CH717147A2 - Hydraulic servo actuator. - Google Patents

Abstract

The hydraulic servo-actuator includes a piston rod (3) and on top of it two pistons (K1, K2) arranged in tandem, both of which are slidably mounted in a separate hydraulic cylinder (Z1, Z2). There are two separate redundant hydraulic circuits (1, 2) that work with the hydraulic system pressure, fed by an assigned hydraulic pump. By lowering and increasing the pressure in a control line (P1S, P2S) through a control valve on one of the piston sides, the piston rod (3) can subsequently be extended and retracted. As a result, an action lever (26) articulated to the end of the piston rod (3), which is also articulated to a further pivot point (27) on the servo actuator, can be swiveled back and forth.

Description

This invention relates to a hydraulic servo actuator with a special construction so that it can be activated in two directions, on the basis of a single pressure accumulator with stationary pressure, solely by temporarily reducing the pressure in a separate pressure area. In particular, it can be used to adjust the rotor blades on a helicopter. The pilot can use three of these servo actuators to change the position of the rotor and its blades so that the helicopter can hover and fly forwards and backwards, to the left or right or up and down. But this hydraulic servo actuator can also be used in all other locations where a mechanical displacement of elements is to be controlled redundantly and safely from a distance.

The object of this invention is to provide such a hydraulic actuator that gets by with a minimal number of parts, can be built very compact, light and inexpensive and whose control is designed as simple as possible, and which is particularly high Operational safety offers as well as secure redundancy.

This object is achieved by a hydraulic servo actuator with a piston rod and two pistons arranged in tandem, both of which are slidably mounted in a separate hydraulic cylinder, to form two separate redundant hydraulic circuits with the same hydraulic system pressure, fed by one associated hydraulic pump, whereby the piston rod can be extended and retracted by lowering and raising the pressure in a control line through a control valve on one of the piston sides, and thereby an action lever articulated at the end of the piston rod, which is also at a further pivot point on the servo -Actuator is articulated, is pivotable back and forth.

Such a servo actuator is presented in an exemplary embodiment with reference to the following drawings. Its structural design is described with the aid of these drawings and its special function and effect are explained.

It shows: Figure 1: The hydraulic servo actuator in a perspective overall view seen obliquely from the rear with its bottom back and forth sliding action lever, which can be pivoted back and forth around the end of a retaining plate with its upper end; FIG. 2: This servo actuator according to FIG. 1 in a perspective side view; FIG. 3: The basic technical and hydraulic principle of the actuator is shown on the basis of a longitudinal section through the actuator; FIG. 4: The servo actuator is also shown in a longitudinal section on the basis of a longitudinal section in a different position of the action lever with one of the two control valves arranged in parallel; FIG. 5: A single control valve SV for a hydraulic circuit of the servo actuator is shown in a longitudinal section; FIG. 6: This individual control valve SV for a hydraulic circuit of the servo actuator from FIG. 5 is shown in a longitudinal section seen from the other, rear side.

The servo actuator is shown in Figure 1 in an overall view, seen in perspective obliquely from behind. It rests here on the floor and contains a frame formed by a rear end plate 34 facing the viewer, closer to the viewer, with a fastening ear 31 and a front end plate 35 further away from the viewer. These two end plates 34, 35 are at their four corners by means of four steel rods 22 braced together, these steel rods 22 penetrating a reinforcing mount 23 in the middle of their length. On top of this reinforcement mount 23 are two control valves SV1, SV2 arranged parallel to one another. Running within the frame formed by the end plates 34, 35 and the steel rods 22, a cylinder 24 can be seen here, which is divided into two sections, formed by two separate cylinders Z1 and Z2. A piston rod 3 extends through these two cylinders Z1 and Z2, protruding from the front of the cylinder Z2 and the end of which is connected to the joint 25 of an action lever 26. The piston rod 3 can move in and out of the cylinders Z1, Z2 and thus move the joint 25 linearly back and forth. The action lever 26 is pivotably connected to the same about the middle of its length via a hinge pin 27 with an end fork 33 of a holding plate 28. At the upper end, the action lever 26 runs out into a receiving fork 29. When the piston rod 3 extends out of the cylinders Z1, Z2, the upper end of the pivot lever 26 pivots with its receiving fork 29 in the opposite direction and vice versa. The holding plate 28 is articulated via the bolts 30 on both sides in the area of the two stationary control valves SV1, SV2. On the piston rod 3 sit in the interior of the cylinder to form two separate hydraulic circuits arranged in tandem, two pistons, as will be shown on the basis of further figures. Two control valves SV1 and SV2 for the two hydraulic circuits are located on the cylinder 24 and its frame. Seen from the left side of the observer, the return line 1 of the first hydraulic circuit can be seen on top of the control valve SV1 and, to the right of it, the return line R2 of the second hydraulic circuit on the control valve SV2. The horizontal connections on the control valves SV1 and SV2 are those for the pressure lines P1 and P2 for the two hydraulic circuits. A system pressure of 40 bar to 80 bar always prevails in the pressure lines P1 and P2, while the hydraulic pressure in the return lines R1 and R2 can be varied between atmospheric pressure and the system pressure. The system pressure is provided by an assigned hydraulic pump, not shown, which supplies a hydraulic accumulator as a hydraulic pressure source or serves directly as a pressure source.

