Internally indexed linear actuator

Abstract

A linear actuator (1) comprising a planetary roller screw (5), the nut part (7) of which is rotationally indexed in relation to a frame (2) by means of a fixed longitudinal axis (12) on which the nut part (7) is slidably arranged.

Description

INTERNALLY INDEXING LINEAR ACTUATOR TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of linear actuators.

[0002] A linear actuator AL is known as partially illustrated in the, comprising a satellite roller screw VRS.

[0003] The satellite roller screw VRS comprises a longitudinal bushing DOL with internal thread (not shown here), shaped to be driven in rotation by the motorized drive means in two opposite directions of rotation about a longitudinal direction DL. The satellite roller screw VRS also comprises a nut element EC arranged inside the longitudinal bushing DOL and comprising a plurality of satellite rollers RS meshing externally with the internal thread of the longitudinal bushing DOL. Said nut element EC is integral with an actuating rod TA and is coupled in rotation with the actuating rod TA.

[0004] In order for the nut element EC and the actuating rod TA to move under the effect of a rotation (in one direction or the other) of the longitudinal sleeve DOL, the nut element EC is immobilized (or indexed) in rotation about the longitudinal direction DL. This indexing is carried out by means of the actuating rod TA which comprises, at its distal end ED, a distal member OD with a non-circular cross-section.

[0005] The screw-in cooperation between the longitudinal sleeve DOL and the nut element EC requires extensive lubrication. The distal member OD therefore has a transverse lubricant supply channel CT for introducing lubricant from the outside into a central channel CC of the actuating rod TA and into the area occupied by the satellite rollers RS.

[0006] A first disadvantage is the fact of having to ensure only indirect indexing of the EC nut element, which constrains the design of the element actuated by the TA actuating rod.

[0007] Another disadvantage is that lubricant supply means must follow the back and forth movements of the TA actuating rod.

[0008] An alternative consisted of providing an actuating rod TA itself having a non-circular cross-section allowing its indexing in rotation relative to the frame of the linear actuator. In this alternative, however, due to the contact surface which is non-circular, it is not possible to ensure a satisfactory seal around the actuating rod TA (at the outlet of the frame) by means of a seal bearing on the actuating rod.

[0009] Document US 11,915,867 B2 describes an actuating rod comprising at its proximal end a nut element which is formed in a single piece with the actuating rod. If it is desired to subject the nut element to metallurgical and / or thermal treatments in order to provide it with appropriate wear resistance characteristics, the actuating rod necessarily undergoes the same treatments. This results in manufacturing complexity with high costs.

[0010] Document US 2005 / 132830 A1 discloses a linear actuator having a structure different from that of the linear actuator of the present invention. In this document, the linear actuator comprises an externally threaded actuating rod cooperating with a roller nut which is fixed to the distal end of a frame. The external thread of the actuating rod does not allow for a satisfactory seal to be provided around the actuating rod at its emergence from the frame.

[0011] A problem addressed by the present invention is to provide a linear actuator that does not require indirect indexing (via the element actuated by the actuating rod).

[0012] Another problem addressed by the invention is to enable satisfactory lubrication of the threaded connection between the longitudinal sleeve and the nut element without having to follow the back and forth movement of the actuating rod.

[0013] At the same time, the present invention aims to provide a satisfactory seal around the actuating rod at the point where it emerges from the frame.

[0014] To achieve these and other objects, the invention provides a linear actuator comprising: - a frame extending in a longitudinal direction between a first end called proximal and a second end called distal, - an actuating rod that can be moved linearly in the longitudinal direction, between a retracted position in which the actuating rod protrudes beyond the second end of the frame by a first length, and at least one extended position in which the actuating rod protrudes beyond the second end of the frame by a second length greater than the first length, - motorized drive means, - a longitudinal sleeve with internal thread, shaped to be driven in rotation by the motorized drive means in two opposite directions of rotation about the longitudinal direction,- a nut element disposed inside the longitudinal sleeve meshing externally with the internal thread of the longitudinal sleeve, said nut element being integral with the actuating rod and coupled in rotation with the actuating rod; according to the invention: - the nut element comprises a longitudinal through passage with a non-circular internal cross-section, - the linear actuator comprises a longitudinal axis extending between a first end and a second end, coupled in rotation and in translation along its first end to the proximal end of the frame, and engaged in the longitudinal through passage of the nut element along an engagement section having an external cross-section shaped to cooperate with the cross-section of the longitudinal through passage of the nut element to oppose any rotation of the nut element about the longitudinal direction.,

