Linear electro-mechanical actuator

Abstract

The present invention relates to a linear electro-mechanical actuator for transferring a rotational motion to a linear motion. The actuator provides a piston being at least partly arranged inside a housing. The actuator further provides a transmission module including a rotating portion having a load-carrying surface and a non-rotating portion being operatively engageable to each other. The transmission module is adapted to transfer a rotational motion of the rotating portion to a linear motion of the piston via the non-rotating portion. The actuator further provides a lubricating member having a porous polymeric matrix and a lubricating material, the load-carrying member being arranged adjacent to the transmission module. Thereby, the actuator allows for lubrication of at least a portion of the load-carrying surface of the rotating portion upon movement of the rotating portion. The linear electro-mechanical actuator may not require, or may at least minimize, the need of relubrication.

Claims

1. A linear electro-mechanical actuator for transferring a rotational motion to a linear motion comprising: a housing defining an inner milieu, a piston extending in an axial direction and moveable in the axial direction, the piston having a distal end and a proximal end and moveable relative to the housing, a transmission module comprising a rotating portion and a non-rotating portion on the rotating portion and moveable in the axial direction and the non-rotating portion being operatively engageable to the piston, the rotating portion is operatively connected to a motor and has an outer load-carrying surface, the transmission module transfers a rotational motion of the rotating portion generated by the motor to a linear motion of the piston in the axial direction via the non-rotating portion, and a lubricating member comprising a porous polymeric matrix and a lubricating material, the lubricating member being present in the inner milieu, and the lubricating member being moveable in the axial direction on the rotating portion and rotationally locked to the non-rotating portion, wherein the lubricating member is adjacent to the transmission module, thereby allowing for lubrication of at least a portion of the load-carrying surface of the rotating portion by the lubricating material upon movement of the rotating portion.

2. The linear electro-mechanical actuator according to claim 1, wherein the lubricating member is disposed between the transmission module and the non-rotating portion, and due to rotation of the rotating portion, the lubricating member moves axially on the rotating part and lubricates substantially the entire load-carrying surface of the rotating portion with the lubricating material.

3. The linear electro-mechanical actuator according to claim 1, wherein the lubricating member is a separate component of the linear actuator.

4. The linear electro-mechanical actuator according to claim 1, wherein the lubricating member has a hollow tube shape with an annular inner surface.

5. The linear electro-mechanical actuator according to claim 1, wherein the rotating portion is a screw and the non-rotating portion is a nut.

6. The linear electro-mechanical actuator according to claim 1, wherein the rotating portion is a nut and the non-rotating portion is a screw.

7. The linear electro-mechanical actuator according to claim 5, wherein the screw is one of a roller screw, a ball roller screw or a sliding screw.

8. The linear electro-mechanical actuator according to claim 5, wherein the nut is either a rolling element nut or a torsionally locket nut.

9. The linear electro-mechanical actuator according to claim 1, further comprising: an opening in the housing allowing the piston to move axially from the inner milieu to an outer milieu; a separating member between the piston and the housing in a radial direction and adjacent to the opening of the housing, the separating member separates the inner milieu from the outer milieu.

10. The linear electro-mechanical actuator according to claim 1, further comprising a load-carrying member between the piston and the housing in the radial direction.

11. The linear electro-mechanical actuator according to claim 1, wherein the housing has the shape of a cylinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiments of the invention.

(2) In FIG. 1, a linear electro-mechanical actuator according to an example embodiment of the present invention is schematically shown in a perspective view.

(3) In FIG. 2, a portion of a linear electro-mechanical actuator according to an example embodiment of the present invention is schematically shown in a perspective view and in an assembled state.

(4) In FIG. 3, a portion of a linear electro-mechanical actuator according to an example embodiment of the present invention is schematically shown in an exploded view.

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

(6) The present invention relates to a linear electro-mechanical actuator 100 for transferring a rotational motion to a linear motion, which is schematically shown in FIG. 1. It should be readily appreciated that the linear electro-mechanical actuator may sometimes be denoted as the linear actuator or the actuator for the sake of simplicity. The actuator comprises a piston 10, a housing 20 and a transmission module 30. In FIG. 1, the example embodiment of the actuator here further comprises a separating member 40, a load-carrying member 60 such as a guiding member 62 and a motor 70. Throughout this description, the piston extends in the axial direction A and in the radial direction R. The linear electro-mechanical actuator further comprises a lubricating member (not shown in FIG. 1) described in more detail below.

