Electromechanical actuator having structural element for improved oil guide

Abstract

The invention relates to a linear actuator (10) having a tightly closed housing (20), a cantilever (70) which can be moved into and out of the housing, and a plurality of components arranged in the linear actuator (10). The assembly is designed such that the flow of lubricating oil through the linear actuator becomes easier, in particular when the boom is quickly moved in and out. This is achieved in that through-holes are provided in some components, through which lubricating oil and gas injected into the housing (20) can flow when moved in and out.

Description

Technical Field

[0001] This disclosure document relates to an electromechanical actuator as described in the preamble of claim 1, such as a lifting cylinder known as an electric cylinder. In particular, this disclosure document studies an electromechanical actuator having a housing and a cantilever linearly movably supported on the housing and having an oil guiding and lubricating structure especially in such an actuator. Background Art

[0002] Such actuators are in principle known in the prior art. Thus, DE 102020212703A1 and DE102020212704 A1 respectively explain a corresponding electric cylinder. DE 102020212703A1 proposes here that the lead screw driving the nut connected to the cantilever is supported such that the piston fluid-tightly separates a first region from a second region at the end of the lead screw. The second region is here a cavity partially filled with lubricating oil in which the lead screw is located. If the lead screw is withdrawn, the pressure in this cavity decreases, and if the lead screw is inserted, the pressure increases due to the pushing of the lead screw. DE102020212704 A1 describes an actuator in which the end block of the housing is fixed not by an annular nut but by a spacer plate and fixing screws passing through the end block and the spacer plate. The rotary bearing is clamped between the end block and the spacer plate by the clamping force of the fixing screws.

[0003] DE 102015221712 A1, regarded as the state of the art, discloses an actuator in which the cantilever extends out of the housing in the direction of the longitudinal axis, in which the lead screw is supported on the housing by means of a rotary bearing so as to be rotatable about the longitudinal axis, and the cantilever can be withdrawn and inserted by means of a nut screwed onto the lead screw. The lead screw is rotated by an electric motor. Here, (frictional) heat is generated especially at the meshing of the helical surfaces of the lead screw and the nut. Therefore, the interior space is filled with a fluid or a mixture of lubricating oil and gas, and cooling channels connect the opposite ends of the interior space. If the nut moves, it displaces the fluid, and the fluid flows through the cooling channels and beside the nut, for example around the rolling elements supporting the nut. Thereby, heat can be effectively transferred to the housing. The cooling channels are formed near the outer surface of the housing such that heat conduction into the ambient air is also very effective. The lubricating structure has a sealed barrier against the external atmosphere to prevent leakage and dirt. Since the volume of the interior space changes as the cantilever is withdrawn and inserted into the housing, it is disadvantageous or even impossible to completely fill it with an incompressible fluid (or theoretically also with a lubricated solid, such as powder). Conversely, satisfactory lubrication and cooling cannot be achieved with pure gas. Therefore, the filling preferably consists of a part (incompressible) lubricating oil and a part (compressible) gas.

[0004] However, especially when the cantilever is quickly moved in and out, the fluid cannot easily pass through the existing cooling channels and flow past the nut, thus generating a strong pressure difference inside the linear actuator. This pressure difference results in a higher idle torque of the shaft, which depends on the shaft speed and thus rises depending on the flow rate. This leads to lower efficiency of the shaft.

[0005] The liquid circulation in the housing proposed in the aforementioned prior art does not solve the problem because the liquid squeezed out of the inner space of the cantilever still has to flow through the nut. Summary of the Invention

[0006] To solve this problem, the linear actuator according to the invention has a plurality of optimized structural elements or components, which further improve the fluid passage in the inner space of the linear actuator. Specifically, the invention provides an electromechanical actuator having the features listed in claim 1. Advantageous improvements are the subject matter of the dependent claims.

[0007] Since the components in the housing are made and arranged such that the lubricating oil can flow through the through holes during the movement of the cantilever, the lubrication is improved and the pressure difference is reduced.

[0008] The through holes can extend parallel to the longitudinal axis of the cantilever, at an angle relative to the longitudinal axis of the cantilever or obliquely, or can also extend radially.

