Patent Description:
Exhaust ducts of engines are subject to thermal stresses. In some applications, thermal gradients between engine casing components, particularly at the joints of casing components, can create areas of high stress at the joints. High stresses are known to reduce the fit at the joints which can cause a loosening of the joints.

A prior art aircraft engine, having the features of the preamble of claim <NUM> is provided in <CIT>. <CIT> relates to a joint structure between a ceramic shaft and a metallic shaft. <CIT> relates to a flange joint assembly.

An aspect of the present invention provides an aircraft gas turbine engine in accordance with claim <NUM>.

The aircraft engine as defined above and described herein may further include one or more or all of the following additional features.

In one embodiment of the above, the interface flange is composed of the first material.

In one embodiment of any of the above, the third coefficient of thermal expansion of the interface flange is equal to the first coefficient of thermal expansion of the generator case flange.

In one embodiment of any of the above, the interface flange is in interference fit with the generator case flange.

In one embodiment of any of the above, the interface flange is an annular body and radially overlaps part of the generator case flange and part of the TSC flange.

In one embodiment of any of the above, the interface flange is disposed radially outwardly of the generator case flange and of the TSC flange relative to the center axis, the interface flange exerting a radially inward force on part of the generator case flange upon the interface flange undergoing thermal expansion.

In one embodiment of any of the above, the interface flange experiences a thermal gradient during operation of the aircraft engine, the interface flange having a first temperature substantially equal to a temperature of the generator case flange at a location where the interface flange engages the generator case flange, the interface flange having a second temperature greater than the first temperature at a location where the interface flange engages the TSC flange.

In one embodiment of any of the above, the TSC flange includes a first portion secured to the generator case flange, and a second portion extending axially away from the first portion relative to the center axis and axially spaced from the generator case flange.

In one embodiment of any of the above, the interface flange is integral with the generator case flange, the interface flange extending substantially axially from the generator case flange relative to the center axis.

In one embodiment of any of the above, the generator case is cantilevered from the TSC at the joint.

In one embodiment of any of the above, the first material of the generator case flange is Titanium, the interface flange is composed of Titanium, and the second material of the TSC flange is Inconel™ <NUM>.

<FIG> illustrates a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication along a longitudinal axis <NUM> a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases.

The gas turbine engine <NUM> includes a core engine casing <NUM> which encloses the turbo machinery of the engine, and an outer casing <NUM> disposed radially outwardly of the core engine casing <NUM> such as to define an annular bypass passage <NUM> therebetween. The air propelled by the fan <NUM> is split into a first portion which flows around the core engine casing <NUM> within the bypass passage <NUM>, and a second portion which flows through the core of the engine <NUM> via a main gas path <NUM>, which is circumscribed by the core engine casing <NUM> and allows the flow to circulate through the compressor section <NUM>, the combustor <NUM> and the turbine section <NUM> as described above.

At an aft end of the engine <NUM>, an exhaust cone <NUM> is centered about, and axially extends along, the longitudinal axis <NUM> of the engine <NUM>. The exhaust cone <NUM> is connected to an aft end of the turbine section <NUM>, and may sometimes be referred to as a "tail cone". The exhaust cone <NUM> has an outer surface 29A which defines an inner wall of the main gas path <NUM> so that the combustion gases flow therearound. The exhaust cone <NUM> has an inner surface 29B which is spaced radially inwardly of the outer surface 29A. The inner surface 29B defines or delimits an internal cavity 29C of the exhaust cone <NUM>. The internal cavity 29C is a void or hollow within the exhaust cone <NUM> which occupies some or all of the internal volume of the exhaust cone <NUM>. As will be described in greater detail below, components of the engine <NUM> may be positioned in the internal cavity 29C.

The gas turbine engine <NUM> includes an exhaust section <NUM> for channeling the combustion gases to an exhaust outlet. The exhaust section <NUM> includes an outer shroud <NUM> surrounding an inner shroud (e.g. the exhaust cone <NUM>). The shroud <NUM> may be referred to as an "exhaust outer shroud". In some embodiments, the shroud <NUM> may form a continuation of the core engine casing <NUM>. A core duct <NUM> is defined radially relative to the longitudinal axis <NUM> between the exhaust cone <NUM> and the shroud <NUM> to provide the main gas path <NUM>.

Referring to <FIG>, a turbine support case (TSC) <NUM> may define part of the outer shroud <NUM>. The TSC <NUM>, sometimes referred to as a turbine exhaust case, is a portion of the core engine casing <NUM> that supports components of the turbine section <NUM>. The TSC <NUM> is an annular body defined about the longitudinal axis <NUM>. The TSC <NUM> is disposed radially outwardly of the exhaust cone <NUM> and may surround some or all of the exhaust cone <NUM> to further define the core duct <NUM>.

