Patent Publication Number: US-2023136870-A1

Title: Connecting arrangement between components of an aircraft engine

Description:
TECHNICAL FIELD 
     The application relates generally to aircraft engines and, more particularly, to systems and methods used to secure together different components of such engines. 
     BACKGROUND OF THE ART 
     In an aircraft engine, some components are secured to one another via mating sections. However, in use, the aircraft engine is subjected to temperatures variations that may induce thermal growth of these mating sections. Because the sections may be made of different material, the thermal growth may vary between them. This may affect how these components are secured together. Hence, improvements are sought. 
     SUMMARY 
     In accordance with a general aspect of the disclosure, there is provided an aircraft engine, comprising: a casing extending circumferentially around a central axis; a support flange secured to the casing and extending circumferentially around the central axis, the support flange having an inner flange face facing the central axis and an outer flange face facing away from the central axis, the support flange including a first material; a component drivingly engaged by a shaft of the aircraft engine, the component having a connecting section extending around the central axis, the connecting section having a connecting face facing away from the central axis, the inner flange face in abutment against the connecting face; and a retaining ring extending circumferentially around the central axis, the retaining ring in abutment against the outer flange face of the support flange, the retaining ring including a second material having a coefficient of thermal expansion being less than that of the first material of the support flange. 
     In accordance with another general aspect, there is provided a connecting system for connecting a component to a casing of an aircraft engine, comprising: a support flange secured to the casing, the support flange extending circumferentially around an axis, the support flange having an inner flange face facing the axis and an outer flange face facing away from the axis, the support flange including a first material, the inner flange face in abutment against a connecting section of the component; and a retaining ring extending circumferentially around the axis, the retaining ring in abutment against the outer flange face of the support flange, the retaining ring including a second material having a coefficient of thermal expansion being less than that of the first material of the support flange such that thermal expansion of the support flange is impeded by the retaining ring. 
     In accordance with another aspect, there is provided method of mounting a component to a casing of a aircraft engine, comprising: engaging a connecting section of the component to a support flange secured to the casing, the support flange including a first material; and disposing a retaining ring around the support flange and in abutment against the support flange to sandwich the support flange between the connecting section and the retaining ring, the retaining ring including a second material having coefficient of thermal expansion being less than that of the first material. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG.  1    is a schematic cross-sectional view of an aircraft engine depicted as a gas turbine engine; 
         FIG.  2    is a schematic cross-sectional view of a portion of the gas turbine engine of  FIG.  1   ; 
         FIG.  3    is an enlarged view of a portion of  FIG.  2   ; 
         FIG.  4 A  is an enlarged view of a portion of  FIG.  3    illustrating a retaining ring and a support flange in a first relative position when the gas turbine engine is powered off; 
         FIG.  4 B  is an enlarged view of the portion of  FIG.  3    illustrating the retaining ring and the support flange in a second relative position when the gas turbine engine is running; and 
         FIG.  5    is a flowchart illustrating steps of mounting a component to a casing of the engine of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates an aircraft engine depicted as a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a compressor section  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. The fan  12 , the compressor section  14 , and the turbine section  18  are rotatable about a central axis  11  of the gas turbine engine  10 . 
     In the embodiment shown, the gas turbine engine  10  comprises a high-pressure spool having a high-pressure shaft  20  drivingly engaging a high-pressure turbine  18 A of the turbine section  18  to a high-pressure compressor  14 A of the compressor section  14 , and a low-pressure spool having a low-pressure shaft  21  drivingly engaging a low-pressure turbine  18 B of the turbine section to a low-pressure compressor  14 B of the compressor section  14  and drivingly engaged to the fan  12 . It will be understood that the contents of the present disclosure may be applicable to any suitable engines, such as turboprops and turboshafts, and reciprocating engines, such as piston and rotary engines without departing from the scope of the present disclosure. 
     Another component  22 , such as an accessory, herein a generator, is drivingly engaged by the low-pressure shaft  21  via a connecting arrangement or connecting system  30 , which will be described further below. The component  22  may be an accessory, such as a pump, an electrical motor, and so on. The component  22  may be located within a tail cone  23  of the gas turbine engine  10 . 
