Steering actuator

Abstract

A steering actuator (1), in particular for a rear-axle steering system (10), comprises a rotational linear transmission (2) with a hollow output element (4) which is rigidly connected to a tubular connecting element (5), an anti-twist mechanism (8) being located on the connecting element (5).

Description

[0001] Steering actuator

[0002] The invention relates to a steering actuator which is particularly suitable for use in a rear axle steering system of a vehicle.

[0003] DE 10 2017 124 388 A1 discloses an electromechanical steering actuator suitable for both front-wheel and rear-wheel steering of a motor vehicle. To convert rotation into linear motion, this steering actuator features a planetary roller gear with a multi-part nut.

[0004] Another steering actuator, which is designed specifically for rear-axle steering, is known from DE 10 2022 104 980 A1. In this case, a hollow push rod is guided in a housing, with an anti-twist device acting between the housing and the push rod.

[0005] DE 10 2009 004 772 A1 describes a method for operating a vehicle with rear-axle steering. The rear-axle steering is intended to be used to influence yaw gain.

[0006] Various steering components designed as hollow bodies intended for use in motor vehicles are disclosed, for example, in documents DE 856 256 B and DE 10 2014 101 711 B4.

[0007] The invention is based on the object of providing a steering actuator that is further developed compared to the prior art and is characterized by a particularly favorable ratio between weight and mechanical strength while being easy to manufacture. This object is achieved according to the invention by a steering actuator having the features of claim 1. According to claim 10, the steering actuator is particularly suitable for use in a rear-axle steering system of a motor vehicle.

[0008] The steering actuator comprises a rotary-linear gear, i.e. a gear that converts a rotation into a linear movement, wherein this gear has a hollow output element that is rigidly connected to a tubular connecting element, wherein an anti-twist device is located on the connecting element.

[0009] The hollow output element can be connected to a tubular connecting element either on one side or on both sides. In either case, the hollow output element, together with the at least one tubular connecting element, forms a rigid arrangement, which is collectively referred to as a steering rod. In addition to its hollow components, i.e., the output element and the at least one connecting element, the steering rod can have one or more solid sections, wherein such a section can in particular be integrated into the rotary-linear transmission. It is also possible to design all output-side elements of the rotary-linear transmission that are firmly connected to the steering rod or directly formed by it as hollow bodies. The production of the hollow bodies, i.e., hollow-shaped rods, is possible in particular using forming processes.This also applies to hollow bodies that have an external structure, in particular a thread structure.

[0010] Regardless of the number of elements comprising the steering rod, the anti-twist device, which prevents the steering rod from twisting relative to the steering actuator housing, is formed by a contour fixed to the housing and by the tubular connecting element. The anti-twist device located on the connecting element can, firstly, support a sufficiently high torque and, secondly, does not restrict the installation space around the hollow output element of the steering actuator in any way. This installation space is particularly useful for the installation of transmission components of the steering actuator.

[0011] Various possible designs of the steering actuator provide for the hollow output element to engage the likewise hollow, i.e., tubular, connecting element. The output element engaging the connecting element can form an overlap region that has a smaller outer diameter than an adjoining tubular section of the connecting element. This means that at least one section of the output element has a smaller diameter than a section of the connecting element. This keeps a particularly generously dimensioned installation space surrounding the steering rod free in the area of ​​the output element for the installation of additional components, in particular transmission and / or drive components, of the steering actuator.This applies particularly to designs in which the connecting element widens with increasing distance from the output element, whereby a tubular section of the connecting element with a constant diameter can be connected to the widening.

[0012] Optionally, a stop is formed on the inner circumferential surface at the transition between the overlap area and the adjacent pipe section, supporting the hollow output element in the axial direction. Regardless of the presence of such a stop, the hollow output element is screwed into the connecting element, for example. Other connection technologies, such as a press fit or a material-to-metal connection, are also possible.

[0013] The rotary-linear gear of the steering actuator, for example, is a planetary roller gear. A planetary roller gear is capable of generating high axial forces with compact external dimensions. For the technological background, reference is made to document DE 10 2018 122 714 A1 as an example. In particular, the planetary roller gear can be a pitch-stable screw drive. This means that every rotation of an input-side element of the gear is converted into a defined feed of an output-side gear element, i.e., no slippage occurs. Pitch-stable planetary roller gears are known, for example, from documents DE 10 2018 116 867 A1, WO 2020 / 164655 A1, and DE 10 2021 104 646 A1. In a pitch-stable planetary roller gear (SPWG), the planet carrier of the gear is driven. Compared to a planetary roller gear with a driven nut, the gear ratio is less extreme.This is accepted in view of the slip-free operation of an SPWG.

[0014] Alternatively, a simple motion thread or a ball screw drive can be considered as a rotary-linear transmission for the steering actuator. In this context, reference is made to documents DE 10 2018 129 372 A1 and DE 10 2016 221 206 B4 as examples.

[0015] Regardless of the design of the rotary-linear transmission, it can be preceded by a rotary-rotary transmission designed as a reduction gear. The latter transmission is, for example, a belt-driven transmission, particularly in the form of a belt drive. If such a reduction gear is omitted, the input element of the rotary-linear transmission can be directly driven electrically.

