Electromechanical actuator with design elements for improved oil flow

Abstract

Linear actuator (10) comprising the following components: a housing (20) and a boom (60), wherein the boom (60) is mounted linearly movable along a longitudinal axis (13) in a first cavity (11) of the housing (20) and protrudes from the housing (20), the boom (60) has a second cavity (12) and a threaded nut (62) which engages with a threaded spindle (40), wherein the threaded nut (62) can be stored in the housing (20) in a rotationally fixed manner, a spindle rotary bearing (43) in which the threaded spindle (40) is mounted at an end facing away from the boom (60) in the housing (20), a motor, preferably an electric motor (14), for rotating the threaded spindle (40), wherein housing (20) and boom (60) comprise a space which is hermetically sealed against the external atmosphere by means of seals (30, 31, 32, 33) and filled with a fluid, wherein the fluid comprises compressible and incompressible components, characterized in that one or more components in the space sealed against the external atmosphere each have at least one longitudinal channel (81 to 84) which allows the fluid to pass through when the state of the linear actuator (10) changes.

Description

Technical field

[0001] The present disclosure relates to an electromechanical actuator, for example a lifting cylinder referred to as an electric cylinder, according to the preamble of claim 1. In particular, the disclosure relates to an electromechanical actuator with a housing and a boom which is linearly movable on the housing, and specifically to the oil guidance and lubrication in such an actuator.

[0002] Such actuators are generally known in the prior art. For example, DE 10 2020 212 703 A1 and DE 10 2020 212 704 A1 each describe a corresponding electric cylinder. DE 10 2020 212 703 A1 proposes mounting a threaded spindle, which drives a nut connected to a cantilever, in such a way that a piston at the end of the threaded spindle fluid-tightly separates a first region from a second region. The second region is a cavity partially filled with lubricating oil, in which the threaded spindle is located. When the threaded spindle extends, the pressure in this cavity decreases; when it retracts, the pressure increases due to the displacement by the spindle. DE 10 2020 212 704 A1 shows an actuator in which an end block of the housing is not fastened via a ring nut, but via an intermediate plate and a fastening screw that passes through the end block and the intermediate plate.The swivel bearing is clamped in place by a clamping force of the fastening screw between the end block and the intermediate plate.

[0003] Further relevant state of the art includes DE 10 2009 007 952 A1, DE 10 2014 114 737 A1, DE 10 2015 221 712 A1, US 2021 / 0 039 771 A1 and JP 2023 19 005 A.

[0004] German patent DE 10 2008 007 793 A1 discloses a linear actuator comprising the following components: a housing and a cantilever, the cantilever being mounted linearly movable along a longitudinal axis in a first cavity of the housing and projecting from the housing. The cantilever has a second cavity and a threaded nut that engages with a threaded spindle. The threaded nut is rotatably mounted in the housing. The linear actuator also includes a spindle pivot bearing in which the threaded spindle is mounted at an end opposite the cantilever in the housing, and an electric motor for rotating the threaded spindle. The housing and cantilever enclose a chamber that is hermetically sealed against the external atmosphere by means of seals and filled with a fluid. The spindle nut in the chamber sealed against the external atmosphere has through-holes that allow the fluid to pass through when the linear actuator changes state.After the change of state is complete, the cavities are pressurized with pressure medium via a hydraulic accumulator to generate a higher holding force.

[0005] The DE 10 2015 221 712 A1, considered the closest available patent, discloses an actuator in which the boom extends out of the housing in the direction of the longitudinal axis. A threaded spindle is rotatably mounted on the housing via a rotary bearing, and the boom can be extended and retracted by means of a nut screwed onto the threaded spindle. The threaded spindle is rotated by an electric motor. Frictional heat is generated, particularly at the threaded engagement point between the spindle and the nut. Therefore, the interior is filled with a fluid or a mixture of lubricating oil and gas, and cooling channels connect opposite ends of the interior. As the nut moves, it displaces the fluid, which flows through the cooling channels and past the threaded nut, for example, around rolling elements that support the nut. This allows the heat to be efficiently transferred to the housing. The cooling channels are positioned close to the outer surface of the housing, ensuring highly efficient heat transfer to the surrounding air as well.The lubrication system is hermetically sealed against the external atmosphere to prevent leakage and contamination. Because the boom extends and retracts within the housing, thus changing the internal volume, a complete filling with an incompressible fluid (or theoretically even with lubricating solids such as powders) is impractical or even impossible. Conversely, satisfactory lubrication and cooling cannot be achieved with pure gas. Therefore, the filling preferably consists of a portion of (incompressible) lubricating oil and a portion of (compressible) gas.