     Referring to  FIGS.  2 - 3   , a portion of the gas turbine engine  10  proximate the tail cone  23  and illustrating the connecting system  30  is shown. The gas turbine engine  10  includes an inner casing  24  defining a flange  24 A. The flange  24 A may be located axially between a vane  18 C of the turbine section  18  and a support strut  25  that extends radially outwardly from the tail cone  23  and that is connected at its outer end to an outer casing  26  ( FIG.  1   ) of the gas turbine engine  10 . The connecting system  30  includes a support flange  31  that is mounted (e.g., fastened, welded, etc) to the flange  24 A of the inner casing  24 . In some embodiments, the support flange  31  may be monolithic with the inner casing  24 . In the embodiment shown, the component  22  as a connecting section  22 A. The connecting section  22 A is sized to be secured to the support flange  31 . In the present embodiment, the connecting section  22 A defines a substantially cylindrical face  22 B and the support flange  31  defines a substantially cylindrical recess that is sized to receive the connecting section  22 A of the component  22 . A spigot fit may therefore be created between the connecting section  22 A and the support flange  31 . Hence, to assemble the component  22  to the support flange  31 , the connecting section  22 A is inserted in an axial direction relative to the central axis  11  in the recess. An annular web  33  extend substantially transversely from a distal end of the support flange  31  toward the central axis  11 . The connecting section  22 A may be bolted or fastened in any suitable way to the annular web  33 . The annular web  33  and the connecting section  22 A may define registering apertures circumferentially distributed about the central axis  11  for receiving suitable fasteners. 
     Referring more particularly to  FIG.  3   , the support flange  31  may extend circumferentially all around the central axis  11 . The support flange  31  as an inner flange face  31 A that faces the central axis  11  and an outer flange face  31 B that faces away from the central axis  11 . The support flange  31  includes a first material, which may be INCONEL 718™. As shown in  FIG.  3   , the connecting section  22 A of the component  22  is secured to the support flange  31 . In the depicted embodiment, the connecting section  22 A is in abutment against the inner flange face  31 A of the support flange  31 . A tight fit engagement or compression fit may be provided between the connecting section  22 A of the component  22  and the support flange  31 . 
     In use, the temperature inside the gas turbine engine  10  may be such that the different components increase in dimension with heat. In the present case, the coefficient of thermal expansion of the support flange  31  may be greater than that of the connecting section of the component  22 . Therefore, the engagement between the support flange  31  and the component  22  may become loose when the gas turbine engine  10  is at operational temperatures because the diameter of the support flange  31  may increase more than a diameter of the connecting section  22 A of the component  22 . 
     Still referring to  FIG.  3   , in the present embodiment, a retaining ring  32  is mounted to the support flange  31 . More specifically, the retaining ring  32  may be in abutment against the outer flange face  31 B of the support flange  31 . The retaining ring  32  may extend circumferentially all around the central axis  11 . According to at least one embodiment, the retaining ring  32  is configured to have an interference fit with the support flange  31 . In some embodiments, the retaining ring  32  may include a plurality of ring sections circumferentially distributed around the central axis  11  and secured to one another. The retaining ring  32  may include a second material that has a coefficient of thermal expansion that is less than that of the first material of the support flange  31 . The second material may include, for instance, titanium. Therefore, in use when the support flange  31  increases in diameter because of thermal expansion it is restrained by the retaining ring  32  that also increases because of thermal expansion, but less then the support flange  31  because of the differences in their coefficients of thermal expansion. Consequently, during an increase of temperature inside the gas turbine engine  10 , the support flange  31  may remain securely connected to the connecting section  22 A of the component  22  thanks to the retaining ring  32  that maintains proper engagement between the support flange  31  and component  22 . Stated differently, thermal expansion of the support flange  31  may be impeded by the retaining ring  32 . 
     In some embodiments, it was observed that repeated cycles of heating and cooling cycles with starting and shutting down the gas turbine engine  10  resulted in the retaining ring  32  moving axially relative to the central axis  11  and relative to the support flange  31 . In some cases, this resulted in the retaining ring slipping off the support flange  31 . As will be explained below, the present connecting system  30  as features that may limit the situation from arising. 
     Still referring to  FIG.  3   , in the present embodiment, the outer flange face  31 B defines a flange recess  31 C and the retaining ring  32  defines a ring protrusion  32 A that extends toward the central axis  11 . The ring protrusion  32 A is at least partially received within the flange recess  31 C. The retaining ring  32  may therefore be axially locked relative to the support flange  31  by the engagement of the ring protrusion  32 A inside the flange recess  31 C. The retaining ring  32  may also define a ring recess  32 B that partially receives a flange protrusion  31 D defined by the outer flange face  31 B of the support flange  31 . An axial width of the ring recess  32 B of the retaining ring  32  is greater than an axial width of the flange protrusion  31 D of the support flange  31 . 
     Referring now to  FIG.  4 A , the flange recess  31 C is bounded on a first axial side by a sloped recess face  31 E. The sloped recess face  31 E extends radially outwardly and axially from a bottom face  31 F of the flange recess  31 C. The ring protrusion  32 A defines a sloped protrusion face  32 C that extends radially outwardly and axially from an end face  32 D of the ring protrusion  32 A. The sloped protrusion face  32 C is in abutment against the sloped recess face  31 E. 
