Linear actuator with hydrostatic threaded nut and hybrid axial bearing

Abstract

Actuator (10) with a housing (20) and a moving body (50) linearly movable in the direction of a longitudinal axis (11) relative to the housing (20), wherein the moving body (50) has a first and a second section (51; 52) which are arranged side by side in the direction of the longitudinal axis (11), wherein the first section (51) extends along the longitudinal axis (11) with a constant outer cross-sectional shape, wherein the second section (52) is provided with an external thread (53), wherein the second section (52) is surrounded by a nut (30) with an internal thread (31), wherein the internal thread (31) engages with the external thread (53), wherein a high-pressure port (12) is arranged on the housing (20), wherein the housing (20) comprises a support surface (23) pointing in the direction of the longitudinal axis (11), wherein the nut (30) has a counter-support surface (33) on the support surface (23) such a situationthat the nut (30) is rotatable relative to the housing (20) with respect to the longitudinal axis (11), wherein a first pressure field (61) is arranged between the support surface (23) and the counter-support surface (33), which is fluidically connected to the high-pressure port (12) via the housing (20), wherein a second pressure field (62) is arranged between the internal thread (31) and the external thread (53), which is fluidically connected to the first pressure field (61) via the nut (30), characterized in that a rolling bearing (40) rotatable with respect to the longitudinal axis (11) is arranged on the side of the nut (30) facing away from the support surface (23), wherein the rolling bearing (40) is installed between the housing (20) and the nut (30) in such a way that it can support hydrostatic forces caused by the first pressure field (61) in the direction of the longitudinal axis (11).

Description

[0001] The invention relates to an actuator according to the preamble of claim 1.

[0002] US Patent 4,276,003 discloses an actuator having a moving body that is linearly movable about a longitudinal axis. A first section of the moving body is used as a pump piston. A second section of the moving body has an external thread that engages with a nut. Both the threaded connection and the nut's rotary bearing are hydrostatically mounted and are supplied with pressurized fluid from a single high-pressure port. The moving body is supported against rotation about its longitudinal axis by the housing in the region of its first section. The nut is connected to an electric motor for rotary drive.

[0003] AT 282 291 B shows a hydrostatic screw drive. JP 2008-069 761 A shows another hydrostatic screw drive. DE 26 30 740 B2 shows a spindle unit for a machine tool. DE 24 04 930 A shows a feed device with a screw drive.

[0004] One advantage of the actuator according to the invention is that it is simpler and less expensive to manufacture. During operation, significantly less leakage occurs, particularly at the rotary bearing of the nut. The resulting operating costs are correspondingly much lower. At the same time, the corresponding axial bearing can withstand considerably higher forces than is the case with US 4,276,003. In particular, the performance capacity of the hydrostatic threaded nut can be fully utilized. The actuator according to the invention is universally applicable and not limited to use as a pump.

[0005] According to claim 1, it is proposed that a rolling bearing rotatable with respect to the longitudinal axis be arranged on the side of the nut facing away from the support surface, wherein the rolling bearing is installed between the housing and the nut such that it can support hydrostatic forces caused by the first pressure field in the direction of the longitudinal axis. The actuator according to the invention is particularly suitable for applications in which high forces occur and only short strokes are performed. The actuator can be operated at high stroke frequencies. It is not necessary to perform separate stroke movements that serve solely for the lubrication of the actuator.

[0006] The first and / or the second pressure field may have an undefined boundary, the first pressure field being formed, for example, by the fact that the support surface and the counter-support surface in the area of ​​the first pressure field are completely flat and perpendicular to the longitudinal axis. Preferably, the first and / or the second pressure field has a defined boundary, which is most preferably defined by at least one recess. The first pressure field is preferably defined by at least one recess, which is arranged within the support surface and / or the counter-support surface such that contact between the support surface and the counter-support surface limits the first pressure field. The recess preferably extends in an annular shape around the longitudinal axis with a constant, in particular rectangular, cross-sectional shape.It is understood that the contact between the support surface and the counter-support surface, apart from the aforementioned recess, is preferably designed such that a thin hydrostatic lubricating film forms there, which most preferably causes the least possible leakage. The load-bearing capacity of the corresponding hydrostatic bearing is determined predominantly by the extent of the recess and to a significantly lesser extent by the contact described above.

