DE102022201361A1 - Linear actuator with hydrostatic threaded nut and hybrid axial bearing - Google Patents

Abstract

The invention relates to an actuator (10) with a housing (20) and a moving body (50) that can be moved linearly in the direction of a longitudinal axis (11) relative to the housing (20), the moving body (50) having a first and a second section (51; 52) which are arranged next to one another in the direction of the longitudinal axis (11), the first section extending with a constant external cross-sectional shape along the longitudinal axis (11), the second section being provided with an external thread (53), the second section (52) is surrounded by a nut (30), the housing (20) comprising a support surface (23) pointing in the direction of the longitudinal axis (11), the nut (30) having a counter-support surface (33) on the support surface (23 ) rests in such a way that the nut (30) can be rotated with respect to the longitudinal axis (11) relative to the housing (20), with a first pressure field (61) being arranged between the supporting surface (23) and the counter-supporting surface (33), which over the Housing (20) is fluidically connected to a high-pressure connection (12), a second pressure field (62) being arranged between the internal thread (31) and the external thread (53), which is connected to the first pressure field (61) via the nut (30). is fluidically connected.According to the invention, on the side of the nut (30) facing away from the support surface (23), a roller bearing (40) that is rotatable with respect to the longitudinal axis (11) is arranged, with the roller bearing (40) being placed between the housing (20) and the Nut (30) is installed so that it can support hydrostatic forces in the direction of the longitudinal axis (11) caused by the first pressure field (61).

Description

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

From the U.S. 4,276,003 an actuator is known which has a moving body linearly movable with respect to a longitudinal axis. A first portion of the moving body is used as a piston of a pump. A second portion of the moving body is provided with an external thread which is screw-engaged with a nut. Both the corresponding screw engagement and the rotary bearing of the nut are designed in the form of a hydrostatic bearing, both of which can be supplied with pressurized fluid together from a high-pressure connection. In the region of its first section, the moving body is supported on the housing against rotation about the longitudinal axis. The nut is in rotary drive connection with an electric motor.

An advantage of the actuator according to the invention is that it is simpler and cheaper to manufacture. During operation, there are significantly fewer leaks, particularly at the pivot bearing of the nut. The resulting operating costs are correspondingly significantly lower. Nevertheless, the corresponding axial bearing can absorb significantly higher forces than with the U.S. 4,276,003 the case is. In particular, the performance of the hydrostatic threaded nut can be fully utilized. The actuator according to the invention can be used universally and not only as a pump.

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

The first and/or the second pressure field can have an undefined border, the first pressure field being formed, for example, in that the support surface and the counter-support surface in the region of the first pressure field are completely flat and perpendicular to the longitudinal axis. The first and/or the second pressure field preferably have a defined border, which is most preferably defined by at least one recess in each case. 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 in such a way that touching contact between the support surface and the counter-support surface delimits the first pressure field. The protruding recess preferably runs with a constant, in particular rectangular, cross-sectional shape in the form of a circular ring around the longitudinal axis. It goes without saying that the physical contact between the support surface and the counter-support surface away from the mentioned recess is preferably designed in such a way that a thin hydrostic lubricating film forms there, which most preferably causes as little leakage as possible. The carrying capacity of the corresponding hydrostatic bearing is determined for the most part by the extent of the recess and to a significantly lesser extent by the physical contact explained above.

The roller bearing can be designed as a deep groove ball bearing, it being preferably an angular ball bearing. The roller bearing can be designed as a tapered roller bearing. It is conceivable that the roller bearing is designed as a bearing package made up of several individual bearings connected in parallel.

The moving body is preferably formed in one piece. It is conceivable that the moving body comprises a number of separate parts which are firmly connected to one another.

The moving body is preferably supported on the housing against rotation about the longitudinal axis. It is conceivable that the outer cross-sectional shape of the first section and a counter-shape on the housing are designed accordingly, in particular deviating from the circular shape. However, the external cross-sectional shape of the first section of the moving body is preferably circular with respect to the longitudinal axis, the anti-twist device explained further below being used most preferably.

The actuator is preferably operated with a pressurized fluid, which is most preferably a liquid, in particular hydraulic oil.

Advantageous developments and improvements of the invention are specified in the dependent claims.

Provision can be made for the roller bearing to be prestressed at least in the direction of the longitudinal axis. The prestressing is preferably designed in such a way that the leakage occurring at the first pressure field is below a predetermined limit value remains, no matter what external load on the actuator, in particular on the moving body attacks.

