Abstract:
A guiding grid of variable geometry comprises a plurality of guiding vanes in a housing in angular distances around a central axis in an axially extending vane space of a predetermined axial distance. Each vane is pivotal about an associated pivoting axis to assume different angles in relation to the central axis and, thus, to form a nozzle of variable cross-section between each pair of adjacent vanes. A nozzle ring supports the vanes around the central axis and forms a first axial limitation of the vane space. A unison ring is displaceable relative to the nozzle ring and is connected to the vanes to pivot them. An annular disk is fixed to the housing and faces the nozzle ring in an axial distance to form a second axial limitation of the vane space and a central opening. Into this opening, a sleeve may be inserted. A fixing arrangement determines the axial position of the annular disk with respect to the housing.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based upon European Patent Application No. 02 020 412,9, filed Sep. 10, 2002, from which priority is claimed. 
   FIELD OF THE INVENTION 
   The present invention relates to a guiding grid or actuator of variable geometry, particularly for a turbine housing having a central outlet pipe. More particularly, the invention relates to a guiding grid which comprises a plurality of guiding vanes arranged in angular distances about a central axis in an axially extending vane space of a predetermined axial distance, each vane being pivotal about an associated pivoting axis to assume different angles in relation to the central axis and, thus, to form a nozzle of variable cross-section between each pair of adjacent vanes. A generally annular nozzle ring for supporting the plurality of pivoting vanes around the central axis forms a first axial limitation of the vane space. A displaceable unison ring is placed around the central axis relative to the nozzle ring in order to vary the geometry of the guiding grid. The unison ring is connected to the vanes in order to pivot them when being displaced to adjust their respective angular position in relation to the central axis. Mechanical interconnections of a unison ring and the vanes are known in the art and can be formed by levers arranged in a rayed configuration and fastened to shafts of the vanes or by gears or any other means known in the art; in any case, the present invention is not restricted to one of these interconnections. 
   Furthermore, the present invention relates to a turbocharger including a guiding grid and further comprising a turbine housing and a releasably attachable bearing housing for supporting a turbine shaft. 
   BACKGROUND OF THE INVENTION 
   Guiding grids of the above-mentioned kind have become known by a multitude of documents, such as U.S. Pat. Nos. 4,179,247 or 5,146,752. U.S. Pat. No. 5,146,752, in particular, illustrates how laborious it is to mount the individual parts of the guiding grid in the housing, since various parts have to be matched, patched and fitted with one another and have to be interconnected, particularly when inserting them into a turbine unit or a turbocharger. It is clear, that such a construction is expensive. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a guiding grid of the kind described at the outset which is easy to assemble and can quickly be mounted. 
   A further object is to reduce mounting expenses by providing a simple and compact construction. 
   These objects are achieved according to the invention in two steps, i.e. first by providing a part (preferably in the form of an annular disk) fixed to the housing, that faces the nozzle ring, and is in an axial distance which corresponds to a predetermined axial distance from the nozzle ring so as to form a second axial limitation of the vane space. As a second step, a sleeve can be inserted into the central opening which comprises a fixing arrangement for determining the axial position of that part or disk with respect to said housing. In this way, the sleeve can be inserted together with the guiding grid as a pre-mounted module into the central opening such that the module can be fastened afterwards. 
   Such a module is particularly beneficial if an annular disk (or disk like body) is provided in a “cartridge” together with the remaining parts of the guiding grid so that the whole preassembled unit can be inserted into a turbine housing. In such an assembly, mounting is considerably simplified and accelerated because mounting is to the annular disk, and not directly to a wall of the turbine housing 
   In principle, mounting can be effected so that the sleeve is only frictionally fixed in the central opening. However, mounting can be done by providing at least one driver flange facing the side of the vanes to plug the sleeve into the central opening of the housing (particularly when providing an annular disk). Preferably, instead of having one or a plurality of peripherally distributed driver flanges, the driver flange will be formed by a radially extending flange of the sleeve which engages the disk at the side of the vane space. 
   The invention also relates to a turbocharger having a guiding grid which comprises a turbine housing and a bearing housing that is releasably attached to the turbine housing and supports the turbine shaft. When mounting the guiding grid, the fact that the bearing housing being releasably attached to the turbine housing allows easy access to the interior of the turbine housing and to a wall surrounding the central opening. Such a turbocharger is characterized by a plug connection for interconnecting the wall of the turbine housing and the guiding grid, thus defining the angular position in peripheral direction of the guiding grid relative to said housing (to avoid any turning movement), while the fixing device defines the axial position of the guiding grid. In this way, the guiding grid is quickly and precisely fastened to the turbine housing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details of the invention will become apparent from the following description of a preferred embodiment of the invention schematically illustrated in the drawings in which 
       FIG. 1  is an axial cross-section of the transitional region between turbine housing and bearing housing of a turbocharger where the guiding grid according to the invention is accommodated; and 
