Patent Publication Number: US-7722336-B2

Title: Compressor wheel

Description:
TECHNICAL FIELD 
   Subject matter disclosed herein relates generally to methods, devices, and/or systems for compressors and, in particular, compressors for internal combustion engines. 
   BACKGROUND 
   Various types of joints exist for connecting a compressor wheel to a shaft. Some joints rely on a bore in the compressor wheel along the axis of rotation. In such joints, a shaft passes through the bore and a nut secures the wheel to the shaft. Other joints rely on a “boreless” compressor wheel. A boreless compressor wheel includes a joint or chamber that extends a distance into the compressor wheel where the distance along the rotational axis typically does not extend to or beyond the z-plane of the compressor wheel. 
   In either instance, the bore or joint must be formed or machined into the compressor wheel. Stresses introduced by such processes may compromise wheel integrity such that a wheel fails during operation. Yet further, if one chooses to use titanium or other hard material for a compressor wheel, machining of a joint can be time and resource intensive. 
   Another concern pertains to balancing a compressor wheel. Boreless compressor wheels pose unique challenges for balancing. Compressor wheels may be component balanced using a balancing spindle and/or assembly balanced using a compressor or turbocharger shaft. Each approach has certain advantages, for example, component balancing allows for rejection of a compressor wheel prior to further compressor or turbocharger assembly; whereas, assembly balancing can result in a better performing compressor wheel and shaft assembly. 
   For conventional boreless compressor wheels, balancing limitations arise due to aspects of the boreless design. In particular, conventional boreless compressor wheels require shallow shaft attachment joints (e.g., typically not extending to or beyond the z-plane) to minimize operational stress. Such shallow joints can introduce severe manufacturing constraints. To overcome such constraints and/or other issues, a need exists for a new compressor wheel joint. Accordingly, various exemplary joints, compressor wheels, balancing spindles, assemblies and methods are presented herein that aim to meet aforementioned needs and/or other needs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the various method, devices, systems, etc., described herein, and equivalents thereof, may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a simplified approximate diagram illustrating a turbocharger with a variable geometry mechanism and an internal combustion engine. 
       FIG. 2  is a cross-sectional view of a prior art compressor assembly that includes a compressor shroud and a compressor wheel having a full bore. 
       FIG. 3  is a cross-sectional View of a prior art compressor assembly that includes a compressor shroud and a conventional “boreless” compressor wheel. 
       FIG. 4  is a cross-sectional view of a prior art compressor wheel assembly that includes a shaft and other components. 
       FIG. 5  is a cross-sectional view of an exemplary compressor wheel assembly that includes an exemplary shaft and other components. 
       FIG. 6  is a cross-sectional view of the exemplary joint of  FIG. 5 . 
       FIG. 7  is a block diagram of an exemplary method for balancing a compressor wheel. 
   

   DETAILED DESCRIPTION 
   Various exemplary devices, systems, methods, etc., disclosed herein address issues related to compressors. An overview of turbocharger operation is presented below followed by a description of conventional compressor wheel joints, exemplary compressor wheel joints and an exemplary method of compressor wheel balancing. 
   Turbochargers are frequently utilized to increase the output of an internal combustion engine. Referring to  FIG. 1 , an exemplary system  100 , including an exemplary internal combustion engine  110  and an exemplary turbocharger  120 , is shown. The internal combustion engine  110  includes an engine block  118  housing one or more combustion chambers that operatively drive a shaft  112 . As shown in  FIG. 1 , an intake port  114  provides a flow path for air to the engine block while an exhaust port  116  provides a flow path for exhaust from the engine block  118 . 
   The exemplary turbocharger  120  acts to extract energy from the exhaust and to provide energy to intake air, which may be combined with fuel to form combustion gas. As shown in  FIG. 1 , the turbocharger  120  includes an air inlet  134 , a shaft  122 , a compressor  124 , a turbine  126 , and an exhaust outlet  136 . A wastegate or other mechanism may be used in conjunction with such a system to effect or to control operation. 