Provision can be made for the nut to be supported radially with respect to the longitudinal axis exclusively via the roller bearing on the housing, with physical contact between the supporting surface and the counter-supporting surface defining a plane which is aligned perpendicularly to the longitudinal axis. The hydrostatic axial bearing on the first pressure field can thus be produced particularly easily, since it does not support any forces radially to the longitudinal axis. The gap dimension at the first pressure field is determined solely by the preload of the roller bearing and not by the dimensions of the components involved in the hydrostatic bearing, as is the case with the U.S. 4,276,003 .

Provision can be made for the housing to include a mandrel which extends along the longitudinal axis and is firmly connected to the remainder of the housing, with the mandrel extending into a recess in the moving body, with the moving body in the region of the recess being non-rotatable with respect to the longitudinal axis Mandrel is supported. This provides an anti-twist device for the moving body without the overall length of the actuator increasing in the direction of the longitudinal axis. The mandrel preferably extends with a constant external cross-sectional shape along the longitudinal axis, most preferably the external cross-sectional shape being in the form of a splined shaft. The recess of the moving body preferably extends with a constant inner cross-sectional shape along the longitudinal axis, with the inner cross-sectional shape being adapted to the outer cross-sectional shape in terms of the non-rotatable support mentioned, with very preferably a small amount of play and/or a narrow gap being present at least in sections.

Provision can be made for a low-pressure connection to be arranged on the housing, with at least one orifice opening being arranged on the outside of the mandrel, with the at least one orifice opening being fluidically connected to the low-pressure connection via the mandrel. All leaks occurring within the housing are preferably routed via the at least one orifice. As a result, the anti-rotation device there is reliably lubricated. Preferably a single orifice is provided. The at least one orifice is preferably permanently fluidically connected to the low-pressure port.

Provision can be made for the at least one orifice opening to be arranged on the mandrel in such a way that the recess in the moving body covers at least one orifice opening over at least 70% of a maximum possible stroke path of the moving body, with said covering defining a gap between the mandrel and the moving body, can get through the permanently pressurized fluid to at least one orifice. This ensures reliable lubrication of the anti-twist device between the mandrel and the moving body.

Provision can be made for the nut to be provided with external teeth adjacent to the roller bearing, with an electric motor being provided which is in rotary drive connection with the nut via the external teeth. As a result, a commercially available electric motor can 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 wheel which meshes with the external toothing is preferably attached to a shaft of the electric motor. The external toothing is preferably designed as a helical toothing.

Provision can be made for the first section of the moving body to emerge from the housing on a linear bearing, with the housing being sealed in a fluid-tight manner with the exception of the high-pressure connection and, if desired, the low-pressure connection. The leaks that inevitably occur inside the housing therefore do not contaminate the area around the actuator. The linear bearing is preferably embodied as a slide bearing, it most preferably providing a seal against the escape of pressurized fluid from the housing.

Provision can be made for the roller bearing to be designed without seals, so that pressurized fluid can pass through the roller bearing inside the housing. Said pressure fluid is caused in particular by leaks in the first and in the second pressure field, and it is preferably discharged from the housing via the low-pressure connection. It is essentially pressureless. The proposed permeability of the roller bearing allows the leakages to flow largely freely within the entire housing. At the same time, the roller bearing is reliably lubricated.

It can be provided that the housing comprises a sleeve that is circular-cylindrical with respect to the longitudinal axis and is firmly connected to the rest of the housing, with the support surface being arranged on the end face of the sleeve, with the high-pressure connection being fluidically connected to the first pressure field via the sleeve. An inner diameter of the sleeve is preferably adapted to a tip circle diameter of the external thread of the moving body with little play.

Provision can be made for the sleeve to be arranged inside the remaining housing, with at least one radial opening. Unpressurized pressure fluid can reach radially inside the sleeve from radially outside the sleeve via the radial opening. In addition to the radial opening and the open roller bearing, no further channels are required in the actuator according to the invention in order to enable the exchange of leaks within the entire interior of the housing. It is ensured that all leaks that occur can reach the low-pressure connection.

It is conceivable that the moving body includes a channel with a function comparable to that of a radial opening. But this would be more difficult to produce.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

• 1 eine perspektivische Ansicht eines erfindungsgemäßen Aktuators;
• 2 einen Längsschnitt des Aktuators nach 1;
• 3 eine Seitenansicht des Aktuators nach 1, wobei das zweite und das dritte Gehäuseteil entfernt sind.