       FIG. 2  is a partial, perspective view of the guiding grid illustrating detail II of  FIG. 1  at a larger scale. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 , a part of a turbine housing  2  of a turbocharger  1  is represented which, typically, comprises a peripheral supply channel  9  for a fluid spirally wound around a central axis R, the fluid being of any nature, even liquid, but in case of a turbocharger supplying exhaust gas of a combustion motor as is known (not shown). This fluid is then supplied in radial direction through a plurality of guiding vanes  7  arranged around the central axis R to a turbine rotor (not shown) rotating about the central axis R. This turbine rotor is mounted, as is known, at the end of a rotor shaft (also not shown) which is supported in bearings  41  and  41 ′ situated within a bearing housing  40  that is releasably attached to the turbine housing  2  and fastened to it by bolts not shown. In the case of a turbocharger, this shaft extends through this bearing housing  40  to a compressor rotor located within a compressor housing that is either releasably attached to the bearing housing or may be integrally formed with it. This compressor may be driven in a known manner by the turbine wheel in the turbine housing via the common shaft, thus being driven by the exhaust gases supplied to the turbine housing  2 . 
   It has already been stated that it is known to make the guiding vanes  7 , which form a generally circular guiding grid, adjustable, thus conferring a variable geometry to the guiding grid in such a manner that the vanes  7  are either pivoted to be inclined towards the central axis R in a more radial direction or to extend approximately tangentially.  FIG. 2  illustrates these conditions and shows an antifriction bearing having rolling bodies in the form of rollers  3  between a unison or adjusting ring  5  and a nozzle ring or vane support ring  6  in which adjusting shafts  8  forming pivoting axes of the guiding vanes  7  are supported. Turning and adjusting the adjusting shafts  8  and of the unison ring  5 , that actuates them, may be done in a known manner as described in U.S. Pat. No. 4,659,295 mentioned above. In any case, the methodology described in the present invention causes a turning movement of the unison ring  5  to pivot relative to the stationary nozzle ring or vane supporting ring  6  which provokes a corresponding pivoting motion of the adjusting shafts  8 . 
   The free lever ends or heads  18  of adjusting levers  19  are held in grooves or recesses  17  of the unison ring  5  and fastened or connected to the adjusting shafts  8 ,. Note that in addition to through-passing recesses  17 , the grooves could also be provided at the inner radial side of the unison ring  5 , as is known, wherein the heads  18  are held so that the heads  18  ensure a pre-centering of the unison ring. Further, it is clear that this is but one of a variety of possible embodiments, and that an adjustment can also be effected and transmitted by slot cams or interengaging gear teeth. 
   In this way, exhaust gas of a combustion motor, supplied via the supply channel  9 , is supplied to a higher or lower extent to the turbine rotor (not shown) which rotates in the interior of the guiding grid formed by the vanes  7 , before the gas is discharged through a pipe  10  extending in axial direction along the central axis R. This discharge pipe  10  is, in the embodiment shown, decoupled from a following continuation  43  by a decoupling space  42 , but can, if desired, be directly connected to an exhaust system. 
   The unison ring  5  has a radially inwards directed rolling surface  20  where the rollers  3  can roll. Preferably, however, this is only provided for compensating tolerances, because in practice it will be preferred if the rollers  3  have a certain play under all operational circumstances both with respect to this rolling surface  20  and in relation to an opposite exterior roller surface  21  of the nozzle ring  6  which forms a shoulder. 
   As shown in  FIG. 2 , relatively few rollers  3  will be necessary if a cage ring or holding ring  22  is utilized. Although the rollers could also run in recesses of this holding ring  22 , it is advantageous if the rollers  3  have axial projections  24  of a smaller diameter which engage holes  25  of the holding ring  22  so that the latter provides an appropriate distance in a peripheral direction on the one hand, while holding and maintaining the rollers  3  firmly in axial direction on their track with respect to the rolling surfaces  20  and  21 . 
   A sealing ring  27  may be inserted into a sealing groove  28  of the nozzle ring  6 . When comparing  FIGS. 1 and 2 , the nozzle ring  6  is situated in the region of a housing wall portion  2   a . In principle, various sealing arrangements are conceivable: Either the sealing ring  27  is formed as a flexible sealing lip engaging the wall  2   a . This, in general, would present no problems, because these parts should not move relative to one another during operation. However, it would also be possible that an additional sealing ring or the sealing ring  27  shown could project into a groove of the wall  2   a , thus forming a kind of labyrinth sealing, and even a combination of both possibilities or an approach known in the art of sealings is conceivable. In any case, this sealing serves to keep dirt and pollution material away from the antifriction bearing  3 ,  20 ,  21 , stemming from the region of the supply channel  9 . 
   In a distance defined by spacers  31  arranged on the nozzle ring around the central axis R, a fastening disk  29  is provided which abuts to to the turbine housing  2  in the region of a housing flange  2   b  best seen in FIG.  1 . The fastening disk  29  is fastened to the nozzle ring  6  by way of bolts  30 , indicated by dotted lines, which extend, for example, through spacers  31 , the spacers  31  providing a somewhat larger space than would correspond to the width of the vanes  7  in axial direction, as is known, in order not to impede their pivoting movement at all temperature ranges. In this way, the guiding grid as shown in  FIG. 2  can readily be pre-assembled to be inserted into the turbine housing  2 . 
