Planetary roller gear arrangement, method for producing planetary roller gear arrangement, and steering actuator

Abstract

The invention relates to a planetary roller gear arrangement (1), in particular for a steering actuator (10), comprising: a drive assembly (5) in which a plurality of planets (21, 22, 23) are guided, each having a groove-shaped profiled section (24); and a threaded spindle (2), which is provided as an output element and into which a central piece (25) of the planet (21, 22, 23) engages, while a lateral piece (26) of the planet (21, 22, 23), which is likewise profiled in a groove-shaped manner and is thinner than the central piece (25), engages with a profiled section (15) of a nut (11), which is rotatably mounted in the drive assembly (5). The drive assembly (5) has two planet carriers (6) which support the planets (21, 22, 23) and which rotate relative to each other such that each planet (21, 22, 23) is inclined by a defined angle (alpha) relative to a straight line which is parallel to the central axis (MA) of the threaded spindle (2) and on which the center of the respective planet (21, 22, 23) lies.

Description

Technical Field

[0001] According to the preamble of claim 1, the invention relates to a planetary roller gear arrangement which is suitable for use in an electromechanical actuator and has a plurality of groove-shaped profiled planetary elements. The invention also relates to a steering actuator having a planetary roller gear arrangement. Furthermore, the invention relates to a method for producing a planetary roller gear arrangement. Background Art

[0002] For example, a universal planetary roller gear is known from DE 10 2021 104 646 A1. The known planetary roller gear, i.e. a rotary linear gear, is part of a steering actuator for a rear axle steering system of a motor vehicle. The rotary drive-side gearing component of the known planetary roller gear is supported on one side on a first housing component of the steering actuator and on the other side on a second housing component of the steering actuator. In the case of DE 102 021 104 646 A1, a pair of angular contact rolling bearings is provided, which are used to mount the aforementioned gearing components. The threaded spindle as the output element of the known steering actuator is guided and connected to a push rod in a manner that is fixed against rotation.

[0003] Another planetary roller gear arrangement having the features of the preamble of claim 1 is disclosed in DE 10 2021 104 649 A1. In this case, the planetary roller gear arrangement is also a component of a steering actuator intended for use in a rear axle steering system of a motor vehicle. The steering actuator according to DE 10 2021 104 649 A1 has two housing parts which form a cavity and are connected to each other by means of a press fit.

[0004] In the case of DE 10 2021 104 646 A1 and in the case of DE 10 2021 104 649 A1, a planetary roller gear is provided which is designed as a pitch-precise planetary screw drive. The advantage of this screw drive, which is also referred to as SPWG for short, compared to a planetary roller gear with a driven spindle nut is that, as the term "pitch-precise" expresses, there is a precisely defined relationship between the angular position of the drive element and the feed of the driven element, i.e. the threaded spindle. In this respect, less extreme transmission ratios can be accepted compared to a planetary screw drive with a driven spindle nut. The terms planetary roller gear and planetary screw drive are used synonymously.

[0005] The actuator for a steering device of a motor vehicle disclosed in DE 10 2020 131 828 A1 also has a planetary screw drive as a gear mechanism, which converts a rotation into a linear motion. The screw drive according to DE 10 2020 131 828 A1 is mounted in a housing by means of a rolling bearing. The rollers of the rolling bearing roll on an elastically deformable thrust washer.

[0006] Compared to the aforementioned prior art, the present invention is based on the object of further developing a planetary roller gear arrangement which is suitable for use in a steering actuator, in particular for a rear-axle steering system, wherein a particularly advantageous tribological behavior is sought for a given installation space. Summary of the invention

[0007] According to the invention, this object is achieved by a planetary roller gear having the features of claim 1. The planetary roller gear can be produced using a method according to claim 9 and is particularly suitable for use in a steering actuator according to claim 10. The embodiments and advantages of the invention explained below in conjunction with the production process also apply analogously to the device, i.e. the planetary roller gear and the steering actuator, and vice versa.