The exhaust section <NUM> includes one or more struts <NUM> extending radially in the core duct <NUM>. In the embodiment shown in <FIG>, the struts <NUM> abut and extend between the exhaust cone <NUM> and the shroud <NUM> to interconnect the exhaust cone <NUM> and the shroud <NUM> and/or the TSC <NUM> together. For example, the exhaust section <NUM> may include a series of circumferentially spaced apart struts <NUM> interconnecting the exhaust cone <NUM> and the shroud <NUM>. The struts <NUM> may be disposed circumferentially equidistant from each other about the longitudinal axis <NUM>.

Referring to <FIG>, a generator <NUM> is disposed in the internal cavity 29C of the exhaust cone <NUM>. The generator <NUM> includes a generator case <NUM> that houses electric and/or mechanical components <NUM> of the generator <NUM>. In <FIG>, the generator <NUM> is an electrical generator <NUM> whose components <NUM> operate to produce electrical power for the engine <NUM> or for an aircraft to which the engine <NUM> may be mounted. The components <NUM> are driven by one or more spools of the engine <NUM>, such as from a low pressure spool of the engine <NUM> that also drives the fan <NUM>. The generator <NUM> may be configured to drive large electrical loads, and may work in conjunction with, or separately from, other electrical machines of the engine <NUM>, such as a starter/generator of an accessory gearbox. Wires, cabling and other connectors, as well as cooling air, may be routed to the inner volume defined by the generator case <NUM> via the radially-extending struts <NUM> which may be hollow and which support the exhaust cone <NUM> from the shroud <NUM>. In an alternate embodiment, the generator <NUM> operates to provide a mechanical output. The generator case <NUM> encloses the electrical components <NUM> and any mechanical components, and defines an outer surface <NUM> of the generator <NUM>. The outer surface <NUM> is spaced radially inwardly from the inner surface 29B of the exhaust cone <NUM>. In an embodiment in which the generator case <NUM> has an annular shape about the longitudinal axis <NUM>, an annular gap or volume of air is defined between the outer surface <NUM> and the inner surface 29B, which may help to thermally insulate the components <NUM> from the hot exhaust gases flowing along the outer surface 29A of the exhaust cone <NUM>. The generator <NUM> and its components <NUM> may be cooled using any suitable medium, such as bypass air. In an embodiment, the generator <NUM> is internally oil cooled. Positioning the generator <NUM> within the exhaust cone <NUM> of the engine <NUM> allows for adding components to the engine <NUM> without increasing the diameter of the engine <NUM>, by at least partially filling a volume of the engine <NUM> (i.e. the internal cavity 29C) that would otherwise remain unused. The generator <NUM> is disposed radially inwardly of the TSC <NUM>. The generator <NUM> may thus be referred to as a "tail cone" generator <NUM>, or as an "exhaust cone" generator <NUM>.

Referring to <FIG>, a joint <NUM> is formed or defined between the TSC <NUM> and the generator case <NUM>. The generator case <NUM>, and thus the generator <NUM>, is mounted to the TSC <NUM>, and thus to the structure of the engine <NUM>, via the joint <NUM>. The TSC <NUM> supports the generator case <NUM>, and thus the generator <NUM>, within the engine <NUM> via the joint <NUM>. In an embodiment, and referring to <FIG>, the generator <NUM> is only supported by the TSC <NUM>. In an embodiment, the generator <NUM> is free of connecting or supporting structure linking the generator case <NUM> to other structure of the engine <NUM>. Referring to <FIG>, the generator case <NUM> is cantilevered from the TSC <NUM> at the joint <NUM>. Referring to <FIG>, the generator case <NUM> (and the components <NUM> housed therein) are fixedly attached to the TSC <NUM> at the joint <NUM>, and the remainder of the generator case <NUM> is suspended within the internal cavity 29C of the exhaust cone <NUM>. The generator <NUM> in an embodiment therefore "floats" within the exhaust cone <NUM> and does not contact the inner surface 29B of the exhaust cone <NUM> during normal operation of the engine <NUM>. In an alternate embodiment, the exhaust cone <NUM> has one or more struts extending radially inwardly from the inner surface 28B and which are mounted to the generator case <NUM> to structurally link the generator case <NUM> to the exhaust cone <NUM>. In an alternate embodiment, the generator case <NUM> is supported from different structure of the engine <NUM> in addition to, or separately from, how the generator case <NUM> is supported by the TSC <NUM> at the joint <NUM>.

The joint <NUM> may take different forms or configurations to achieve the functionality ascribed to it herein. One possible configuration for the joint <NUM> is shown in <FIG>. The joint <NUM> includes, or is composed of, multiple joint members. Referring to <FIG>, one of the joint members is a TSC flange <NUM> and another joint member is a generator case flange <NUM>. The TSC flange <NUM> is part of the TSC <NUM>, and the generator case flange <NUM> is part of the generator case <NUM>. The TSC flange <NUM> and the generator case flange <NUM> are secured to one another using any suitable mechanism or feature, for example bolts <NUM>, in order to mount the generator <NUM> to the TSC <NUM>. The TSC flange <NUM> and the generator case flange <NUM> are annular bodies which extend circumferentially about the longitudinal axis <NUM>, such that the joint <NUM> is an annular joint <NUM>.