     Referring to  FIGS.  4 A- 4 B , the support flange  31  is movable in a radial direction relative to the central axis  11  toward the retaining ring  32  between a first position depicted in  FIG.  4 A  to a second position depicted in  FIG.  4 B . The first position corresponds to a state in which the gas turbine engine  10  is powered off and at a temperature corresponding to that of an environment in which the gas turbine engine  10  is located and the second position corresponds to a state in which the gas turbine engine  10  is powered on and at steady-state operational temperatures. The temperature of the retaining ring  32  and support flange  31  in the first position of  FIG.  4 A  may be about 70 degrees Fahrenheit, whereas, in the second position of  FIG.  4 B , the temperature of the retaining ring  32  and support flange  31  may be about 350 degrees Fahrenheit. A radial distance relative to the central axis  11  between the end face  32 D of the ring protrusion  32 A and the bottom face  31 F of the flange recess  31 C is less in the second position of  FIG.  4 B  then it is in the first position of  FIG.  4 A . In other words, the ring protrusion  32 A extends deeper inside the flange recess  31 C in the second position than in the first position. 
     Because both of the sloped recess face  31 E and the sloped protrusion face  32 C are substantially parallel to one another and angled relative to the central axis  11 , radial movements between the retaining ring  32  and a support flange  31  translates into an axial movement along the central axis  11  between the retaining ring  32  and a support flange  31 . More specifically, and in the embodiment shown, upon the retaining ring  32  and the support flange  31  increasing in their respective diameters because of the thermal expansion along directions depicted by arrows A 1  on  FIG.  4 B , the retaining ring  32  moves axially along a direction depicted by arrow A 2  until it abuts a shoulder  31 G defined by the support flange  31  on a second axial side of the flange recess  31 C and that is facing the retaining ring  32 . The shoulder  31 G may extend substantially perpendicularly from the outer flange face  31 B of this support flange  31 . In operating temperatures, the retaining ring  32  may be biased against the shoulder  31 G by the engagement of the two sloped faces  31 E,  32 C. 
     Therefore, at each cooling and heating cycle, engagement of the two slope faces  32 C,  31 E pushes the retaining ring  32  toward the shoulder  31 G and realigns the ring protrusion  32 A with the flange recess  31 C. Consequently, the retaining ring  32  may remain properly engaged to the support flange  31  regardless of the number of cooling and heating cycles the gas turbine engine  10  is subjected to. In other words, the ramp between the parts may cause the retaining ring  32  to be seated during every thermal cycle. The retaining ring  32  may be installed by thermal differential between the support flange  31  and retaining ring  32 . The normalization of temperatures may produce an interlock as explain above. In the present embodiment, the retaining ring  32  may remain engaged to the support flange  31  without any fasteners. In other words, engagement of the retaining ring  32  to the support flange  31  may be free of fasteners. 
     Referring now to  FIG.  5   , a method of mounting the component  22  to the inner casing  24  of the gas turbine engine  10  is shown at  500 . The method  500  includes engaging the connecting section  22 A of the component  22  to the support flange  31 , which is secured to the inner casing  24 , at  502 . As previously explained, the support flange  31  includes a first material. Then, the method  500  includes disposing the retaining ring  32  around the support flange  31  and in abutment against the support flange  31  to sandwich the support flange  31  between the connecting section  22 A and the retaining ring  32 , at  504 . As previously explained, the retaining ring  32  includes a second material that has a coefficient of thermal expansion that is less than that of the first material. 
     In the embodiment shown, the disposing of the retaining ring  32  around the support flange  31  includes inserting the ring protrusion  32 A of the retaining ring  32  inside the flange recess  31 C of the support flange  31 . In the present embodiment, the method  500  includes putting the two sloped faces  32 C,  31 E against one another such that thermal expansion of the support flange  31  in the radial direction relative to the central axis  11  induces an axial movement of the retaining ring  32  relative to the support flange  31 . 
     According to at least some embodiments would like but the ring  32  is designed to have an interference fit with the support flange  31 . At assembly, the support flange  31  will be cooled so the ring  32  can be easily pressed on and locked into place when it reaches normal temperatures. The thickness of the ring  32  will be balanced against the thickness of the flange  31  to produce an expansion rate at the spigot fit to match the mating component (e.g. the generator). 
     According to at least some embodiments, the geometry defined by the contact diameters between the support flange and the retaining ring, the relative thickness of the flange spigot and retaining ring, the relative expansion coefficient between the two materials of the support flange and the retaining ring, and the Young modulus of the two materials are all selected in combination relative to the characteristics of the operating envelope of the support flange such that thermal expansion of the support flange is impeded by the retaining ring. 
     The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.