Planetary roller gear, steering actuator and rear-axle steering system

Abstract

A planetary roller gear (1), in particular for an actuator of a rear-axle steering system, comprises a planet carrier (10) in which multiple planets (6) with no-lead profiles are guided and mesh with a likewise no-lead profile (11) of a nut (12). Respective damping elements (18, 24, 25) are inserted between sliding bearing elements (17) that bear the planets (6) and the planet carrier (10).

Description

[0001] Planetary roller gears, steering actuator and rear axle steering

[0002] The invention relates to a planetary roller gear according to the preamble of claim 1. Furthermore, the invention relates to a steering actuator and a rear-axle steering system.

[0003] A generic planetary roller gear is known, for example, from DE 10 2021 121 736 A1. DE 10 2021 121 736 A1 describes in detail a set of components for assembling pitch-accurate planetary roller gears, particularly for electromechanical actuators of rear-axle steering systems.

[0004] Another planetary roller gear is disclosed in DE 10 2009 040 606 B4. This planetary roller gear is equipped with a length measuring system. A sensor of the length measuring system is connected to a spindle nut.

[0005] Planetary roller gears with a multi-part nut are known, for example, from DE 10 2013 213 704 A1 and DE 10 2018 122 714 A1. A planetary roller gear with an elastic nut is described in DE 10 2010 011 821 B4.

[0006] Various design options for rear-axle steering systems, each comprising an electromechanical actuator that works with a planetary roller gear and an upstream reduction gear, are known, for example, from the documents DE 10 2022 110 510 A1 and DE 10 2018 129 119 A1.

[0007] Planetary roller gears are generally designed to convert rotation into linear motion, capable of generating considerable axial forces despite their compact external dimensions. The individual, pitchless planets of a planetary roller gear mesh with a single- or multi-start thread of a lead screw, resulting in an axial offset between the planetary profiles. The defined guidance of the planets within the planetary roller gear is therefore particularly important. All planets engage a nut, which can be constructed in one or more parts.

[0008] The invention is based on the object of specifying a planetary roller gear which is further developed compared to the prior art, has a compact and easy-to-manufacture design and which is suitable, among other things, for use in an actuator of a rear axle steering system of a motor vehicle and is characterized by high operational reliability and favorable acoustic behavior.

[0009] This object is achieved according to the invention by a planetary roller gear having the features of claim 1. The planetary roller gear is suitable, among other things, for use in a steering actuator according to claim 9. According to claim 10, the steering actuator can be an actuator of a rear-axle steering system of a motor vehicle.

[0010] The planetary roller gear, in a known basic design, comprises a planetary carrier in which several planets with a pitchless profile are guided, which mesh with a nut with a pitchless profile. According to claim 1, a damping element is inserted between the plain bearing elements that support the planets and the planetary carrier.

[0011] The damping elements provided for in the application, inserted between the two non-profiled ends of each planet and the planet carrier, are not only compatible with the required precise guidance of the planets, but even act to ensure self-alignment of the planets. The acoustic behavior of the planetary roller gear is positively influenced by the damping elements. In one possible design of the planetary roller gear, each damping element has a sleeve-like basic shape that surrounds the associated plain bearing element. The width of the damping element, measured in the axial direction of the planet, can correspond to the width of the plain bearing element.

[0012] Other designs of the planetary roller gear provide for the damping element to have a ring shape concentric with the center axis of the nut and the planet carrier, with all plain bearing elements located on the same end face of the planetary gear assembly being held in the same damping element. In such cases, a pair of damping elements exists, with the planets arranged between the two annular damping elements.

[0013] Such designs include, for example, variants of the planetary roller gear in which the damping element has a cylindrical sleeve extension engaging in an annular groove of the planet carrier. The inner diameter of the sleeve extension can correspond at least approximately to the diameter of a cylinder concentric with the center axis of the planetary roller gear, on whose surface the center axes of all planets lie. In these variants, the damping element, with its cylindrical outer circumferential surface, can, for example, contact a bearing ring of an axial roller bearing that supports the nut in the planet carrier. The axial roller bearing can be designed, in particular, as an axial roller bearing or axial needle bearing.

[0014] Another variant, which belongs to the same group of designs, provides for the damping element to have a radially outward-facing flange that rests against an inner surface of the planet carrier. In this variant, the flange contacts, for example, a plain bearing ring provided for supporting the nut in the planet carrier. There is no necessary connection between the described design options for the pair of damping elements and the rolling or plain bearings provided for supporting the nut in the planet carrier. For example, it is possible to combine a damping element that has a sleeve extension with a plain bearing between the nut and the planet carrier. It is also possible for a bearing ring of a rolling bearing that supports the nut in the planet carrier to rest against a flange of the damping element.

