Abstract:
A bearing system, which may be used particularly for hot-air valves, comprising a fixed roller bearing and a floating roller bearing is provided wherein a spherical shape of the inner raceways of each bearing, a spherical shape of the rollers of each bearing, a spherical shape of the fixed bearing&#39;s outer raceway and a cylindrical shape of the floating bearing&#39;s outer raceway may enable the bearing system to compensate for all mechanically and thermally induced deflections and linear expansion of a valve&#39;s shaft relative to the valve&#39;s housing, thus reducing a risk of shortening the useful lifetime of either the fixed roller bearing or the floating roller bearing.

Description:
FIELD 
     The present disclosure relates to a bearing system, and methods of use thereof, particularly for hot-air valves. 
     BACKGROUND 
     A hot-air valve may be used to regulate gas flow in different areas of a gas turbine engine, particularly for aircraft or power generation applications. In certain cases the hot-air valve may have a so called butterfly design, in which a shaft and a disc fixed to the shaft regulate the gas flow through the hot-air valve, particularly by opening and closing a tubular cross-section of a gas line containing the gas flow by a quarter-turn of the shaft. The gas flowing through the hot-air valve may be characterized by a wide temperature range from 219.3 K (−65° F.) to 810.9 K (1,000° F.), and a pressure range from 68.95 kPa (10 psi) to 1.379 MPa (200 psi). 
     With the objective of rotating the shaft and disc with minimum torque, even under full pressure, the shaft may be supported at each end by a low friction rolling element ball bearing. Each of the low friction rolling element ball bearings may comprise a rotating inner ring fixed to the shaft and a standing outer ring fixed to a housing, with balls as rolling elements in between. 
     The need for lower fuel consumption of gas turbines, particularly in the aviation industry, has led to a need to operate hot-air valves with higher gas temperatures and higher gas pressures. For example, for an upcoming new gas turbine engine planned to power single aisle, double engine aircraft like the Boeing 737max or the Airbus 320neo, the requirements of the hot-air valve have been increased to a temperature range of 219.3 K (−65° F.) to 977.6 K (1,300° F.) and a pressure of up to 3.103 MPa (450 psi). 
     Although thermo and mechanical loads have increased in this new application, the size and weight of the valve may not increase, as such would offset the fuel consumption decrease. As a result, all parts of the hot-air valve may be expected to experience larger thermal expansion/displacement caused by the increased temperature range, and larger mechanical deflection caused by the higher pressure and the decreasing stiffness of the valve materials with the increased temperature. More particularly, the shaft may be expected to show more elastic deflection and more linear extension relative to the housing, which has to be compensated by the bearings to avoid the risk of additional internal loads between the bearing elements resulting in a shortened useful life of the bearing. 
     In light of the foregoing, a need exists in industry to address the aforementioned deficiencies and inadequacies of current low friction rolling element ball bearings, particularly for hot-air valves in aviation applications exposed to the above described increased thermal and mechanical requirements. 
     SUMMARY 
     A bearing system, which may be used particularly for hot-air valves, comprising a fixed roller bearing and a floating roller bearing is provided wherein a spherical shape of the inner raceways of each bearing, a spherical shape of the rollers of each bearing, a spherical shape of the fixed bearing&#39;s outer raceway and a cylindrical shape of the floating bearing&#39;s outer raceway may enable the bearing system to compensate for all mechanically and thermally induced deflections and linear expansion of a valve&#39;s shaft relative to the valve&#39;s housing, thus reducing a risk of shortening the useful lifetime of either the fixed roller bearing or the floating roller bearing. 
     In one embodiment of the present disclosure, a bearing system is provided which comprises a fixed roller bearing and a floating roller bearing. The fixed roller bearing comprises a fixed bearing inner raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; a fixed bearing outer raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; and a plurality of fixed bearing spherical rollers located between the fixed bearing inner raceway and the fixed bearing outer raceway. The floating roller bearing comprises a floating bearing inner raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; a floating bearing outer raceway having a width formed by a cylindrical surface; and a plurality of floating bearing spherical rollers located between the fixed bearing inner raceway and the fixed bearing outer raceway. 
