Patent Publication Number: US-8534996-B1

Title: Vane segment tip clearance control

Description:
FEDERAL RESEARCH STATEMENT 
     None. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit to an earlier filed U.S. Provisional Application 61/096,942 filed on Sep. 15, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to gas turbine engines, and more specifically to a compressor with tip clearance control between vane segments and rotor blade tips. 
     2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     A multiple stage compressor, such as that used in a gas turbine engine, includes several rows or stages of rotor blades positioned between the same number of rows or stator vanes. A row of stator vanes is positioned directly in front of a row of rotor blades and function to guide the air flow into the rotor blades at a most optimal angle for higher performance. Because there is relative rotation between the blade and the vane structures, a gap is formed in which the fluid passing through the compressor can leak around the blades. If this gap or clearance is too large, the efficiency of the compressor will be affected. The gaps are formed between the rotor blade tips and an outer shroud surface, and between the rotor blade platforms or root section and the stator blade inner shroud assembly. 
     The gap or clearance between the stator and the rotor sections can change during operation of the compressor. Also, thermal loads can also cause the gaps to change due to material growth. Thus, to provide improved performance of the compressor, systems that regulate the gap spacing are used. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide for an axial flow compressor with blade tip clearance control. 
     An annular arrangement of stator vane segments, each with a plurality of stator vanes extending inward, is connected to an annular sync ring through a pair of eccentric cranks. A piston fixed to the sync ring is moved by application of fluid pressure to one of two piston chambers. Movement of the sync ring produces a radial displacement of the stator vane segments to control the blade tip clearance. 
     One or more rectangular actuators are connected to the sync ring to move the sync ring in a circumferential direction. An integral actuator is formed within an outer casing section with the sync ring positioned on the inside of the outer casing. The integral actuator piston is rigidly attached to the sync ring by bolts, and with the sync ring carries a compliant seal within a seal groove to provide a seal for the rectangular pressure chambers and the rectangular piston that moves within the chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a schematic view of the integral piston secured to the sync ring, and the eccentric cranks connecting the sync ring to the stator vane segments. 
         FIG. 2  shows a schematic view of the control valve arrangement with respect to the rectangular pressure chamber and piston assembly. 
         FIG. 3  shows a schematic view of a 180 degree segment of the sync ring and stator vane segments with the eccentric cranks and rectangular piston. 
         FIG. 4  shows a side view of the rectangular piston connected to the sync ring with the control valve spool positioned in the valve chamber. 
         FIG. 5  shows the rectangular actuator housing positioned over the sync ring that is connected to the stator vane segment through the eccentric cranks, and the valve spool extending into the control valve housing. 
         FIG. 6  shows a cross section view of the rectangular actuator with the piston secured to the sync ring, and the two pressure chambers formed between the piston and the actuator housing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a section of the sync ring and stator vane segments with the eccentric crank connection between them. The sync ring  13  is a full 360 annular ring that can be formed from several segments rigidly connected together is order to assemble it in place within the compressor. One or more rectangular pistons  14  are rigidly fixed to the sync ring  13  each by two bolts  15 . A top housing  16  of the rectangular actuator housing is connected by the two bolts  15  to the rectangular piston  14 . a control valve  17  is shown in relation to the rectangular actuator piston  14 . A plurality of stator vane segments  11  is located radial inward from the sync ring  13  as seen in  FIG. 1 . A plurality of stator vanes extends from an inner surface of each vane segment and forms a gap with a surface on the rotor of the compressor. The inner surface of the vane segment forms a gap with the blade tips of the compressor. Each vane segment  11  is connected to the sync ring  13  by two eccentric cranks  12 . The eccentric cranks  12  include an axial member that rotates within a hole in an outer extension of the vane segment  11  and a radial member that pivots within a hole of the sync ring  13 . The eccentric crank is offset in the axial hole of the vane segment outer extension so that rotation of the crank displaces the vane segment in a radial direction. Circumferential movement of the sync ring  13  will pivot the eccentric crank  12  and produce this radial displacement. 
     One or more rectangular actuators are connected to the sync ring  13  to move the sync ring  13  in a circumferential direction. An integral actuator  14  is formed within an outer casing section with the sync ring  13  positioned on the inside of the outer casing. The integral actuator piston is rigidly attached to the sync ring  13  by bolts  15 , and with the sync ring  13  carries a compliant seal  18  within a seal groove to provide a seal for the rectangular pressure chambers and the rectangular piston that moves within the chamber. 
