GB2562239A

GB2562239A - Servovalve

Info

Publication number: GB2562239A
Application number: GB1707353.7A
Authority: GB
Inventors: W Syska Andrew; R Wilson Heather
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2017-05-08
Filing date: 2017-05-08
Publication date: 2018-11-14
Anticipated expiration: 2037-05-08
Also published as: GB201707353D0; GB2562239B

Abstract

A servovalve including an actuator with first and second piezoelectric members and a fuel control system including such a servovalve are provided. The servovalve comprises: first and second inlets 47, 48 for inflow of fluid at corresponding first and second pressures to an actuator space; a fluid outlet 60 from the actuator space; and an actuator located in the actuator space. The actuator has mechanically coupled first and second piezoelectric members 50. Each of the piezoelectric members 50 is deflectable under the application thereto of an electrical driving signal to deflect that member. The deflection in turn deflects the mechanically coupled other member 50, such that the coupled members are controllably movable together between first and second deflection configurations under the application of the electrical driving signal selectably to either one of the coupled members. The servovalve is arranged such that: movement of the coupled members 50 towards the first deflection configuration increases fluid communication between the first inlet 47 and the outlet 60 and decreases fluid communication between the second inlet 48 and the outlet 60; and movement of the coupled members 50 towards the second deflection configuration increases fluid communication between the second inlet 48 and the outlet 60 and decreases fluid communication between the first inlet 47 and the outlet 60. A fuel control system including such a servovalve, and a gas turbine engine including such a fuel control system are also disclosed.

Description

SERVOVALVE

Field of the Present Disclosure

The present disclosure relates to a servovalve.

Background

Servovalves are used in engine fuel control systems to convert an electric signal into a pressure signal, which can then be used in a range of control applications. The pressure signal may be generated by means of movement of a mechanism between a set of nozzles, where the movement of the mechanism is related to an input electrical signal. In particular, an electro-magnetically controlled torque motor can be used to rotate an armature depending on the current signal input. This rotation causes a flow guide, for example a flapper or jet pipe, to move between a set of nozzles, which alters the differential pressure at output control ports. A fuel control system for a gas turbine engine may incorporate a number of such devices.

For example, Figure 2(A) and (B) of US 2006/0130455 shows a fuel system comprising a metering unit and a staging unit and having four servovalves, in this case all based on flapper mechanisms.

Conventional servovalves of this type have multiple parts and can have relatively high failure rates. In particular, the fine wire nature of the torque motor can cause problems with robustness and reliability in the harsh operating environment of an aeroengine fuel control system.

It would be desirable to improve the reliability and robustness of servovalves.

Summary

Accordingly, in a first aspect, the present invention provides a servovalve including: a first inlet for inflow of fluid at a first pressure to an actuator space; a second inlet for inflow of fluid at a second pressure to the actuator space; a fluid outlet from the actuator space; and an actuator located in the actuator space and having mechanically coupled first and second piezoelectric members, each of the piezoelectric members being deflectable under the application thereto of an electrical driving signal to deflect that member, which deflection in turn deflects the mechanically coupled other member, such that the coupled members are controllably movable together between first and second deflection configurations under the application of the electrical driving signal selectably to either one of the coupled members; wherein the servovalve is arranged such that movement of the coupled members towards the first deflection configuration increases fluid communication between the first inlet and the outlet and decreases fluid communication between the second inlet and the outlet, and movement of the coupled members towards the second deflection configuration increases fluid communication between the second inlet and the outlet and decreases fluid communication between the first inlet and the outlet.

Providing an actuator for the servovalve which is based on piezoelectric members rather than an electro-magnetic torque motor allows the device to be formed from fewer and simpler components, thereby improving the robustness and reliability of the device. Further, by having two piezoelectric members, either one of which can be driven by the electrical driving signal, the servovalve has built in redundancy such that if one of the members fails, the driving signal can be applied to the other member to allow the device to continue to operate.

In a second aspect, the present invention provides a fuel control system for a gas turbine engine including one or more servovalves according to the first aspect. Thus the fluid used in the servovalve can be fuel.

In a third aspect, the present invention provides a gas turbine engine having the fuel control system according to the second aspect.

Optional features of the present disclosure will now be set out. These are applicable singly or in any combination with any aspect of the present disclosure.