     In another embodiment of the present disclosure a hot-air valve is provided which comprises a shaft rotatable on at least two bearings located within a housing, wherein a first bearing of the two bearings is a fixed roller bearing and a second bearing of the two bearings is floating roller bearing. The fixed roller bearing comprises a fixed bearing inner raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; a fixed bearing outer raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; and a plurality of fixed bearing spherical rollers located between the fixed bearing inner raceway and the fixed bearing outer raceway. The floating roller bearing comprises a floating bearing inner raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; a floating bearing outer raceway having a width formed by a cylindrical surface; and a plurality of floating bearing spherical rollers located between the fixed bearing inner raceway and the fixed bearing outer raceway. The valve is operable in a temperature range of at least 219.3 K (−65° F.) to 977.6 K (1,300° F.), and/or to a pressure of up to 3.103 MPa (450 psi). 
     In another embodiment of the present disclosure a method of operating a valve is provided which comprises providing a hot-air valve, comprising a shaft rotatable on at least two bearings located within a housing, wherein a first bearing of the two bearings is a fixed roller bearing and a second bearing of the two bearings is floating roller bearing. The fixed roller bearing comprises a fixed bearing inner raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; a fixed bearing outer raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; and a plurality of fixed bearing spherical rollers located between the fixed bearing inner raceway and the fixed bearing outer raceway. The floating roller bearing comprises a floating bearing inner raceway having a width formed by a spherical surface, wherein the spherical surface is defined by a radius; a floating bearing outer raceway having a width formed by a cylindrical surface; and a plurality of floating bearing spherical rollers located between the fixed bearing inner raceway and the fixed bearing outer raceway. The method may further comprise exposing the shaft to mechanical loads which bend the shaft along an axis of rotation of the shaft, and compensating for the bending of the shaft and mechanical loads placed on the fixed bearing and floating bearing by tilting the fixed bearing inner ring in the fixed bearing outer ring relative to the axis of rotation and tilting the floating bearing inner ring in the floating bearing outer ring relative to the axis of rotation and/or exposing the shaft to thermal loads which lengthen the shaft axially, and compensating for the lengthening of the shaft by displacing the floating bearing inner ring axially within the floating bearing outer ring. 
    
    
     
       FIGURES 
       The above-mentioned and other features of this disclosure, and the manner of attaining them, will become more apparent and better understood by reference to the following description of embodiments described herein taken in conjunction with the accompanying figures, wherein: 
         FIG. 1  depicts a cross-sectional view of a hot-air valve in an open configuration/position with a rolling bearing system constructed in accordance with the present disclosure; 
         FIG. 2A  depicts a cross-sectional view of a fixed bearing of the rolling bearing system of  FIG. 1  with an inner ring and an outer ring aligned to each other; 
         FIG. 2B  depicts a cross-sectional view of the fixed bearing of the rolling bearing system of  FIG. 2A  with the inner ring tilted relatively to the outer ring; 
         FIG. 2C  depicts a cross-sectional view of the fixed bearing of the rolling bearing system of  FIG. 2A  with the inner ring at a maximum tilt angle relative to the outer ring; 
         FIG. 3A  depicts a cross-sectional view of a floating bearing of the rolling bearing system of  FIG. 1  with an inner and an outer ring aligned to each other; 
         FIG. 3B  depicts a cross-sectional view of the floating bearing of the rolling bearing system of  FIG. 3A  with the inner ring tilted relatively to the outer ring; 
         FIG. 3C  depicts a cross-sectional view of the floating bearing of the rolling bearing system of  FIG. 3A  with the inner ring tilted and displaced axially relatively to the outer ring; 
         FIG. 3D  depicts a cross-sectional view of the floating bearing of the rolling bearing system of  FIG. 3A  with the inner ring at a maximum tilt angle relative to the outer ring; and 
         FIG. 4  depicts a cross-sectional view of the hot-air valve of  FIG. 1  in a closed configuration/position with the rolling bearing system constructed in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It may be appreciated that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention(s) herein may be capable of other embodiments and of being practiced or being carried out in various ways. Also, it may be appreciated that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting as such may be understood by one of skill in the art. 
     Broadly, the present disclosure provides a rolling bearing system for hot-air valves wherein the rolling bearing system may compensate for all mechanically induced deflection and thermally induced linear expansion of the valve shaft relative to the valve housing without generating additional internal loads between the bearing elements. 
