Planetary roller gear, steering actuator and rear axle steering

Abstract

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

Description

[0001] 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.

[0002] A planetary gear system of this type 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 gradient-preserving planetary gear systems, in particular for electromechanical actuators of rear axle steering systems.

[0003] Another planetary gear unit is disclosed in DE 10 2009 040 606 B4. This planetary gear unit is equipped with a length measuring system. In this case, a sensor of the length measuring system is connected to a spindle nut.

[0004] Planetary roller gears with a multi-part nut are known, for example, from DE 10 2013 213 704 A1 and from DE 10 2018 122 714 A1. A planetary roller gear with an elastic nut is disclosed in DE 10 2010 011 821 B4.

[0005] 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 documents DE 10 2022 110 510 A1 and DE 10 2018 129 119 A1.

[0006] Planetary gear units are generally designed to convert rotation into linear motion, and are capable of generating considerable axial forces despite their compact external dimensions. The individual planets of a planetary gear unit, each with a flat profile, mesh with a single- or multi-start thread on a threaded spindle, resulting in an axial offset between the planet profiles. Therefore, the precise guidance of the planets within the planetary gear unit is of particular importance. All planets contact a nut, which can be of a single or multiple component.

[0007] The invention is based on the objective of providing a planetary gear unit that is further developed compared to the prior art, compact and easy to manufacture, 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.

[0008] This problem is solved according to the invention by a planetary gear unit with the features of claim 1. The planetary gear unit 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 for the rear axle steering of a motor vehicle.

[0009] The planetary gear drive comprises, in a basic design known per se, a planet carrier in which several planets with a flat profile are guided and mesh with a similarly flat profile of a nut. According to claim 1, a damping element is inserted between the sliding bearing elements that support the planets and the planet carrier.

[0010] The damping elements, as specified in the application and inserted between the two unprofiled ends of each planet and the planet carrier, are not only compatible with the required precise guidance of the planets, but even promote self-alignment of the planets. The acoustic behavior of the planetary gear drive is positively influenced by the damping elements.

[0011] In one possible design of the planetary roller gear, each damping element has a sleeve-shaped base that surrounds the associated sliding bearing element. The width of the damping element, measured in the axial direction of the planet, can correspond to the width of the sliding bearing element.

[0012] Other designs of the planetary gear system provide that the damping element has a ring shape concentric with the central axis of the nut and the planet carrier, with all sliding bearing elements located on one and the same end face of the planetary assembly being held in the same damping element. In such cases, there is thus a pair of damping elements, with the planets arranged between the two ring-shaped damping elements.

[0013] Such designs include, for example, variants of the planetary gear system in which the damping element has a cylindrical sleeve extension that engages 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 central axis of the planetary gear system, on whose surface the central 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, which supports the nut in the planet carrier. The axial roller bearing can be designed, in particular, as an axial roller bearing or an axial needle bearing.

[0014] Another variant, belonging to the same group of designs, features a damping element with a radially outward-facing flange that rests against an inner surface of the planet carrier. In this variant, the flange contacts, for example, a sliding bearing ring intended for supporting the nut in the planet carrier.

[0015] There is no necessary relationship between the described design options for the pair of damping elements and the rolling or sliding bearings provided for supporting the nut in the planetary carrier. For example, it is possible to combine a damping element with a sleeve extension with a sliding bearing between the nut and the planetary carrier. Similarly, a bearing ring of a rolling bearing that supports the nut in the planetary carrier may abut a flange of the damping element.

[0016] Finally, a damping element, which has both a sleeve extension and a radially outwardly directed flange, can optionally be combined with either a rolling bearing or a plain bearing, with the aforementioned bearing being provided for supporting the nut of the planetary gear unit in the planet carrier. Regardless of the geometry of the damping elements, assemblies comprising at least one plain bearing element in addition to the damping 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.

[0017] In all the designs described above, the planet carrier can be the driven element of the planetary gear drive. The planetary gear drive is thus designed as a pitch-preserving screw drive. The nut functions neither as a driving nor a driven element. A less extreme gear ratio compared to planetary gear drives with a driven nut or threaded spindle is accepted.

[0018] 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 system for steering the front wheels of a vehicle. Furthermore, applications in brake, clutch, or transmission actuators are also possible.

[0019] Several embodiments of the invention are explained in more detail below with reference to a drawing. These drawings show, in some cases in a simplified form: Fig. 1 Components of a planetary roller gear with damped planets in side view, Fig. 2 the arrangement according Fig. 1 in front view, Fig. 3. Sectional view of a planetary roller gear with a roller bearing between a planet carrier and a nut, Fig. 4 in a representation analogous Fig. 3 a planetary roller gear with a sliding bearing between a planet carrier and a nut, Fig. 5 one for use in planetary gear sets according to the Fig. 1, Fig. 2, Fig. 3 to Fig. 4 sliding rings provided.

[0020] Unless otherwise stated, the following explanations apply to all embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0021] A planetary gear set, designated by reference numeral 1, comprises a threaded spindle 2, the thread of which is designated 3. Profiles 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 transitions into two relatively thin side sections 8, which are provided with a profile 5. All profiles 4, 5 of the planet 6 are of zero pitch.

