Patent ID: 12259029

DETAILED DESCRIPTION

Among other things, the linear actuator1comprises a screw drive2. The screw drive2comprises a threaded nut3and a threaded spindle4. The threaded nut3is connected to an extension arm tube3a. The threaded spindle4is coupled or can be coupled to a motor EM for torque transmission, so that the threaded nut3and the extension arm tube3acan be moved in a linear manner by a rotation of the threaded spindle4. Regardless of the position the extension arm tube3ais in, a first end of the threaded spindle4.E1projects into the extension arm tube3.aand is connected to a piston K. The second end of the threaded spindle4opposite to the first end4.E1is labeled as4.E2. The piston K partitions an interior space IR formed by means of the extension arm tube3.ainto a first region IRB1on the side of the piston K opposite to the threaded nut3and a second region IRB2on the side of the piston K facing the threaded nut3in such a way that the first and the second region IRB1, IRB2are separated from one another in a fluid-tight manner.

On its outer perimeter, the piston K has a groove for receiving at least one sealing ring. The sealing ring, preferably an O-ring or R-ring, makes it possible to seal the sealing gap that forms between the piston K and the extension arm tube3aparticularly well. The end of the extension arm tube3afacing away from the threaded nut3is preferably closed by means of a plug.

The threaded nut3is embodied as a fluid-tight annular piston RK or comprises a fluid-tight annular piston RK. The annular piston RK delimits an annular fluid space RR configured between a housing G of the linear actuator1and the extension arm tube3.ain a fluid-tight manner. The hydraulically effective surface of the annular fluid space RR is the same size as the hydraulically effective surface of the first region IRB1. The first region IRB1and the annular fluid space RR can be fluidically connected to one another by means of a switching valve SV having an open and a closed position SVO, SVG.

The annular piston RK and the switching valve SV are shown inFIG.1bandFIG.2b. For the sake of clarity,FIG.1a,FIG.2aandFIG.3do not show the switching valve SV. The switching valve SV and the connected flow connections are shown inFIG.1bandFIG.2bas a hydraulic diagram in contrast to the other components. The switching valve SV in particular has two switch positions, namely the open position SVOand the closed position SVG. In the open position SVO, a pressurized fluid DF can flow back and forth between the annular fluid space RR and the first region IRB1through the switching valve SV without significant pressure losses. In the closed position SVG, flow between the annular fluid space RR and the first region IRB1is prevented by the switching valve SV. The threaded nut3can then be held axially in position with the aid of the pressurized fluid DF, so that a hydraulic brake of the linear actuator1is formed by means of the switching valve SV and the pressurized fluid DF disposed in the annular fluid space RR and in the first region IRB1.

A lubricating fluid for lubricating and/or cooling the screw drive2could be provided in the second region IRB2of the interior space IR, in which case then mixing of the lubricating fluid and the pressurized fluid DF is prevented, in particular by means of piston K.

To fluidically connect the first region IRB1and the annular fluid space RR, a first pressure relief valve DBV1is disposed between the first region IRB1and the annular fluid space RR in terms of flow parallel to the switching valve SV in such a way that the pressure that can be produced in the first region IRB1by means of a pressurized fluid DF can be limited upward in that the pressurized fluid DF can be conducted out of the first region IRB1into the annular fluid space RR via the first pressure relief valve DBV1.

To fluidically connect the annular fluid space RR and the first region IRB1, a second pressure relief valve DBV2is disposed between the annular fluid space RR and the first region IRB1in terms of flow parallel to the switching valve SV and in particular in terms of flow parallel to the first pressure relief valve DBV1in such a way that the pressure that can be produced in the annular fluid space RR by means of the pressurized fluid DF can be limited upward in that the pressurized fluid DF can be conducted out of the annular fluid space RR into the first region IRB1via the second pressure relief valve DBV2.

The parallel connection of the switching valve SV, the first pressure relief valve DBV1and the second pressure relief valve DBV2means that, during operation of the linear actuator1, substantially equal pressures prevail on the sides of these valves facing the annular fluid space RR. This parallel connection moreover also means that, during operation of the linear actuator1, substantially equal pressures likewise prevail on the sides of these valves facing the first region IRB1.

The switching valve SV, the first pressure relief valve DBV1, and in particular the second pressure relief valve DBV2, are embodied as a common structural unit with a common valve housing.

