Mechanical feedback control device for a redundant hydraulic actuator

Abstract

 A mechanical feedback control device (38) for a redundant hydraulic actuator (1) having two hydraulic cylinders (2, 3) operated by respective hydraulic valves (20, 21) and interposed between a fixed connection (9) and a movable connection (11) of the actuator (1); the device (38) having an input lever (40) connected to two feedback rods (43) connected to the movable connection (11) of the actuator, and a transmission lever (44) which, when moved by the input lever (40), rotates a pin (55) to activate two shafts (64, 65) controlling respective slides (34, 35) of the valves. The input lever, the transmission lever (44) and the pin (55) form a closed-loop structure for transmitting displacement to each of the shafts (64, 65), so that each of the slides (34, 35) can be moved via two different kinematic chains.

Description

[0001] The present invention relates to a mechanical feedback control device for a redundant hydraulic actuator, and particularly suitable for an aircraft servocontrol.

[0002] As is known, in certain engineering applications where safety is involved, such as aircraft hydraulic servocontrols, redundant actuators are used comprising two (or more) hydraulic cylinders, each with a respective independent hydraulic circuit, so that, in the event one of the cylinders or hydraulic circuits breaks down, control is assured by the other cylinder.

[0003] A typical example of the use of redundant actuators is in the flight controls of a helicopter, to which reference is made herein purely by way of example.

[0004] Known redundant actuators are normally of two types: with parallel-body and series-body cylinders.

[0005] In the parallel-body solution, the cylinder bodies are side by side and parallel and fixed to a first attachment on the actuator; and the ends of the rods are connected to a second attachment on the actuator assembly, located along the centerline between the rods.

[0006] In the series-body solution, the two cylinder bodies are coaxial and positioned end to end; and the actuator has a common rod with two pistons sliding inside the respective bodies.

[0007] Each of the hydraulic control circuits of the respective actuators comprises a respective mechanically controlled valve, the slide of which is operated by the pilot via a control mechanism connected to the joystick. The outer casings of the valves are normally fixed side by side to the cylinder bodies so that the relative slides can be operated simultaneously by one control device.

[0008] Control devices of the above type are normally feedback controlled, i.e. the control mechanism is designed to detect and correct any error between the command imparted and the actual position assumed by the actuator. Feedback control may be effected mechanically, in which case, the control mechanism normally comprises a pair of feedback rods having one end connected to the output member of the actuator; and a pair of transmission levers operating the respective slides and connected to the input lever and, via this, to the respective feedback rods to receive and transmit to the slides displacements proportional to the difference between the displacements of the input lever and the respective feedback rods.

[0009] A major drawback of the above known solution is that a fault on one of the kinematic chains between the input lever and each of the valve slides may impair the redundancy of the hydraulic system by leaving only one circuit operative, and so exposing the actuator to further faults with potentially catastrophic consequences.

[0010] It is an object of the present invention to provide a mechanical feedback control device for a redundant actuator, designed to eliminate the aforementioned drawbacks typically associated with known devices.

[0011] According to the present invention, there is provided a mechanical feedback control device as claimed in Claim 1.

[0012] A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a view in perspective of a redundant actuator featuring a control device in accordance with the present invention;

Figure 2 shows a hydraulic diagram of the Figure 1 actuator;

Figure 3 shows a view in perspective of the feedback control device of the Figure 1 actuator;

Figure 4 shows a section along line IV-IV in Figure 1.

[0013] Number 1 in Figures 1 and 2 indicates as a whole a redundant servocontrolled hydraulic actuator for operating the flight controls of an aircraft, and in particular for transmitting and amplifying control forces from the joystick to the rocker plate of a helicopter.

[0014] Actuator 1 substantially comprises a top first hydraulic cylinder 2 and a bottom second hydraulic cylinder 3 having respective bodies 4, 5 of axis A and arranged in series with a common intermediate head 6 and respective end heads 7, 8.

[0015] Head 8 of bottom cylinder 3 is fitted with a bottom connecting member 9 for connecting actuator 1 to a fixed constraint on the helicopter (not shown).

[0016] Actuator 1 comprises a rod 10, of axis A, common to both cylinders 2 and 3, and which projects upwards through head 7 and has a second top connecting member 11 for connecting actuator 1 to the rocker plate (not shown) of the helicopter.

[0017] Rod 10 has two pistons 14, 15 sliding in fluidtight manner inside respective bodies 4, 5. More specifically, piston 14 defines, with heads 7 and 6, a top chamber 16 and a bottom chamber 17 of top cylinder 2; and piston 15 defines, with heads 6 and 8, a top chamber 18 and a bottom chamber 19 of cylinder 3.