[0015] Finally, a damping element, which has both a sleeve extension and a radially outward-facing flange, can be combined optionally with a rolling bearing or a plain bearing, with the aforementioned bearing being provided for supporting the nut of the planetary roller gear in the planet carrier. Regardless of the geometry of the damping elements, assemblies which, in addition to the damping element, comprise at least one plain bearing element can be efficiently manufactured using multi-component injection molding. The plain bearing elements are, in particular, metal parts, for example, made of a non-ferrous metal alloy. The damping elements are, in particular, made of a non-metallic material, for example, a plastic suitable for injection molding.

[0016] In all of the designs described above, the planetary carrier can be the driven element of the planetary roller gear. The planetary roller gear is thus designed as a lead-stable screw drive. The nut functions neither as a driving element nor as an output element. A less extreme transmission ratio is accepted compared to planetary roller screw drives with a driven nut or threaded spindle.

[0017] The planetary roller gear is suitable not only for use in a rear-axle steering actuator, but also, for example, in a steer-by-wire steering system for steering the front wheels of a vehicle. Applications in brake, clutch, or transmission actuators are also possible. Several exemplary embodiments of the invention are explained in more detail below with reference to a drawing. These show, partly simplified:

[0018] Fig. 1 Components of a planetary roller gear with damped planets in side view,

[0019] Fig. 2 the arrangement according to Figure 1 in front view,

[0020] Fig. 3 shows a section of a planetary roller gear with a roller bearing between a planet carrier and a nut,

[0021] Fig. 4 in a representation analogous to Figure 3 a planetary roller gear with a plain bearing between a planet carrier and a nut,

[0022] Fig. 5 shows a sliding ring intended for use in the planetary roller gears according to Figures 1 to 4.

[0023] Unless otherwise stated, the following explanations refer to all embodiments. Corresponding or essentially equivalent parts are identified by the same reference numerals in all figures.

[0024] A planetary roller gear, designated overall by the reference numeral 1, comprises a threaded spindle 2, the thread of which is designated 3. Profilings 4 of several planets 6 mesh with the thread 3. The profiles 4 are formed in a central section 7 of each planet 6. The central section 7 merges into two comparatively thin side sections 8, which are provided with a profile 5. All profiles 4, 5 of the planet 6 are designed without a pitch. Adjacent to the two side sections 8, each planet 6 tapers off in the form of an end section 9 with a smooth cylindrical shape. The end sections 9 are mounted in a planet carrier 10 in a manner described in more detail below.

[0025] During operation of the planetary roller gear 1, the planets 6 contact the threaded spindle 2 exclusively with their central sections 7. The profiles 5 of the side sections 8, on the other hand, mesh with profiles 11 of a nut 12, which are also pitchless. The nut 12 can be designed in one or more parts, whereby in the case of a multi-part design, the nut parts can be preloaded against each other.

[0026] The nut 12 is mounted relative to the planet carrier 10 by means of bearings 13, 14 such that axial forces can be transmitted between the nut 12 and the planet carrier 10. However, a transmission of torque via the nut 12 is not provided in the present case. Instead, an outer sleeve 15 is provided for this purpose, which is firmly connected to the planet carrier 10. The outer sleeve 15 has a toothing 16 in its central region, viewed in the axial direction, which can be used to drive the assembly comprising the outer sleeve 15 and the planet carrier 10 by means of a belt. Thanks to the driven planet carrier 10, the planetary roller gear 1 is designed as a pitch-stable screw drive (SPWG).

[0027] To support the planets 6 in the planet carrier 10, the exemplary embodiments feature sliding sleeves 17 of a uniform shape, into which the ends 9 of the planets 6 are inserted. In all cases, damping elements 18, 24, 25 are connected between the sliding sleeves 17, i.e., plain bearing elements, and the planet carrier 10. The damping elements 18, 24, 25 can be manufactured, in particular, from an elastomer.

[0028] In the embodiment according to Figures 1 and 2, the damping elements 18 have a simple ring shape, with the width of the damping elements 18, measured in the axial direction of the planets 6 and thus of the entire planetary roller gear 1, corresponding to the width of the sliding sleeves 17. A separate damping element 18 is assigned to each end section 9 of each planet 6.

[0029] The damping elements 18, 24, 25 positively influence the noise behavior of the planetary roller gear 1 and contribute to the self-alignment of the planets 6 during operation of the planetary roller gear 1. This applies to all embodiments. Furthermore, the damping elements 18, 24, 25 have a positive effect on the service life of the individual components of the planetary roller gear 1, in particular the planets 6 including their bearings, as well as the planetary roller gear 1 as a whole, including the threaded spindle 2.