       FIG. 2  shows a schematic view of the sync ring and vane segment assembly from an opposite side that  FIG. 1  show. the sync ring  13  and eccentric crank  12  connection to the vane segments  11  is shown with the control valve  17  and its valve spool  21  shown on this side of the actuator piston. Axial movement of the spool valve will apply pressure to one of the two rectangular actuator chambers to move the rectangular piston to one of two sides of the actuator. As seen in  FIGS. 1 and 2 , the sync ring  13  and the rectangular piston  14  and the outer actuator housing  16  form one rigid integral piece that moves together as one unit. 
       FIG. 3  shows a 180 degree segment of the stator vane segments with four vane segments  11  each connected by two eccentric cranks  12  to the sync ring  13 . The actuator outer housing  16  and the control valve  17  are shown in relation to the sync ring  13 . More than one actuator is used to move the sync ring  13  because the sync ring  13  is a full 360 degree annular ring and to more evenly apply the force to move the sync ring  13 . 
       FIG. 4  shows a cross section view through a cut of the actuator and the connection to the sync ring  13 . The rectangular piston  14  and the outer actuator housing  16  are secured to the sync ring  13  with the two bolts  15 . The control valve  17  is shown in its relative position extending along one side of the actuator housing. Circumferential movement of the sync ring  13  will pivot the eccentric crank  12  and cause the vane segment  11  to be displaced in the radial direction. 
       FIG. 5  shows the rectangular actuator with the actuator housing  21  that is secured to an engine casing so that the actuator housing  21  does not move. The rectangular piston and the outer actuator housing  15  are shown with the two bolts  15  that connect the outer actuator housing to the rectangular piston. The outer actuator housing  16  moves circumferentially with the sync ring  13  and form an outer enclosure for the two actuator pressure chambers on the sides of the rectangular actuator piston  14 . The actuator housing  21  includes two ports  22  for the supply and exhaust of the fluid used to drive the actuator piston  14 . The spools on the control valve  17  regulate the fluid pressure from the source through the two ports  22 . In the preferred embodiment, the pressure source to drive the actuator is bleed off air from one or more stages of the compressor. One stage is at a higher pressure than another stage, and thus the pressure source can be regulated by choosing which stage to bleed off the compressed air from. The sync ring  13  will form a bottom wall of the actuator pressure chamber while the outer actuator housing  16  will form the top wall. The actuator housing  21  that does not move will form the two side walls and the two end walls of the chambers. The rectangular piston  14  will move in the circumferential direction towards one of the two end walls of the stationary actuator housing  21 . 
       FIG. 6  shows a cross section view of the actuator connected to the sync ring  13 . The piston  14  is connected to the sync ring  13  with the two bolts  15 . The piston defines a pressure chamber  24  with the actuator housing  21 . Seals  26  provide for a fluid seal between the sync ring  13  and the actuator housing  21 . The actuator housing  21  is fixed to the engine casing and therefore does not move. The rectangular piston  14  is moved circumferentially by application of the bleed off air from one stage of the compressor. Movement of the actuator  14  moves the sync ring  13 , which then moves the vane segments  11  through the pivoting motion of the eccentric cranks  12 . 
     The motive fluid used to drive the actuation piston  14  can be the pressure differential between the compressor supply pressure of one of its stages and atmospheric pressure. In this case, the compressor stage pressure is directly connected to one piston actuation chamber  24  and the atmospheric pressure connected to the opposite chamber to produce a differential pressure about equal to the pressure supplied from the stage of the compressor. This is only a differential pressure and not a flow of compressed air from that stage that is used to drive the actuator piston  14 , so not much compressed air is wasted in the pneumatic control of the sync ring. The differential pressure required for movement of a certain actuation piston  14  would be met by tapping into the compressor stage that can supply that amount of pressure related to the atmospheric pressure. 
     In a gas turbine engine, the compressor has many stages of rotor blades and stator vanes. Each stage or row of stator vanes can be connected to a segmented vane assembly that is radially displaced by the eccentric crank and sync ring assembly of the present invention. The vane tip and rotor blade tip spacing can be controlled by the circumferential movement of the sync ring  13 . Each stage of vanes and blades can be independently controlled by its own separate sync ring and eccentric crank assembly of the present invention.