Rolling screw drive and method for assembling a rolling screw drive

Abstract

A rolling screw drive (1), in particular in the form of a planetary rolling screw drive, a roller screw drive, or an inverse roller screw drive, comprises a threaded spindle (2) with an external thread (5), a plurality of planets (4), and a spindle nut (3) with an internal profile (6). Each planet (4) has a profiled central section (7) which engages in the external thread (5) of the spindle nut (3), and two similarly profiled, thinner side sections (9) compared to the central section (7), each of which meshes with a section of the internal profile (6) of the spindle nut (3). End sections (11) of each planet (4) adjoining the side sections (9) are held in recesses (14) of separate guide disks (12, 13). Each recess (14) has a mounting retaining contour (15) and a separate operating retaining contour (16) for holding the planet (4).

Description

[0001] The invention relates to a rolling screw drive constructed according to the preamble of claim 1, suitable, for example, for use in an electromechanical actuator, in particular in the form of a planetary rolling screw drive, a roller screw drive, or an inverse roller screw drive. The invention further relates to a method for assembling a rolling screw drive.

[0002] A generic rolling screw drive, namely a planetary rolling screw drive, which is also generally referred to as a planetary rolling screw drive, is known, for example, from DE 10 2011 075 950 B4. The known planetary rolling screw drive has several elongated, groove-profiled planets, which are received at their respective ends in guide rings. Two separate guide rings may be present, which are not necessarily mirror images of each other. DE 10 2011 075 950 B4 further describes an embodiment in which the guide rings are connected to each other by webs.

[0003] A planetary roller screw drive described in WO 2011 / 113724 A1 has planets mounted in centering disks. Each centering disk has a corresponding number of planets distributed around its circumference with bores or slots into which the planets' pins engage. A preloading device keeps the planets engaged even when the planetary roller screw drive is unloaded, so that the conversion of a relative rotation between the nut and the lead screw of the planetary roller screw drive into an axial displacement between the aforementioned screw drive elements, i.e., the lead screw and the lead screw nut, occurs with very low slippage.

[0004] A roller screw drive disclosed in DE 10 2021 202 539 A1, like the devices according to documents DE 10 2011 075 950 B4 and WO 2011 / 113724 A1, comprises several rollers, i.e., planets, which have a flat profile, i.e., are provided with unhelical grooves. In the case of DE 10 2021 202 539 B4, a cage is configured to press a spindle of the roller screw drive into a radially centered position in a nut.

[0005] The invention is based on the objective of further developing rolling screw drives, which - for example in the form of planetary rolling screw drives - convert a rotation into a linear motion, compared to the prior art, particularly from a manufacturing technology perspective.

[0006] This problem is solved according to the invention by a rolling screw drive with the features of claim 1. In particular, the rolling screw drive is a planetary rolling screw drive. The problem is also solved by a method for mounting a rolling screw drive designed according to claim 8. Wherever a planetary rolling screw drive is mentioned in this text, the corresponding descriptions are transferable to other designs of rolling screw drives, provided no technical contradictions arise. Likewise, embodiments and advantages of the invention explained in connection with the mounting method also apply mutatis mutandis to the device according to the application, i.e., the rolling screw drive, and vice versa.

[0007] The planetary gear drive, or other rolling screw drive, comprises, in a basic design known per se, a threaded spindle with an external thread, a plurality of planets, and a spindle nut with an internal profile. Each planet, whose diameter is generally referred to as the roller diameter (Ro), has a profiled central section that engages with the external thread of the threaded spindle. In particular, the profile of the central section is groove-shaped, i.e., without a pitch. Adjacent to the central section, i.e., the section with diameter Ro, are two similarly profiled, in particular grooved, i.e., without a pitch, side sections of the planet, which are thinner than the central section. Each of these side sections meshes with a section of the internal profile of the spindle nut.The end sections of each planet, adjoining the two side sections, are held in recesses of separate guide discs.

[0008] According to claim 1, each recess formed in the guide disc for selectively holding the planet in different positions has a mounting holding contour and an operating holding contour separate from it.