Changing the relative amounts of fluid communication between the inlets and the outlet can be used to convert the electric signal into a pressure signal in various ways. For example, one option is to generate a pressure signal at the outlet. However, preferably the servovalve is configured such that: the first pressure varies in inverse relationship to the degree of fluid communication between the first inlet and the outlet, and the second pressure varies in inverse relationship to the degree of fluid communication between the second inlet and the outlet. In this way, the differential pressure between the first and second pressures is controllable by moving the coupled members between the first and second deflection configurations. Thus the differential pressure can be continuously and smoothly varied by changing the electrical driving signal and can be used in a variety of control applications. In such an arrangement, any fluid flow through the outlet can merely be a spill flow, which typically is not used for control applications. For example, the servovalve may further include: a first feed line feeding the first inlet with fluid, and a second feed line feeding the second inlet with fluid. The first feed line can then have a first restriction orifice upstream of the first inlet, and the second feed line can have a second restriction orifice upstream of the second inlet, each restriction orifice restricting flow in its feed line such that the fluid pressure in that feed line downstream of the restriction orifice and at the respective inlet varies in inverse relationship to changes in the degree of fluid communication between the respective inlet and the outlet. Conveniently, the first feed line may then open downstream of its restriction orifice to a first control port, and the second feed line may then open downstream of its restriction orifice to a second control port. With such an arrangement, the differential pressure between the first and second pressures at respectively the first and second control ports is controllable by moving the coupled members between the first and second deflection configurations. Conveniently, the servovalve may include a common supply port which supplies both the first and the second feed lines with pressurised fluid upstream of their respective restriction orifices.

The first and second inlets may be fluid jet nozzles.

The electrical driving signal can be a driving voltage or a driving current.

The piezoelectric members may be spaced apart by a gap, and the servovalve arranged such that the gap fills with fluid from the inlets en route to the outlet. In this way, fluid pressure can be equalised around and between the members, which can help to reduce stress in the, typically ceramic, piezoelectric material of the members, and also reduce opposition to deflection. Conveniently, the outlet may be a drain from the gap.

The piezoelectric members may be parallel, planar members which are deflectable out of their respective planes. For example, the piezoelectric members may be coaxial annuli which are deflectable out of their respective planes to adopt domed conformations. The planar piezoelectric members may clamped to opposite sides of a central clamp ring which extends around outer perimeters of the piezoelectric members. The actuator may further have a pair of outer clamp rings which are clamped to the outer perimeters of the piezoelectric members at opposite, outwardly-facing sides thereof. In such an arrangement, the clamp ring(s) may have smoothly curved clamping surfaces such that, when the piezoelectric members deflect, they rock smoothly over the curved clamping surfaces. This can help to increase deflection while securely holding the planar piezoelectric members.

The actuator may further have respective washers mediating the contacts between the piezoelectric members and the clamp ring(s). For example the washers, which can combine an electrical insulating function and a friction reduction function, may be formed of PTFE.

When the piezoelectric members are parallel, planar members, the actuator may have an elongate target piece which extends axially through central apertures of the piezoelectric members. In the first deflection configuration a first end of the target piece can then be maximally spaced from the first inlet and an opposite second end of the target piece can be minimally spaced from or block the second inlet, and in the second deflection configuration the first end of the target piece can be minimally spaced from or block the first inlet and the second end of the target piece can be maximally spaced from the second inlet. The piezoelectric members may be clamped to opposite sides of a further central clamp ring which extends around inner perimeters of the piezoelectric members at their central apertures. In addition, the actuator may have a further pair of outer clamp rings which are clamped to the inner perimeters of the piezoelectric members at opposite, outwardly-facing sides thereof. Conveniently, the further pair of outer clamp rings can be provided by respective portions of the target piece. For example a first portion of the target piece can provide one of these clamp rings and the first end for blocking the first inlet, and a second portion of the target piece can provide the other of these clamp rings and the second end for blocking the second inlet. The portions of the target piece can be joined by a suitable fastening arrangement (e.g. threads) which applies a clamping force across these clamp rings. As with the first-mentioned clamp rings, the further clamp ring(s) may have smoothly curved clamping surfaces such that, when the piezoelectric members deflect, they rock smoothly over the curved clamping surfaces. Similarly, the actuator may have respective washers (e.g. PTFE washers) mediating the contacts between the piezoelectric members and the further clamp ring(s).