     Referring now to the  FIGS. 1 and 2A-2C ,  FIG. 1  depicts a cross-sectional view of a hot-air valve  10  according to the present disclosure. Hot-air valve  10  may be particularly configured and arranged, through design and selection of materials, to operate over a temperature range of 219.3 K (−65°) F. to 977.6 K (1,300° F.), and/or to a pressure of up to 3.103 MPa (450 psi), such as for aviation (aircraft) applications. 
     As shown, hot-air valve  10  comprises a planar, circular valve baffle  12 , in the form of a disc, coupled to a rotatable shaft  14 . Valve baffle  12  is used to open and close a circular hot-air passageway  16 , particularly with a quarter-turn of rotatable shaft  14  in a known manner. As shown, valve baffle  12  is in open configuration or position. In such position, the hot-air  18  can pass through the valve  10  since the valve baffle  12  is aligned parallel to the hot-air flow  18 . 
     Rotatable shaft  14  may be assembled and seated in a tubular (circular) shaped housing  20  which defines hot-air passageway  16 . Rotatable shaft  14  may be arranged to rotate relative to housing  20 , particularly to open and close hot-air passageway  16  with valve baffle  12 , with the assistance of a rolling bearing system  30  which comprises at least one bearing  32 ,  34  which encompasses each opposing end of the rotatable shaft  14 . As shown, bearing  32  more particularly comprises a fixed bearing, while bearing  34  more particularly comprises a floating bearing. The bearings  32 ,  34  may have an outer diameter in a range of 1.27 cm (0.5 inch) to 12.7 cm (5.0 inch). 
     As used herein, a fixed bearing  32  may be understood as a bearing which is configured and arranged to inhibit axial displacement between the shaft  14  and the housing  20 , while a floating bearing  34  may be understood as a bearing which is configured and arranged to permit axial displacement between the shaft  14  and the housing  20 , such as due to thermal expansion and contraction of the shaft  14  relative to the housing  20 . 
     The fixed bearing  32  may comprise a plurality of rollers  40  (as opposed to balls) located between an inner race  42  and outer race  44 . In such instance, fixed bearing  32  may be more accurately referred to as a fixed roller bearing. As shown, rollers  40  more particularly comprise spherical rollers  46 . 
     The spherical rollers  46  may comprise one or more of the following materials: martensitic stainless steel (e.g. BG42), nickel/cobalt base alloy (e.g. MP159) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). The spherical rollers  46  may also essentially consist of, or consist of, martensitic stainless steel (e.g. BG42), nickel/cobalt base alloy (e.g. MP159) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     The spherical rollers  46  have a convex spherical roller surface  48  which extends along the longitudinal axis/width W SR  of the spherical roller  46  and completely around the outer circumference of the spherical roller  46 , which results in the spherical roller  46  increasing in diameter from the longitudinal side end faces  47  of the spherical roller  46  to the longitudinal center of the spherical roller  46 , with the longitudinal center of the spherical roller  46  having the greatest diameter. 
     As shown, the curvature of the spherical roller surface  48  is defined by a constant radius which extends continuously along the complete longitudinal axis/width W SR  of the spherical roller  46 . However, it should be understood that in other embodiments, the curvature of the spherical roller surface  48  may be defined by a constant radius which extends only along a substantial portion of longitudinal axis/width W SR  of the spherical roller  46 , such as greater than 90% of the longitudinal axis/width W SR  of the spherical roller  46 . 
     The inner race  42  may be formed unitary with the shaft  14  (i.e. as a single component) or, more particularly, may be formed as a separate component. As shown, inner race  42  is formed as a separate component from shaft  14 , particularly as a single piece annular inner ring  50 . Inner ring  50  is mechanically coupled to the shaft  14  such that the inner ring  50  remains in a fixed position relative to the shaft  14 , i.e. does not move axially along the length of the shaft  14  or rotate independent of the shaft  14 . The inner ring  50  may be mechanically coupled to the shaft  14  via an interference (press) fit. 
