Abstract:
A turbine engine has a rotor shaft rotatably carried within a non-rotating support structure. A seal is carried by the support structure circumscribing the shaft and having a flexible sealing element for sealing with the shaft. A chamber is located between the seal and support structure. A fluid is carried within the chamber and damps radial excursion of a seal axis from a support structure axis. The seal may be a full annulus or may be segmented. The fluid may be contained within one or more elastomeric bladders.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (1) Field of the Invention  
           [0002]    This invention relates to shaft seals, and more particularly to turbine engine shaft seals.  
           [0003]    (2) Description of the Related Art  
           [0004]    In turbomachinery applications, it is often necessary to provide a seal between a rotating shaft and a housing element. At the seal, the shaft typically has symmetry around a central axis (e.g., the shaft has a cylindrical surface area). The shaft axis is normally coincident with the axis of rotation and with an axis of the housing in which the seal is mounted. However, vibration may induce small local oscillatory excursions of the axis of rotation. Brush and labyrinth seals may have sufficient compliance in their respective bristle packs and labyrinth teeth to accommodate relatively minor excursions. To accommodate greater excursions, there may be a non-rigid mounting of the seal element to the housing. This mounting permits excursions of the shaft axis to radially shift the seal relative to the housing to avoid damage to the seal.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    A turbine engine has a rotor shaft rotatably carried within a non-rotating support structure. A seal is carried by the support structure circumscribing the shaft and having a flexible sealing element for sealing with the shaft. A chamber is located between the seal and support structure. A fluid is carried within the chamber and damps radial excursion of a seal axis from a support structure axis. The seal may be a full annulus or may be segmented. The fluid may be contained within one or more elastomeric bladders.  
           [0006]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a longitudinal semi-schematic sectional view of a turbine engine.  
         [0008]    [0008]FIG. 2 is a partial semi-schematic longitudinal sectional view of a seal system of the engine of FIG. 1.  
         [0009]    [0009]FIG. 3 is a partial semi-schematic transverse sectional view of the seal system of FIG. 2, taken along line  3 - 3 .  
         [0010]    [0010]FIG. 4 is a partial semi-schematic longitudinal sectional view of an alternate seal system.  
         [0011]    [0011]FIG. 5 is a partial semi-schematic transverse sectional view of an alternate seal system. 
     
    
       [0012]    Like reference numbers and designations in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0013]    [0013]FIG. 1 shows a turbine engine  20  having a housing case  22  containing concentric high and low pressure rotor shafts  24  and  25 . The shafts are mounted within the case for rotation about an axis  500  which is normally coincident with central longitudinal axes of the housing and shafts. The high pressure rotor shaft  24  is driven by the blades of a high pressure turbine section  26  to in turn drive the blades of a high pressure compressor  27 . The low pressure rotor shaft  25  is driven by the blades of a low pressure turbine section  28  to in turn drive the blades of a low pressure compressor section  29  and a fan  30 .  
         [0014]    The rotor shafts are supported relative to the case by a number of bearing systems. The rotor shafts may be sealed relative to the case by sealing systems  40  which may include brush sealing elements, labyrinth sealing elements, or the like.  
         [0015]    [0015]FIG. 2 shows further details of an exemplary sealing system  40 . The exemplary system includes a brush seal  50  having a bristle pack  52  secured in a seal body comprising a pair of backing plates  54  and  56 . The plates  54  and  56  are respectively designated as the side plate and the back plate and sandwich the bristle pack on respective high and low pressure sides thereof. In the exemplary embodiment, the bristle roots are secured between the plates with bristle tips extending inward therefrom to contact the shaft outer surface  60 . Bristle and plate materials are typically various metal alloys such as nickel- or cobalt-based superalloys and the plates and bristle roots may thus be secured by welding. Additional shorter bristles may intervene between the sealing bristles contacting the shaft and the backplate. The tips of these bristles may be closer to the rotor than is the inboard surface of the backplate. Such an arrangement provides additional support to the sealing bristles during true running operation while limiting the chance of damage during a rotor excursion.  
         [0016]    The seal  50  is contained within an annular seal backing/mounting ring  62 . The ring  62  includes an annular sleeve portion  64  having interior and exterior surfaces  66  and  68 . On the low pressure side, a short flange  70  extends radially inward from the surface  66 . The seal is accommodated within the ring such that an exterior rim surface  72  of the seal contacts the interior surface  66  while a downstream radial surface of the plate  56  contacts an upstream radial surface of the flange  70 . A retaining ring  74  is captured in a groove in the surface  66  so that a downstream surface of the ring  74  contacts an upstream surface of the plate  56  to sandwich the seal  50  between the plate  74  and flange  70  to firmly retain the seal relative to the mounting ring.  
         [0017]    The mounting ring  62  is accommodated within a compartment in the case defined by respective downstream and upstream surfaces  80  and  82  of upstream and downstream walls  81  and  83  and an interior surface  84  of an annular wall  85 . Upstream and downstream rims of the sleeve  64  carry o-rings  90  for sealing with the surfaces  80  and  82 . The mounting ring  62  includes a pair of upstream and downstream seal rings  94  and  96  extending radially outward from the exterior surface  68 . Exemplary seal rings may be similarly formed to split piston rings. They may be formed by a casting and machining process. Hoop stress in the seal rings may allow them to maintain engagement with the mounting ring while freely sliding radially within the channels  100  and  102 . Fluid pressure may allow the seal rings to seat axially against radial surfaces of the channels.  
