Patent Publication Number: US-7717669-B2

Title: Load absorption arrangements for gas turbine engines

Description:
The present invention relates to load absorption arrangements for use in gas turbine engines. The invention also relates to variable stator vane positioning systems including load absorption arrangements. 
     Variable stator vanes are used in gas turbine engines to control airflow through a multi-stage compressor. In the event of breakdown of airflow through the compressor, a condition known as ‘surge’ can occur in which high pressure air is expelled from the combustor into the compressor stages, thereby causing a sudden reversal of the airflow through the compressor and a resultant sudden loss of engine thrust. 
     Under surge conditions, the reversed airflow can impart a significant shock load onto the variable stator vanes, inducing rotational vibration. Most of this shock load is transmitted to the stator vane positioning system, the components of which may be damaged as a result. It would be desirable to reduce the likelihood of such damage occurring in such situations and/or similar situations. 
     According to a first aspect of the present invention, there is provided a load absorption arrangement for absorbing loads in a variable stator vane positioning system, the arrangement comprising a release means having a first operating condition to enable the load absorption arrangement to transmit load, and a second operating condition operable above a predetermined load in which the release means can release to enable the load absorption arrangement to absorb the load thereon. 
     The release means may comprise a fluid containment housing which may contain a fluid. The release means may comprise a valve which may be in a closed position when the release means is in the first operating condition, and may be in an open position when the release means is in the second operating condition. The valve may be operable to retain the fluid within the housing when the release means is in the first operating condition, and may be operable to release the fluid from the housing when the release means is in the second operating condition. The fluid may be an incompressible fluid. 
     The release means may comprise a fluid displacement member for displacing the fluid. The fluid displacement member may be operable to displace the fluid when the release means is in the second operating condition, and may be operable to displace the fluid from the housing. 
     The fluid displacement member may divide the fluid containment housing into first and second fluid containment compartments. When the release means is in the second operating condition, the fluid displacement member may be operable to displace the fluid between the compartments. The fluid displacement member may be a piston. 
     The release means may include a fluid transfer conduit, which may extend between the first and second fluid containment compartments. The fluid transfer conduit may include the valve. 
     The release means may include positioning means which may locate the arrangement in a predetermined position when the release means is in the first operating condition. The positioning means may comprise a resilient means which may be locatable within the fluid containment housing. 
     The resilient means may include a resilient member which may be located within the first fluid containment compartment and may be operable between the fluid containment housing and the fluid displacement member to bias the fluid displacement member in first direction. The resilient means may include a further resilient member which may be located within the second fluid containment compartment and may be operable between the fluid containment housing and the fluid displacement member to bias the fluid displacement member in a second direction, which may be opposite to the first direction. 
     The resilient member and further resilient member may abut respectively opposite surfaces of the fluid displacement member. The respective stiffness of the resilient members may define the predetermined position of the arrangement when the release means is in the first operating condition. The resilient member and further resilient member may each comprise a spring. 
     According to a second aspect of the present invention, there is provided a variable stator vane positioning system for use in a gas turbine engine, the system including a load absorption arrangement for absorbing shock loads within the system. 
     The load absorption arrangement may be as described above. 
     The system may include a control rod which may comprise the load absorption arrangement. The system may include an actuator which may comprise the load absorption arrangement. 
     According to a third aspect of the present invention, there is provided a gas turbine engine including a variable stator vane positioning system as described above. 
    
    
     
       Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:— 
         FIG. 1  is a diagrammatic cross-sectional view of a part of a gas turbine engine; 
         FIG. 2  is a detailed view of a compressor section of the gas turbine engine of  FIG. 1 ; 
         FIG. 2   a  is a diagrammatic view of a stator vane positioning system; 
         FIG. 3  is a diagrammatic cross-sectional view of a load absorption arrangement; and 
         FIG. 4  is a diagrammatic cross-sectional view of a modified load absorption arrangement. 
     
    
    