     Inner ring  50  may comprise one or more of the following materials: martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Inner ring  50  may also essentially consist of, or consist of, martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Inner ring  50  further comprises a U-shaped annular groove  52  into which spherical rollers  46  may be seated. As shown, the bottom of the annular groove  52  has a concave spherical raceway surface  54  which extends along the longitudinal axis/width W AG  of the annular groove  52  and completely around the outer circumference of the inner ring  50 . Also as shown, the concave spherical raceway surface  54  of inner ring  50  has a spherical curvature which is substantially the same as the spherical curvature of the convex spherical roller surface  48  of spherical rollers  46 . More particularly, the concave spherical raceway surface  54  of inner ring  50  is defined by a radius which is substantially equal (i.e. within design tolerance) to the radius which defines the convex spherical roller surface  48  of spherical rollers  46 . However, in alternative embodiments, the concave spherical raceway surface  54  of inner ring  50  may be defined by a radius which is greater than the radius which defines the convex spherical roller surface  48  of spherical rollers  46 . For example, the concave spherical raceway surface  54  of inner ring  50  may be defined by a radius which is 1% to 10% greater than the radius which defines the convex spherical roller surface  48  of spherical rollers  46 . 
     As shown, the curvature of the spherical raceway surface  54  is defined by a constant radius which extends continuously along the complete longitudinal axis/width W AG  of the annular groove  52 . However, it should be understood that in other embodiments, the curvature of the spherical raceway surface  54  may be defined by a constant radius which extends only along a substantial portion of longitudinal axis/width W AG  of the annular groove  52 , such as greater than 90% of the longitudinal axis/width W AG  of the annular groove  52 . 
     The outer race  44  may be formed unitary with the housing  20  (i.e. as a single component) or, more particularly, may be formed as a separate component. As shown, outer race  44  is formed as a separate component from housing  20 , particularly as a single piece annular outer ring  56 . Outer ring  56  is mechanically coupled to the housing  20  such that the outer ring  56  remains in a fixed position relative to the housing  20 . The outer ring  56  may be mechanically coupled to the housing  20  via an interference (press) fit. 
     Outer ring  56  may comprise one or more of the following materials: martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Outer ring  56  may also essentially consist of, or consist of, martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Outer ring  56  further comprises a concave spherical raceway surface  58 . As shown, the concave spherical raceway surface  58  of outer ring  56  extends along the longitudinal axis/width W OR  of the outer ring  56  and completely around the inner circumference of the outer ring  56 . Also as shown, the concave spherical raceway surface  58  of outer ring  56  has a spherical curvature which is substantially the same as the spherical curvature of the convex spherical roller surface  48  of spherical roller  46 . More particularly, the concave spherical raceway surface  58  of outer ring  56  is defined by a radius which is substantially equal (i.e. within design tolerance) to the radius which defines the convex spherical roller surface  48  of spherical roller  46 . However, in alternative embodiments, the concave spherical raceway surface  58  of outer ring  56  may defined by a radius which is greater than the radius which defines the convex spherical roller surface  48  of spherical roller  46 . For example, the concave spherical raceway surface  58  of outer ring  56  may defined by a radius which is 1% to 10% greater than the radius which defines the convex spherical roller surface  48  of spherical roller  46 . 
     As shown, the curvature of the spherical raceway surface  58  is defined by a constant radius which extends continuously along the complete longitudinal axis/width W OR  of the outer ring  56 . However, it should be understood that in other embodiments, the curvature of the spherical raceway surface  58  may be defined by a constant radius which extends only along a substantial portion of longitudinal axis/width W OR  of the outer ring  56 , such as greater than 90% of the longitudinal axis/width W OR  of the outer ring  56 . 
     The fixed bearing  32  may additionally include a cage  60 , which separates the spherical rollers  46  from each other. The optional cage  60  may be guided by the lands of the inner ring  50  and/or by the side faces  47  and/or the outer diameter of the spherical rollers  46 . 
     A possible mechanical means to hold the outer ring  56  of the fixed bearing  32  in the housing  20  may be cover  62 . A possible mechanical means to hold the inner ring  50  of the fixed bearing  32  to the shaft  14  may be fastener (nut)  64 . 
     Referring now to  FIGS. 1 and 3A-3D , the floating bearing  34  may comprise a plurality of rollers  70  (as opposed to balls) located between an inner race  72  and outer race  74 . In such instance, floating bearing  34  may be more accurately referred to as a floating roller bearing. As shown, the rollers  70  more particularly comprise spherical rollers  76 . The spherical rollers  76  may comprise or essentially consist of ceramic, and more particularly silicon nitride. 
     The spherical rollers  76  have a convex spherical roller surface  78  which extends along the longitudinal axis/width W SR  of the spherical roller  76  and completely around the outer circumference of the spherical roller  76 , which results in the spherical roller  76  increasing in diameter from the longitudinal side end faces  77  of the spherical roller  76  to the longitudinal center of the spherical roller  76 , with the longitudinal center of the spherical roller  76  having the greatest diameter. 
