60, 450, 460, 550, 560). [4] Actuator of a steer-by-wire steering system of a motor vehicle according to one of the preceding claims, characterized by that the compressible element (70, 465, 470, 565, 570) is slidably mounted on the spindle (444, 444, 544) with its second end facing away from the first end by means of a plain bearing, preferably an axial / radial bearing (468, 471). [5] Actuator of a steer-by-wire steering system of a motor vehicle according to one of the preceding claims, characterized by that the compressible element (70, 465, 470, 565, 570) is formed from at least one elastic material, preferably an elastomer, most preferably a microcellular or compact polyurethane elastomer. [6] Actuator of a steer-by-wire steering system of a motor vehicle according to one of the preceding claims, characterized by that the compressible element (70, 465, 470, 565, 570) is preferably designed in the form of a hollow cylinder or a hollow cylindrical truncated cone. [7] Actuator of a steer-by-wire steering system of a motor vehicle according to one of the preceding claims, characterized bythat the sliding bearing connected to the second end of the compressible element (70, 465, 470, 565, 570) is in the form of a sliding disk (566, 571) or a sliding bushing (468, 478), preferably made of PTFE or of a metal body coated with PTFE. [8] Actuator of a steer-by-wire steering system of a motor vehicle according to claim 6, characterized by that the spindle nut (43, 443, 543) is guided radially relative to the spindle (44, 444, 544) by means of the at least one axial / radial bearing (468, 471). [9] Actuator of a steer-by-wire steering system of a motor vehicle according to claim 6 or 7, characterized bythat the at least one axial / radial bearing (468, 471) has at least one of its ends, preferably a radially inwardly projecting sealing lip, so that when connected, preferably at the end, to the spindle nut (43, 443, 543), a seal is formed with respect to the spindle (44, 444, 544), so that lubricant for the movement thread is kept within the limits of the spindle nut (43, 443, 543). [10] Method for improving the smooth running of an actuator (10) of a steer-by-wire steering system (12) according to one of the preceding claims, characterized bythat a compressible element (70, 465, 470, 565, 570) is selected at least as a function of the vibration behavior of at least the spindle (44, 444, 544) and as a function of the stick-slip behavior previously determined for the spindle (44, 444, 544) used in the movement thread of the spindle drive (41, 441, 541), taking into account the expected longitudinal and / or transverse forces (F, Q) acting on the spindle. [11] Method according to claim 10, characterized bythat when selecting the compressible element (70, 465, 470, 565, 570) the available installation space is taken into account, in particular with regard to its radial extent, wherein with regard to the axial extent of the compressible element the transmission of the steer-by-wire steering (12) is preferably taken into account, wherein the effect of the compressible element (70, 465, 470, 565, 570) only begins when it comes into contact between the spindle nut (43, 443, 543) and the bearing sleeve (50, 60, 450, 460, 550, 560).

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