[0009] The mounting retaining contour loses its function after the assembly of the roller screw drive, particularly a planetary roller drive, is complete. It is only used again during disassembly. It has been shown that by creating an additional mounting retaining contour, spaced apart from the operating retaining contour (where the end section of the planet is located during normal operation of the planetary roller drive), a significant simplification and increased reliability during assembly and, if necessary, disassembly can be achieved without requiring a substantial increase in space. The individual planets, generally referred to as rollers, can be moved from their mounting position (i.e., the position defined by the mounting retaining contour) to their operating position (i.e., the position defined by the operating retaining contour) by a purely radial displacement.Removing the planets from the guide discs is not necessary to switch between the mounting position and the operating position.

[0010] The application procedure for assembling a planetary roller drive or other rolling screw drive comprises the following steps: - Provision ◯ two threaded drive elements, namely a threaded spindle and a spindle nut, wherein one of the two threaded drive elements is provided as the drive element and the other threaded drive element as the output element of the rolling screw drive to be mounted, ◯ a plurality of elongated, profiled planets, which are intended for direct interaction with both threaded drive elements, as well as ◯ two guide discs, each designed to guide one end of each planet and having recesses into which the end of a planet can be optionally received in a mounting position or in an operating position spaced apart from it, - Formation of an assembly consisting of all planets and the two guide discs, with each planet initially being in the assembly position, - Assembling the aforementioned component with one of the two threaded drive elements, - Relocation of each planet from its assembly position to the operating position, - Completing the rolling screw drive by adding the second screw drive element.

[0011] There are therefore two different ways to form an assembly that includes the planets and the guide discs, and then to combine this assembly with one of the two threaded drive elements:

[0012] According to a first variant, the mounting and holding contours are located radially outside the operating holding contours. The planetary gears are initially inserted into the recesses of the guide discs in such a way that all end sections of the planetary gears are guided within the mounting and holding contours, i.e., in the radially outermost position. This forms an assembly into which the spindle can be inserted without any interfering edges and without any screwing movements. The arrangement, which in addition to the planetary gears and the guide discs includes one of the two threaded drive elements, in this case the lead screw, is called a component group to distinguish it from the previously given assembly, which does not yet include either of the two threaded drive elements. In short: The component group is created from the aforementioned assembly by adding one of the threaded drive elements.

[0013] Once the component group is assembled, the planets are pressed inwards, thus moving them into their operating position. The entire component group, now configured for operation, is then screwed into the second threaded drive element, in this case the lead screw nut. This completes the planetary gear set, apart from any seals and connecting or auxiliary elements, such as snap rings to secure the axial position of individual components. Alternatively, the planetary gear set can be completed by screwing the lead screw nut onto the previously assembled component group.

[0014] In this variant of the planetary gear set, where the mounting contours are located radially outside the operating contours (meaning the planets must be pressed inwards during assembly), the centers of the planets held by the mounting contours describe an outer mounting circle with a diameter DP_1a. The centers of the planets held by the operating contours describe an inner end-position circle with a diameter DP_2i. Simultaneously, a circular cylinder circumscribing the lead screw defines an interference edge circle with a diameter DP_S. Any contours that must be overcome when assembling the aforementioned assembly of planets and guide discs with the lead screw must be attributed to the lead screw in this case. The following relationships apply: DP_S<(DP_1a−Ro) DO_S>(DP_2i−Ro)

[0015] If the planetary gear unit, assembled as described (the first variant), needs to be disassembled, the entire component group, in this case a spindle-roller ring unit, must first be unscrewed from the spindle nut, also known as the nut ring. The planets can then be moved outwards into their mounting position with minimal force. Finally, the threaded spindle can be removed from the assembly that includes the guide discs and the planets. Alternatively, the threaded spindle can be unscrewed from the assembly while the planets are still in their operating position.

[0016] According to a second variant, the mounting and holding contours are located radially within the operating holding contours, relative to the central axis of the planetary gear unit. In this case, the pre-assembled unit is initially designed to be as slim as possible, meaning that a circle drawn through the central axes of all planets, lying in a plane perpendicular to the central axis of the entire assembly and thus of the subsequent planetary gear unit, has the smallest possible diameter. The slim assembly can be inserted into the spindle nut, again without any interfering edges, without having to rotate any of the assembly components or the spindle nut itself. Once the intended axial position of the assembly relative to the spindle nut is reached, the planets are pressed outwards into their operating position. Finally, the lead screw can be screwed into the assembly to complete the planetary gear unit.In this case, too, the planetary roller gear can be disassembled in reverse order.

