GB2367595A - Actuator mechanism for variable angle vanes having a unison ring directly connected to a vane spindle - Google Patents

Abstract

An actuator mechanism for a variable angle vane array in a fluid flow machine such as a gas turbine or compressor has vanes 14 pivoted between positions giving maximum and minimum fluid flow by a unison ring 20 connected directly to vane spindles 16. In the embodiment the unison ring is split into two halves 22,24, the front half 22 having gear teeth 28 which mesh with gear teeth 26 in the spindles 16. The gear teeth 28 may be cut integrally to the front half 22, or inserted locally on pads. The rear half 24 has a tab 30 which locates in indentation 32 in the spindles 16 to limit angular movement to prevent blockage in the event of failure.

Description

Actuator Mechanism for Variable Angle Vanes The present invention relates to an actuator mechanism for an array of variable vanes in an axial fluid flow machine. It is particularly concerned with variable area vanes suitable for use in the compressor or turbine sections of gas turbines engines.

To optimise the performance of gas turbine engines arrays of variable vanes are used in both the compressor and turbine sections of the engine. The vanes pivot about spindles to vary the angle of the vanes with respect to a flow of fluid passing through the engine.

In a conventional arrangement each array of vanes are actuated simultaneously by a common unison ring. The spindle of each blade in the array is attached to the unison ring via a lever. When the actuating ring is rotated the levers pivot the vanes about the spindles. The vanes pivot in unison to change the angle of the vanes.

The present invention provides an improved actuator mechanism for an array of variable vanes. The improved actuator mechanism seeks to provide consistent and accurate vane positioning and reduces hysteresis. A failsafe is provided on the mechanism to prevent the vanes moving to a position which blocks the flow of air through the vanes.

According to the present invention an actuator mechanism for a variable angle vane array in a fluid flow machine, the vanes being pivotable between positions giving maximum and minimum fluid flow delivery, comprises a spindle on which each vanes is secured for effecting pivotable movement thereof, and a unison ring connected directly to the vane spindles for simultaneous transmission of pivoting movement to each vane.

In the preferred embodiment of the present invention the unison ring is connected directly to the vane spindles via gear teeth. Gear teeth are provided on the unison ringwhich mesh with gear teeth provided on the vane spindles to effect pivotable movement thereof.

Preferably the unison ring and each of the vane spindles are provided with features which restrict the pivotable movement of the vanes.

In the preferred embodiment of the present invention the unison ring is provided with a tab which locates in a indentation in the vane spindles to restrict the pivotable movement of the vanes.

The present invention will now be described by way of example and with reference to the accompanying figures in which; Figure 1 is a pictorial view of part of a compressor incorporating variable vanes having a conventional actuation mechanism.

Figure 2 is a view of part of an actuator mechanism in accordance with the present invention.

Figure 3 is a cross-sectional view along line A-A in figure 2.

Figure 4 is a cross-sectional view along line B-B in figure 2.

Referring to figure 1, the compressor section 10 of a gas turbine engine incorporates a number of stages of pivotable vanes 14.

Each vane 14 pivots about a spindle 16, the radially outer end 17 of which projects through the compressor casing 12. All of the vanes 14 are caused to pivot simultaneously in the same direction on command from a control system of the gas turbine engine (not shown).

The vanes 14 are rotated about the spindles 16 by levers 18. One end of each lever 18 is attached to the radially outer ends 17 of one of the spindles 16 whilst the other end is attached to a unison ring 20. Each of the unison rings 20 extends around the compressor casing 12 and is actuated by hydraulic rams (not shown).

A problem with this conventional arrangement is that it has been known for the levers 18 to fail in service, which results in a malschedule in the orientation of the

vanes 14. The levers 18 also introduce hystersis into the system, which prevents consistent and accurate location of the vanes 14.

Figures 2-4 show a vane actuation mechanism in accordance with the present invention. The unison ring 20 is split into two halves 22 and 24, one half of which is provided with a series of gear teeth 26. The gear teeth 26 may be cut into the front half 22 of the unison ring 20 or are inserted locally into the unison ring 20 on pads.

The radially outer end 17 of each vane spindle 16 is also provided with gear teeth 28. The gear teeth 28 on the spindles 16 mesh with the gear teeth 26 on the unison ring 20 to rotate the vanes 14. The gear teeth 26 & 28 mesh so that the angle of the vanes 14 with respect to the fluid flow through the compressor section 10 of the engine can be varied.

The rear half 24 of the unison ring 20 is provided with a tab 30, which locates in a localised indentation 32 in the vane spindles 16. The tab 30 locates in the indentation 32 to limit the total angular movement of the vanes 14.

Rotation of the unison ring 20 is by actuators (not shown) which may be hydraulic. The vane spindles 16 are driven directly by the unison ring 20. This ensures consistent and accurate vane positioning and reduces hysteresis.

The provision of a failsafe mechanism 30 and 32 ensures that the pivotal movement of the vanes 14 is restricted. This prevents the vanes 16 from blocking the flow of air through the compressor 10 when a failure occurs.

It will be appreciated by one skilled in the art that whilst the present invention has been described with reference to variable vanes 14 in the compressor section 10- of a gas turbine engine it is also applicable to the turbine section. The invention is also applicable to any other area of an axial flow machine where variables are employed to vary the power extracted therefrom.

Claims (10)

1. Claims : 1. An actuator mechanism for a variable angle vane array in a fluid flow machine, the vanes being pivotable between positions giving maximum and minimum fluid flow delivery, comprising a spindle on which each vanes is secured for effecting pivotable movement thereof, and a unison ring connected directly to the vane spindles for simultaneous transmission of pivoting movement to each vane.
2. 2. An actuator mechanism as claimed in claim 1 in which the unison ring and the spindles are provided with gear teeth whereby in operation the teeth mesh to effect pivotable movement of the vanes.
3. 3. An actuator mechanism as claimed in claim 2 in which the unison ring is split into two halves.
4. 4. An actuator mechanism as claimed in claim 3 in which the gear teeth are attached to one half of the unison ring.
5. 5. An actuator mechanism as claimed in any of claims 2-4 in which the gear teeth are an integral part of the unison ring.
6. 6. An actuator mechanism as claimed in any of claims 2-4 in which the gear teeth are inserted locally into the unison rings on pads.
7. 7. An actuator mechanism as claimed in any preceding claim in which means are provided to restrict the pivotable movement of the vanes.
8. 8. An actuator mechanism as claimed in claim 7 in which the means for restricting the pivotable movement of the vanes is a tab that locates in a corresponding indentation.
9. 9. An actuator mechanism as claimed in claim 8 in which the tab is provided on the unison ring and locates in a corresponding indentation in the spindle of the vane.
10. 10. An actuator mechanism as hereinbefore described with reference to and as shown in figures 2-4.