[0007] The rolling bearing can be designed as a deep groove ball bearing, preferably an angular contact ball bearing. The rolling bearing can also be designed as a tapered roller bearing. It is conceivable that the rolling bearing is designed as a bearing assembly consisting of several individual bearings connected in parallel.

[0008] The moving part is preferably formed in one piece. It is conceivable that the moving part comprises several separate parts that are firmly connected to each other.

[0009] The moving body is preferably supported against rotation about its longitudinal axis on the housing. It is conceivable that the outer cross-sectional shape of the first section and a corresponding shape on the housing are designed accordingly, deviating in particular from a circular shape. However, the outer cross-sectional shape of the first section of the moving body is preferably circular with respect to the longitudinal axis, and most preferably the anti-rotation device described below is used.

[0010] The actuator is preferably operated with a pressure fluid, which is most preferably a liquid, in particular hydraulic oil.

[0011] The dependent claims specify advantageous further developments and improvements of the invention.

[0012] It can be provided that the rolling bearing is preloaded at least in the direction of the longitudinal axis. The preload is preferably designed such that the leakage occurring at the first pressure field remains below a predetermined limit value, regardless of the external load acting on the actuator, in particular on the moving body.

[0013] It can be provided that the nut is supported radially with respect to the longitudinal axis solely by the rolling bearing on the housing, with contact between the bearing surface and the counter-bearing surface defining a plane that is oriented perpendicular to the longitudinal axis. The hydrostatic thrust bearing at the first thrust field is thus particularly easy to manufacture, since it does not support any forces radially to the longitudinal axis. The clearance at the first thrust field is determined solely by the preload of the rolling bearing and not by the dimensions of the components involved in the hydrostatic support, as in US 4,276,003.

[0014] The housing may include a mandrel extending along the longitudinal axis, which is rigidly connected to the remaining housing. The mandrel extends into a recess in the moving body, and the moving body is supported against the mandrel in the region of the recess, preventing rotation about the longitudinal axis. This provides anti-rotation protection for the moving body without increasing the actuator's overall length in the direction of the longitudinal axis. The mandrel preferably extends along the longitudinal axis with a constant outer cross-sectional shape, which is most preferably designed as a splined shaft.The recess of the moving body preferably extends along the longitudinal axis with a constant inner cross-sectional shape, wherein the inner cross-sectional shape is adapted to the outer cross-sectional shape in the sense of the aforementioned rotationally fixed support, wherein most preferably a small clearance and / or at least a narrow gap is present in sections.

[0015] It can be provided that a low-pressure connection is arranged on the housing, with at least one outlet opening arranged on the outside of the mandrel, wherein the at least one outlet opening is fluidically connected to the low-pressure connection via the mandrel. Preferably, all leakage occurring within the housing is directed through the at least one outlet opening. Consequently, the anti-rotation device located there is reliably lubricated. Preferably, a single outlet opening is provided. The at least one outlet opening is preferably permanently fluidically connected to the low-pressure connection.

[0016] It can be provided that at least one outlet opening is arranged on the mandrel such that the recess of the moving body covers at least one outlet opening over at least 70% of the maximum possible stroke of the moving body, wherein said coverage defines a gap between the mandrel and the moving body through which pressurized fluid can continuously reach the at least one outlet opening. This ensures reliable lubrication of the anti-rotation device between the mandrel and the moving body.

[0017] It can be provided that the nut adjacent to the rolling bearing is equipped with external teeth, and an electric motor is provided which is connected to the nut via the external teeth for rotary drive. This allows a commercially available electric motor to be used as a cost-effective drive. The axis of rotation of the electric motor is preferably arranged parallel to the longitudinal axis. A gear is preferably attached to a shaft of the electric motor, which meshes with the external teeth. The external teeth are preferably designed as helical teeth.

