Electromechanical Linear Actuator

Abstract

An electromechanical linear actuator having a threaded drive, which comprises a threaded nut connected to a cantilever tube and a lead screw connected to a hollow shaft of an electric motor via a rotationally fixed connection in such a way that, by a rotation of the hollow shaft and the lead screw, the threaded nut and the cantilever tube are linearly movable. An axial design length of the electromechanical linear actuator in the maximally retracted state is minimized in that a holding brake for the lead screw and a first rotary bearing for bearing the lead screw on a housing of the linear actuator are arranged within the hollow shaft.

Claims

1. An electromechanical linear actuator, comprising: a threaded drive which comprises a threaded nut connected to a cantilever tube and a lead screw connected to a hollow shaft of an electric motor via a rotationally fixed connection, such that by a rotation of the hollow shaft and the lead screw the threaded nut and the cantilever tube are linearly movable, wherein a holding brake for the lead screw and a first rotary bearing for bearing the lead screw on a housing of the linear actuator are arranged within the hollow shaft.

2. The electromechanical linear actuator according to claim 1, wherein the housing comprises a first hollow beam which projects into the hollow shaft of the electric motor and whose inner circumference serves to receive the first rotary bearing arranged on the outer circumference of the lead screw.

3. The electromechanical linear actuator according to claim 1, wherein a second rotary bearing is arranged between the outer circumference of a second hollow beam of the housing projecting into the hollow shaft of the electric motor and the inner circumference of the hollow shaft in an end region of the electric motor facing away from the cantilever tube.

4. The electromechanical linear actuator according claim 1, wherein a screw support configured as a piston is arranged on the lead screw in an end region of the lead screw facing away from the rotationally fixed connection via which the lead screw is rotatably borne in the cantilever tube and via which the cantilever tube is also guided linearly along the end region of the lead screw.

5. The electromechanical linear actuator according to claim 1, wherein the first rotary bearing comprises two tapered roller bearings or spherical roller bearings in an O-arrangement.

6. The electromechanical linear actuator according claim 3, wherein the second rotary bearing comprises a radial groove ball bearing.

7. The electromechanical linear actuator according to claim 3, wherein the second rotary bearing is configured as a floating bearing, such that a heat-induced relative movement between the hollow shaft and the second hollow beam in the longitudinal direction of the hollow shaft is enabled.

8. The electromechanical linear actuator according to claim 1, wherein a rotary encoder arranged on a front face of the lead screw facing away from the cantilever tube (3a) is arranged within the hollow shaft.

9. The electromechanical linear actuator according to claim 1, wherein a transmission arranged between the hollow shaft and the lead screw, in the form of a planetary train, is arranged within the hollow shaft.

10. The electromechanical linear actuator according to claim 9, wherein the transmission is arranged in the longitudinal direction of the lead screw between the holding brake and the first rotary bearing.

11. The electromechanical linear actuator according to claim 1, wherein the holding brake is configured as a mechanical brake.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Preferred embodiments are shown in further detail below with reference to the accompanying figures.

[0035] FIG. 1 schematically shows an electromechanical linear actuator according to a preferred embodiment of the disclosure in a three-dimensional view.

[0036] FIG. 2 shows a schematic cross-sectional view of the electromechanical linear actuator of FIG. 1.

[0037] FIG. 3 shows an enlarged cut-out of the sectional view of the electromechanical linear actuator of FIG. 2.

DETAILED DESCRIPTION

[0038] FIG. 1 shows the exemplary embodiment of the electromechanical linear actuator 1, which can also be referred to as an electric cylinder, in a perspective three-dimensional view. FIG. 2 shows a schematic representation of the electromechanical linear actuator 1 according to FIG. 1 in a cross-sectional view, which runs through a longitudinal axis of the electromechanical linear actuator 1 and in an XY plane. The electromechanical linear actuator 1 has, among other things, a threaded drive 2, which comprises a threaded nut 3 connected to a cantilever tube 3a and a lead screw 4 connected to a hollow shaft EM.h of an electric motor EM via a rotationally fixed connection 5 in such a way that, by a rotation of the hollow shaft EM.h and the lead screw 4, the threaded nut 3 and the cantilever tube 3.a are linearly movable.

[0039] A holding brake B for the lead screw 4 and a first rotary bearing L.sub.1 for bearing the lead screw 4 on a housing G of the linear actuator 1 are arranged within the hollow shaft EM.h.

[0040] The housing G comprises a first hollow beam G.t.sub.1, which projects into the hollow shaft EM.h of the electric motor EM and whose inner circumference serves to receive the first rotary bearing L.sub.1 arranged on the outer circumference of the lead screw 4.

[0041] The electric motor EM and the adjacent components are also shown in particular in the enlarged cut-out shown in FIG. 3.

[0042] The cantilever tube 3.a, whose rotation is prevented, is fixedly connected to a ball joint KG and can be extended out of the housing G. A first end of the linear actuator 1 is formed by means of this ball joint KG. In a maximally extended state, the linear actuator 1 has its maximum length, which is in particular measured between a joint center KG.sub.M of the ball joint KG and a joint center of a further joint arranged on the side of the linear actuator 1 opposite the ball joint KG and fixedly connected to the housing, said further joint being not further described herein. In a maximally retracted state, the linear actuator 1 has its minimum length. In the maximally retracted state, the cantilever tube 3.a barely protrudes from the housing G, or not at all. The cantilever tube 3.a is borne in the end region of the housing G facing the ball joint KG by means of a sliding bearing (not described in further detail) in the housing G. During the retraction or extension of the cantilever tube 3.a, the lead screw 4 rotates. It is not moved linearly in the longitudinal direction 1.

