Steering actuator for a steering system of a motor vehicle, and steering system for a motor vehicle

Abstract

The present invention relates to a steering actuator for a steering system of a motor vehicle, comprising an actuator rod which can be linearly translated in a housing axially in the direction of its longitudinal axis (A) and which has a guide portion which is axially displaceably and slidably mounted in a passage (71) of a sliding bushing fitted in the housing, wherein the guide portion has a non-round guide cross-section which is interlockingly secured, in a corresponding non-round passage cross-section of the passage (71), against rotation about the longitudinal axis. In order to provide improved play-free guidance, the invention proposes that the sliding bushing has two bearing portions (72a, b) which are rotationally loaded against one another about the longitudinal axis and are braced against the guide portion.

Description

[0001] Steering actuator for a motor vehicle steering system and steering system for a motor vehicle

[0002] State of the art

[0003] The invention relates to a steering actuator for a steering system of a motor vehicle, comprising an actuator rod which is linearly displaceable translationally axially in the direction of its longitudinal axis in a housing, which has a guide section which is axially displaceable and slidably mounted in a passage of a sliding bushing installed in the housing, wherein the guide section has a non-circular guide cross-section which is positively secured in a corresponding non-circular passage cross-section of the passage with respect to rotation about the longitudinal axis.

[0004] In a motor vehicle steering system, a steering actuator is used to generate the mechanical steering angle of one or more steerable wheels.

[0005] A steering actuator of this type has an actuator rod that is axially adjustable in its longitudinal direction, defined by its longitudinal axis, usually transversely to the direction of travel relative to the vehicle body. The actuator rod can be articulated to the steering knuckles of the two steerable wheels of a vehicle axle, and in the case of individual wheel steering, it can be connected to a single steerable wheel. The translational displacement of the actuator rod causes the steerable wheels to turn.

[0006] The actuator rod can be moved within the housing by means of a motorized linear drive, for example, a spindle drive, as described in the prior art, for instance, in DE 10 2018 124 905 A1. For rotationally secure linear guidance, the actuator rod known from this document has a guide section with a non-circular guide cross-section. This section slides axially through a passage in a sliding sleeve with a correspondingly adapted passage cross-section. To compensate for thermal expansion, the sliding sleeve is designed to be flexible. However, it is possible that after prolonged operation, play may develop between the actuator rod and the sliding sleeve in the area of ​​the non-circular guide cross-section. This can lead to noise generation.

[0007] 240570P10WO In view of the problem explained above, it is an object of the present invention to provide an improved backlash-free guide.

[0008] Description of the invention

[0009] This problem is solved according to the invention by the steering actuator with the features of claim 1 and the steering system according to claim 13. Advantageous further developments are set out in the dependent claims.

[0010] In a steering actuator for a steering system of a motor vehicle, comprising an actuator rod that is linearly displaceable translationally axially in the direction of its longitudinal axis in a housing, the guide section having a guide section which is axially displaceable and slidably mounted in a passage of a sliding bushing installed in the housing, wherein the guide section has a non-circular guide cross-section which is positively locked in a corresponding non-circular passage cross-section of the passage with respect to rotation about the longitudinal axis, it is provided according to the invention that the sliding bushing has two bearing sections which are rotationally loaded against each other about the longitudinal axis and clamped against the guide section.

[0011] The two bearing sections, which are hereinafter referred to synonymously as the two bearing sections, are arranged coaxially to the axis in the axial direction, one after the other.

[0012] They can be arranged adjacent to each other, for example, without axial spacing or, alternatively, with axial spacing. Each of the two bearing sections has an axial passage, i.e., an axially through opening with a non-circular cross-section. Both bearing sections are axially penetrated by the guide section, which is slidably guided in each of the two passages. The bearing sections can be mounted radially displaced to generate additional radial preload.

[0013] Due to the non-circular cross-sectional shape of the guide section, which preferably extends uniformly over the entire axial length of the guide segment, guide surfaces inclined against the circumferential direction, i.e., perpendicular to the tangential direction, are formed on the outside of the guide segment. These surfaces slide against corresponding bearing surfaces formed in the inner passage, thus creating a positive fit effective in the circumferential direction. This prevents the actuator rod from rotating in the sliding bushing.