[0015] The longitudinal axis, fixed relative to the frame, thus makes it possible to immobilize the nut element in rotation about the longitudinal direction by cooperation with the cross-section of the longitudinal through passage of the nut element. Indirect rotational indexing of the nut element, via the actuating rod, is thus no longer necessary.

[0016] The movements of the actuating rod between its retracted position and its at least one extended position are caused by the cooperation of the longitudinal sleeve with internal thread with the nut element. The actuating rod can thus protrude from the frame along a section with a smooth cylindrical side wall and a circular cross-section. It is thus possible to ensure a satisfactory seal around the actuating rod (at the outlet of the frame) by means of a seal (O-ring for example) bearing on the actuating rod.

[0017] Preferably, the nut element, although being integral with the actuating rod and coupled in rotation with the actuating rod, is separate from the actuating rod. In other words, the nut element and the actuating rod are not formed from a single piece: they are formed from two separate pieces (said pieces being able to be assemblies). This makes it possible to subject the nut element to metallurgical and / or thermal treatments providing it with appropriate wear resistance characteristics without having to subject the actuating rod to the same treatments. This results in simplicity of manufacture with lower costs.

[0018] Advantageously, the nut element may comprise a plurality of satellite rollers meshing externally with the internal thread of the longitudinal sleeve. The linear actuator is then provided with a satellite roller screw giving it good compactness and allowing it to withstand significant forces during its operation.

[0019] Preferably, the longitudinal through passage of the nut element may have an internal cross-section substantially complementary to the external cross-section of the engagement section of the longitudinal axis.

[0020] For good compactness, the actuating rod may comprise an internal housing capable of slidingly receiving the second end of the longitudinal axis along at least part of said engagement section.

[0021] In such a case, to limit any possible friction between the engagement section and the actuating rod, the inner housing of the actuating rod may be cylindrical, with a cross-section having dimensions greater than the largest dimension of the cross-section of said engagement section, and arranged to avoid any lateral contact with said engagement section.

[0022] Preferably, the longitudinal axis may comprise:- an internal longitudinal passage formed from its first end and extending longitudinally to the engagement section,- a transverse passage formed in the engagement section and putting the internal longitudinal passage into communication with the external volume situated around the engagement section of the longitudinal axis, so that lubricant supply means make it possible to introduce a lubricant from the outside of the frame into the internal longitudinal passage as far as the meshing zone between the longitudinal sleeve and the nut element.

[0023] This allows lubricant to be supplied to the satellite rollers by means which are not subject to the movements of the actuating rod.

[0024] Advantageously, it can be provided that:- a transverse passage is provided in the nut element from the longitudinal through passage,- said transverse passage is shaped so as to correspond to the transverse passage provided in the engagement section in order to ensure that the lubricant flows from the engagement section to the meshing zone between the longitudinal sleeve and the nut element.

[0025] Advantageously, it can be provided that:- the actuating rod slides in the distal end of the frame along a cylindrical sliding section with a circular cross-section,- the frame comprises sealing means comprising an annular seal arranged in contact with said sliding section along a contact surface that is at least substantially circular and preferably along a substantially cylindrical contact surface with a circular cross-section.

[0026] This ensures satisfactory sealing around the actuating rod, particularly to prevent lubricant leakage. SUMMARY DESCRIPTION OF THE DRAWINGS

[0027] Other objects, characteristics and advantages of the present invention will emerge from the following description of particular embodiments, made in relation to the attached figures, among which:

[0028] This is a partial and schematic view in longitudinal section of a linear actuator according to the prior art;

[0029] This is a partial and schematic view in longitudinal section of a particular embodiment of a linear actuator according to the present invention, with an actuating rod arranged in a retracted position;

[0030] This is a partial and schematic view in longitudinal section of the linear actuator of the, with an actuating rod arranged in an intermediate position;

[0031] This is a partial and schematic view in longitudinal section of the linear actuator of the, with an actuating rod arranged in an extended position;

[0032] This is a schematic perspective and partial longitudinal sectional view of a nut element and a threaded bushing of the linear actuator of the ;

[0033] Theis a schematic cross-sectional view of a nut element and a threaded bushing of the linear actuator of the; and

[0034] This is a schematic perspective view of part of the linear actuator of the. DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] When identical reference numerals are used in several figures, embodiments or variations of the invention, these reference numerals designate identical or similar elements in each of the figures, embodiments or variations.

