GB2394015A

GB2394015A - Powerplant shaft with vibration damping device

Info

Publication number: GB2394015A
Application number: GB0223799A
Authority: GB
Inventors: Stephen Harland Watson; John William Allen
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2002-10-12
Filing date: 2002-10-12
Publication date: 2004-04-14
Also published as: GB0223799D0

Abstract

A powerplant, e.g. a ducted fan gas turbine engine (10, figure 1), contains a rotatable shaft 16 and an associated stage of blades (12, figure 1), a shaft vibration damping ring 26 structure surrounding said shaft in indirect contact therewith via a bearing housing 24 of an associated shaft bearing 18, a fixed structure 20 surrounding said ring structure to enable limited radial movement of the ring structure and means to effect clamping of said ring structure to provide vibration damping in the event of shaft orbiting due to a load imbalance during operational rotation. In one embodiment a chamber 22 contains a number of annular plates 32, alternate ones of which engage the ring 26 and the wall of chamber 22 respectively and a spring as the vibration damping device. In another embodiment a thick annular ring (40, figure 3) and spigots (44, 46, figure 3) are used as the vibration damping device.

Description

POWERPLANT SHAFT WITH VIBRATION DAMPING DEVICE

The present invention relates to a shaft which in use, is required to rotate about a fixed axis. The invention 5 has particular efficacy when utilised in a fluid or gas propulsion powerplant, eg a steam turbine powerplant, a gas turbine engine, or a ducted fan gas turbine engine. All of the aforementioned units include rotatable shafts which carry stages of blades in known manner, for the purpose of 10 either maintaining rotation of the associated shaft in order to drive say an electrical machine, or a ship's propeller, or to generate thrust with which to propel an aircraft through the air.

In all the powerplants briefly described hereinbefore, 15 the or stage of blades is carried on a disk which is fastened to the shaft for corotation at high speed.

Should one or more blades break away from the disk during rotation, immediate huge out of balance loads are generated and the shaft starts to orbit in the plane containing the 20 disk and associated remaining blades.

Efforts have been made to counter the effects of excessive vibration which is generated immediately after maximum orbit is reached, particularly in ducted fan engines that power aircraft. The aircraft must continue to 25 fly, and the resulting air flow through the now shut down engine causes the fan to windmill, hence the vibration.

The present invention seeks to provide a powerplant having a rotary shaft and associated blades, that includes a vibration damping device.

30 The present invention comprises in combination a powerplant containing a rotatable shaft and associated stage of blades, orbiting shaft vibration damping ring structure surrounding said shaft in indirect contact therewith via a bearing housing of an associated shaft

bearing, fixed structure surrounding said ring structure and proportioned so as to enable limited effectively radial movement of at least a part of said ring structure therewithin, and including means to effect clamping of said 5 ring structure whereby to provide vibration damping friction therebetween, so that should said shaft start orbiting due to the occurrence of a load imbalance during its operational rotation, thus effectively radially displacing said ring structure, said vibration damping 10 effect is transmitted to said shaft via said ring structure. The invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a ducted fan gas 15 turbine engine including a rotary shaft carrying a stage of fan blades.

Figure 2 is an axial cross sectional part view of the shaft of Figure 1 including a vibration damping ring structure in accordance with one aspect of the present 20 invention.

Figure 3 is an axial cross sectional part view of the shaft of Figure 1 including a vibration damping ring structure in accordance with a further aspect of the present invention.

25 Referring to Figure 1, a ducted fan gas turbine engine 10 of the kind used to power an aircraft includes a front mounted stage of fan blades 12, which is fixed to a disk 14 at the upstream end of a rotary shaft 16. Shaft 16 is supported near its upstream end by a roller bearing 18, 30 which in turn, is supported in fixed, ie non rotatable structure 20. The arrangement described so far is such that if during operational rotation of fan 12, a blade detaches from disk 14, the out of balance forces generated thereby would cause shaft 16 to orbit about its true axis

of rotation, and in so doing, would damage the structure 20, possibly to the point of destroying it. Even if initial damage is minimal, the resulting vibration as the fan windmills, the engine having been shut down, could 5 bring about more mechanical degradation.

Referring now to Figure 2, herein an angular chamber 22 is provides on the front face of fixed structure 20, and partly encloses the housing 24 of roller bearing 18. A thin ring 26 surrounds bearing housing 24, in sliding 10 engagement therewith via mating part spherical surfaces 28 and 30. The interior of chamber 22 contains a number of annular plates 32, alternate ones of which engage ring 26 and the bore wall of chamber 22 respectively. Plates 32 are permanently urged together in the present example by 15 springs 34, only one of which is shown, the axial forces exerted thereby on the plates 32 being sufficient to ensure that during normal engine operating conditions, the friction between the engaging portions of their surfaces is greater than any radial forces exerted thereon, by shaft 16 20 via bearing 18, housing 24 and ring 26.