[0008] With a basic design known per se, a planetary roller gear comprises a drive assembly in which a plurality of elongated planetary elements aligned approximately parallel to the center axis of the gear assembly are guided. By definition, the drive assembly is formed entirely or partially by a cage guiding the planetary elements. Each planetary element has sections of different diameters, wherein groove-shaped, i.e. pitch-free profiled sections are formed. A threaded spindle serves as a displaceable output element of the planetary roller gear, the center piece of the planetary element, i.e. the central groove-shaped profiled section, engaging in the thread of the threaded spindle, while the side pieces of the planetary element, which are also profiled in a groove-shaped manner and have a smaller diameter than the center piece, mesh with the profiled section of a nut, i.e. the spindle nut, which is rotatably mounted in the drive assembly.

[0009] The drive assembly of the planetary roller gear according to the invention has two planet carriers, which support the planets and are formed essentially or completely in a mirror-image manner and rotate relative to each other so that each planet is tilted by a defined angle relative to a straight line, which is parallel to the center axis of the threaded spindle and on which the center of the respective planet lies. The planet carriers form part of the aforementioned cage, which is a drive-side element of the planetary roller gear. The angle by which the two planet carriers rotate relative to each other generally does not correspond to the tilt angle of the planets.

[0010] The invention is based on the consideration that the planets of a planetary roller gear can in principle be guided through a gap in two planet carriers, wherein the two planet carriers can be formed in a substantially disk-shaped manner and arranged parallel to one another. The given gap together with the possible flexibility of the planet carriers leads to a constraint on the planets, which constraint can have an adverse effect on wear depending on the operating conditions. In addition, the constraint on the planets can lead to different mechanical loads being subjected to different planets of the gear arrangement. According to conventional, undisclosed methods, an attempt can be made to offset the described disadvantages by guiding the planets in a more precise manner so as to allow at most the slightest deviation of the planets from their alignment parallel to the thread spindle.

[0011] The solution according to the invention deliberately avoids this approach and instead provides a defined non-parallel arrangement of the planets relative to the central axis of the threaded spindle and thus relative to the central axis of the entire planetary roller gear device. Surprisingly, it is the deviation of the alignment of the substantially bolt-shaped planets from an arrangement parallel to the central axis of the entire gear device that contributes to a more uniform contact pattern and thus significantly reduced wear.

[0012] According to one possible embodiment, the two planet carriers have a receiving portion provided for sliding bearing of the non-profiled end pins of the planets, which receiving portion is inclined to the same extent as the planets relative to a plane applicable to the respective planet carrier and orthogonal to the center axis. By precisely adapting the receiving portion to the inclined position of the center axis of the planets, edge loads on the planet carriers or other load peaks that could lead to material removal on the planet carriers can be avoided as far as possible. This is particularly important in embodiments in which the planet carriers are made of plastic.

[0013] A further possible development is that the receptacle in which the planets are guided on both sides is formed by a sliding bushing integrated into the planet carrier, which can be displaced to a limited extent in its radial direction. In contrast to the bearing of the sliding bushing, which includes a degree of freedom in the radial direction, the receptacle formed in the sliding bushing for the end piece of the planet can be circular, so that the aforementioned degree of freedom is omitted in this regard, which is advantageous in terms of lubrication.

[0014] Regardless of the specific design of the receptacle for the planet, the planet is tilted, ie constrained, in particular tilted by an angle of min. 0.1° and max. 3.0°, for example by an angle of min. 0.5° and max. 1.0°.

[0015] According to various possible embodiments in which there is an even number of planets, for example twelve planets, the planets can be divided into two equally large planet subgroups, wherein the following relationship applies to the first subgroup:

[0016] α=(tan -1(P / (π·D))) / 2±(tan -1 (P / (π·D))) / 4+(tan -1 (P / (π·D))) / 8,

[0017] Among them, α indicates the inclination angle of the planet, P indicates the pitch of the thread of the main shaft, and D indicates the pitch circle diameter of the main shaft.

