STABILITY AND CONTROL AUGMENTATION SYSTEM ACTUATOR

Abstract

A stability and control augmentation system (SCAS) actuator is operable for actuating a flight control surface of an aircraft. The SCAS actuator includes an actuator housing having a first aperture, a second aperture and a hydraulic chamber therebetween. A piston extends through the actuator housing. Fluid inlets are in fluid communication with regions of the hydraulic chamber. A first end portion of the piston is arranged to slide through the first aperture without a seal between the first end portion and the first aperture. A second end portion of the piston is arranged to slide through the second aperture without a seal between the second end portion and the second aperture. An intermediate portion of the piston is arranged to slide in the hydraulic chamber without a seal between the intermediate portion and the hydraulic chamber.

Claims

1. A stability and control augmentation system actuator operable for actuating a flight control surface of an aircraft, wherein the stability and control augmentation system actuator comprises: an actuator housing comprising a first aperture, a second aperture and a hydraulic chamber between the first aperture and the second aperture; a piston comprising a first end portion extending through the first aperture, an intermediate portion in the hydraulic chamber and a second end portion extending through the second aperture, wherein the piston is arranged for linear motion with respect to the actuator housing; a first fluid inlet in fluid communication with a first region of the hydraulic chamber proximal to the first aperture; and a second fluid inlet in fluid communication with a second region of the hydraulic chamber proximal to the second aperture; wherein the first end portion is arranged to slide through the first aperture without a seal between the first end portion and the first aperture; wherein the second end portion is arranged to slide through the second aperture without a seal between the second end portion and the second aperture; and wherein the intermediate portion is arranged to slide in the hydraulic chamber without a seal between the intermediate portion and the hydraulic chamber.

2. The stability and control augmentation system actuator as claimed in claim 1, wherein the hydraulic chamber has an internal cross section that is greater than the internal cross section of the first and/or second apertures; and wherein the intermediate portion of the piston comprises a flange that extends radially outwards into the hydraulic chamber.

3. The stability and control augmentation system actuator as claimed in claim 1, wherein the first aperture has a cross-section that is substantially constant with respect to an axial direction; or wherein the second aperture has a cross-section that is substantially constant with respect to the axial direction; or wherein the hydraulic chamber has a cross-section that is substantially constant with respect to the axial direction.

4. The stability and control augmentation system actuator as claimed in claim 1, wherein the cross-section of the first end portion is substantially equal to the internal cross-section of the first aperture; or wherein the cross-section of the second end portion is substantially equal to the internal cross-section of the second aperture; or wherein the cross-section of the intermediate portion is substantially equal to the internal cross-section of the hydraulic chamber.

5. The stability and control augmentation system actuator as claimed in claim 1, wherein the first end portion has a cross-section that is substantially constant with respect to the axial direction; and/or wherein the second end portion has a cross-section that is substantially constant with respect to the axial direction; or wherein the intermediate portion has a cross-section that is substantially constant with respect to the axial direction.

6. The stability and control augmentation system actuator as claimed in claim 1, wherein substantially the entire surface of the first aperture engages with the first end portion of the piston; or wherein substantially the entire surface of the second aperture engages with the second end portion of the piston; or wherein substantially the entire surface of the intermediate portion of the piston engages with the hydraulic chamber.

7. The stability and control augmentation system actuator as claimed in claim 1, wherein the first end portion and the first aperture have a clearance of less than 20 microns; or wherein the second end portion and the second aperture have a clearance of less than 20 microns; or wherein the intermediate portion and the hydraulic chamber have a clearance of less than 20 microns.

8. The stability and control augmentation system actuator as claimed in claim 1, wherein the first aperture is arranged to engage with the first end portion of the piston such as to allow a leakage of hydraulic fluid from the hydraulic chamber; or wherein the second aperture is arranged to engage with the second end portion of the piston such as to allow a leakage of hydraulic fluid from the hydraulic chamber; or wherein the intermediate portion of the piston is arranged to engage with the hydraulic chamber such as to allow a leakage of hydraulic fluid between the first and second regions of the hydraulic chamber.

9. The stability and control augmentation system actuator as claimed in claim 1, wherein the stability and control augmentation system actuator comprises a first fluid outlet defined in stability and control augmentation system actuator on the opposite side of the first aperture from the first region of the hydraulic chamber; or wherein the stability and control augmentation system actuator comprises a second fluid outlet defined in the stability and control augmentation system actuator on the opposite side of the second aperture from the second region of the hydraulic chamber.

10. The stability and control augmentation system actuator as claimed in claim 1, wherein the stability and control augmentation system actuator comprises a linear variable differential transformer arranged to determine the position of the piston; wherein the linear variable differential transformer is sealed against the actuator housing.

11. The stability and control augmentation system actuator as claimed in claim 10, wherein the stability and control augmentation system actuator comprises a first fluid outlet defined in stability and control augmentation system actuator on the opposite side of the first aperture from the first region of the hydraulic chamber; and wherein the first fluid outlet is in fluid communication with the linear variable differential transformer.

12. The stability and control augmentation system actuator as claimed in claim 1, wherein the stability and control augmentation system actuator comprises a biasing mechanism arranged to bias the piston.

13. The stability and control augmentation system actuator as claimed in claim 12, wherein the stability and control augmentation system actuator comprises a second fluid outlet defined in the stability and control augmentation system actuator on the opposite side of the second aperture from the second region of the hydraulic chamber; and wherein the second fluid outlet is in fluid communication with the biasing mechanism.