[0009] Since the main components in the housing rotate, they sink into the oil during each revolution in the oil-gas mixture. The oil may adhere to the through holes and the outer surface of the rotating components during passage and be carried to the parts outside the oil and the fixed components. Thereby, the lubrication of the "dry" (in the gas part) components is further improved and the friction between the moving and fixed components is further minimized.

[0010] In a preferred embodiment, the shaft seal ring has through holes along the main radial direction, which can allow oil to pass through. These holes can also have an axial component and a component along the circumferential direction, that is, "obliquely" extend through the shaft seal ring.

[0011] In another preferred embodiment, corresponding through holes are provided in at least one rotary bearing for supporting the cantilever. The cantilever is preferably supported in the housing by at least two rotary bearings, especially rolling bearings. Openings can be provided in the cage for the rolling elements in these rotary bearings and through holes can be provided in the rolling elements, such as hollow rollers, and / or in the bearing rings.

[0012] In yet another embodiment, at least one through-hole is provided in the lead screw. The lead screw is a component in a linear actuator, which rotates on the one hand and causes a linear movement of the cantilever on the other hand. Therefore, in the case of a rapid state change or movement of the linear actuator, the maximum flow resistance is expected on the lead screw, and thus the through-holes on the lead screw and in its environment can minimize the problem of pressure difference.

[0013] In addition, at least one through-hole can be provided in the sliding piston that supports the lead screw on the cantilever side. Particularly preferably, this through-hole is combined with the through-hole in the lead screw.

[0014] In another preferred embodiment, as a supplementary or alternative solution to the through-holes explained so far, through-holes are provided in the nut. This through-hole preferably extends parallel to the longitudinal axis of the actuator in addition.

[0015] In another preferred embodiment, at least one through-hole is provided in the rolling elements, especially planetary gears, that support the lead screw in the nut. Since planetary gears and similar rolling elements have a relatively small diameter, in this embodiment, it is advantageously suitable to drill a part of the rolling element or each rolling element.

[0016] In addition, it is preferably stipulated that the amount of oil and gas initially introduced into the actuator is such that the internal pressure in the actuator does not significantly exceed the value of 2 MPa in the fully inserted state of the actuator and does not significantly fall below the value of 0.8 MPa in the fully withdrawn state. For such a filling state, the pressure load is small in the inserted state, and there is also hardly any force that can squeeze dirt into the linear actuator acting on the seal in the withdrawn state. In addition, only a relatively small pressure difference may be formed during rapid movement in this way. Therefore, this pressure range is preferred.

[0017] Even though "through-holes" are mentioned here, it is obvious to those skilled in the art that the corresponding feasible solutions for the passage of fluids can be established not only by drilling, but also by additive manufacturing, milling, etching or in other ways, and the only decisive factor is that fluids can flow through these "through-holes". Description of the Drawings

[0018] Wherein:

[0019] Figure 1 is a diagram for explaining the system structure according to the first embodiment of the present disclosure document;

[0020] Figure 2 As from Figure 1The enlarged cutout portion of is a diagram of a first rotary bearing;

[0021] Figure 3 As from Figure 1 is an enlarged cutout of the end of the housing of the linear actuator remote from the first rotary bearing, ie the lower end of the tube in which the cantilever is guided; and

[0022] Figure 4 Also as from Figure 1 The enlarged cut-away portion is an illustration of a portion of the nut and its environment. DETAILED DESCRIPTION

[0023] Embodiments of the present disclosure are described below based on the associated figures.

[0024] First embodiment

[0025] According to the following Figure 1 The main components of the linear actuator 10 are explained. Figures 2 to 4 Modifications to individual components are shown.

[0026] Figure 1 The linear actuator 10 is shown in section. Along the longitudinal axis 13 from left to right in the figure (in the reading direction), the linear actuator 10 comprises as a structural assembly an electric motor 14, which is coupled to a lead screw 40 at a first end 41 thereof, which is supported in a lead screw rotation bearing 43. The lead screw rotation bearing 43 comprises two tapered roller bearings in an O-arrangement in the present embodiment and is received in a bearing seat 21 in the electric motor 14. The bearing seat 21 forms a housing 20 together with a tube 22 and a guide 23 for a cantilever 60 (to be explained later). A thread (not shown) is provided on the lead screw 40. A nut 62 cooperating with the lead screw 40 is received in the tube 22 in a rotationally fixed and linearly movable manner. In the figure, the nut 62 is shown in a simplified manner as being screwed directly on the lead screw 40, but in reality the lead screw 40 and the nut 62 are coupled to each other as is common in the prior art via rolling bodies, not shown here, such as planetary gears.