The generator case flange <NUM> (and possibly the generator case <NUM> as a whole) is composed of a first material. The TSC flange <NUM> (and possible the TSC <NUM> as whole) is composed of a second material that is different from the first material of the generator case flange <NUM>. By "different", it is understood that the first material has a material composition that is different from the material composition of the second material. The composition of the first material is not identical to the composition of the second material. The first material and the second material may, for example, be metals that contain one or more similar metal alloys, but the concentration of the one or more metal alloys in the first metal is not the same as the concentration of the one or more metal alloys in the second metal. In one possible and non-limiting example of the material composition of the TSC flange <NUM> and of the generator case flange <NUM>, the first and second materials are first and second metals. The first metal of the generator case flange <NUM> is Titanium or an alloy thereof, and the second metal of the TSC flange <NUM> is Inconel™ <NUM>. Inconel™ <NUM> is a metal composition of nickel-chromium alloys. The specific composition of alloys within Inconel™ <NUM> may be defined as of the filing date of the present application. Thus, in the example of first and second metals provided above, the joint <NUM> is defined primarily by the two different metals of the TSC flange <NUM> and of the generator case flange <NUM>, and may therefore be referred to as a "bimetallic" joint <NUM>. The bimetallic or "bi-material" joint <NUM> supports the generator <NUM> within a tailcone or exhaust cone <NUM>.

The first and second materials may be non-metallic. In one possible and non-limiting example of the material composition of the TSC flange <NUM> and of the generator case flange <NUM>, the first and second materials are composite materials. In one possible and non-limiting example of composite materials for the TSC flange <NUM> and of the generator case flange <NUM>, one of the TSC flange <NUM> and the generator case flange <NUM> is composed of carbon fibers encased in a suitable matrix and assuming the form of an annular body or ring, thereby forming a carbon fiber ring. The other of the TSC flange <NUM> and the generator case flange <NUM> is fiberglass assuming the form of an annular body or ring, thereby forming a fiberglass ring. If it is desired to impart additional flexibility to the composite materials, cut-outs or striations can be formed in the composite materials. Thus, in the example of first and second composite materials provided above, the joint <NUM> is defined primarily by the two different composite materials of the TSC flange <NUM> and of the generator case flange <NUM>, and may therefore be referred to as a "bi-material" joint <NUM>.

In the configuration where the joint <NUM> is "bimetallic", the first metal of the generator case flange <NUM> defines a first coefficient of thermal expansion, and the second metal of the TSC flange <NUM> defines a second coefficient of thermal expansion. The coefficient of thermal expansion describes how the generator case flange <NUM> and the TSC flange <NUM> will change as they experience changes in temperature during operation of the engine <NUM>. In some instances, the coefficient of thermal expansion measures the fractional change in size (e.g. length or volume) per degree change in temperature. A metal that has a lower coefficient of thermal expansion will undergo less change in size than a metal that has a higher coefficient of thermal expansion. As will be described in greater detail below, the first coefficient of thermal expansion of the first metal of the generator case flange <NUM> is different from the second coefficient of thermal expansion of the second metal of the TSC flange <NUM>. The coefficient of thermal expansion is a property resulting from the material composition of the TSC flange <NUM> and of the generator case flange <NUM>, and thus the description above about the coefficients of thermal expansion applies mutatis mutandis to the configuration of the joint <NUM> which is non-metallic, or where only one of the first and second materials is metallic.

The generator case flange <NUM> may take different forms or configurations to achieve the functionality ascribed to it herein. One possible and non-limiting configuration for the generator case flange <NUM> is shown in <FIG>. The generator case flange <NUM> extends axially relative to the longitudinal axis <NUM> from the outer surface <NUM> of the generator case <NUM> to join with the TSC flange <NUM>. In the depicted embodiment, the generator case flange <NUM> includes an inner portion 48A, an outer portion 48B disposed radially outwardly of the inner portion 48A, and a center portion 48C disposed radially between the inner and outer portions 48A,48B. The radially outer portion 48B has an outer segment 48BO that extends axially from the outer surface <NUM> of the generator case <NUM> to an inner segment 48BI. The inner segment 48BI extends substantially radially relative to the longitudinal axis <NUM> to the center portion 48C. The inner and outer segments 48BI,48BO of the outer portion 48B provide the outer portion 48B with an "L" cross-sectional shape. The radially inner portion 48A extends axially and radially from the outer surface <NUM> of the generator case <NUM> to the center portion 48C. The inner, outer, and center portions 48A,48B,48C of the generator case flange <NUM> are annular bodies extending circumferentially about the longitudinal axis <NUM>. The center portion 48C is spaced axially apart from the outer surface <NUM> of the generator case <NUM> by the inner and outer portions 48A,48B. An annular gap 48D is defined between the center portion 48C and the outer surface <NUM> of the generator case <NUM>. The annular gap 48D is delimited by the inner, outer, and center portions 48A,48B,48C of the generator case flange <NUM>, and by the outer surface <NUM> of the generator case <NUM>.

