Patent Description:
Turbine shrouds are radially located on a turbine support case (TSC) about the tip of the turbine blades to control blade tip clearance. The turbine shrouds are typically segmented in the circumferential direction to allow for thermal expansion. While various framework have been developed for supporting the shroud segments in position in the turbine case, continued improvements are suitable.

<CIT> discloses a seal assembly for a gas turbine engine. <CIT> discloses an assembly of a CMC part and a metallic element a method of manufacturing for such an assembly. <CIT> discloses a CMC blade outer air seal arrangement. <CIT> discloses a stator ring for the high-pressure turbine of a turbomachine.

In one aspect of the invention, there is provided a turbine section as claimed in claim <NUM>.

<FIG> illustrates an aircraft engine of a type preferably provided for use in subsonic flight, and generally comprising in serial flow communication an air inlet <NUM>, a compressor <NUM> for pressurizing the air from the air inlet <NUM>, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, a turbine <NUM> for extracting energy from the combustion gases, and a turbine exhaust case (TEC) <NUM> through which the combustion gases exit the engine <NUM>. The turbine <NUM> includes a low pressure (LP) turbine 14a (also known as a power turbine) drivingly connected to an input end of a reduction gearbox (RGB) <NUM>. The RGB <NUM> has an output end drivingly connected to an output shaft <NUM> configured to drive a rotatable load (not shown). For instance, the rotatable load can take the form of a propeller or a rotor, such as a helicopter main rotor. According to the illustrated embodiment, the compressor and the turbine rotors are mounted in-line for rotation about the engine centerline <NUM>.

The expressions "forward" and "aft" used herein refer to the relative disposition of components of the engine <NUM>, in correspondence to the "forward" and "aft" directions of the engine <NUM> and aircraft including the engine <NUM> as defined with respect to the direction of travel. In the embodiment shown, a component of the engine <NUM> that is "forward" of another component is arranged within the engine <NUM> such that it is located closer to the output shaft <NUM>. Similarly, a component of the engine <NUM> that is "aft" of another component is arranged within the engine <NUM> such that it is further away from the output shaft <NUM>.

The turbine <NUM> generally comprises one or more stages of circumferentially spaced-apart rotor blades <NUM> extending radially outwardly from respective rotor disks, with the blade tips being disposed closely adjacent to an annular turbine shroud <NUM> supported from a turbine shroud support <NUM> (<FIG>) of a turbine support case <NUM>. The shroud support <NUM> can be integral to the turbine case <NUM> or provided as a separate intermediate framework between the turbine case <NUM> and the turbine shroud <NUM>. The turbine shroud <NUM> is circumferentially segmented to accommodate differential thermal expansion during operation. The shroud <NUM> comprises a plurality of circumferentially adjoining shroud segments 22a concentrically arranged around the periphery of the turbine blade tips so as to define a portion of the radially outer boundary of the engine gas path <NUM>. The shroud segments 22a may be individually supported and located within the turbine support case <NUM> so as to collectively form a continuous shroud ring about the turbine blades <NUM>. <FIG> and <FIG> illustrate an example of one such turbine shroud segments 22a.

Referring concurrently to <FIG> and <FIG>, it can be appreciated that the shroud segment 22a has a unitary shroud body including a circumferentially arcuate platform <NUM> extending axially from a leading edge <NUM> to a trailing edge <NUM> relative to a hot gas flow (see flow arrows A in <FIG>) passing through the turbine shroud <NUM>, and circumferentially between opposite first and second lateral sides <NUM>, <NUM> (<FIG>). The platform <NUM> has a radially inner gas path surface <NUM> facing towards the axis <NUM> and an opposed radially outer surface <NUM> facing away from the axis <NUM>. The unitary shroud body further comprises axially spaced-apart forward and aft hooks <NUM>, <NUM> projecting integrally radially outwardly from the radially outer surface <NUM> of the platform <NUM>. The hooks <NUM>, <NUM> each have a radially extending leg portion 40a, 42a and an axially extending rail portion 40b, 42b for engagement with a corresponding hook structure of the turbine shroud support <NUM>. According to one or more embodiments, the shroud support <NUM> is provided in the form of a shroud hanger integral to the turbine support case <NUM> (see <FIG>). The exemplified shroud support <NUM> comprises forward and aft hooks projecting from a radially inner surface of the case <NUM> and having axially extending rail portions 24a, 24b for engagement with the corresponding rail portions 40b, 42b of the forward and aft hooks <NUM>, <NUM> of the shroud segment 22a. The rail portions 24a, 24b define together with the radially inner surface of the turbine case <NUM> a pair of axially forwardly open cavities for axially receiving respective rail portions 40b, 42b of the forward and aft hooks <NUM>, <NUM> of the shroud segment 22a. The forward and aft rail portions 24a, 24b may extend continuously along a full circumference of the turbine case <NUM>.