[0027] Now, if the electric motor 14 rotates the lead screw 40, the nut 62 moves left and right in the tube 22. The cantilever 60 is connected to the nut 62 and is thus moved out of and into the housing 20. Here, the cantilever is guided in the third housing part 23 of the housing 20. The third housing part 23 additionally seals the interior space against the external environment at the guiding part of the cantilever 60. In addition, a piston 50, a piston rotary bearing 51 and an end plate 52 are provided. The piston 50 abuts substantially fluid-tightly against the inner circumferential surface 61 of the cantilever 60 such that it seals the first cavity 11 in the tube 22 and the second cavity 12 in the cantilever 60 relative to each other, where the second cavity is arranged on the side of the piston 50 facing away from the lead screw rotary bearing 43.

[0028] According to the invention, a plurality of the components mentioned above have through-holes or longitudinal channels in order to improve, in particular during rapid movement in and out, the flushing or passage of lubricating oil and gas as fluids and thereby reduce the pressure difference explained above. Thus, a first longitudinal channel 81 is provided as a through-hole in the lead screw 40. A second longitudinal channel 82 (or multiple channels) is provided in the bearing housing 21. A third longitudinal channel 83 is in the piston 50, and a fourth longitudinal channel 84 runs through an adapter 70 provided in the lead screw nut 62. In addition to the longitudinal channels, inclined or radial through-holes, such as the radial hole 24 in the bearing housing 21, can also facilitate the passage of lubricating and cooling fluids.

[0029] Through such through-holes in the components in a tightly sealed space, fluids can flow through the interior space of the linear actuator 10 with as little resistance as possible. Thereby, the efficiency is improved as explained above.

[0030] The first cavity 11 in the bearing housing 21 is at least partially filled with liquid as explained. The nut 62 is open at its two ends facing each other along the longitudinal axis 13 such that liquid can flow through the nut 62 during movement of the cantilever 60.

[0031] For the present invention, as can be seen in Figure 2 a first longitudinal channel 81 is exemplarily arranged inside the lead screw 40, which extends along the longitudinal axis 13, where the first longitudinal channel 81 is fluidly connected to the first cavity 11 at its ends facing each other along the longitudinal axis 13 such that liquid can flow through the first longitudinal channel 81 during movement of the cantilever 60, bypassing the nut 6 regardless of the position of the cantilever 60.

[0032] The lead screw rotary bearing 43 is preferably constructed as a rolling bearing, which can include a plurality of tapered roller bearings or axial-spherical roller bearings. For example, in Figure 2It can be seen that there are two tapered roller bearings in an O-shaped arrangement, serving as the lead screw rotary bearings 43.

[0033] The nut 62 and the lead screw 40 are preferably in helical surface engagement through rolling elements, especially in the form of a planetary gear lead screw drive, where the rolling elements are corresponding planetary gear rollers. However, it is also conceivable that the nut 62 and the lead screw 50 are in helical surface engagement in the form of a ball screw drive, where the rolling elements are balls, and the balls preferably rotate continuously. In the case adjacent to the rolling elements, cavities are provided in the nut 62 through which the fluid can flow. In the case of the planetary gear or roller, in addition, drill holes can be provided along its axial direction through the roller or the planetary gear to further reduce the resistance to the fluid flow.

[0034] The fluid includes fractions of gas and liquid. The liquid is preferably oil, especially lubricating oil. The part of the first cavity 11 remaining beside the liquid is preferably filled with gas, especially air or nitrogen. The gas quantity is preferably designed such that the volume change of the first cavity associated with the movement of the cantilever causes a small overpressure or negative pressure, which would burden the seal of the first cavity. For example, depending on the size and lift of the actuator, a maximum overpressure of 2 to 3 MPa is sought when the actuator is moved in, and a maximum negative pressure of 0.2 to 0.5 MPa is sought when the actuator is fully moved out.

[0035] As can be Figure 2 seen, the first longitudinal channel 81 penetrates the lead screw rotary bearing 43. The lead screw 40 has at least one first orifice 91 on its outer circumferential surface 45 on the side of the lead screw rotary bearing 43 facing away from the nut 62. Through the first orifice, the first longitudinal channel 81 is fluidly connected to the first cavity 11 respectively, so that at least a part of the liquid flows through the lead screw rotary bearing 43 during the movement of the cantilever 60.