When a blade breaks away from disk 14 during operational rotation of shaft 16, the out of balance forces immediately generated cause shaft 16 to attempt an orbital manner of rotation. Momentarily that movement is thwarted 25 by a spigot 36 on bearing housing 24 colliding with a spigot 38 on the inner wall surface of housing 20. The spigot 38 then breaks and shaft 16 along with roller bearing 18, bearing housing 24 and ring 26, extends its radius of orbit and in so doing overcomes the frictional 30 forces acting on plates 32 and pushes those plates 32 engaged by ring 26 in a direction effectively radially outwards, until they also abut the bore wall of chamber 22.

Thereafter shaft 16 rolls around within roller bearing 18 in orbital manner, whilst roller bearing 18, bearing

housing 24, ring 26 and those plates 32 that have been trapped between shaft 16 and the remaining plates 32, are forced to follow an involute path around the bore surfaces of the remaining plates 32.

5 The out of balance forces generated as described hereinbefore, are rapidly dissipated to relatively low levels, firstly by the momentary containment of shaft 16 by the spigot 38, followed by the absorbing of energy during the overcoming of the frictional resistance to movement of 10 plates 32 relative to each other when shaft 16 starts to orbit. Shut down of the engine reduces the speed of rotation of shaft 16 to that induced by ambient air flow through the fan, and any vibration that may develop as a result therefrom, is damped to acceptable levels, by virtue 15 of the springs 34 maintaining plates 38 in frictional engagement. Referring now to Figure 3, again the shaft 16 rotates within a roller bearing 18 which in turn is supported by a fixed, ie non rotatable housing 20 via a bearing housing 20 24. Housing 20 includes chamber 22 in which the radially outer portion of a thick annular ring 40 resides, its rim being radially spaced from the bore wall 42 of chamber 22.

Opposing spigots 44 and 46 are formed on the inner wall surfaces of chamber 22, their spacing being proportioned so 25 as to clamp ring 40 between them. The radially inner portion of ring 40 extends to bearing housing 24, so that its bore wall 48 engages the outer diameter thereof.

In a blade off situation in an engine which includes a vibration damping device as described with reference to 30 Figure 3, initially the attempt by shaft 16 to start orbiting is momentarily resisted by a flange 50 on bearing housing 24 engaging a spigot 52 on the fixed structure 20.

The spigot then breaks and shaft 16 starts to orbit and in so doing, overcomes the clamping force exerted by spigots

44 and 46 on ring 40, thus moving ring 40 in a direction effectively radially outwards, until it engages the bore wall 42 of chamber 22. Any rotary movement of the assembly which occurs thereafter will be described with respect to 5 Figure 2 herein.

Having read this specification, the person skilled in

the art, knowing the operational speeds of shaft 16, the weight of the assembly and the coefficient of friction of appropriate materials for use in the manufacture of the 10 clamping devices, will be able to calculate the clamping forces to be applied in order to effect the desired damping of vibration resulting from loss of a blade.

Claims

1. In combination, a powerplant containing a rotatable shaft and associated stage of blades, shaft vibration 5 damping ring structure surrounding said shaft in indirect contact therewith via a bearing housing of an associated shaft bearing, fixed structure surrounding said ring structure and proportioned so as to enable limited, effectively radial movement of at least a part of said ring 10 structure therewithin, and including means to effect clamping of said ring structure whereby to provide vibration damping friction therebetween so that should said shaft start orbiting due to the occurrence of a load imbalance during its operational rotation, thus effectively 15 radially displacing said ring structure, said vibration damping effect is transmitted to said shaft via said ring structure.

2. The combination of claim 1 wherein said ring structure comprises a plurality of rings, alternate ones of which via 20 their rims, engage the opposing wall surface of said surrounding fixed structure, and the remainder via their bores, engage said bearing housing.

3. The combination as claimed in claim 2 wherein said clamping means comprises spring means mounted between a 25 wall of said fixed structure surrounding said rings, and the opposing face of the ring adjacent thereto.

4. The combination of claim 1 wherein said ring structure comprises a single ring which via its bore, engages said bearing housing, its rims being in radially spaced 30 relationship with the opposing bore wall of the fixed structure.

5. The combination of claim 4 wherein the clamping means comprises axially spaced spigots on opposing radial faces

of said fixed structure, said spacing being such as to provide an appropriate clamping action on said ring.

6. The combination as claimed in any of claims 1 to 5 wherein the powerplant is a gas turbine engine.

5

7. The combination as claimed in claim 6 wherein the gas turbine engine includes a ducted fan.

8. A combination substantially as described in this specification and with reference to Figure 2 of the

accompanying drawings.

10

9. A combination substantially as described in this specification and with reference to Figure 3 of the

accompanying drawings.