Patent Publication Number: US-11035254-B2

Title: Sheet metal turbine housing with cast core

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/419,472, filed Jan. 30, 2017. 
     The subject matter described here is related to the subject matter described in U.S. patent application Ser. No. 15/419,320, issued as U.S. Pat. No. 10,472,988, U.S. patent application Ser. No. 15/419,381, issued as U.S. Pat. No. 10,436,069, and U.S. patent application Ser. No. 15/419,429, issued as U.S. Pat. No. 10,494,955, all filed Jan. 30, 2017. 
    
    
     TECHNICAL FIELD 
     The subject matter described herein relates generally to flow control systems, and more particularly, to turbine housings for use in turbocharger systems. 
     BACKGROUND 
     Turbocharger systems are frequently used to improve the efficiency of internal combustion engines. Two-stage turbocharger systems can be used to further improve the engine efficiency over a single-stage turbocharger system including a single turbine and a single compressor. While use of two-stage turbocharger systems may be desirable in automotive vehicles, for example, to achieve fuel economy targets or other environmental goals, the combination of the added financial cost in conjunction with the size, packaging, assembly, or installation constraints may be prohibitive. Additionally, introducing turbines into the exhaust gas flow can reduce the temperature of the exhaust gas and may reduce the effectiveness of downstream emissions control devices, such as a catalytic converter. Accordingly, it is desirable to provide a turbine housing having lower thermal inertia while also achieving other performance objectives and maintaining structural integrity. 
     BRIEF SUMMARY 
     Turbine assemblies and related turbocharger systems having direct turbine interfaces are provided. An exemplary turbine assembly includes a bypass valve assembly structure including a guide portion, an inner sheet metal shell including an inner inlet portion and a volute portion providing an outer contour of a volute, wherein an end of the inner inlet portion is surrounded by the guide portion and spaced apart from the bypass valve assembly structure, and an outer sheet metal shell radially surrounding at least a portion of the volute portion and including an outer inlet portion surrounding the inner inlet portion and contacting the guide portion of the bypass valve assembly. 
     In another embodiment, turbine housing assembly includes a cast metal structure having an inlet opening and a bypass opening transverse to the inlet opening, an inner sheet metal shell including an inner base portion having an end disposed within the inlet opening and a volute portion that defines an outer contour of a volute, and an outer sheet metal shell that surrounds the volute portion and includes an outer base portion that circumscribes the inner base portion, wherein the outer base portion is joined to the cast metal structure and the end of the inner base portion is freestanding with respect to the cast metal structure. 
     In yet another embodiment, a turbine housing assembly includes a cast bypass valve assembly structure including a guide portion about an inlet opening and a bypass opening transverse to the inlet opening, an inner sheet metal shell including an inner inlet portion and a volute portion that defines an outer contour of a volute, wherein an end of the inner inlet portion is disposed within the inlet opening and surrounded by the guide portion, and an outer sheet metal shell that surrounds the volute portion and includes an outer inlet portion circumscribing the inner inlet portion and contacting the guide portion of the bypass valve assembly, wherein the outer inlet portion is joined to the cast bypass valve assembly structure and the end of the inner inlet portion is freestanding with respect to the cast bypass valve assembly structure. 
     Another embodiment of a turbine housing assembly includes an inner shell having an inner base portion defining an inlet and a volute portion defining an outer contour of a volute in fluid communication with the inlet. The turbine housing assembly also includes an outer shell circumscribing the volute portion in a radial plane and including an outer base portion circumscribing the inner base portion, wherein the inner shell comprises a first plurality of sheet metal structures joined to one another in the radial plane, the outer shell comprises a second plurality of sheet metal structures, and first portions of the second plurality of sheet metal structures surrounding the volute portion are joined to one another in an axial plane transverse to the radial plane. 
     In another embodiment, a turbine housing assembly includes an inner shell comprising a first plurality of sheet metal structures joined to one another at a first seam in a radial plane and an outer shell comprising a second plurality of sheet metal structures joined to one another at a second seam in an axial plane transverse to the radial plane. The inner shell includes a volute portion defining an outer contour of a volute in the radial plane, the outer shell substantially surrounds the volute portion and encloses the volute portion in an axial direction, and an outer base portion of the outer shell circumscribes an inner base portion of the inner shell that defines an inlet in fluid communication with the volute. 
     In yet another embodiment, a turbine housing assembly includes an inner sheet metal shell comprising a first pair of sheet metal structures coupled together along a radial plane orthogonal to a turbine wheel rotational axis and an outer sheet shell comprising a second pair of sheet metal structures coupled together along a first plane transverse to the radial plane. Each of the first pair of sheet metal structures includes a volute portion defining an outer contour of a volute in the radial plane and a base portion defining an inlet in fluid communication with the volute, and each of the second pair of sheet metal structures includes an arcuate portion radially overlapping at least a portion of the volute portions in the radial plane and an outer base portion radially overlapping at least a portion of the base portions in a second plane transverse to the radial plane. 
     Another embodiment of a turbine housing assembly includes an inner shell defining an inner inlet portion and a volute portion providing an outer contour of a volute, the inner shell comprising a first plurality of sheet metal structures coupled together in a first plane, an outer shell surrounding the volute portion and defining an outer inlet portion circumscribing the inner inlet portion, the outer shell comprising a second plurality of sheet metal structures coupled together in a second plane transverse to the first plane, and one or more energy absorbing members coupled to an inner surface of the outer shell between the outer shell and the inner shell. 
     In another embodiment, a turbine housing assembly includes an inner shell comprising a first pair of sheet metal structures joined to one another at a first joint in a radial plane, an outer shell comprising a second pair of sheet metal structures joined to one another about the inner shell at a second joint in an axial plane transverse to the radial plane, the second pair of sheet metal surfaces each having an inner surface, and a pair of energy absorbing members on a respective one of the inner surfaces of the second pair of sheet metal structures, wherein the pair of energy absorbing members are disposed proximate an interface between the second pair of sheet metal structures. 
     In yet another embodiment, a turbine housing assembly includes a thinner inner sheet metal shell comprising a first pair of sheet metal structures interfacing and joined to one another in a radial plane orthogonal to a turbine wheel rotational axis, and a thicker outer sheet shell comprising a second pair of sheet metal structures interfacing and joined to one another in a first plane transverse to the radial plane, and a third pair of arcuate sheet metal structures, wherein each of the first pair of sheet metal structures includes a volute portion defining an outer contour of a volute in the radial plane and a base portion defining an inlet in fluid communication with the volute, each of the second pair of sheet metal structures includes an arcuate portion radially overlapping at least a portion of the volute portions in the radial plane and an outer base portion radially overlapping at least a portion of the base portions in a second plane transverse to the radial plane, and each of the arcuate sheet metal structures is disposed between the volute portions of the first pair of sheet metal structures and the arcuate portion of a respective sheet metal structure of the second pair of sheet metal structures. 