[0018] It can be provided that the first section of the moving body exits the housing at a linear bearing, the housing being fluid-tight except for the high-pressure port and, optionally, the low-pressure port. Any leakage that inevitably occurs inside the housing thus does not contaminate the actuator's surroundings. The linear bearing is preferably designed as a sliding bearing, and most preferably provides a seal against the escape of pressurized fluid from the housing.

[0019] It can be provided that the rolling bearing is designed without seals, allowing pressurized fluid inside the housing to pass through the bearing. This pressurized fluid is caused in particular by leaks at the first and second pressure fields, and is preferably discharged from the housing via the low-pressure port. It is essentially pressureless. The proposed permeability of the rolling bearing allows for a largely unimpeded flow of the leaks within the entire housing. At the same time, the rolling bearing is reliably lubricated.

[0020] The housing may include a sleeve that is circularly cylindrical with respect to its longitudinal axis and is rigidly connected to the remaining housing, with the support surface located at the end face of the sleeve, and the high-pressure port being fluidically connected to the first pressure field via the sleeve. The inner diameter of the sleeve is preferably adapted to a tip diameter of the external thread of the moving body with minimal clearance.

[0021] The sleeve can be arranged within the remaining housing, having at least one radial opening. Pressureless fluid can flow through this radial opening from radially outside the sleeve to radially inside it. Besides the radial opening and the open rolling bearing, no further channels are required in the actuator according to the invention to allow for the exchange of leakage fluid within the entire housing interior. It is ensured that all leakage fluids can reach the low-pressure connection.

[0022] It is conceivable that the moving body includes a channel with a function comparable to a radial opening. However, this would be more difficult to manufacture.

[0023] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0024] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a perspective view of an actuator according to the invention; Fig. 2 a longitudinal section of the actuator according to Fig. 1; Fig. 3. A side view of the actuator. Fig. 1, with the second and third housing parts removed.

[0025] Fig. Figure 1 shows a perspective view of an actuator 10 according to the invention. The actuator 10 comprises a housing 20 from which a moving body 50 projects in the direction of a longitudinal axis 11. An electric motor 70 is attached to the housing 20, by means of which the moving body 50 can be moved back and forth in the direction of the longitudinal axis 11. The first section 51 of the moving body 50, which can project from the housing 20, is preferably cylindrical with respect to the longitudinal axis 11. A fastening means (not shown) for a further assembly can be arranged at its free end, wherein, for example, a ball joint head may be provided.

[0026] The housing 20 is designed to essentially fluid-tightly enclose the internal components, with pressure fluid only able to enter and exit the housing 20 via the high- and low-pressure ports 12 and 13. The pressure fluid is preferably a liquid, and most preferably hydraulic oil. The housing 20 comprises a first, second, third, and fourth housing part 81, 82, 83, and 84, which are arranged side by side along the longitudinal axis 11 in the specified order and are firmly connected to one another, in particular by bolting. The second housing part 82 is preferably a casting. It has a cup-shaped section 85, which in particular accommodates the nut (No. 30 in Fig. 2) and the sleeve (No. 22 in Fig. 2) surrounds. The open end of the pot-shaped section 85 is closed by the first housing part 81, which is designed as a flat plate of constant thickness and has a circular rim with respect to the longitudinal axis 11. The high-pressure port 12 is directly attached to the first housing part 81, positioned at a distance from the longitudinal axis 11. The mandrel 21 is attached to the first housing part 81 concentrically with respect to the longitudinal axis 11 and projects into the interior of the housing 20. The low-pressure port 13 is arranged on the mandrel 21, concentrically with respect to the longitudinal axis 11.

[0027] The second housing part 82 has a lateral bulge 86, the shape of which corresponds to the gear (No. 71 in Fig. 2) is adapted inside. The electric motor 70 is attached externally to the lateral bulge 86, in particular by screws.

