Abstract:
A turbine housing assembly includes a tubular piston disposed in a bore of a turbine housing and axially slidable between a closed position and an open position for blocking a nozzle by an amount dependent on axial positioning of the piston. A bypass control member is disposed in the turbine housing and is slidable between a no-bypass position closing a bypass passage and a open bypass opening the bypass passage. The piston is structured and arranged to slide relative to the bypass control member for a part of a full stroke of the piston from the closed position toward the open position thereof, and then to engage the bypass control member and cause the bypass control member to slide together with the piston as the piston further slides toward the open position thereof such that the bypass control member is moved toward the bypass position.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to exhaust gas-driven turbochargers, and relates more particularly to exhaust gas-driven turbochargers having a variable turbine nozzle of the axially sliding piston type for varying the size of the nozzle that leads into the turbine wheel so as to regulate flow into the turbine wheel. 
     Regulation of the exhaust gas flow through the turbine of an exhaust gas-driven turbocharger provides known operational advantages in terms of improved ability to control the amount of boost delivered by the turbocharger to the associated internal combustion engine. The regulation of exhaust gas flow is accomplished by incorporating variable geometry into the nozzle that leads into the turbine wheel. By varying the size of the nozzle flow area, the flow into the turbine wheel can be regulated, thereby regulating the overall boost provided by the turbocharger&#39;s compressor. 
     Variable-geometry nozzles for turbochargers generally fall into two main categories: variable-vane nozzles, and sliding-piston nozzles. Vanes are often included in the turbine nozzle for directing the exhaust gas into the turbine in an advantageous direction. Typically a row of circumferentially spaced vanes extend axially across the nozzle. Exhaust gas from a chamber surrounding the turbine wheel flows generally radially inwardly through passages between the vanes, and the vanes turn the flow to direct the flow in a desired direction into the turbine wheel. In a variable-vane nozzle, the vanes are rotatable about their axes to vary the angle at which the vanes are set, thereby varying the flow area of the passages between the vanes. 
     In the sliding-piston type of nozzle, the nozzle may also include vanes, but the vanes are fixed in position. Variation of the nozzle flow area is accomplished by an axially sliding piston that slides in a bore in the turbine housing. The piston is tubular and is located just radially inwardly of the nozzle. Axial movement of the piston is effective to vary the axial extent of the nozzle leading into the turbine wheel, thus varying the “throat area” at the turbine wheel inlet. When vanes are included in the nozzle, the piston can slide adjacent to radially inner (i.e., trailing) edges of the vanes; alternatively, the piston and vanes can overlap in the radial direction and the piston can include slots for receiving at least a portion of the vanes as the piston is slid axially to adjust the nozzle. 
     There are times during the operation of a turbocharger when it is desired to pass as much flow through the turbine housing as possible. For example, it may be desirable to minimize the backpressure felt by the engine during certain operating conditions, and this is accomplished by reducing the flow restriction downstream of the engine as much as possible. In a sliding piston-type variable turbine nozzle, the downstream flow restriction is reduced by fully opening the piston to maximize the throat area at the turbine wheel inlet. However, in some cases, even fully opening the piston may not allow as much flow to pass as may be desired. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above needs and achieves other advantages, by providing a turbine housing assembly for a variable-nozzle turbocharger, in which an integrated bypass feature is arranged in the turbine housing assembly for allowing a proportion of exhaust gas to pass from the turbine housing chamber through a bypass passage without passing through the turbine wheel or the bore in the turbine housing. In one embodiment of the invention, the turbine housing assembly includes a tubular piston disposed in the bore of the turbine housing and axially slidable between a closed position and an open position for blocking the nozzle by an amount dependent on axial positioning of the piston so as to regulate flow into the turbine wheel. A bypass control member is disposed in the turbine housing and is slidable between a no-bypass position closing the bypass passage and a bypass position opening the bypass passage. The bypass member preferably is biased by a biasing device toward the no-bypass position. The piston is structured and arranged to slide relative to the bypass control member for a part of a full stroke of the piston from the closed position toward the open position thereof, and then to engage the bypass control member and cause the bypass control member to slide together with the piston as the piston further slides toward the open position thereof such that the bypass control member is moved toward the bypass position. 
     The bypass control member in one embodiment is generally ring-shaped or annular and concentrically surrounds the piston, and the piston includes a radially outwardly extending portion that is spaced from the bypass control member when the piston is in the closed position and that engages the bypass control member when the piston is slid toward the open position to cause the bypass control member to slide with the piston. The radially outwardly extending portion of the piston can comprise a flange extending from an upstream end of the piston. 