     Another embodiment of a turbine housing assembly includes a core structure having a voided inner region defining an axial outlet and an outer surface defining an inner contour of a volute, an inner sheet metal shell comprising an inner base portion defining an inlet in fluid communication with the volute and a volute portion defining an outer contour of the volute, wherein at least a portion of the core structure defining the axial outlet extends in an axial direction through an opening in the inner sheet metal shell defined by the volute portion, and an outer sheet metal shell surrounding the volute portion and including an outer base portion circumscribing the inner base portion. 
     In another embodiment, a turbine housing assembly includes an inner sheet metal shell comprising a first pair of sheet metal structures joined to one another in a radial plane orthogonal to a turbine wheel rotational axis, wherein each of the first pair of sheet metal structures includes a volute portion defining an outer contour of a volute in the radial plane and an opening for an axial outlet and a base portion defining an inlet in fluid communication with the volute. The turbine housing assembly also includes a core structure disposed within the opening, the core structure having a voided inner region defining the axial outlet and an outer surface defining an inner contour of the volute, and an outer sheet metal shell comprising a second pair of sheet metal structures joined to one another about the inner sheet metal shell in a first plane transverse to the radial plane. 
     In yet another embodiment, a turbine housing assembly includes a cast bypass valve assembly structure including a guide portion about an inlet opening and a bypass opening oblique to the inlet opening, an inner sheet metal shell including an inner inlet portion and a volute portion defining an outer contour of a volute, wherein an end of the inner inlet portion is disposed within the inlet opening and received by the guide portion, a cast core structure disposed within an opening defined by the volute portion of the inner sheet metal shell, the core structure having a surface defining an inner contour of the volute, and an outer sheet metal shell surrounding the volute portion and including an outer inlet portion circumscribing the inner inlet portion and contacting the guide portion of the bypass valve assembly structure, wherein the outer inlet portion is joined to the cast bypass valve assembly structure and the end of the inner inlet portion is freestanding with respect to the cast bypass valve assembly structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the subject matter will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
         FIG. 1  is a schematic illustration of a two-stage turbocharger system in one or more exemplary embodiments; 
         FIG. 2  is a perspective view of an exemplary turbine housing assembly suitable for use in the two-stage turbocharger system of  FIG. 1  in one or more exemplary embodiments; 
         FIGS. 3-4  are plan views of the turbine housing assembly of  FIG. 2 ; 
         FIG. 5  is an exploded perspective view of the turbine arrangement of  FIGS. 2-4 ; 
         FIG. 6  is a cross-sectional view of the turbine arrangement of  FIGS. 2-5 , taken along line  6 - 6  in  FIG. 3 ; 
         FIG. 7  is a partial cross-sectional view of the turbine arrangement of  FIG. 6  taken along the line  7 - 7  in  FIG. 6 ; and 
         FIG. 8  depicts a top view of the bypass valve assembly structure in the turbine arrangement of  FIGS. 2-6  in accordance with one or more exemplary embodiments; and 
         FIG. 9  is an enlarged cross-sectional view of a portion of the turbine arrangement of  FIG. 6  in accordance with one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the subject matter described herein relate to turbocharger systems that include one or more turbine stages having a multilayer sheet metal housing. As described in greater detail below in the context of  FIGS. 2-8 , in exemplary embodiments described herein, the turbine housing includes an inner sheet metal shell that defines at least a portion of the volute for a turbine wheel and an outer sheet metal shell that radially encloses the inner sheet metal shell while also enclosing the inner sheet metal shell in the axial direction opposite the turbine wheel. It should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the present disclosure. In addition, while the figures shown herein depict an example with certain arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. It should also be understood that the drawings are merely illustrative and may not be drawn to scale. 
     As used herein, the term “axial” refers to a direction that is generally parallel to or coincident with an axis of rotation, axis of symmetry, or centerline of a component or components. For example, in a cylinder or disc with a centerline and generally circular ends or opposing faces, the “axial” direction may refer to the direction that generally extends in parallel to the centerline between the opposite ends or faces. In certain instances, the term “axial” may be utilized with respect to components that are not cylindrical (or otherwise radially symmetric). For example, the “axial” direction for a rectangular housing containing a rotating shaft may be viewed as a direction that is generally parallel to or coincident with the rotational axis of the shaft. Furthermore, the term “radially” as used herein may refer to a direction or a relationship of components with respect to a line extending outward from a shared centerline, axis, or similar reference, for example in a plane of a cylinder or disc that is perpendicular to the centerline or axis. In certain instances, components may be viewed as “radially” aligned even though one or both of the components may not be cylindrical (or otherwise radially symmetric). Furthermore, the terms “axial” and “radial” (and any derivatives) may encompass directional relationships that are other than precisely aligned with (e.g., oblique to) the true axial and radial dimensions, provided the relationship is predominately in the respective nominal axial or radial direction. 
     As described in greater detail below, the inner sheet metal shell includes a pair of sheet metal structures that face one another in the axial direction and are substantially circumferentially joined to one another in a radial plane to define the outer portion of the volute. The inner sheet metal shell includes a central opening for receiving a core structure that defines an axial outlet for the turbine. The core structure includes an inner voided region that receives and supports a nose of a turbine wheel that rotates in the radial plane within a central region that is radially circumscribed by the volute. At least a portion of the outer surface of the core structure faces an inner surface of the inner sheet metal shell and is contoured to define the inner portion of the volute opposite the outer portion of the volute defined by the contoured inner surface of the inner sheet metal shell. In other words, the core structure and the inner sheet metal shell cooperatively define the volute for the turbine that radially surrounds the turbine wheel. 
     The outer sheet metal shell includes a second pair of sheet metal structures that face one another in a direction aligned with the radial plane and are joined in an axial plane that is transverse to or otherwise intersects the radial plane in which the inner sheet metal shell is joined. In this regard, the inner and outer sheet metal shells provide a biaxial housing configuration for the volute of the turbine. In exemplary embodiments, the inner sheet metal structures are relatively thin to reduce the thermal inertia associated with the exhaust gas passageway while the outer sheet metal structures are thicker to provide added containment robustness. In some embodiments, the thickness of the outer sheet metal structure is at least twice the thickness of the inner sheet metal structure. Additionally, in exemplary embodiments, energy absorbing members (or dampers) are provided on inner surfaces of the outer shell sheet metal structures at locations susceptible to impact. In one or more embodiments, the total combined thickness of the inner sheet metal, the outer sheet metal, and the energy absorbing members is substantially equal to the thickness of a corresponding cast housing structure that would otherwise be utilized in lieu of the sheet metal shells. In some embodiments, the total combined thickness of the inner sheet metal, the outer sheet metal, and the energy absorbing members is greater than the thickness of a corresponding cast housing structure to provide equal or greater robustness as the cast component. In this regard, the energy absorbing members may allow for the thickness of the sheet metal shells at or near the inlet and/or the outlet of the turbine housing to have a combined thickness that is less than the cast component thickness while still achieving sufficient containment at or around the volute portion of the turbine housing. 