According to the illustrated embodiment, the rail portions 40b, 42b of the forward and aft hooks <NUM>, <NUM> of the shroud segment 22a project axially in an aft direction and the corresponding rail portions 24a, 24b of the shroud hanger axially project in a forward direction. However, it is understood that the axial orientation of the mating pairs of rail portions 24a, 40b and 24b, 42b could be inverted. In addition, the axial orientation of the forward and aft hooks <NUM>, <NUM> does not need to be the same.

Referring jointly to <FIG>, <FIG> and <FIG>, it can be appreciated that the shroud segment 22a further comprises at least one separate anti-rotation pin <NUM> adapted to be pre-assembled to the unitary shroud body of the shroud segment 22a prior to the installation of the shroud segment 22a inside the turbine case <NUM>. The term "pin" is herein intended to broadly refer to a small projection piece that projects out from a host part for engagement with a surrounding framework. For instance, the pin could be provided in the form of a peg, a tab, a fastener, etc. joined to the shroud body of the shroud segment 22a.

According to the example illustrated in <FIG>, <FIG>, the pin <NUM> has a cylindrical shank portion 50a extending axially from an enlarged head portion 50b. The shank portion 50a is engageable into a pin receiving hole <NUM> defined in the unitary shroud body of the shroud segment 22a. , The pin <NUM> and the shroud body are assembled with an interference fit (also known as a press or friction fit assembly). The shank portion 50a of the pin <NUM> may be forcibly pushed into the mating hole <NUM> using a tap from a hammer on the head portion 50b of the pin <NUM>. A thermal treatment may also be used to produce a shrink fit interference. A combination of force and thermal expansion/contraction may also be used. According to other embodiments outside the subject-matter of the claims, the pin <NUM> could be welded, brazed, riveted or otherwise suitably joined to the shroud body of the shroud segment 22a.

According to one or more embodiments, the pin receiving hole <NUM> is defined in the radially extending leg portion 40a, 42a of one of the hooks <NUM>, <NUM>. In the particular example shown in <FIG> and <FIG>, the hole <NUM> extends axially through the radially extending leg portion 42a of the aft hook <NUM>. However, it is understood that the hole <NUM> could have been defined in the radially extending leg portion 40a of the forward hook <NUM> or even in another portion of the shroud body. Referring jointly to <FIG>, it can be appreciated that the hole <NUM> and, thus, the pin <NUM> are positioned radially between the platform <NUM> and the axially extending rail portion 42b. The head portion 50b projects from the radial leg portion 42a in an axially aft direction radially underneath the rail portion 42b for engagement with a corresponding anti-rotation/localisation abutment on the shroud support <NUM>. For instance, the anti-rotation/localisation abutment can take the form of a slot <NUM> (<FIG>) defined in the distal end of the rail portion 24b of the aft hook of the shroud support <NUM>. The slot <NUM> has a forwardly axially open end for allowing axial insertion of the head portion 50b of the pin <NUM> in the slot <NUM> as the shroud segment 22a is axially inserted in an aft direction inside the turbine case <NUM> via the forward open end thereof. The head portion 50b of the pin <NUM> is sized to loosely fit inside the slot <NUM> between the circumferentially spaced-apart sidewalls thereof. The loose fit facilitates the angular alignment of the pin <NUM> with the slot <NUM> during assembly. The engagement of the head portion 50b of the pin <NUM> in the slot <NUM> allows to angularly locate the shroud segment 22a relative to the engine case <NUM> in a predetermined "clocking" position around the engine centerline <NUM> and to lock the shroud segment 22a against rotation relative to the engine case <NUM> (i.e. allows to secure the "clocking" position of the shroud segment 22a relative to the turbine case <NUM>).

As can be appreciated from <FIG>, a forward annular seal <NUM> is mounted in the forward rail cavity between the radially inner surface of the turbine case <NUM> and the radially outer surface of the rail portion 40b of the forward hook <NUM> of the shroud segment 22a. By mounting the pin <NUM> on the shroud segment 22a and, more particularly, by positioning the pin <NUM> on a radially inner side of the rail portion 42b of the aft hook <NUM> of the shroud segment, enough room is created for the positioning of an aft annular seal <NUM> in the radial gap between the radially inner surface of the turbine case <NUM> and the radially outer surface of the rail portion 42b of the aft hook <NUM> of the shroud segment 22a. In some applications, the use of such a second crush seal band allows to improve the sealing of the shroud <NUM>. As mentioned above, the placement of the pin <NUM> on the shroud segment 22a radially between the platform <NUM> and the rail portions of the hooks <NUM>, <NUM> allows to use two crush seal bands, a first one on the forward hook <NUM> and second one on the aft hook <NUM>.