[0017] In the second variant of the planetary gear drive, the centers of the planets held by the mounting contours describe an inner mounting circle with a diameter DP_1i, whereas the centers of the planets held by the operating contours describe an outer end-position circle with a diameter DP_2a. Furthermore, in the second variant, a circular cylinder inscribed in the spindle nut defines a disturbance edge circle with a diameter DP_M. Analogous to the definition of the disturbance edge circle around the threaded spindle, in the case of the disturbance edge circle defined by the spindle nut, interfering contours connected to the respective threaded drive element, here the spindle nut, must also be taken into account. This means that no interfering contours lie within the disturbance edge circle. The following relationships apply: (DP_1i+Ro) <DP_M DP_M<(DP_2a+Ro)

[0018] In both described variants, the difference between the diameter of the mounting circle and the diameter of the end position circle in the operational state of the planetary roller gear can, for example, correspond to at least 15% and at most 40% of the roller diameter of the planets. Likewise, in both variants, the mounting retaining contour and the operating retaining contour can form two detent positions, which can be changed by overcoming at least slight elastic restoring forces.

[0019] In modified versions, the device according to the application can, for example, be a roller screw drive in which each of the components – threaded spindle, rollers, and nut – has a thread. A design of the roller screw drive as an inverted roller screw drive is also possible. In this case, the rollers of the screw drive are held in an axially fixed position relative to the threaded spindle.

[0020] Two embodiments of the invention are explained in more detail below with reference to a drawing. This drawing shows: Fig. 1 Components to be assembled, namely two guide discs and an exemplary planet, of a rolling screw drive designed as a planetary rolling gear, Fig. 2 a detail of the arrangement according to Fig. 1 in frontal view, with the planet locked in a mounting position, Fig. 3 in a representation analogous Fig. 3 one of the two guide discs and the planet moved into the operating position, i.e. radially inwards, Fig. 4 and Fig. 5 in schematic side views the planetary gear with which also in the Fig. 2 and Fig. 3 visible planets in mounting or operating position, Fig. 6 and Fig. 7 geometric features of the planetary roller gear in the assembly process according to Fig. 1, wherein the planet shown as an example is in its assembly or operating position, Fig. 8 components, namely two guide discs and an exemplary planet, of another rolling screw drive designed as a planetary rolling gear, Fig. 9 a detail of a guide disc of the planetary roller gear according to Fig. 8 in perspective view, Fig. 10, Fig. 11 in views analogous Fig. 4 and Fig. 5 the planetary roller gear according Fig. 8 with the planet shown as an example in assembly or operating position, Fig. 12 - 14 geometric features of the planetary roller gear in the assembly process according to Fig. 8, wherein the planet shown in the figures is in a pre-assembly, an assembly, or an operating position.

[0021] Unless otherwise stated, the following explanations refer to both embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0022] A rolling screw drive, designated by reference numeral 1, is designed as a planetary roller drive in both embodiments. The planetary roller drive 1 is suitable, for example, for use in an electromechanical actuator (not shown). For the basic design and function of the planetary roller drive 1, reference is made to the prior art cited above.

[0023] The planetary roller screw drive 1 comprises a threaded spindle 2 and a spindle nut 3, which is also referred to as a nut ring or simply as a nut. The nut 3 can function as the drive element of the roller screw drive 1, while the threaded spindle 2 can be used as a rotationally fixed, sliding output element. Conversely, it is also possible to drive the threaded spindle 2 rotaryally and use the nut 3 as a linearly adjustable output element of the roller screw drive 1.

[0024] Between the threaded spindle 2 and the nut 3 are planetary gears 4, which are generally referred to as rollers. The threaded spindle 2 and the spindle nut 3 are collectively referred to as threaded drive elements.