     As shown, the curvature of the spherical roller surface  78  is defined by a constant radius which extends continuously along the complete longitudinal axis/width W SR  of the spherical roller  76 . However, it should be understood that in other embodiments, the curvature of the spherical roller surface  78  may be defined by a constant radius which extends only along a substantial portion of longitudinal axis/width W SR  of the spherical roller  76 , such as greater than 90% of the longitudinal axis/width W SR  of the spherical roller  76 . 
     The inner race  72  may be formed unitary with the shaft  14  (i.e. as a single component) or, more particularly, may be formed as a separate component. As shown, inner race  72  is formed as a separate component from shaft  14 , particularly as a single piece annular inner ring  80 . Inner ring  80  is mechanically coupled to the shaft  14  such that the inner ring  80  remains in a fixed position relative to the shaft  14 , i.e. does not move axially along the length of the shaft  14  or rotate independent of the shaft  14 . The inner ring  80  may be mechanically coupled to the shaft  14  via an interference (press) fit. 
     Inner ring  80  may comprise one or more of the following materials: martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Inner ring  80  may also essentially consist of, or consist of, martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Inner ring  80  further comprises a U-shaped annular groove  82  into which spherical rollers  76  may be seated. As shown, the bottom of the annular groove  72  has a concave spherical raceway surface  84  which extends along the longitudinal axis/width W AG  of the annual groove  82  and completely around the outer circumference of the inner ring  80 . Also as shown, the concave spherical raceway surface  84  of inner ring  80  has a spherical curvature which is substantially the same as the spherical curvature of the convex spherical roller surface  48  of spherical roller  46 . More particularly, the concave spherical raceway surface  84  of inner ring  80  is defined by a radius which is substantially equal (i.e. within design tolerance) to the radius which defines the convex spherical roller surface  78  of spherical roller  76 . However, in alternative embodiments, the concave spherical raceway surface  84  of inner ring  80  may defined by a radius which is greater than the radius which defines the convex spherical roller surface  78  of spherical roller  76 . For example, the concave spherical raceway surface  84  of inner ring  80  may defined by a radius which is 1% to 10% greater than the radius which defines the convex spherical roller surface  78  of spherical roller  76 . 
     As shown, the curvature of the spherical raceway surface  84  is defined by a constant radius which extends continuously along the complete longitudinal axis/width W AG  of the annular groove  82 . However, it should be understood that in other embodiments, the curvature of the spherical raceway surface  84  may be defined by a constant radius which extends only along a substantial portion of longitudinal axis/width W AG  of the annular groove  82 , such as greater than 90% of the longitudinal axis/width W AG  of the annular groove  82 . 
     The outer race  74  may be formed unitary with the housing  20  (i.e. as a single component) or, more particularly, may be formed as a separate component. As shown, outer race  74  is formed as a separate component from housing  20 , particularly as a single piece annular outer ring  86 . Outer ring  86  is mechanically coupled to the housing  20  such that the outer ring  86  remains in a fixed position relative to the housing  20 . The outer ring  86  may be mechanically coupled to the housing  20  via an interference (press) fit. 
     Outer ring  86  may comprise one or more of the following materials: martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Outer ring  86  may also essentially consist of, or consist of, martensitic stainless steel (e.g. BG42, Cronidur 30, XD15NW), carburizing stainless steel (e.g. CSS-42L, Pyrowear 675), powder metal high speed steel (e.g. Rex 20, Rex 76, ASP 2042, ASP 2060), nickel/cobalt base alloy (e.g. MP159), nickel base alloy (e.g. Inconel 718), cobalt base alloy (e.g. Stellite 6, Stellite 19, Stellite 190, Tribaloy 800) and ceramic (e.g. silicon nitride, partially stabilized zirconia, fully stabilized zirconia, silicon carbide and alumina). 
     Outer ring  86  further comprises a cylindrical raceway surface  88 . As shown, the cylindrical raceway surface  88  of outer ring  86  extends along the longitudinal axis/width W OR  of the outer ring  86  and completely around the inner circumference of the outer ring  86 . 
     In contrast to the outer ring  56  of the fixed bearing  32 , wherein the raceway surface  58  of outer ring  56  has a curvature which is substantially the same or greater than the curvature of the roller surface  48  of spherical roller  46 , the raceway surface  88  of outer ring  86  of the floating bearing  34  does not have a curvature which is substantially the same or greater than the curvature of the raceway surface  88  of spherical roller  76 . Such distinction will be discussed in greater detail below. 
     The floating bearing  34  may additionally include a cage  90 , which separates the spherical rollers  70  from each other. A possible mechanical means to hold the outer ring  86  of the floating bearing  34  in the housing  20  may be cover  92 . A possible mechanical means to hold the inner ring  80  of the floating bearing  34  to the shaft  14  may be fastener (nut)  94 . 
     Referring more particularly to  FIGS. 2A-2C , there is shown a cross-sectional view of the fixed bearing  32  of  FIG. 1  mounted to the shaft  14  in two different kinematic situations. The different kinematic situations may be understood to be associated with the hot-air valve  10  being in an open configuration/position in  FIG. 2A , and the hot-air valve  10  being in a close configuration/position in  FIG. 2B . 
     As shown in  FIG. 2A , the inner ring  50  is in alignment with the outer ring  56 . In other words, when the inner ring  50  is in alignment with the outer ring  56 , each of the inner ring  50 , spherical rollers  46  and outer ring  56  have a transverse center plane TCP which is the same plane, which is shown perpendicular to the longitudinal axis LA. However, in  FIG. 2B , when shaft  14  is shown to bend/deflect (particularly as a result of the hot-air valve being closed  10  and the hot-air  18  applying force/pressure to valve baffle  12 ), only the inner ring  50  and the spherical rollers  46  have a common transverse center plane TCP. 
     As shown in  FIG. 2B , in contrast to  FIG. 2A , the inner ring  50  and spherical rollers  46  are no longer aligned with the outer ring  56  as set forth above with respect to  FIG. 2A . More particularly, due to the bending of the shaft  14 , the transverse center plane of the inner ring TCP IR  and the transverse center plane of the spherical rollers TCP IR  are each tilted about their intersection with the longitudinal axis LA, shown at center (pivot) axis A, such that they are no longer in the same plane as the transverse center plane of the outer ring TCP OR . As shown, the transverse center plane of the inner ring TCP IR  and the transverse center plane of the spherical rollers TCP SR  are tilted at a tilt angle TA relative to the transverse center plane of the outer ring TCP OR . As best shown by  FIG. 2C , with the arrangement, a maximum tilt angle TA may be achieved when a longitudinal end  47  of the spherical roller  46  makes contact with the longitudinal end  57  of the outer ring  56 . For the present application, the tilt angle TA may range from plus or minus 6 degrees (i.e. +/−6 degrees), and more particularly plus or minus 2 degrees (i.e. +/−2 degrees). 
     Based on the design presented above, the inner ring  50 , the spherical rollers  46  and the optional cage  60  are able to tilt about center (pivot) axis A relatively to the outer ring  56  as shown in  FIG. 2B . As a result, possible bending of the shaft  14  may be compensated for without losing bearing functionality, without generating additional internal loads between the spherical rollers  46 . 
     Referring now more particularly to  FIGS. 3A-3D , there is shown a cross-sectional view of the floating bearing  34  of  FIG. 1  mounted to the shaft  14  in three different kinematic situations. The different kinematic situations may be understood to be associated with the hot-air valve  10  being in an open configuration/position in  FIG. 3A , and the hot-air valve  10  being in a close configuration/position in  FIGS. 3B and 3C . 
     As shown in  FIG. 3A , the inner ring  80  is in alignment with the outer ring  86 . In other words, when the inner ring  80  is in alignment with the outer ring  86 , each of the inner ring  80 , spherical rollers  76  and outer ring  86  have a transverse center plane TCP which is the same plane, which is shown perpendicular to the longitudinal axis LA. However, in  FIG. 3B , when shaft  14  is shown to bend/deflect (particularly as a result of the hot-air valve being closed  10  and the hot-air  18  applying force/pressure to valve baffle  12 ), only the inner ring  80  and the spherical rollers  76  have a common transverse center plane TCP. 
     As shown in  FIG. 3B , in contrast to  FIG. 3A , the inner ring  80  and spherical rollers  76  are no longer aligned with the outer ring  86  as set forth above with respect to  FIG. 3A . More particularly, due to the bending of the shaft  14 , the transverse center plane of the inner ring TCP IR  and the transverse center plane of the spherical rollers TCP SR  are each tilted about their intersection with the longitudinal axis LA, shown at center (pivot) axis B, such that they are no longer in the same plane as the transverse center plane of the outer ring TCP OR . As shown, the transverse center plane of the inner ring TCP IR  and the transverse center plane of the spherical rollers TCP SR  are tilted at a tilt angle TA relative to the transverse center plane of the outer ring TCP OR . As best shown by  FIG. 3D , with the arrangement, a maximum tilt angle TA may be achieved when a longitudinal end  77  of the spherical roller  76  makes contact with the longitudinal end  87  of the outer ring  86 . For the present application, the tilt angle TA may range from plus or minus 6 degrees (i.e. +/−6 degrees), and more particularly plus or minus 2 degrees (i.e. +/−2 degrees). 
     Referring now to  FIG. 3C , as set forth above, outer ring  86  of floating bearing  34  comprises a cylindrical raceway surface  88 , whereas the outer ring  56  of fixed bearing  32  comprises a spherical raceway surface  58 . As such, inner ring  80  and rollers  76  are able to be displaced axially and travel along the longitudinal axis within and relative to the outer ring  86 , particularly in response to axial displacement of shaft  14 . Inner ring  80  and rollers  76  may travel axially as shown by axial displacement AD. 
     Based on the design presented above, the inner ring  80 , the spherical rollers  76  and the optional cage  90  are able to tilt and tilt about pivot axis B relatively to the outer ring  86  as shown in  FIG. 3B . As a result, possible bending of the shaft  14  therefore may be compensated without losing bearing functionality and without generating additional internal loads between the spherical rollers  76 . In addition, since the raceway surface  88  of the outer ring  86  is cylindrical, the inner ring  80 , the spherical rollers  76  and the optional cage  90  are able to move axially with axial displacement AD relatively to the outer ring  86 . Axial displacement AD and tilting are possible at the same time without losing bearing functionality and without generating additional internal loads between the bearing elements as shown in  FIG. 3C . 
       FIG. 4  depicts a cross-sectional view of the hot-air valve  10  of  FIG. 1  in closed configuration/position. Resulting from a quarter-turn of the shaft  14  with the attached valve baffle  12  and the inner rings  50  and  80  of the bearings  32  and  34 , respectively, relative to the housing  3  and the outer rings  56  and  86  of the bearings  32  and  34 , respectively, the valve baffle  12  closes the tubular passage  16  of the housing  20  and stops the gas flow  18 . As a result, gas pressure is building up on one side of the valve baffle  12 , which results a bending of shaft  14  and valve disc  13 . 
     By tilting the inner rings  50  and  80 , the spherical rollers  46  and  76  and the optional cages  60  and  90  relatively to the outer rings  56  and  86  of the fixed bearing  32  and the floating bearing  34 , respectively, the bending of the shaft  14  is compensated for in the fixed bearing  32  and the floating bearing  34 . Additionally, the floating bearing  34  compensates different temperature induced linear expansion of shaft  14  and housing  20  by axial movement of the inner ring  80 , the spherical rollers  76  and the possible cage  90  relatively to the outer ring  86 . Both bending of the shaft  14  and linear thermal expansion of the shaft  14  relative to housing  20  is compensated by the bearing system without losing bearing functionality and without inducing additional loads onto the bearing rings  50 ,  80 ,  56 ,  86 , the spherical rollers  46 ,  76  and the optional cages  60 ,  90 . All four rings of the bearing system, i.e. inner ring  50 , inner ring  80 , outer ring  56  and outer ring  86 , remain fixed to the housing  20  and to the shaft  14  or may be integral with housing  20  and shaft  14 . A possible mechanical means of a fixture of the outer bearing rings  56  and  86  to the housing may be covers  62  and  92 , while a possible mechanical means of a fixture of the inner rings  50  and  80  to the shaft  14  may be fasteners (nuts)  64  and  94 . 
     While a preferred embodiment of the present invention(s) has been described, it should be understood that various changes, adaptations and modifications can be made therein without departing from the spirit of the invention(s) and the scope of the appended claims. The scope of the invention(s) should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. Furthermore, it should be understood that the appended claims do not necessarily comprise the broadest scope of the invention(s) which the applicant is entitled to claim, or the only manner(s) in which the invention(s) may be claimed, or that all recited features are necessary.