[0014] 240570P10WO guided securely around the longitudinal axis.

[0015] The guide surfaces of the guide section and the corresponding bearing surfaces of the sliding bushing form the sliding surfaces of the sliding guide, which are in sliding contact with each other. The invention utilizes two properties of the non-circular sliding guide, namely, firstly, that the guide section is positively locked against rotation in the through-section, and secondly, that when the guide cross-section is subjected to a rotational load relative to the sliding bushing, the sliding surfaces are pressed against each other in sliding contact.

[0016] The two bearing sections of the sliding bushing according to the invention can preferably be identical, or at least of a similar design, and both have sliding surfaces in sliding contact with the guide section. According to the invention, a rotational or torsional torque, which can be referred to as a preload torque, is exerted between the two bearing sections. This generates a relative rotational or torsional load about the longitudinal axis, which acts in the direction of a relative rotation or torsion of the two bearing sections. In this process, one bearing section, with its sliding surfaces (i.e., the bearing surfaces), bears against the corresponding sliding surfaces of the guide section (i.e., the guide surfaces) in the circumferential direction, which are opposite to the direction of rotation of the rotational load. Corresponding to the reaction torque, which is directed opposite to the preload torque, the other bearing section bears against its sliding surfaces (i.e.,The bearing surfaces are oriented circumferentially against the corresponding sliding surfaces of the guide section, which are opposite to the direction of rotation of the rotary load. This mutual rotary support clamps the sliding surfaces of both bearing sections in backlash-free sliding contact against the corresponding guide surfaces of the guide section.

[0017] One advantage of the invention is that a backlash-free guide for the actuator rod can be achieved with minimal effort, independent of dimensional tolerances, temperature fluctuations, or other influences. A further advantage is that the contact force in the sliding contact, which is crucial for the frictional resistance of the sliding guide, can be precisely defined and predetermined by the design of the preload torque, independent of the dimensional tolerances of the sliding bushing.

[0018] It is also advantageous that the rotary clamping of the two bearing sections can be implemented with a small installation space requirement.

[0019] 240570P10WO It is advantageous that the bearing sections are elastically loaded against each other.

[0020] The elastic load generates a preload moment between the two bearing sections with respect to rotation about the axis. In other words, this creates a torsionally elastic arrangement of the two bearing sections. This ensures backlash-free sliding contact between the sliding surfaces in every operating situation. Any manufacturing and operating tolerances can be easily compensated for, thus ensuring consistent and reliable guidance of the actuator rod throughout its service life.

[0021] A preferred embodiment can be achieved by placing a preloading device between the two bearing sections, which exerts a preloading moment that rotates the bearing sections relative to each other about the longitudinal axis.

[0022] The preloading device generates a preload moment, i.e., a torsional moment, which acts on the two bearing sections to twist them relative to each other about their longitudinal axis, i.e., to subject them to a rotational load against each other, as described above. The preloading device presses the sliding guide surfaces of the guide section and the passage in each of the two bearing sections against each other without any play.

[0023] The preloading device can be designed to generate a defined preload torque and a defined contact force, thereby generating a correspondingly defined frictional torque.

[0024] The preloading device can also be implemented by utilizing an elastic material property of the bearing sections. For example, the two bearing sections can be fixed at an angular offset relative to each other by the preloading device. This causes the bearing sections to deform elastically, preferably circumferentially, and thus press against the guide section without play.

[0025] An advantageous further development is that the preloading device is integrated with the sliding bushing.

[0026] The pre-tensioning device may include force or torque generating means that are such as-

[0027] The 240570P10WO, together with the sliding bushing, is designed so that it loads the two bearing sections in opposite directions of rotation around the longitudinal axis. This allows for an advantageously compact design.

[0028] Alternatively, it is possible that force or moment generating means are effectively arranged between one or both bearing sections and the housing, through which a preload moment is exerted on the bearing sections.