[0025] The thread, i.e., external thread, of the threaded spindle 2 is designated by 5. The spindle nut 3 has a groove-shaped internal profile 6 in sections and can be made up of several parts, whereby in particular individual nut parts can be preloaded against each other in order to operate the rolling screw drive 1 with preload.

[0026] Each planet 4 has an elongated shape with graduated diameters. A central section 7 of the planet 4 represents its thickest section, which defines the diameter of the planet 4, referred to as the roller diameter Ro. The central section 7 is provided with a grooved profile 8, which, during normal operation of the planetary roller drive, engages in the external thread 5 of the threaded spindle 2.

[0027] On both sides of the central section 7, comparatively thin side sections 9 adjoin. The side sections 9 are each provided with a groove-shaped profile 10, which meshes with the internal profile 6 of the spindle nut 3 during operation of the roller screw drive 1. In each of the embodiments shown in the figures, the roller screw drive 1 comprises six planets 4. Likewise, embodiments with a different number of planets 4, in particular with at least three and at most twelve planets 4, are possible.

[0028] To adapt to the geometry of the external thread 5, at least individual profiles of 8 different planets 4 are offset from each other in the axial direction of the threaded spindle 2 and thus of the entire planetary gear set 1. In particular, three different planets 4 can exist, with a first group of three planets 4 being installed in a first orientation and a second group of three planets 4, which is composed in the same way as the first group of three, being installed in the planetary gear set 1 in the opposite orientation.

[0029] End sections 11 of each planet 4 connect to the side sections 9. In contrast to the central section 7 and the side sections 9, the end sections 11 have a smooth cylindrical shape. Each end section 11 is held in a separate guide disk 12, 13. In the exemplary embodiment according to the Fig. 1 to 7 a pair of identical guide discs 12 and in the embodiment according to 8 to 13 a pair of identical guide discs 13 are used.

[0030] Each guide disk 12, 13 has several recesses 14 corresponding to the number of planets 4. The recess 14 is contoured such that the planet 4 can be held either in an assembly holding contour 15 or in an operating holding contour 16, which is spaced radially away from the assembly holding contour 15 of the guide disk 12, 13 and thus of the entire planetary gear set 1 to be mounted. In all configurations, that is, as long as the planets 4 are in the assembly position with end sections 11 inserted into the assembly holding contours 15, as well as in the operational configuration in which the end sections 11 are guided by the operating holding contours 16, i.e., have assumed their operating position, the central axes of all planets 4 are aligned parallel to the central axis of the pair on guide disks 12, 13.By overcoming a small elastic restoring force, changes between the mounting position and the operating position are possible. The mounting holding contours 15 and the operating holding contours 16 thus represent detent contours.

[0031] In the exemplary embodiment according to the Fig. 1 to 7, the mounting retaining contours 15 are located radially outside the operating retaining contours 16. This means that for assembly purposes, as shown in the Fig. 1, Fig. 2, Fig. 4 and Fig. Figure 6 illustrates that the planets 4 are initially engaged so far outwards in the recesses 14 of the guide discs 12 that operation of the roller screw drive 1 would not yet be possible. An outer mounting circle MKa placed through the centers of all planets 4, which is Fig. The assembly shown in figure 6 has a diameter DP_1a. The arrangement of all planets 4 and both guide disks 12 is referred to as assembly 17. After assembly 17, as shown in the Fig. 1, Fig. 2, Fig. 4 and Fig. As can be seen in part in Figure 6, once the assembly has been completed, the threaded spindle 2 can be easily inserted into this assembly 17. A contact edge circle (SKS) must be taken into account, which defines the threaded spindle 2, in particular its external thread 5, including any other contours associated with the threaded spindle 2 that must be overcome during assembly. The diameter of the contact edge circle (SKS) is specified as DP_S.

[0032] The arrangement consisting of assembly 17 and threaded spindle 2 is referred to as component group 18. Starting from the in Fig. In the sketched form of component group 18, with planets 4 provisionally fixed in the mounting holding contours 15, the planets 4 are pressed radially inwards, so that the ones in the Fig. 3, Fig. 5 and Fig. Figure 7 illustrates the configuration of component group 18, with planets 4 finally guided in the operating holding contours 16. In this operational state, the centers of the planets 4 describe an end position circle EK, the diameter of which is given by DP_2i.