[0043] A length in the maximally retracted state is minimized in that the holding brake B and the first rotary bearing L.sub.1 are arranged within the hollow shaft EM.h.

[0044] A second rotary bearing L.sub.2 is arranged between the outer circumference of a second hollow beam G.t.sub.2 of the housing G projecting into the hollow shaft EM.h of the electric motor EM and the inner circumference of the hollow shaft EM.h in an end region of the electric motor EM facing away from the cantilever tube 3a.

[0045] The second rotary bearing L.sub.2 is thus arranged in the end region of the electric motor EM facing the further joint fixedly connected to the housing.

[0046] A screw support 4.a preferably configured as a piston is arranged on the lead screw 4 in an end region of the lead screw 4 facing away from the rotationally fixed connection 5, via which the lead screw 4 is rotatably borne in the cantilever tube 3a and via which the cantilever tube 3a is also guided linearly along the end region of the lead screw 4.

[0047] Thus, on the one hand, the rotation of the lead screw 4 in the cantilever tube 3a and, on the other hand, the linear movement (work stroke) of the cantilever tube 3a opposite (the end region of) the lead screw 4 is enabled. The screw support 4.a can thus also be referred to as a sliding pin bearing.

[0048] The first rotary bearing L.sub.1 preferably comprises two tapered roller bearings or spherical roller bearings in an O-assembly.

[0049] The second rotary bearing L.sub.2 comprises a radial groove ball bearing.

[0050] The second rotary bearing L.sub.2 is configured as a floating bearing, so that, for example, a heat-induced relative movement between the hollow shaft EM.h and the second hollow beam G.t.sub.2 in the longitudinal direction 1 of the hollow shaft EM.h is enabled.

[0051] An electric motor EM configured as a hollow shaft motor and a threaded drive 2 configured as a planetary (rolling) threaded drive are arranged in the housing G. More specifically, when viewed radially from the outside to the inside, the parts are assembled as follows: first the windings of the electric motor EM, then the hollow shaft EM.h of the electric motor EM, then a sleeve-like main body of the threaded nut 3, then roller-shaped planets of the threaded nut 3, and finally the lead screw 4 completely inside. A radial distance is provided between the hollow shaft EM.h and the main body of the threaded nut 3. By contrast, embodiments of the threaded nut 3 without such planets are contemplated.

[0052] The threaded nut 3, in particular its main body, is fixedly connected to an end portion of the cantilever tube 3a. The assembly consisting of the threaded nut 3 and the cantilever tube 3a and the ball joint KG is only linearly movable, which is in particular also enabled by means of a support element AE, which comprises a sliding stone GL movably borne in the longitudinal direction 1 for receiving a bolt BZ to be passed through a joint head KG.sub.K of the ball joint KG, so that the cantilever tube 3a can be supported on the bolt BZ with respect to a rotation about the longitudinal axis of the lead screw 4.

[0053] Furthermore, a dampening element DM for dampening axial impacts is preferably arranged between the ball joint KG and the end of the cantilever tube 3a facing away from the housing G. The end of the cantilever tube 3a facing away from the housing G is fixedly connected to the support element AE passing by the dampening element DM or comprises this support element AE.

[0054] The hollow shaft EM.h is connected to the lead screw 4 in a central region by means of the rotationally fixed connection 5. For example, a hollow shaft-side positive locking element and a screw-side positive locking element of the rotationally fixed connection 5 are configured and attached to one another in such a way that the hollow shaft EM.h and the rotationally fixed connection 5 and the lead screw 4 form a non-bending, rotatable assembly.

[0055] Due to the rigid design, the bearing of the rotating assembly consisting of lead screw 4, the rotationally fixed connection 5, and the hollow shaft EM.h can only be carried out with two bearing points, namely the first rotary bearing L.sub.1 and the second rotary bearing L.sub.2.

[0056] A rotary encoder 6, which is arranged on a front face of the lead screw (4) facing away from the cantilever tube 3a, is arranged within the hollow shaft EM.h.

[0057] The rotary encoder 6 is preferably configured as an absolute rotary encoder. A position determination of the cantilever tube 3a is thus possible without a distance measuring system.

[0058] It is contemplated that, between the hollow shaft EM.h and the lead screw 4, a transmission, preferably a planetary transmission, is arranged within the hollow shaft EM.h.

[0059] The transmission is interposed in the rotationally fixed connection 5 in such a way that a torque transfer between the hollow shaft EM.h and the lead screw 4 is ensured, but also with the transformation or reduction ratio generated by the transmission.

[0060] The transmission could be arranged in the longitudinal direction 1 of the lead screw 4 between the holding brake B and the first rotary bearing L.sub.1.

[0061] The holding brake B is configured as a mechanical brake. By means of a brake actuator, a part of the holding brake B associated with the lead screw 4 and a part of the holding brake B associated with the housing G can be pressed against one another.

[0062] With the holding brake B, the lead screw 4 and thus also the electric motor EM can be fixed opposite the housing G.

LIST OF REFERENCE NUMERALS

[0063] 1. Electromechanical linear actuator [0064] 2. Threaded drive [0065] 3. Threaded nut [0066] 3.a Cantilever tube [0067] 4. Lead screw [0068] 4.a Screw support [0069] 5. Rotationally fixed connection [0070] 6. Rotary encoder [0071] EM Electric motor [0072] EM.h Hollow shaft [0073] B Holding brake [0074] L.sub.1 First rotary bearing [0075] L.sub.2 Second rotary bearing [0076] G Housing [0077] G.t.sub.1 First hollow beam [0078] G.t.sub.2 Second hollow beam [0079] KG Ball joint [0080] KG.sub.M Joint center [0081] KG.sub.K Joint head [0082] AE Support element [0083] GL Slide stone [0084] BZ Bolt [0085] l Longitudinal direction