[0029] The aforementioned design may provide that the preloading device has a spring element.

[0030] A spring element forms an elastic element which acts on the two bearing sections in such a way that the spring force generates a spring moment which, as a preload or torsional moment, forces the two bearing sections in opposite directions of rotation, i.e., rotationally oppositely loaded.

[0031] A spring element can be provided with minimal effort and inserted between the bearing sections. It can, for example, be designed as a wire or leaf spring made of spring steel, acting as a tension or compression spring at a radial distance from the longitudinal axis and circumferentially against the two bearing sections.

[0032] It is possible that the preloading device is arranged axially between the bearing sections.

[0033] This design can be essentially mirror-symmetrical to a mirror plane perpendicular to the longitudinal axis. The bearing sections are located opposite each other on either side of the mirror plane. The preloading device, which may, for example, include one or more spring elements, can be arranged in the region of the mirror plane.

[0034] It is advantageous for the sliding bushing to have at least one sliding element.

[0035] The sliding element is arranged in the area of ​​a bearing section and has at least one, preferably several, sliding surfaces distributed around the circumference, which are in sliding contact with the corresponding guide surfaces of the guide section at least partially.

[0036] 240570P10WO It is advantageous that each bearing section has at least one sliding element. The sliding elements of the two bearing sections can preferably be identical, of the same type, or mirror-symmetrical.

[0037] It is possible for at least two sliding elements to be designed separately, for example, for installation in the two bearing sections. Alternatively, it is also conceivable and possible to use a single, continuous sliding element. This can then preferably be designed to be flexible or deformable in order to enable the relative rotational movement of the two bearing sections provided for in the invention. This can reduce the manufacturing and assembly effort.

[0038] Preferably, the sliding bushing is made of plastic.

[0039] Preferably, at least the sliding surfaces can be made of or have a plastic composition. This allows for a low-friction and low-wear sliding pair with a metallic sliding surface, for example, a guide surface of the actuator rod, which is preferably made of steel. This enables a smooth-running and low-wear sliding bearing.

[0040] It is advantageous for the sliding bushing to be formed entirely or partially as an injection-molded plastic part made of a thermoplastic elastomer. This allows for easy and flexible adaptation to different shapes with minimal effort. Preferably, the sliding bushing as a whole, or one or both bearing sections, can each be formed as a single injection-molded plastic part, or at least incorporate one such part.

[0041] Furthermore, it is conceivable and possible to integrate the preloading device with one or more plastic components. For example, a spring element, such as one made of spring steel, can be completely or partially encapsulated in plastic using injection molding, thereby permanently bonding it to one or both bearing sections. The spring element can also be completely encapsulated in plastic, for example, to create a one-piece sliding bushing where both bearing sections and the spring element are integrated into a single injection-molded plastic part.

[0042] It is possible that the guide section is prismatic in shape.

[0043] 240570P10WO The prismatic design corresponds to a polygonal guide cross-section, which can be, for example, a uniform or irregular triangle, quadrilateral, hexagon, or other polygon. The polygon may have rounded edges in its profile. The passage between both bearing sections of the sliding bushing has a corresponding polygonal cross-section, thus creating a positive fit effective against rotation about the longitudinal axis. The sliding surfaces are formed by the opposing prismatic faces of the polygon.

[0044] The invention clamps the prism surfaces against each other in sliding contact. This enables reliable and uniform sliding guidance.

[0045] Further training may stipulate that the sliding bushing has a sensor device.

[0046] The sensor device can, for example, be configured to detect a linear displacement of the actuator rod relative to the sliding bushing. For this purpose, a known sensor-receiver arrangement can be used to detect absolute or relative position measurements in the direction of the longitudinal axis, such as capacitive or inductive incremental encoders, optical measuring elements, or the like. This allows the instantaneous position of the actuator rod in the steering actuator, which correlates with the mechanical steering angle of the wheel(s) steered by the steering actuator, to be reliably and accurately detected.

[0047] Additionally or alternatively, the sensor elements can be designed to detect a bending and / or torsional moment acting between the actuator rod and the sliding bushing. It is also conceivable and possible to use a relative displacement or rotation of the two bearing sections to determine externally acting moments.