[0028] The third housing part 83 is designed as a circular cylindrical tube with a constant wall thickness with respect to the longitudinal axis 11, and is rigidly connected to the second housing part 82. It is conceivable to manufacture the second and third housing parts 82 and 83 as a single piece. The fourth housing part 84 forms a mounting flange, which is preferably arranged at the end of the third housing part 83 where the moving element 50 projects from the housing 20. The third and fourth housing parts 83 and 84 can be manufactured as a single piece.

[0029] Fig. Figure 2 shows a longitudinal section of actuator 10. Fig. 1. The moving body 50 is formed in one piece. It has a first and a second section 51; 52, which are directly adjacent to each other along the longitudinal axis 11. The first section 51 is cylindrical with respect to the longitudinal axis 11. The second section 52 is provided with an external thread 53 concentric with the longitudinal axis 11, which in this case has a trapezoidal profile. A recess 54 is arranged within the second section 52, which extends along the longitudinal axis 11 with a constant internal cross-sectional shape and is open towards the first housing part 81. The separate mandrel 21 projects into the recess 54, extending along the longitudinal axis 11 with a constant external cross-sectional shape. The external cross-sectional shape is designed in the manner of a splined shaft, with the aforementioned internal cross-sectional shape being adapted to the external cross-sectional shape with minimal clearance.Accordingly, the moving body 50 is supported against rotation with respect to the longitudinal axis 11 on the mandrel 21, the mandrel 21 being in turn attached to the first housing part 81. The aforementioned splined connection allows movement of the moving body 50 along the longitudinal axis 11.

[0030] Inside the mandrel 21 is a channel 87, which runs concentrically with respect to the longitudinal axis 11 in sections. At one end, the channel 87 opens onto the low-pressure port 13 on the outside of the housing 20. At the opposite end, the channel 87 has a discharge opening 25, which is located on the outer circumferential surface of the mandrel 21. The discharge opening 25 is covered by the recess 54 with a narrow gap in every possible position of the moving body 50. The leakage occurring within the housing 20 is conveyed to the low-pressure port 13 via the channel 87. The arrangement of the discharge opening 25 described above ensures that the splined shaft engagement between the mandrel 21 and the recess 54 is reliably lubricated by the pressure fluid from the leakage. The position of the outlet opening 25 also defines the oil level level inside the housing 20, which depends on the installation position of the actuator 10.

[0031] A nut 30 is arranged around the second section 52, which has an internal thread 31 that engages with the external thread 53 of the moving body 50. A second pressure field 62 is arranged between the internal thread 31 and the external thread 53, and is supplied with pressurized fluid from the high-pressure port 12. Corresponding hydrostatic threaded drives are known, for example, from AT 282291 B. The entire contents of AT 282291 B are incorporated by reference and made part of the present application, with particular reference to the design of the recesses on the nut 30 that define the second pressure field 62.

[0032] In contrast to the moving body 50, the nut 30 is rotatable relative to the housing 20 with respect to the longitudinal axis 11. The corresponding rotary bearing comprises a rolling bearing 40 and a hydrostatic first pressure field 61.

[0033] The housing 20 comprises a separate sleeve 22, which is designed in the form of a circular cylindrical tube with constant wall thickness with respect to the longitudinal axis 11. The inner diameter of the sleeve 22 is adapted to the head diameter of the external thread 53 with minimal clearance. The sleeve 22 is connected by its Fig. The sleeve 22 is attached at its right end to the inside of the first housing part 81, in particular by screws. At the opposite end, the sleeve 22 has a support surface 23, which is flat and oriented perpendicular to the longitudinal axis 11. A similarly flat counter-support surface 33 of the nut 30 rests against the support surface 23. A recess 60 is arranged within the support surface 23 and / or within the counter-support surface 33, which defines the extent of the first pressure field 61. The recess 60 extends in an annular shape around the longitudinal axis 11 with a constant cross-sectional shape, which is, for example, rectangular. The recess 60 is permanently fluidically connected to the high-pressure port 12 via the channel 88 in the sleeve 22. At least one further channel 89 in the nut 30 fluidically connects the first pressure field 61 to the second pressure field 62, so that at the center of both pressure fields 61; 62 the same pressure is applied.The leaks deliberately occurring at pressure fields 61; 62 are directed via the outlet opening 25 to the low-pressure connection 13.