     The turbine housing in one embodiment defines a guide space adjacent the bypass passage and the bypass control member includes a cylindrical portion that slides within the guide space. The bypass control member includes a flange portion extending radially inwardly from the cylindrical portion and positioned to be engaged by the radially outwardly extending portion of the piston. A compression spring can be disposed between the flange portion of the bypass control device and a portion of the turbine housing for biasing the bypass control member toward the no-bypass position. 
     Actuation of the piston can be accomplished in various ways, such as by mechanical linkage connected with the piston and operated by a suitable actuator. Alternatively, in one embodiment of the invention, the piston includes a cylindrical portion and the turbine housing defines an annular space that receives the cylindrical portion of the piston for guiding the piston&#39;s axial sliding movement. Seals for sealing the piston are disposed between radially outer and radially inner surfaces of the cylindrical portion of the piston and corresponding opposing surfaces of the annular space. The turbine housing defines a fluid passage extending through the turbine housing and connected with the annular space for communicating fluid to the annular space such that a fluid pressure differential applied through the fluid passage to the annular space causes a force to be exerted on the piston to move the piston axially relative to the turbine housing. A compression spring can be arranged in the turbine housing for biasing the piston in opposition to the fluid pressure differential. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  is an isometric view, partially cut away to show internal details, of a turbine housing assembly for a turbocharger, in accordance with one embodiment of the invention; 
         FIG. 2  is sectioned isometric view of the turbine housing assembly, showing the piston in a closed position; 
         FIG. 3  is a view similar to  FIG. 2 , showing the piston in a partially open position; 
         FIG. 4  is a view similar to  FIG. 2 , showing the piston in a fully open position; 
         FIG. 4A  is a magnified view of a portion of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present inventions now will be described more fully hereinafter with reference to the accompanying drawings in which some but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
       FIGS. 1 through 4  and  4 A depict a turbine housing assembly  20  for a turbocharger in accordance with one embodiment of the invention. The turbine housing assembly is shown mounted to one side of a center housing  22  of the turbocharger. The center housing defines a bore  23  that houses bearings (not shown) for a rotatable shaft (not shown) of the turbocharger. A compressor wheel (not shown) is mounted on one end of the shaft and is housed in a compressor housing (not shown) that is attached to the opposite side of the center housing  22 . A turbine wheel (not shown) is mounted on the other end of the shaft and is housed in a turbine housing  32  of the turbine housing assembly. The turbine housing defines a generally annular chamber  34  that surrounds the turbine wheel and receives engine exhaust gas for driving the turbine wheel. The exhaust gas flows generally radially inwardly from the chamber  34  through a nozzle  36  defined by the turbine housing and other components (as further described below) and flows through the turbine wheel, which turns the flow toward an axial direction. 
     The turbine housing  32  defines an axial bore  38  in which the turbine wheel resides at an upstream end of the bore. The exhaust gas that has flowed through the wheel is discharged through a downstream end of the bore  38 . 
     A piston  40  is mounted in the bore  38  of the turbine housing such that the piston is axially slidable relative to the turbine housing. The piston is tubular in configuration. The piston is disposed between the nozzle  36  and the turbine wheel, and is movable to various axial positions for regulating the size of the nozzle flow area through which exhaust gas can flow from the chamber  34  to the turbine wheel. The piston  40  is received within the bore  38  and is slidable relative to the turbine housing. An array of circumferentially spaced vanes  42  is mounted on a heat shield  44  mounted between the turbine housing  32  and center housing  22  proximate the turbine wheel. The vanes  42  are positioned to extend partway across the axial extent of the nozzle  36 . In a closed position of the piston  40 , an upstream end of the piston is abutting or closely proximate to the vanes  42  as shown in  FIGS. 1 and 2 , and accordingly the exhaust gas that flows through the nozzle is constrained to flow through the spaces between the vanes  42 . In an open position of the piston, the upstream end of the piston is spaced from the vanes  42  as in  FIGS. 3 and 4 , in which case some of the exhaust gas flows through the vanes  42  and an additional amount of exhaust gas flows through an opening defined between the ends of the vanes  42  and the end of the piston. The closed position of the piston thus provides a relatively greater amount of flow restriction than does the open position. Adjustment of the piston position can be used for regulating the flow into the turbine wheel, thereby regulating the overall boost provided by the turbocharger to an internal combustion engine to which the turbocharger is coupled. 