The invention is explained in more detail below with reference to the accompanying drawings. It shows:

• 1 a perspective view of an actuator according to the invention;
• 2 a longitudinal section of the actuator 1 ;
• 3 a side view of the actuator 1 , with the second and third housing parts removed.

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 protrudes in the direction of a longitudinal axis 11. An electric motor 70 is fastened 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 protrude from the housing 20, is preferably circular-cylindrical with respect to the longitudinal axis 11. A fastening means (not shown) for a further subassembly can be arranged at its free end, a ball joint head being able to be provided, for example.

The housing 20 is designed in such a way that it essentially encloses the parts in its interior in a fluid-tight manner, with only the high and the low-pressure connection 12; 13 pressure fluid can get into the housing 20 or out of the housing 20 . The pressurized fluid is preferably a liquid and most preferably hydraulic oil. The housing 20 comprises a first, a second, a third and a fourth housing part 81; 82; 83; 84, which are arranged next to one another in the specified order along the longitudinal axis 11, whereby they are firmly connected to one another, in particular screwed together. The second housing part 82 is preferably designed in the form of a cast part 82 . It has a cup-like section 85, which in particular contains the nut (No. 30 in 2 ) and the sleeve (No. 22 in 2 ) surrounds. The open end of the pot-like section 85 is closed with the first housing part 81, which is in the form of a flat plate with a constant thickness, wherein it has a border that is circular with respect to the longitudinal axis 11. FIG. The high-pressure connection 12 is arranged directly on the first housing part 81 , being placed at a distance from the longitudinal axis 11 . The mandrel 21 is attached to the first housing part 81 concentrically to the longitudinal axis 11 , protruding into the interior of the housing 20 . The low-pressure connection 13 is arranged on the mandrel 21, specifically concentrically to the longitudinal axis 11.

The second housing part 82 has a lateral bulge 86, the shape of which corresponds to the toothed wheel (No. 71 in 2 ) is adjusted inside. The electric motor 70 is fastened, in particular screwed, to the outside of the lateral bulge 86 .

The third housing part 83 is designed as a circular-cylindrical tube with a constant wall thickness with respect to the longitudinal axis 11 , it being firmly connected to the second housing part 82 . It is conceivable that the second and the third housing part 82; 83 to run in one piece. The fourth housing part 84 forms a fastening flange, which is preferably arranged at the end of the third housing part 83 at which the moving body 50 protrudes from the housing 20 . The third and fourth housing part 83; 84 can be formed in one piece.

2 shows a longitudinal section of the actuator 10 after 1 . In the present case, the moving body 50 is designed in one piece. It has a first and a second section 51; 52, which are directly adjacent to one another along the longitudinal axis 11. The first section 51 is circular-cylindrical with respect to the longitudinal axis 11 . The second section 52 is provided with an external thread 53 which is concentric to the longitudinal axis 11 and has a trapezoidal profile in the present case. A recess 54 is arranged within the second section 52 and extends along the longitudinal axis 11 with a constant internal cross-sectional shape, being open towards the first housing part 81 . The separate mandrel 21 protrudes into the recess 54, extending along the longitudinal axis 11 with a constant outer cross-sectional shape. The outside cross section In the present case, the shape is in the form of a splined shaft, with the inner cross-sectional shape mentioned being adapted to the outer cross-sectional shape with little play. Accordingly, the moving body 50 is supported on the mandrel 21 in a rotationally fixed manner with respect to the longitudinal axis 11 , the mandrel 21 in turn being fastened to the first housing part 81 . Said multi-wedge connection allows movement of the moving body 50 along the longitudinal axis 11 .

Inside the mandrel 21 there is a channel 87 which in sections runs concentrically with respect to the longitudinal axis 11 . At one end, the channel 87 opens out at the low-pressure connection 13 on the outside of the housing 20 . At the opposite end, the channel 87 has an orifice 25 which is arranged on the outer peripheral surface of the mandrel 21. The mouth opening 25 is covered in every possible position of the moving body 50 by the recess 54 with a narrow gap. The leaks occurring within the housing 20 are discharged to the low-pressure connection 13 via the channel 87 . The arrangement of the orifice 25 explained above means that the spline shaft engagement between the mandrel 21 and the recess 54 is reliably lubricated by the pressure fluid from the leaks. The position of the orifice 25 also defines the oil level within the housing 20, this being dependent on the installation position of the actuator 10.

