Abstract:
A selective rotation arrangement for a shaft, the arrangement including a housing mountable spaced from the shaft and an engagement member with distal and proximal ends which is selectively movable relative to the housing towards or away from the shaft between an operating position towards the shaft and a rest position clear of the shaft, the engagement member having a gear member at the distal end thereof which is engageable with the shaft in the operating position to permit turning of the shaft by the engagement member, but is disengaged from the shaft in the rest position.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is entitled to the benefit of British Patent Application No. GB 0901059.6, filed on Jan. 23, 2009. 
     FIELD OF THE INVENTION 
     This invention concerns a selective rotation arrangement for a shaft, a selective rotation arrangement for a shaft on a gas turbine engine, and a gas turbine engine including a selective rotation arrangement for a shaft. 
     BACKGROUND OF THE INVENTION 
     Conventionally, gas turbine aircraft engines have the external power taken through a geared external drive from the high pressure rotor system.  FIG. 1  diagrammatically shows such a gas turbine engine  10  with three drive shafts  12 ,  14 ,  16 . The shaft  12  will be connected to the fan (not shown), whilst the shaft  14  is connected to the intermediate pressure compressor with a rotor  18 . The shaft  16  is connected to the rotor  20  of the high pressure compressor. The intermediate casing and internal gearbox  22  is located between the rotors  18 ,  20 . Downstream of the compressors are the combustor  24 , high pressure turbine  26 , intermediate pressure turbine  28 , and low pressure turbine  30 . 
     Having an external drive attached to the high pressure compressor system has a secondary function, enabling hand or ground cranking of the high pressure rotor  20  to enable inspection thereof through boroscope access ports in the casing. 
     The demand for electric power within aircraft is increasing and this makes it beneficial for power to be extracted from the intermediate power compressor system. With the intermediate power compressor, more power is available at low speed without compromising compressor stability. In view of this, proposals have been made to use a concentric high power/intermediate power external drive. With this system a switchable clutch type coupling has been provided to connect the intermediate pressure and high pressure spools for starter assist. 
     A feature of this arrangement is that the high power drive is permanently connected to the high power rotor, thereby providing a means for enabling rotation of the high pressure rotor for inspection. With this arrangement though, the high pressure gear is only required for starting but is permanently connected to the high pressure rotor, and therefore spins under normal running which is a source of windage loss and reduced reliability. 
     It may therefore be desirable just to provide a drive off the intermediate pressure shaft, but there is then the problem of enabling turning of the high pressure rotor to enable inspection. 
     Proposals have been made to enable a tool to engage with the high pressure spool gear by being inserted into the internal gearbox. It is however undesirable to break into a clean oil chamber with an external tool that could allow ingress of damaging dirt or grit. Other proposals have also been made, including for instance inserting a geared tool into the bearing chamber, but again there is the possibility of the ingress of dirt into the chamber. It is also necessary to provide a substantial access hole to enable a sufficiently robust tool to be used which could for example be used with a seized high pressure spool. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a selective rotation arrangement for a shaft, the arrangement including a housing mountable spaced from the shaft and an engagement member with distal and proximal ends which is selectively movable relative to the housing towards or away from the shaft between an operating position towards the shaft and a rest position clear of the shaft, the engagement member having a gear member at the distal end thereof which is engageable with the shaft in the operating position to permit turning of the shaft by the engagement member, but is disengaged from the shaft in the rest position. 
     A resilient urging arrangement may be provided engageable between the housing and the engagement member to urge the engagement member into the rest position. 
     The resilient urging arrangement may include a spring engageable between the engagement member and the housing. 
     A tool engagement formation may be provided on the proximal end of the engagement member to enable a tool to engage therewith to cause rotation of the engagement member. 
     The housing may include a passage along a part of which the engagement member is slidably movable between the operating and rest positions. The passage may extend substantially radially in use relative to the shaft. The selective rotation arrangement may be configured such that in use the passage extends at least partially downwardly from the shaft. 
     One or more seals may be provided between the engagement member and the housing. 
     The invention also provides a selective rotation arrangement for a shaft on a gas turbine engine, the arrangement being according to any of the preceding six paragraphs, with the engagement member being selectively engageable with a gear on or connected to the or one of the drive shafts of the engine. 
     The selective rotation arrangement may be arranged such that the engagement member is selectively engageable with a gear on the high pressure compressor rotor shaft. 
     The invention further provides a gas turbine engine, the engine including a selective rotation arrangement according to either of the preceding paragraphs. 