     In exemplary embodiments, the inlet of the sheet metal turbine housing defined by the inner and outer sheet metal shells is joined to a bypass valve assembly, which is realized as a cast metal. As described in greater detail below, the bypass valve assembly includes one or more guide portions or grooves adapted to receive the inlet portion of the outer sheet metal shell for joining the outer sheet metal shell to the bypass valve assembly in a manner that hermetically seals the outer sheet metal shell to the bypass valve assembly. In this regard, a feature of the bypass valve assembly encloses or otherwise circumscribes the end of the inlet portion of the outer sheet metal shell. The inlet portion of the inner sheet metal shell extends into the bypass valve assembly further than the end of the inlet portion of the outer sheet metal shell to minimize leakage but remains spaced apart from the bypass valve assembly by an air gap so that the inner sheet metal shell is floating or freestanding with respect to the bypass valve assembly. In other words, the inner sheet metal shell does not contact the bypass valve assembly and is spaced a distance apart from the bypass valve assembly by the air gap. While a bypass valve of the bypass valve assembly may be operated to reduce or prevent exhaust gas flow through the turbine and thereby mitigate the impact of the thermal inertia of the turbine housing, in exemplary embodiments described herein, the bypass valve is closed at low engine revolutions per minute (RPMs) to boost intake air. Thus, reducing the thermal inertia of the exhaust gas passageway decreases the amount of cooling of the exhaust gas attributable to the turbine housing, which in turn, helps to mitigate any potential impact of the turbine on downstream emissions control devices during startup conditions. 
       FIG. 1  depicts an exemplary embodiment of a two-stage turbocharger system  100  that includes a pair of turbocharger arrangements  110 ,  120 , and may be designed for and utilized with any sort of vehicle, such as, for example, heavy-duty or performance automotive vehicles to light-duty automotive vehicles. A first turbocharger arrangement  110  includes a first compressor  112  having an inlet arranged to receive ambient air downstream of an air filter  102  for compression to provide charge air for the cylinders of the vehicle engine  106 . The first turbine  114  is coaxially and concentrically aligned with the first compressor  112  and includes a turbine wheel mounted or otherwise coupled to the compressor wheel (or impeller) of the low pressure compressor  112  via a common rotary shaft  115 . The first turbocharger arrangement  110  also includes a bypass arrangement  116  operable to selectively bypass the first turbine  114  and allow at least a portion of the exhaust gas to flow through a bypass valve associated with the bypass arrangement  116  to a downstream emissions arrangement  108  via ducting or another conduit without entering a volute for the turbine wheel. As described in greater detail below, in exemplary embodiments, the bypass arrangement  116  is realized as a cast metal structure that is joined or otherwise mounted to the housing of the turbine  114 . 
     The second turbocharger arrangement  120  includes a second compressor  112  having an inlet arranged to receive charge air downstream of the first compressor  112  for further compression (e.g., supercharging) subject to operation of a bypass arrangement  128 . In this regard, when the bypass arrangement  128  is open to bypass the second compressor  122 , charge air from the first compressor  112  flows from the outlet of the first compressor  112  and through ducting or another conduit to an inlet of a charge air cooler  104  before provision to the engine intake or inlet manifold without entering a volute for the compressor wheel or without otherwise impacting the second compressor wheel. The second turbine  124  is coaxially and concentrically aligned with the second compressor  122  and includes a turbine wheel mounted or otherwise coupled to the compressor wheel of the compressor  122  via a common rotary shaft  125 . The second turbocharger arrangement  120  also includes a bypass arrangement  126  operable to selectively bypass the second turbine  124  and allow at least a portion of the exhaust gas from the engine cylinders  106  to flow from the exhaust manifold(s) through a bypass valve associated with the bypass arrangement  126  to an inlet of the first turbine  114  via ducting or another conduit without entering a volute for the turbine wheel or otherwise impacting the turbine wheel. 
     By virtue of the so-called “series” configuration of the turbines  114 ,  124 , the pressure of the input exhaust gases at the second turbine inlet is greater than the pressure of the exhaust gases at the first turbine inlet, and accordingly, the second turbine  124  may alternatively be referred to herein as the high-pressure (HP) turbine while the first turbine  114  may alternatively be referred to herein as the low-pressure (LP) turbine. Similarly, by virtue of the so-called “series” configuration of the compressors  112 ,  112 , the pressure of the input exhaust gases at the second compressor inlet is greater than the pressure of the exhaust gases at the first turbine inlet, and accordingly, the second compressor  122  may alternatively be referred to herein as the high-pressure (HP) compressor while the first compressor  112  may alternatively be referred to herein as the low-pressure (LP) compressor. 
     In exemplary embodiments, the emissions arrangement  108  includes a catalytic converter or similar emissions control device having an efficacy that is influenced by the temperature of the exhaust gas at its inlet. Accordingly, it is desirable to minimize the thermal inertia associated with the turbocharger system  100  downstream of the exhaust manifold(s) of the engine  106  to facilitate a higher exhaust gas temperature at the inlet of the emissions arrangement  108 . In the configuration depicted in  FIG. 1 , during startup conditions or at revolutions per minute (RPM) below a transition threshold, the low-pressure turbine bypass arrangement  116  is closed to achieve exhaust gas flow through the LP turbine  114  and corresponding operation of the LP compressor  112  to provide charge air to the engine  106 . The transition threshold may be chosen as an RPM at which the likelihood of the LP turbine  114  becoming saturated or choked is greater than a LP turbine threshold percentage. Similarly, the HP bypass arrangements  126 ,  128  may also be closed to achieve exhaust gas flow through the HP turbocharger arrangement  120  until reaching a second transition threshold at which the likelihood of the HP turbine  124  becoming saturated or choked is greater than a HP turbine threshold percentage. 
     In exemplary embodiments, the HP turbine bypass arrangement  126  begins being regulated or opened at an initial transition threshold that is less than that of the LP turbine bypass arrangement  116  (e.g., 1500 RPM versus 4500 RPM), so that exhaust gas flow through the LP turbine  114  is more consistent and greater than that through the HP turbine  124  during operation of the turbocharger system  100 . Thus, reducing the thermal inertia associated with the LP turbine  114  has a greater impact on the effectiveness of the emissions arrangement  108 . Accordingly, as described in greater detail below, in exemplary embodiments described herein, the LP turbine  114  includes a multilayer sheet metal housing that defines at least a portion of the exhaust gas passageway through the LP turbine  114 , and thereby reduces thermal inertia of the LP turbine  114 . 
