FR3095486A1 - SATELLITE SCREW MECHANISM - Google Patents

Abstract

A satellite roller screw mechanism (100) comprising a screw (110) with an external thread (110F); a nut (130) coaxially surrounding the screw and provided with an internal thread (130F); rollers (120) each provided with an external thread (120F) and interposed between the screw and the screw and the nut, each roller having ends each provided with an external toothing preceded by a cylindrical seat of identical diameter to the tooth head diameter; open guides (150) comprising open circular notches in the shape of a "C", rounded at their ends, serving as a guide and positioning bearing for the rollers, the cylinder seats of which act as journals (120T) rotating inside the notches of said guides in such a way that the opening of at least one circular notch is strictly less than the journal diameter of the rollers and that it is not necessary to resort to an additional tool to ensure the maintenance of the rollers in the axial position, radial and angular, when mounting or removing the screw of the planet roller mechanism (100). Figure to be published: Fig. 1A

Description

SATELLITE ROLLER SCREW MECHANISM

The present invention relates to the field of satellite roller screws.

A satellite roller screw mechanism typically comprises a screw (male part) provided with an external thread, a nut (female part) coaxially surrounding the screw and provided with an internal thread, rollers each provided with an external thread and interposed between the external thread of the screw and the internal thread of the nut; which rollers are grouped together and guided by roller holders commonly called guides or spacer rings, which are mounted coaxially to the screw between it and the nut.

In the case of a so-called “standard” satellite roller screw, the guides are mounted in such a way as to form, with the nut and the rollers, a mechanical subassembly that is entirely separable from the screw and capable of moving axially along it. -this. Whereas in the case of a so-called "reversed" satellite roller screw, the guides are mounted in such a way as to form with the screw and the rollers a mechanical sub-assembly which is entirely separable from the nut and can move axially at the interior of it.

US patent 9267587 B2 discloses roller ends made of journals which cooperate with circular orifices acting as bearings, which orifices are arranged in guides each blocked or immobilized in translation, towards the outside of the nut, by a ring rubber band or a circlip. Such guides maintain the rollers in the axial, radial and angular position depending on whether the nut or screw is removed or inserted, depending on the type of planetary roller screw mechanism, during assembly or disassembly operations.

Thus, the function of the guides is twofold: to hold the rollers in position and to permanently ensure between the latter an identical angular spacing over time.

Documents FR 2942016 B1 and EP 2792907 A1 disclose a satellite roller screw mechanism comprising another type of guide, called open, having radial notches in the shape of a "U" and self-centering, on the one hand not requiring additional means for their immobilization and, on the other hand, making it possible to maximize the useful length of the thread on the central part of the rollers.

The guides with radial and self-centering notches of documents FR 2942016 B1 and EP 2792907 A1 have the disadvantage of not ensuring, unlike those of US patent 9267587 B2, the maintenance of the rollers when the screw is removed from the nut. or when inserted into it. The rollers then separate from the open guides because said rollers can slide freely and radially, under the effect of their own weight, along the openings formed by the "U"-shaped notches and fall within the nut. in the case of a standard roller screw or fall outside the screw in the case of an inverted roller screw; the reason being that the opening of said notches is greater than or equal to the diameter of the journals of the rollers with which they cooperate. These open guides then require the use of an appropriate additional tool, which retains the rollers in position, temporarily or permanently, in the said notches. This is detrimental to assembly and disassembly operations since it represents a considerable cost of tools in terms of manufacturing and maintenance of the satellite roller screw mechanisms equipped with said open guides; or requiring special precautions for said operations, making them difficult or extremely delicate.

A roller screw mechanism according to the invention proposes an improvement of the open guides with notches which guarantee the maintenance of the rollers in position and avoid a separation of said rollers from these guides.

A satellite roller screw mechanism according to the invention comprises a screw provided with an external thread; a nut coaxially surrounding the screw and provided with an internal thread; rollers each provided with an external thread and interposed between the screw and the nut so that the external thread of the roller meshes with the external thread of the screw and the internal thread of the nut, each roller having two ends each provided with an external toothing, each external toothing having, in cross-section, an external diameter less than or equal to the bottom diameter of the external thread of the rollers, two synchronization teeth coaxial with the screw and in which the external teeth mesh rollers; and open guides which angularly and evenly separate the rollers; which guides each mounted on each smooth surface on the edge of the external teeth and juxtaposed to the thread of each roller are provided with a plurality of bearings having the appearance of circular notches in the shape of a rounded "C" at their ends and which cooperate with a smooth surface acting as a journal for the roller.