Referring to <FIG>, the center portion 48C has a centering protrusion 48CP that extends axially outwardly from a bolt face 48CS of the center portion 48C. The bolt face 48CS has a radial orientation, and is the part of the center portion 48C that is located axially furthest from the outer surface <NUM> of the generator case <NUM>. In the embodiment shown in <FIG>, the centering protrusion 48CP has a gap 48CG extending axially. In an alternate embodiment, the centering protrusion 48CP is full-bodied and the gap 48CG is not present. The centering protrusion 48CP is inserted within a centering aperture 38AA of the TSC flange <NUM>, so as to properly align the bolt face 48CS against a corresponding bolt face 38AS of the TSC flange <NUM> when they are brought together, thereby helping to ensure that the bolts <NUM> are properly aligned. The center portion 48C includes bolt holes extending through the bolt face 48CS to receive the bolts <NUM>. The centering aperture 38AA may form a relatively loose fit with the centering protrusion 48CP, thereby allowing the generator case flange <NUM> and the TSC flange <NUM> to abut against each other while minimising any fight between the generator case flange <NUM> and the TSC flange <NUM> as they are being centered as described below.

The TSC flange <NUM> may take different forms or configurations to achieve the functionality ascribed to it herein. One possible and non-limiting configuration for the TSC <NUM> is shown in <FIG>. The TSC flange <NUM> extends radially inwardly relative to the longitudinal axis <NUM> from the core duct <NUM> and main gas path <NUM> defined by the shroud <NUM> to join with the center portion 48C of the generator case flange <NUM>. In the depicted embodiment, the TSC flange <NUM> includes an inner portion 38A, an outer portion 38B disposed radially outwardly of the inner portion 38A, and a center portion 38C disposed radially between the inner and outer portions 38A,38B. The radially outer portion 38B has a radial orientation for abutment against, and securement to, another part of the TSC <NUM>. The radially inner portion 38A has a radial orientation and defines the bolt face 38AS for abutting against the bolt face 48CS of the generator case flange <NUM>. The inner portion 38A includes one or more of the centering apertures 38AA to receive therethrough the one or more centering protrusions 48CP of the generator case flange <NUM>. The inner portion 38A may have one or more aperture walls 48AW which define the centering apertures 38AA (see <FIG>). The centering apertures 38AA are slightly larger than the centering protrusions 48CP in order to more easily receive the centering protrusions 48CP therein and avoid fight between the generator case flange <NUM> and the TSC flange <NUM> when they are being centered as described below, such that the centering apertures 38AA act as a timing feature. The inner portion 38A includes bolt holes extending through the bolt face 38AS to receive the bolts <NUM>, thereby securing the TSC flange <NUM> to the generator case flange <NUM>.

Referring to <FIG>, the center portion 38C of the TSC flange <NUM> has an inner arm 38CI, an outer arm 38CO spaced radially outwardly from the inner arm 38CI, and an end 38CE disposed radially between the inner and outer arms 38CI,38CO and connected thereto. The inner and outer arms 38CI,38CO have a substantially axial orientation relative to the longitudinal axis <NUM>, but also extend along a radial direction. The end 38CE has a substantially radial orientation, and is the part of the center portion 38C that is positioned axially furthest from the generator case flange <NUM>. The inner arm 38CI, the outer arm 38CO, and the end 38CE of the center portion 38C may form a "hairpin" cross-sectional shape. An annular gap 38D is delimited by the inner arm 38CI, the outer arm 38CO, and the end 38CE of the center portion 38C of the TSC flange <NUM>, and by the generator case flange <NUM>. The inner arm 38CI, the outer arm 38CO, and the end 38CE of the center portion 38C help to thermally insulate and isolate the inner portion 38A of the TSC flange <NUM> from the hotter outer portion 38B which is exposed to the hot exhaust gases in the core duct <NUM>. During operation of the engine <NUM>, the inner portion 38A of the TSC flange <NUM> may be at a lower temperature than the outer portion 38B, and the inner portion 38A may be at a lower temperature than the center portion 38C of the TSC flange <NUM>. Other possible shapes for the TSC flange <NUM> are possible. For example, in another possible configuration, the center portion 38C extends substantially radially between the inner portion 38A and the outer portion 38B.