[0018] Cylinders 2, 3 are controlled by respective known valves 20, 21 shown schematically in Figure 2 and housed in respective casings 22, 23 fixed to the outside of bodies 4, 5 of respective cylinders 2, 3. Casings 22, 23 are located side by side and connected integrally to each other to form substantially a single valve body 51.

[0019] Valves 20, 21 are continuously positionable, four-way, three-position types with a center closed setting.

[0020] Valve 20 has a supply port 24; a drain port 25; and two work ports 26, 27 connected to respective top and bottom chambers 16 and 17 of top cylinder 2.

[0021] Similarly, valve 21 has a supply port 30; a drain port 31; and two work ports 32, 33 connected to respective top and bottom chambers 18 and 19 of bottom cylinder 3.

[0022] Valves 20, 21 have respective known slides 34, 35 (Figure 4) for defining the port connections and flow sections of the respective valves. Slides 34, 35 are housed inside respective casings 22, 23, are movable axially along respective axes B, C parallel to each other and to axis A of actuator 1, and are offset axially so that a bottom end of slide 34 is located alongside a top end of slide 35.

[0023] Slides 34, 35 are controlled in parallel by a feedback control device 38 shown in Figures 3 and 4.

[0024] Device 38 substantially comprises an input lever 40 connected to a control member (not shown) forming part of a manual control mechanism operated by the joystick (not shown); two feedback rods 43 connecting top connecting member 11 to input lever 40; and a transmission lever 44 for transmitting control displacements from input lever 40 to slides 34, 35 of valves 20, 21.

[0025] More specifically, input lever 40 is substantially U-shaped and comprises a central connection 45 hinged to the control member (not shown); and two substantially parallel arms 46 on opposite sides of valve body 51. Each of arms 46 has a free end 47 connected to a bottom end 48 of a respective feedback rod 43 by a hinge 49 of axis D perpendicular to axis A; and rods 43 have respective top ends 50 connected to top connecting member 11.

[0026] Transmission lever 44 is also substantially U-shaped, and has two arms 54 on opposite sides of valve body 51 and hinged to valve body 51 by a common pin 55, which has an axis E parallel to axis D and perpendicular to axes A, B and C, is fitted through valve body 51 inside a transverse through seat 62, and is supported inside seat 62 in rotary manner by conventional supporting and sealing assemblies 61 not described in detail.

[0027] The ends 56 of pin 55 are connected rigidly to arms 54 of transmission lever 44. To simplify assembly, ends 56 of pin 55 are inserted inside respective C-shaped inserts 57 (Figure 3) fitted inside respective longitudinally-open end seats 58 on arms 54; and ends 56 of pin 55 are locked inside inserts 57, and inserts 57 inside respective seats 58, by means of respective screws 59 cooperating with respective tangential milled portions 60 on ends 56 of pin 55.

[0028] Arms 54 of transmission lever 44 are hinged to corresponding arms 46 of input lever 40 by respective pins 63 having an axis F parallel to axis E and on the opposite side of axis E to axis D.

[0029] Pin 55, connected rigidly to lever 44 so as to rotate integrally with it as described above, supports radial shafts 64, 65 parallel to each other and extending radially from pin 55 towards respective slides 34, 35 of valves 20, 21. More specifically, shafts 64, 65 are fitted through respective diametrical holes 66 in pin 55, are retained inside the holes by respective stop pins 67, and terminate with respective substantially spherical heads 68.

[0030] Heads 68 of shafts 64, 65 engage - with a minimum amount of radial clearance but with freedom to slide relatively in an axial direction - respective diametrical through holes 69 in slides 34, 35, so as to define respective spherical joints 70, 71; and shafts 64, 65 define cams integral with pin 55 and for converting the rotation of transmission lever 44 into simultaneous axial translation of slides 34, 35.

[0031] Shafts 64, 65 are assembled inside respective casings 22, 23 of valves 20, 21 through respective holes 74, which intersect seat 62, have respective axes parallel to each other and perpendicular to axes E, B, and C, and are closed by respective caps 75.

[0032] Operation of control device 38 will now be described as of a balance condition in which actuator 1 is stationary in a given position, and both valves 20, 21 are in the central position.

[0033] Manual operation of the joystick moves central connection 45 of input lever 40 (perpendicularly to the Figure 4 plane) so that lever 40 rotates in either direction about axis D, thus moving pins 63 and, consequently, transmission lever 44, which rotates with pin 55 about axis E, so that slides 34, 35 of valves 20, 21 are moved by shafts 64, 65 from the central position into such a position as to move cylinders 2, 3, in the desired direction, into a given target position.