[0018] In this case, the following relationship applies for a second planetary set of the same size:

[0019] α=(tan -1 (P / (π·D))) / 2±(tan -1 (P / (π·D))) / 4-(tan -1 (P / (π·D))) / 8,

[0020] This means that not all planets of a gear arrangement have to be tilted to exactly the same degree.

[0021] The thread of the threaded spindle may be a single-start thread or a multi-start thread, in particular a double-start thread.In various possible embodiments of the planetary roller gear arrangement, the number of planets is typically between six and eighteen.

[0022] Regardless of the number of planets, the method for producing a planetary roller gear arrangement generally comprises the following steps:

[0023] - providing a threaded spindle, a plurality of elongated stepped and bolt-shaped planets with a groove-shaped profile, and a drive assembly comprising two substantially annular planet carriers, wherein each planet carrier has a number of receptacles corresponding to the number of planets for receiving in each case an end pin of a planet,

[0024] - providing a multi-part nut provided with a groove-shaped profiled section provided for contacting the planetary element and two rolling bearings, in particular rolling bearings in the form of ball bearings or roller bearings, provided for mounting the nut in the drive assembly,

[0025] - The planets, nuts and rolling bearings are inserted into the drive assembly, and the threaded spindle is arranged concentrically in the drive assembly so that each planet is tilted by an angle relative to a plane through the relative rotation between the two planet carriers, in which the center of the corresponding planet and the center axis of the threaded spindle are located, and the angle is at least 0.1° and at most 3.0°.

[0026] The relative rotation between the two planet carriers is maintained throughout the service life of the planetary roller gear arrangement.

[0027] The planetary roller gear arrangement is particularly suitable for use as a rotary linear gear arrangement in a steering actuator of a motor vehicle. A steering actuator can basically be designed as an actuator for steering the rear wheels of a vehicle or as an actuator for steering the front wheels of a vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Several exemplary embodiments of the present invention are explained in more detail below with the aid of the accompanying drawings. In the drawings:

[0029] Figure 1 shows components of a planetary roller gear arrangement used in an actuator of a rear axle steering system of a motor vehicle,

[0030] Figure 2 A planetary roller gear arrangement is shown in cross section,

[0031] Figure 3 The components of a planetary roller gear arrangement are shown in front view,

[0032] Figure 4 shows details of a planet carrier suitable for use in a planetary roller gear arrangement for a steering actuator,

[0033] Figure 5 The three-dimensional diagram shows Figure 1 and Figure 2 The planet carrier of the device. DETAILED DESCRIPTION

[0034] Unless otherwise specified, the following description relates to all exemplary embodiments. In all figures, components that correspond to each other or have substantially the same function are denoted by the same reference numerals.

[0035] The planetary roller gear arrangement 1 is provided for use in a steering actuator 10 of a rear axle steering system of a motor vehicle. With regard to the basic function of a planetary roller gear arrangement in an actuator of a rear axle steering system, reference is made to the prior art cited at the outset.

[0036] The planetary roller gear 1 serves to move a threaded spindle 2, whose thread is indicated by 3, in the transverse direction of the vehicle. The center axis of the threaded spindle 2 and therefore of the entire planetary roller gear 1 is indicated by MA. The end section 4 of the threaded spindle 3 is articulated to other chassis elements, not shown, in order to change the steering angle of the rear wheels of the motor vehicle in a manner known per se.

[0037] The input side components of the planetary roller gear device 1 are collectively referred to as the drive component 5. The drive component 5 includes two planet carriers 6 that are basically in the shape of an annular disk, two retaining racks 7 that are also in the shape of an annular disk, and a sleeve 8. Figure 2As can be seen, the sleeve 8, which is concentric with the center axis MA, has a constriction on its outer peripheral surface, in which the external toothing 9 is formed. An electrically driven toothed belt runs on the external toothing 9 as part of a belt drive connected upstream of the planetary roller gear 1. The shaft of the electric motor, not shown, which drives the belt, is aligned in the z direction, i.e. parallel to the center axis MA. The x-axis and the y-axis span a plane, with the center axis MA representing the surface normal relative to this plane.