       FIGS. 2-9  depict an exemplary embodiment of a turbine housing assembly  200  suitable for use in the turbocharger system  100  of  FIG. 1 , and in particular, with the LP turbine  114 . In this regard,  FIG. 6  depicts the turbine housing assembly  200  when a rotating assembly  650  including a turbine wheel  610  (e.g., turbine wheel) and a corresponding compressor wheel  652  (e.g., compressor wheel) is inserted into the turbine housing assembly  200  and joined or mounted with a flange  240 . 
     With initial reference to  FIGS. 2-7 , the turbine housing assembly  200  includes a turbine housing defined by an inner sheet metal shell  202 ,  204 , an outer sheet metal shell  206 ,  208 , and a central core structure  220 . The inner sheet metal shell  202 ,  204  includes a first sheet metal structure  202  that faces a second sheet metal structure  204  in an axial direction (the x reference direction) aligned with (or parallel to) the rotational axis  600  of the turbine wheel  610  such that the sheet metal structures  202 ,  204  interface and are joined in a radial plane that is aligned with (or parallel to) the plane in which the turbine wheel  610  rotates (the yz reference plane). For purposes of explanation, the inner sheet metal structure  202  closest to the turbine wheel  610  may alternatively be referred to herein as the proximal inner sheet metal structure and the inner sheet metal structure  204  farthest from the turbine wheel  610  may alternatively be referred to herein as the distal inner sheet metal structure. The outer sheet metal shell  206 ,  208  includes a first outer sheet metal structure  206  that faces a second outer sheet metal structure  208  in a direction substantially perpendicular to the rotational axis  600  of the turbine wheel  610  (e.g., in the z reference direction) such that the outer sheet metal structures  206 ,  208  interface and are joined in an axial plane that is aligned with (or parallel to) the rotational axis  600  of the turbine wheel  610  (the xy reference plane) and orthogonal to the plane in which the inner sheet metal structures  202 ,  204  are joined. 
     With reference to  FIGS. 4-7 , the inner sheet metal structures  202 ,  204  are formed to include respective base portions  203 ,  205  that cooperatively define a radial inlet  700  tangential to a volute  212 . The volute  212  is a voided region providing a scroll-shaped exhaust gas passageway, and the volute  212  is defined by substantially circular portions  213 ,  215  that are integral with the base portions  203 ,  205  in concert with a core structure  220 . In this regard, the interior surfaces  601 ,  603  of the base portions  203 ,  205  are contoured and configured in concert with a tongue  218  to direct exhaust gas tangentially into the volute  212  at the inlet  700  to the volute  212 . The interior surfaces  402 ,  602  of the volute portions  213 ,  215  are contoured to define the outer contour of the scroll-shaped voided region of the volute  212  that narrows moving radially from the inlet  700  to the opposing end of the tongue  218  that separates the volute  212  from the inlet  700 . 
     As best illustrated in  FIGS. 5-6 , each of the inner sheet metal structures  202 ,  204  includes a flange or similar feature  214 ,  216  that extends radially outward from the volute portions  213 ,  215  to provide an area for coupling the inner sheet metal structures  202 ,  204  circumferentially about the volute portions  213 ,  215 . In the illustrated embodiment, the flange  216  of the proximal inner sheet metal structure  204  extends radially outward by a distance that is greater than or equal to the distance by which the flange  214  of the distal inner sheet metal structure  202  extends to facilitate welding the flange  214  of the distal inner sheet metal structure  202  to the flange  216  of the proximal inner sheet metal structure  204  substantially circumferentially about the volute portions  213 ,  215 . In one example, the proximal inner sheet metal structure  204  and the distal inner sheet metal structure  202  are each composed of a ferritic stainless steel material (e.g., SUS430J1L) and are coupled together via by tungsten inert gas (TIG) welding. 
     As best illustrated in  FIG. 5 , each of the substantially circular volute portions  213 ,  215  of the inner sheet metal structures  202 ,  204  defines an interior opening  217 ,  219  that is substantially circular and coaxially and concentrically aligned with the rotational axis  600  of the turbine wheel  610  to receive a central core structure  220 . The central core  220  includes an interior voided region  222  (or hole or bore) coaxially and concentrically aligned with the rotational axis  600  of the turbine wheel  610  that includes a substantially circular or counterbore portion  224  for receiving and engaging a nose  611  of the turbine wheel  610 . The interior voided region  222  also includes a contoured portion  226  having a circumference that increases moving away from the turbine  610  along the axial direction (the x direction) aligned with the rotational axis of the turbine  610  to define an axial outlet for the turbine  610 . Stated another way, a diameter of the contoured portion  226  varies along a length of the contoured portion  226 , such that the diameter of the contoured portion  226  at a first end is different than the diameter of the contoured portion  226  at a second end. The distal end (or outlet end) of the core  220  includes a lip or similar feature  656  that receives an outlet pipe  256 , as described in greater detail below. 
     Referring to  FIGS. 4 and 6-7 , the central core  220  includes a tongue portion  218  that defines or otherwise separates the volute  212  from the tangential inlet thereto. As best illustrated in  FIGS. 4 and 7 , the central core  220  also includes a substantially continuous contoured outer surface  228  that faces the contoured inner surfaces  402 ,  602  of the volute portions  215 ,  217  of the inner sheet metal structures  202 ,  204  to define the inner contour of the voided region providing the scroll-shaped exhaust gas passageway for the volute  212 . In exemplary embodiments, the central core structure  220  is realized as a unitary cast metal structure that is welded or otherwise affixed to the distal inner sheet metal structure  202 , for example, by TIG welding about the opening  217  in the distal sheet metal structure  202 , as described in greater detail below. In one example, the central core structure  220  is composed of cast ferritic stainless steel material (e.g., SUS430). 
     With reference to  FIG. 2-6 , the outer sheet metal structures  206 ,  208  are formed to include respective base portions  223 ,  225  that cooperatively surround the inlet portions  203 ,  205  of the inner sheet metal structures  206 ,  208  in a plane (the xz reference plane) that is transverse or orthogonal to the radial plane (the yz reference plane) in which the turbine wheel  610  rotates. The outer sheet metal structures  206 ,  208  also include arcuate portions  227 ,  229  that cooperatively enclose or surround the volute portions  213 ,  215  of the inner sheet metal structures  202 ,  204  radially (e.g., in the yz reference plane). As best illustrated in  FIGS. 2-3 , in exemplary embodiments, one of the outer sheet metal structures  206  includes a receiving feature  280  formed therein which is configured to overlap and mate with the other of the outer sheet metal structures  208  about the interface between the outer sheet metal structures  206 ,  208  to facilitate joining the outer sheet metal structures  206 ,  208  to one another. In one example, the outer sheet metal structures  206 ,  208  are each composed of a ferritic stainless steel material (e.g., SUS409L) and are coupled together via by TIG welding. In this regard, the inner sheet metal shell  202 ,  204  and the outer sheet metal shell  206 ,  208  may be realized using different ferritic stainless steel materials. 