   In order to be able to insert the module thus created into the turbine housing  2  in a quick and precise way, it is connected to a sleeve  45  insertable into the central axial pipe  10  and having a central opening  53  so that this sleeve, in principle, needs only to be inserted into this discharge pipe  10 . To facilitate this, the sleeve  45  has at least one flange  46  which engages and brings with it the disk  29 , and thus preferably the whole guiding grid module, when being inserted into the discharge pipe  10 , thus determining the axial position of the module. If in this context the term “at least one driver flange”  46  is used, it should be understood that it would be possible to provide a plurality of driver flange-like claws or projections protruding in radial direction, particularly distributed in equal angular distances. However, it is preferred, if, as shown in  FIG. 2 , the driver member is formed as a driver flange  46  which extends in radial direction from the sleeve and grasps behind the disk  29  at the side of the vanes and the vane space, although it would, in principle, also be possible to have radially interengaging projections and recesses of the disk  29  and the sleeve  45 . 
   Particularly from  FIG. 1  it can be seen that it is advantageous if the disk  29  has at least one recess  47  adjacent the central opening. This recess  47  is engaged by at least one driver flange member  46  preferably so that the driver flange&#39;s surface towards the vane space is flush and aligned with that surface of the disk  29  that faces the nozzle ring  6 . In the case explained above where a plurality of radial projections are distributed over the circumference of the sleeve  45 , a plurality of corresponding recesses distributed over the circumference could be provided. In this way, fixing of the guiding grid module against any rotation about the central axis R could be effected at the same time. However, machining several individual and precise recesses into the sleeve  45  is more difficult to produce, for which reason it is preferred it the recess  47  is formed as a groove extending in peripheral direction of the sleeve  45  (see FIG.  2 ).  FIG. 1  shows clearly that with equal axial width of the groove  47  and the driver flange  46 , the latter is flush with the surface of the disk  29  so that flow conditions in the vane space, i.e. in the region of the vanes  7 , are not affected. Of course, an annular groove  47  could also be used if the sleeve  45  had several individual projections as driver flange members arranged in an angular distance from one another, but this could result in disturbing the flow of exhaust gas streaming to the vanes  7  and the turbine rotor situated within the circle of vanes which form the guiding grid. 
   For fixing the module in peripheral direction, preferably a bore  48  ( FIG. 2 ) and/or  48 ′ ( FIG. 1 ) is provided in the disk  29  which receives a pin (or bolt) mounted in the turbine housing  2 , i.e. in the wall  2   b . It has already been pointed out above that fixing in peripheral direction against turning of the disk  29  could also be provided by at least one recess and a corresponding projection. According to another alternative, the arrangement could be reversed so that the disk  29  comprises a, p.e. integral, pin inserted into a hole of the wall  2   b . Furthermore, fixing in peripheral direction could also be effected by way of threaded bolts, although this is not preferred due to the resulting higher working and mounting expenses. 
   In the embodiment shown, the turbine housing  2  is machined in such a way that inserting the sleeve  45  is effected by screwing it by way of a thread  50 . Therefore, an inner thread (corresponding to thread  50 ) has to be cut into the axial pipe  10  into which a corresponding outer thread of the sleeve can be screwed. In principle, axial determination of the position of the disk  29  can be ensured as soon as the disk  29  engages and abuts the, preferably parallel, wall  2   b . However, vibrations during operation can result in loosening the thread connection. Therefore, it may be desired to weld the sleeve  45  to the wall  2   b  either as an alternative or in addition. Another alternative can consist in press fitting and/or plastically deforming the sleeve  45  when inserting it into the axial pipe  10 . 
   Furthermore, it is convenient to provide a heat shield  32 ′ between the bearing housing  40  and the vane space surrounded by the guiding grid and vanes  7 . This heat shield props, in this embodiment, against a surface of the guiding grid, on the one hand, which surface is preferably provided on the nozzle ring  6 . To this end, the nozzle ring  6  may have at least one radially inwards directed (with respect to the central axis R) projection  54 . As in the case of the above-mentioned recesses, it would also be possible to provide a plurality of projections  54  distributed over the inner circumference of the nozzle ring  6 , but for production reasons it is preferred to arrange a radially inwards directed flange as the projection  54 . On the other hand, the heat shield engages and props against a wall of the bearing housing  40 , as is shown in FIG.  1 . Of course, other configurations and arrangements are also possible. 
   This is also merely one of a variety of different possible embodiments. For it would equally be possible to use other known means for securing the thread  50 , such as a counter nut (e.g. in form of a threaded sleeve), which may be screwed, when seen in  FIG. 1 , at the left side. Another possibility could consist in screwing a clamping screw into the axial pipe  10  which protrudes as a projection towards the interior of the pipe  10  and clamps the sleeve  45  securely. Furthermore, it would be possible to provide other projections (as indicated at  52  in  FIG. 1 ) which engages a recess  51  (either formed as a through-hole, as in  FIG. 1 , or being only in the outer surface of sleeve  45  in order to determine the axial position of the sleeve  45  and the guiding grid with vanes  7 . This latter approach will be difficult if a rigid sleeve  45  is used, but it would be possible to form the left end of the sleeve  45  (with respect to  FIG. 1 ) as springy tongues which, for example engage corresponding axial grooves of the discharge pipe  10 , and which may be latched into appropriate snap-in projections (or vice-versa: at least one snap-in projection being provided on a tongue to snap into a hole of the axial pipe  10 ). In principle, however, the recesses  51  may be conveniently provided to engage an appropriate tool when mounting. 
   A further possibility within the scope of the present invention could reside in determining the final position of a guiding grid module by an adjusting arrangement rather than by the surface of the wall  2   b . For example, at least one adjusting screw, preferably several ones, could be screwed into the wall from the left side (with respect to  FIG. 1 ) to determine with their right-hand end (as an abutment) that plane where the disk  29  should lie. 
   