A nut 30 is arranged around the second section 52 and has an internal thread 31 which in turn is screw-engaged 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 pressure fluid from the high-pressure connection 12 . Corresponding hydrostatic screw drives are, for example, from AT 282291B known. The entire content of AT 282291B is referred to and made part of the present application, particular reference being made to the design of the recesses on the nut 30 which define the second pressure field 62 .

In contrast to the moving body 50, the nut 30 can be rotated relative to the housing 20 with respect to the longitudinal axis 11. The corresponding rotary bearing comprises a roller bearing 40 and a hydrostatic first pressure field 61.

The housing 20 comprises a separate sleeve 22 which is designed in the form of a tube which is circular-cylindrical with respect to the longitudinal axis 11 and has a constant wall thickness. The inner diameter of the sleeve 22 is adapted to the tip circle diameter of the external thread 53 with little play. The sleeve 22 is with its in 2 right end attached to the inside of the first housing part 81, in particular screwed. At the opposite end, the sleeve 22 has a support surface 23 which is flat and aligned perpendicular to the longitudinal axis 11 . A counter-support surface 33 , which is also flat, of the nut 30 rests on the support surface 23 . A recess 60 , which defines the extent of the first pressure field 61 , is arranged within the supporting surface 23 and/or within the counter-supporting surface 33 . The recess 60 runs with a constant cross-sectional shape in the form of a circular ring around the longitudinal axis 11, the cross-sectional shape mentioned being, 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 fluidly connects the first pressure field 61 to the second pressure field 62, so that in the center of both pressure fields 61; 62 the same pressure is applied. The at the pressure fields 61; Leaks that occur deliberately are routed via the orifice 25 to the low-pressure connection 13 .

A hydraulically effective area of the first pressure field 61 is preferably equal to a hydraulically effective area of the second pressure field. As a result, between the two pressure fields 61; 62 a balance of power.

Arranged on the side of nut 30 facing away from support surface 23 is roller bearing 40 , which in the present case is designed as a single-row angular contact ball bearing, being rotatable with respect to longitudinal axis 11 . The corresponding outer ring is accommodated in a separate bearing holder 90, the bearing holder 90 being fastened on the inside of the second housing part 82, in particular screwed or pressed. The corresponding inner ring is accommodated directly on the nut 30. The roller bearing 40 is preferably prestressed, with the level of this prestress being decisive for the leakage at the first pressure field 61 when no external load acts on the moving body 50 . At this point, the stiffening effect of the massive bearing holder 90 should be pointed out. Said pretension 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 runs around the longitudinal axis 11 with a constant cross-sectional shape, it most preferably being designed in one piece.

The roller bearing 40 is preferably designed without seals, so that the pressure fluid that is present in the interior of the housing 20 due to the leaks can pass through the roller bearing 40 . As a result, the roller bearing 40 is lubricated on the one hand. On the other hand, it will be safe ensures that the leaks, no matter where they occur, can flow out to the low-pressure connection 13. In this context, reference is also made to the radial breakthrough (No. 24 in 3 ) referenced.

On the outside of the nut 30 there is external toothing 34 which is preferably designed in the manner of a helical gear wheel. The external toothing 34 meshes with an adapted gear wheel 71 which is firmly accommodated on the shaft of the electric motor 70 . The nut 30 can thus be rotated by the electric motor 70 . As a result, the moving body 50 executes a linear movement along the longitudinal axis 11 . Because of the hydrostatic bearing explained, high forces can be exerted. A force acting on the free end of the moving body is preferably directed towards the support surface 23 .

The linear bearing 26 in the area of the first section 51 of the moving body 50 should also be pointed out, which is preferably formed from plain bearings. On the one hand, the linear bearing 26 guides the first section 51 of the moving body 50 along the longitudinal axis 11. The linear bearing 26 also 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.

3 10 shows a side view of the 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, 3 right end of the moving body 50 almost completely encloses. To nonetheless the outside of the in 3 Subassembly shown leaks to the low pressure port (#13 in 2 ) To be able to dissipate out, at least one radial opening 24 is provided in the sleeve 22. The radial opening 24 is preferably designed in the form of a circular bore, which is aligned perpendicularly to the longitudinal axis 11 .