Such a common structural unit then comprises two connections, wherein one is connected to the first region IRB1and one is connected to the annular fluid space RR. The other fluidic connections to the valves are then implemented by means of flow channels configured in the valve housing.

A braking force which acts on the extension arm tube3.aand the threaded nut3in the direction of an end of the extension arm tube3.afacing away from the threaded spindle4can be produced by means of the first pressure relief valve DBV1as a function of the flow resistance of the first pressure relief valve DBV1.

If this braking force produced by means of the first pressure relief valve DBV1during operation of the linear actuator1is greater than force otherwise acting on the extension arm tube3.aand the threaded nut3, the threaded nut3is held in position by means of the braking force; i.e. a length of the linear actuator1does not change. Such other forces can be applied to the linear actuator1from the outside, e.g. via moving bodies coupled to the linear actuator and associated loads, or theoretically also by means of the motor EM. Preferably, however, the motor EM is not operated against the braking force.

A braking force which acts on the extension arm tube3.aand the threaded nut3in the direction of an end of the threaded spindle4facing away from the piston K can be produced by means of the second pressure relief valve DBV2as a function of the flow resistance of the second pressure relief valve DBV2.

If this braking force produced by means of the second pressure relief valve DBV2during operation of the linear actuator1is greater than force otherwise acting on the extension arm tube3.aand the threaded nut3, the threaded nut3is held in position by means of this braking force; i.e. a length of the linear actuator1does not change.

The first region IRB1of the interior space IR of the extension arm tube3.ais optionally connected to a pressure accumulator P in order to be able to produce a specific relief pressure in the first region IRB1by means of the pressure accumulator P.

A first shut-off valve AV1is then disposed fluidically between the first region IRB1and the pressure accumulator P.

The pressure accumulator can be embodied in a variety of ways. When the extension arm tube3aretracts, the pressurized fluid DF flows from the first region IRB1to the pressure accumulator P when the first shut-off valve AV1is open to the pressure accumulator P. When the extension arm tube3aextends, the pressurized fluid DF flows from the pressure accumulator P to the first region IRB1when the first shut-off valve AV1is open to the pressure accumulator P. The pressure accumulator P in particular makes it possible to produce a constant relief pressure in the first region IRB1.

The annular fluid space RR can optionally be pressurized, preferably by means of a pressure source DQ.

A second shut-off valve AV2is then disposed fluidically between the annular fluid space RR and the pressure source DQ.

The pressure source DQ is connected to an outer perimeter of the housing G adjacent to the annular fluid space RR. The pressure source DQ can be embodied in a variety of ways, for example also as a further pressure accumulator. When the annular piston RK retracts, the pressurized fluid DF flows from the pressure source DQ to the annular fluid space RR when the second shut-off valve AV2is open to the pressure source DQ. When the annular piston RK extends, the pressurized fluid DF flows from the annular fluid space RR to the pressure source DQ when the second shut-off valve AV2is open to the pressure source DQ. The pressure source DQ can be in particular used to produce a constant pressure in the annular fluid space RR. The pressure source DQ and the pressure accumulator P can be fluidically coupled to one another via the first shut-off valve AV1, the switching valve SV and the second shut-off valve AV2. Such a coupling is avoided in normal operation, but, over a longer period of operation, the fundamental possibility leads to pressurized fluid DF from the pressure source DQ mixing with pressurized fluid DF from the pressure accumulator P.

Since their use is optional, the pressure accumulator P, the pressure source DQ, the first shut-off valve AV1and the second shut-off valve AV2are shown with dashed lines.

The linear actuator1can be held in position as described above so that the length of the linear actuator1does not change. The linear actuator1can moreover be operated in the following four quadrants:in a first quadrant, the extension arm tube3ais moved out of the housing G against a force F which acts on the extension arm tube3atoward the housing G by means of energy provided by the motor EM;in a second quadrant, the extension arm tube3ais moved into the housing G by means of a force F which acts on the extension arm tube3atoward the housing G, while energy can be recuperated by means of the motor EM;in a third quadrant, the extension arm tube3ais moved into the housing G against a force F which acts on the extension arm tube3aaway from the housing G by means of energy provided by the motor EM;in a fourth quadrant, the extension arm tube3ais moved out of the housing G by means of a force F which acts on the extension arm tube3aaway from the housing G, while energy can be recuperated by means of the motor EM.