     
       
             
           
             
             
             
             
           
         
             
                 
             
             
               Reference Number List 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                1 
               Turbocharger 
                2 
               Turbine housing 
             
             
                3 
               Rollers 
                4 
               Bearing housing 
             
             
                5 
               Unison ring 
                6 
               Nozzle ring 
             
             
                7 
               Guiding vanes 
                8 
               Adjusting shafts 
             
             
                9 
               Supply channel 
               10 
               Pipe 
             
             
               17 
               Recesses 
               18 
               Heads 
             
             
               19 
               Adjusting levers 
               20 
               Rolling surface 
             
             
               21 
               Exterior roller surface 
               22 
               Cage ring 
             
             
               23 
                 
               24 
               Axial projections 
             
             
               25 
               Holes 
               26 
             
             
               27 
               Sealing ring 
               28 
               Sealing groove 
             
             
               29 
               Disk 
               30 
               Bolts 
             
             
               31 
               Traversing sleeves 
               32′ 
               Heat shield 
             
             
               40 
               Bearing housing 
               41, 41′ 
               Bearings 
             
             
               42 
               Decoupling space 
               43 
               Following continuation 
             
             
               44 
               Spacer 
               45 
               Sleeve 
             
             
               46 
               Driver flange 
               47 
               Recess 
             
             
               48 
               Bore 
               49 
               Pin 
             
             
               50 
               Thread 
               51 
               Recess 
             
             
               52 
               Projections 
               53 
               Central opening 
             
             
               54 
               Nozzle ring projection