[0030] In the design according to Figure 3, the axial bearing 13, which supports the nut 12 in the planet carrier 10, is designed as a rolling bearing, namely an axial roller bearing. A bearing designated 19 contacts both an inner side of the planet carrier 10, designated 20, and the damping element, designated here 24. In this case, the damping element 24 is annular, the central axis of which coincides with the central axis of the entire planetary roller gear 1. All end sections 9, which are arranged on the same end face of the arrangement of all planets 6, are held in the same damping element 24, with the number of sliding sleeves 17 inserted into the damping element 24 corresponding to the number of planets 6. Overall, the planets 6 are thus guided in a pair of damping elements 24.

[0031] In order to anchor each damping element 24 in the planet carrier, the damping element 24 in the case of Figure 3 has on its side facing the planet carrier 10 a cylindrical sleeve extension 21 which is inserted into a recess formed as an annular groove on the inner side 20 of the planet carrier 10.

[0032] The embodiment according to Figure 4 also features an annular damping element, designated here by 25. The damping element 25 has a radially outwardly directed flange 22. The flange 22 rests on the one hand against the inner side 20 of the planet carrier 10 and, on the other hand, contacts a plain bearing ring 23 belonging to the bearing 14, with which the nut 12 is mounted in the planet carrier 10. In addition to the damping element 25, the plain bearing ring 23 also acts as a damping element of the planetary roller gear 1.

[0033] In the embodiments according to Figures 3 and 4, material of the damping elements 24, 25 is also located on the end faces of the planets 6. The damping provided in the axial direction also has a damping effect on axial movements of the nut 12, which represents a further significant contribution to noise damping and wear reduction.

[0034] In all embodiments, assemblies comprising sliding sleeves 17, damping elements 18, 24, 25 and parts of the planet carrier 10 can be provided as prefabricated units and installed as a whole in the planetary roller gear 1.

[0035] List of reference symbols

[0036] Planetary roller gear

[0037] threaded spindle

[0038] thread

[0039] Profiling the midsection of a planet

[0040] Profiling the lateral section of a planet

[0041] planet

[0042] Middle section

[0043] Page section

[0044] final section

[0045] planet carrier

[0046] Profiling the mother

[0047] Mother

[0048] Bearings, rolling bearings

[0049] Bearing, plain bearing

[0050] Outer sleeve

[0051] Gearing

[0052] Sliding sleeve, plain bearing element

[0053] Damping element

[0054] bearing ring

[0055] Inside of the planet carrier

[0056] sleeve process

[0057] flange

[0058] plain bearing ring

[0059] Damping element

[0060] Damping element

Claims

Patent claims 1. Planetary roller gear (1), with a planet carrier (10) in which several planets (6) with a pitchless profile are guided, which mesh with a likewise pitchless profile (11) of a nut (12), characterized in that a damping element (18, 24, 25) is inserted between the plain bearing elements (17) supporting the planets (6) and the planet carrier (10).

2. Planetary roller gear (1) according to claim 1, characterized in that the damping element (18) has a sleeve-shaped basic shape surrounding the plain bearing element (17).

3. Planetary roller gear (1) according to claim 1, characterized in that the damping element (24, 25) has a ring shape concentric with the central axis of the nut (12) and the planet carrier (10), wherein all the plain bearing elements (17) located on one and the same end face of the arrangement of all the planets (6) are held in the same damping element (24, 25).

4. Planetary roller gear (1) according to claim 3, characterized in that the damping element (24, 25) has a cylindrical sleeve extension (21) engaging in an annular groove of the planet carrier (10).

5. Planetary roller gear (1) according to claim 4, characterized in that the damping element (24, 25) contacts with its outer peripheral surface a bearing ring (18) of an axial roller bearing (13) which supports the nut (12) in the planet carrier (10).

6. Planetary roller gear (1) according to claim 3, characterized in that the damping element (24, 25) has a radially outwardly directed flange (22) lying against an inner surface (20) of the planet carrier (10).

7. Planetary roller gear (1) according to claim 6, characterized in that the flange (22) contacts a plain bearing ring (23) provided for mounting the nut (12) in the planet carrier (10).

8. Planetary roller gear (1) according to one of claims 1 to 7, characterized in that the planet carrier (10) is provided as its drive element.

9. Steering actuator comprising a planetary roller gear (1) according to claim 1.

10. Rear-axle steering of a motor vehicle comprising a steering actuator according to claim 9.

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