[0006] Especially during rapid extension and retraction of the boom, the fluid cannot easily flow through the existing cooling channels and past the threaded nut, resulting in a significant differential pressure inside the linear actuator. This differential pressure leads to a higher no-load torque of the axis, which increases depending on the axis speed and thus the flow velocity. This results in a lower efficiency of the axis.

[0007] The fluid circulation in the housing proposed in the aforementioned prior art does not solve the problem because the fluid displaced from the interior of the boom still has to pass through the threaded nut.

[0008] To solve this problem, the linear actuator according to the invention comprises several optimized design elements or components that further improve fluid flow within the linear actuator. Specifically, the invention provides an electromechanical actuator with the features listed in claim 1. Advantageous embodiments are the subject of the dependent claims.

[0009] Because the components in the housing are designed and arranged in such a way that the lubricating oil can flow through through holes when the boom moves, lubrication is improved and the pressure difference is reduced.

[0010] The through holes can run parallel to the longitudinal axis, at an angle or obliquely to the longitudinal axis of the boom, or radially.

[0011] Since key components within the housing rotate, they are immersed in the oil-gas mixture with each revolution. Oil can adhere to the through-holes and the outer surfaces of the rotating parts as it passes through, and be carried to areas outside the oil and to stationary parts. This further improves the lubrication of parts located "dry" (in the gas component) and minimizes friction between moving and stationary parts.

[0012] In a preferred embodiment, a shaft seal, or simply sealing ring, has through-holes in a predominantly radial direction that are permeable to oil. These holes can also have an axial component as well as a component in the circumferential direction, i.e., run "obliquely" through the sealing ring.

[0013] In a further preferred embodiment, corresponding through-holes are provided in at least one rotary bearing for supporting the boom. The boom is preferably supported in the housing by at least two rotary bearings, in particular rolling bearings. These rotary bearings may have openings in cages for the rolling elements as well as through-holes in the rolling elements, for example hollow rollers, and / or in the bearing rings.

[0014] In a further embodiment, at least one through-hole is provided in the threaded spindle. The threaded spindle is the component in the linear actuator that both rotates and causes a linear movement of the arm. Therefore, the greatest flow resistance is to be expected at the threaded spindle during rapid changes of state or movements of the linear actuator, and consequently, through-holes on and around the threaded spindle can minimize the problem of pressure differentials.

[0015] Furthermore, at least one through-hole can be provided in the sliding piston, which supports the spindle on the side of the boom. This through-hole is particularly preferably combined with a through-hole in the threaded spindle.

[0016] In another preferred embodiment, a through-hole is provided in the threaded nut in addition to or as an alternative to the through-holes described so far. This through-hole preferably extends parallel to the longitudinal axis of the actuator.

[0017] In a further preferred embodiment, at least one through-hole is provided in rolling elements, in particular planets, which support the threaded spindle in the threaded nut. Since planets and similar rolling elements have relatively small diameters, it is advantageous in this embodiment to bore through part or all of the rolling elements centrally.

[0018] Preferably, the initial quantity of oil and gas introduced into the actuator is set such that, in the fully retracted state, the internal pressure in the actuator does not significantly exceed 2 MPa, and in the fully extended state, it does not significantly fall below 0.8 MPa. At such fill levels, the pressure load is low in the retracted state, and even in the extended state, there are hardly any forces acting on the seals that could force contaminants into the linear actuator. Furthermore, even with rapid operation, only small pressure differentials can build up. Therefore, this pressure range is preferred.

[0019] Even though the term "through holes" is used here, it is obvious to experts that the corresponding passageways for fluid can be created not only by drilling, but also by additive manufacturing, milling, etching or other means, and that the only crucial factor is that fluid can flow through these "through holes". Brief description of the characters Fig. Figure 1 is a representation illustrating a system structure according to the state of the art; Fig. Figure 2 is a representation of a first pivot bearing as an enlarged section from Fig. 1; Fig. Figure 3 is a representation of an end of the linear actuator housing furthest from the first pivot bearing, namely the end of a tube in which the boom is guided, as an enlarged section of Fig. 1; and Fig. Figure 4 is a representation of parts of a threaded nut and its surroundings, also as an enlarged section of Fig. 1. Description of the exemplary implementations

[0020] The following are examples of embodiments of the present disclosure based on the accompanying figures. First embodiment

[0021] Based on the Fig. 1. The essential components of a linear actuator 10 are explained below, according to which modifications of individual components according to the invention are based on the Fig. 2 to 4 will be displayed.

