Patent Application
20080018054
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
The seal support 46 is a nonrotating, axially-extending component and defines a radially-facing secondary scaling surface 47. In the illustrated example it is a continuous 3600 ring, but it could be configured as a segmented annular structure, or an array of individual supports. Its aft end 52 has a radially-extending flange 54 which is secured to the diffuser 12′ by one or more fasteners 56. Its forward end 58 carries one or more spring seats 60. In this example there are five spring seats equally-spaced around the perimeter of the seal support 46; however the spring seats 60 could alternatively be configured as a continuous or segmented annular structure. As best seen in
The seal body 48 is an annular component which may be continuous or segmented, and has a generally L-shaped cross section with a radially extending portion 70 and an axially extending portion 72.
A plurality of pullback springs 73 are disposed between the spring seats 60 and a radially-outwardly extending flange 74 of the seal body 48. The aft end of each pullback spring 73 is located in a spring pocket 76 of the flange 74, or other suitable locating feature. The pullback springs 73 serve to displace the seal body 48 away from the rotor 44. This function is described in more detail below. As illustrated, there are five compression-type coil springs, but other types and numbers of springs may be used.
A secondary seal 78, for example a piston ring of a known type, is disposed in a groove 80 in the flange 74, and seals against the axially facing secondary sealing surface 47 of the spring support assembly 46. The piston ring may be of a known type which provides a continuous (or nearly continuous) circumferential seal. The purpose of the secondary seal 78 is to prevent leakage through a path between the seal body 48 and the seal support 46, which is subject to the same pressure differential as the primary seal, while allowing axial movement of the seal body 48. It should be noted that the specific configuration of the seal components and mounting structure described above is not critical and may be varied to suit a particular application without affecting the functional aspects of the seal assembly 42.
As shown in
The second primary sealing surface 82 includes a planar inner portion 82A and an outer portion 82B, separated by an annular groove 83. The outer portion 82B includes at least one, and optionally a plurality of annular, radially spaced-apart, axially-extending seal teeth 88 which are intended to form a circuitous or tortuous flow path for radial fluid flow, to limit flow from the primary flow path to the secondary flow path. In the illustrated example, there are two seal teeth 88A and 88B with tapered cross-sectional profiles, separated by annular, rounded-bottom grooves 90. The teeth 88 could also protrude from a planar surface if desired. It should also be understood that the seal tooth configuration could be reversed, i.e. the seal teeth 88 could be formed on the first primary sealing surface 50 instead.
The configuration of the second primary sealing surface 82 may be defined in part by various characteristics of the seal teeth 88, including the number of seal teeth 88, their height “H” in an axial direction, their tip width “W”, their included angle in cross-section “A”, their divergence in or out from an axial direction, referred to as a slant angle “S” (note that this angle is very small in the illustrated example), their radial spacing or pitch “P”, and the total radial extent or length of the seal teeth 88, denoted “L”. Nonlimiting examples of these dimensions are as follows: tooth height H about 0.38 mm (0.015 in.), tooth angle A is about 10°, the slant angle S about 0° to about 45°, tip width W about 0.13 mm (0.005 in.) to about 0.76 mm (0.030 in.), and pitch P about 1.3 mm (0.05 in.) to about 3.8 mm (0.15 in.). These values may be altered to suit a specific application.
In the illustrated example, the first primary sealing surface 50 has an inner portion 50A, and an outer portion 503B which is offset axially forward of the inner portion 50A by a distance “D” (see
In operation, the seal body 48 forms a seal in cooperation with the rotor 44. The pullback springs 73 hold the seal body 48 away from the rotor 44 to prevent contact between the two components when the engine is stopped. As the engine operating speed increases, the fluid pressures in the engine's primary and secondary flowpath areas increase, and accordingly the seal assembly 42 is subjected to increasing pressures acting on its axially facing surfaces, the effect of which is to cause the seal body 48 to move towards the rotor 44. By choosing the relative surface areas of the different portions of the seal body 48, the number and dimensions of passages 86, 87, and the dimensions of the pullback springs 73 in a known manner, the seal assembly 42 is hydrostatically pressure balanced at a selected operating condition. Accordingly, the second primary sealing surface 82 never contacts the first primary sealing surface 50, but operates with a small axial clearance, for example about 0.05 mm (0.002 in.) to about 0.13 mm (0.005 in.). The low operating clearance of the aspirating seal assembly 42 combined with the complex flow path through the seal teeth 88 and between the first and second primary sealing surfaces 50 and 82 minimizes leakage.
The second primary sealing surface 182 includes at least one, and optionally a plurality of annular, radially spaced-apart, axially-extending seal teeth 188 which are intended to form a circuitous or tortuous flow path in a radial direction. In the illustrated example, there are three seal teeth 188A, 188B, and 188C with tapered cross-sectional profiles, separated by annular, rounded-bottom grooves 190.
The characteristics of the seat between the first and second primary sealing surfaces 150 and 182 may be altered to suit a specific application in a manner similar to that described above for the seal assembly 48.
An annular seal groove 92 with a rounded bottom is formed in the first primary sealing surface 150. The corresponding seal tooth 188C has a greater height in the axial direction than the other seal teeth 188A and 188B, and will protrude into the seal groove 92 during operation to further reduce leakage.
These seal assemblies offer the complex leakage path of a labyrinth seal, and thus reduce leakage compared to a flat face seal. However, in contrast to prior art labyrinth seals which can rub against the adjacent components, the clearance between the seal elements is controlled so that the seal teeth will not rub against the seal rotor. This offers efficient sealing both at the time of manufacture of the engine and also after extended time in service.
The foregoing has described a face seal assembly. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention.
