Abstract:
A movable vane control system is disclosed for use with a gas turbine engine having a turbine axis of rotation. The system includes a plurality of rotatable turbine vanes in a gas flow path within a turbine case of the gas turbine engine. A first vane position sensor having a first distance sensor is configured to sense the distance between the first distance sensor and a surface portion of a first of said plurality of vanes or a first movable target connected to the first vane. Additionally, the first distance sensor, the first vane surface portion, the first movable target, or a combination thereof is configured to provide a variable distance between the first distance sensor and the first vane surface portion or first movable target that varies as a function of a position of the first vane.

Description:
[0001]    This invention was made with Government support under contract number N00014-09-D-0821 awarded by the United States Navy. The Government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to gas turbine engines, and in particular, to positioning movable vanes on gas turbine engines. In some gas turbine engines, movable vanes are used to adjust the angle of air flow into turbine and compressor sections. This is typically accomplished using an actuator to rotate the movable vanes via a mechanical linkage. A sensor can be integrated with or connected to the actuator to provide feedback on the position of the actuator. 
         [0003]    Sensors on the actuator can confirm the level of deployment of the actuator, but do not provide feedback on the actual angular position of the vanes. Because of errors in each link between the actuator and the movable vane, the position of the actuator may not be indicative of the position of the movable vane. Uncertainties in the angular position of movable vanes have lead engine designers to build additional margin into engine designs, leading to un-optimized fuel burn efficiencies, performance reductions due to compensation with turbine stage design, and premature engine repair. 
         [0004]    The challenges for determining vane position can be especially difficult in the turbine section of a gas turbine engine. The space for location of the sensor is small. Additionally, the turbine vanes are in hot environment (greater than 1000° C.) and therefore the vane angle cannot be measured using conventional angle measurement sensors such as RVDTs or resolvers. Also, the hot environment also creates challenges such as thermal thermal. At high temperatures, thermal expansion of the installation assembly is excessive which can introduce errors greater than 20% in gap measurements. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to the present invention, a movable vane control system for use with a gas turbine engine having a turbine axis of rotation comprises a plurality of turbine vanes in a gas flow path within a turbine case of the gas turbine engine. The vanes are rotatable along a vane axis to provide an angular adjustment of the vane with respect to the gas flow path. An actuator is operatively connected to the plurality of vanes. A first vane position sensor comprising a first distance sensor is configured to sense the distance between the first distance sensor and a surface portion of a first of said plurality of vanes or a first movable target connected to the first vane. Additionally, the first distance sensor, the first vane surface portion, the first movable target, or a combination thereof is configured to provide a variable distance between the first distance sensor and the first vane surface portion or first movable target that varies as a function of a position of the first vane. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  is a schematic side view of a gas turbine engine; 
           [0008]      FIG. 2  is a schematic perspective view of a portion of a gas turbine engine including a movable vane control system; 
           [0009]      FIG. 3  is a schematic side view of a portion of a vane position detection portion of a movable vane control system including a movable target; 
           [0010]      FIG. 4  is a schematic side view of a portion of a vane position detection portion of a movable vane control system that includes a movable target and a reference distance sensor; and 
           [0011]      FIG. 5  is a schematic side view of a portion of a vane position detection portion of a movable vane control system that includes a movable target having a variable distance surface portion. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]      FIG. 1  is a schematic side view of gas turbine engine  10 . Gas turbine engine  10  includes compressor section  14 , combustor section  16 , and turbine section  18 . Low pressure spool  20  (which includes low pressure compressor  22  and low pressure turbine  24  connected by low pressure shaft  26 ) and high pressure spool  28  (which includes high pressure compressor  30  and high pressure turbine  32  connected by high pressure shaft  34 ) each extend from compressor section  14  to turbine section  18 . Propulsion fan  36  is connected to and driven by low pressure spool  20 . A fan drive gear system  38  may be included between the propulsion fan  36  and low pressure spool  20 . Air flows from compressor section  14  to turbine section  18  along engine gas flow path  40 . In alternative embodiments, gas turbine engine  10  can be of a type different than that illustrated with respect to  FIG. 1 , such as a turboprop engine or an industrial gas turbine engine. The general construction and operation of gas turbine engines is well-known in the art, and does not require further detailed description herein. 
         [0013]      FIG. 2  is a perspective view of a portion a gas turbine engine turbine section  14  including movable vane control system  42 , which includes actuator  44 , mechanical linkage assembly  46 , movable vanes (not shown) connected to vane stems  48  that extend through case  55  of turbine section  14 . Two of the movable vanes depicted in  FIG. 2  have vane position sensors  52  associated therewith. Mechanical linkage assembly  46  includes torque converter  56 , synchronization ring  58 , and vane arms  60 . In the illustrated embodiment, torque converter  56  includes crank  64  connected to actuator  44  via shaft  66  and connected to synchronization ring  58  via shaft  68 . Torque converter  56  pivots on shaft  70 , which extends between supports  72  and  74 . In alternative embodiments, torque converter  56  can be another type of torque converter that functions to increase torque. Synchronization ring  58  is connected to the vane stems  48  via vane arms  60 . In alternative embodiments, actuator  44  can be connected to movable vanes without use of synchronization ring  58 . 