[0034] Motion is transmitted from connection 45 to shafts 64, 65 via a closed-loop structure defined by input lever 40, transmission lever 44, and pin 55, none of which elements are therefore structurally critical, since, even in the event of failure, an alternative route always exists by which to drive both shafts 64, 65.

[0035] The displacement of rod 10 of actuator 1, and therefore of connecting member 11 with respect to connecting member 9, is fed back by rods 43 to input lever 40, which rotates transmission lever 44 in a direction opposite the operating direction. When the position of connecting member 11 corresponds to the manual operation target position, i.e. in the absence of a position error, lever 44 restores slides 34, 35 of valves 20, 21 to the central position, so that actuator 1 is restored once more to a balance position.

[0036] Feedback control device 38 is capable of reacting to external interference loads to maintain the desired position of actuator 1. That is, in the presence of an interference load, rod 10 tends to move away from the balance position; which displacement is transmitted by feedback rods 43 to input lever 40, which, via transmission lever 44, shifts slides 34, 35 of valves 20, 21 from the central position, thus producing a difference in pressure between respective chambers 16, 17 and 18, 19 of cylinders 2, 3, and hence a reaction capable of withstanding the load.

[0037] Cylinders 2, 3 have a common rod 10 but operate fully independently of each other. In the event either of cylinders 2, 3 breaks down owing to a mechanical fault on the cylinder or relative hydraulic circuit, the other cylinder is fully capable of ensuring operation of the actuator.

[0038] The advantages of feedback control device 38 according to the present invention will be clear from the foregoing description.

[0039] By virtue of the closed-loop structure defined by input lever 40, transmission lever 44 and pin 55, two kinematic chains are always available for transmitting control from connection 45 to both shafts 64, 65, so that any interruption in either one of the kinematic chains - e.g. failure of an arm on lever 40 or lever 44, or of pin 55 itself - in no way impairs control transmission to both slides 34, 35 or the full efficiency of device 38.

[0040] Clearly, changes may be made to device 38 without, however, departing from the scope of the accompanying Claims. In particular, the construction design and constraints of levers 40, 44 may differ. For example, to enhance the redundancy characteristics of the device, input lever 40 may be formed in two symmetrical halves (i.e. by "cutting" lever 40 along line M in Figure 4), so that any cracks in one half are prevented from spreading to the other.

[0041] It should also be pointed out that device 38 may be applied to any redundant servocontrol, regardless of the number and relative arrangement of the hydraulic cylinders, providing the relative hydraulic valves are arranged side by side.

Claims

1. A mechanical feedback control device for a redundant hydraulic actuator (1) comprising at least a first hydraulic cylinder (2) and a second hydraulic cylinder (3), both interposed between a first connecting member (9) connected to a fixed constraint, and a second connecting member (11) connected to a movable member controlled by said actuator (1); said cylinders (2, 3) being operated hydraulically by respective mechanically controlled valves (20, 21) arranged side by side and having respective slides (34, 35) movable along respective axes (B, C); said device (38) comprising:

an input lever (40) having connecting means (45) connected to and for receiving control displacements from manual control means;

at least one feedback member (43) connected to said input lever (40) and to said second connecting member (11) to transmit feedback displacements to said input lever (40); and

transmission means (44; 55; 64, 65) interposed between said input lever (40) and each of the slides (34, 35) of said valves (20, 21);

   characterized in that said input lever (40) and said transmission means (44; 55) define a closed-loop structure controlling the displacements of both said slides (34, 35), so that each of said slides (34, 35) can be moved by two different kinematic chains (46, 54, 55).

2. A device as claimed in Claim 1, characterized in that said transmission means (44; 55; 64, 65) comprise a common pin (55) rotating about a respective axis (E) perpendicular to the axes (B, C) of said slides (34, 35); and cam means (64, 65) for converting rotations of said pin (55) into linear displacements of said slides (34, 35).

3. A device as claimed in Claim 2, characterized in that said input lever (40) is substantially U-shaped, and comprises a central connection (45), and two lateral arms (46) each connected to a respective said feedback member (43); said transmission means comprising a substantially U-shaped transmission lever (44) having two arms (54), each connected rigidly to a respective end (56) of said pin (55); said arms (46) of said input lever (40) being connected to the respective said arms (54) of said transmission lever (44) to form, with said pin (55), the respective said kinematic chains (46, 54, 55) controlling the displacement of said slides (34, 35).

4. A device as claimed in Claim 2 or 3, characterized in that said cam means comprise two control shafts (64, 65) extending radially from said pin (55) and connected to the respective said slides (34, 35) by respective spherical joints (70, 71).

Drawing