The main advantage of these open guides with circular and rounded notches is to facilitate assembly and disassembly of the screw, as they completely eliminate the risk of disengagement when the screw is inserted into the roller screw mechanism or when it is withdrawn. of the roller screw mechanism, by preventing the rollers from migrating radially inwards of the nut or outwards of the screw depending on whether the roller screw mechanism is, respectively, standard or reverse.

In addition, said open guides of the invention do not require, for their stop in translation, rushes or elastic rings, or even circlips since imprisoned on either side between the synchronization teeth, the nut and the roller thread.

The roller screw mechanism according to the invention can advantageously have the following characteristics:

- the guides, according to a preferred arrangement of the invention, are each sandwiched between the internal face of each synchronization toothing and the internal face of the nut delimiting the internal thread of the nut, and cooperate with the rollers of the standard roller screw mechanism;

- each open guide, according to the invention, comprises bearings resembling circular notches in the shape of a "C" rounded at its ends and, these cavities being open inwards, that is to say towards the screw, for a standard satellite roller screw;

- each open guide, according to the invention, comprises bearings resembling circular notches in the shape of a "C" rounded at its ends and, these cavities being open outwards, that is to say towards the nut, for an inverted satellite roller screw;

- the opening of at least one circular notch in the shape of a "C" is strictly less than the diameter of the journal of the roller with which it cooperates, and

- each open guide can radially have a solid structure or a wire structure depending on the degree of compactness or optimization of the useful length of the net in engagement sought.

The invention can also extend to an actuation device comprising a satellite roller screw mechanism mounted on a rod and coupled to a mechanical or electromechanical drive system.

Brief description of the drawings

The present invention will be better understood and other advantages will appear on reading the detailed description of the embodiments taken by way of non-limiting examples and illustrated by the appended drawings, in which:

- Figure 1A shows an exploded view of a satellite roller screw of a first mode of the invention showing the open guides, with their notches open inwards, that is to say on the external thread screw;

- Figure 2A is a sectional view along the longitudinal axis of the mechanism of Figure 1A, once assembled, showing the position of the open guides within the structure relative to the other components;

- figure 3A is a partial longitudinal view and a transverse view of a roller within the mechanism of figure 2A;

- Figure 4A is a cross-sectional view of one of the open guides of Figure 1A mounted on a plurality of rollers;

- Figure 5A shows a partial zooming on a roller in a notch of Figures 4A;

- Figure 1B shows an exploded view of a satellite roller screw of a second mode of the invention, showing the open guides, with their notches open outwards, that is to say open on the internal thread of the nut;

- Figure 2B is a sectional view along the longitudinal axis of the mechanism of Figure 1B, once assembled, showing the position of the open guides within the structure relative to the other components of the mechanism;

- Figure 3B is a cross-sectional view showing one of the open guides of Figure 2B mounted on a plurality of rollers;

- Figure 4B shows a partial zooming on a roller in a notch of Figures 3B;

- figure 1C illustrates the massive structure of an open guide respectively for a standard roller screw and an inverted roller screw;

- figure 2C illustrates the wire structure of an open guide respectively for a standard roller screw and an inverted roller screw;

- Figure 3C showing an actuator incorporating a satellite roller screw mechanism of Figure 1A equipped with the open guides of the invention.

Description of a first embodiment

A first embodiment of the invention is described with the aid of FIGS. 1A to 5A.

As illustrated by FIGS. 1A to 2A, a standard satellite roller screw mechanism 100 according to a first embodiment typically comprises a screw 110, a nut 130 arranged around the screw coaxially thereto, a plurality of rollers 120 interposed between the screw and the nut and longitudinal axes parallel to that of the screw, crowns 140 each fixed in the housing at one end of the nut 130 and provided with synchronization teeth 140D.

Screw 110 and rollers 120 have 110F and 120F external threads, respectively, and the nut has 130F internal threads. The rollers further comprise external teeth 120D located at their ends and which frame the central threaded part of the rollers, so that they mesh with the synchronization teeth 140D of the crowns 140.

The profiles of the 120D and 140D teeth are combined with each other and it can be an involute or involute of a circle, cycloidal, circular profiles, trochoidal profiles or even a combination of these profiles.

In this particular embodiment, the teeth of the rollers, according to FIG. 3A, are cut on a cylindrical bearing surface of length greater than the useful length L u of the teeth. Moreover, as illustrated in FIG. 3A, the diameter of the head D t of the teeth 120D is less than the diameter D f of the external thread 120F of the rollers. We also note there, between the teeth and the thread of the roller, a more or less smooth or grooved 120T zone, of length L t and of the same diameter as the diameter of the head of the teeth. This zone 120T results from the output of the tooth-cutting tool on said cylindrical surface and acts as a journal cooperating with the guides 150 which create the angular spacing of the various rollers 120. The length L t of this journal is a function of the cutting length of the teeth on the ends of the rollers, and is preferably greater than or equal to 1 millimeter.

In this configuration, according to Figures 1A and 2A, we note the presence of open guides 150 mounted coaxially to the screw between the latter and the nut. The open guides 150 are spacer rings which can be described as inner rings because they are associated with the nut 130 and located inside it. The guides 150 are attached either to the internal face 130X of the nut delimiting the internal thread of said nut, or to the chamfer of the external thread 120F of the rollers, or both. The open guides 150 of the mechanism comprise a plurality of notches 150I compatible in number with that of the rollers as shown in FIG. 4A. The installation of the open guides 150 in the nut 130 precedes that of the synchronization teeth 140 and their fixing on the nut 130.

Each notch 150I can be thought of as a semi-open "C" shaped hole, with rounded ends 150a resembling hooks, facing the inside of the nut, as illustrated by Figures 4A and 5A. The opening of each notch 150I has a spacing value V e less than the diameter D t of the pin, which prevents the rollers from escaping from the notches 150I of the guides 150.

The guides 150 are preferably solid and thick in the radial direction between two notches 150I; which gives them excellent rigidity. The guides are mounted axially, by insertion along the longitudinal axis 170 of the mechanism.

The rollers 120 are held in position in the notches 150I of the guides 150 by the rounded hooks, which does not involve any tooling when the screw 110 is inserted or removed from the satellite roller screw mechanism.

Description of a second embodiment

A second embodiment of the invention is described using Figures 1B to 4B.

While the first embodiment deals with a standard planetary roller screw 100, the second embodiment deals with an inverted planetary roller screw 100' illustrated by Figures 1B and 2B, which is based on the same principle of operation than the standard roller screw, but whose nut system is reversed, the crowns 140 being eliminated, the internal synchronization teeth 140D being replaced by external teeth 140'D carried by the crown 140' fixed to the screw 110' , for example, by pins not shown or by gluing, or by crimping, etc. The open guides 150 are replaced by the open guides 150', and the screw and 110' and the nut 130' being adapted to the previous modifications.

The 140’D external teeth can also be glued or fixed by small fixing screws on the 110’ screw. The 140’D external teeth are fitted and fixed after inserting the 150’ open guides on the 110’ screw.

In FIG. 1B, we find the screw 110' and the nut 130' with, between the two, the various rollers 120 and the open guides 150' whose notches are rounded at the ends and oriented towards the outside of the screw.

Each open guide 150' is sandwiched, according to FIG. 2B, between the external thread 110'F of the screw 110' and the flat face of the external teeth 140'D for synchronization of the crown 140'D.

In this second embodiment, the rollers 120 are identical to those which have been described previously as regards their structure as illustrated by FIGS. 1A and 1B, but they are kept spaced apart by means of the open guides 150' which are different from the open guides 150. The guides 150', represented in FIGS. 1B to 2B, turn around the screw 110' and the notches 150'E, in the shape of a "C" and with rounded ends 150'a, which accommodate the cylindrical bearing surface 120T of the rollers 120, are open towards the outside, that is to say towards the nut, as shown in FIG. 3B.

As illustrated in FIG. 4B, here again, the opening has a clearance value Ve that is less than the diameter D t of the journal of the roller, which prevents the rollers from leaking from the open guides. The radial holding function is thus ensured.

Whatever the embodiment, the notches of the open guides 150 or 150' of the invention, as illustrated by FIGS. 1C and 2C, have the shape of a "C" opening, with rounded ends 150a or 150'a , unlike a "U" shape, with flat and non-rounded ends, the notches of the guides as described in the documents FR 2942016 B1 and EP 2792907 A1. This circular "C" shape suitably calculated, allows the retention of the rollers in the event of assembly or disassembly of the nut or the screw depending on whether it is a standard roller screw or a roller screw. reversed.

In general, the opening Ve of the notches can be expressed according to the relationship:

V e = k x D t

where D t is the diameter of the pin or head diameter of the teeth of the rollers 150 or 150', k a non-zero constant whose value is strictly less than 1 and preferably between 0.5 and 0.8 to ensure a function effective and reliable retention or maintenance of the rollers in the notches. It is determined by taking into account the material parameters, the rigidity to be given to the open guides 150 or 150' and the expected service life of the roller screw mechanism.

Due to the opening V e strictly less than the diameter D t of the pin of the roller and given the massive appearance of the guides described above, it is impossible to mount the rollers 120 radially in the notches 150I through the inside of the nut , or to mount the rollers 120 radially in the notches 150'E from the outside of the screw, if the material is of very high hardness and rigidity. However, the guides can be made of steel, bronze, composite, ceramic but also plastic. Additional recesses can therefore be provided to lighten the mass of the guides or to give them a certain flexibility. In this case, the rollers can be mounted radially, from the inside or from the outside depending on the case, by clipping them manually or using a suitable tool in the notches 150I or 150'E of said guides. Once installed, the rollers 120 can no longer come out under the effect of their own weight, which is insufficient to widen the opening of the notches 150I or 150'E in the opposite direction. The retention of the rollers 120 is then achieved by the "C" shape of the notches.

Alternatively, as illustrated by FIG. 2C, the guides 150 and 150' can also have a wire structure made of a thin strip of material in the radial direction, which can have a square, rectangular, circular or arbitrary cross-section. The wire structures are distinguished from the solid structures of FIG. 1C by the fact that between two consecutive notches, 150I or 150'E, of the open guides, there is essentially a vacuum in the circumferential direction. The advantage of wire guides is, on the one hand, to further reduce the length L t of the 120T pin, that is to say of the more or less smooth zone between the external teeth at the ends and the threaded part of the roller, thus maximizing the useful length of the net in engagement and, on the other hand, to confer on the open guides 150 and 150' a relative overall flexibility necessary to clip, during assembly, the rollers 120 respectively in the notches 150I and 150'E .

Equipped with a wire structure, the 150 and 150' open guides can be combined, at will, with any type of existing roller. For rollers whose 120D teeth interfere with the 120F thread, only radial mounting by means of clipping is possible, whereas for rollers where the 120D teeth do not interfere with the 120F thread, as in the case of FIG. It is possible either to insert them by clipping into the notches 150 and 150', or to mount them axially, along the longitudinal axis 170 of the satellite roller screw mechanism, the open guides 150 or 150' wired.

The 150 and 150' open guides, whether wire or solid, can be manufactured by any of the following techniques: milling, molding, plastic deformation, powder sintering, turning, drilling, 3D printing, etc.

An actuator shown schematically in FIG. 3C takes advantage of the satellite roller screw mechanism 100 described above, secured to a rod 210 which may consist of the screw 110, and coupled to a mechanical or electromechanical drive means 220, by example to form a mechanical jack, but it is also possible to use the mechanism 100' instead of the mechanism 100.

Claims (7)

– Satellite roller screw mechanism comprising a screw (110;110') provided with an external thread (110F;110'F); a nut (130; 130') coaxially surrounding the screw and provided with an internal thread (130F; 130'F); rollers (120) each provided with an external thread (120F) and interposed between the screw and the nut so that the external thread of the roller meshes with the external thread of the screw and the internal thread of the nut , each roller having two ends each provided with an external toothing (120D), each external toothing having, in cross section, an external diameter (D t ) less than or equal to a bottom diameter (D f ) of the external thread of the rollers ; which rollers are positioned and retained by open guides (150; 150'), comprise circular notches (150I; 150'E), rounded at their ends, which notches (150I; 150E') cooperate like bearings with the rollers ( 120),
characterized in that the ratio ( k ), representing the opening V e of at least one circular notch (150I; 150'E) of the open guides (150; 150') divided by the journal diameter (D t ), is strictly less than 1. – The roller screw mechanism according to claim 1, characterized in that each open guide (150) comprises circular notches (150I), in the form of “C”, open towards the inside of the nut (130) and rounded, guiding and maintaining the axial, angular and radial position of the rollers (120). – The roller screw mechanism according to claim 1, characterized in that each open guide (150') comprises circular notches (150'E), in the form of a "C", open towards the outside of the screw (130 ') and rounded, guiding and maintaining the axial, angular and radial position of the rollers (120'). – The roller screw mechanism according to any one of the preceding claims, characterized in that the ratio ( k ), representing the opening V e of at least one circular notch (150I; 150'E) of the open guides ( 150;150') divided by the journal diameter (D t ), preferably between 0.50 and 0.8. – The roller screw mechanism according to any one of the preceding claims, characterized in that at least one of the open guides (150; 150') has a wire structure, or a thin section. – The roller screw mechanism according to any one of the preceding claims, characterized in that at least one of the open guides (150; 150') allows the rollers (120) to be clipped therein radially during assembly. - Actuating device, characterized in that it comprises a satellite roller screw mechanism (100, 100') according to any one of the preceding claims, mounted on a rod (210) and coupled to a drive system electromechanical.