[0022] Fig. Figure 1 shows a section of a linear actuator 10. Along a longitudinal axis 13 in the figure, from left to right (in the reading direction), the linear actuator 10 comprises, as assemblies, an electric motor 14 coupled to a threaded spindle 40 at its first end 41, which is supported in a spindle slewing bearing 43. In the present embodiment, the spindle slewing bearing 43 comprises two tapered roller bearings in an O-arrangement and is received in a bearing support 21 at the electric motor 14. The bearing support 21, together with a tube 22 and a third housing part 23 acting as a guide for a (later explained) cantilever 60, forms a housing 20. A thread (not shown) is provided on the threaded spindle 40. A threaded nut 62, which interacts with the threaded spindle 40, is mounted in the tube 22 so as to be rotationally fixed and linearly movable.In the figures, the threaded nut 62 is shown, for simplicity, as being screwed directly onto the threaded spindle 40; however, in reality, the threaded spindle 40 and the threaded nut 62 are coupled to each other via rolling elements, such as planetary gears, which are not shown here, as is common in the prior art.

[0023] When the electric motor 14 rotates the threaded spindle 40, the threaded nut 62 moves left and right within the tube 22. The arm 60 is connected to the threaded nut 62 and thus extends and retracts from the housing 20. The arm is guided within a third housing part 23 of the housing 20. This third housing part 23 also seals the interior of the arm 60's guide against the external environment. Furthermore, a piston 50, a piston pivot bearing 51, and an end plate 52 are provided. The piston 50 rests against an inner circumferential surface 61 of the arm 60 in a substantially fluid-tight manner, sealing a first cavity 11 in the tube 22 and a second cavity 12 in the arm 60 against each other. The second cavity is located on the side of the piston 50 facing away from the spindle pivot bearing 43.

[0024] According to the invention, several of the aforementioned components have through-holes or longitudinal channels to improve the flushing or passage of lubricating oil and gas as fluids, particularly during rapid extension and retraction, and thereby reduce the pressure differential described above. For example, a first longitudinal channel 81 is provided as a through-hole in the threaded spindle 40. A second longitudinal channel 82 (or several channels) is provided in the bearing support 21. A third longitudinal channel 83 is located in the piston 50, and a fourth longitudinal channel 84 penetrates an adapter part 70 provided on the threaded nut 62. In addition to the longitudinal channels, skew or radial through-holes, such as a radial bore 24 in the bearing support 21, can also facilitate the passage of lubricating and cooling fluids.

[0025] These through-holes in the components, which are located in a hermetically sealed space, allow the fluid to flow through the interior of the linear actuator 10 with minimal resistance. This improves efficiency, as explained above.

[0026] As explained, a first cavity 11 in the bearing support 21 is at least partially filled with a liquid. The threaded nut 62 is open at its two ends opposite each other in the direction of the longitudinal axis 13, such that the liquid can flow through the threaded nut 62 when the boom 60 moves.

[0027] An example of the invention is the interior of the threaded spindle 40 as shown in Fig. 2 a first longitudinal channel 81 is arranged, which extends along the longitudinal axis 13, wherein the first longitudinal channel 81 is fluidically connected to the first cavity 11 at its ends opposite each other along the longitudinal axis 13 in such a way that the fluid can flow through the first longitudinal channel 81 when the boom 60 is moved, bypassing the threaded nut 62, regardless of the position of the boom 60.

[0028] The spindle slewing bearing 43 is preferably designed as a rolling bearing, and may comprise several tapered roller bearings or axial spherical roller bearings. For example, in Fig. 2 Two tapered roller bearings in an O-arrangement can be identified as spindle rotary bearings 43.

[0029] The threaded nut 62 and the threaded spindle 40 preferably engage via rolling elements, particularly in the manner of a planetary screw drive, wherein the rolling elements are the corresponding planetary rollers. However, it is also conceivable that the threaded nut 62 and the threaded spindle 40 engage in the manner of a ball screw drive, wherein the rolling elements are balls that preferably rotate endlessly. Adjacent to the rolling elements, cavities are provided in the threaded nut 62 through which the fluid can flow. In the case of planetary or rollers, bores can also be provided in their axial direction through the rollers or planetary gears, respectively, to further reduce the resistance to the fluid flow.

