Abstract:
The invention concerns a turbocharger with a variable geometry turbine comprising a mobile cylindrical piston ( 70 ) to modify the cross-section of the input nozzle to the turbine. Vanes ( 90 ) extending from a heat shield ( 92 ) for adjusting the flow of the nozzle are contacted by the piston in a first closed position. In a second open position, the piston is spaced apart from the vanes, thereby increasing the input nozzle cross-section.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to variable geometry turbochargers. More particularly, a turbocharger is provided having a sliding piston creating a variable nozzle turbine inlet with vanes extending across the nozzle in a closed position of the piston.  
           [0003]    2. Description of the Related Art  
           [0004]    High efficiency turbochargers employ variable geometry systems for turbine nozzle inlets to increase performance and aerodynamic efficiency. Variable geometry systems for turbochargers have typically been of two types; rotating vane and piston. The rotating vane type exemplified by U.S. Pat. No. 5,947,681 entitled PRESSURE BALANCED DUAL AXLE VARIABLE NOZZLE TURBOCHARGER provide a plurality of individual vanes placed in the turbine inlet nozzle which are rotatable to decrease or increase nozzle area and flow volume. The piston type, which is exemplified by U.S. Pat. Nos. 5,214,920 and 5,231,831 both entitled TURBOCHARGER APPARATUS, and U.S. Pat. No. 5,441,383 entitled VARIABLE EXHAUST DRIVEN TURBOCHARGERS, employs a cylindrical piston or wall which is movable concentric with the axis of rotation of the turbine to reduce the area of the nozzle inlet. In most cases, the piston type variable geometry turbocharger incorporates vanes with fixed angle of attack with respect to the airflow, which are either mounted to the piston or a stationary nozzle wall opposite the piston and are received in slots in the opposing surface during motion of the piston.  
           [0005]    In piston type variable geometry turbochargers in the prior art, the challenge has been maximizing aerodynamic performance balanced with tolerancing of mating surfaces, particularly of vanes and receiving slots that are employed in most designs which are subjected to extreme temperature variation and mechanical stress, as well as providing means for actuating the piston in a readily manufacturable configuration.  
         SUMMARY OF THE INVENTION  
         [0006]    A turbocharger incorporating the present invention has a case having a turbine housing receiving exhaust gas from an exhaust manifold of an internal combustion engine at an inlet and having an exhaust outlet, a compressor housing having an air inlet and a first volute, and a center housing intermediate the turbine housing and compressor housing. A turbine wheel is carried within the turbine housing for extracting energy from the exhaust gas. The turbine wheel is connected to a shaft extending from the turbine housing through a shaft bore in the center housing and the turbine wheel has a substantially full back disc and multiple blades. A bearing carried in the shaft bore of the center housing supports the shaft for rotational motion and a compressor impeller is connected to the shaft opposite the turbine wheel and enclosed within the compressor housing.  
           [0007]    A substantially cylindrical piston is concentric to the turbine wheel and movable parallel to an axis of rotation of the turbine wheel. A plurality of vanes extend substantially parallel to the axis of rotation from a heat shield which is engaged at its outer circumference between the turbine housing and center housing and extends radially inward toward the axis of rotation. An actuator is provided for moving the piston from a first position proximate the heat shield to a second position is distal the heat shield. In the first position, a radial surface of the piston engages the end of the vanes. In the second position, the piston is spaced from the vanes creating a larger cross section nozzle with partial flow of exhaust gas from the turbine volute through the vanes and partial flow through an open annulus directly into the turbine. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The details and features of the present invention will be more clearly understood with respect to the detailed description and drawings in which:  
         [0009]    [0009]FIG. 1 is a cross-section elevation view of a turbocharger employing an embodiment of the invention with the piston in the closed position;  
         [0010]    [0010]FIG. 2 a cross-section elevation view of the turbocharger of FIG. 1 with the piston in the open position;  
         [0011]    [0011]FIG. 3 is a cross section partial elevation view of a second embodiment of the invention with a staggered joint seal for the piston, with the piston in the closed position; and  
         [0012]    [0012]FIG. 4 is a cross section partial elevation view of the embodiment of FIG. 3 with the piston in the open position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    Referring to the drawings, FIG. 1 shows an embodiment of the invention for a turbocharger  10  which incorporates a turbine housing  12 , a center housing  14  and a compressor housing  16 . Turbine wheel  18  is connected through shaft  20  to compressor wheel  22 . The turbine wheel converts energy from the exhaust gas of an internal combustion engine provided from an exhaust manifold (not shown) to a volute  24  in the turbine housing. The exhaust gas is expanded through the turbine and exits the turbine housing through outlet  26 .  