     Alternatively, the preceding claims wherein the arrangement comprises an indexing device to provide a fixed position or rotation of the shaft. 
     Preferably, the indexing device comprises any one or more of the group comprising a ratchet, a sprag clutch and a brake. 
     Preferably, the arrangement comprises a main axis, the main axis arranged radially to a rotational axis of the shaft, but may be within 45 degrees of a radial line to a rotational axis of the shaft. 
     The engine may be arranged such that external power is taken from the intermediate pressure compressor rotor shaft. 
     The selective rotation arrangement may be mounted on an external casing of the engine. 
     A mounting arrangement may be provided on the casing of the engine to enable a tool to be selectively mounted thereon. The mounting arrangement may be configured such that when a tool is mounted thereon the tool engages with the engagement member to urge the engagement member to the operating position, and such that rotation of the tool causes rotation of the engagement member and hence of the engine drive shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic sectional view through a typical multishaft gas turbine engine which is not according to the invention; 
         FIG. 2  is a diagrammatic cross-sectional view through a selective rotation arrangement according to the invention in a rest condition; 
         FIG. 3  is a similar view to  FIG. 2  but with the arrangement in use and in an operating condition; 
         FIG. 4  is a diagrammatic axial view of part of a gas turbine engine incorporating the arrangement of  FIG. 2 ; 
         FIG. 5  is a similar view to  FIG. 2  but of a modified arrangement according to the invention; and 
         FIG. 6  is a cross sectional view through part of a further modified arrangement according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 2 to 4  show a selective rotation arrangement  32  selectively engageable with a high pressure compressor rotor shaft  34  of an aircraft gas turbine engine. The arrangement  32  is mounted to the external casing  36  of the engine, and an opening  38  is provided through the casing  36 . The arrangement  32  includes a sleeve  40  which is concentrically mounted on the inside of the casing  36  relative to the opening  38 . The sleeve  40  is mounted by a mounting flange  42 , engaging around the opening  38  on the inner side of the casing  36 . The sleeve  40  has a radially inwards smaller opening  44 . 
     An engagement member  46  is slideably moveable along the sleeve  40 . The engagement member  46  includes a sleeve part  48  which has an enlarged proximal head  50  which is slideably moveable in the sleeve  40 . A seal  52  is provided around the head  50 . A tool engagement formation  54  is provided inside the head  50 . The formation  54  may be in the form of a spline or square lobe, or other appropriate formation. 
     A distal part  56  of the sleeve part  48  is of reduced diameter, and this receives a sleeve mounting portion  58 , so as to provide a substantially continuous outer surface, of a gear member  60 . The gear member  60  includes a bevel gear  62  which is engageable with a corresponding bevel gear  64  on the high pressure rotor shaft  34 . The gear member  60  is mounted to the sleeve part  48  by a fastening  66  engaging through the distal end of the sleeve part  48 . 
     A further seal  68  in the form of an O ring or otherwise is provided around the inside of the sleeve opening  44 , and is engageable against the sleeve mounting portion  58  of the gear member  60 . A compression spring  70  is located between the radially inner side of the proximal head  50 , and the surroundings of the opening  44 . The compression spring  70  urges the engagement member  46  radially outwards such that in a rest position as shown in  FIG. 2 , the gears  62  and  64  are spaced from each other and disengaged. 
       FIG. 3  shows the arrangement  32  in use. Here a tool assembly  72  is mounted by a service pad  74  on the casing  36  concentrically with the opening  38 . A tool motor  76  is provided on the service pad  74  connected to a controller  78  for operation of the assembly  72 . The motor  76  is connected to a tool member  80  which has on its distal end  82  an appropriate formation to engage with the tool engagement formation  54 . A flange  84  is provided around the tool member spaced a little from the distal end  82 , and in an in use condition as shown in  FIG. 3 , the flange  84  engages substantially against the proximal end of the sleeve  40 . 
     The arrangement  32  can be used for instance for inspection of the high pressure rotor when the engine is out of use. The tool assembly  72  can be selectively fitted as shown in  FIG. 3 , on the casing  36 . The tool member  80  engages against the sleeve part  48  urging the sleeve part  48  against the compression spring  70  such that the bevel gear  62  is urged into engagement with the bevel gear  64 . The controller  78  can then be used as required to rotate the tool assembly  72 , and hence the high pressure rotor shaft  34  and rotor to enable the blades thereof to be inspected. 