Referring to <FIG>, another joint member of the joint <NUM> is an interface flange <NUM>. The interface flange <NUM> is an annular body or ring that extends axially between, and engages, both the TSC flange <NUM> and the generator case flange <NUM>. In so doing, the interface flange <NUM> forms a thermal and structural link between the TSC flange <NUM> and the generator case flange <NUM>, and further strengthens the joint <NUM>. The joint <NUM> in the depicted embodiment includes three flanges <NUM>,<NUM>,<NUM>. Referring to <FIG>, the interface flange <NUM> is separate from both the TSC flange <NUM> and the generator case flange <NUM>. In an alternate embodiment, and as described in greater detail below, the interface flange <NUM> is integral with the generator case flange <NUM>.

Referring to <FIG>, the interface flange <NUM> extends substantially axially between a first end 58A that is engaged with the generator case flange <NUM>, and a second end 58B that is engaged with the TSC flange <NUM>. The first end 58A has a radially-extending portion 58AR that extends radially inwardly to a first end face 58AF that is engaged with a radially-outer face of the center portion 48C of the generator case flange <NUM>. The second end 58B has a second end face 58BF that is engaged with the inner arm 38CI of the center portion 38C of the TSC flange <NUM>. The first end face 58AF is disposed radially inwardly of the second end face 58BF. The second end 58B of the interface flange <NUM> is spaced radially inwardly from the hot outer portion 38B of the TSC flange <NUM>, and is further thermally isolated from the hot outer portion 38B by the "hairpin" structure of the center portion 38C. The "hairpin" in the structural support TSC flange <NUM> helps the interface flange <NUM> to thermally insulate the generator case <NUM>.

The engagement of the interface flange <NUM> with the TSC flange <NUM> and with the generator case flange <NUM> may take different forms. For example, and referring to <FIG>, the interface flange <NUM> is in press fit, or interference fit, with the TSC flange <NUM> and the generator case flange <NUM>. The first and second end faces 58AF,58BF of the interface flange <NUM> are in a tight tolerance fit with the TSC flange <NUM> and with the generator case flange <NUM>. Referring to <FIG>, this interference fit is caused by the interference flange <NUM> being an annular body or ring which is disposed radially outwardly of both the generator case flange <NUM> and of the TSC flange <NUM> relative to the longitudinal axis <NUM>. The interface flange <NUM> is an annular body that radially overlaps part of the generator case flange <NUM> and part of the TSC flange <NUM>. Referring to <FIG>, the interface flange <NUM> is a continuous annular body, forming a single-piece ring. In an alternate embodiment, the interface flange <NUM> is composed of circumferentially separate and interconnected segments.

This radial positioning and tight fit of the interface flange <NUM> allows it to exert a radially inward force or pressure on part of the TSC flange <NUM> and upon part of the generator case flange <NUM>. The radial inward compressive force helps to locate the bolt face 38AS of the TSC flange <NUM> with the bolt face 48CS of the generator case flange <NUM>, and thus helps to counter vibrations or other movements which might cause the bolt faces 38AS,48CS to become misaligned during thermal expansion of one or both of the TSC flange <NUM> and of the generator case flange <NUM> when the engine <NUM> is operating. In an embodiment, the radial inward force exerted by the interface flange <NUM> is exerted when the interface flange <NUM> undergoes thermal expansion while the engine <NUM> is operating.

In an embodiment, and referring to <FIG>, the second end 58B of the interface flange <NUM> is fixedly attached to the TSC flange <NUM>. In the depicted embodiment, a rivet <NUM> is driven through the second end 58B and into the inner arm 38CI of the center portion 38C of the TSC flange <NUM>. Other techniques for fixedly attaching the interface flange <NUM> to the TSC flange <NUM> are possible, such as pinning or brazing. In such an embodiment, the radial inward force exerted by the interface flange <NUM> is applied against part of the generator case flange <NUM>, such as against the center portion 48C. The interface flange <NUM> and the generator case flange <NUM> are thus free of mechanical interconnection, the two flanges <NUM>,<NUM> only being linked to one another through a compressive friction fit. In such an embodiment, the part of the interface flange <NUM> which engages the generator case flange <NUM> may be referred to as a "spigot" that forms an interference fit with the generator case flange <NUM> when the interface flange <NUM> undergoes thermal expansion during operation of the engine <NUM>. The compressive radial force exerted by the interface flange may help to locate the generator <NUM> by centering the generator case flange <NUM> with the TSC flange <NUM>.