[0036] In Figures 2 to 7 is schematically illustrated a particular embodiment of linear actuator 1 according to the present invention. This linear actuator 1 comprises: - a frame 2 extending in a longitudinal direction II between a first end 2a called proximal and a second end 2b called distal, - an actuating rod 3 linearly movable in the longitudinal direction II between a retracted position (), in which the actuating rod 3 protrudes beyond the second end 2b of the frame 2 by a first length L1, and at least one extended position (), in which the actuating rod 3 protrudes beyond the second end 2b of the frame 2 by a second length L2 greater than the first length L1, - motorized drive means 4,- a longitudinal sleeve 6 with internal thread 6a (the internal thread 6a is visible in the but is not shown in the other figures so as not to complicate them unnecessarily), shaped to be driven in rotation by the motorized drive means 4 in two opposite directions of rotation around the longitudinal direction II, - a nut element 7 arranged inside the longitudinal sleeve 6 meshing externally with the internal thread 6a of the longitudinal sleeve 6, said nut element 7 being integral with the actuating rod 3 and coupled in rotation with the actuating rod 3.,

[0037] The nut element 7, although being integral with the actuating rod 3 and coupled in rotation with the actuating rod 3, is distinct from the actuating rod 3. The nut element 7 and the actuating rod 3 are not formed from a single piece: they are formed from two distinct pieces.

[0038] Here, the motorized drive means 4 comprise an electric motor which is shown only schematically in Figures 2 to 4. Said electric motor however comprises, in a conventional manner, a rotor secured to the longitudinal sleeve and a stator secured to the frame 2.

[0039] Also shown only schematically in Figures 2 to 4 are an encoder 9 and an electromagnetic brake 10. The encoder 9 makes it possible to know the parameters (angular position, direction and speed of rotation in particular) of the rotational movement of the longitudinal sleeve 6 around the longitudinal direction II relative to the frame 2. The electromagnetic brake 10 is shaped so as to stop the rotation of the longitudinal sleeve 6 around the longitudinal direction II in the event of a break in the electrical power supply to the motorized drive means 4.

[0040] It can be seen more particularly in Figures 5 and 6 that the nut element 7 comprises a plurality of satellite rollers 8a to 8i meshing externally with the internal thread 6a of the longitudinal sleeve 6. The linear actuator 1 thus comprises a satellite roller screw 5 comprising the longitudinal sleeve 6 and the nut element 7. However, as an alternative, a ball screw could be used to ensure the helical connection between the longitudinal sleeve 6 and the nut element 7.

[0041] We see more particularly on lacquer: - the nut element 7 comprises a longitudinal passage 7a passing through with a non-circular internal cross-section, - the linear actuator 1 comprises a longitudinal axis 12, extending between a first end 12a and a second end 12b, coupled in rotation and in translation along its first end 12a to the proximal end 2a of the frame 2, and engaged in the longitudinal passage passing through 7a of the nut element 7 along an engagement section 12c having an external cross-section shaped to cooperate with the cross-section of the longitudinal passage passing through 7a of the nut element 7.

[0042] In this case, the longitudinal through passage 7a with a non-circular internal cross-section comprises six longitudinal grooves 11a to 11f extending radially relative to the longitudinal direction II. For its part, the engagement section 12c of the longitudinal axis 12 comprises six longitudinal ribs 13a to 13f which are each received in one of the six grooves 11a to 11f. The longitudinal through passage 7a of the nut element 7 thus has an internal cross-section substantially complementary to the external cross-section of the engagement section 12c of the longitudinal axis 12.