[0022] Following the two side sections 8, each planet 6 terminates in a smooth cylindrical end section 9. The end sections 9 are mounted in a planet carrier 10 in a manner described in more detail below.

[0023] During operation of the planetary 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 that are also without a pitch. The nut 12 can be made in one or more parts, whereby in the case of a multi-part design the nut parts can be preloaded against each other.

[0024] The nut 12 is mounted 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, the transmission of torque via the nut 12 is not intended in this case. Instead, an outer sleeve 15, which is rigidly connected to the planet carrier 10, serves this purpose. The outer sleeve 15 has a toothed section 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 drive element, namely a belt. Thanks to the driven planet carrier 10, the planetary gear set 1 is designed as a pitch-preserving screw drive (SPWG).

[0025] For mounting the planets 6 in the planet carrier 10, sliding sleeves 17 of uniform shape are provided in the exemplary embodiments, into which the end sections 9 of the planets 6 are inserted. Damping elements 18, 24, 25 are in all cases connected between the sliding sleeves 17, i.e., sliding bearing elements, and the planet carrier 10. The damping elements 18, 24, 25 can be manufactured, in particular, from an elastomer.

[0026] In the exemplary embodiment according to the Fig. 1 and Fig. 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 gear train 1, corresponding to the width of the sliding sleeves 17. Each end section 9 of each planet 6 is assigned a separate damping element 18.

[0027] The damping elements 18, 24, 25 positively influence the noise characteristics of the planetary gear set 1 and contribute to the self-alignment of the planets 6 during operation of the planetary gear set 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 gear set 1, in particular the planets 6 including their bearings, as well as the planetary gear set 1 as a whole, including the threaded spindle 2.

[0028] In terms of design Fig. The bearing 13, which supports the nut 12 in the planet carrier 10, is designed as a rolling bearing, specifically an axial roller bearing. A bearing ring designated 19 contacts both an inner surface of the planet carrier 10, designated 20, and the damping element designated 24. The damping element 24 is ring-shaped, and its central axis coincides with the central axis of the entire planetary gear set 1. All end sections 9, located on the same end face of the planetary gear set 6, are held in the same damping element 24. The number of sliding sleeves 17 inserted into the damping element 24 corresponds to the number of planetary gear sets 6. Thus, the planetary gear sets 6 are guided in a pair of damping elements 24.

[0029] To anchor each damping element 24 in the planet carrier, the damping element 24 has, in the case of Fig. 3 on its side facing the planet carrier 10 a cylindrical sleeve extension 21 which is inserted into a recess designed as an annular groove on the inside 20 of the planet carrier 10.

[0030] Also in the embodiment according to Fig. 4 is a ring-shaped damping element, here designated 25. The damping element 25 has a radially outwardly directed flange 22. The flange 22 rests on one side against the inner surface 20 of the planet carrier 10 and on the other side contacts a sliding 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 sliding bearing ring 23 also acts as a damping element of the planetary gear 1.

[0031] In the embodiments according to the Fig. 3 and Fig.4 The 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 makes a further significant contribution to noise reduction and wear reduction.

[0032] In all embodiments, assemblies consisting of 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. Reference symbol list 1 planetary roller gear 2 threaded spindles 3 threads 4 Profiling the central section of a planet 5 Profiling the side section of a planet 6 Planet 7 Middle section Section 8 9 Final Section 10 planetary carriers 11 Profiling the mother 12 Mother 13. Bearings, rolling bearings 14 Bearing, plain bearing 15 Outer sleeve 16 gear teeth 17 Sliding sleeve, sliding bearing element 18 damping element 19 bearing ring 20 Inside of the planetary carrier 21. Sleeve extension 22 flange 23 Plain bearing ring 24 damping element 25 damping element

Claims

Planetary gear set (1), with a planet carrier (10) in which several pitchless profiled planets (6) are guided, which mesh with a pitchless profile (11) of a nut (12), characterized in that a damping element (18, 24, 25) is inserted between the sliding bearing elements (17) supporting the planets (6) and the planet carrier (10). Planetary roller gear (1) according to claim 1, characterized in that the damping element (18) has a sleeve-shaped basic form surrounding the sliding bearing element (17). Planetary roller gear (1) according to claim 1, characterized in that the damping element (24, 25) has a ring shape concentric to the central axis of the nut (12) and the planet carrier (10), wherein all sliding bearing elements (17) located on one and the same end face of the arrangement of all planets (6) are held in the same damping element (24, 25). 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). Planetary roller gear (1) according to claim 4, characterized in that the damping element (24, 25) contacts with its outer circumferential surface a bearing ring (19) of an axial bearing (13) which supports the nut (12) in the planet carrier (10). Planetary gear unit (1) according to claim 3, characterized in that the damping element (24, 25) has a radially outwardly directed flange (22) abutting an inner side (20) of the planet carrier (10). Planetary roller gear (1) according to claim 6, characterized in that the flange (22) contacts a sliding bearing ring (23) provided for the storage of the nut (12) in the planet carrier (10). 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. Steering actuator comprising a planetary roller gear (1) according to claim 1. Rear axle steering of a motor vehicle, comprising a steering actuator according to claim 9.

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