     Once an inspection procedure has been completed the tool assembly  72  can be removed by dismounting the service pad  74 . Removal of the tool member  80  from the sleeve part  48  should cause the sleeve part  48  to move radially outwards under the force of the spring  70  and hence cause the gears  62 ,  64  to disengage from each other. 
     The direction of the helix on the high pressure bevel gear  64  can be arranged to ‘throw’ the gear member  60  out of engagement when the engine is started, if disengagement has not occurred due to the force of the spring  70 . 
     The tool assembly  72  or another tool arrangement can be used to simply hold the high pressure rotor shaft  34  against rotation, for example to enable minor damage on the rotor blades to be repaired or dressed out. 
       FIG. 4  is a diagrammatic axial view which shows the external drive  86  coming from the intermediate pressure drive shaft  88 , with the external drive extending substantially downwardly. The arrangement  32  is angularly spaced from the external drive  86  upwardly, but is arranged such that the opening  38  still points downwardly to prevent debris and dirt locating in the opening  38  during use. 
     There is thus described an arrangement which permits selective rotation of the high pressure rotor shaft, whilst enabling drive to be taken from the intermediate pressure shaft. The arrangement does not affect normal working of the engine, and is only operable when a tool is inserted into the opening in the casing, and urged against the arrangement. The assembly therefore readily permits inspection and servicing of the high pressure rotor without affecting normal use of the engine in anyway. 
     The arrangement  32  has a main axis  33  about which its rotatable parts turn. As shown, and preferably, the arrangement is configured so that the main axis  33  is perpendicular or radially aligned to the engine axis  12 . Nonetheless, the main axis may be leant forwardly or rearwardly along the engine axis by up to 45 degrees. 
       FIG. 5  shows an alternative arrangement  132 . The arrangement  132  is similar to the arrangement  32  in most respects, and only the differences are thus noted. In the arrangement  132  the engagement member  146  has an extension part  149  of a length such that the proximal end  151  thereof is substantially flush with the casing  36 , and again provides a tool engagement formation  154 . In this instance the engagement formation  154  is therefore approximately flush with the outer surface of the casing  36 . 
     As an alternative to the opening  38  pointing downwardly, or in addition to this safeguard, a selectively openable flap  190  may be provided, as is illustrated in  FIG. 6 . Here the flap  190  is attached to the casing  36  by a sprung hinge  192 , such that in a rest position the flap  190  will automatically move to close the opening  38 . When access to the opening  38  is required, the flap  190  can be pivoted outwardly in the direction shown by the arrow  194  against the force exerted by the sprung hinge  192 . 
     The present invention is particularly suitable for rotating a rotor stage of a gas turbine engine so that each blade is presented to inspection equipment and/or repair/maintenance equipment which is in a fixed position. Alternatively, the rotor stage again can be rotated so that inspection or maintenance equipment can be rotated to each of an annular array of stators or an annular component that is static. Although the motor  76  may be accurately controlled to rotate the rotor or shaft  34  a particular amount, a further indexing device  77  can be incorporated into the arrangement  32  to provide a positive and fixed positioning of the rotor or shaft. A fixed position of the rotor allows more substantial maintenance operations on the rotor components. Furthermore, the indexing device  77  is capable of allowing predetermined degrees of rotation so that each blade or part of a blade of the rotor may be brought into view or reach of the inspection or maintenance equipment. 
     The indexing device  77  is a simple ratchet as is well known in the art, but can be a sprag clutch can be substituted. These devices allow rotation in one direction whilst preventing rotation in the other and against any maintenance operation force that might be applied. To positively locate the rotor the motor is operated to index the rotor in the next ratchet position and is then reversed to accurately lock the rotor against the ratchets anti-rotation features. Alternative to the ratchet or sprag clutch, the indexing device  77  may be a simple brake mechanism with a single brake pad or a calliper mechanism. 
     Still further the indexing device  77  may be a plate with an array of holes into which a biased pin may be inserted. The pin may be retracted or inserted into the hole by an electronically operated solenoid device. 
     It should be noted that the gearing  62 ,  64  permits multiple rotations of the arrangement  32  for each revolution of the rotor or shaft  34  which results in good positional accuracy. 
     Various other modifications may be made without departing from the scope of the invention. For instance the assembly may be usable with different tools or types of tools. A different biasing arrangement could be used. Whilst the invention has been described for a particular application in an aircraft gas turbine engine, the invention can be used in other locations in this type or other types of gas turbine engines. Furthermore, it is to be realised that the invention can be used for selective rotation of shafts in a wide range of different applications.