[0034] A hydraulically effective area of ​​the first pressure field 61 is preferably equal to a hydraulically effective area of ​​the second pressure field. This results in a force equilibrium between the two pressure fields 61 and 62.

[0035] On the side of the nut 30 facing away from the support surface 23, the rolling bearing 40 is arranged, which in this case is designed as a single-row angular contact ball bearing and is rotatable with respect to the longitudinal axis 11. The corresponding outer ring is received in a separate bearing holder 90, the bearing holder 90 being attached internally to the second housing part 82, in particular by screws or press fittings. The corresponding inner ring is received directly on the nut 30. The rolling bearing 40 is preferably preloaded, the magnitude of this preload being decisive for the leakage at the first pressure field 61 when no external load acts on the moving body 50. The stiffening effect of the solid bearing holder 90 should be noted here. The aforementioned preload therefore causes only a slight elastic deformation of the second housing part 82.The bearing holder 90 is preferably designed in the form of a closed ring which rotates around the longitudinal axis 11 with a constant cross-sectional shape, and is most preferably formed in one piece.

[0036] The rolling bearing 40 is preferably designed without seals, so that the pressurized fluid present due to leaks in the interior of the housing 20 can pass through the rolling bearing 40. This lubricates the rolling bearing 40 and ensures that leaks, wherever they occur, can flow towards the low-pressure port 13. Reference is also made to the radial opening (No. 24 in [reference to figure]). Fig. 3) referred.

[0037] An external toothing 34 is provided on the outside of the nut 30, preferably in the form of a helical gear. The external toothing 34 meshes with a matching gear 71, which is fixedly mounted on the shaft of the electric motor 70. This allows the nut 30 to be set into rotary motion by the electric motor 70. Consequently, the moving body 50 performs a linear movement along the longitudinal axis 11. Due to the hydrostatic bearing described above, high forces can be exerted. A force acting at the free end of the moving body is preferably directed towards the support surface 23.

[0038] It should also be noted that the linear bearing 26 is located in the area of ​​the first section 51 of the moving body 50, and is preferably designed as a sliding bearing. The linear bearing 26 guides the first section 51 of the moving body 50 along the longitudinal axis 11. Furthermore, the linear bearing 26 forms a seal against the escape of pressurized fluid from the interior of the housing 20. It is preferably designed analogously to a corresponding linear bearing on a hydraulic cylinder.

[0039] Fig. Figure 3 shows a side view of actuator 10. Fig. 1, with the second and third housing parts removed. It can be seen that the sleeve 22 together with the first housing part 81 forms the in Fig. 3 almost completely encloses the right end of the moving body 50. In order to nevertheless, the area outside the in Fig. 3 shown sub-assembly leaks to the low-pressure connection (No. 13 in Fig.2) To allow the fluid to escape, at least one radial opening 24 is provided in the sleeve 22. The radial opening 24 is preferably in the form of a circular bore that is oriented perpendicular to the longitudinal axis 11. Reference sign 10 Actuator 11 Longitudinal axis 12 High-pressure connection 13 Low-pressure connection 20 cases 21 Dorn 22 Sleeve 23 Support surface 24 radial penetration of the sleeve 25 Mouth opening at Dorn 26 linear bearings 30 mother 31 internal threads 33 Counter support surface 34 External teeth 40 rolling bearings 50 moving bodies 51 first section 52 second section 53 external threads 54 Exclusion 60 Recesses that define the first print area 61 first print field 62 second print field 70 electric motor 71 gear 81 first housing part 82 second housing part 83 third housing part 84 fourth housing part 85 pot-shaped section of the second housing part 86 lateral bulge of the second housing part 87 Canal in Dorn 88 Channel in the sleeve 89 Channel in the mother 90 bearing holders