     Additionally, the outer sheet metal structures  206 ,  208  include contoured outlet portions  282 ,  284  that narrow moving away from the turbine wheel  610  in the axial direction (the x reference direction) to substantially enclose the inner sheet metal structures  202 ,  204  in the axial direction (the x reference direction) opposite the turbine wheel  610 . As illustrated, the extension of the outer shell  206 ,  208  in the direction parallel to the turbine wheel rotational axis  600  away from the turbine wheel  610  defined by the contoured outlet portions  282 ,  284  is greater than the extension of the inner shell  202 ,  204  away from the turbine wheel  610  in the direction parallel to the turbine wheel rotational axis  600 . At the same time, the extension of the inner shell  202 ,  204  substantially perpendicular to the turbine wheel rotational axis  600  as defined by the inner base portions  203 ,  205  is greater than the extension of the outer shell  206 ,  208  substantially perpendicular to the turbine wheel rotational axis  600  as defined by the outer base portions  223 ,  225 . 
     The contoured outlet portions  282 ,  284  define a substantially circular interior opening  230  that is coaxially and concentrically aligned with the rotational axis of the turbine wheel  610 , with the opening  230  also having a diameter that is less than the diameter of the circular interior openings  217 ,  219  defined by the inner sheet metal structures  202 ,  204 . That said, it should be noted that depending on the embodiment, the axial outlet opening  230  defined by the outer sheet metal structures  206 ,  208  may be off-axis or angled relative to the rotational axis of the turbine  610 , for example, due to packaging constraints or the like. The ends  241 ,  243  of the outer sheet metal structures  206 ,  208  defining the axial outlet opening  230  are coupled to a substantially-planar flange  238  via an outlet pipe  256  and collar  258  for coupling the turbine housing assembly  200  to a fluid conduit for carrying exhaust gas axially exiting the turbine wheel  610  to downstream emissions devices (e.g., a catalytic converter  108 ), as described in greater detail below. 
     Opposite the contoured outlet portions  282 ,  284  defining the axial outlet opening  230 , each of the outer sheet metal structures  206 ,  208  includes a lip or similar receiving feature  607  defining at least a portion of a substantially circular opening  608  configured to receive a substantially circular flange  240  for mounting the turbine housing assembly  200  to the rotating assembly  650 . The rotating assembly generally includes the turbine wheel  610  and the compressor wheel  652  coupled to the turbine wheel  610  via a common rotary shaft  654 . As best illustrated in  FIG. 6 , in exemplary embodiments, the inner circumference of the opening  608  defined by the axial ends  245 ,  247  of the outer sheet metal structures  206 ,  208  proximal to the turbine  610  (or distal to the axial outlet) is greater than or equal to an outer circumference of the flange  240  such that a portion of the flange  240  is received within the opening  608 . Thus, the outer sheet metal shell  206 ,  208  defines a bearing opening  608  having a radial dimension that is greater than that of the volute  212  while also defining an opposing outlet opening  230  having a radial dimension that is less than that of the bearing opening  608  and the volute  212 . Generally, the bearing flange  240  includes a plurality of bores  404  distributed about a perimeter or circumference of the flange  240 , which each receive a respective fastener  640 . The fasteners  640  engage with the bores  404  to mount, support, or otherwise couple the flange  240 , and thereby the turbine housing assembly  200 , to the rotating assembly  650 . It should be understood, however, that the flange  240  may be coupled to the rotating assembly  650  via any technique, such as an interference fit, welding, etc. 
     Still referring to  FIGS. 2-6 , the ends  233 ,  235  of the base portions  223 ,  225  of the outer sheet metal structures  206 ,  208  are joined or otherwise coupled to a bypass valve assembly structure  232  that includes an opening  270  for a valve (e.g., bypass arrangement  116 ) that is operable to allow exhaust gas to selectively bypass the tangential inlet to the volute  212 , and thereby bypass the turbine  610 . In this regard, the bypass opening  270  extends along an axis that is oblique to the axis of the inlet opening  632 , as illustrated in  FIGS. 4, 6 and 8 . In exemplary embodiments, the bypass valve assembly structure  232  is realized as a unitary cast metal material that includes a flange  231  (or lip) that receives and circumscribes the ends  233 ,  235  of the base portions  223 ,  225  of the outer sheet metal structures  206 ,  208  in the axial plane (the xz reference plane) transverse to the radial plane (the yz reference plane) in which the turbine wheel  610  rotates. 
     As best illustrated in  FIGS. 6 and 8 , the bypass valve assembly structure  232  also includes a corresponding guide portion  234  having an outer circumference that is less than or equal to an inner circumference of the lip feature  231  and an inner circumference that is less than or equal to an inner circumference of the ends  233 ,  235  of the combined outer sheet metal base  223 ,  225  for receiving and supporting the ends  233 ,  235  of the outer sheet metal base portions  223 ,  225 . In this regard, the guide portion  234  may be realized as a shelf or surface about the perimeter of an inlet opening  632  in the bypass valve assembly structure  232  that includes one or more features  802 ,  804 ,  806 ,  808  that engage the ends  233 ,  235  of the outer sheet metal base portions  223 ,  225 . The features  802 ,  804 ,  806 ,  808  may have distinct or different shapes and be spaced apart about the perimeter of the guide portion  234 , and the features  802 ,  804 ,  806 ,  808  may be configured to mate with corresponding features on the base portions  223 ,  225  of the outer sheet metal structures  206 ,  208  when the outer sheet metal structures  206 ,  208  are inserted into the bypass valve assembly structure  232 . The overlapping portion of the lip  231  is subsequently welded to the outer surfaces of the outer sheet metal base portions  223 ,  225  about its perimeter to hermetically seal the outer sheet metal structures  206 ,  208  to the bypass valve assembly structure  232 . 
     Referring to  FIG. 6 , the bypass valve assembly structure  232  further includes an accommodation portion  236 . The accommodation portion  236  may comprise a countersink defined in the inlet opening  632  of the bypass valve assembly structure  232 . The accommodation portion  236  generally has an outer circumference that is less than or equal to an inner circumference of the ends  233 ,  235  of the combined outer sheet metal base  223 ,  225 . The accommodation portion  236  is further recessed into the bypass valve assembly structure  232  relative to the guide portion  234  to accommodate extension of the inner sheet metal base portions  203 ,  205  into the bypass valve assembly structure  232  without contacting the bypass valve assembly structure  232 . In this regard, the ends  237 ,  239  of the base portions  203 ,  205  of the inner sheet metal structures  202 ,  204  extend into the bypass valve assembly structure  232  (in the −y reference direction) by a distance (d 1 ) relative to the end of the lip feature  231  that is greater than the distance (d 2 ) that the outer sheet metal base ends  233 ,  235  extend beyond the end of the lip feature  231  into the bypass valve assembly structure  232  to minimize leakage between the inner and outer sheet metal shells. At the same time, an air gap or separation distance  630  is maintained between the ends  237 ,  239  of the inner sheet metal base portions  203 ,  205  and the accommodation portion  236  of the bypass valve assembly structure  232  so that the inner sheet metal base portions  203 ,  205  do not contact the bypass valve assembly structure  232  and are freestanding with respect to the bypass valve assembly structure  232 . 