Different shapes and/or configurations for the interface flange <NUM> are possible which still allow it to achieve the functionality ascribed to it herein. For example, and referring to <FIG>, the interface flange <NUM> is a curved annular body or ring extending from a first end 158A engaged with a radially-outer face of the center portion 48C of the generator case flange <NUM>, to a second end 158B spaced axially apart from the first end 158A. The second end 158B has a second end face 158BF that is engaged with the inner arm 38CI of the center portion 38C of the TSC flange <NUM>. In another possible configuration, and referring to <FIG>, the interface flange <NUM> is a radially-extending annular body or ring extending from a first end 258A engaged with a radially-outer face of the center portion 48C of the generator case flange <NUM>, to a second end 258B spaced axially and radially apart from the first end 258A. The second end 258B has a second end face 258BF that is engaged with the outer arm 38CO of the center portion 38C of the TSC flange <NUM>. In another possible configuration, and referring to <FIG>, the interface flange <NUM> is an axially and radially extending annular body or ring extending from a first end 358A engaged with a radially-outer face of the center portion 48C of the generator case flange <NUM>, to a second end 358B spaced axially apart from the first end 358A. The second end 358B has a second end face 358BF that is engaged with the end 38CE of the center portion 38C of the TSC flange <NUM>.

In another possible configuration, the interface flange <NUM>,<NUM>,<NUM>,<NUM> is integral with the generator case flange <NUM>, and extends substantially axially from the center portion 48C of the generator case flange <NUM> to the second end 58B,158B,258B,358B. The interface flange <NUM>,<NUM>,<NUM>,<NUM> may be integral with the generator case flange <NUM> in an embodiment where the interface flange <NUM>,<NUM>,<NUM>,<NUM> is composed of the same first material of the generator case flange <NUM>. In one such possible configuration, the first metal of the generator case flange <NUM> is Titanium, and the interface flange <NUM>,<NUM>,<NUM>,<NUM> is also composed of Titanium in the same concentrations as in the first metal. The second metal of the TSC flange is Inconel™ <NUM>, and is thus different from the first metal and from the metal of the interface flange <NUM>,<NUM>,<NUM>,<NUM>. Making the "spigot" material of the interface flange <NUM>,<NUM>,<NUM>,<NUM> to be the same as that of the generator case flange <NUM> (e.g. Titanium) may allow for the Titanium spigot to grow tight with the Inconel™ <NUM> of the TSC flange <NUM> and exert the radial or compressive pressure for centering the bolt faces 38AS,48CS. Other pairings of the first and second metals of the bimetallic joint <NUM> configuration are possible. For example, the first metal of the generator case flange <NUM> is Aluminum, and the interface flange <NUM>,<NUM>,<NUM>,<NUM> is also composed of Aluminum in the same concentrations as in the first metal, whereas the second metal of the TSC flange <NUM> is Inconel™ <NUM>. In another possible configuration of the bimetallic joint <NUM>, the interface flange <NUM>,<NUM>,<NUM>,<NUM> is composed of a metal that is different from the first metal of the generator case flange <NUM>. For example, the interface flange <NUM>,<NUM>,<NUM>,<NUM> may be composed of Invar (FeNi36 or 64FeNi) metal and the first metal of the generator case flange <NUM> is Titanium or Aluminum. In another possible configuration, the interface flange <NUM>,<NUM>,<NUM>,<NUM> is integral with the TSC flange <NUM>, and extends substantially axially from the inner arm 38CI of the TSC flange <NUM> to the first end 58A. The interface flange <NUM>,<NUM>,<NUM>,<NUM> may be integral with the TSC flange <NUM> in an embodiment where the interface flange <NUM>,<NUM>,<NUM>,<NUM> is composed of a metal that is different from the second metal of the TSC flange <NUM>.

Referring to <FIG>, the interface flange <NUM>,<NUM>,<NUM>,<NUM> defines a third coefficient of thermal expansion that is equal to or less than the first coefficient of thermal expansion of the generator case flange <NUM>. The third coefficient of thermal expansion of the interface flange <NUM>,<NUM>,<NUM>,<NUM> is also less than the second coefficient of thermal expansion of the TSC flange <NUM>. The interface flange <NUM>,<NUM>,<NUM>,<NUM> will thus undergo the same or less thermal expansion as the generator case flange <NUM> during operation of the engine <NUM>. The interface flange <NUM>,<NUM>,<NUM>,<NUM> will thus undergo less thermal expansion than the TSC flange <NUM> during operation of the engine <NUM>. In an embodiment, the first coefficient of thermal expansion of the generator case flange <NUM> is less than the second coefficient of thermal expansion of the TSC flange <NUM>, such that the generator case flange <NUM> will undergo less thermal expansion than the TSC flange <NUM> during operation of the engine <NUM>. The third coefficient of thermal expansion of the interface flange <NUM>,<NUM>,<NUM>,<NUM> is thus similar to that, or less than that, of the cooler second joint member (i.e. the generator case flange <NUM>) and less than that of the hotter first joint member (i.e. the TSC flange <NUM>). In an embodiment, the third coefficient of thermal expansion of the interface flange <NUM>,<NUM>,<NUM>,<NUM> is the same as the second coefficient of thermal expansion of the generator case flange <NUM>, such that the interface flange <NUM>,<NUM>,<NUM>,<NUM> matches the generator case flange <NUM> on thermal expansion, and allows the flanges <NUM>,<NUM>,<NUM>,<NUM>,<NUM> to expand thermally together. In such an embodiment, the third coefficient of thermal expansion of the interface flange <NUM>,<NUM>,<NUM>,<NUM> is the same as the second coefficient of thermal expansion of the generator case flange <NUM> because the interface flange <NUM>,<NUM>,<NUM>,<NUM> and the generator case flange <NUM> are composed of the same first material.