Brief Description of the Drawings

Embodiments of the present disclosure will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a longitudinal cross-section through a ducted fan gas turbine engine;

Figure 2 shows a perspective external view of a servovalve;

Figure 3 shows a perspective view of internal features of the servovalve;

Figure 4 shows a longitudinally sectioned perspective view through the servovalve;

Figure 5 shows a longitudinal cross-section through the servovalve; and

Figure 6 shows more detailed views of regions A and B of Figure 5.

Detailed Description and Further Optional Features

With reference to Figure 1, a ducted fan gas turbine engine is generally indicated at 10 and has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, an intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.

During operation, air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate-pressure compressor 13 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate-pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high-pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate-pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan. A fuel control system of the engine is typically under the control of the engine’s engine electronic controller (EEC), and may have a main pump unit comprising a low pressure pump which draws fuel from a fuel tank of the aircraft and supplies the fuel at boosted pressure to the inlet of a high pressure pump. The low pressure pump typically comprises a centrifugal impeller pump while the high pressure pump may comprise one or more twin pinion gear pumps.

The low pressure and the high pressure pumps are typically connected to a common drive input, which is driven by the engine high-pressure shaft via an engine accessory gearbox. The inter-stage flow between the low pressure and the high pressure pumps is typically used to cool engine lubrication oil in a fuel/oil heat exchange.

The high pressure pump feeds pressurised fuel to a fuel metering valve of a hydromechanical unit (HMU) of the fuel control system, the metering valve being operable by the EEC to control the rate at which fuel is allowed to flow via a pressure raising and shut-off valve of the HMU to a delivery line and thence to burners of the engine. A staging unit may be provided between the HMU and the burners to implement burner staging control. Servovalves can be used within the HMU and staging unit, e.g. to control the metering valve, the shut-off valve, a fuel splitting valve of the staging unit, and fuel pressure actuated ancillary devices (such as variable inlet guide vanes and variable stator vanes).

Figure 2 shows a perspective external view of such a servovalve, Figure 3 shows a perspective view of internal features of the servovalve, Figure 4 shows a longitudinally sectioned perspective view through the servovalve, Figure 5 shows a longitudinal cross-section through the servovalve, and Figure 6 shows more detailed views of regions A and B of Figure 5.

The servovalve has a case formed from body housing 31, and a cover 32 which is fastened to housing by bolts 33 with wire thread inserts 34. The housing and the cover are sealed at a series of stepped interfaces by respective sealing rings 35-37.

The body housing 31 and the cover 32 define an interior actuator space in which are located parallel and coaxial first and second piezoelectric discs 50. These are spaced apart by a first central clamp ring 54 extending around outer perimeters of the piezoelectric discs, and a second central clamp ring 58 extending around inner perimeters of central apertures of the discs. In addition, at the outwardly-facing sides of the discs are a pair of first outer clamp rings 55a, 55b at the outer perimeters of the discs, and a pair of second outer clamp rings 59a, 59b at the inner perimeters of the discs. A wave washer 41 applies a clamping load across the first outer clamp rings 55a, 55b and the first central clamp ring 54. The second outer clamp rings 59a, 59b, by contrast, are formed as integral parts of an elongate target piece that extends through the central apertures of the discs and through the second central clamp ring 58. The target piece has a nut portion 52 which provides one of the second outer clamp rings 59a and a screw portion 53 which provides the other one of the second outer clamp rings 59b. The nut portion and the screw portion are screwed together to apply a clamping load across the second outer clamp rings 59a, 59b and the second central clamp ring 58.

As discussed in more detail below, each of the piezoelectric discs 50 is deflectable out of its respective plane in either direction by the application of a driving voltage or current. This deflection gives the annulus of each disc a domed shape. Inner 56 and outer 57 PTFE washers mediate the contact between the clamp rings 54, 55a, 55b, 58, 59a, 59b and the piezoelectric discs 50. The washers electrically insulate the electric current present in discs from the, typically steel, clamp rings. They also provide low friction interfaces with the discs and the clamp rings to accommodate the deflection, thereby reducing wear and increasing disc life. In addition, the clamping surfaces of the clamp rings are smoothly curved so that when the piezoelectric members deflect, they rock smoothly over the curved clamping surfaces.

