Patent Publication Number: US-2007113550-A1

Title: Turbocharger with a thin-walled turbine housing having a floating flange attachment to the centre housing

Description:
The present invention relates to a turbocharger having a thin-walled turbine housing connected by a floating flange attachment comprising a floating flange ring.  
      Turbochargers are well known and widely used in connection with combustion engines. Exhaust gas from an engine is supplied to and drives a turbine wheel which drives a compressor wheel. The compressor wheel compresses air and discharges it into combustion chambers of respective cylinders. The thus compressed air contains an increased amount of oxygen per volume unit to enhance the combustion of fuel and thus to generate more power. Generally, the exhaust gas supplied to the turbine wheel is passed through an inlet and a volute to the turbine wheel and then exits through an outlet. In order to provide a light-weight turbine, the volute can simply be formed by a thin-walled turbine housing surrounding the turbine wheel and being connected to the center housing.  
      One example of an attachment of the thin-walled housing to the center housing is shown in the international application No. WO 02/06637 A1. Therein, the turbocharger comprises a center housing and an insert accommodating a turbine wheel. The center housing and the insert are connected to each other by means of bolts at their circumferentially outer portions. A thin-walled turbine housing surrounds the insert so as to constitute a volute through which the exhaust gas is supplied to drive the turbine wheel. A circumferential end portion of the thin-walled housing contacts the circumferential outer portion of the insert and an U- or V-band is laid around the outer portions of the center housing, the insert and the thin-walled housing and is tightened by bolts so as to clamp the end portion of the thin-walled housing to the insert. Thus, an attachment of the thin-walled housing to the remainder of the turbocharger is achieved.  
      The object of the invention is to provide an improved turbocharger having a thin-walled exhaust housing and a method for assembling thereof. A particular aim is to provide a reliable, leak proof and compact attachment of the thin-walled exhaust housing.  
      According to one aspect of the invention, the above object is achieved by a turbocharger having the features of claim  1  and claim  19 , respectively. Preferable embodiments of the turbocharger are set forth in the subclaims.  
      In an exemplary embodiment of the invention, a turbocharger has a center housing and a thin-walled exhaust housing, wherein both housings are connected to each other at cylindrical end portions thereof by use of a floating flange ring having a clamping surface which upon applying an axial load exerts at least an axial force component for urging the end portion of the thin-walled housing against the end portion of the center housing. The use of an axial load enables good sealing properties of the housing portions. The floating flange ring can provide a sufficient stiffness, so that the axial load is securely provided at the whole circumference of the ring so as to secure an appropriate sealing reliability.  
      According to exemplary embodiments, the clamping surface may be slanted so as to exert a radial force component additionally to the axial force component. Furthermore, the clamping surface may be slanted such that said radial component is directed towards an axial center axis of said housing portions.  
      Additionally, the turbocharger may further comprise a counter part to the floating flange ring having a clamping surface on the side opposite to the clamping surface of the floating flange ring with respect to a flange-like projection forming the cylindrical end portion of the center housing. Furthermore, the attachment device may comprise at least a screw for applying said axial load between said counter part and said floating flange ring.  
      The floating flange ring may also be provided with at least three boss portions each receiving one of the screws, the boss portions projecting radially from the floating flange ring, and three washers, forming the counter parts, may be provided with the screws.  
      In an exemplary embodiment the bosses receive said screws in through holes and the screws may be tightened by means of nuts. The advantage of the through holes resides in that they are easy to machine. Alternatively, the bosses may receive said screws in blind holes having inner threads. This allows a space-saving arrangement and an easy assembly of the attachment device since no nuts are required to tighten the screws.  
      Furthermore, the bosses may be positioned at regular intervals on the circumference of the floating flange ring, which brings a well balanced distribution of the sealing forces between the housing portions induced by the axial loads of the screws in the bosses.  