14. The stability and control augmentation system actuator as claimed in claim 12, wherein the biasing mechanism comprises one or more bellows; and wherein the one or more bellows are sealed against the actuator housing.

15. The stability and control augmentation system actuator as claimed in claim 12, wherein the biasing mechanism comprises a sensor arranged to detect the presence of hydraulic fluid.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0052] One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures in which:

[0053] FIG. 1 shows a schematic cross-sectional view of a SCAS actuator; and

[0054] FIG. 2 shows a Stability and Control Augmentation System (SCAS) including the SCAS actuator shown in FIG. 1.

DETAILED DESCRIPTION OF DRAWINGS

[0055] FIG. 1 shows a schematic cross-sectional view of a SCAS actuator.

[0056] The SCAS actuator 1 comprises an actuator housing 2 in which a piston 10 is housed for linear motion within the actuator housing. The housing has apertures 4, 6 at each end through which end portions 12, 16 of the piston extend. The housing has a hydraulic chamber 8 between its apertures, in which an intermediate portion 14 of the piston is located and moves. The end portions 12, 16 of the piston engage with the respective apertures 4, 6 of the actuator housing, with no seals being located between the end portions and the respective apertures. The intermediate portion 14 of the piston engages with the hydraulic chamber 8, with no seal being located between the intermediate portion of the piston and the hydraulic chamber.

[0057] The intermediate portion of the piston divides the hydraulic chamber into two regions 20, 24 that are supplied with hydraulic fluid through respective fluid inlets 18, 22. The differential pressure across the two regions 20, 24 of the hydraulic chamber acts to move the piston 10 of the SCAS actuator 1.

[0058] The first end 12 of the piston extends through the first aperture 4 of the actuator housing 2. A linear variable differential transformer (LVDT) 26 is attached to the actuator housing 2 and the first end 12 of the piston on the other side of the first aperture 4. The LVDT is used to measure the position of the piston 10 relative to the actuator housing 2. The measured position is used to send feedback signals to a flight control system (FCS) of the aircraft.

[0059] The LVDT 26 is sealed against the actuator housing 2 around the first aperture 4. A first return fluid line 32 is in fluid communication with the inside of the LVDT.

[0060] The second end 16 of the piston extends through the second aperture 6 of the actuator housing 2. An actuator rod end 28 is mounted onto the second end 16 of the piston. The rod end 28 facilitates connection of the piston 10 to the moving parts of the helicopter, e.g. via a mechanical linkage.

[0061] Metal bellows 30 surround the second end 16 of the piston and act to seal the second aperture 6 of the actuator housing 2. A second return fluid line 34 is in fluid communication with the inside of the metal bellows 30.

[0062] FIG. 2 shows a Stability and Control Augmentation System (SCAS) in which the SCAS actuator 1 shown in FIG. 1 may be implemented. The SCAS provides stability and control augmentation to a flight control surface. The SCAS partially controls operation of an actuator (that, in turn, actuates a flight control surface of an aircraft), via a mechanical linkage from the SCAS actuator 1. The SCAS does this by being operable to modulate (e.g. fractionally adjust) input from an input linkage that is controlled by, e.g., a pilot, to fine-tune operation of the actuator. The SCAS therefore operates in addition to input into the input linkage, to provide adjustment of the actuator, e.g. to counteract vibrations in the actuator or a downstream flight control surface.

[0063] The SCAS includes a valve system 101 that controls (e.g. permits or prevents, as needed) a flow of hydraulic fluid (from a hydraulic fluid supply) to the opposed regions 20, 24 of the hydraulic chamber 8 of the SCAS actuator 1, via the respective fluid inlets 18, 22 (see FIG. 1) to thereby control operation of the SCAS actuator 1. The valve system does this by opening and closing fluid flow paths therein, in response to control signals from a flight control system (FCS) of the aircraft.

[0064] The position of the SCAS actuator 1 is thereby controlled by controlling operation of the valve system 101. The position of the piston 10 of the SCAS actuator 1 is measured by the LVDT 26 in the SCAS actuator 1. The measured position is used to send feedback signals to the FCS of the aircraft.

[0065] A return fluid system is connected to the first and second return fluid lines 32, 34 of the SCAS actuator 1. Hydraulic fluid can thus be returned to the hydraulic fluid system, e.g. following leakage from the first and/or second regions 20, 24 of the hydraulic chamber 8.

[0066] Thus the SCAS actuator, in embodiments of the present disclosure, does not possess any seals between the piston and the actuator housing, on the moving surfaces of the piston and the surfaces of the actuator housing that mate with each other and which the piston moves relative to the actuator housing. This helps to provide more predictable friction between the piston and the actuator housing and so gives the SCAS actuator a more predictable and reliable behaviour, e.g. owing to a reduction in the gain of the frequency response from the fly by wire input. This contrasts with conventional SCAS actuators which are trying to stop internal leakage by providing additional seals between the piston and the actuator housing, which further compounds the problem.

[0067] The lacks of seals between the piston and the actuator housing also helps to provide controlled internal leakage, e.g. between the first and second regions of the hydraulic chamber, and helps to give a stable frequency response for the SCAS actuator. Not having seals between the piston and the actuator housing also helps to provide a compact SCAS actuator, that has less mass than conventional SCAS actuators, thus helping to give a cost saving design.