Reference List

10

actuator

11

longitudinal axis

12

high pressure connection

13

low pressure connection

20

Housing

21

mandrel

22

sleeve

23

support surface

24

radial breakthrough of the sleeve

25

orifice on the mandrel

26

linear bearing

30

Mother

31

inner thread

33

counter support surface

34

external teeth

40

roller bearing

50

moving body

51

first section

52

second part

53

external thread

54

recess

60

Recess defining the first pressure field

61

first pressure field

62

second pressure field

70

electric motor

71

gear

81

first housing part

82

second housing part

83

third case part

84

fourth part of the housing

85

pot-like section of the second housing part

86

lateral bulge of the second housing part

87

channel in the thorn

88

channel in the sleeve

89

canal in the mother

90

storekeeper

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US4276003 [0002, 0003, 0012]
• AT 282291B [0030]

Claims (11)

Actuator (10) with a housing (20) and a moving body (50) that can be moved linearly in the direction of a longitudinal axis (11) relative to the housing (20), the moving body (50) having a first and a second section (51; 52), which are arranged next to one another in the direction of the longitudinal axis (11), the first section extending with a constant external cross-sectional shape along the longitudinal axis (11), the second section (52) being provided with an external thread (53), the second section ( 52) is surrounded by a nut (30) with an internal thread (31), the internal thread (31) being in screwed engagement with the external thread (53), a high-pressure connection (12) being arranged on the housing (20), the housing (20) comprises a support surface (23) pointing in the direction of the longitudinal axis (11), wherein the nut (30) bears against the support surface (23) with a counter-support surface (33) in such a way that the nut (30) relative to the longitudinal axis (11 ) is rotatable relative to the housing (20), a first pressure field (61) being arranged between the supporting surface (23) and the counter-supporting 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 is fluidically connected to the first pressure field (61) via the nut (30), characterized in that on the bearing surface (23 ) facing away from the nut (30), a roller bearing (40) that is rotatable with respect to the longitudinal axis (11) is arranged, the roller bearing (40) being installed between the housing (20) and the nut (30) in such a way that it is exposed to the first pressure field (61) can support caused hydrostatic forces in the direction of the longitudinal axis (11). Actuator (10) after claim 1 , wherein the roller bearing (40) is preloaded at least in the direction of the longitudinal axis (11). 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 roller bearing (40) on the housing (20), with a physical contact between the support surface (23) and the counter-support surface (33) defines a plane perpendicular to the longitudinal axis (11). Actuator (10) according to any one of the preceding claims, wherein the housing (20) comprises a mandrel (21) extending along the longitudinal axis (11) and fixedly connected to the remainder of the housing (20), the mandrel (21) extends into a recess (54) of the movement body (50), the movement body (50) being supported on the mandrel (21) in a rotationally fixed manner with respect to the longitudinal axis (11) in the region of the recess (54). Actuator (10) after claim 4 , a low-pressure connection (13) being arranged on the housing (20), at least one orifice opening (25) being arranged on the outside of the mandrel (21), the at least one orifice opening (25) being connected via the mandrel (21) to the low-pressure connection ( 13) is fluidically connected. Actuator (10) after claim 5 , wherein the at least one orifice opening (25) is arranged on the mandrel (21) in such a way that the recess (54) of the moving body (50) covers at least one orifice opening (25) over at least 70% of a maximum possible stroke of the moving body (50), said covering defining a gap between the mandrel (21) and the moving body (50) through which permanently pressurized fluid can reach the at least one orifice (25). Actuator (10) according to one of the preceding claims, wherein the nut (30) is provided with external teeth (34) adjacent to the roller bearing (40), an electric motor (70) being provided which is connected to the nut via the external teeth (34). (30) is in rotary drive connection. Actuator (10) according to one of the preceding claims, wherein the first section (51) of the moving body (50) emerges from the housing (20) on a linear bearing (26), the housing (20) with the exception of the high-pressure connection (12) and if desired, the low-pressure connection (13) is sealed in a fluid-tight manner. Actuator (10) after claim 8 , wherein the roller bearing (40) is formed without seals, so that pressurized fluid inside the housing (20) can pass through the roller bearing (40). Actuator (10) according to one of the preceding claims, wherein the housing (20) comprises a circular-cylindrical sleeve (22) with respect to the longitudinal axis (11) which is fixedly connected to the remaining housing (20), the support surface (23) being on the front side of the sleeve (22), the high-pressure connection (12) being fluidically connected to the first pressure field (61) via the sleeve (22). Actuator (10) after claim 10 , referring back to claim 8 or 9 , wherein the sleeve (22) is arranged within the remaining housing (20), wherein it has at least one radial opening (24).

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