[0030] The fluid comprises a gas and a liquid component. The liquid is preferably oil, in particular lubricating oil. The portion of the first cavity 11 remaining after the liquid is preferably filled with a gas, in particular air or nitrogen. The gas volume is preferably designed such that the volume change of the first cavity associated with the movement of the boom causes minimal overpressure or underpressure that would stress the seal of the first cavity. For example, depending on the size and stroke of the actuator, a maximum overpressure of 2 to 3 MPa is targeted when the actuator is retracted and a maximum underpressure of 0.2 to 0.5 MPa when the actuator is fully extended.

[0031] As from Fig. As can be seen in Figure 2, the first longitudinal channel 81 passes through the spindle pivot bearing 43. The threaded spindle 40 has at least one first opening 91 on its outer circumferential surface 45 on the side of the spindle pivot bearing 43 facing away from the threaded nut 62, through which the first longitudinal channel 81 is fluidically connected to the first cavity 11 in such a way that at least a part of the fluid flows through the spindle pivot bearing 43 when the boom 60 is moved.

[0032] Furthermore, from the Fig. Figure 2 shows that the threaded spindle 40 in this embodiment has a spindle sealing surface 44 that is circularly cylindrical with respect to the longitudinal axis 13 on its outer circumferential surface 45. The first opening 91 is arranged in the direction of the longitudinal axis 13 between a spindle sealing surface 44 and the spindle rotary bearing 43. The spindle sealing surface 44 is in sealing contact with a separate sealing ring 30, as an example of a seal. The sealing ring 30 is attached to the housing 20 in such a way that it seals the first cavity 11.

[0033] As another in Fig. 2. A recognizable detail in the illustrated embodiment is a separate, cup-shaped sealing carrier 31 with a base 32 and an annular rim 33 spaced apart from the base 32. The sealing ring 30 is attached to the sealing carrier 31 in the area of ​​the base 32, with the rim 33 of the sealing carrier 31 being attached radially outside and adjacent to the spindle rotary bearing 43 on the housing 20. Furthermore, the housing 20 has in the Fig. In the embodiment shown in Figure 2, at least one second longitudinal channel 82 extends radially outside the spindle bearing 43, each channel having a second opening 92 and a third opening 93 opposite the second opening 92 in the direction of the longitudinal axis 13. The second opening 92 opens into the cup-shaped sealing carrier 31. The third opening 93 opens into the first cavity 11 on the side of the spindle bearing 43 opposite the second opening 92, such that the fluid can flow through the second longitudinal channel 82 bypassing the spindle bearing 43 when the boom 60 moves.

[0034] The second longitudinal channel 82 is in the embodiment of the Fig. 2 completely arranged on the bearing support 21, which accommodates the spindle rotary bearing 43. At least one second longitudinal channel 82 can be provided, as in Fig. Figure 2 illustrates a radial bore 24 which leads from the second longitudinal channel 82 into the interior of the bearing support 21.

[0035] As in Fig. As can be seen in Figure 2, at least one first opening 91 on the threaded spindle 40, and preferably all first openings 91, are each formed by a single, straight bore 46 which opens into the first longitudinal channel 81. The straight bore 46 preferably opens into the longitudinal channel 81 at an inner circumferential surface. As shown in Figure 2, the opening is formed by a single, straight bore 46 which opens into the first longitudinal channel 81. Fig. As shown in Figure 2, it is preferably circular-cylindrical in shape.

[0036] Fig. Figure 3 shows another end of the housing 20, namely the end of the tube 22 in which the boom 60 is guided. As in Fig. As can be seen in Figure 3, the first longitudinal channel 81 opens at its end face into a second end 42 of the threaded spindle 40. A cup-shaped sliding piston, or piston 50 in the following, is rotatably mounted about its longitudinal axis 13 at the second end 42 of the threaded spindle 40 via a piston pivot bearing 51. The piston pivot bearing 51 is designed such that the fluid can flow through it when the boom 60 moves. The piston pivot bearing can be designed as a rolling bearing or as a sliding bearing. In the case of a sliding bearing (not shown here), the bearing gap is preferably large enough to allow the fluid to flow through it.

[0037] Furthermore, in this embodiment, the piston 50 includes the third longitudinal channel 83, which opens into the first cavity 11. The third longitudinal channel 83 bypasses the piston pivot bearing 51 in such a way that, when the boom 60 moves, the fluid can flow through the third longitudinal channel 83, bypassing the piston pivot bearing 51.

