GB2393774A

GB2393774A - Shafts axially coupled by a spring-loaded member

Info

Publication number: GB2393774A
Application number: GB0223029A
Authority: GB
Inventors: Alan Robert Maguire
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2002-10-03
Filing date: 2002-10-03
Publication date: 2004-04-07
Also published as: GB0223029D0

Abstract

A pair of nested shafts 10 and 16 wherein the outer shaft 10 has two axially spaced shoulders 12 and 14 and the inner shaft 16 has one external shoulder 18 which abuts one of the internal shoulders 12. The other end of the inner shaft 16 has an annular groove 20 and means therein 22 (46, fig 2 or 56, fig 3) which are moveable partly out therefrom by spring action to engage the other internal shoulder 14 to complete axial coupling of the shafts. The shaft coupling may be used in a gas turbine engine.

Description

( 1 AXIALLY COUPLED SHAFTS

The present invention relates to an assembly of nested shafts coupled together for co-rotation about a common axis 5 and in a common direction.

Nested coupled shaft assemblies present difficulties regarding their retention in fixed axial relationship during their operational rotation. For example, when nested co-rotary shafts are utilised in a gas turbine 10 engine, it is the practice to connect them via helical splines, the pitch of which is such as to drive the two shafts together, by virtue of an axial load exerted on one shaft being transmitted to the other shaft in the same direction. Excessive relative axial movement is avoided by 15 engagement of appropriate shoulders.

A drawback of such an arrangement is that unless the shafts are also locked together by other mechanical means, eg screwed nuts and tab washers, then on removal of the operating load when the engine stops, the shafts will 20 separate by a small amount. On start up of the engine again, the shafts will move together again, thus generating a considerable fretting action with consequent wear.

Not all gas turbine engine can be assembled in a manner that will allow the use of screwed fastenings to 25 axially fix a nested shaft assembly. Consequently the present invention seeks to provide a nested co-rotary shaft assembly including means other than screwed nut devices with which to retain one shaft within the other shaft.

According to the present invention a rotary multi 30 s --r assembly comprises a pair of hollow nested shafts, t:- outer shaft having two axially spaced internal so-; ders intermediate its ends, and the inner shaft has c-- external shoulder which abuts a radial face of one of s: internal shoulders, and at its nested end includes an

annular groove and means therein which are moveable partly out therefrom by springs action so as to engage an at least nearly radial face of the other internal shoulder so as to complete axial coupling of said shafts and prevent relative 5 axial movement therebetween whether static or corotating.

The invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is an axial cross sectional part view of a pair of nested coupled shafts in accordance with the 10 present invention.

Figure 2 is a cross section view of an alternative form of retention means in accordance with the present invention, in a plane normal to the axis of the shaft assembly of Figure 1.

15 Figure 3 is a cross sectional view of a further alternative form of retention means in accordance with the present invention, in a plane normal to the axis of the shaft assembly of Figure 1.

Figure 4 depicts an alternative form of construction 20 of the inner end of the nested shaft of the assembly.

Flqure 5 is a diagrammatic sketch of a ducted fan gas turbine engine incorporating a pair of nested coupled shafts in accordance with the present invention.

Referring to Figure 1 a shaft 10 has two axially 25 spaced internal shoulders 12 and 14 intermediate its ends.

A second shaft 16 nests within shaft 10 and has an external shoulder 18 which, when shaft 16 is inserted within shaft 10 to a desired position, abuts shoulder 12. Shaft 16 is thus prevented from further movement through shaft 10.

30 The end portion of shaft 16 within shaft 10 has an annular groove 20 formed in its outer surface and a spring split ring 22 is fitted therein. Groove 20 and split ring 22 are so proportioned as to enable split ring 22 to lie totally within groove 20 so as to enable insertion of shaft

16 within shaft 10, ie split ring 22 can pass through the bore 24 defined by shoulder 14. Having passed through the bore 24, the radial faces of shoulders 12 and 18 will engage and split ring 22 will open and engage the face of 5 shoulder 14 thus locking shafts 10 and 16 together.

It is important that the locking action described hereinbefore prevents relative axial movement between shafts 10 and 16 so as to obviate fretting and to this end shafts 10 drives shaft 16 via engaging helical splines 32 10 and 33, the helices of which are of a hand that applies an axial load on shaft 16 to push it into the interior of shaft 10 until shaft 16 has penetrated sufficiently to allow shoulders 12 and 18 to engage and split ring 22 to expand onto the radial or near radial face of shoulder 14.