         [0014]    An exemplary vane position sensor that can be used as vane position  52  or  54  is depicted in  FIG. 3 . As shown in  FIG. 3 , vane position sensor  52  includes a distance sensor  76 . Exemplary distance sensors include those that depend utilize an electromagnetic signal directed onto a target whose distance is to be detected, such as radio frequency (RF) distance sensors or microwave sensors by receiving an excitation signal  78  from controller  79  and returning an output signal  80 . A movable target for the distance sensor  76  is provided by inner threaded member  82  (which can also serve as vane stem  48 ) that is disposed in outer threaded member  84  that is fixed to the turbine case  55 . Inner threaded member  82  is operatively connected to blade  50  (only the end portion of blade  50  near the turbine case  55  is illustrated). By operatively connected, it is meant that the inner blade rotates along with the rotation of blade  50  in direction  86 , although the actual physical connection can be direct or indirect. Distance sensor  76  also includes measuring waveguide  88 , which directs a signal onto the inner threaded member  82 , and reference waveguide that directs a signal onto outer threaded member  84 . Distance sensor  76  is mounted such that the distance  85  between it and the outer threaded member remains fixed during rotation of the vane  50 . This is accomplished, for example, by fixedly mounting the distance sensor  76  to the turbine case  55 . During rotation of the vane  50  in direction  86 , the inner threaded member  82  also rotates in direction  86 , and the action of the threads causes inner threaded member to move up or down along the vane&#39;s rotation axis  89  as a function of the degree of rotation. Distance sensor  76  measures the distance  83  between itself and the moving inner threaded member  82 , which can be compared for reference against the measured distance  85  between the distance sensor  76  and the outer threaded member  84  to help compensate for effects of thermal expansion and other deformations that could affect the distance measurements by the distance sensor  76 . In alternative embodiments, the distance sensor  76  can be mounted so that it maintains a fixed distance to the part of the movable member that is movable axially along the vane axis  89  (in this case inner threaded member  82 ). Computing the difference between the fixed target position and moving target position can reduce the effects of tolerance stack and thermal variation such as is experienced in the turbine section of a gas turbine engine. Using this configuration for measuring displacement will provide an accurate measurement of the vane position. In addition, it provides a friction free (zero dead-band) system of measurement as there are no contacting surfaces to affect the mechanical movement. 
         [0015]    Another exemplary embodiment of the vane position sensor  52  is shown in  FIG. 4 .  FIG. 4  uses a similar component layout to  FIG. 3  with like numbering of components, with a couple of differences. Instead of using measurement and reference waveguides, the  FIG. 4  distance sensor  76  includes a separate measurement distance sensor  92  and a reference distance sensor  94 . Also, inner member  82 ′ and outer member  84 ′ do not have threads to provide axial movement along the vane axis  89  as in  FIG. 3 . Instead, inner member includes a ramp portion  96  on a surface portion facing the distance sensor  76 . Ramp portion  96  can be angled between 0° and 90° relative to the vane axis  89 , or can even be an irregular shaped surface. When inner member  82 ′ rotates along with rotation of the vane  50 , the signal from measurement sensor  92  (or alternatively from a measurement waveguide such as in  FIG. 3 ) will strike a different spot on the ramped surface portion  96  depending on the degree of rotation of the inner member  82 ′, providing a measured distance  83 ′ that varies as a function of the position of vane  50 . 
         [0016]    In some embodiments, a surface portion configured to provide a variable distance between itself and a distance sensor can be attached to or included as part of the vane instead of on a movable member that extends through the turbine case. This allows the distance sensor to be positioned inside the turbine case where it has a direct view of the actual vane to remove the linkage through the turbine case as a potential source of measurement inaccuracy. Such an exemplary embodiment is depicted in  FIG. 5 , where vane  50  has a ramp portion  96 ′ on a surface portion facing the distance sensor  76 . Ramp portion  96 ′ can be angled between 0° and 90° relative to the vane axis  89 , or can even be an irregular shaped surface. When vane  50  rotates, the signal from measurement sensor  92  (or alternatively from a measurement waveguide such as in  FIG. 3 ) will strike different spots on the ramped surface portion  96 ′ depending on the degree of rotation of the vane  50 , providing a measured distance  83 ″ that varies as a function of the position of vane  48 . Reference sensor  94  provides a signal to detect the distance  85 ″ from the non-ramped surface portion of the vane  50 . 
         [0017]    In operation, controller  79  signals actuator  44  to actuate vane  50 . Actuator  44  responds by actuating torque converter  56 , which moves synchronization ring  58  and consequently moves vane arms  60  to rotate the vanes. Vane position sensor  52  sends a vane position signal representing sensed angular position of vane  50  to controller  84 . Using the vane position signal and optionally an actuator position signal from an actuator position sensor (not shown), controller  84  can determine whether vane  50  is positioned correctly or if the angular position of variable vane  50  should be adjusted. Thus, angular position of vane  50  can be adjusted based on the position signal from vane position sensor  52 . In some embodiments, controller  84  can use signals from a plurality of vane position sensors (e.g., 1-4 sensors) spaced around the turbine. In a more specific embodiment, four vane position sensors are used evenly spaced around the turbine. 
         [0018]    The invention can be utilized on any adjustable airfoil blades in the gas turbine engine, including those in the relatively low temperature compressor section and those in the relatively high temperature turbine section that is exposed to combustion exhaust gases. Distance sensors such as RF sensors can be configured to be resistant to the conditions found in the turbine section of a gas turbine engine. 
         [0019]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.