The Figure 2 shows this servo activator in a perspective side view. Here, too, one recognizes the cylinder 24 running along the bottom with the two linearly successive cylinders Z1 and Z2 in its interior. The cylinder 24 is held in a stable manner in the frame of the steel rods 22 and the end-side end plates 34, 35 with which the steel rods 22 are braced. The end plate 34 located here at the right end of the cylinder 24 forms a fastening ear 31 with which the servo actuator is fastened to a bolt on a stationary machine or system part. On top of the reinforcement mount 23 are the two control valves SV1 and SV2 for the two hydraulic circuits, one being assigned to cylinder Z1 and the other to cylinder Z2. On the outside of the control valves SV1, SV2, a retaining plate 28 is hinged to the reinforcement mount 23 via the stationary bolts 30 and thus indirectly to the actuator. At the front end, this holding plate 28 is articulated to the action lever 26 via a fork 33 formed there and the hinge pin 27. This action lever is articulated on the end of the piston rod 3 via the bolt 25. The piston rod 3 runs out into a fastening ear 32 at the front. When the piston rod 3 extends out of the cylinder 24, it pushes the bolt 25 forwards or to the left in the picture and the action lever 26 is pivoted about the stationary bolt 27. If the section of the action lever 26 below the bolt 27 is pulled into the cylinder, the section above the bolt 27 moves forwards or to the left in the picture and vice versa. At the upper end of the action lever 26 one recognizes a fork 29 to which any element to be actuated can be articulated.

The relationships inside the cylinder 24 inferred from FIG. 3. The cylinder 24 is divided into two cylinder sections Z1 and Z2, and each of these sections is in operative connection with its own separate hydraulic circuit 1, 2, namely a hydraulic circuit 1 on the left and a hydraulic circuit 2 on the right Image. The configuration with two separate hydraulic circuits 1, 2 that function separately from one another offers the important, indispensable and safe redundancy required for such a servo actuator, for example in aviation. Should one of the two hydraulic circuits 1, 2 fail, the other hydraulic circuit can continue to work. The actuator has a total of four hydraulic connections, namely P1 and P2 for the pressure lines with hydraulic pressure at the system pressure, fed by a hydraulic pump (not shown), as well as two return lines R1 and R2 in which the hydraulic oil flows back from the control valve SV1, SV2 without pressure or to atmospheric pressure. These lines carry hydraulic oil at a control pressure P1S and P2S, which expresses with the letter S that this pressure is used to control the actuator.

The two cylinders Z1, Z2 each include two pistons K1, K2ein arranged in tandem on a common piston rod 3. These separate a total of four different pressure chambers A1, A2; B1, B2 from one another. The two pressure chambers A1, A2 on the one hand and the pressure chambers B1, B2 on the other hand have different effective areas for the hydraulic pressure prevailing in the cylinder. The effective areas in the chambers A1, B1 on the adjacent pistons are approximately twice as large as those in the other associated chambers A2, B2 on the other side of the pistons. In FIG. 3 it can be seen that the cylinder Z2 encloses a chamber B2 which has approximately half the effective area on the piston K2 compared to the effective area of the chamber B1 located on the other side of the piston K2.

In that chamber A2, B2 with the smaller effective area, in the figure 3 in each case the chamber on the left side of the pistons K1, K2, there is always the respective system pressure P2 or P1 of approx. 40 bar to 80 bar. Only chamber A1 of cylinder Z1 and chamber B1 of cylinder Z2 are required to control pistons K1, K2. The control valves SV1, SV2 therefore only have an influence on these chambers A1 and B1 to the right of the pistons K1, K2, in that the pressure in these pressure chambers A1, B1 is reduced or increased again compared to the system pressure as required, after which the pistons K1, K2 depending on the which side then has the greater force, move in the respective direction.