15 Clearly having expanded split ring 22 must also still engage the side walls 30 of groove 20. Therefore, a bore 34 is provided so as to prevent split ring 22 from expanding too much. By this means shafts 10 and 16 remain firmly locked together in the axial sense whether rotation 20 thereafter of the assembly is or is not occurring. In a preferred embodiment of the invention the engaging faces of split ring 22 and shoulder 14 are provided with identical conical chamfers having included angles of nominally 160.

This ensures that when contact therebetween is made it will 25 be contact over their full opposing surface areas.

The driving action by shaft 10 on shaft 16 can be achieved by a first operational rotation of the assembly.

Alternatively it can be achieved by rotating shaft 1 with appropriate tooling in what would be the operational 30 a. rection after fitting the assembly in an associated engine, the assembly thus becoming permanently locked from :'"'t point onwards.

Referring now to Figure 2 in this embodiment of the --sent invention, the split ring 22 is substituted by a

( 4 number of T shaped flat members, the cross pieces 46 of which are curved to follow the shape of bore 34. The legs 48 slide in radial slots 50 through the bottom of groove 20. On rotation induced or operational of shaft 10 shaft 5 16 is moved sufficiently to allow springs 52 to urge the T members radially outwards to engage the face of shoulder 14 as described hereinbefore with respect to Figure 1.

Referring now to Figure 3 in this embodiment of the present invention pawls 56 are pivotally mounted within 10 groove 20 and are spring loaded so as to be urged outwards of groove 20 and into engagement with the face of shoulder 14. The springs (not shown) are coiled around respective axles 58 and have one end fastened to groove structure, and the other end fastened to respective pawls 56.

15 Referring now to Figure 5 which is an example of final positioning of shaft 16 by operational rotation. A ducted fan gas turbine engine 60 includes a stage of turbine blades 62 connected via a turbine disc 64 to drive shaft 10. Shaft 16 is nested within shaft 10 and is connected to 20 drive other features (not shown). The shape of the turbine blades will be such as to drive shaft 10 via disc 64 in a direction which will drive shaft 16 further within shaft 10. As the turbine rotation accelerates during operation an increasing force will be applied by shaft 10 on shaft 25 16, thus moving it further into shaft 10. At the same time the retaining means will expand their conical surfaces sliding on the opposing conical surface on shoulder 14 (Figure 1) until shoulders 12 and 18 (Figure 1) abut, which will coincide with the retaining means having reached their 30 fully expanded engagement with shoulder 14, thus locking shafts 10 and 16 together.

Claims

Claims:

1. A rotary multi shaft assembly comprising a pair of hollow nested shafts, the outer shaft having two axially spaced internal shoulders intermediate its ends, and the 5 inner shaft has one external shoulder which abuts a radial fact of one of said internal shoulders and its nested end includes an annular groove and means therein which are moveable partly out therefrom by spring action so as to engage an at least nearly radial face of the other internal 10 shoulder so as to complete axial coupling of said shafts and thereby prevent relative movement therebetween whether static or co-rotating.

2. A rotary multi shaft assembly as claimed in claim 1 wherein said means in said groove is a resilient split 15 ring.

3. A rotary multi shaft assembly as claimed in claim 2 wherein the engaging faces of said split ring and said other shoulder are formed radially of the axis of rotation of said assembly.

20 4. A rotary multi shaft assembly as claimed in claim 2 wherein the engaging faces of said split ring and said other shoulder are identically chamfered to form conical profiles having a common included angle of nominally 160 .

5. A rotary multi shaft assembly as claimed in claim 1 25 wherein said means in said groove are a plurality of approximately T profiled members, the leg portions of which are slidably fitted in slots through the bottom of said groove, and their cross pieces are curved to enable conformance of their side faces with said face of said 30 other shoulder and include spring means with which to urge them radially outwards from said groove into contact with said face of said other shoulder.

i. A rotary multi shaft assembly as claimed in claim 5 :ne,-ein said engaging faces of said cross pieces side faces

and said other shoulder are identically chamfered to form conical profiles having a common included angle of nominally 160 .

7. A rotary multi shaft assembly as claimed in claim 1 5 wherein said means in said groove comprise a plurality of pawls respectively pivotally connected via one end to the interior side walls of said groove via axles and spring members so as to enable spring pivoting of said pawls outwards from said groove into contact with said face of 10 said other shoulder.

8. A rotary multi shaft assembly as claimed in claim 7 wherein said engaging faces of said pawls and said other shoulder are identically chamfered to form conical profiles having a conical included angle of nominally 160 .

15 9. A rotary multi shaft assembly substantially as described in this specification and with reference to any

of Figures 1 to 4 of this specification.

10. A rotary multi shaft assembly as claimed in any previous claim when assembled in the turbine structure of a 20 gas turbine engine.

(