GB2470586A

GB2470586A - Eccentric joint for actuator connection rod.

Info

Publication number: GB2470586A
Application number: GB0909150A
Authority: GB
Inventors: Crispin David Bolgar
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2009-05-29
Filing date: 2009-05-29
Publication date: 2010-12-01
Also published as: GB0909150D0

Abstract

A mechanism for actuating movement of an element of a gas turbine engine has a connection rod 51 for transmitting movement between two components (one shown 52). The rod 51 extends between two joints (one shown at 50) which couple the rod 51 to the components 52. At least one of the joints 50 has an eccentric or off-centre arrangement which allows the position of the corresponding end of the rod 51 to be translated relative to the respective component 52. The eccentric arrangement may take the form of a bush 54 with an off centre cylindrical passage 56.

Description

MECHANISM FOR ACTUATING MOVEMENT OF AN ELEMENT OF A GAS

TURBINE ENGINE

The present invention relates to a mechanism for actuating movement of an element of a gas turbine engine.

Mechanical linkage mechanisms can be used to provide rotational control of annular arrays of vanes in a compressor of a gas turbine engine. Such mechanisms might comprise a bell crank, rotatable about a fulcrum, an actuation connection rod pivotably connected to an input arm to the bell crank and a control connection rod pivotably connected to an output arm of the bell crank.

Movement of the actuation connection rod rotates the bell crank which in turn causes motion of the control connection rod. This motion can then be used to drive a unison ring which changes the angles of a row of vanes.

In more elaborate compressor vane variable mechanisms, two bell cranks can be provided between the actuation connection rod and the control connection rod, with a further connection rod connecting an output arm of the first bell crank to an input arm of the second bell crank.

Other compressor vane variable mechanisms can be based on a crankshaft arrangement, in which connection rods extending from a rotatable crankshaft are used to drive unison rings.

Conventional mechanisms use adjustable length connection rods to compensate for component tolerances which can result in variation in the distances to be spanned by the rods. The adjustability is achieved using rod ends attached to a central rod portion via screw threads. These screw threads are in opposite directions for the two ends of the rod, allowing the length of the rod to be adjusted in the manner of a turnbuckle.

However, adjustable length connection rods of this type are relatively heavy and costly.

Accordingly, a first aspect of the present invention provides a mechanism for actuating movement of an element of a gas turbine engine, the mechanism having: a connection rod for transmitting movement between two components, the rod extending between two joints which couple the rod to the components, wherein at least one of the joints has an eccentric arrangement which allows the position of the corresponding end of the rod to be translated relative to the respective component.

Thus, by incorporating the eccentric arrangement into the joint a three-part screw-threaded connection rod can be dispensed with, allowing a wider range of connection rod designs and materials to be used. In particular, to save weight, an I-beam or hollow section connection rod can be adopted. Also, materials with high specific strengths and/or stiffnesses, such as carbon fibre composites, metal matrix composites and aluminium alloys, can more easily be used to form the rod, also saving weight.

The mechanism may have any one or combination of the following optional features.

Typically, both of the joints have an eccentric arrangement allowing the position of the corresponding end of the rod to be translated relative to the respective component.

The eccentric arrangement may be provided by a bush having an outer mount surface that is off-centre relative to a hole through the bush, the end of the rod being mounted to the mount surface and the component coupling to the joint through the hole.

However, other arrangements are also possible. For example, the eccentric arrangement can be provided by having a bearing (such as a spherical bearing) at the end of the rod, and a mount hole through the bearing by which the bearing is mounted to the joint, the mount hole being eccentric to the bearing centre line. Another arrangement is for the joint to have a bolt which attaches the end of the rod to the component, wherein the bolt has respective portions which locate against the component and the end of the rod (either directly or via intermediate parts such as a bush), the portions being eccentric to one another.

Typically, either or both of the joints allows the rod to pivot about an axis of rotation relative to the respective component. For example, the or each joint may include a spherical bearing at the end of the rod.

Either or both of the components may be a bell crank.