The interface flange <NUM>,<NUM>,<NUM>,<NUM> may thus help to achieve two functions: <NUM>) to alleviate the thermal mismatch between the structural TSC flange <NUM> and the generator case flange <NUM> during operation of the engine <NUM>, and <NUM>) to exert a radially inward pressure or compression when the interface flange <NUM>,<NUM>,<NUM>,<NUM> expands thermally in order to help locate the face 38CS of the structural TSC flange <NUM> where the bolt <NUM> is. Such a bi-material flange joint <NUM> allows for maintaining a tight fit between the joint members while also being able to endure high temperature deltas at different areas in the joint <NUM>. For example, during operation of the engine <NUM>, there may be an important thermal mismatch between the TSC flange <NUM> and the generator case flange <NUM> which may cause thermal stresses. By thermally matching the spigot material of the interface flange <NUM>,<NUM>,<NUM>,<NUM> to the material of the generator case flange <NUM>, the interface flange <NUM>,<NUM>,<NUM>,<NUM> may be able to grow tight with the structural TSC flange <NUM> during engine operation and minimize the growth at the spigot area of the interface flange <NUM>,<NUM>,<NUM>,<NUM> allowing a tight fit to be maintained through the running range of the engine <NUM>. By maintaining a tight interference fit with the interface flange <NUM>,<NUM>,<NUM>,<NUM>, it may be possible to eliminate vibration that may result from thermal expansion of the TSC flange <NUM>. Maintaining a tight fit at all running conditions may help to prevent engine unscheduled removal and unplanned maintenance caused by premature wear at the mechanical interfaces of the joint <NUM>, and/or may prevent dynamic/vibrations issues for the mated components.

During operation of the engine <NUM>, the temperature varies throughout the joint <NUM>. In most instances, the joint <NUM> is hottest at the TSC flange <NUM> and coolest at the generator case flange <NUM>. The temperature may also vary throughout the interface flange <NUM>,<NUM>,<NUM>,<NUM>. The interface flange <NUM>,<NUM>,<NUM>,<NUM> may experience a thermal gradient during operation of the engine <NUM> between its axially spaced-apart first and second ends 58A,58B,158A,158B,258A,258B,358A,358B. The interface flange <NUM>,<NUM>,<NUM>,<NUM> may have a first temperature that is substantially equal to a temperature of the generator case flange <NUM> at a location where the interface flange <NUM>,<NUM>,<NUM>,<NUM> engages the generator case flange <NUM>, for example in the configuration where the interface flange <NUM>,<NUM>,<NUM>,<NUM> and the generator case flange <NUM> have the same or similar coefficients of thermal expansion. The interface flange <NUM>,<NUM>,<NUM>,<NUM> may have a second temperature at a location where the interface flange <NUM>,<NUM>,<NUM>,<NUM> engages the TSC flange <NUM> that is greater than the first temperature. Thus, during operation of the engine <NUM>, there may be a temperature variation throughout the interface flange <NUM>,<NUM>,<NUM>,<NUM>, where part of the spigot in contact with generator case flange <NUM> has the same or similar temperature as the generator case flange <NUM>, and the temperature gradually increases along an axial direction through the interface flange <NUM>,<NUM>,<NUM>,<NUM> toward the second end 58B, 158B,258B,358B thereof to achieve approximately the same temperature as the TSC flange <NUM>. This may create thermal stress in the interface flange <NUM>,<NUM>,<NUM>,<NUM> over time, but this may not be consequential because the interface flange <NUM>,<NUM>,<NUM>,<NUM> is an engine component that may be easily replaced. Alternatively, any thermal stress in the interface flange <NUM>,<NUM>,<NUM>,<NUM> may be reduced due to the length of the interface flange <NUM>,<NUM>,<NUM>,<NUM> which may allow the temperature gradient to be distributed over a longer distance.

