Mid turbine frame system for gas turbine engine

• US 8,061,969 B2
• Filed: 11/28/2008
• Issued: 11/22/2011
• Est. Priority Date: 11/28/2008
• Status: Active Grant

• Current Assignee: Pratt & Whitney Canada Corporation (Rtx Corporation)
• Original Assignee: Pratt & Whitney Canada Corporation (Rtx Corporation)
• Inventors: Pietrobon, John, Durocher, Eric, Nguyen, Lam
• Primary Examiner(s): Blum; David S
• Application Number:
  US12/325,000
• Publication Number:
  US 20100135770A1
• Time in Patent Office: 1,089 Days
• Field of Search: 415/69, 607/96
• US Class Current: 415/69
• CPC Class Codes: F01D 21/045 special arrangements in stators or in rotors dealing with breaking-off of part of rotor
• CPC Class Codes: F01D 21/08 Restoring position
• CPC Class Codes: F01D 25/162 Bearing supports
• CPC Class Codes: F01D 25/28 Supporting or mounting arrangements, e.g. for turbine casing
• CPC Class Codes: F01D 9/065 Fluid supply or removal conduits traversing the working fluid flow, e.g. for lubrication-, cooling-, or sealing fluids see also F01D25/16, F01D25/24 and F01D25/26

Abstract

A gas turbine engine mid turbine frame having an inner case supporting at least one bearing and at least three spokes extending radially outwardly to an outer case, the mid turbine frame having an interturbine duct extending through the mid turbine frame, the interturbine duct spaced axially closer to an upstream turbine disc than a bearing supporting structure of the mid turbine frame and mounted axially slidingly relative to the bearing supporting structure to substantially isolate the bearing supporting structure from axial loads, for example such as disc loads incurred in the unlikely event a turbine disc shaft shears within the engine.

Claims

1. A gas turbine engine defining a central axis of rotation, and further defining axial and radial directions in the engine relative to the axis, the engine comprising:

a gas path defined through the engine for directing combustion gases to pass through a turbine rotor having a central disc mounted to a shaft and airfoils extending radially from the disc, the flow of gas through the gas path in use defining upstream and downstream directions within the engine;

an interturbine duct extending downstream from the turbine rotor, the interturbine duct defined by inner and outer annular shrouds, the shrouds separated by struts extending radially across the gas path, the struts and shrouds co-operating to provide a passageway through the interturbine duct, the interturbine duct inner shroud having a upstream edge disposed axially downstream of the turbine disc, the upstream edge having a diameter not greater than a diameter of the turbine disc such that, in use during a shaft shear event permitting the turbine disc to move axially rearwardly, the disc will contact the inner shroud the upstream edge;

a mid turbine frame having an outer mid turbine frame case encircling an annular inner mid turbine frame case, the inner and outer mid turbine frame cases connected by at least three spokes extending radially therebetween, the spokes passing through passageways defined through the interturbine duct, the mid turbine frame inner case having a upstream edge spaced axially downstream of the interturbine duct upstream edge, the spokes axially spaced apart from an inner periphery of the passageways;

an annular engine case connected to a downstream end of the mid turbine frame outer case, the engine case axially abutting a downstream end portion of the interturbine duct outer shroud substantially about an outer circumference of the interturbine duct outer shroud; and

wherein the mid turbine frame upstream edge and spokes are respectively spaced from the interturbine duct upstream edge and passageway inner periphery an axial distance greater than an expected interturbine duct upstream edge axial deflection during said shaft shear event such that the interturbine duct inner shroud, struts and outer shroud provide a load path for transmitting loads form the turbine disc to the engine case during said shaft shear event.

2. The gas turbine engine of claim 1 wherein the interturbine duct and mid turbine frame are configured relative to one another such that load path transfers substantially all of the loads induced by the turbine disc during said shaft shear event.

3. The gas turbine engine of claim 1 wherein the interturbine duct inner shroud is supported in a radial direction by the mid turbine frame inner case, thereby permitting the interturbine duct to move axially substantially free of axial load transfer to the mid turbine frame inner case.

4. The gas turbine engine of claim 1 wherein the interturbine duct outer shroud is supported in a radial direction by the mid turbine frame outer case in a manner which permits the interturbine duct to move axially rearwardly during said shaft shear event substantially free of axial load transfer to the mid turbine frame outer case.

5. The gas turbine engine of claim 1 wherein the interturbine duct includes a circumferential array of airfoil vanes radially extending between the inner and outer interturbine duct shrouds, the vane array providing a portion of the load path.

6. The gas turbine engine of claim 5 wherein the interturbine duct is provided as an assembly of circumferential segments, each of the segments comprising a unitary body including inner and outer shroud segments, at least one said strut and a plurality of said airfoils, the inner and outer shroud segments providing a portion of the inner and outer shrouds respectively.

7. The gas turbine engine of claim 5 wherein the downstream end portion of the interturbine duct outer shroud abutted by the engine case is substantially axially aligned with the vane array.

8. A method of providing for load transfer from turbine disc to an engine case during a turbine shaft shear event causing the turbine disc to move axially aft, the method comprising the steps of:

a) providing a mid turbine frame to the engine, the mid turbine frame having an inner case supporting at least one bearing and at least three spokes extending radially outwardly to a mid turbine frame outer case, the mid turbine frame having an interturbine duct extending through the mid turbine frame from an interturbine duct upstream edge to an interturbine duct downstream edge, the interturbine duct having inner and outer shrouds defining the duct, the inner and outer shrouds connected by a plurality of radial members extending between them, the spokes extending across a gas path defined by the interturbine duct;

b) spacing the interturbine duct inner shroud at the upstream edge closer to the turbine disc than an upstream end of the mid turbine frame inner case;

c) permitting relative axial movement between the interturbine duct and the spokes;

d) restraining axial rearward movement of the interturbine duct using a downstream engine case connected a downstream end of the mid turbine frame; and

wherein steps b)-d) thereby define a load path for transferring said shaft shear disc loads from the interturbine duct inner shroud upstream edge to the downstream engine case, the load path substantially independent of the mid turbine frame inner case and mid turbine frame spokes.