[0043] The longitudinal ribs 13a to 13f thus cooperate by complementarity of shapes with the longitudinal grooves 11a to 11f to oppose any rotation of the nut element 7 around the longitudinal direction II.

[0044] As is more particularly visible in Figures 2 to 4, the actuating rod 3 comprises an internal housing 14 capable of slidingly receiving the second end 12b of the longitudinal axis 12 along at least a part of said engagement section 12c.

[0045] To avoid friction that could interfere with the back-and-forth movements of the actuating rod 3, the inner housing 14 of the actuating rod 3 is cylindrical with a cross-section having dimensions greater than the largest dimension of the cross-section of said engagement section 12c. Here in practice, the inner housing 14 of the actuating rod 3 is cylindrical with a circular cross-section with a diameter D14 (Figures 2 to 4) that is greater than the outer diameter D13 defined by the longitudinal ribs 13a to 13f (), and is arranged in alignment to avoid any lateral contact with said engagement section 12c.

[0046] Still in Figures 2 to 4, it can be seen that the longitudinal axis 12 comprises:- an internal longitudinal passage 12d formed from its first end 12a and extending longitudinally to the engagement section 12c,- a transverse passage 12e formed in the engagement section 12c and putting the internal longitudinal passage 12d into communication with the external volume situated around the engagement section 12c of the longitudinal axis 12.

[0047] Lubricant supply means (not shown) can thus be connected to the inlet port 15 to introduce a lubricant from outside the frame 2 into the internal longitudinal passage 12d into the area occupied by the satellite rollers 8a-8i meshing with the longitudinal bushing 6.

[0048] When using the linear actuator, a lubricant is injected by lubricant supply means continuously or intermittently into the internal longitudinal passage 12d via the fixed inlet port 15. The lubricant is pressurized in the internal longitudinal passage 12d and spreads until it reaches the transverse passage 12e. The lubricant then enters the transverse passage 12e. When the nut element 7 translates in the longitudinal direction II, it transiently and intermittently reaches an intermediate lubrication position () in which a transverse passage 16 provided in the nut element 7 corresponds to the transverse passage 12e (): lubricant then escapes from the transverse passage 12e towards the satellite rollers 8a to 8i by passing through the transverse passage 16.This ensures satisfactory lubrication of the meshing zone between the longitudinal sleeve 6 and the nut element 7 (here provided by means of the satellite rollers 8a to 8i).

[0049] We see more particularly on lacquer: - the actuating rod 3 slides in the distal end 2b of the frame 2 according to a cylindrical sliding section 3a with a circular cross-section, - the frame 2 comprises sealing means 17 comprising an annular seal 18 arranged in contact with said sliding section 3a according to a contact surface at least substantially circular and preferably according to a substantially cylindrical contact surface with a circular cross-section.

[0050] In this case, as can be seen better in Figures 2 to 4, the annular seal 18 is a double-lip seal. Each lip is arranged in contact with said sliding section 3a along a substantially circular contact surface. Being close to each other, the two lips provide a substantially cylindrical contact surface with a circular cross-section.

[0051] When using the linear actuator 1 according to the present invention, the motorized drive means 4 rotate the longitudinal sleeve 6 about the longitudinal direction II. The nut element 7 is indexed in rotation about the longitudinal direction II by means of the longitudinal axis 12.

[0052] The screwing cooperation between the internal thread of the longitudinal sleeve 6 and the external thread of the satellite rollers causes a translation of the nut element 7 in the longitudinal direction, the direction of which depends on the direction of rotation of the longitudinal sleeve 6.

[0053] By moving in translation along the longitudinal direction II, the nut element 7 causes a translational movement of the actuating rod 3 relative to the frame 2 in order to move the actuating rod between its retracted () and extended () positions. The movement of the actuating rod 3 is a pure translational movement, without rotation around the longitudinal direction II, due to the rotational indexing of the nut element 7 (to which the actuating rod 3 is integral) by the longitudinal axis 12.

[0054] When the nut element 7 moves into the intermediate position (), the transverse passage 16 provided in the nut element 7 comes into correspondence with the transverse passage 12e: lubricant then escapes from the transverse passage 12e towards the satellite rollers 8a to 8i by passing through the transverse passage 16 to ensure satisfactory lubrication of the satellite rollers 8a to 8i.