For the extension of the piston rod 3, the chambers A1, B1 to the right of the pistons K1, K2 are flooded with the associated system pressure P1 or P2. Because of the twice as large effective area on the pistons K1, K2, the resulting pressure force is therefore twice as large. This results in an imbalance of forces and the pistons K1, K2 move to the left in this case and they push the piston rod 3 accordingly to the left, which causes the action lever 26 in the figure to pivot clockwise, as indicated by arrows.

Conversely, to retract the piston rod 3, so to move the same in the picture from left to right, the chambers A1, B1 with the associated return R1, R2 connected and the pressure in these chambers A1, B1 is lowered to the ambient pressure and there is again Imbalance of forces. The other chambers A2, B2 with the system pressure, which is always present there, press against the ambient pressure with the developed pressure force and the pistons K1, K2 move to the right. The piston rod 3 moves into the cylinder 24. Correspondingly, the pivot rod 26 is pivoted about the stationary bolt 27 in the counterclockwise direction in the figure.

If the position of the piston rod 3 is to be maintained, the chambers A1, B1 to the right of the piston K1, K2 are not connected to the associated return line or to the associated system pressure, but are locked by means of the control valve SV1, SV2. Accordingly, the volume of the chambers A1, B1 must remain unchanged. An equilibrium will be established with the counterforce due to the prevailing system pressure in the other chambers A2, B2, but the smaller effective area on the pistons K1, K2 there. There is therefore an equilibrium of forces. Even if a mechanical force acts on the piston rod 3 from the outside, it cannot move, but is hydraulically held in its fixed position.

Each cylinder Z1, Z2 has an associated control valve SV as shown in FIG. These two control valves SV1 and SV2 are arranged above the cylinder 24 on the reinforcement socket 23. In the picture you can only see the control valve SV1 facing the viewer, while the second SV2 behind this first one is covered and cannot be seen. One of the valves of the first control valve SV1 connects the chamber A1, B1 with the associated return (ambient pressure) and the other valve connects the chamber A1, B1 with the associated system pressure (approx. 80 bar). The control valves only have an influence on chambers A1, B1, each of the pistons K1, K2 in the picture on the right. In the following, the control valve SV1 of the cylinder Z2 is shown in a section, as is shown in FIG.

The control valves SV are geometrically designed so that in the closed state no hydraulic forces act in the axial direction on the piston or the valves. It does not matter whether a valve or its piston is pressurized on the left or right side. This pressure neutrality is achieved in that the pressure forces on all impact surfaces or active surfaces on the pistons 7, 8 cancel each other out. In detail, the inclined surfaces 10 on the piston 8, which is acted upon by the compression spring 6 from the left in the picture, and which inclined surfaces 10 lie in the space 16 which surrounds the piston 8 and which are directed against the compression spring 6, develop the same force as the inclined surfaces 12, which are in this space 16 act in the opposite direction. Equally, the inclined surfaces 11 on the piston 7, which lie in the space 15 which surrounds the piston 7 and which are directed against the compression spring 5 in the picture to the right of the piston 7, develop the same force as the inclined surfaces which act in the opposite direction in this space 15, and that in each case regardless of the current axial position of the piston. In the position shown in FIG. 5, the pistons 7, 8 lie with their inclined surfaces 11, 12 in a sealing manner on the edges 21, 22 in their cylinders. The control valve SV is actuated by pivoting the lever about the lever arm 13 about its pivot axis 14. If the actuating lever 36, which here protrudes upwards behind the valve, is pivoted outside, for example, clockwise in the figure, i.e. to the right in the figure, the end of the lever 13 connected to it, which is between the two pistons 7, 8 around the pivot axis, presses 14 is pivotable, the piston 7 from its currently shown position, in which it is pressed sealingly against the edge 22 on the cylinder with its inclined surfaces 11 force of the compression spring 5, against the compression spring 5 to the right, while piston 8 with its inclined surface 12 strikes the edge 21 on its cylinder 19 in a sealing manner and so cannot be shifted further to the right. As a result, the pressure inlet 17 from P1, P2 and the inlet further against the compression spring 5 are opened.

The small valve 34 below the control cartridge is used to close the two chambers of the corresponding cylinder briefly as soon as one of the two system pressures coincides, so that you can continue working with the other cylinder with the hydraulic circuit still intact.