      Additionally, adjacent to a tip end of the clamped end portion of the thin-walled housing portion a notch may be provided in the floating flange ring so as to be able to receive said tip end. Thus, a certain clearance for the thin-walled housing is provided, preventing stresses at the tip end portion of the thin-walled housing which could be provoked if the notch would not be provided. Furthermore, the notch also reduces stresses in the area of the notch itself.  
      Moreover, a single counter part in the form of a ring may be provided having bores at positions corresponding to the bosses for receiving each of the screws. This reduces the number of components and simplifies the assembling of the turbocharger.  
      The turbocharger may further comprise a sealing device disposed between the projection and the clamped end portion of the thin-walled housing. The sealing device improves sealing performance and further reduces stresses at the components to be connected. In an exemplary embodiment, the sealing device may have a four-sided cross-section one side of which may be slanted to be substantially parallel to the slanted clamping surface of the flange ring. Thus, the axial load provoked by the screws exerts an axial force component and a radial force component in the sealing device. Since the sealing device may also be in contact with the projection, an outer surface of an insert being mounted to the center housing and the clamped end portion of the thin-walled exhaust housing, the force components in the sealing device can then act on the two sides of the sealing device which are perpendicular to each other and which are opposite to the slanted side of the sealing device. This further improves the sealing performance since, in this case, the active sealing surface is enlarged, i.e. the two above mentioned perpendicular sides of the sealing device are activated.  
      Additionally, the sealing device may be made from a resilient material further improving sealing performance and reducing stresses.  
      Further, the cylindrical end portion of the exhaust housing may be slanted to be parallel to the slanted clamping surface of the floating flange ring. This will be advantageous in view of reducing stress when the sealing device having a slanted side is not provided.  
      The projection may have a substantially rectangular cross-section. Furthermore, the side of the projection facing the clamped end portion of the thin-walled exhaust portion may be parallel to the latter. This contributes to mountability and sealing performance of the turbocharger.  
      Furthermore, an exemplary method for assembling a turbocharger with a thin-walled housing, an inlet, a center housing and an insert is provided. The method comprises the following steps: orientating and holding a center housing assembly comprising the center housing and the insert by means of a jig; setting a thin-walled assembly comprising the thin-walled housing and the floating flange ring on the center housing assembly; bringing the inlet in contact with a jig portion which has a fixed orientation with respect to the jig so as to set the orientation of the inlet relative to the turbocharger. 
    
    
      In the following, further technical solutions of the object of the invention are described in detail with reference being made to the enclosed drawings, in which:  
       FIG. 1  is a sectional view of a part of a turbocharger where a turbine housing is connected to a center housing with a floating flange ring according to an embodiment of the invention;  
       FIG. 2  is another sectional view of a part of the turbocharger wherein the turbine housing is connected to a center housing with the floating flange ring according to the embodiment of the invention;  
       FIG. 3  is a schematic front view of the floating flange according to the embodiment the invention (a view from the left side in  FIG. 1  or  2 );  
       FIG. 4  is a perspective view of a part of the turbocharger, wherein the turbine housing is connected to the center housing with the floating flange ring according to the embodiment of the invention, wherein a thin-walled housing is partly cut away for illustrative reasons. 
    
    
      A turbocharger according to the embodiment shown in  FIG. 1  comprises substantially a compressor housing (not shown) for accommodating a compressor wheel, a center housing  1  for accommodating a bearing assembly and a turbine housing assembly  2  for accommodating a turbine wheel  3 . A shaft  4  extends through the center housing  1  so as to connect the turbine wheel  3  to the compressor wheel. Thus, the rotation of the turbine wheel  3  can be transmitted to the compressor wheel for compressing inlet air for an engine. The turbine wheel  3  is driven by exhaust gas coming from the engine and flowing through a volute  5  and an exhaust gas flow channel  33  (refer to  FIG. 2 ) to the turbine wheel  3 . A variable nozzle device  6  is interposed between the center housing  1  and a insert  11  which will be described latex. By means of the variable nozzle device  6 , the rotational speed of the turbine wheel  3 , and as well a rotational speed of the compressor wheel, can be set in accordance to the position of the variable nozzle device  6 . The volute  5  is defined by a volute portion  13   a  of a thin-walled exhaust housing  13  (shown in  FIG. 4 ) and the insert  11  which are parts of the turbine housing assembly  2 . As shown in  FIG. 4 , the exhaust housing  13  further comprises an inlet portion  13   b  and an outlet portion  13   c , these portions  13   a ,  13   b ,  13   c  being sheet metal parts (or casting parts) which are welded or formed together so as to constitute the thin walled exhaust housing  13 .  