One of the components may be a crank shaft. One of the components may be a unison ring.

The mechanism may be, for example, a vane angle adjustment mechanism, a bleed air adjustment mechanism, or a nozzle area adjustment mechanism.

Another aspect of the invention provides a gas turbine engine having the mechanism of the first aspect (the mechanism optionally having any one or combination of the optional features of the first aspect) Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows schematically a gas turbine engine; Figure 2 shows detail of an intermediate pressure compressor; Figure 3 shows a mechanism for operating intermediate compressor unison rings; Figure 5 shows a joint according to the present invention for coupling connection rods to respective components; and Figure 6 shows in more detail a bush of the joint of Figure 4.

Figure 1 shows schematically a gas turbine engine generally indicated at 10 and having a principal and rotational axis X-X. The engine 10 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 exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines both the intake 11 and a bypass duct 22 which defines a bypass exhaust nozzle 20.

The gas turbine engine 10 works in the conventional manner so that air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow into the intermediate pressure compressor 13 and a second air flow which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow 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 core nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines 16, 17, 18 respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.

Figure 2 shows detail of an intermediate pressure compressor 13. A row of variable inlet guide vanes (VIGVs) 24 is positioned before the first row of compressor blades of the intermediate pressure compressor. A first row of variable stator vanes (VSV15) 26 is then positioned behind the first row of compressor blades and before the second row of blades 27, and a second row of variable stator vanes (VSV25) 28 is positioned behind the second row of blades.

When the compressor speed reduces, the axial velocity of the inlet air becomes low relative to the blade speeds.

This increases the incidence of the air onto the blades.

If the incidence increases too far aerodynamic stall can occur. To overcome this problem, the VIGV5 and the VSVs can rotate about their axes, changing the angles of the vanes and thereby altering the incidence of the airflow onto the blades.

The angles of the VIGV5 or VSV5 of a row are changed by circumferentially rotating a respective unison ring 29, each VIGV or VSV being joined to the unison ring by a respective lever 30. Depending on compressor and engine performance, the unison ring is rotated under the control of an actuator, a linkage arrangement operatively connecting the actuator to the unison ring.

Thus, variable vanes can be used where high pressure ratios are required across a single compressor (e.g. intermediate 13 and/or high 14) . As a compressor speed is reduced from its optimal design value the variable vanes are progressively closed to maintain an acceptable gas angle onto the downstream rotor blades. This prevents the compressor 13, 14 from surging, which can result in a loss of engine thrust and damage to turbomachinery.

Figure 3 shows a mechanism for operating intermediate compressor unison rings. The mechanism comprises a hydraulic actuator 31 (typically using engine fuel as the operating fluid) which drives a ram 32 in its length direction. The distal end of the ram is connected to an input arm of a first bell crank 33. A VIGV control connection rod 34 extends from a first output arm of the first bell crank to the VIGV unison ring (not shown) . An intermediate connection rod 35 extends from a second output arm of the first bell crank to an input arm of a second bell crank 36. Two VSV control connection rods 37, 38 extend from respective output arms of the second bell crank to the VSV1 and VSV2 unison rings (not shown) The connection rods 34, 35, 37, 38 are of conventional type, each having respective rod ends attached to a central rod portion via screw threads. The ends of the connection rods are coupled to their respective components by joints which allow each rod to pivot about an axis of rotation relative to the respective component.

Figure 4 shows a cross section through an alternative mechanism for operating intermediate compressor unison rings. The mechanism comprises a hydraulic actuator (not shown) which drives a ram (not shown) connected to clevis 41 of crank shaft 40. The crank shaft, supported at bearings 42, 43, rotates about axis 0-0. Respective connection rods (not shown) extending, out of the plane of the page, from joints at further devises 44, 45, 46 then transmit movement to unison rings 47, 48, 49.

Figure 5 shows a joint 50 according to the present invention for coupling connection rods to respective components. In a mechanism for operating intermediate compressor unison rings, the rods can perform the same function as the rods of the mechanisms of Figures 3 and 4.