[0033] In the exemplary embodiment according to the Fig. For positions 1 to 7, in which the planets 4 are to be pressed from the outside in when changing from the assembly to the operating position, the following relations apply: DP_S<(DP_1a−Ro) DP_S>(DP_2i−Ro)

[0034] The exemplary embodiment according to the Fig. 8 to 14 differs from the embodiment according to the Fig. 1 to 7 are achieved by pressing the planets 4 from the inside out during assembly. Accordingly, the assembly holding contours 15 are located radially within the operating holding contours 16.

[0035] The assembly 17, formed from the planets 4 and the guide discs 13, initially exhibits the following: Fig. 12. The resulting constellation is referred to as the pre-assembly constellation. In this configuration, the planets 4 are tangent to the inner contours of the guide disk 13. A circle, designated TK, passing through the centers of the planets 4, has a diameter D_k. Starting from this pre-assembly position, the planets 4 are moved into the assembly position by overcoming moderate elastic restoring forces. Fig. 8, Fig. 10 and Fig. 13. The planets 4 are snapped into the mounting retaining contours 15. It is also possible to successively move the individual planets 4 from their respective pre-assembly position to the assembly position.

[0036] In the next step, the assembly 17 formed from the planets 4 and the two guide discs 13 is to be assembled with the spindle nut 3 to form a component group 18, as shown in Fig. 10 can be seen. The four planets initially remain in the Fig. 13. Mounting position shown as an example using a single planet 4. An inner mounting circle MKi placed through the centers of all planets 4, which is in Fig. The figure shown in 13 has a diameter DP_1i.

[0037] Furthermore, in Fig. Figure 13 shows a disturbance edge circle SKM, which is formed by the contours of the spindle nut 3 and possibly by contours of other parts connected to it, which may be touched during assembly, and has a diameter DP_M. As shown in Figure 13, a disturbance edge circle SKM is shown, which is formed by the contours of the spindle nut 3 and possibly by contours of other parts connected to it, which may be touched during assembly, and has a diameter DP_M. Fig. As can be seen from 13, the planets 4 lie within the disturbance edge circle SKM, so that the assembly 17 can be inserted into the spindle nut 3 by a purely linear movement.

[0038] After the assembly 17 has been positioned relative to the spindle nut 3 in the intended manner, the planets 4 are moved from the inside out into their operating position by overcoming moderate restoring forces, so that the arrangement follows the Fig. 11 and Fig. 14 results.

[0039] In the exemplary embodiment according to the Fig. The following relationships apply to numbers 8 to 14: (DP_1i+Ro) <DP_M DP_M<(DP_2a+Ro), where, in this case as well, the roller diameter Ro denotes the diameter of the planets 4. The diameter of the end position circle EK is, in the exemplary embodiment, according to the Fig. 8 to 14, in which the planets 4 are moved outwards during assembly, are indicated by DP_2a. Reference symbol list 1. Roller screw drive, planetary roller gear 2 threaded spindles 3 Spindle nut 4 Planet, Role 5 external threads 6 Internal profiling 7 Middle section 8 Profiling of the central section Section 9 10 Profiling the page section 11 Final Section 12 Guide disc, first embodiment ( Fig. 1 to 7) 13 Guide disc, second embodiment ( Fig. 8 to 14) 14 Exclusion 15 Mounting / holding contour 16 Operating stop contour 17 Assembly consisting of planets 4 and guide discs 12, 13 18 Component Group D_k Diameter of the circle TK DP_1a Diameter of the outer mounting circle DP_1i Diameter of the inner mounting circle DP_2i Diameter of the end position circle, with planets pushed radially inwards DP_2a Diameter of the end position circle, with planets pushed radially outwards DP_M Diameter of the interference edge circle of the spindle nut DP_S Diameter of the interference edge circle of the threaded spindle EK Endlagenkreis MKa outer assembly circle MKi inner assembly circle Ro roller diameter SKM interference edge circle of the spindle nut SKS interference edge circle of the threaded spindle TK circle with tangential contact of the planets on the guide disk

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