      As shown in another sectional view of a part of the turbocharger in  FIG. 2 , the nozzle device  6  comprises a nozzle ring  7  and an unison ring  8  which are rotatable relatively to each other by actuating a cam  10  so as to adjust an inclination of vanes  9  mounted to the nozzle ring  7 .  
      As shown in  FIGS. 1 and 2 , the insert  11  comprises a tube portion  11   b  partly surrounding the turbine wheel  3  and a radially outward extending ring portion  11   a  connected to the tube portion  11   b . The ring portion  11   a  constitutes, together with the nozzle ring  7 , the exhaust gas flow channel  33  in which the vanes  9  are positioned to control the exhaust gas flow. Furthermore, the insert  11  comprises an attachment ring portion  11   c  which is connected to the ring portion  11   a  of the insert  11  via support posts  12 . The support posts  12  are kept as small as possible so as not to interfere the exhaust gas flow into the exhaust gas flow channel  33  accommodating the vanes  9 . Finally, the insert  11  is fixed to the center housing  1  via bolts  25  engaging the attachment ring portion  11   c.    
      The insert  11  is surrounded by the thin-walled exhaust housing  13  having the inlet  13   b  and defining the volute  5  together with the insert  11 . Accordingly, the exhaust gas coming from an engine (not shown) can enter the inlet  13   b , flows through the volute  5  and through the plurality of exhaust gas flow channels  33  defined by the ring portion  11   a  of the insert  11 , the nozzle ring  7  and the vanes  9 , thus driving the turbine wheel  3  according to the adjustable inclination of the vanes  9 , and then the exhaust gas exits through the outlet  13   c  connected to the tube portion  11   b.    
      The center housing  1  comprises a circumferentially extending flange portion  27 , forming a projection, having a substantially rectangular cross-sectional shape. This flange portion  27  has a larger outer diameter compared to that of the insert  11 . Furthermore, the turbine side face of the flange portion  27  is, compared to the turbine side face of the center housing  1 , offset in a direction towards the compressor side. Between these offset faces, a circumferentially extending groove  30  is disposed radially inward of the flange portion  27  so as to receive an annular projection  32  axially protruding from the attachment ring portion  11   c  of the insert  11 . When assembling these parts together, a radially acting support and positioning means for the insert  11  is defined.  
      To fix the thin-walled exhaust housing  13  to the assembly of the center housing  1  a floating flange ring  16  according to the invention is used, which is shown in a front view in  FIG. 3 . The floating flange ring  16  is substantially ring shaped and has an inner diameter fitting to the outer diameter of the flange portion  27  of the center housing  1  (refer to  FIGS. 1 and 2 ). Five bosses  18  are located at regular intervals at the outer circumferential area of the flange ring  16 . Each boss  18  has a bore (blind hole)  19  extending in the axial direction of the floating flange ring  16  while having its aperture on the side facing the center housing  1 . The bores  19  are provided with threads so as to receive screws  23 . The floating flange ring  16  is floatingly mounted on the thin-walled exhaust housing  13 —i.e. no form fit in the radial direction thereof is provided—so as to abut the internal surface of the outer diameter portion of the thin-walled exhaust housing  13  against the center housing  1  of the turbocharger.  