   The turbine  126  optionally includes a variable geometry unit and a variable geometry controller. The variable geometry unit and variable geometry controller optionally include features such as those associated with commercially available variable geometry turbochargers (VGTs), such as, but not limited to, the GARRETT® VNT™ and AVNT™ turbochargers, which use multiple adjustable vanes to control the flow of exhaust across a turbine. 
     FIG. 2  shows a cross-sectional view of a typical prior art compressor assembly  124  suitable for use in the turbocharger system  120  of  FIG. 1 . The compressor assembly  124  includes a housing  150  for shrouding a compressor wheel  140 . The compressor wheel  140  includes a rotor  142  that rotates about a central axis (e.g., a rotational axis). A bore  160  extends the entire length of the central axis of the rotor  142  (e.g., an axial rotor length); therefore, such a rotor is referred to at times as a full-bore rotor. An end piece  162  fits onto an upstream end of the rotor  142  and may act to secure a shaft and/or to reduce disturbances in air flow. In general, such a shaft has a compressor end and a turbine end wherein the turbine end attaches to a turbine capable of being driven by an exhaust stream. 
   Referring again to the compressor wheel  140 , attached to the rotor  142 , are a plurality of compressor wheel blades  144 , which extend radially from a surface of the rotor. As shown, the compressor wheel blade  144  has a leading edge portion  144  proximate to a compressor inlet opening  152 , an outer edge portion  146  proximate to a shroud wall  154  and a trailing edge portion  148  proximate to a compressor housing diffuser  156 . The shroud wall  154 , proximate to the compressor wheel blade  144 , defines a section sometimes referred to herein as a shroud of compressor volute housing  150 . The compressor housing shroud wall after the wheel outlet  156  forms part of a compressor diffuser that further diffuses the flow and increases the static pressure. A housing scroll  158 ,  159  acts to collect and direct compressed air. 
   Some symmetry exists between the upper portion of the housing scroll  158  and the lower portion of the housing scroll  159 . In general, one portion has a smaller cross-sectional area than the other portion; thus, substantial differences may exist between the upper portion  158  and the lower portion  159 .  FIG. 2  does not intend to show all possible variations in scroll cross-sections, but rather, it intends to show how a compressor wheel may be positioned with respect to a compressor wheel housing. 
     FIG. 3  shows a cross-sectional view of a conventional prior art compressor wheel rotor  324  that includes a “boreless” compressor wheel  340  suitable for use in the turbocharger system  120  of  FIG. 1 . The compressor assembly  324  includes a housing  350  for shrouding a compressor wheel  340 . The compressor wheel  340  includes a rotor  342  that rotates about a central axis. Attached to the rotor  342 , are a plurality of compressor wheel blades  344 , which extend radially from a surface of the rotor. As shown, the compressor wheel blade  344  has a leading edge portion  344  proximate to a compressor inlet opening  352 , an outer edge portion  346  proximate to a shroud wall  354  and a trailing edge portion  348  proximate to a compressor housing diffuser  356 . The shroud wall  354 , proximate to the compressor wheel blade  344 , defines a section sometimes referred to herein as a shroud of compressor volute housing  350 . The compressor housing shroud wall after the wheel outlet  356  forms part of a compressor diffuser that further diffuses the flow and increases the static pressure. A housing scroll  358 ,  359  acts to collect and direct compressed air. 
     FIG. 3  shows a z-plane as coinciding substantially with a lowermost point of an outer edge or trailing edge portion  348  of the blade  344 . A bore or joint  360  centered substantially on a rotor axis exists at a proximate end of the rotor  342  for receiving a shaft. Throughout this disclosure, the bore or joint  360  is, for example, a place at which two or more things are joined (e.g., a compressor wheel and a shaft or a spindle, etc.). Compressor wheels having a joint such as the joint  360  are sometimes referred to as “boreless” compressor wheels in that the joint does not pass or extend through the entire length of the compressor wheel. Indeed, such conventional boreless compressor wheels do not have joints that extend to the depth of the z-plane. The joint  360  typically receives a shaft that has a compressor end and a turbine end wherein the turbine end attaches to a turbine capable of being driven by an exhaust stream. For purposes of compressor wheel balancing, the joint  360  may receive a balancing spindle; however, such a balancing spindle cannot extend to or beyond the z-plane because of the joint depth. As discussed below with respect to  FIG. 4 , an important parameter in machining such a joint pertains to the distance between the z-plane and the end of the joint. 
