ACTUATOR

Abstract

An actuator includes a housing and a piston including an axis. The piston and housing are configured to move relative to each other along the axis. The housing comprises at least one chamber for holding a fluid, the piston being positioned partially within the chamber. A seal configured to isolate the fluid in the chamber is positioned between the piston and the housing. The seal includes a seal body and an energiser. At least one pressure relief conduit is located between the energiser and the chamber. The pressure relief conduit configured to relieve fluid pressure built up in a region between the energiser and the chamber.

Claims

1. An actuator comprising: a housing comprising at least one chamber for holding a fluid; a piston comprising an axis, the piston positioned partially within the chamber; and a seal positioned between the piston and the housing, the seal configured to isolate a fluid in the chamber; wherein the piston and the housing are configured to move relative to each other along the axis; wherein one of the piston or the housing comprises a seal groove in which the seal is positioned, the seal comprising a seal body and an energiser, the energiser biasing the seal body against the other of the piston or the housing; wherein the actuator comprises at least one pressure relief conduit located between the energiser and the chamber, and configured to relieve fluid pressure built up in the region between the energiser and the chamber.

2. An actuator according to claim 1, wherein the piston and housing are configured to move relative to each other under the action of the fluid.

3. An actuator according to claim 1, further comprising: a cavity defined between the seal groove, the seal body and the energiser, wherein the pressure relief conduit is configured to fluidly communicate the chamber with the cavity.

4. An actuator according to claim 3, wherein the pressure relief conduit is configured to limit a rate of fluid transfer between the cavity and the chamber to a given rate of fluid transfer.

5. An actuator according to claim 1, wherein the piston comprises a piston head which defines a movable boundary of the chamber.

6. An actuator according to claim 1, wherein the seal is configured to isolate a relatively high pressure fluid within the chamber on a first side of the seal from a relatively low pressure fluid on a second side of the seal.

7. An actuator according to claim 1, further comprising a control spool, wherein the control spool is configured to selectively communicate a fluid supply with the chamber, such that a pressure within the chamber increases.

8. An actuator according to claim 7, wherein the control spool is configured to selectively communicate a fluid exhaust with the chamber, the fluid exhaust having a pressure which is lower than a pressure of the fluid supply.

9. An actuator according to claim 1, wherein the pressure relief conduit is formed in a radially extending surface of the seal groove.

10. An actuator according to claim 1, wherein the pressure relief conduit extends at least partially in an axial direction through the housing between the chamber and the energiser.

11. A wing flap system comprising: an actuator as claimed in claim 1.

12. An aircraft comprising: an actuator as claimed in claim 1.

13. A method of operating an actuator according to claim 1, the method comprising: supplying a fluid to the chamber, the fluid having a fluid pressure which is higher than a pressure on a side of the seal which is exterior to the chamber; and moving the piston and the housing relative to each other under the action of the fluid pressure.

14. A method of modifying an actuator comprising: providing an actuator, the actuator comprising: a housing comprising a chamber, the chamber for holding a fluid; a piston comprising an axis, the piston positioned partially within the chamber; a seal positioned between the piston and the housing, the seal configured to isolate a fluid in the chamber; wherein the piston and the housing are configured to move relative to each other along the axis along the axis, and wherein one of the piston or the housing comprises a seal groove in which the seal is positioned, the seal comprising a seal body and an energiser, the energiser biasing the seal body against the other of the piston or the housing; and forming a pressure relief conduit between the energiser and the chamber.

15. A method according to claim 14, wherein the forming comprises etching, machining or milling the pressure relief conduit feature into one of the piston and the housing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

[0032] FIG. 1 shows a schematic of a hydraulic actuator (e.g., in accordance with conventional arrangements and embodiments of the invention) in a resting position;

[0033] FIG. 2 shows a schematic of a hydraulic actuator (e.g. the actuator of FIG. 1) in an active position;

[0034] FIG. 3 shows a schematic of a hydraulic actuator (e.g. the actuator of FIG. 1 or 2) in a displaced position;

[0035] FIG. 4A shows a dynamic seal for a hydraulic actuator wherein a chamber is in a pressurised state;

[0036] FIG. 4B shows the dynamic seal of FIG. 4A wherein the chamber is in an equalised state;

[0037] FIGS. 5A and 5B show residual errors in housing displacement and control spool position when employing the seal of FIG. 4A;

[0038] FIG. 6 shows a dynamic seal in accordance with embodiments;

[0039] FIG. 7 shows another dynamic seal in accordance with embodiments;

[0040] FIG. 8 shows the performance characteristics of a dynamic seal in accordance with embodiments;

[0041] FIG. 9 shows the performance characteristics of another dynamic seal in accordance with embodiments; and

[0042] FIG. 10 shows an aircraft in accordance with embodiments.