(7) The piston 10 has a distal end 14 and a proximal end 16. The piston 10 extends in an axial direction A and has an outer load-carrying surface 12. The piston 10 is moveable relative to the housing 20 in the axial direction A. The housing 20 has an opening 22 being adapted to receive the distal end 14 of the piston 10. The housing 20 defines an inner milieu 101. Here, the housing 20 has the shape of a circular cylinder.

(8) As shown in FIG. 1, the piston 10 is at least partly arranged inside the housing 20. The part of the piston 10a being arranged inside the housing is arranged in the inner milieu 101. The part of the piston 10b extending outside the housing is arranged in the outer milieu 102. In a fully retracted state, the piston 10 is mainly, such as entirely, arranged in the inner milieu 101. In a fully extended state, the piston 10 is mainly, such as entirely, arranged in the outer milieu 102. In FIG. 1, the piston is in a partly extended state.

(9) The transmission module 30 is operatively connected to the proximal end of the piston 10 and adapted to transfer a rotational motion generated by the motor 70 to a linear motion of the piston 10 in the axial direction A. The transmission module 30 is arranged inside the housing 20 in the inner milieu 101 of the actuator 100.

(10) Although not strictly required, the transmission module 30 here comprises a rotatable screw 33 with a non-rotatable nut (not shown) running thereon. The screw extends over the full length of the actuator and sets the operating length of the actuator. The nut is held in a non-rotatable state, and is displaced when the screw shaft is rotated by the motor 70. The transmission module 30 is at least partly arranged inside the piston 10.

(11) As mentioned above, the linear actuator may typically, but not strictly necessarily, include a separating member. The separating member 40 is arranged adjacent the opening of the housing 20 and in between the piston 10 and the housing 20 as seen in a radial direction R.

(12) The separating member 40, herein shown as a scraper 44, separates the inner milieu 101 from the outer milieu 102 at an opening 22 of the housing adapted to receive the distal end 14 of the piston. The scraper 44 further serves to clean the outer surface 12 of the piston when retracting from the outer milieu 102 into the inner milieu 101.

(13) As mentioned above, the linear actuator may typically, but not strictly necessarily, include a load-carrying member such as a guiding member. In the example embodiment shown in FIG. 1, the guiding member 62 here is arranged in the inner milieu in between the piston and the housing as seen in the radial direction R. The guiding member 62 may be arranged either closer to the proximal end of the piston or closer to the distal end of the piston. In FIG. 1, the guiding member is arranged rather in the centre part of the piston. The guiding member serves to keep the piston 10 on track during its linear movements in the axial direction A. In particular, the guiding member serves to guide the piston such that it travels efficiently as it moves in the axial direction relative the housing.

(14) In FIGS. 2 and 3, a portion of the linear electro-mechanical actuator 100 in FIG. 1 is shown in more detail, namely, the lubricating member 50 and its surroundings. FIG. 2 shows the lubricating member 50 and its surroundings in an assembled state, while FIG. 3 is an exploded view of the lubricating member 50 and its surroundings. All features of the actuator 100 are not explicitly shown in either or both of FIGS. 2-3.

(15) The piston 10 having a distal end (not shown) and a proximal end 16 extends in the axial direction A. The proximal end 16 is arranged inside the housing 20, and, thus, in the inner milieu 101.

(16) The transmission module 30 is also arranged inside the housing 20, thus, in the inner milieu 101 of the actuator. The transmission module 30 comprises a rotating portion 32 and a non-rotating portion 36 being operatively engageable to each other. The rotating portion 32 has here an outer load-carrying surface, which here is threaded (34 in FIG. 2). The non-rotating portion 36 has here an inner threaded surface (38 in FIG. 3). The non-rotating portion 36 is operatively connected to the proximal end 16 of the piston 10 and the rotating portion 32 is operatively connected to a motor (not shown in FIGS. 2-3). The transmission module 30 is adapted to transfer a rotational motion of the rotating portion 32 generated by the motor to a linear motion of the piston 10 in the axial direction A via the non-rotating portion 36.

(17) In FIGS. 2-3, the proximal end 16 of the piston is operatively connected to the non-rotating portion 36, herein shown as a nut 37. The nut 37 is operatively engageable with the rotating portion 32, herein shown as a screw 33. However, it should be readily appreciated that in all of the embodiments of the present invention, the transmission module may not necessarily consists of a screw and a nut. Further, it should also be readily appreciated that in alternative embodiments, the non-rotating portion may be the screw and the rotating portion may be the nut.

(18) As illustrated in FIG. 2, the lubricating member 50 is present inside the housing 20, thus, in the inner milieu 101 of the actuator 100. The lubricating member 50 is arranged adjacent to the transmission module 30, and more specifically adjacent to the non-rotating portion 36, herein the nut 37. Preferably, the lubricating member is also arranged adjacent to the load-carrying surface of the rotating portion 32, herein the outer threaded surface 34 of the screw 33.