Referring to <FIG>, the bi-material joint <NUM> is a flange structure in hot sections of the engine <NUM> or other power plants. The flange structure consists of a structural flange (i.e. the TSC flange <NUM>) that is exposed to high temperatures during operation of the engine <NUM>, and which is mounted to a generator case <NUM> which experiences and operates at much lower temperatures. The structural TSC flange <NUM> is made from a different material (e.g. Inconel™ <NUM>) than the material (e.g. Titanium) of the generator case <NUM>, such that the structural TSC flange <NUM> has a different coefficient of thermal expansion than the coefficient of thermal expansion of the generator case <NUM>. The bi-material joint <NUM> also has a "bridging" flange (i.e. the interface flange <NUM>,<NUM>,<NUM>,<NUM>) that extends between the generator case <NUM> and the TSC flange <NUM>. The bridging interface flange <NUM>,<NUM>,<NUM>,<NUM> is made of a material that may be the same as the first material of the generator case <NUM>, such that the coefficient of thermal expansion of the interface flange <NUM>,<NUM>,<NUM>,<NUM> is the same as, or less than, the coefficient of thermal expansion of the generator case <NUM>. In an embodiment, the interface flange <NUM>,<NUM>,<NUM>,<NUM> is a ring which exerts a radially-inward pressure on the generator case flange <NUM> to help locate the generator case <NUM> relative to the TSC flange <NUM>.

In light of the preceding, there is disclosed herein a flange arrangement in hot sections of an engine or other power plants which connects a hot structural flange to a cooler component, where the flange arrangement has a mechanical interface structure that extends between the hot structural flange and the cooler component, and where the interface structure has a coefficient of thermal expansion that is similar to that of the cooler material and less than that of the hotter material.

There is disclosed a method of assembling a bi-material joint <NUM>. The method comprises assembling a first flange <NUM> composed of a first material and having a first coefficient of thermal expansion to a second flange <NUM> composed of a second material and having a second coefficient of thermal expansion. The method comprises engaging an interface flange <NUM>,<NUM>,<NUM>,<NUM> to both of the first and second flanges <NUM>,<NUM> and interference fitting the interface flange <NUM>,<NUM>,<NUM>,<NUM> to at least the first flange <NUM>. The interface flange <NUM>,<NUM>,<NUM>,<NUM> has a third coefficient of thermal expansion that is less than or equal to the first coefficient of thermal expansion, and less than the second coefficient of thermal expansion. The method comprises securing the first flange <NUM> to the second flange <NUM> to form the bi-material joint <NUM>. The method may include brazing or pinning the interface flange <NUM>,<NUM>,<NUM>,<NUM> to the second flange <NUM>. The method may include machining the interface flange <NUM>,<NUM>,<NUM>,<NUM> as a single piece. Machining the interface flange <NUM>,<NUM>,<NUM>,<NUM> as one piece may help to minimize tolerance stackup and maintain the same tolerance as the single piece second flange <NUM> while allowing greater thermal differential to be tolerated. The method may include replacing or repairing the interface flange <NUM>,<NUM>,<NUM>,<NUM>.

The expression "substantially axially" used herein refers to a directional vector of a component described herein, where the magnitude of the directional vector in the axial direction relative to the longitudinal axis <NUM> is greater than the magnitude of the directional vector in the radial direction relative to the longitudinal axis <NUM>. The expression "substantially radially" used herein refers to a directional vector of a component described herein, where the magnitude of the directional vector in the radial direction relative to the longitudinal axis <NUM> is greater than the magnitude of the directional vector in the axis direction relative to the longitudinal axis <NUM>.

Claim 1:
An aircraft gas turbine engine (<NUM>), comprising:
an exhaust cone (<NUM>) defining a center axis (<NUM>) and an internal cavity (29C);
a generator case (<NUM>) within the internal cavity (29C) of the exhaust cone (<NUM>), the generator case (<NUM>) having a generator case flange (<NUM>) composed of a first material defining a first coefficient of thermal expansion;
a turbine support case (TSC) (<NUM>) having a TSC flange (<NUM>); and
a joint (<NUM>) between the TSC (<NUM>) and the generator case (<NUM>), the generator case flange (<NUM>) secured to the TSC flange (<NUM>) at the joint (<NUM>);
characterised in that
the TSC flange (<NUM>) is composed of a second material defining a second coefficient of thermal expansion, the second material being different from the first material;
the joint (<NUM>) comprising an interface flange (<NUM>; <NUM>; <NUM>; <NUM>) engaged with the generator case flange (<NUM>) and with the TSC flange (<NUM>), the interface flange (<NUM>...<NUM>) defining a third coefficient of thermal expansion being equal to or less than the first coefficient of thermal expansion, the third coefficient of thermal expansion being less than the second coefficient of thermal expansion; and
the interface flange (<NUM>...<NUM>) is disposed radially outwardly of the generator case flange (<NUM>) and of the TSC flange (<NUM>) relative to the center axis (<NUM>), the interface flange (<NUM>...<NUM>) exerting a radially inward force on part of the TSC flange (<NUM>) and upon the interface flange (<NUM>...<NUM>) and one or both of the TSC flange (<NUM>) and the generator case flange (<NUM>) undergoing thermal expansion.