The first region IRB1can be pressurized with relief pressure by means of the pressure accumulator P and a control device ST of the linear actuator1during operation of the linear actuator1in the first and the second quadrant in order to reduce a contact force which acts between the threaded spindle4and the threaded nut3. In the first quadrant, the first shut-off valve AV1is used to ensure that the first pressure relief valve DBV1is not also pressurized with relief pressure by means of the pressure accumulator P; i.e. a fluidic connection between the first region IRB1and the first pressure relief valve DBV1is interrupted. Likewise, in the second quadrant, the first shut-off valve AV1could be used to ensure that the first pressure relief valve DBV1is not also pressurized with relief pressure by means of the pressure accumulator P; i.e. a fluidic connection between the first region IRB1and the first pressure relief valve DBV1is interrupted. In the second quadrant, however, it is also conceivable that the first pressure relief valve DBV1is pressurized with relief pressure by means of the pressure accumulator P as well, i.e. the fluidic connection between the first region IRB1and the first pressure relief valve DBV1is enabled when the switching valve SV is closed, so that, when retracting, the threaded nut3and the extension arm tube3aare braked by means of the first pressure relief valve DBV1and at the same time the contact force which acts between the threaded spindle4and the threaded nut3is reduced.

For this purpose, the control device ST is accordingly coupled to the pressure accumulator P, the switching valve SV and the first shut-off valve AV1. The motor EM, which is preferably embodied as an electric motor, is also coupled to the control device ST for control and/or regulation of said Motor. In the first and fourth quadrants, the motor EM and thus the threaded spindle4rotate in the same rotation direction.

During operation of the linear actuator1in the third and fourth quadrants, the annular fluid space RR can be pressurized by means of the control device ST, and preferably by means of the pressure source DQ, in order to reduce the contact force which acts between the threaded spindle4and the threaded nut3.

In the third quadrant, the second shut-off valve AV2is used to ensure that the second pressure relief valve DBV2is not also pressurized by means of the pressure source DQ; i.e. a fluidic connection between the annular fluid space RR and the second pressure relief valve DBV2is interrupted. Likewise, in the fourth quadrant, the second shut-off valve AV2could be used to ensure that the second pressure relief valve DBV2is not also pressurized by means of the pressure source DQ; i.e. a fluidic connection between the annular fluid space RR and the second pressure relief valve DBV2is interrupted. In the fourth quadrant, however, it is also conceivable that the second pressure relief valve DBV2is pressurized by means of the pressure source DQ as well, i.e. the fluidic connection between the annular fluid space RR and the second pressure relief valve DBV2is enabled when the switching valve SV is closed, so that, when extending, the threaded nut3and the extension arm tube3aare braked by means of the second pressure relief valve DBV2and at the same time the contact force which acts between the threaded spindle4and the threaded nut3is reduced.

For this purpose, the control device ST is furthermore accordingly coupled to the pressure source DQ and the second shut-off valve AV2. In the second and third quadrants, the motor EM and thus the threaded spindle4rotate in the same rotation direction, which is opposite to the rotation direction in the first and fourth quadrants,

The first embodiment of the linear actuator1ofFIGS.1aand1bcomprises a damping element DM. The damping element DM is disposed on the end of the extension arm tube3afacing away from the housing G and between the end of the extension arm tube3afacing away from the housing G and a ball joint KG for damping axial impacts. A joint center KGM of the ball joint KG coincides with the longitudinal axis of the threaded spindle4.

InFIG.1aand1b, the end of the extension arm tube3afacing away from the housing G is fixedly connected to a support element AE which leads past the damping element DM or comprises such a support element AE. The support element AE comprises a sliding block GL, which is mounted such that it can move in longitudinal direction1and is provided for receiving a bolt BZ which passes through a joint head KGK of the ball joint KG, so that the extension arm tube3acan be supported on the bolt BZ with respect to a rotation about the longitudinal axis of the threaded spindle4.

The second embodiment example of the linear actuator1shown inFIGS.2aand2blikewise comprises a ball joint KG disposed on the end of the extension arm tube3afacing away from the housing G and an associated support element AE. InFIGS.2aand2bas well, the support element AE comprises a sliding block GL, which is mounted such that it can move in longitudinal direction1and is provided for receiving a bolt BZ which passes through a joint head KGK of the ball joint KG, so that the extension arm tube3acan be supported on the bolt BZ with respect to a rotation about the longitudinal axis of the threaded spindle4. Since no or only very small movements of the bolt BZ in longitudinal direction of the linear actuator1are to be expected due to the lack of a damping element, the sliding block GL could also be omitted in the second embodiment example of the linear actuator1.