Claims

[1] Actuator (10) with a housing (20) and a moving body (50) which is linearly movable in the direction of a longitudinal axis (11) relative to the housing (20), wherein the moving body (50) has a first and a second section (51; 52) which are arranged next to one another in the direction of the longitudinal axis (11), wherein the first section (51) extends with a constant external cross-sectional shape along the longitudinal axis (11), wherein the second section (52) is provided with an external thread (53), wherein the second section (52) is surrounded by a nut (30) with an internal thread (31), wherein the internal thread (31) is in screw engagement with the external thread (53), wherein a high-pressure connection (12) is arranged on the housing (20), wherein the housing (20) comprises a support surface (23) pointing in the direction of the longitudinal axis (11), wherein the nut (30) is provided with a counter-support surface (33) on the Support surface (23) in such a way,that the nut (30) is rotatable relative to the housing (20) with respect to the longitudinal axis (11), wherein a first pressure field (61) is arranged between the support surface (23) and the counter-support surface (33), which is fluidically connected to the high-pressure connection (12) via the housing (20), wherein a second pressure field (62) is arranged between the internal thread (31) and the external thread (53), which second pressure field (62) is fluidically connected to the first pressure field (61) via the nut (30), characterized by that a rolling bearing (40) which is rotatable with respect to the longitudinal axis (11) is arranged on the side of the nut (30) facing away from the support surface (23), wherein the rolling bearing (40) is installed between the housing (20) and the nut (30) in such a way that it can support hydrostatic forces caused by the first pressure field (61) in the direction of the longitudinal axis (11). [2] Actuator (10) according to claim 1, wherein the rolling bearing (40) is preloaded at least in the direction of the longitudinal axis (11). [3] Actuator (10) according to one of the preceding claims, wherein the nut (30) is supported radially with respect to the longitudinal axis (11) exclusively via the rolling bearing (40) on the housing (20), wherein a contact between the support surface (23) and the counter-support surface (33) defines a plane which is oriented perpendicular to the longitudinal axis (11). [4] Actuator (10) according to one of the preceding claims, wherein the housing (20) comprises a mandrel (21) extending along the longitudinal axis (11) and being fixedly connected to the remaining housing, wherein the mandrel (21) extends into a recess (54) of the moving body (50), wherein the moving body (50) is supported on the mandrel (21) in the region of the recess (54) in a rotationally fixed manner with respect to the longitudinal axis (11). [5] Actuator (10) according to claim 4, wherein a low-pressure connection (13) is arranged on the housing (20), wherein at least one orifice (25) is arranged on the outside of the mandrel (21), wherein the at least one orifice (25) is fluidically connected to the low-pressure connection (13) via the mandrel (21). [6] Actuator (10) according to claim 5, wherein the at least one orifice (25) is arranged on the mandrel (21) such that the recess (54) of the moving body (50) covers at least one orifice (25) over at least 70% of a maximum possible stroke of the moving body (50), wherein said coverage defines a gap between the mandrel (21) and the moving body (50) through which pressure fluid can permanently reach the at least one orifice (25). [7] Actuator (10) according to one of the preceding claims, wherein the nut (30) is provided with an external toothing (34) adjacent to the rolling bearing (40), wherein an electric motor (70) is provided which is in rotary drive connection with the nut (30) via the external toothing (34). [8] Actuator (10) according to one of the preceding claims, wherein the first portion (51) of the moving body (50) emerges from the housing (20) at a linear bearing (26), wherein the housing (20) is fluid-tightly closed with the exception of the high-pressure connection (12) and the low-pressure connection (13). [9] Actuator (10) according to claim 8, wherein the rolling bearing (40) is formed without seals so that pressure fluid inside the housing (20) can pass through the rolling bearing (40). [10] Actuator (10) according to one of the preceding claims, wherein the housing (20) comprises a sleeve (22) which is circularly cylindrical with respect to the longitudinal axis (11) and which is fixedly connected to the remaining housing, wherein the support surface (23) is arranged on the end face of the sleeve (22), wherein the high-pressure connection (12) is fluidically connected to the first pressure field (61) via the sleeve (22). [11] Actuator (10) according to claim 10, dependent on claim 8 or 9, wherein the sleeve (22) is arranged within the remaining housing, having at least one radial opening (24).

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