[0016] In all embodiments, the steering actuator is suitable not only as an actuator for a rear-axle steering system, but also, for example, as an actuator for a steer-by-wire steering system designed as a front-wheel steering system. In both cases, the hollow design of both the output element attributable to the rotary-linear transmission and the associated connecting element results in a weight saving of the order of 50% compared to conventional, non-stressed designs. Optionally, rolling contact surfaces within the rotary-linear transmission, particularly in the form of a planetary roller screw drive, are formed directly by a surface of the hollow output element. In the case of a planetary roller screw drive, the planets of this transmission contact the aforementioned rolling contact surfaces. If the rotary-linear transmission is a ball screw drive, the rolling elements, i.e., balls, of the screw drive roll on the corresponding surfaces.

[0017] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0018] Fig. 1 Components of a steering actuator for a rear axle steering in a schematic sectional view,

[0019] Fig. 2 Parts of the steering actuator in a sectioned perspective view.

[0020] A steering actuator, designated overall by reference numeral 1 and only partially shown in the figures, comprises a rotary-linear gear 2, sketched in Figure 1, which in this case is designed as a planetary roller gear, and a multi-part linkage 3, also referred to as a steering rod. The steering rod 3 is articulated at both ends in a known manner to further chassis components (not shown), which enable adjustment of the steering angle of the rear wheels of the vehicle equipped with the steering actuator 1. Regarding the basic structure of the rear-axle steering system, designated overall by 10, which includes the steering actuator 1, reference is made to the cited prior art.

[0021] The rod assembly 3 comprises a hollow output element 4 of the rotary-linear gear 2 and a tubular connecting element 5. In contrast to the illustration in Figure 2, the right end of the rod assembly 3, formed by the output element 4, and the left end of the rod assembly 3, formed by the connecting element 5, can be identically shaped. Between the two hollow elements 4, 5 there is an overlap area 6, which is only partially shown in Figure 1. In the overlap area 6, the output element 4 is screwed into the connecting element 5. The reference numeral 7 denotes the corresponding screw connection. A stop 12, effective in the longitudinal direction of the rod assembly 3, is formed on the inner circumferential surface of the connecting element 5.

[0022] Adjacent to the screw connection 7 and the stop 12, to the left in the arrangement according to Figure 2, the connecting element 5 widens into a pipe section 13 of comparatively large diameter. Located in the pipe section 13 is an anti-twist device 8, which prevents the rod 3 from twisting in the housing (not shown) of the steering actuator 1.

[0023] The anti-twist device 8 comprises a securing element 11 surrounding the tubular section 13, which in the present case is fixed to the tubular section 13 by means of a bolt 9 and, together with the rod 3, is displaceable in the axial direction of the rear-axle steering 10, i.e., in the transverse direction of the motor vehicle. The completely tubular output element 4 has, as can be seen from Figure 2, a non-uniform diameter, wherein the diameter of the section of the output element 4 screwed into the connecting element 5 is smaller than a section of the output element 4 further away from the connecting element 5. The outer diameter of the latter section corresponds, as can be seen further from Figure 2, at least approximately to the diameter of the tubular section 13.

[0024] Regarding the features of the planetary roller gear 2, reference is made to the roughly schematic representation in Figure 1. The planetary roller gear 2 comprises a plurality of planets 15, which are guided in a cage (not shown) and each contact a thread (also not shown) on the rod end 3 and a nut 14. In contrast to the thread formed by the rod end 3, the planets 15 are profiled without a pitch. Likewise, the nut 14 of the planetary roller gear 2 has a profiled without a pitch. In the present case, the planets 15 directly contact the thread of the planetary roller gear 2 provided by the hollow output element 4.

[0025] The nut 14 can be directly electrically driven or represent the output element of a reduction gear connected upstream of the rotary-linear gear 2, for example, in the form of a belt drive. It is also possible to drive the cage of the planetary roller gear 2. Alternatively, another gear that converts rotation into linear motion, for example, a ball screw, can be used as the rotary-linear gear 2.

[0026] List of reference symbols

[0027] Steering actuator

[0028] Rotary-linear gears, planetary roller gears

[0029] rods, handlebar

[0030] Output element

[0031] connecting element

[0032] Overlap area

[0033] screw connection

[0034] Anti-twist device

[0035] bolt

[0036] Rear-axle steering

[0037] securing element

[0038] stop

[0039] Pipe section

[0040] Mother

[0041] planet

Claims

Patent claims 1 . Steering actuator (1 ), comprising a rotary-linear gear (2) with a hollow output element (4) which is rigidly connected to a tubular connecting element (5), wherein an anti-twist device (8) is located on the connecting element (5).

2. Steering actuator (1) according to claim 1, characterized in that the hollow output element (4) engages in the connecting element (5).

3. Steering actuator (1) according to claim 2, characterized in that an overlap region (6) is formed by the output element (4) engaging in the connecting element (5), which overlap region has a smaller outer diameter than an adjoining pipe section (13) of the connecting element (5).

4. Steering actuator (1) according to claim 3, characterized in that at the transition between the overlap region (6) and the adjoining tube section (13) on the inner circumferential surface, a stop (12) supporting the hollow output element (4) in the axial direction is formed.

5. Steering actuator (1) according to one of claims 2 to 4, characterized in that the hollow output element (4) is screwed into the connecting element (5).

6. Steering actuator (1) according to one of claims 1 to 5, characterized in that a planetary roller gear is provided as the rotary-linear gear (2).

7. Steering actuator (1) according to claim 6, characterized in that the planetary roller gear (2) has a driven nut (14).

8. Steering actuator (1) according to claim 6, characterized in that the planetary roller gear (2) is designed as a pitch-stable screw drive (SPWG).

9. Steering actuator (1) according to one of claims 1 to 5, characterized in that the rotary-linear gear (2) is designed as a ball screw drive.

10. Rear axle steering (10), comprising a steering actuator (1) according to claim 1.

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