      As shown in  FIGS. 1 and 2 , the cross-sectional shape of the flange ring  16  at the portions between the bosses  18  is substantially L-shaped having an axially extending limb  20  and a radially extending limb  21 . An inner face of the axially extending limb  20  fits with the outer diameter of the flange portion  27 . An inner diameter of the radially extending limb  21  is smaller than the outer diameter of the flange portion  27  but larger than the outer diameter of the insert  11 . The radially extending limb  21  is tapered from the tip thereof—a radially inner end of the radially extending limb  21 —to the transition to the axially extending limb  20 —a radially outer end of the radially extending limb  21 . Accordingly, the thickness of the radially extending limb  21  increases in the radial outward direction and thus a inner slanted side  26   b  of the limb  21  is defined. A notch  22  is formed at the inner transition between the limbs  20  and  21 .  
      The cross-sectional shape of the floating flange ring  16  at the portion of the bosses  18  (refer to  FIG. 1 ) corresponds substantially to that of the portion between the bosses  18  (refer to  FIG. 2 ) but is additionally adapted to receive the screw  23 .  
      A four-sided sealing ring  24  made from a resilient material is provided such that one side thereof is in contact with the radially outer surface of the insert  11  and another face is in contact with the turbine side surface of the flange portion  27  of the center housing  1 . A third side  26  of the sealing ring  24  is slanted with respect to the other sides, which are perpendicular/parallel to each other. The third side  26  is parallel to and faces the slanted side  26   b  of the radial limb  21  of the floating flange ring  16 . A circumferential extending end portion  28  of the thin-walled exhaust housing  13  is sandwiched between the sealing ring  24  and the limb  21  of the floating flange ring  16 . The end portion  28  is parallel to the slanted sides  26 ,  26   b.    
      As shown in  FIG. 1 , a washer  29 , forming a counter part according to the invention, having a through hole is aligned with the bore  19  of the boss  18  at the compressor side of the flange portion  27 , i.e. the side opposite to the sealing  24  with respect to the flange portion  27  (left side in  FIG. 1 ). The washers  29  extend radially inwardly over the boss  18  so as to engage the flange portion  27 .  
      The length of the limb  20  is such that a small gap is defined between the floating flange ring  16  and the washer  29 . When the screw  23  is tightened, the limb  21  presses the end portion  28  of the thin-walled exhaust housing  13  against the sealing ring  24  by pressing washers  29  against flange portion  27 . Thus, the gap is minimized and the sealing ring  24  is compressed due to the axial load generated by the screw. Since the floating flange ring  16  has a certain stiffness, the axial pressure against the sealing ring  24  is sufficient also at the portions of the floating flange ring  16  between the bosses  18  and therefore the sealing performance is good all over the whole circumferentially extending attachment of the thin walled exhaust housing  13  to the center housing  1  and the insert  11 .  
      Furthermore, due to the slanted side  26  of the sealing ring  24  and the slanted side  26   b  of the limb  21 , the sealing ring  24  is compressed with an axial and a radial component against the turbine side face of the flange portion  27  and the radial outer face of the insert  11 , respectively. Due to the two force components also two sides of the sealing ring  24  are activated and thus the active sealing surface is enlarged. This leads to an enhanced sealing performance of the attachment of the thin walled exhaust housing  13  to the center housing  1 .  
      Additionally, since the turbine side face of the center housing  1  is offset in a direction towards the turbine compared to the turbine side face of the flange portion  27 , a shear force in the annular projection  32  of the insert  11  can be reduced when tightening the bolts  23 , leading to an improved reliability of the insert  11 .  
      The attachment device as described above allows a larger axial clamp load in the joint due to the use of a convenient number of screws of convenient dimension.  
      The invention is not restricted to the above described embodiment and can be changed in various modifications.  
      For example, in the above described embodiment five bosses  18  are used for tightening the floating flange ring  16 . However, an appropriate number of bosses  18  and bolts  23  can be provided for different dimensions or pressure conditions of the floating flange ring  16 .  
      Alternatively, instead of using a plurality of single washers  29  it is possible to use one single washer ring having bores corresponding to the bores  19  of the flange ring  16 . This reduces the number of components and simplifies the assembly.  
      Furthermore, the sealing ring  24  may be omitted and instead of the slanted side of the sealing ring  24  a respective side of the flange portion  27  may be suitably slanted.