DETAILED DESCRIPTION

[0043] Initial attempts to improve on the residual error have focussed on the use of dynamic seals 10, 11 including a seal body 16 and seal energiser 14 provided in a seal groove 13 surrounding the piston 12 (see FIGS. 4A and 4B). Each of the seal body 16, seal energiser 14 and the seal groove 13 may be annular in shape. However, other shapes and configurations are also envisaged (e.g., a cuboid piston may be used in conjunction with four separate linear dynamic seals, or may comprise dynamic seals on some surfaces but not on others). Similarly, the seal body 16 may comprise a continuous (e.g., annular) shape and the seal energiser 14 may be discontinuous (e.g., comprise a plurality of energising elements which are interconnected or discrete from one another). The seal body 16 may be sized to fit a width of the groove 13 (e.g., to have a seal width which is be equal to the width of the groove 13). The seal body 16 may comprise a resilient material. Selecting appropriate sizing and materials for the seal body 16 can help prevent the seal from moving freely within the groove 13, thereby preventing slippage of the piston and positional inaccuracies. The seal energiser 14 applies pressure on the seal body 16 in a radial direction, so as to improve the sealing quality between the piston 12 and the housing 8 (e.g., by increasing friction between the seal body 16 and an opposing sealing surface). The seal energiser 14 may comprise a width which is less than a width of the seal groove 13. A cavity 17 (free space or vacancy) may be provided between the seal groove 13, the seal body 16 and the seal energiser 14. The cavity 17 may span the width of the seal groove 13 (e.g., connecting forward and rear/reverse sides of the seal groove). Alternatively, the cavity 17 may be confined to a side (e.g., forward or reverse side) of the seal groove 13. Corresponding cavities 17 may be provided on both sides (e.g., forward or reverse sides) of the energiser 14.

[0044] The seal groove 13 may be provided in the housing 8 with the seal body 16 positioned radially inwardly of the seal energiser 14 such that it is biased against the piston 12. Alternatively, the seal groove 13 may be provided in the piston 12 itself with the seal body 16 positioned radially outwardly of the seal energiser 14 such that it is biased against the housing 8.

[0045] With reference to FIG. 4A, during operation of the hydraulic actuator, and when a relatively high pressure fluid is communicated with one of the chambers 2 (e.g., the forward chamber 2B is in a pressurised state), the correspondingly high chamber pressure P1, P2 (generally referred to as PA), is communicated to the seal body 16 (e.g., via an annular axial channel defined between the piston 12 and housing 8). The communication of this relatively high chamber pressure PA to the seal body 16 causes the seal body 16 to deform (e.g., periodically compress) and high pressure fluid to enter the seal groove 13 housing the energiser 14. Advantageously, this causes the chamber pressure PA to be communicated to the seal groove 13 (e.g. to a cavity 17 defined between the seal groove 13, the seal body 16 and the seal energiser 14) and creates an additional energising pressure, PE, on the seal body 16. The provision of this energising pressure PE occurs in concert with the presence of relatively high chamber pressure PA. Thus, the firmness of the seal 10, 11 engagement (i.e. the friction between the seal 10, 11 and an opposing sealing surface) is modulated with the chamber pressure PA and the driving force of the actuator 1. The increased friction is not detrimental when there is a high pressure, as the high pressure creates proportionally high driving force. This reduces the positional error and allows for much smoother operation since the magnitude of the resistance to movement increases and decreases relative to the driving force for movement.