At opposite ends of the target piece are further spaces within the body housing 31 and the cover 32 and containing respectively a nozzle holder 49 for a first nozzle 47, and a further nozzle holder 49 for a second nozzle 48. The nozzles are inlets for fluid (e.g. fuel) into the actuator space. Galleys formed in the body housing and the cover allow fluid to be transmitted to respectively the first and second nozzles. A flow return outlet 60 is formed in the base of the body housing to drain the actuator space.

More particularly, the galleys provide a first feed line 62 and a second feed line 63. Both feed lines are supplied with pressurised fluid from a common supply port 64. The feed lines diverge shortly after this port and proceed via respective first 65 and second 66 restriction orifices to feed fuel to the further spaces containing the nozzle holders 49. From the space for one of the nozzle holders, the fluid is split between the first nozzle 47 and a first control port 67, and from the space for the other of the nozzle holders, the fluid is split between the second nozzle 48 and a second control port 68. Conveniently, the control ports can be at the ends of respective extensions ofthe feed lines 62, 63 beyond the nozzle holder spaces.

The piezoelectric discs 50, clamp rings 54, 55a, 55b, 58, 59a, 59b, washers 56, 57 and target piece together provide an actuator which is operable to convert an electrical signal in the form of the driving voltage or current into a fluid pressure signal. The leads for the electrical signal enter the body housing 31 through a hermetic seal 69 held in place by front and rear circlips.

At any one time, one of the discs is selected as active and the other inactive. When the drive voltage or current is applied to the active disc, it produces a deflection of the disc which moves one end of the target piece towards the first 47 or second 48 nozzle, thereby decreasing fluid communication between that nozzle and the outlet 60 (and in the limit completely blocking the nozzle). At the same time the opposite end of the target piece is moved away from the other nozzle, thereby increasing fluid communication between that nozzle and the outlet. Moreover the piezoelectric discs 50 are sized to account for the additional stiffness of the inactive disc. Thus not only does the active disc move the inactive disc during normal operation, but if the active disc fails (e.g. due to a loss of drive voltage or other disc failure), the other disc can be selected as active. In this way the actuator has a level of redundancy that can accommodate a disc failure. Furthermore, the discs can be sized to account for increased sticking friction caused by any contaminant in the fluid. Typically dimensions of each disc are a diameter of about 50 mm and a thickness of about 0.7 mm. This produces a range of movement of each end of the target piece of about 90 pm.

The central clamp rings 54, 58 are configured to allow both piezoelectric discs 50 to deflect around them. These, in conjunction with the target piece, mechanically couple the discs, and allow control to be switched between the discs without affecting the combined deflection configuration of the discs. The first clamp rings 54, 55a, 55b also contain openings therein which allow the electrical leads to extend to their contacts on the discs and allow fluid to enter the gap between the two discs from the first 47 and the second 48 nozzles. In this way, the discs can be completely immersed in fluid from the nozzles, providing pressure equalisation around all sides of the discs, as shown by the arrows in Figure 5. The openings can be one or more suitable slots or holes formed in the tops of the first clamp rings, as shown in view A of Figure 6. This pressure equalisation reduces stress in the, typically ceramic, piezoelectric material of the discs, and also reduces opposition to deflection. One or more similar openings in the bottom of the first central clamp ring 54, shown in view B of Figure 6, provide a flow path from the gap between the two discs to the flow return outlet 60. An anti-rotation screw 61 in the outlet can project into a bottom opening of the first central clamp ring 54 to prevent rotation of the actuator.

Varying the electrical signal changes the relative amounts of fluid communication between the first 47 and second 48 fluid nozzles and the flow return outlet 60. This in turn smoothly and continuously changes the pressure differential between the first 67 and the second 68 control ports. The pressure differential can then be used to control a given element of the HMU or staging unit, as discussed above. Any flow out of the outlet 60 is merely a spill return.

More particularly, both the first 62 and the second 63 feed lines receive fluid at the same pressure from the common supply port 64. However, this fluid has to pass through the first 65 and the second 66 restriction orifices before arriving at the nozzles 47, 48. Moving the nut portion 52 end of the target piece away from the first nozzle 47 increases fluid communication between that nozzle and the outlet 60, which results in a pressure drop in the first feed line 62 downstream of the first restriction orifice 65, and specifically a pressure drop at the first control port 67. In addition, the same deflection of the piezoelectric discs 50 that moves the nut portion end of the target piece away from the first nozzle moves the screw portion 53 end of the target piece towards the second nozzle. This decreases the fluid communication between the second nozzle 48 and the outlet, and because of the second restriction orifice 66 in the second feed line 63 produces a pressure increase at the second control port 68. Evidently, movement of the target piece in the opposite direction has the opposite effect on the pressure differential between the control ports.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

All references referred to above are hereby incorporated by reference.