         [0014]    The compressor housing incorporates an inlet  28  and an outlet volute  30 . A backplate  32  is connected by bolts  34  to the compressor housing. The backplate is, in turn, secured to the center housing using bolts (not shown) or cast as an integral portion of the center housing. A V-band clamp  40  and alignment pins  42  connect the turbine housing to the center housing.  
         [0015]    A bearing  50  mounted in the shaft bore  52  of the center housing rotationally support the shaft. A sleeve  58  is engaged intermediate the thrust surface and compressor wheel. A rotating seal  60 , such as a piston ring, provides a seal between the sleeve and backplate.  
         [0016]    The variable geometry mechanism for the present invention includes a substantially cylindrical piston  70  received within the turbine housing concentrically aligned with the rotational axis of the turbine. The piston is longitudinally movable by a spider  72 , having three legs in the embodiment shown, attaching to the piston and attaching to an actuating shaft  74 . The actuating shaft is received in a bushing  76  extending through the turbine housing and connects to an actuator  77 . For the embodiment shown, the actuator is mounted to standoffs on the turbine housing using a bracket  78 .  
         [0017]    The piston slides in the turbine housing through a low friction insert  82 . A cylindrical seal  84  is inserted between the piston and insert. The piston is movable from a closed position shown in FIG. 1, substantially reducing the area of the inlet nozzle to the turbine from the volute  24 . In a fully open position, a radial projection  86  on the piston is received against insert face  88  that limits the travel of the piston.  
         [0018]    Nozzle vanes  90  extend from a heat shield  92 . In the closed position of the piston, the vanes are engaged by the face of the radial projection on the piston. The heat shield outer periphery is engaged between the turbine housing and center housing. The shield is contoured to extend into the cavity of the turbine housing from the interface between the center housing and turbine housing and provide and inner wall for the turbine inlet nozzle.  
         [0019]    [0019]FIG. 2 shows turbocharger of FIG. 1 with the piston  70  in the open position. An open annular channel  94  is created intermediate the vanes and the face of the radial projection. Exhaust gas flow through the vanes and annular channel which comprises the open nozzle is directionally stabilized by the vanes. Modulation of the nozzle flow can be accomplished by positioning the piston at desired points between the fully open and fully closed position.  
         [0020]    The actuation system for the piston in the embodiment shown in the drawings, is a pnuematic actuator  77  attached to bracket  78  as shown in FIGS. 1 and 2.  
         [0021]    [0021]FIG. 3 shows a second embodiment of the invention incorporating a piston  70   a  which is fabricated from sheet metal or a thin wall casting having a substantially U shaped cross section to incorporate an outer ring  94  parallel to the direction of translation of the piston and an inner ring  96  extending to attach to a plate  98  for connection to the actuating rod  74 . The outer ring of the piston is received in a slot  100  in the turbine housing and the inner ring is closely received by the inner circumferential wall of the turbine housing outlet thereby creating a staggered joint seal for the piston. In the closed position, the web of the U shaped piston engages the vanes to create the minimum area nozzle.  
         [0022]    [0022]FIG. 4 shows the embodiment of FIG. 3 with the piston in the open position, and the web of the piston separated from the vanes providing the clear annular space previously described for the open nozzle providing maximum nozzle inlet area. Engagement of the rim of outer ring  94  with the end of the slot  100  or alternatively, engagement of the web of the U with the adjacent face  88   a  of the turbine housing limits the travel of the piston.  
         [0023]    Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications and substitutions are within the scope and intent of the present invention as defined in the following claims.