[0036] In addition, as can be Figure 2 seen, the lead screw 40 has a lead screw sealing surface 44 that is cylindrical with respect to the longitudinal axis 13 on its outer circumferential surface 45 in this embodiment. The first orifice 91 is correspondingly arranged along the direction of the longitudinal axis 13 between the lead screw sealing surface 44 and the lead screw rotary bearing 43. The lead screw sealing surface 44 is in sealing contact with a separate sealing ring 30. The sealing ring 30 is fixed to the housing 20 such that it seals the first cavity 11.

[0037] In the shown embodiment, as can be Figure 2Another detail seen is that a separate can-shaped sealing base 31 is provided, which has a bottom 32 and an annular edge 33 spaced apart from the bottom 32. The sealing ring 30 is fixed to the sealing base 31 in the region of the bottom 32, wherein the edge 33 of the sealing base 31 is fixed to the housing 20 radially outside the lead screw rotary bearing 43 and adjacent to the lead screw rotary bearing. In addition, the housing 20 has at least one second longitudinal channel 82 radially outside the lead screw rotary bearing 43 in the embodiment shown, and the second longitudinal channels each have a second orifice 92 and a third orifice 93 opposed to the second orifice 92 along the direction of the longitudinal axis 13. The second orifice 92 opens into the can-shaped sealing base 31. The third orifice 93 opens into the first cavity 11 on the side of the lead screw rotary bearing 43 opposed to the second orifice 92 such that liquid can flow through the second longitudinal channel 82 while bypassing the lead screw rotary bearing 43 when the cantilever 60 moves. Figure 2 In the embodiment shown, the housing 20 has at least one second longitudinal channel 82 radially outside the lead screw rotary bearing 43, and the second longitudinal channels each have a second orifice 92 and a third orifice 93 opposed to the second orifice 92 along the direction of the longitudinal axis 13. The second orifice 92 opens into the can-shaped sealing base 31. The third orifice 93 opens into the first cavity 11 on the side of the lead screw rotary bearing 43 opposed to the second orifice 92 such that liquid can flow through the second longitudinal channel 82 while bypassing the lead screw rotary bearing 43 when the cantilever 60 moves.

[0038] In Figure 2 the embodiment, the second longitudinal channels 82 are completely arranged on the bearing housing 21 receiving the lead screw rotary bearing 43. As shown in Figure 2 it is possible to assign a radial bore 24 to at least one second longitudinal channel 82, which radial bore leads from the second longitudinal channel 82 into the interior of the bearing housing 21.

[0039] As can be seen in Figure 2 at least one first orifice 91, preferably all first orifices 91, on the lead screw 40 are each formed by a respective single straight bore 46 leading into the first longitudinal channel 81. The straight bore 46 preferably opens into the longitudinal channel on the inner circumferential surface of the longitudinal channel 81. As shown in Figure 2 the bore is preferably cylindrical.

[0040] Figure 3 shows the other end of the housing 20, i.e., the end of the tube 22, in which the cantilever 60 is guided. As can be seen in Figure 3 the first longitudinal channel 81 opens into the second end 42 of the lead screw 40 on the end side. The can-shaped sliding piston or briefly the piston 50 is received on the second end 42 of the lead screw 40 in a rotatable manner about the longitudinal axis 13 by means of a piston rotary bearing 51. The piston rotary bearing 51 is configured such that fluid can flow through the piston rotary bearing 51 when the cantilever 60 moves. The piston rotary bearing can be made as a rolling bearing or as a sliding bearing. In the case of a sliding bearing (not shown here), the bearing clearance is preferably configured to be large enough such that fluid can flow through it.

[0041] In addition, the piston 50 includes a third longitudinal passage 83 in the present embodiment, and the third longitudinal passage merges into the first cavity 11. The third longitudinal passage 83 passes by the side of the piston rotary bearing 51 so that fluid can flow through the third longitudinal passage 83 while bypassing the piston rotary bearing 51 during the movement of the cantilever 60.