[0046] It has been found that when the pressure between chambers equalises, such that chamber pressure PA is reduced towards the null pressure P0, the seal body 16 recovers from deformation. As the seal body 16 is no longer deformed, the chamber pressure PA is no longer communicated to the seal groove 13 or cavity 17 meaning that higher pressure fluid is effectively trapped behind the seal body 16. The energising pressure PE is therefore greater than the chamber pressure PA (see FIG. 4B), which means that the seal 10, 11 engagement remains firmer than necessary. As a result, and with reference to FIG. 5A, excess friction causes a small residual error 24 to remain.

[0047] FIG. 5A shows the positional behaviour of a hydraulic actuator with dynamic seals 10, 11 as it is repeatedly moved between a forward position and a rear position. Here it can be seen that the output or actual position 22 of the actuator closely follows the input or set point position 20 of the actuator (e.g., as set by a controller or operator). However, though a step change is provided at the input 20, the change in output position 22 instead slows slightly as it approaches the set point (exaggerated for illustrative purposes). The output position also fails to reach the set point with a residual error 24 present in both the forward and reverse step changes. It is believed that these residual errors are the product of the aforementioned trapped fluid occurring in the corresponding forward and rear seals causing excess friction between the piston 12 and housing 8.

[0048] FIG. 5B shows the corresponding position of the control spool 26 (normalised relative to the actuator pressure) when the actuator is repeatedly moved between a forward position and a rear position as in FIG. 5A. Here it can be seen that, following its initial step change, the control spool 4 does not fully return its null position such that it presents an offset 28 from the null position as a result of the residual error of the housing position. This offset 28 can cause further problems when the actuator 1 is next commanded to move. For example, if the output position of the actuator has to be finely tuned (e.g., in high precision aircraft operations), an initial offset in the opposite direction to travel (e.g., forward instead of reverse) can create a response delay. Similarly, the response can be unexpectedly fast if an offset is present is the same direction of travel. This can create undesirable variation in the performance of the actuator 1.

[0049] As shown in FIGS. 6 and 7, in order to further improve on actuator 1 performance, and to better modulate seal engagement with the piston 12 and/or housing 8, one or more pressure relief features (or pressure communication features) may be provided within the seal groove 13. The pressure relief features may comprise one or more pressure relief conduits 30.

[0050] The pressure relief features serve to better communicate the chamber pressure PA with the energising pressure PE. In so doing, energising pressure PE does not become trapped within the seal groove (e.g., within a cavity 17 defined between the seal groove 13, the seal body 16 and the seal energiser 14) and the residual error caused by unintentional energising of the seal is eliminated.

[0051] The pressure relief conduit 30 may comprise a channel or passage extending in a generally axial direction (e.g., parallel to the piston axis 9). The channel or passage direction may also comprise a radial component (see FIG. 6).

[0052] Alternatively, the pressure relief conduit may be formed at least partly on a surface of the seal groove 13. For example, the pressure relief conduit 30 may be formed (e.g., drilled, etched or engraved) in a radially-extending side face 31 (forward or rear annular face) of the seal groove (see FIG. 7 which shows a cross section intersecting a radially extending pressure relief conduit 30). Similarly, the pressure relief conduit may be formed as a cut or slit through a wall (e.g., an entire axial width of a wall) of the seal groove, thereby extending axially between the chamber and the seal body for at least an entire radial distance of the seal body (not shown).

[0053] The pressure relief conduit 30 may be provided at the point of manufacture of the actuator. Alternatively, the pressure relief conduit 30 may be formed by modifying an existing actuator 1. For example, the pressure relief conduit 30 may be introduced (e.g. retrofitted) during a maintenance operation of an actuator 1, so as to improve the actuator's performance. The conduit 30 may link with the chamber 2 via an annular axial channel (e.g., a channel defined between the piston 12 and housing 8, see FIG. 7).

[0054] It has been found that placing the pressure relief conduit 30 in the seal groove, as opposed to placing a pressure relief feature in the seal body 16 itself, leads to greatly enhanced performance. This is because modifying the seal body 16 can give rise to unpredictable results and reduce the integrity of the seal, leading to increase wear and maintenance requirements of the actuator. Further, as the seal body may comprise resilient material, any pressure relief features formed therein may deform and act unpredictably. It is also more difficult to tune the response behaviour of the pressure relief feature when present in the seal body, as the behaviour of the seal body may change with time.