[0048] Furthermore, sensor elements can be provided that respond to deformation of the actuator rod. Elastic torsion and / or bending of the actuator rod can be generated by the forces acting during operation. Monitoring these actuator parameters enables monitoring of the load during operation and thus reliable detection of potentially damaging overloads or malfunctions.

[0049] Preferably, the actuator rod is designed to interact with a drive unit.

[0050] The drive unit serves to linearly displace the actuator rod within the housing of the

[0051] 240570P10WO Steering actuator. For example, the drive unit may have a motor-driven spindle drive. The actuator rod has a spindle thread extending over an axial threaded section and engaging a spindle nut. This nut is axially fixed and supported within the housing and can be rotated relative to the longitudinal axis by a motor. According to the known operating principle of a spindle drive, specifically a plunge spindle drive, the rotation of the spindle nut is converted into a linear axial displacement of the actuator rod. Preferably, the spindle drive can be designed as a ball screw drive, with the spindle nut being a ball nut (recirculating ball nut) and the spindle thread being a corresponding ball screw.

[0052] It may be provided that the sliding bushing has an additional sliding section with a circular through-cross-section.

[0053] The additional sliding section has a circular opening cross-section with a diameter corresponding to the diameter of an envelope of the non-circular guide cross-section. This sliding section can form an axial extension of the sliding bushing and can provide additional support transverse to the longitudinal axis.

[0054] The sliding bushing can have a circular or non-circular outer cross-section. A non-circular cross-section offers the advantage that the sliding bushing can be positively fitted into the steering actuator housing.

[0055] The invention further comprises a steering system for a motor vehicle comprising a steering actuator with an actuator rod which is axially movable in the direction of its longitudinal axis in a housing and which can be coupled to at least one steerable wheel via at least one tie rod, wherein, according to the invention, the steering actuator is designed according to one of the embodiments or combinations thereof described above.

[0056] Preferably, the steering actuator according to the invention can be used in a steer-by-wire steering system of a motor vehicle. In this system, manually entered steering commands are electronically detected by rotary sensors and converted into control commands that actuate an electric motor drive unit of the steering actuator.

[0057] 240570P10WO Description of the drawings

[0058] Advantageous embodiments of the invention are explained in more detail below with reference to the drawings. Specifically, they show:

[0059] Fig. 1 shows a schematic representation of a steering system according to the invention.

[0060] Fig. 2 shows a cross-section BB through the steering actuator according to Fig. 1 ,

[0061] Fig. 3 shows a longitudinal section along axis A through the steering actuator according to Fig. 1 ,

[0062] Fig. 4 shows a schematically isolated view of the sliding guide of the steering actuator according to the invention as shown in Figs. 2 and 3.

[0063] Fig. 5 shows a sliding bushing of a steering actuator according to the invention as shown in Figs. 1-4.

[0064] Fig. 6 shows a second embodiment of a sliding guide for the steering actuator according to the invention in a view as in Fig. 4.

[0065] Embodiments of the invention

[0066] In the various figures, identical parts are always marked with the same reference symbols and are therefore usually only named or mentioned once.

[0067] Fig. 1 schematically shows a steer-by-wire steering system 1, which includes a steering column 2. This column has a support unit 21 that can be mounted on a vehicle body (not shown), on which a steering spindle 22 is rotatably mounted about its longitudinal axis L. At its rear end, on the driver's side, relative to the direction of travel, a steering wheel 23 is fixedly mounted to the steering spindle 22 for inputting manual steering commands.

[0068] The steering column 2 contains a rotation angle and torque detection sensor system (not shown in detail) which converts a steering command introduced into the steering spindle 22 by turning the steering wheel 23 into an electrical control signal.

[0069] 240570P10WO The control signal is transmitted via an electrical control line 3 to an electric steering actuator 4 according to the invention.

[0070] The steering actuator 4 – shown in detail in Figures 2 to 6 – has an actuator rod 5 that extends along an axis A, the so-called actuator axis, transversely to the vehicle's direction of travel. The actuator rod 5 is axially displaceable in its longitudinal direction defined by the axis A within a housing 41 (actuator housing), as indicated by the double arrow. The housing 41 has connecting elements (not shown) for attachment to a vehicle body (not shown).

[0071] The two outer ends of the actuator rod 5 are each connected to a steerable wheel 61 via a tie rod 6, so that an axial displacement of the actuator rod 5 causes a steering angle of the wheel 61 relative to the road surface 62.

[0072] To generate a steering input, the steering actuator 4 has an electrically controllable electromechanical drive via the control line 3, with an electric motor 42 attached to the housing 41. The motor 42 can drive an axially supported spindle nut 43, which is rotatably mounted in the housing 41 and is visible in Figures 2 and 3. A spindle thread 51 formed on the actuator rod 5 engages with this spindle nut. In this way, a linear spindle drive is formed, in which the actuator rod 5 can be moved axially, i.e., back and forth in its longitudinal direction, relative to the housing 41 by the appropriate direction of rotation of the motor 42, as indicated by the double arrow.

[0073] The spindle nut 43 can preferably be designed as a ball screw nut.

[0074] Fig. 2 shows a cross-section BB perpendicular to axis A, and Fig. 3 a longitudinal section along axis A. Fig. 4 shows the spindle drive formed from the actuator rod 5 together with the spindle nut 43 in a schematically isolated perspective view.

[0075] The actuator rod 5 has a cylindrical base body, which can be made, for example, of steel rod material. The spindle thread 51 and a guide section 52 are integrated into this base body.

[0076] The guide section 52 is arranged at an axial distance from the spindle thread 51 and extends in the axial direction. It is guided axially in a sliding bushing 7 according to the invention, which is mounted in the housing 41.

[0077] 240570P10WO The guide section 52 has a prismatic, triangular guide cross-section extending from the circular-cylindrical base cross-section of the actuator rod 5. This guide cross-section has three guide surfaces 53, which are planar in this example and evenly distributed around the circumference, extending axially parallel to axis A.

[0078] Fig. 5 shows a greatly enlarged, separate representation of the sliding bushing 7 according to the invention. This has an axially through passage 71 in which, in the operating state according to Fig. 4, the guide section 52 is axially displaceable.

[0079] The sliding bushing 7 has two axially consecutive bearing sections 72a and 72b, which are identical in design and are hereinafter collectively referred to as the bearing sections 72. The through-opening 71 extends axially through both bearing sections 72 and, corresponding to the triangular guide cross-section, has a triangularly shaped through-opening cross-section. This secures the guide section 52 in the through-opening 71 against rotation about the axis A.

[0080] Each bearing section 72a, b has on its inside three bearing surfaces 73 evenly distributed around the circumference, which are in sliding contact with the corresponding guide surfaces 53 of the guide section 52.

[0081] A support ring 74 is arranged between the bearing sections 72, the support ring having axially projecting support arms 75 beyond the bearing sections 72. Circumferentially acting spring elements 76 are arranged between the support arms 75 and the bearing sections 72. These spring elements are supported circumferentially by a support arm 75 and by the outer circumference of a bearing section 72a, b. As a result, the two bearing sections 72 are elastically supported against the support ring 74 with respect to rotation about the axis A, and thus also torsionally elastically supported against each other.

[0082] As shown in Fig. 5, the support arms 75 are offset from each other in the circumferential direction, so that the two bearing sections 72a, b have an angular offset. The spring elements 76 subject the two bearing sections 72a, b to opposite elastic loads with respect to rotation about the axis A. In other words, an elastic torsional moment T is generated, which is schematically indicated by the opposite arrows T in the circumferential direction.

[0083] 240570P10WO Due to the elastic torsional load on the two bearing sections 72a, b, their bearing surfaces 73 are clamped against the corresponding guide surfaces 53 of the guide section 52. This results in backlash-free sliding guidance of the guide section 52 in the sliding bushing 7.

[0084] Fig. 7 shows, in a representation analogous to Fig. 4, a second embodiment of a sliding bushing 7 according to the invention. In addition to the basic structure according to Fig. 5, this has an additional sliding section 77 with a circular through-cross-section. This forms, as it were, a hollow cylindrical extension, which can be connected, for example, to one of the bearing sections 72 or the support ring 74.

[0085] The bearing sections 72 can be designed as injection-molded plastic parts made of a low-friction and wear-resistant plastic. It is possible that the two bearing sections 72a and 72b are identical in shape. The support ring 74 can be made of metal or plastic. The spring elements 76 can have elastic metal and / or plastic components.

[0086] 240570P10WO Reference list

[0087] 1 Steering system

[0088] 2 Steering column

[0089] 21 Carrying unit

[0090] 22 Steering spindle

[0091] 23 Steering wheel

[0092] 3 Control line

[0093] 4 Steering actuator

[0094] 41 Housing (actuator housing)

[0095] 42 Engine

[0096] 43 Spindle nut

[0097] 5 actuator rod

[0098] 51 Spindle thread

[0099] 52 Leadership section

[0100] 53 guide surfaces

[0101] 6 tie rod

[0102] 61 wheel

[0103] 62 lanes

[0104] 7 sliding bushing

[0105] 71st round

[0106] 72a, b Storage section

[0107] 73 storage area

[0108] 74 Support ring

[0109] 75 Support arm

[0110] 76 Spring element

[0111] 77 Gliding section

[0112] L Longitudinal axis

[0113] A actuator axis

[0114] T Torsional moment

[0115] 240570P10WO

Claims

PATENT CLAIMS 1. Steering actuator (4) for a steering system (1) of a motor vehicle, comprising an actuator rod (5) which is linearly displaceable translationally axially in the direction of its longitudinal axis (A) in a housing (41), the actuator rod having a guide section (52) which is axially displaceable and slidably mounted in a passage (71) of a sliding bushing (7) installed in the housing (41), wherein the guide section (52) has a non-circular guide cross-section which is positively locked in a corresponding non-circular passage cross-section of the passage (71) with respect to rotation about the longitudinal axis (A), characterized in that the sliding bushing (7) has two bearing sections (72a, b) which are rotationally loaded against each other about the longitudinal axis (A) and clamped against the guide section (52).

2. Steering actuator according to claim 1, characterized in that the bearing sections (72a, b) are elastically loaded against each other.

3. Steering actuator according to one of the preceding claims, characterized in that a preloading device (74, 76) is provided between the two bearing sections (72a, b) which exerts a preloading moment (T) rotating the bearing sections (72a, b) relative to each other about the longitudinal axis (A).

4. Steering actuator according to claim 3, characterized in that the preloading device (74, 76) is integrated with the sliding bushing (7).

5. Steering actuator according to one of the preceding claims 3 or 4, characterized in that the preloading device (74, 76) has a spring element (76).

6. Steering actuator according to one of the preceding claims 3 to 5, characterized in that the preloading device (74, 76) is arranged axially between the bearing sections (72a, b).

7. Steering actuator according to one of the preceding claims, characterized in that the sliding bushing (7) has at least one sliding element. 240570P10WO 8. Steering actuator according to one of the preceding claims, characterized in that the sliding bushing (7) comprises a plastic.

9. Steering actuator according to one of the preceding claims, characterized in that the guide section (52) is prismatically shaped.

10. Steering actuator according to one of the preceding claims, characterized in that the sliding bushing (7) has a sensor device.

11. Steering actuator according to one of the preceding claims, characterized in that the actuator rod (5) interacts with a drive device (42).

12. Steering actuator according to one of the preceding claims, characterized in that the sliding bushing (7) has an additional sliding section (77) with a circular through-cross-section.

13. Steering system (1) for a motor vehicle comprising a steering actuator (4) with an actuator rod (5) which is axially movable in the direction of its longitudinal axis (A) in a housing (41) and can be coupled to at least one steerable wheel (61) via at least one tie rod (6), characterized in that the steering actuator (4) is designed according to one of the preceding claims. 240570P10WO

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