Actuation system

Abstract

The invention relates to an actuation system comprising a nut (1) rotatably mounted in a casing (2) and an actuation screw (3) mounted in the nut, forming an interface (4) between the outer periphery (5) and inner periphery (6) thereof, the interface being equipped with a circulation path (7) for a plurality of rolling bodies which is arranged to be able to actuate the translation of the screw (3) by rotating the nut (1), the nut (1) having a rear radial bearing surface (20) which is arranged to axially bear against a complementary radial bearing surface (21) of the casing (2), a sliding element (22) being inserted between the bearing surfaces to allow the relative rotation thereof.

Description

[0001] DESCRIPTION

[0002] Actuation system

[0003] The invention relates to a system for actuation of a mechanical module by linear displacement of an actuation member.

[0004] It applies in particular to the actuation of a mechanical module requiring a small displacement of the component but under a high load, such as for example a brake caliper of a motor vehicle.

[0005] Actuation systems are known which include a nut mounted for rotation in a housing, and a screw forming the actuating element which is mounted in said nut.

[0006] The actuation system is of the "ball screw" type, presenting, at the interface between the nut and the screw, a circulation path of a plurality of rolling bodies, said path being arranged to be able to actuate, by rotation of the nut, the axial translation of the screw.

[0007] In particular, the nut is mounted for rotation in the housing by means of a front bearing to guide said rotation, said bearing being arranged to ensure optimal actuation, in particular by radially holding the nut / screw assembly during said actuation.

[0008] In some applications, the nut / screw assembly is subjected to significant axial forces, particularly in reaction to the actuation thrust on the module, which must be taken up to ensure the reliability of the actuation depending on the translation stroke of the screw.

[0009] To do this, unless the guide bearing used is made more complex, it is necessary to provide a rotating axial stop device for the nut / screw assembly, the placement of which is at the expense of the space, particularly the radial space, of the actuation system.

[0010] The invention aims to improve the prior art by proposing in particular an actuation system which is arranged to ensure optimal recovery of axial actuation forces, and this in a reduced radial footprint.

[0011] To this end, the invention proposes an actuation system comprising a nut mounted for rotation in a housing and an actuation screw mounted in said nut forming an interface between their respective outer and inner peripheries, said interface being equipped with a circulation path of a plurality of rolling bodies which is arranged to be able to actuate the translation of the screw by rotation of the nut, the nut having a rear radial bearing surface which is arranged in axial support on a complementary radial bearing surface of the housing, a sliding element being interposed between said bearing surfaces to allow their relative rotation.

[0012] Other objects and advantages of the invention will become apparent in the following description, made with reference to the accompanying figures, in which:

[0013] [Fig.1] shows in axial section an actuation system according to one embodiment of the invention,

[0014] [Fig.1a] being an enlargement of the upper part of figure 1;

[0015] [Fig.2] is an enlargement of a cross-section of the actuation system of figure 1a, centered on a portion of rolling body recirculation;

[0016] [Fig.3] represents, in perspective top view, the nut of the actuation system of the previous figures;

[0017] [Fig.4] represents, in perspective top view, an insert carrying a portion of recirculation of the rolling bodies equipping the nut according to figure 3.

[0018] In relation to these figures, a system for actuation of a mechanical module by linear displacement of an actuation member is described below, in particular a module requiring a small displacement of the member but under a high load, such as for example a brake caliper of a motor vehicle.

[0019] The actuation system includes a nut 1 mounted for rotation in a housing 2, and an actuation screw 3 for said device which is mounted in said nut, forming a radial interface 4 between the outer periphery 5 of said screw and the inner periphery 6 of said nut.

[0020] In the description, the terms for positioning in space are taken with reference to the actuation system as represented in the figures. Thus:

[0021] - the terms "exterior" and "interior" are defined with respect to the axis A of rotation of the nut 1, respectively for a location far and close to said axis;

[0022] - the terms "axial" and "radial" are also defined in relation to this axis A, and refer to a direction respectively following this axis A and moving away from or towards it;

[0023] - the terms "front" and "rear" are defined in relation to the direction of actuation, for a location respectively on the left and right in particular on figure 1.

[0024] The interface 4 is equipped with a circulation path 7 for a plurality of rolling bodies, for example in the form of spherical balls, which is arranged to be able to actuate, by rotation of the nut 1 around the axis A, the translation of the screw 3 along this same axis A, between a deployed forward position - respectively retracted backward - to actuate - respectively disengage - the module to be actuated.

[0025] In relation to the figures, each of the outer peripheries 5 and inner peripheries 6 of the screw 3 and nut 1 respectively is provided with a helical thread 5a, 6a, said threads being arranged radially opposite each other to form a helical circulation path 7. The circulation path 7 has at least one portion 7a for recirculating rolling elements from a downstream zone to an upstream zone, in order to prevent them from exiting said path during the relative movements of the screw 3 and the nut 1.

[0026] In the description, the terms "upstream" and "downstream" are taken in reference to the direction of movement of rolling bodies in the traffic path, which depends on the direction of rotation of nut 1, and therefore on the direction of translation of screw 3.

[0027] In the embodiment shown, the circulation path 7 has several internal recirculation portions 7a between two adjacent thread portions 8 5a. To achieve this, the nut 1 has cavities 9, each extending radially between its outer periphery and its helical thread 6a, each being equipped with an insert 10 on which an internal recirculation portion 7a is formed.

[0028] In particular, as shown in Figure 3, the nut 1 comprises three cavities 9 distributed angularly at 90° around its outer periphery.

[0029] In relation to figures 2 and 4, each insert 10 is fixed in a cavity 9, presenting an inner face 11 which is arranged radially opposite the helical thread 5a of the screw 3, said inner face having a portion 7a of internal recirculation thread which connects the two adjacent portions 8 of the thread 5a radially opposite which it is arranged.

[0030] Each cavity 9 has a substantially oblong geometry, as well as two outer portions 9a and inner portion 9b separated by a step 12, the insert 10 being engaged in the inner portion 9b and having two outer tabs 13 each provided with a bead 14 to allow their snapping onto said step.

[0031] In an alternative not shown, the circulation path 7 may have an external circulation portion between two end portions of the threads 5a, 6a, said portion also being able to be formed between two inserts arranged for this purpose in cavities of said nut.

[0032] In relation to Figures 1 and 1a, the outer periphery of the nut has a front axial bearing surface 15 on which an inner ring 16 of a bearing 25 is fixed by press fitting, said bearing comprising an outer ring 17 fixed by press fitting on a complementary axial bearing surface 18 of the housing 2, as well as a row of rolling bodies 19 allowing the rotation of the nut 1 in said housing.

[0033] The bearing shown is positioned in front of the nut 1, that is to say as close as possible to the module to be actuated, and includes a row of spherical rolling bodies 19 which allow the nut 1 / screw 3 assembly to be held radially in the housing 2 in order to ensure optimal actuation.

[0034] The nut 1 also has a rear radial bearing surface 20 which is arranged in axial support on a complementary radial bearing surface 21 of the housing, a sliding element 22 being interposed between said bearing surfaces to allow their relative rotation.

[0035] This arrangement ensures good absorption of axial forces exerted on the nut 1 / screw 3 assembly, particularly in reaction to the actuation thrust on the module, in that said assembly is placed in rotating axial stop on the housing 2 in order to guarantee the reliability of the actuation according to the translation stroke of the screw 3.

[0036] In addition, the rear radial reach 20 can be easily implemented in the actuation system, without negative impact on its overall dimensions, particularly radial.

[0037] In the embodiment shown, the rear radial bearing 20 extends internally from a rear axial peripheral bearing 23 of the nut 1, so that the rotating axial stop function can be implanted in the radial footprint of said nut.

[0038] The sliding element 22 can also be interposed between the rear axial peripheral bearing 23 and a complementary axial bearing 24 of the housing 2, so as to be able to contribute to a resumption of the radial forces exerted on the nut 1 / screw 3 assembly.

[0039] Advantageously, the rear axial peripheral bearing surfaces 23 and front 15 of the nut 1 extend substantially along the same diameter D, which makes it possible to limit the radial bulk of the actuation system, in particular by being able to limit the size of the bearing 25 for guiding the rotation of the nut 1.

[0040] According to one embodiment, the sliding element 22 comprises at least one layer of material, in particular polymer, having a coefficient of friction lower than that of the material, in particular metallic, forming respectively the nut 1 and the housing 2.

[0041] In the figures, the sliding element 22 comprises a self-lubricating plain bearing having a rigid frame 26, in particular metallic, on which at least one layer of antifriction material is deposited. In particular, the plain bearing may comprise a steel frame 26 on which a copper coating and then a polytetrafluoroethylene (PTFE)-based coating are successively deposited.

[0042] In relation to Figures 1 and 1a, the rigid frame 26 is associated with the nut 1, and for this purpose comprises an axial annular ring 26a which is axially fitted onto the rear axial peripheral wall 23, said ring having a rear edge of which extends internally a radial fold 26b which, at the end of the fitting, bears axially against the rear radial bearing surface 20. In particular, the coating layers enabling sliding are provided on the outer wall of the rigid frame 26, at the interface with the bearing surfaces 21, 24 of the housing 2 respectively. According to the embodiment shown, the nut 1 has a rear edge 27 which is equipped with means 28 for driving the rotation of said nut, in particular by means of an electric motor, said means being in the form of gear lugs.Advantageously, the means 28 are formed radially inside the rear radial bearing 20, which allows them to be positioned within the radial space of the nut 1 and the radial force recovery function, and thus to limit the overall radial space of the actuation system.

Claims

DEMANDS 1. Actuation system comprising a nut (1) rotatably mounted in a housing (2) and an actuating screw (3) mounted in said nut forming an interface (4) between their respective outer (5) and inner (6) peripheries, said interface being equipped with a circulation path (7) for a plurality of rolling bodies arranged to actuate the translation of the screw (3) by rotation of the nut (1), said system being characterized in that the nut (1) has a rear radial bearing surface (20) which is disposed in axial support on a complementary radial bearing surface (21) of the housing (2), a sliding element (22) being interposed between said bearing surfaces to allow their relative rotation.

2. Actuating system according to claim 1, characterized in that the sliding element (22) is further interposed between a rear axial peripheral bearing surface (23) of the nut (1) and a complementary axial bearing surface (24) of the housing (2).

3. Actuation system according to one of claims 1 or 2, characterized in that the sliding element (22) comprises at least one layer of material having a coefficient of friction lower than that of the material forming respectively the nut (1) and the housing (2).

4. Actuation system according to any one of claims 1 to 3, characterized in that the sliding element (22) comprises a self-lubricating plain bearing having a rigid frame (26) on which an antifriction material is deposited.

5. Actuation system according to claim 4, characterized in that the rigid frame (26) is associated with the nut (1).

6. Actuation system according to any one of claims 1 to 5, characterized in that the rear radial bearing surface (20) extends internally from a rear axial peripheral bearing surface (23) of the nut (1).

7. Actuation system according to any one of claims 1 to 6, characterized in that the outer periphery of the nut (1) has a front axial bearing surface (15) on which the inner ring (16) of a bearing (25) is fixed, said bearing comprising an outer ring (17) fixed on a complementary bearing surface (18) of the housing (2) and a row of rolling elements (19) allowing the rotation of the nut (1) in the housing (2).

8. Actuating system according to claims 6 and 7, characterized in that the rear axial peripheral bearing surfaces (23) and front axial bearing surfaces (15) of the nut (1) extend substantially along the same diameter (D).

9. Actuation system according to any one of claims 1 to 8, characterized in that the nut (1) has a rear edge (27) which is equipped with means (28) for rotational drive.

10. Actuation system according to claim 9, characterized in that the drive means (28) are formed radially inside the rear radial bearing (20).

11. Actuation system according to any one of claims 1 to 10, characterized in that each of the outer (5) and inner (6) peripheries of respectively the screw (3) and the nut (1) is provided with a helical thread (5a, 6a), said threads being arranged opposite each other to form a helical circulation path (7).

12. Actuation system according to any one of claims 1 to 11, characterized in that the traffic path (7) has at least one portion (7a) of recirculation of rolling bodies from a downstream area to an upstream area of ​​said path.

13. Actuation system according to claim 12 when it depends on claim 11, characterized in that the circulation path (7) has several portions (7a) of internal recirculation between two portions (8) of adjacent threads (5a).

14. Actuation system according to claim 13, characterized in that the nut (1) has cavities (9) each extending between the outer periphery and the thread (6a) of said nut, each of said cavities being equipped with an insert (10) on which a recirculation portion (7a) is formed.

15. Actuation system according to claim 14, characterized in that the insert (10) is fixed in the cavity (9) with an inner face (11) disposed opposite the thread (5a), said face having a portion (7a) of recirculating thread which connects the two adjacent portions (8) of threads (5a).

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