[0055] Placing the pressure relief feature in the seal groove 13 of the piston 12 or housing also allows for enhanced tuning of the performance and behaviour of the actuator. For example, because the piston and/or housing is typically manufactured from an inelastic material (e.g., a metallic material), it is possible to form highly defined (micrometre or nanometre scale) features therein. Thus, the communication between the seal groove 13 or cavity 17 and the chamber 2 can be metered and tuned so as to control the speed at which the chamber pressure PA and energising pressure PE equalise.

[0056] With reference to FIGS. 6 and 8, when a relatively large channel is employed as a pressure relief conduit 30 (as illustrated in FIG. 6), the chamber pressure PA and energising pressure PE are freely communicated with each other. In this case the actuator will exhibit a rapid (near instant) response time as the energising pressure PE is quickly reduced with chamber pressure such that the seal firmness is synchronised with the pressure difference between forwards and reverse chambers 2A, 2B. Thus, the driving force for moving the housing is synchronised with the resistance to movement such that a low resistance is present when the chamber pressure PA is reduced towards the null pressure P0. Accordingly, the housing can continue to move without significant resistance to the set point and, consequently, no residual error 24 is present between the input or set point position 20 and the output or actual position 22 of the housing. Similarly, the control spool 4 is allowed to move to its null position such that no offset 28 is present and the undesirable variation in the performance of the actuator can be abated.

[0057] Alternatively, as illustrated in FIG. 9, when a relatively smaller channel is employed as a pressure relief conduit 30 (here denoted as 30), the flow between the seal groove 13 or cavity 17 and chamber 2 can be constricted. Stated differently, the pressure relief conduit 30 can be configured to limit the rate of fluid transfer between the energiser 14 and the chamber 2 to a set or given rate of fluid transfer. In this way the rate of equalisation between chamber pressure PA and energising pressure PE can be reduced to a relatively slower rate. Here, again, the housing 8 can continue to move to the set point such that no residual error 24 is present, but it may take longer to do so. In this way the actuator 1 can be configured to create a dampened response (e.g. inertial dampening, or soft closing) which may be preferential in certain applications where relatively rapid and high inertia movements are detrimental (e.g., heavy machinery). Again, the control spool 4 is allowed to move to its null position (albeit over a longer period of time) such that no offset 28 is present and the undesirable variation in the performance of the actuator can be abated.

[0058] It is contemplated that many other techniques may be used to tune the response of the actuator. The size and frequency of the pressure relief conduits 30 can be modified to tailor response behaviour of movable housing. Similarly, shape of the pressure relief conduit 30 can be modified (e.g., v-shaped groove, conical passage) so as to modify the response behaviour. If a channel is used as pressure relief conduit 30, the channel may be a straight channel or a curved channel. The channel may have a constant cross-section or a variable cross-section. For example, the channel may constrict to a narrow orifice or nozzle.

[0059] Used herein the term fixed is intended to define an element which is secured to a first (e.g., major) body (e.g., a wing 102 on an aircraft 100, as shown in FIG. 10). Similarly, the term movable is intended to define an element which is secured to a second (e.g., minor) body which is movable relative to the first body (e.g., a flap 104). Embodiments include an aircraft 100 or wing flap system 106 comprising the described actuators. Whilst exemplary embodiments have been described in relation to a fixed piston and movable housing, it should be noted that the disclosed seal configurations may equally be applied to the reverse configuration of a fixed housing and movable piston. Although described as fixed, it should also be appreciated that the fixed element (piston or housing) may be pivotally attached to a fixed structure (e.g., an aircraft bulkheadnot shown).

[0060] Further, one or more pressure relief conduits 30 may be provided only on one side (e.g., forward or rear) of the seal groove 13, or may be provided on both sides of the seal groove 13 (e.g., to corresponding cavities 17 on either side of the energiser 14). For example, when employing the described seal configuration between chambers 2 (e.g., circumscribing the piston head 3), it may be beneficial to communicate both chambers 2A, 2B to respective sides of the seal groove 13 such that the energising pressure PE may be provided from either of the chambers 2A, 2B (e.g., from which ever of the chambers is in communication with the relatively high pressure supply 5).

[0061] The teachings herein may also be applied to other fluidic actuators known in the art, e.g., pneumatic actuators.

[0062] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.

[0063] While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims