Abstract:
A seal apparatus provides the seal between inner and outer elements. The seal apparatus has a flexible sealing element for forming a seal with a first of the inner and outer elements. At least one support element is secured to the sealing element. The seal further includes means for magnetically interacting with the first element to bias the seal relative to the first element.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to shaft seals, and more particularly to turbine engine shaft seals 
     (2) Description of the Related Art 
     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 or clearance 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 
     A seal apparatus provides the seal between inner and outer elements. The seal apparatus has a flexible sealing element for forming a seal with a first of the inner and outer elements. At least one support element is secured to the sealing element. The seal further includes means for magnetically interacting with the first element to bias the seal relative to the first element. 
     Such an apparatus may be used in a turbine engine. The engine includes a rotor shaft carried by a support structure. The support structure carries a seal assembly circumscribing the shaft and having a flexible sealing element conforming a seal with the shaft. The rotor carries a rotor magnetic element and the seal carries a seal magnetic element positioned to interact with the rotor magnetic element to bias the seal assembly toward a coaxial relation with the shaft. 
     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 
         FIG. 1  is a semi-schematic longitudinal sectional view of a turbine engine. 
         FIG. 2  is a partial semi-schematic longitudinal sectional view of a seal system of the engine of FIG.  1 . 
         FIG. 3  is a semi-schematic longitudinal sectional view of the seal system of the engine of FIG.  1 . 
         FIG. 4  is a semi-schematic transverse sectional view of the seal system of  FIG. 3 , taken along line  4 — 4 . 
         FIG. 5  is a semi-schematic longitudinal sectional view of the seal system of the engine of  FIG. 1  in an initial excursion stage. 
         FIG. 6  is a semi-schematic transverse sectional view of the seal system of  FIG. 5 , taken along line  6 — 6 . 
         FIG. 7  is a semi-schematic longitudinal sectional view of the seal system of the engine of  FIG. 1  in a second excursion stage. 
         FIG. 8  is a semi-schematic transverse sectional view of the seal system of  FIG. 7 , taken along line  8 — 8 . 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       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 . 
     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. 
       FIG. 2  shows further details of the exemplary sealing system  40 . The system includes a brush seal  50  having a bristle pack  52  secured in a seal body  54 . The seal body comprises a high pressure side backing plate  56  and a low pressure side backing element formed by the combination of a backing plate  58  and a shield  60 . In an exemplary embodiment, the bristle pack  52 , backing plate  56 , backing plate  58 , and shield  60  are of generally annular configuration. Extending downstream from its upstream face along its inboard side, the backing element  58  has an annular inwardly and upstream open compartment  62  containing a magnetic element  64 . An exemplary element is formed approximately as a square-section annulus of a permanent magnet. An exemplary permanent magnet is an aluminum-nickel-cobalt (alnico) magnet. The shield  60  is secured along the upstream faces of the backing plate  58  and magnetic element  64 . The bristle pack lies along the upstream face of the shield  60  and at its outboard end is secured between the upstream face of the shield and the downstream face of the backing plate  56 . An exemplary securing is by welding (e.g., TIG or electron beam). Extending upstream from its downstream face, the backing plate  56  has an annular pocket  80  along an inboard portion. The pocket  80  accommodates the bristles during flexing of the bristles. The seal  50  is captured within an inwardly-open annular pocket or channel  84  formed by annular shoulders in a pair of mated upstream and downstream housing elements  86  and  88 . In a normal running condition, there is a headspace or clearance having a radial span  520  between the seal periphery  90  and the base  92  of the pocket  84 . 
       FIG. 2  further shows the shaft  24  as having its own magnetic element in the exemplary form of a magnetic coating  100 . The coating is applied over a portion of the exterior surface  102  of a metallic component of the shaft. The coating has a longitudinal span  522 . The span is advantageously positioned to extend at least partially immediately inboard of the magnetic element  64 , more preferably fully beneath such element and, in the illustrated embodiment, more broadly under the entire seal  50 . For wear resistance, the magnetic coating may be comprised of magnetic particles in a wear-resistant matrix or may itself be covered by an additional wear-resistant layer. In normal true-running operation, the bristle tips contact the shaft. There is clearance between the inboard surfaces of the rigid components  56 ,  58 ,  60  and  64  of the seal. For purposes of illustration, in the exemplary embodiment this is shown as a single clearance of radial span  524 , although the different components may well have different clearances.  FIGS. 3 and 4  show the shaft running in a true condition. 
       FIGS. 5 and 6  show an initial excursion of the shaft axis  502  relative to the housing axis  500 . The rotor excursion brings the outer surface magnetic coating  100  toward the inboard surface of the magnetic element  64  near one diametric location  540  and away therefrom near an opposite diametric location  542 . When this occurs, increased magnetic repulsion between the coating  100  and element  64  near the location  540  and reduced repulsion near the location  542  will tend to push the seal to move its axis toward the displaced shaft axis  502 . Thus the seal will be shifted within the channel  84  to at least partially realign the seal axis  504  with the shaft axis  502  (FIGS.  7  and  8 ). If the shaft axis  502  returns to align with the axis  500 , a similar magnetic interaction will tend to bring the seal axis back into alignment with both such axes. 
     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, the magnetic coating on the shaft may be replaced by a separately-formed magnetic element. Exemplary elements could include a permanent magnet (e.g., an alnico sleeve on the shaft or a circumferential array of permanent magnet inserts in compartments in the shaft). Similarly, the magnetic element of the seal body could be replaced by a coating or by an array of permanent magnets. 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.