[0038] Fig. Figure 4 shows a preferred embodiment in which an adapter part 70 is provided on the threaded nut 62, which has an internal thread 73, an external thread 74, a radially inwardly projecting first collar 71, and a radially outwardly projecting second collar 72. The extension 60 is screwed into the internal thread 73 and clamped against the first collar 71. The threaded nut 62 is screwed onto the external thread 74 and clamped against the second collar 72. As shown in Figure 4, the extension 60 is screwed into the internal thread 73 and clamped against the first collar 71. Fig. As can be seen in Figure 4, the adapter part 70 is also permeated in the direction of the longitudinal axis 13 by at least a fourth longitudinal channel 84, so that the entire fluid which flows through the threaded nut 62 when the boom 60 is moved flows through the at least one fourth longitudinal channel 84.

[0039] In this embodiment, the total flow resistance of the at least one fourth longitudinal channel 84 is designed such that, during movement of the boom 60, between 10% and 40% of the fluid flows through the threaded nut 62, while the remaining portion flows through the first longitudinal channel 81. Such a distribution has proven advantageous from the perspectives of flow, strength, and wear.

Claims

[1] Linear actuator (10) comprising the following components: a housing (20) and a boom (60), wherein the boom (60) is mounted linearly movable along a longitudinal axis (13) in a first cavity (11) of the housing (20) and protrudes from the housing (20), the boom (60) has a second cavity (12) and a threaded nut (62) which engages with a threaded spindle (40), wherein the threaded nut (62) can be stored in the housing (20) in a rotationally fixed manner, a spindle rotary bearing (43) in which the threaded spindle (40) is mounted at an end facing away from the boom (60) in the housing (20), a motor, preferably an electric motor (14), for rotating the threaded spindle (40), wherein housing (20) and boom (60) comprise a space which is hermetically sealed against the external atmosphere by means of seals (30, 31, 32, 33) and filled with a fluid, wherein the fluid comprises compressible and incompressible components, characterized by , that one or more components in the space sealed against the external atmosphere each have at least one longitudinal channel (81 to 84) which allows the fluid to pass through when the linear actuator (10) changes state. [2] Linear actuator (10) according to claim 1, wherein the components comprise a sealing ring (30). [3] Linear actuator (10) according to one of claims 1 or 2, wherein a longitudinal channel is provided in at least one rotary bearing (43, 51) for supporting the boom (60). [4] Linear actuator (10) according to one of claims 1 to 3, wherein a longitudinal channel (81) is provided in the threaded spindle (40). [5] Linear actuator (10) according to one of claims 1 to 4, further comprising a preferably cup-shaped piston (50) which is rotatably mounted about the longitudinal axis (13) at the second end (42) of the threaded spindle (40) via a piston rotary bearing (51). [6] Linear actuator (10) according to claim 5, wherein a longitudinal channel (83) is provided in the piston (50). [7] Linear actuator (10) according to one of claims 1 to 6, wherein a longitudinal channel is provided in the threaded nut (62) which further preferably extends parallel to the longitudinal axis (13) of the linear actuator (10). [8] Linear actuator (10) according to one of claims 1 to 7, further comprising an adapter part (70) provided on the threaded nut (62), which has an internal thread (73), an external thread (74), a radially inward projecting first collar (71) and a radially outward projecting second collar (72), wherein the cantilever (60) is screwed into the internal thread (73) and clamped against the first collar (71), and the threaded nut (62) is screwed onto the external thread (74) and clamped against the second collar (72). [9] Linear actuator (10) according to any one of claims 1 to 8, wherein the fluid in the hermetically sealed space of the linear actuator (10) comprises a liquid and a gaseous component, wherein the amounts of the liquid and gaseous components are determined such that in a maximally retracted state of the linear actuator (10) the internal pressure in the linear actuator (10) does not substantially exceed a value of 2 MPa, and the internal pressure in a maximally extended state does not substantially fall below a value of 0.8 MPa. [10] Linear actuator (10) according to one of claims 1 to 9, wherein the threaded spindle (40) has a circular cylindrical spindle sealing surface (44) on its outer circumferential surface (45) with respect to the longitudinal axis (13), wherein the at least one first opening (91) is arranged in the direction of the longitudinal axis (13) between the spindle sealing surface (44) and the spindle rotary bearing (43), wherein the spindle sealing surface (44) is in sealing contact with a separate sealing ring (30), and wherein the sealing ring (30) is attached to the housing (20) in such a way that it seals the first cavity (11).

Images