         [0018]    Exterior annular rim portions of the rings  94 ,  96  are captured within radial channels  100  and  102  in the surface  84 . The channel bases are of sufficiently greater diameter than the sealing ring rims to permit the sealing rings (and thus the mounting ring) a desired amount of radial float relative to the case. The sealing rings and portions of the sleeve  64  and wall  85  between the rings bound a first chamber  120  containing a fluid  122 . Exemplary fluids are oils, water and air. Advantageously in a turbine engine application, the fluid is useful in an operational range of 150° C. to 550° C. (e.g., is non-flammable and does not undergo a phase change or decompose).  
         [0019]    The fluid  122  may be introduced to the chamber  120  through a port  124  in the wall  85 . A fluid source may comprise a reservoir  130  such as a sump tank or pressure vessel. To deliver the fluid from the reservoir, a pump  132  is connected to the reservoir via a conduit  134 . The pump is connected to the port  124  via a conduit  136  in which a pressure regulator  138  is positioned. The pressure regulator is in turn coupled to the reservoir via a conduit  140  for returning excess fluid to the reservoir.  
         [0020]    In operation, there may be leakage of the fluid around the rings  94  and  96  into chambers  144  and  146  between the sleeve  64  and wall  85  respectively upstream and downstream of the rings  94  and  96 . Ports  150  and  152  are provided in the wall  85  on respective upstream and downstream sides of the rings  94  and  96  to permit a return of leaked fluid from the chambers  144  and  146  to the reservoir via a return conduit system  160 .  
         [0021]    [0021]FIG. 3 shows exemplary segmenting of the case and seal system. The exemplary case is longitudinally split into two 180° sections along a planar split interface  520 . To maintain the integrity of the ring  62 , its interfaces are provided with shiplap/tongue &amp; groove connections. The seal  50  is split into nominal 90° segments along four planar interfaces  524 . The interfaces  524  are at an off-radial angle so as to be locally parallel to the bristles. The mounting ring  62  is similarly split or may be split in two, similar to the case.  
         [0022]    In operation, a radial excursion of the shaft axis relative to the case axis will apply a net force to the bristles. The force is transmitted to the rigid portions of the seal (e.g., the plates and fixed outboard bristle ends. In doing this, the bristles may flex. Advantageously the pump and regulator maintain sufficient fluid pressure that, given fluid viscosity, density, and other properties, permit the fluid to damp radial excursion of the seal induced by the force. It may be possible for the engine control system (not shown) to regulate pressure based upon engine operating conditions to provide a desired degree of damping.  
         [0023]    [0023]FIG. 4 shows an alternate sealing system  200 . Elements in common with the exemplary sealing system  40  are referenced with like numerals. In this embodiment, the seal  50  is similarly held within a mounting ring  210 . The mounting ring  210  is captured within a channel  212  formed in a housing wall  214 . A flexible annular bladder  216  (e.g., formed of a suitable elastomer) is positioned between an exterior surface  218  of the mounting ring  210  and a base surface  220  of the channel  212 . The bladder contains a fluid  224 . The bladder is coupled via one or more ports  226  in the housing to supply lines  228  from a pump  230  delivering the fluid from a reservoir  232 . A regulator  234  is positioned in the supply lines and has a return line  238  for returning fluid to the reservoir  232 .  
         [0024]    In operation, the sealing system  200  could be controlled in a similar fashion to the system  40 . For an excursion of the seal, the bladder will be locally compressed at one diametric location and locally expanded at the opposite location. Thus the elasticity and other properties of the bladder are relevant to the degree of resistance offered to seal excursions. Relative to the system  40 , this elasticity may provide a greater degree of resistance (e.g. a spring constant) to excursion for a given degree of damping. Relative to the system  40 , the system  200  may be particularly useful with compressible fluids. Automated control of fluid pressure in the system  200  may provide a high degree of control of seal support. In such an automated system, speed and vibration (e.g., actual vibration levels measured via proximity probes) parameters could be measured and further control inputs could be provided indicating other conditions of operation (e.g., whether the engine was accelerating or decelerating). At startup conditions, a very low pressure could be applied to permit the seal to accommodate the rotor excursions (known as “critical vibration”) typical at startup. In stable running conditions, higher pressure could be maintained to keep the seal centered. This may be desirable to prevent high cycle vibration (HCV) from affecting the seal. At lower pressures, the seal may be more prone to HCV. It may be possible to use the engine&#39;s compressor as a source of high pressure fluid.  
         [0025]    [0025]FIG. 5 shows an alternate sealing system  300  in which the bladder is itself segmented into four segments or smaller bladders  310  positioned end-to-end circumscribing the shaft. Each exemplary bladder  310  extends around somewhat less than 90° of the shaft. The bladder segments are positioned approximately coincident with segments of the seal  50  and its mounting ring  312 . Each bladder segment is connected via a case port  314  to a common header supply lines and associated equipment as in the embodiment of FIG. 3. Operation of the system  300  may be generally similar to that of the system  200 . The use of separate bladder segments may tend to further increase the effective spring constant for a given fluid type and pressure, bladder material, and the like. Additionally, there exists a possibility of fully or partially independent control over the pressure in the bladder segments giving rise to the possibility of an active positioning of the seal under automated control.  
         [0026]    One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, environmental considerations may influence parameters of seal construction. Similar seals could be used in non-rotating (e.g., static) brush seal applications. In such applications, wear and heat generation may be of less concern than compacting the bristle pack. Such compacting can cause flaring of the bristle tips (brooming) and/or cause the bristles to be permanently deformed to increase the bristle pack inner diameter. Additional features are possible such as a seal anti-rotation features (e.g., radial pins or tabs mounted to the seal and riding in slots in the case). Accordingly, other embodiments are within the scope of the following claims.