Index of digits

Functional diagram (Figures 3 and 4)

1.2 hydraulic circuits 3 piston rod with two pistons K1, K2 Z1 cylinder right in the picture Z2 cylinder left in the picture K1 piston right in the picture K2 piston left in the picture SV1 servo valve to hydraulic circuit 1 SV2 servo valve to hydraulic circuit 2 A1 Hydraulic chamber to the right of piston K1 with system pressure 40-80bar A2 hydraulic chamber to the left of piston K1 with ambient pressure B1 hydraulic chamber to the right of piston K2 with system pressure 40-80bar B2 hydraulic chamber to the left of piston K2 with ambient pressure

Control valve SV

P1S control pressure in hydraulic circuit 1 P2S control pressure in hydraulic circuit 2 R1 return hydraulic circuit 1 R2 return hydraulic circuit 2 5 compression spring right 6 compression spring left 7 movable piston right 8 movable piston left 9 against the compression spring 5-directional pressure surfaces on the piston 7 10 against the compression spring 6-directional pressure surfaces on the piston 6 11 pressure surfaces facing away from the compression spring 5 on the piston 7 12 pressure surfaces facing away from the compression spring 6 on the piston 6 13 lever for loading and actuating the piston 14 pivot axis of the lever arm 15 the piston 7 circumferential recesses 16 the piston 8 circumferential recesses 17 pressure line for piston 7 18 pressure line for piston 8 19 cylinder for piston 7, 8 20 pressure line to piston 7 21 stop edge for piston 7 22 stop edge for piston 8

Parts on the outside of the actuator

22 steel rods 23 reinforcement socket 24 cylinder, containing cylinder sections Z1 and Z2 25 joint at the bottom of the action lever 26 pivotable action lever 27 pivot pin in the middle of the length of the action lever 28 retaining plate 29 receiving fork at the free end of the action lever 30 stationary bolt for the retaining plate 31 mounting ear at the back of the actuator 32 fastening ear at the front of the actuator 33 fork at the front of the retaining plate 28 34 rear end plate 35 front end plate 36 lever on the outside of the SV for pivoting the lever arm 13 P1S control pressure for hydraulic circuit 1 P2S control pressure for hydraulic circuit 21 P1 high pressure inlet hydraulic circuit 1 P2 high pressure inlet hydraulic circuit 2 R1 Return hydraulic circuit 1 R2 Return hydraulic circuit 2

Claims (4)

1.Hydraulic servo actuator with a piston rod (3) and on it two pistons (K1, K2) arranged in tandem, both of which are slidably mounted in a separate hydraulic cylinder (Z1, Z2), to form two separate redundant hydraulic circuits (1 . can be extended and retracted, and thereby an action lever (26) articulated at the end of the piston rod (3), which is also articulated to a further pivot point (27) on the servo actuator, can be swiveled back and forth. 2. Hydraulic servo actuator according to claim 1, characterized in that after failure of one of the two hydraulic circuits (1, 2) the other of the hydraulic circuits (1, 2) for control purposes between atmospheric pressure and 40bar to 80bar upper pressure limit by means of a mechanical-hydraulic acting control valve (SV1, SV2) can be lowered and raised again and thus the hydraulic servo actuator remains functional. 3. Hydraulic servo actuator according to one of the preceding claims, characterized in that the pistons (K1, K2) are axially displaceable in their cylinders (Z1, Z2) by the pistons (K1, K2) on their working side in the pressure chambers ( A1, B1) offer a larger area exposed to hydraulic pressure than on their opposite side, where the area exposed to hydraulic pressure is reduced by the piston rod (3, 4), and that each hydraulic cylinder (Z1, Z2) has its own control valve (SV1, SV2) is connected, one being connected to the supply lines (P1, P2) at system pressure to the pressure chambers (A1, B1) of the pistons (K1, K2) and one to the return line (R1, R2) at ambient pressure, and on each control valve (SV1, SV2) there is a valve (34), by means of which the two pressure chambers of the corresponding cylinder (Z1, Z2) can be closed as soon as one of the two system pressures coincides and the other cylinder is still intact Hy hydraulic circuit remains functional. 4. Hydraulic servo actuator according to claim 1, characterized in that in each servo valve (SV1, SV2) a movable lever (13) to be activated is arranged on a shaft (14), at the end of which a piston (7 , 8) strikes on opposite sides, and beyond the two pistons (7, 8) these are each loaded by a compression spring (6, 7), pressure lines (17, 17) in the pressure cylinder (19) opposite the recesses (15, 16) 18) open out and the recesses (15, 16) are designed in such a way that surfaces (11, 12; 13, 14) which are inclined with respect to the axial direction and which compensate for the pressures acting on them so that the piston (7 , 8) remains pressure-neutral and therefore no axial forces act on the pistons (7, 8).