The threaded spindle4is coupled to a hollow shaft EM.h of the motor EM embodied as an electric motor via a rotationally fixed connection5.

Due to the rigid design, the rotating assembly consisting of the threaded spindle4, the rotationally fixed connection5and the hollow shaft EM.h can be mounted with only two mounting points, namely a first pivot bearing L1and a second pivot bearing L2.

A rotary encoder6is disposed on an end face of the threaded spindle4facing away from the extension arm tube3a, namely at the second end4.E2of the threaded spindle4.

The rotary encoder6is preferably embodied as an absolute rotary encoder. This makes it possible to determine the position of the extension arm tube3awithout a travel measuring system.

In a maximally retracted state of the extension arm tube3.a, the threaded nut3ofFIG.1band2bis preferably disposed at least partly completely inside the hollow shaft EM.h.

FIGS.1band2bshow the threaded nut3adjacent to the hollow shaft EM.h, but also not in the maximally retracted state. The threaded nut3could be moved even further to the left in accordance with the position shown inFIGS.1band2bby a corresponding further rotation of the threaded spindle4.

FIG.3shows a schematic sectional view of a further embodiment of a mounting of an electric motor EM and sections of the screw drive2of the linear actuator1. The omitted components can be taken analogously from the first and the second embodiment examples of the linear actuator1.

InFIG.3, an additional, preferably mechanical, holding brake B for the threaded spindle4and the first pivot bearing L1for mounting the threaded spindle4on the housing G of the linear actuator1are disposed inside the hollow shaft EM.h. InFIGS.1band2b, on the other hand, the first pivot bearing L1is disposed laterally adjacent to the hollow shaft EM.h.

A length of the linear actuator1in the maximally retracted state is minimized in that the holding brake B and the first pivot bearing L1are disposed inside the hollow shaft EM.h.

InFIG.3, the housing G comprises a first hollow carrier G.t1, which projects into the hollow shaft EM.h of the electric motor EM and the inner perimeter of which serves to receive the first pivot bearing L1disposed on the outer perimeter of the threaded spindle4.

InFIG.3, a second pivot bearing L2is disposed between the outer perimeter of a second hollow carrier G.t2of the housing G which projects into the hollow shaft EM.h of the electric motor EM and the inner perimeter of the hollow shaft EM.h in an end region of the electric motor EM facing away from the extension arm tube3a. InFIGS.1band2b, on the other hand, the second pivot bearing L2is disposed on the outer perimeter of the hollow shaft EM.h.

The first pivot bearing L1preferably comprises two tapered roller bearings in an O-arrangement. The second pivot bearing L2comprises a radial deep groove ball bearing. The first pivot bearing L1is configured as a fixed bearing, and the second pivot bearing L2is configured as a floating bearing.

It is conceivable that a hydraulically effective surface of the annular fluid space RR is not the same size as the hydraulically effective surface of the first region IRB1, and the first region IRB1and the annular fluid space RR can then be fluidically connected to one another via a reservoir by means of a switching valve SV having an open and a closed position, which is not shown in the figures for the sake of clarity. The switching valve SV is in particular configured such that the reservoir can only be pressurized with pressurized fluid DF when the switching valve SV is in the open position SVO.

LIST OF REFERENCE SIGNS

1Linear Actuator2Screw drive3Threaded nut3.aextension arm tube4Threaded spindle4.E1First end of the threaded spindle44.E2Second end of the threaded spindle45Rotationally fixed connection6Rotary encoderEM Electric motorEM.h Hollow shaftK PistonIR Interior spaceIRB1First region of the interior space IRIRB2Second region of the interior space IRP Pressure accumulatorRK Annular pistonG HousingRR Annular fluid spaceDQ Pressure sourceSV Switching valveSVOOpen position of the switching valve SVSVGClosed position of switching valve SVDBV1First pressure relief valveDBV2Second pressure relief valveAV1First shut-off valveAV2Second shut-off valveDF Pressurized fluidST Control deviceDM Damping elementKG Ball jointKGMJoint centerKGKJoint headAE Support elementGL Sliding blockBZ BoltB Holding brakeL1First pivot bearingL2Second pivot bearingG.t1First hollow carrierG.t2Second hollow carrierI Longitudinal direction