     Referring to  FIG. 1 , a gas turbine engine is generally indicated at  10  and 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 an exhaust nozzle  19 . 
     The gas turbine engine  10  works in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  which produces two air flows: a first air flow into the intermediate pressure compressor  13  and a second air flow which provides 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  and  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13 , and the fan  12  by suitable interconnecting shafts. 
     Referring to  FIG. 2 , the compressor section  20  of the gas turbine engine  10  comprises a casing  22  and a plurality of sets of rotor blades  24  mounted for rotation about a longitudinal axis of the compressor  20 . Upstream of each set of rotor blades  24  is mounted a set of variable stator vanes  26 , each rotatably mounted in the casing  22 . 
     A stator vane actuator ring  28  extends circumferentially around the outside of the casing  22  adjacent to each set of stator vanes  26 . Each stator vane  26  is mechanically connected to an adjacent actuator ring  28  by a variable stator vane actuating lever  30 . 
     Each actuator ring  28  is circumferentially rotatable in either direction about the longitudinal axis of the compressor  20 , as indicated by arrow A. This is achieved by use of a stator vane positioning system (see  FIG. 2   a ) which comprises an actuator  150 , an actuator control linkage  152  which transmits movement from the actuator to a crankshaft  154 , and a plurality of control rods  156  each connected at one end to the crankshaft  154  and at the other end to a respective actuator ring  28 . When the stator vane positioning system is operated, movement is transmitted from the actuator  150  via the actuator control linkage  152  to the crankshaft  154 , which is caused to rotate. This rotational movement is transmitted by each control rod  156  to a respective actuator ring  28 . Rotational movement of an actuator ring  28  is then transmitted by each of the plurality of actuating levers  30  to the respective set of variable stator vanes  26 , causing them to rotate. 
     Referring to  FIGS. 3 and 4 , there is shown a load absorption arrangement  40 ,  140  for absorbing loads, such as shock loads, in a variable stator vane positioning system of a gas turbine engine. The arrangement  40 ,  140  comprises generally a release means  42 ,  142  having a first operating condition to enable the load absorption arrangement  40 ,  140  to transmit load, and a second operating condition, which is operable above a predetermined load, in which the release means  42 ,  142  can release to enable the load absorption arrangement  40 ,  140  to absorb the load thereon. 
     In more detail and referring to  FIG. 3 , the release means  42  comprises a fluid containment housing  44  which is generally cylindrical and has an annular wall  46  defining a bore  48 . The housing  44  includes a first end  50  which is closed and a second end  52  which includes a centrally located aperture  54 . The first end  50  includes an attachment member  56  to enable the load absorption arrangement  40  to be incorporated into a stator vane positioning system, as will be described in more detail hereinafter. The attachment member  56  includes an aperture  58  for receiving a fastener or other suitable means for securing the arrangement  40  in position. 
     The release means  42  further comprises a displacement member in the form of a piston arrangement  60 , part of which is located within the housing  44  for slidable movement within the housing  44  in the longitudinal direction between the first and second ends  50 ,  52 . The piston arrangement  60  is of generally conventional construction and includes a piston, which may be in the form of a disc  62 , which engages an inner surface  64  of the annular wall  46  to create a fluid tight seal between the inner surface  64  and the disc  62 . The piston arrangement  60  also includes an elongate rod  66  which extends through the aperture  54 , a fluid tight seal being created between the elongate rod  66  and the aperture  54 . 
     An attachment member  68  is provided at the distal end of the rod  66  which, in combination with the attachment member  56 , enables the arrangement  40  to be incorporated into a stator vane positioning system, as will be described hereinafter. The attachment member  68  includes an aperture  70  for receiving a fastener or other means suitable for securing the arrangement  40  in position. 
     The housing  44  contains an incompressible fluid  72 , such as oil, and the disc  62  divides the housing  44  into first and second fluid containment compartments  74 ,  76  such that a portion of the fluid  72  is retained within the first compartment  74  and a portion in the second compartment  76 . The release means  42  includes a conduit  78  which extends between the first and second compartments  74 ,  76  to enable transfer of the incompressible fluid  72  between the compartments  74 ,  76 , and hence sliding movement of the disc  62  within the housing  52 , when the release means  40  is in the second operating condition. 
     The release means  42  also includes a valve  80  which is operable between a closed position in which it prevents transfer of the incompressible fluid  72  between the compartments  74 ,  76 , and hence prevents movement of the disc  62 , and an open position in which it permits transfer of the incompressible fluid  72  between the compartments  74 ,  76 , and hence allows movement of the disc  62 . 
     The release means  42  further includes resilient positioning means in the form of first and second springs  82 ,  84  which are operable to locate the arrangement  40  in a predetermined position when the release means  42  is in the first operating condition. The first spring  82  is located in the first fluid containment compartment  74  and abuts respectively the first end  50  of the housing  44  and the disc  62 , such that the first spring biases the disc  62  in a first direction away from the first end  50 . The second spring  84  is located in the second fluid containment compartment  76  and abuts respectively the second end  52  of the housing and the disc  62 , such that the second spring  84  biases the disc  62  in a second direction, opposite to the first direction, towards the first end  50  of the housing  44 . 
     The respective stiffness of each spring  82 ,  84  determines the equilibrium resting position of the disc  62  within the housing  44  and appropriate spring stiffnesses are chosen depending upon the desired predetermined position of the disc  62 . 