The individual shroud segments 22a may be cut from a circumferentially continuous shroud ring obtained from a turning manufacturing process on a computer numerical control (CNC) machine. Such a machining process is economical compared to casting or metal injection molding (MIM) processes. Still according to one or more embodiments, the pin receiving holes <NUM> are machined in the individual shroud segment 22a either prior or after cutting of the segments. Machining the pin receiving hole <NUM> in the shroud segments 22a instead of in the turbine case <NUM> contributes to reduce the risk that the turbine case <NUM>, which is a much more expensive part than the shroud segments 22a, be rejected for non-conformance related to this additional machining operation. Indeed, the transfer of a feature (e.g. pin receiving hole) that needs precise machining from an expensive part with limited machining access to a less expensive "sacrificial" component (e.g. shroud segment) with easier machining access as several advantages from a manufacturing point of view. Also by mounting the pins <NUM> of the shroud segments 22a, the pins <NUM> can be more easily replaced together with the shroud segments when need be. This contributes to minimize the operation on the turbine case <NUM> at overhaul and, thus, the risk of inadvertently damaging the turbine case <NUM>.

Still according to one or more embodiments, the pins <NUM> are installed on the shroud segments with a tight fit assembly. This method of assembly allows the pins <NUM> to be removed from their respective host and replaced by a new pin if need be during maintenance operations. The pins <NUM> and the body of the shroud segments 22a can be made of a same or different material. For instance, both the pins <NUM> and the shroud segments 22a could be made of Inconel <NUM> or from other suitable high temperature resistant materials. While the illustrated embodiment has one pin <NUM> per shroud segment 22a, it is understood that one or more pins can be installed on each segment or selected ones of the shroud segments.

The shroud segments 22a with the pins <NUM> pre-assembled thereon are individually installed inside the turbine case <NUM>. First, the pin <NUM> of a first one of the shroud segments 22a is angularly aligned in a circumferential direction with a corresponding one of the slots <NUM> in the shroud support <NUM> and then the first shroud segment 22a is axially loaded into the turbine case <NUM> so as to axially slide the rail portions 40b, 42b of the forward and aft hooks <NUM>, <NUM> over the forward and aft rail portions 24a, 24b of the shroud support <NUM>. Once, the first segment has been properly positioned in the turbine case <NUM> with its pin <NUM> axially engaged in the associated slot <NUM>, a second segment is installed and the procedure is repeated until all segments have been loaded into position within the turbine case <NUM>.

Claim 1:
A turbine section (<NUM>) for a gas turbine engine (<NUM>) comprising:
a turbine support case (<NUM>) extending circumferentially around an axis (<NUM>), the turbine support case (<NUM>) having a shroud supporting structure (<NUM>);
a circumferential array of turbine blades (<NUM>) disposed within the turbine support case (<NUM>) for rotation about the axis (<NUM>); and
a circumferentially segmented turbine shroud (<NUM>) mounted inside the turbine support case (<NUM>) about the circumferential array of turbine blades (<NUM>), the circumferentially segmented turbine shroud (<NUM>) including a plurality of shroud segments (22a) disposed circumferentially one adjacent to another, each of the shroud segments (22a) comprising a shroud body including:
a platform (<NUM>) having a radially inner surface (<NUM>) facing towards the axis (<NUM>) and a radially outer surface (<NUM>) facing away from the axis (<NUM>);
forward and aft hooks (<NUM>,<NUM>) extending from the radially outer surface (<NUM>) of the platform (<NUM>) for engagement with the shroud support structure (<NUM>) on the turbine support case (<NUM>);
a pin receiving hole (<NUM>) extending axially in a radially extending leg portion (40a, 42a) of one of the forward and aft hooks (<NUM>,<NUM>) of the shroud body;
characterised by
an anti-rotation pin (<NUM>) engaged in the pin receiving hole (<NUM>), the anti-rotation pin (<NUM>) projecting outwardly from the pin receiving hole (<NUM>) for engagement with a corresponding anti-rotation abutment (<NUM>) on the shroud support structure (<NUM>), wherein the anti-rotation pin (<NUM>) has a shank portion (50a) pressed fit in the pin receiving hole (<NUM>) and an enlarged head portion (50b) loosely received in a localisation slot (<NUM>) defined in a distal end of a rail portion (24a, 24b) of the shroud supporting structure (<NUM>).