[0042] Figure 4 A preferred embodiment is shown in which the adapter 70 is provided on the nut 62, which has an internal thread 73, an external thread 74, a first flange 71 protruding radially inward, and a second flange 72 protruding radially outward. The cantilever 60 is screwed into the internal thread 73 and clamped toward the first flange 71. The nut 62 is tightened onto the external thread 74 and clamped toward the second flange 72. As can be seen Figure 4 from, the adapter 70 is also penetrated by at least one fourth longitudinal passage 84 in the direction of the longitudinal axis 13 so that all the liquid flowing through the nut 62 during the movement of the cantilever 60 flows through at least one fourth longitudinal passage 84.

[0043] In the present embodiment, the total flow resistance of at least one fourth longitudinal passage 84 is designed such that between 10% and 40% of the liquid flows through the nut 62 during the movement of the cantilever 60, while the remaining portion flows through the first longitudinal passage 81. Such a distribution has proven to be advantageous from the viewpoints of flow, strength, and wear.

Claims

1. A linear actuator (10), comprising the following components: The housing (20) and Cantilever (60), The cantilever arm (60) is supported in a first cavity (11) of a housing (20) in a manner that allows linear movement along a longitudinal axis (13) and extends out of the housing (20), the cantilever arm (60) having a second cavity (12) and a nut (62) that is in helical engagement with the threaded spindle (40), The nut (62) can be mounted in a rotationally fixed manner in the housing (20). a spindle rotary bearing (43), in which the spindle (40) is supported in the housing (20) at the end facing away from the cantilever (60); a motor, preferably an electric motor (14), for rotating the lead screw (40), The housing (20) and the cantilever (6) enclose a space which is hermetically sealed from the external atmosphere by means of seals (23, 30, 31, 32, 33, 51) and which contains a fluid, wherein the fluid comprises compressible and incompressible components. It is characterized in that One or more components each have at least one through-hole (81 to 84) in a space that is sealed off from the external atmosphere, which allows a fluid to pass through when the state of the linear actuator (10) changes.

2. The linear actuator (10) of claim 1, wherein the component comprises a shaft sealing ring (30).

3. The linear actuator (10) according to any one of claims 1 or 2, wherein a through hole is provided in at least one rotary bearing (43, 51) for supporting the cantilever (60).

4. The linear actuator (10) according to any one of claims 1 to 3, wherein a through hole (81) is provided in the lead screw (40).

5. The linear actuator (10) according to any one of claims 1 to 4 further comprises a piston (50) which is preferably designed in the shape of a pot and is received on the second end (42) of the threaded spindle (40) via a piston rotary bearing (51) in a manner that allows rotation about the longitudinal axis (13).

6. The linear actuator (10) according to claim 5, wherein a through hole (83) is provided in the piston (50).

7. The linear actuator (10) according to claim 1, wherein a through-hole is provided in the nut (62), the through-hole further preferably extending parallel to the longitudinal axis (13) of the linear actuator (10).

8. The linear actuator (10) according to any one of claims 1 to 7, further comprising an adapter (70) which is arranged on the nut (62) and has an internal thread (73), an external thread (74), a first flange (71) protruding radially inwardly and a second flange (72) protruding radially outwardly, wherein the cantilever (60) is screwed into the internal thread (73) and clamped against the first flange (71), and the nut (62) is screwed onto the external thread (74) and clamped against the second flange (72).

9. A linear actuator (10) according to any one of claims 1 to 8, wherein the fluid in the tightly closed space of the linear actuator (10) includes liquid and gaseous portions, wherein the amounts of the liquid and gaseous portions are specified so that in a state in which the linear actuator (10) is moved in to the maximum extent, the internal pressure in the linear actuator (10) does not significantly exceed a value of 2 MPa and in a state in which the linear actuator is moved out to the maximum extent, the internal pressure does not significantly fall below a value of 0.8 MPa.

10. A linear actuator (10) according to any one of claims 1 to 9, wherein the screw (40) has a cylindrical screw sealing surface (44) about the longitudinal axis (13) on its outer circumferential surface (45), wherein the at least one first opening (91) is arranged between the screw sealing surface (44) and the screw rotary bearing (43) respectively along the direction of the longitudinal axis (13), wherein the screw sealing surface (44) is in sealing contact with a separate sealing ring (30), and wherein the sealing ring (30) is fixed on the housing (20) so that it seals the first cavity (11).

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