     As best illustrated in  FIGS. 5-7 , in exemplary embodiments, an energy absorbing member  260 ,  262  is provided on an interior surface of each of the outer sheet metal structures  206 ,  208 . In one example, the energy absorbing members  260 ,  262  are disposed between the respective outer sheet metal structure  206 ,  208  and the inner sheet metal structures  202 ,  204 . In this example, the energy absorbing members  260 ,  262  are arcuate sheet metal structures that substantially conform to the interior surface of the respective outer sheet metal structure  206 ,  208  and are welded (e.g., spot welding) to the interior surface of the respective outer sheet metal structure  206 ,  208  at locations that overlap portions of the outer sheet metal structures  206 ,  208 . In this regard, by virtue of the shape of the outer sheet metal structures  206 ,  208 , the upper portions of the outer sheet metal structures  206 ,  208  distal to the base portions  223 ,  225  where the outer sheet metal structures  206 ,  208  interface may be more susceptible to wheel burst. Accordingly, the energy absorbing members  260 ,  262  may be strategically placed to radially surround at least a portion of the volute  212  defined by the inner sheet metal structures  202 ,  204  adjacent to the location where the outer sheet metal structures  206 ,  208  are joined to provide additional radial containment. 
     In exemplary embodiments, the axial dimension (or width) of the energy absorbing members  260 ,  262  parallel to the turbine rotational axis  600  is configured to radially overlap portions the volute  212  for containment purposes, but without extending beyond the volute  212  in the axial direction to minimize the amount of material and weight contributed to the turbine housing assembly  200  by the energy absorbing members  260 ,  262 . In this regard, the energy absorbing members  260 ,  262  and the volute  212  may be coplanar with the edges or ends of the energy absorbing members  260 ,  262  that are distal to the turbine  610  being substantially aligned with the distal extent of the volute  212  in the radial plane, as best illustrated in  FIGS. 5-6 . At the same time, the radial dimension (or length) of the energy absorbing members  260 ,  262  is also chosen to minimize the amount of material and weight contributed to the turbine housing assembly  200  by the energy absorbing members  260 ,  262  while strategically providing radial containment at the desired locations. 
     In one or more exemplary embodiments, the thickness of the outer sheet metal structures  206 ,  208  is greater than the thickness of the inner sheet metal structures  202 ,  204 , that is, the outer sheet metal structures  206 ,  208  may be formed from a metal sheet having a thickness that is greater than the metal sheet used to form the inner sheet metal structures  202 ,  204 . In this regard, the metal sheet used to form the inner sheet metal structures  202 ,  204  may be made as thin as practicable for thermal performance, with a thicker metal sheet being used for the outer sheet metal structures  206 ,  208  to obtain a resulting combined thickness that achieves the desired containment and reliability. For example, in one embodiment, the wall thickness of the volute portions  213 ,  215  of the inner sheet metal structures  202 ,  204  is approximately 1.2 millimeters (mm) and the wall thickness of the arcuate portions  227 ,  229  of the outer sheet metal structures  206 ,  208  is approximately 3 mm to provide a total thickness of about 4.2 mm, which corresponds to the wall thickness of a corresponding cast component of similar dimensions. 
     In one or more embodiments, the thickness of the energy absorbing members  260 ,  262  is chosen to achieve the casting thickness at the locations of the outer sheet metal structures  206 ,  208  most susceptible to loss of containment. For example, if the cast component thickness is 4.5 mm, and the inner sheet metal structures  202 ,  204  have a wall thickness of approximately 1.2 mm and the outer sheet metal structures  206 ,  208  have a wall thickness of approximately 3 mm, the thickness of the energy absorbing members  260 ,  262  may be chosen to be approximately 0.3 mm to achieve a combined thickness of 4.5 mm. In yet another embodiment, the same type of sheet metal is used for the outer sheet metal structures  206 ,  208  and the energy absorbing members  260 ,  262 , and the thicknesses of the outer sheet metal structures  206 ,  208  and the energy absorbing members  260 ,  262  substantially identical and chosen to provide the cast component thickness. For example, if the cast component thickness is 4.5 mm and the inner sheet metal structures  202 ,  204  have a wall thickness of 1.3 mm, then both the outer sheet metal structures  206 ,  208  and the energy absorbing members  260 ,  262  may have a thickness of approximately 1.6 mm to achieve a combined thickness of 4.5 mm. Thus, the thickness of the outer sheet metal structures  206 ,  208  and the energy absorbing members  260 ,  262  may be dictated by the thickness of the inner sheet metal structures  202 ,  204  and the required amount of containment, which, in turn, allows for the thickness of the inner sheet metal structures  202 ,  204  to be optimized to achieve the desired performance qualities. 
     Still referring to  FIGS. 2-8 , to fabricate the turbine housing assembly  200 , the core structure  220  is inserted into the opening  217  of the distal inner sheet metal structure  202 , and the distal inner sheet metal structure  202  is joined to the core structure  220  by tungsten inert gas (TIG) welding circumferentially about the opening  217  to an outer surface of the core structure  220  facing the axial outlet opposite the turbine wheel  610  to hermetically seal the distal sheet metal structure  202  to the core structure  220 . The ends of the proximal inner sheet metal structure  204  that define the opening  219  for receiving the turbine wheel  610  are inserted into a corresponding opening defined by the flange  240  and joined circumferentially about the opening  219  by TIG welding to hermetically seal the sheet metal structure  204  to the flange  240 . Thereafter, the inwardly facing ends of the inner sheet metal structures  202 ,  204  are joined to one another by TIG welding about the interface between the inner sheet metal structures  202 ,  204  in the radial plane to hermetically seal the inner sheet metal structures  202 ,  204  to one another in the axial direction. Thus, the volute portions  213 ,  215  are substantially circumferentially welded to one another at the portions where the rims  214 ,  216  meet to provide a hermetically sealed radial outer contour for the volute  212 . The resulting welding seam or joint about the inner sheet metal structures  202 ,  204  resides in a radial plane (e.g., the yz reference plane) that is substantially parallel to the plane in which the turbine wheel  610  rotates and substantially perpendicular to the turbine wheel rotational axis  600 . 