     FIG. 4  shows a cross-sectional view of a prior art compressor wheel assembly that includes a compressor wheel  340 , a thrust collar  370 , a ring  372  and a shaft  380 . The compressor wheel  340  includes a joint  360  Δz b  indicates a distance between the end of the joint  360  and the z-plane. In the prior art compressor wheel  340 , a maximum in stress occurs at or near the end of the joint  360  and along the z-axis. Integrity of the wheel  360  typically decreases as the distance Δz b  diminishes; thus, the position of the end surface of the joint  360  must be carefully manufactured with respect to the z-plane of the wheel  340  and with respect to surface imperfections. 
     FIG. 4  shows another distance Δz c , which represents an overhang distance as measured from the z-plane to the end surface of the wheel  340  where, for example, the wheel meets the thrust collar  370 . The overhang distance or length can affect stability and, in general, a short overhang results in greater stability (e.g., bearing stability, rotordynamic stability, etc.). The conventional boreless wheel  340  also includes a radial distance Δr j  along the joint length that may vary with respect to axial position. Such a distance may be used to calculate an overhang volume and, hence, an overhang mass. Overhang properties such as mass and extended distance from the z-plane may be used to determine stability. 
   A typical compressor wheel and shaft assembly includes a thrust collar that forms a portion of a thrust bearing assembly. Such an assembly may include a thrust spacer sleeve, a ring and/or other components. A thrust space sleeve is typically threaded onto a shaft to axially bearing engagement with a shoulder, such as a thrust collar or the like, forming a portion of the thrust bearing assembly and being rotatable with the shaft. In this manner, the sleeve spaces the compressor wheel axially relative to the thrust collar. In addition, the sleeve advantageously receives seal rings in its outer diameter grooves where the seal rings engage the inner diameter surface of the backplate wall shaft opening to prevent lubricant passage from the center housing into the compressor housing. As shown in  FIG. 4 , a ring  372  is positioned between the thrust collar  370  and the compressor wheel  340 . While a ring is shown in  FIG. 4 , a carbon seal, labyrinth seal or other mechanism may be used. 
     FIG. 5  shows a cross-sectional view of an exemplary compressor wheel assembly that includes a compressor wheel  540 , a thrust collar  570 , a ring  572  and a shaft  580 . The exemplary compressor wheel  540  includes an extension  549  for insertion in a joint  590  of the exemplary shaft  580 . In this example, the extension  549  extends a distance Δz max  along the z-axis from the z-plane. The exemplary wheel  540  includes a thrust collar distance Δz c  from the z-plane to a surface that, for example, meets the thrust collar  570 . The ring  572  may be positioned between a surface of the compressor wheel  540  and a surface of the thrust collar  570 . As shown, the exemplary compressor wheel  540  includes a substantially annular surface at a distance of Δz c  from the z-plane and in a plane substantially normal to the axis of rotation. This surface may act to seat the thrust collar  570 . A notch or other surface may confine the ring  572  between the thrust collar  570  and the wheel  540 . 
   Various exemplary wheels include a distance from the z-plane (e.g., Δz c ) to a surface or position from which an extension extends. This distance may be less than the distance from the z-plane to the end of a conventional boreless or bored compressor wheel that does not have such an extension. For various exemplary compressor wheels, the ratio of Δz c  to Δz max  can vary, as appropriate, for example, to achieve a shift in the center of gravity away from the nose of the wheel.(e.g., in comparison to a wheel having a bore or conventional boreless design), etc. In various examples, a compressor wheel extension reduces the distance from the z-plane to an operational shaft of a turbocharger when compared to a conventional compressor wheel. 