However, unlike the joints shown in Figures 3 and 4, the joint of Figure 5 has an eccentric arrangement which allows the position of the end of the rod 51 to be translated relative to the component 52. This also allows the rods to dispense with an arrangement in which rod ends are attached to a central rod portion via screw threads.

More specifically, the connection rod 51 ends in a spherical bearing 53 which allows the rod to pivot about an axis of rotation relative to the component 52. The bearing is mounted on a bush 54, which is shown in more detail in Figure 6. The bush has an outer mount surface 55 for the bearing and a bolt hole 56, the mount surface being eccentric to the bolt hole. A bolt 57 passes through the hole 56 to attach to the component.

During rigging of a mechanism for operating intermediate compressor unison rings which utilises the connection rods 51, firstly the actuator, ram, vanes and unison rings are fixed in position. When subsequently coupling a connection rod, the bush 53 is inserted into the spherical bearing of the rod end and rotated until it is possible to pass the bolt 56 through the bush and component 52. As the effective mount point position of the connection rod relative to the component can be adjusted using this eccentric arrangement, there is no requirement to adjust the length of the rod.

Thus the connection rod 51 can have a fixed length, without sacrificing the capability to compensate for component tolerances, which can result in variation in the distance to be spanned by the rod. Further, as it is no longer necessary to have a three-piece design with separate rod ends and a central section, it becomes possible to use a wide variety of connection rod designs and manufacturing techniques. For example, to reduce weight, the rod could be formed as e.g. an I-beam or a thin-walled hollow tube.

The rod could be cast, forged or machined. The rod could be formed from carbon composite, metal matrix composite or aluminium alloy to achieve the required attributes for a specific application.

In Figures 5 and 6 the eccentric arrangement is provided by the off-centre bolt hole 56 of bush 54.

However, other ways of providing an eccentric arrangement include, for example, having a mount hole for the spherical bearing 53 which is eccentric to the bearing centre line, or using a bolt where the portions locating against the component 52 and the bush (or directly against the spherical bearing if no bush is present) are eccentric to one another. Essentially, some part of the joint, by virtue of having eccentric axes, allows the position of the end of the rod to be translated relative to the component.

In Figures 5 and 6 the invention is described in relation to a vane angle adjustment mechanism. However, the invention could also be applied e.g. as a mechanism for varying turbine nozzle guide vanes, for bleeding air, or for adjusting a variable area nozzle.

Jhile 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.

Claims

CLAIMS1. A mechanism for actuating movement of an element of a gas turbine engine, the mechanism having: a connection rod (51) for transmitting movement between two components (52), the rod extending between two joints (50) which couple the rod to the components, wherein at least one of the joints has an eccentric arrangement which allows the position of the corresponding end of the rod to be translated relative to the respective component.
2. A mechanism according to claim 1, wherein both of the joints have an eccentric arrangement which allows the position of the corresponding end of the rod to be translated relative to the respective component.
3. A mechanism according to claim 1 or 2, wherein the eccentric arrangement is provided by a bush (54) having an outer mount surface (55) that is off-centre relative to a hole (56) through the bush, the end of the rod being mounted to the mount surface and the component coupling to the joint through the hole.
4. A mechanism according to any one of the previous claims, wherein either or both of the joints allows the rod to pivot about an axis of rotation relative to the respective component.
5. A mechanism according to any one of the previous claims, wherein, the or each end of the connection rod terminates in a spherical bearing (53) at the respective joint.
6. A mechanism according to any one of the previous claims which is a vane angle adjustment mechanism.
7. A mechanism according to any one of the previous claims which is a bleed air adjustment mechanism.
8. A mechanism according to any one of the previous claims which is a nozzle area adjustment mechanism.
9. A gas turbine engine having the mechanism of any one of the previous claims.
10. A mechanism for actuating movement of an element of a gas turbine engine as any one herein disclosed with reference to and/or as shown in the Figures 5 and 6.