[0038] A cavity is formed between the threaded spindle 2 and the sleeve 8, in which the other components of the planetary roller gear 1 are arranged. These components include a nut 11, which comprises two nut parts 12, 13 screwed together, and a locking nut 14. The nut parts 12, 13 each have a groove-shaped profile section 15. The entire nut 11, i.e. the spindle nut, is mounted in the drive assembly 5 by means of two rolling bearings 16, which in this case are axial rolling bearings. Each rolling bearing 16 has a roller as a rolling element 17, which is guided in a rolling bearing cage 18. The rolling elements 17 roll on an inner angle ring 19 and an outer angle ring 20, wherein the inner angle ring 19 is in contact with one of the two nut parts 12, 13, and the outer angle ring 20 is in contact with one of the cage discs 7 formed in a mirror-image manner to each other.

[0039] Furthermore, rod-shaped planetary parts 21, 22, 23 of the first, second and third types are arranged in the drive assembly 5 in the cavity around the threaded spindle 2. Each planetary part 21, 22, 23 has a groove-shaped, i.e. pitch-free profiled section 24. The profiled sections 24 can be found both in the central part 25 and in the adjacent side parts 26.

[0040] The side pieces 26 of the planets 21, 22, 23 have the same cylindrical basic shape as their central piece 25, but exhibit a smaller diameter. The central piece 25 of each planet 21, 22, 23 is in contact only with the thread 3 of the spindle 2, while the profiled section 24 of the side piece 26 engages only with the profiled section 15 of the nut 11. For the two end faces of each planet 21, 22, 23, it ends in the form of a non-profiled end pin 27, which directly adjoins one of the two side pieces 26.

[0041] The end pin 27 is mounted in a sliding manner in a receiving portion 28 of the planet carrier 6. The individual planets 21, 22, 23 differ from one another in that the profiled sections 24 of the center piece 25 are slightly offset from one another in the axial direction, i.e. in the z direction, in order to accommodate the thread 3. In the present case, the thread 3 is designed as a double-start thread with a pitch P and a pitch diameter D, i.e. a pitch diameter. The planets 21, 22, 23 are each inserted into the drive assembly 5 twice in a first orientation and twice in the opposite orientation, i.e. rotated 180°. This means that there are a total of twelve planets 21, 22, 23 between the threaded spindle 2 and the nut 11.

[0042] The relationship between a specific rotation of the planet carrier 6 about the center axis MA and the resulting displacement of the thread spindle 2 guided in a rotationally fixed manner along the center axis MA is clearly defined, just like a simple feed thread, which is synonymous with the pitch-precise nature of the planetary roller gear 1. During operation of the planetary roller gear 1, the rolling of the planets 21, 22, 23 also causes the nut 11 to rotate, wherein this rotation is not utilized in any way. The rolling bearing 16 serves only to transmit axial forces during operation of the planetary roller gear 1.

[0043] Axial forces are also transmitted between the center piece 25 of the planets 21, 22, 23 and the threaded spindle 2. In order to optimize the interaction between the planets 21, 22, 23 and the thread 3, each planet 21, 22, 23 is tilted at an angle α. This tilting relates to the plane in which both the center axis MA and the center of the respective planet 21, 22, 23 lie. If the angle α is zero, the longitudinal axes of the planets 21, 22, 23 will be aligned parallel to the center axis MA. The angle α is in practice in the range between 0.5° and 1°. Figure 1 , the angle α is shown in an exaggerated manner.