Claims

1. A servovalve including: a first inlet (47) for inflow of fluid at a first pressure to an actuator space; a second inlet (48) for inflow of fluid at a second pressure to the actuator space; a fluid outlet (60) from the actuator space; and an actuator located in the actuator space and having mechanically coupled first and second piezoelectric members (50), each of the piezoelectric members being deflectable under the application thereto of an electrical driving signal to deflect that member, which deflection in turn deflects the mechanically coupled other member, such that the coupled members are controllably movable together between first and second deflection configurations under the application of the electrical driving signal selectably to either one of the coupled members; wherein the servovalve is arranged such that movement of the coupled members towards the first deflection configuration increases fluid communication between the first inlet and the outlet and decreases fluid communication between the second inlet and the outlet, and movement of the coupled members towards the second deflection configuration increases fluid communication between the second inlet and the outlet and decreases fluid communication between the first inlet and the outlet.

2. A servovalve according to claim 1 which is configured such that the first pressure varies in inverse relationship to the degree of fluid communication between the first inlet and the outlet, and the second pressure varies in inverse relationship to the degree of fluid communication between the second inlet and the outlet; whereby the differential pressure between the first and second pressures is controllable by moving the coupled members between the first and second deflection configurations.

3. A servovalve according to claim 2, further including: a first feed line (62) feeding the first inlet with fluid, and a second feed line (63) feeding the second inlet with fluid; wherein the first feed line has a first restriction orifice (65) upstream of the first inlet, and the second feed line has a second restriction orifice (66) upstream of the second inlet, each restriction orifice restricting flow in its feed line such that the fluid pressure in that feed line downstream of the restriction orifice and at the respective inlet varies in inverse relationship to changes in the degree of fluid communication between the respective inlet and the outlet.

4. A servovalve according to claim 1 or 2, wherein the piezoelectric members are spaced apart by a gap, and the servovalve is arranged such that the gap fills with fluid from the inlets en route to the outlet.

5. A servovalve according to any one of the previous claims, wherein the piezoelectric members are parallel, planar members which are deflectable out of their respective planes.

6. A servovalve according to claim 5, wherein the piezoelectric members are coaxial annuli which are deflectable out of their respective planes to adopt domed conformations.

7 A servovalve according to claim 5 or 6, wherein the piezoelectric members are clamped to opposite sides of a central clamp ring (54) which extends around outer perimeters of the piezoelectric members.

8. A servovalve according to claim 7, wherein the actuator further has a pair of outer clamp rings (55a, 55b) which are clamped to the outer perimeters of the piezoelectric members at opposite, outwardly-facing sides thereof.

9. A servovalve according to claim 7 or 8, wherein the clamp ring(s) have smoothly curved clamping surfaces such that, when the piezoelectric members deflect, they rock smoothly over the curved clamping surfaces.

10. A servovalve according to any one of claims 7 to 9, wherein the actuator has respective washers (57) mediating the contacts between the piezoelectric members and the clamp ring(s).

11. A servovalve according to any one of claims 5 to 10, wherein the actuator has an elongate target piece which extends axially through central apertures of the piezoelectric members, in the first deflection configuration a first end of the target piece being maximally spaced from the first inlet and an opposite second end of the target piece being minimally spaced from or blocking the second inlet, and in the second deflection configuration the first end of the target piece being minimally spaced from or blocking the first inlet and the second end of the target piece being maximally spaced from the second inlet.

12. A servovalve according to claim 11, wherein the piezoelectric members are clamped to opposite sides of a further central clamp ring (58) which extends around inner perimeters of the piezoelectric members at their central apertures.

13. A servovalve according to claim 12, wherein the actuator has a further pair of outer clamp rings (59a, 59b) which are clamped to the inner perimeters of the piezoelectric members at opposite, outwardly-facing sides thereof.

14. A fuel control system for a gas turbine engine including one or more servovalves according to any one of the previous claims.

15. A gas turbine engine having the fuel control system according to claim 14.