[0055] The present invention is not limited to the embodiments which have been explicitly described, but it includes the various variations and generalizations contained within the scope of the following claims.

Claims

Linear actuator (1) comprising:- a frame (2) extending in a longitudinal direction (II) between a first end (2a) called proximal and a second end (2b) called distal,- an actuating rod (3) linearly movable in the longitudinal direction (II) between a retracted position, in which the actuating rod (3) protrudes beyond the second end (2b) of the frame (2) by a first length (L1), and at least one extended position, in which the actuating rod (3) protrudes beyond the second end (2b) of the frame (2) by a second length (L2) greater than the first length (L1),- motorized drive means (4),- a longitudinal sleeve (6) with internal thread (6a), shaped to be driven in rotation by the motorized drive means (4) in two opposite directions of rotation about the longitudinal direction (II),- a nut element (7) arranged inside the longitudinal sleeve (6) meshing externally with the internal thread (6a) of the longitudinal sleeve (6), said nut element (7) being integral with the actuating rod (3) and coupled in rotation with the actuating rod (3), characterized in that: - the nut element (7) comprises a longitudinal through passage (7a) with a non-circular internal cross-section, - the linear actuator (1) comprises a longitudinal axis (12) extending between a first end (12a) and a second end (12b), coupled in rotation and in translation along its first end (12a) to the proximal end (2a) of the frame (2),and engaged in the longitudinal through passage (7a) of the nut element (7) along an engagement section (12c) having an external cross-section shaped to cooperate with the cross-section of the longitudinal through passage (7a) of the nut element (7) to oppose any rotation of the nut element (7) about the longitudinal direction (II)., Linear actuator (1) according to claim 1, characterized in that the nut element (7) and the actuating rod (3) are formed from two separate parts. Linear actuator (1) according to one of claims 1 or 2, characterized in that the nut element (7) comprises a plurality of satellite rollers (8a-8i) meshing externally with the internal thread (6a) of the longitudinal sleeve (6). Linear actuator (1) according to any one of claims 1 to 3, characterized in that the longitudinal through passage (7a) of the nut element (7) has an internal cross-section substantially complementary to the external cross-section of the engagement section (12c) of the longitudinal axis (12). Linear actuator (1) according to any one of claims 1 to 4, characterized in that the actuating rod (3) comprises an internal housing (14) capable of slidingly receiving the second end (12b) of the longitudinal axis (12) along at least part of said engagement section (12c). Linear actuator (1) according to claim 5, characterized in that the inner housing (14) of the actuating rod (3) is cylindrical, with a cross-section having dimensions (D14) greater than the largest dimension (D13) of the cross-section of said engagement section (12c), and arranged to avoid any lateral contact with said engagement section (12c). Linear actuator (1) according to any one of claims 1 to 6, characterized in that the longitudinal axis (12) comprises:- an internal longitudinal passage (12d) formed from its first end (12a) and extending longitudinally to the engagement section (12c),- a transverse passage (12e) formed in the engagement section (12c) and putting the internal longitudinal passage (12d) into communication with the external volume situated around the engagement section (12c) of the longitudinal axis (12), so that lubricant supply means make it possible to introduce a lubricant from the outside of the frame (2) into the internal longitudinal passage (12d) as far as the meshing zone between the longitudinal sleeve (6) and the nut element (7). Linear actuator (1) according to claim 7, characterized in that:- a transverse passage (16) is provided in the nut element (7) from the longitudinal through passage (7a),- said transverse passage (16) is shaped so as to correspond to the transverse passage (12e) provided in the engagement section (12c) in order to ensure a path for the lubricant from the engagement section (12c) to the meshing zone between the longitudinal sleeve (6) and the nut element (7). Linear actuator (1) according to any one of claims 1 to 8, characterized in that:- the actuating rod (3) slides in the distal end (2b) of the frame (2) along a cylindrical sliding section (3a) with a circular cross-section,- the frame (2) comprises sealing means (17) comprising an annular seal (18) arranged in contact with said sliding section (3a) along a contact surface that is at least substantially circular and preferably along a substantially cylindrical contact surface with a circular cross-section.

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