[0044] In accordance with Figure 1 In the exemplary embodiment of FIG. 5 , the following relationship applies to the six planets 21 , 22 , 23 inserted into the drive assembly 5 in the first orientation:

[0045] α=(tan -1 (P / (π·D))) / 2±(tan -1 (P / (π·D))) / 4+(tan -1

[0046] (P / (π·D))) / 8

[0047] The following relationship applies to the other six planets 21 , 22 , 23 , i.e. the planets 21 , 22 , 23 inserted into the drive assembly 5 in the opposite orientation:

[0048] α=(tan-1 (P / (π·D))) / 2±(tan -1 (P / (π·D))) / 4-(tan -1

[0049] (P / (π·D))) / 8

[0050] The constraint of the planets 21, 22, 23 indicated by the angle α with the relative rotation between the two planet carriers 6 contributes significantly to the uniform introduction of forces into the two planet carriers 6 during operation of the planetary roller gear 1. This means that at least approximately the same torque, i.e. the drive torque, acts on the two planet carriers 6.

[0051] Like the inclination angle α of the planetary element 21, the inclination of the receiving portion 28 is Figure 1 The Figure 5 As indicated in FIG. 1 , there are two sets of three opposite receiving portions 28 into which the planets 21, 22, 23 are to be inserted in a first orientation and two sets of three opposite receiving portions 28 into which the associated planets 21, 22, 23 are to be inserted in an opposite orientation in the planet carrier 6. The orientation of the planets 21, 22, 23 can be visually determined by means of a marking on one of the end faces of each planet 21, 22, 23, as shown in FIG. Figure 3 shown.

[0052] Figure 4 Shown is suitable for use according to Figure 1 A modification of the planet carrier 6 in a planetary roller gear 1 of FIG. 1 is provided. In this case, the planet carrier 6 has a total of twelve elongated holes 29, in each of which a sliding bushing 30 is guided displaceably in the radial direction of the planet carrier 6 and thus in the radial direction of the entire planetary roller gear 1 to a limited extent. In this case, the receiving portion 28 for the end pin 27 of one of the planetary parts 21, 22, 23 is formed by the sliding bushing 30.

[0053] and Figure 1 The same is true in Figure 4 In the case of , the center axis of each receiving portion 28 is also inclined at an angle α relative to a straight line parallel to the center axis MA of the threaded spindle 2. Due to the circular cross-sectional shape of the receiving portion 28 formed as an orifice in the sliding bushing 30, the conditions for forming a stable lubricating film between the end pin 27 and the receiving portion 28 are particularly good compared to a groove-shaped receiving portion.

[0054] Reference numerals list

[0055] 1 Planetary roller gear

[0056] 2 Threaded spindle

[0057] 3 Thread

[0058] 4 End section of threaded spindle

[0059] 5 Drive components

[0060] 6 Planet carrier

[0061] 7 Cage plate

[0062] 8 Sleeve

[0063] 9 External teeth

[0064] 10 Steering actuator

[0065] 11 Nut

[0066] 12 Nut part

[0067] 13 Nut part

[0068] 14 Lock nut

[0069] 15 Grooved special-shaped section of the nut part

[0070] 16 Rolling bearings

[0071] 17Rolling elements, rollers

[0072] 18 Rolling bearing cage

[0073] 19 inner corner ring

[0074] 20 External Angle Ring

[0075] 21. Type I planetary components

[0076] 22. Second type of planetary parts

[0077] 23. The third type of planetary parts

[0078] 24. Groove-shaped profiled section of planetary component

[0079] 25 Centerpiece

[0080] 26 Special shaped side pieces

[0081] 27 Non-profiled end pins

[0082] 28 Receptacle for planetary element

[0083] 29 Long hole

[0084] 30 Sliding bushing

[0085] α Angle

[0086] D Diameter

[0087] MA Center Axis

[0088] P pitch.