     The turbine housing assembly  20  includes an integrated bypass for allowing some exhaust gas to bypass the turbine wheel and turbine housing bore  38 . More particularly, the turbine housing defines a bypass passage  50  for allowing a portion of exhaust gas to flow from the chamber  34  through the bypass passage  50  without passing through the turbine wheel or turbine housing bore. A bypass control member  52  is disposed in the turbine housing and is slidable between a no-bypass position closing the bypass passage ( FIGS. 1-3 ) and a bypass position opening the bypass passage ( FIGS. 4 and 4A ). The bypass control member  52  is generally ring-shaped or annular in configuration and concentrically surrounds the piston  40 . A compression spring  54  is compressed between the turbine housing and the bypass control member and urges the bypass control member toward its no-bypass position. The turbine housing defines a guide space  51  adjacent the bypass passage  50 , and the bypass control member includes a cylindrical portion  52   a  ( FIG. 4A ) that slides within the guide space. The engagement of the cylindrical portion  52   a  in the guide space  51  also serves to discourage exhaust gas from flowing around the bypass control member into the turbine housing bore  38 , by creating a circuitous pathway between the bypass control member and turbine housing. 
     The piston  40  has a radially outwardly projecting flange  56  at its upstream end. The flange  56  is arranged to abut the bypass control member  52  when the piston  40  has moved to a partially open position, as depicted in  FIG. 3 . The bypass control member includes a flange portion  52   b  extending radially inwardly from the cylindrical portion  52   a  and positioned to be engaged by the flange  56  of the piston. 
     The piston  40  is able to move even farther in the downstream direction. With further movement of the piston  40  toward its fully open position, the bypass control member  52  begins to move along with the piston  40  such that the bypass passage  50  begins to be opened.  FIGS. 4 and 4A  show the bypass control member in a fully open position. 
     The piston can be actuated in various ways. For example, a mechanical linkage (not shown) can be connected with the piston and operated by a suitable actuator (not shown). Alternatively, in one embodiment of the invention as illustrated, the actuation of the piston  40  in the opening direction is accomplished using fluid pressure differential that acts on the piston. More specifically, the piston  40  is axially slidable within an annular cavity or guide space  60  defined by the turbine housing. The piston is sealed within the guide space  60  by a sealing arrangement. In one embodiment, the sealing arrangement can comprise an outer seal  62  arranged between a radially outer surface of the piston and a radially outer wall of the guide space  60 , and an inner seal  64  arranged between a radially inner surface of the piston and a radially inner wall of the guide space  60 . A fluid passage  66  is defined in the turbine housing and connects with the portion of the guide space  60  sealed by the seals  62 ,  64 . Exertion of a differential fluid pressure through the passage  66  causes fluid pressure to act on the piston  40  for axially moving the piston. In the illustrated embodiment, exertion of a vacuum through the passage  66  moves the piston toward the open position. 
     A compression spring  68  is arranged to exert a force on the piston  40  tending to move the position to its closed position. The spring  68  is compressed between an upstream-facing surface  70  of the turbine housing  32  and a radially outward projection  72  on the piston. The projection  72  can comprise a snap ring mounted in a groove in the outer surface of the piston. The spring  68  thus acts on the piston in an opposite direction to that of the fluid pressure when vacuum is exerted on the space  60 . When enough vacuum is exerted to overcome the spring force on the piston, the piston moves toward the open position. Various partially open piston positions can be achieved by suitably regulating the degree of vacuum exerted on the space  60  so that the spring force and fluid force balance each other at different points along the full piston stroke. 
     It is also possible to configure the turbine housing and piston so that a fluid pressure differential causes the piston to close, while a compression spring urges the piston toward the open position. 
     In operation, at low engine speeds and low throttle settings the piston  40  typically is in its closed position as in  FIGS. 1 and 2 , since exhaust gas flow rates are low at such conditions. At other operating conditions demanding greater exhaust gas flow rates (e.g., rapid acceleration, high engine speeds, etc.), the piston  40  can be moved to a partially open position such as in  FIG. 3  to allow greater gas flow rate into the turbine wheel. The bypass control member  52  may still be in a closed or no-bypass position, as shown. At extreme operating conditions where the maximum possible exhaust gas flow rate is desired, the piston is moved to the fully open position as in  FIGS. 4 and 4A  so that the bypass control member  52  is moved to an open or bypass position. In this condition, some exhaust gas flows from the chamber  34  through the nozzle  36  into the turbine housing bore as illustrated by the arrow  74  in  FIG. 4A , while an additional amount of exhaust gas flows from the chamber through the bypass passage  50  as illustrated by the arrow  76 , thereby bypassing the turbine housing bore. 
     Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.