     As illustrated by the detailed view of region  900  in  FIG. 9 , in exemplary embodiments, the core structure  220  is not welded or joined to the proximal inner sheet metal structure  204 , so that the core structure  220  is freestanding with respect to the proximal inner sheet metal structure  204 . In particular, at ambient temperatures, the tongue portion  218  of the core structure  220  proximate the inlet is spaced apart from a corresponding tongue feature in the proximal inner sheet metal structure  204  separating the interior portion of the volute  212  from the inlet by an air gap  902  having a nonzero separation distance to accommodate thermal expansion of the inner sheet metal structure  204 , and thereby reduce stress on the tongue portion  218  of the core structure  220 . In this regard, the air gap  902  may be chosen to provide a separation distance at ambient temperatures that results in at least some separation distance being maintained at elevated exhaust gas temperatures during operation. In some embodiments, the inner sheet metal structure  204  may contact the tongue portion  218  of the core structure  220  during operation but only do so at or near its maximal thermal expansion, so that any stress imparted on the core structure  220  is minimized. For example, in one embodiment, the air gap  902  or separation distance between the tongue portion  218  and the corresponding tongue feature in the proximal inner sheet metal structure  204  is about 0.5 millimeters at ambient temperatures so that at a maximum operating temperature of 850° Celsius, the tongue portion  218  and the corresponding tongue feature in the proximal inner sheet metal structure  204  contact one another without causing any significant stress on either of the core structure  220  or the sheet metal structure  204 . 
     After assembling the inner sheet metal structures  202 ,  204  with the core structure  220  and bearing flange  240 , an axial outlet pipe  256  is inserted into a corresponding guide feature formed in the inner surface of the distal end of the outlet portion  226  of the core structure  220  and joined to the inner surface of the outlet portion  226  about the proximal end of the outlet pipe  256  by TIG welding, thereby hermetically sealing the axial outlet pipe  256  to the core structure  220 . An outlet collar  258  is provided over the distal end of the outlet pipe  256 . 
     Still referring to  FIGS. 2-6 , the energy absorbing members  260 ,  262  are joined to the inner surfaces of the respective outer sheet metal structures  206 ,  208  by spot welding. Thereafter, the upper portions of outer sheet metal structures  206 ,  208  opposite the base portions  223 ,  225  are joined about the assembled inner sheet metal structures  202 ,  204  by TIG welding the overlapping portions of the outer sheet metal structures  206 ,  208  together in the xy reference plane to radially enclose the volute portions  213 ,  215  in the yz reference plane. In this regard, a welding seam extends along the radius (or diameter) of the arcuate portions  227 ,  229  from the outlet ends  241 ,  243  of the outer sheet metal structures  206 ,  208  along the overlapping interface between the sheet metal structures  206 ,  208  (e.g., where the receiving feature  280  of structure  206  overlaps the end  243  of structure  208 ). The resulting welding seam or joint between the outer sheet metal structures  206 ,  208  resides in an axial plane that is substantially parallel to the turbine wheel rotational axis  600  and substantially perpendicular or transverse to the plane in which the turbine wheel  610  rotates, as best illustrated by  FIGS. 2-3 . In this regard, the plane the welding seam between the outer sheet metal structures  206 ,  208  resides in is substantially perpendicular or otherwise transverse to the radial plane in which the welding seam between the inner sheet metal structures  202 ,  204  resides, and the portion of the welding seam between arcuate portions  227 ,  229  opposite the inlet opening  632  and radially surrounding the volute  212  extends in an axial direction substantially parallel to a turbine wheel rotational axis  600 . 
     Additionally, the distal ends  241 ,  243  of the outer sheet metal structures  206 ,  208  defining the axial outlet opening  230  are welded circumferentially about the outlet collar  258 , which, in turn, supports the distal end of the outlet pipe  256  extending from the core structure  220  in the radial plane (the yz reference plane). In exemplary embodiments, the welding of the outlet pipe  256  to the outlet ends  241 ,  243  of the outer sheet metal structures  206 ,  208  and the welding of the upper portions of outer sheet metal structures  206 ,  208  are performed during the same welding process step. 
     The ends  233 ,  235  of the base portions  223 ,  225  are inserted into the guide portion  234  of the cast bypass valve structure  232 . The base portions  223 ,  225  of the outer sheet metal structures  206 ,  208  are then joined in the xy reference plane by TIG welding the interface between the outer sheet metal structures  206 ,  208  from the outlet pipe  256  to the interface with the bypass valve assembly structure  232 . The perimeter of the lip  231  of the guide portion  234  is also welded to the overlapped outer surfaces of the outer sheet metal structures  206 ,  208  in a plane substantially parallel to the turbine wheel rotational axis  600  (e.g., the xz reference plane) to hermetically seal the outer sheet metal structures  206 ,  208  to the bypass valve structure  232 . Thus, the outer sheet metal structures  206 ,  208  and the bypass valve structure  232  cooperatively enclose the inner sheet metal structures  202 ,  204  radially, with the outer sheet metal structures  206 ,  208  and the bearing flange  240  enclosing the inner sheet metal structures  202 ,  204  axially. In exemplary embodiments, the welding of the lower portions of the outer sheet metal structures  206 ,  208  and the welding of the outer sheet metal base portions  223 ,  225  with the bypass valve assembly structure  232  are performed during the same welding process step. It should be noted that by virtue of the axial interface between the outer sheet metal structures  206 ,  208 , the distance or amount of welding required to join the outer sheet metal structures  206 ,  208  is reduced as compared to welding circumferentially in a radial plane (e.g., a radial or diametric welding seam as compared to a circumferential welding seam). 
     As described above, the inlet ends of the base portions  237 ,  239  of the inner sheet metal structures  202 ,  204  extend further into the bypass valve structure  232  than the ends  233 ,  235  of the outer sheet metal base portions  223 ,  225  (e.g., into the recessed portion  236 ) to minimize any leakage at the inlet via the air gap between the ends of the inner base portions  237 ,  239  and the bypass valve structure  232  and into any gaps or spaces between the inner sheet metal structures  202 ,  204  and the outer sheet metal structures  206 ,  208 . The separation distance between the inner base portions  237 ,  239  and the bypass valve structure  232  accommodates thermal expansion of the inner sheet metal structures  202 ,  204  resulting from the exhaust gas flow. 