Claims

1. A planetary roller gear device (1), comprising a drive assembly (5), in which a plurality of planetary parts (21, 22, 23) are guided, each planetary part having a groove-shaped profiled section (24), and comprising a threaded spindle (2), which is arranged as an output element, and in which a center piece (25) of the planetary parts (21, 22, 23) engages, while a lateral piece (26) of the planetary parts (21, 22, 23) which is also profiled in a groove-shaped manner and thinner than the center piece (25) meshes with a profiled section (15) of a nut (11), which is rotatably mounted in the drive assembly (5), characterized in that The drive assembly (5) has two planet carriers (6), which support the planetary elements (21, 22, 23) and rotate relative to each other so that each planetary element (21, 22, 23) is inclined at a defined angle (α) relative to a straight line, which is parallel to the central axis (MA) of the threaded spindle (2) and the center of the corresponding planetary element (21, 22, 23) is located on the straight line.

2. The planetary roller gear device (1) according to claim 1, characterized in that The planet carrier (6) has a receiving portion (28) arranged to slidingly support the non-profiled end pins (27) of the planetary parts (21, 22, 23), and the receiving portion is inclined to the same extent as the planetary parts (21, 22, 23) relative to a plane applicable to the corresponding planet carrier (6) and orthogonal to the central axis (MA).

3. The planetary roller gear device (1) according to claim 1 or 2, characterized in that: The receiving portion (28) is formed by a sliding bushing (30) which is integrated into the planet carrier (6) and is displaceable to a limited extent in its radial direction.

4. The planetary roller gear device (1) according to any one of claims 1 to 3, characterized in that The inclination angle (α) of the planets (21, 22, 23) is at least 0.1° and at most 3.0°.

5. The planetary roller gear device (1) according to any one of claims 1 to 4, characterized in that The threaded spindle (2) has a double-start thread (3).

6. The planetary roller gear device (1) according to any one of claims 1 to 5, characterized in that A number of planetary elements (21, 22, 23) divisible by two is installed in the drive assembly (5), wherein for a first subset of the planetary elements (21, 22, 23), the following relationship applies: α=(tan -1 (P / (π·D))) / 2±(tan -1 (P / (π·D))) / 4+(tan -1 (P / (π·D))) / 8 And for the remaining equally large subgroups of planetary elements (21, 22, 23), the following relationship applies, α=(tan -1 (P / (π·D))) / 2±(tan -1 (P / (π·D))) / 4-(tan -1 (P / (π·D))) / 8 Therein, P indicates the thread pitch, and D indicates the thread pitch diameter of the thread (3) of the thread spindle (2).

7. The planetary roller gear device (1) according to any one of claims 1 to 6, characterized in that Two axial rolling bearings (16) are provided for mounting the nut (11) in the drive assembly (5).

8. The planetary roller gear device (1) according to any one of claims 1 to 7, characterized in that The planet carrier (6) is designed as a plastic part.

9. A method for producing a planetary roller gear device (1), the method comprising the following steps: - providing a threaded spindle (2), a plurality of planets (21, 22, 23) and a drive assembly (5) comprising two planet carriers (6), wherein each planet carrier (6) has a number of receptacles (28) corresponding to the number of planets (21, 22, 23) for receiving in each case an end pin (27) of a planet (21, 22, 23), - providing a multi-part nut (11) arranged to contact the planetary elements (21, 22, 23) and two rolling bearings (16) arranged to mount the nut (11) in the drive assembly (5), - The planetary parts (21, 22, 23), the nut (11) and the rolling bearing (16) are inserted into the drive assembly (5), and the threaded spindle (2) is arranged concentrically in the drive assembly (5), so that each planetary part (21, 22, 23) is inclined by an angle (α) relative to a plane due to the relative rotation between the two planet carriers (6), and the center of the corresponding planetary part (21, 22, 23) and the center axis (MA) of the threaded spindle (2) are located in the plane, and the angle is at least 0.1° and at most 3.0°.

10. A steering actuator (10) comprising an electrically driven planetary roller gear device (1) designed according to claim 1.

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