(19) The lubricating member 50 is arranged at a minor distance from (i.e. adjacent to) the non-rotating portion 36 as seen in the axial direction A. The lubricating member 50 is arranged at a minor distance from the rotating portion 32 as seen in the radial direction R. The lubricating member is typically arranged in between the rotating portion 32 and the housing 20 as seen in the radial direction R, as shown in FIG. 2.

(20) The lubricating member 50 here has the shape of a bushing 52. However, it should be readily appreciated that in all of the embodiments of the present invention, the lubricating member may not necessarily be a bushing. Accordingly, the lubricating member may be provided in several different forms as long as the lubricating member can include a porous polymeric matrix and a lubricating material while fulfilling the required function of the lubricating member.

(21) In FIG. 2, the bushing 52 is arranged about the rotating portion 32, herein the screw 33. The screw 33 has a threaded outer surface 34. The nut 37 and the bushing 52, respectively, have a threaded inner surface (shown as 38 in FIG. 3 of the nut 37). The threading of the screw 33 and the threading of the nut 37 and the bushing 52, respectively, are generally complementary and typically have the same pitch.

(22) Thus, in order to ensure a smooth operation of the linear actuator, the rotating member 32 should be freely moveable in the axial direction A relative to at least the lubricating member 50. The lubricating member 50 should preferably be rotationally locked to the non-rotating portion 36 in order to ensure said smooth operation including the transfer of the rotational motion of the rotating portion 32 to a linear motion of the piston 10 by means of the non-rotating portion 36. As seen in FIG. 2, the non-rotating portion 36 may include a recess 39 in which at least a portion of the lubricating member 50 may fit. Such as herein shown, the recess 39 typically has the same, or at least a similar, crosscut as the lubricating member 50. Typically, the lubricating member 50 is not load-carrying.

(23) Further, the load-carrying member 60 is shown in FIGS. 2-3. The load-carrying member 60 is arranged at the proximal end 16 of the piston, at least when the piston is in its fully retracted state. The load-carrying member 60 is entirely arranged in the inner milieu 101. As seen in FIG. 2, the load-carrying member 60 is arranged in between the piston 10 and the housing 20 as seen in the radial direction R. The load-carrying member 60 here has the general shape of a sleeve. The load-carrying member 60 surrounds almost the entire periphery of a cross-section of the piston. The load-carrying member 60 is arranged about the piston 10.

(24) The arrangement of the linear electro-mechanical actuator, shown in general in FIG. 1 and more in detail in FIGS. 2 and 3, allows for lubrication of at least a portion of the outer load-carrying surface 34 of the rotating portion 32 by the lubricating material of the lubricating member 50 upon movement of the rotating portion 32.

(25) In all of the embodiments of the present invention, there is provided a linear electro-mechanical actuator which is capable of improving the application of the lubrication in terms of precision and functionality, while providing a precise amount of a lubricating material. In this context, the linear electro-mechanical actuator according to the present invention may not even require relubrication. More specifically, by the arrangement of the linear electro-mechanical actuator as described above, it becomes possible to assemble the actuator easily in a dry state of the lubricating member, i.e. with no smeary grease, or other form of liquid or semi-liquid lubricating material, present except in the porous polymeric matrix of the lubricating member. In addition, the linear electro-mechanical actuator may easily be used due to a relatively controlled consumption of lubricating material causing substantially no leakage of lubricating material as well as due to its tolerance to e.g. washing as well as the linear electro-mechanical actuator may allow for environmentally friendly handling of the lubricating member including the unconsumed lubricating material at end of service life, in particular when provided as a separate member.

REFERENCE NUMBERS

(26) 100 linear electro-mechanical actuator 101 inner milieu 102 outer milieu A axial direction R radial direction 10 piston 10a part of piston in the inner milieu 10b part of piston in the outer milieu 12 outer load-carrying surface of the piston 14 distal end of the piston 16 proximal end of the piston 18 cross-section of the piston 19 periphery of the cross-section of the piston 20 housing 22 opening being adapted to receive the distal end of the piston 30 transmission module 32 rotating portion 33 screw 34 threaded outer surface (load-carrying surface of the rotating portion) 36 non-rotating portion 37 nut 38 threaded inner surface (load-carrying surface of the non-rotating portion) 39 recess 40 separating member 42 sealing member 44 scraper 50 lubricating member 52 bushing 60 load-carrying member 62 guiding member 70 motor