     In use, the arrangement  40  is incorporated into a stator vane positioning system of the gas turbine engine  10  to enable the absorption of loads, for example shock loads which may arise due to engine surge, within the system. The arrangement  40  may be incorporated into, or constitute, the actuator control linkage which connects the actuator to the crankshaft, as described above, so that the arrangement  40  is able to absorb load transmitted from any of the stator vane actuator rings  28 . Alternatively or additionally, the arrangement  40  may be incorporated into, or constitute, each of the control rods which connect the crankshaft to a respective stator vane actuator ring. In both cases, the manner of operation of the arrangement  40  is the same and is described below. 
     During normal operation of the engine  10 , when the stator vane positioning system is subjected to normal loading, the release means  42  is in the first operating condition so that the arrangement  40  can transmit load from the actuator to each of the stator vane actuator rings  28  to enable the stator vanes  26  to be set to a desired angular position. In the first operating condition, the valve  80  is in the closed position such that transfer of the incompressible fluid  72  between the first and second fluid containment compartments  74 ,  76  is prevented. Because the fluid  72  is incompressible and fluid tight seals are present between the inner surface  64  and the disc  62  and also the elongate rod  66  and the aperture  54 , movement of the piston arrangement  60  is prevented and the arrangement  40  is substantially rigid to enabling it to transmit load. 
     When the stator vane positioning system and thus the arrangement  40  is subjected to a load which is above a predetermined load, the release means  42  releases so that it is in the second operating condition and can absorb the load. In the second operating condition, the valve  80  is in the open position and thus permits transfer of the incompressible fluid  72  between the first and second fluid containment compartments  74 ,  76  via the conduit  78 . The disc  62  is thus able to move within the housing  44  and transmission of the load between the attachment members  56 ,  68  is prevented or reduced. When the arrangement  40  is incorporated into, or constitutes, the actuator control linkage, the load transmitted to the actuator is reduced or eliminated, and the likelihood of damage to the actuator is thereby reduced. When the arrangement  40  is incorporated into, or constitutes, each of the control rods connecting the crankshaft to the actuator rings  28 , the load transmitted to the crankshaft, the actuator control linkage and the actuator is reduced or eliminated, and the likelihood of damage to these components is thereby reduced. 
     The valve  80  is chosen so that it is in the open position only when the load experienced by the arrangement  40  is above a predetermined level, and this will normally be the minimum level at which damage to the components of the stator vane positioning system may occur. 
     When the load experienced by the arrangement  40  has reduced to less than the predetermined level and the release means  42  returns to the first operating condition, the springs  82 ,  84 , at least one of which will have been compressed as a result of movement of the disc  62 , bias the disc  62  back to its original and predetermined equilibrium position, during which movement transfer of the incompressible fluid  72  back along the conduit  78  between the fluid containment compartments  74 ,  76  will occur. When the disc  62  is in the predetermined position, the valve  80  closes to again prevent transfer of the fluid  72  between the compartments  74 ,  76  and thereby enable the arrangement  40  to transmit load. 
       FIG. 4  illustrates a modified load absorption arrangement  140  which is similar to the arrangement  40  and in which corresponding components are given corresponding reference numerals. 
     The arrangement  140  is designed to replace the actuator of a stator vane positioning system and comprises first and second fluid transfer ducts  143 ,  144  operable to transfer fluid respectively to and from the first and second fluid containment compartments  74 ,  76 . Each of the ducts  143 ,  144  is connected to a fuel system of the gas turbine engine  10  and fuel can be injected into or removed from each of the compartments  74 ,  76 . The fuel is incompressible and when the release means  142  is in the first operating condition with the valve  80  in the closed position, transfer of the fuel into or from the compartments via the ducts  143 ,  144  causes movement of the piston  60  to a desired position. This movement is transmitted via the actuator control linkage, crankshaft and control rods to the actuator rings  28  causing them to rotate and in turn causing rotation of the variable stator vanes  26  to a desired angular position. 
     Each of the first and second fluid transfer ducts  142 ,  144  includes a respective valve  146 ,  148 , and the valves are closed when the stator vanes  26  have been set to the desired angular position. A fuel control arrangement is provided to control the valves  146 ,  148  and transfer of the fuel into and from the respective compartments  74 ,  76 . 
     The arrangement  140  operates in the same way as the arrangement  40  to absorb loads which are above a predetermined level. However, the release means  142  does not include springs  82 ,  84  to set the predetermined position of the disc  62 , since its position when the release means  142  is in the first operating condition will vary dependent upon the desired angular position of the variable stator vanes  26 . Therefore, when the load reduces to below the predetermined level and the release means  142  returns to the first operating condition, the fuel control arrangement operates to reset the piston  60  to the correct position to provide the desired angular position of the variable stator vanes  26 . 
     There is thus provided a load absorption arrangement  40 ,  140  for absorbing loads in a variable stator vane positioning system of a gas turbine engine  10 . The arrangement  40 ,  140  is compact and lightweight and can be easily incorporated into a variable stator vane positioning system. Moreover, an arrangement  140  can be provided in an existing system by modifying the actuator to include a conduit  78  and a valve  80 . An existing actuator can thus be upgraded with relative ease. 
     Although embodiments of the invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that various modifications to the examples given may be made without departing from the scope of the present invention, as claimed. For example, a fluid other than oil or fuel may be employed provided that the fluid is incompressible. Resilient members other than springs  82 ,  84  may be used in the arrangement  40 , or alternative means for locating the disc  62  in a predetermined position may be employed. The attachment members  56 ,  68  may be of a different configuration. 
     Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings, whether or not particular emphasis has been placed thereon.