     The outlet collar  258  is inserted into a corresponding opening in the exhaust outlet flange  238  and is circumferentially welded to the inner surface of the opening in the flange  238  to hermetically seal the exhaust gas passageway. In some embodiments, the axial outlet ends of the outlet pipe  256  and the outlet collar  258  are both welded circumferentially to the inner surface of the opening in the flange  238  concurrently to effectively weld all three structures  238 ,  256 ,  258  together and seal the outlet end of the exhaust gas passageway. In exemplary embodiments, the exhaust outlet flange  238  is formed from or otherwise realized using sheet metal. As illustrated in  FIG. 2 , in some embodiments, the outlet ends of the outer sheet metal structures  206 ,  208  defining the axial outlet opening  230  that receives the outlet pipe  256  and collar  258  may be spaced apart or otherwise offset from the outlet flange  238 . Thus, the outlet pipe  256  and collar  258  may accommodate variations in the position or orientation of the flange  238  with respect to the outer sheet metal structures  206 ,  208  during manufacturing or assembly. That said, by virtue of circumferentially welding the outlet ends of the outer sheet metal structures  206 ,  208  to the collar  258 , which, in turn is welded to the outlet pipe  256  and the outlet flange  238 , the axial outlet exhaust gas passageway is hermetically sealed from the core structure  220  to the ducting downstream of the flange  238 . In this regard, the outlet pipe  256  and collar  258  provide a hermetically sealed passageway when the axial outlet portion  226  of the core  220  is not welded or sealed to the outer sheet metal structures  206 ,  208 . 
     After the turbine housing assembly  200  is fabricated, the turbine nose portion  211  of the assembly  250  is inserted into the corresponding portion  224  of the core structure  220 , with the assembly  250  being mounted or otherwise joined to the turbine housing assembly  200  using the flange  240  in a manner that hermetically seals the flange  240  to the assembly  250 . In exemplary embodiments, the turbine nose portion  211  includes one or more sealing rings circumscribing the outer surface of the turbine nose portion  211  to hermetically seal the axial outlet from the turbine wheel  610  with the opening  222  for the axial outlet provided within the core structure  220 . Variable geometry members (e.g., guide vanes or the like) may be provided within the assembly  250  about the turbine wheel  610  and configured to regulate, control, or otherwise influence the exhaust gas flow from the volute  212  to the turbine wheel  610 , as will be appreciated in the art. 
     By virtue of the inner sheet metal structures  202 ,  204  defining at least the outer contour of the volute  212  and the inlet thereto, the percentage of surface area encountered by the exhaust gas that is sheet metal is increased, which, in turn reduces the reduction in exhaust gas temperature at the opening in the exhaust outlet flange  238  relative to the exhaust gas temperature upon entry to the bypass valve structure  232 . Additionally, the inner sheet metal structures  202 ,  204  are relatively thin, to further reduce the thermal inertia associated with the exhaust gas flow through the volute  212 . Thus, the effectiveness of downstream emissions devices may be improved. The relatively thicker outer sheet metal structures  206 ,  208  provide containment for the volute  212  while also being constructed from sheet metal to reduce thermal inertia. At the same time, the bypass valve structure  232  is realized as a cast metal to support the remaining components of the turbine housing assembly  200  subject to any external loading caused by the ducting joined to the valved opening  270 , ducting joined to the exhaust outlet flange  238 , or the assembly  250  joined to the turbine housing assembly  200 . The cast bypass valve structure  232  also helps maintain the opening  270  (e.g., by avoiding closure due to thermal expansion or deformation) and support robust and reliable operation of the bypass valve components (e.g., the valve, the arm or actuation element for the valve, and the bushings or other components that facilitate actuation) across a range of variable temperature and mass flow conditions and subject to potentially varying amounts of external loading. Additionally, the core structure  220  is realized as a cast metal to similarly provide robust and reliable operation across a range of variable temperature and mass flow conditions, namely, by providing a tongue portion  218  and other surfaces of the volute  212  that are less susceptible to deformation, thermal expansion, or the like. That said, by virtue of the volute portions  213 ,  215  and base inlet portions  203 ,  205  provided by the inner sheet metal structures  202 ,  204 , the exposed surface area within the volute  212  and the inlet thereto that is realized as a cast metal may be reduced or otherwise minimized to achieve a corresponding reduction in the thermal inertia associated with the turbine housing assembly  200 . 
     By virtue of the flanges  214 ,  216  about the radial interface between the inner sheet metal structures  202 ,  204 , the area for the welding seam joining the inner sheet metal structures  202 ,  204  may be increased to facilitate a more consistent and stable weld about the circumferential interface of the volute portions  213 ,  215 , and thereby may improve welding quality. Improved weld quality in concert with the radial seam orientation may result in improved stiffness for purposes of improved containment and may also help minimize volute deformation. Additionally, the welding seam direction for the weld joining the outer sheet metal structures  206 ,  208  minimizes the welding length (radially or diametrically versus circumferentially), which is advantageous for containment capability, which is further augmented by the increased thickness of the outer sheet metal structures  206 ,  208 . The additional energy absorbing members  260 ,  262  radially overlapping the volute  212  further improve containment, with placement of the energy absorbing members  260 ,  262  proximate the joint between the outer sheet metal structures  206 ,  208  reinforcing relatively flatter sections of the outer sheet metal structures  206 ,  208  radially circumscribing the volute  212 . At the same time, the axial and radial dimensions of the energy absorbing members  260 ,  262  may be minimized so that they only radially overlap the volute  212  at strategically advantageous locations to reduce material costs and weight. 
     As described above in the context of  FIG. 1 , at startup, the valve in the opening  270  is closed so that exhaust gas flows through the volute  212  and impacts the turbine wheel  610  before exiting the axial outlet  222 ,  230  to downstream emissions devices  108 . By limiting the cast metal surface area encountered by the exhaust gas to the tongue  218  and contoured surface  228  of the core structure  220  and the outlet  222  of the core structure  220 , the effective thermal inertia of the turbine housing assembly  200  relative to a corresponding cast turbine housing assembly is reduced. As a result, the exhaust gas that reaches the downstream emissions devices  108  has a higher temperature relative to a cast turbine housing assembly, and as a result, the performance of the downstream emissions device  108  is improved. At the same time, the sheet metal may also be utilized to minimize the size, weight, form factor, or the like associated with the turbine housing assembly  200  without compromising burst containment by virtue of the configuration described herein. 
     For the sake of brevity, conventional techniques related to turbines, compressors, turbochargers, wastegates, bypass valves, ducting, catalytic converters, emissions controls, and other functional aspects of the systems (and the individual operating components of the systems) may not be described in detail herein. Furthermore, the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the subject matter. 
     The foregoing description may refer to elements or components or features being “coupled” together. As used herein, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically. Thus, although the drawings may depict one exemplary arrangement of elements, additional intervening elements, devices, features, or components may be present in an embodiment of the depicted subject matter. In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, the terms “first,” “second,” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. Similarly, terms such as “upper”, “lower”, “top”, and “bottom” refer to directions in the drawings to which reference is made. 
     The foregoing detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any theory presented in the preceding background, brief summary, or the detailed description. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the subject matter. It should be understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the subject matter as set forth in the appended claims. Accordingly, details of the exemplary embodiments or other limitations described above should not be read into the claims absent a clear intention to the contrary.