     FIG. 6  shows a cross-sectional view of an exemplary joint that includes a compressor wheel  540  and a shaft  580  such as those shown in  FIG. 5 .  FIG. 6  shows various dimensions including a distance Δz r  from the z-plane to a point where the exemplary wheel  540  reaches a substantially constant outer radius with respect to the z-axis; a distance Δz S  from the z-plane to the outermost axial point of the exemplary shaft  580 ; a diameter d Pi , which represents an inner pilot diameter of the extension  549 ; a distance Δz e , which represents the axial length of the extension  549 ; a diameter d Po , which represents an outer pilot diameter of the extension  549 ; and a diameter d S , which represents a shaft diameter. 
   The exemplary shaft  580  includes a joint  590  to receive the extension  549 . The example of  FIG. 6  shows the joint  590  as including an optional contoured end surface. In general, the shaft  580  has a substantially constant outer diameter proximate the compressor wheel  540 . A constant outer diameter acts to minimize stress of the shaft  580 . Consequently, the presence of the joint  590  in the shaft  580  does not necessitate stress reduction measured or concerns such as those associated with a conventional boreless wheel where outer radius varies significantly along the z-axis. 
   Various exemplary compressor wheels allow for a reduced overhang length compared to conventional boreless compressor wheels. A reduction in overhang length may also allow for a reduction in overall length of a compressor section of, for example, a turbocharger and thereby yielding a stable rotor and turbocharger system. 
   In the example of  FIG. 6 , the exemplary compressor wheel  540  includes a first pilot diameter d Pi  for alignment with the thrust collar  570  and a second pilot diameter d Po  for alignment with a pilot surface of the joint  590  of the exemplary shaft  580 . Disposed between the pilot surfaces are threads or other engagement mechanism or means (e.g., bayonet, etc.). The exemplary shaft  580  includes a corresponding or complimentary threads or engagement mechanism or means (e.g., bayonet, etc.). 
   An exemplary joint may be defined by one or more regions, volumes, surfaces and/or dimensions. For example, the exemplary joint  590  includes a proximate region (e.g., consider diameter d Pi ), an intermediate region (e.g., consider threads) and a distal region (e.g., consider diameter d Po ). Such regions may be referred to as pilot regions and/or co-pilot regions or threaded regions, as appropriate. An intermediate region or other region may include threads or other fixing mechanism (e.g., bayonet, etc.). Where threads are included, the threads typically match a set of threads of an exemplary compressor wheel. 
   An exemplary joint may include one or more annular constrictions, for example, disposed near a juncture between regions where the one or more annular constrictions decrease in diameter with respect to increasing length along the axis of rotation and may form a surface disposed at an angle with respect to the axis of rotation. A constriction may act to minimize or eliminate any damage created by machining (e.g., boring, taping, etc.). 
   Materials of construction for an exemplary compressor wheel are not limited to aluminum and titanium and may include stainless steel, etc. Materials of construction optionally include alloys. For example, Ti-6Al-4V (wt.-%), also known as Ti6-4, is alloy that includes titanium as well as aluminum and vanadium. Such alloy may have a duplex structure, where a main component is a hexagonal α-phase and a minor component is a cubic β-phase stabilized by vanadium. Implantation of other elements may enhance hardness (e.g., nitrogen implantation, etc.) as appropriate. 
   An exemplary compressor wheel may include, for component balancing, a balancing unit that cooperates with one or more features of the compressor wheel (e.g., extension features). For example, a balancing unit may include a joint such as the joint  590  of the exemplary shaft  580 . 
     FIG. 7  shows a block diagram of an exemplary method  700 . The method  700  commences in a start block  704 , which includes providing a compressor wheel and a balancing machine having a balancing unit. In a fixation block  708 , the balancing unit receives an exemplary extension. For example, an operator may insert the extension, at least partially, into a joint of a balancing unit. Such a joint may include one or more pilot surfaces that receive one or more pilot surfaces of the extension. 
   A balance block  712  follows wherein a balancing process occurs. In general, balancing is dynamic balancing. After the balancing, in a removal block  716 , the compressor wheel extension is removed from the joint of the balancing unit. Next, in another fixation block  720 , an exemplary shaft receives the extension wherein other components are positioned or assembled as appropriate. The method  700  may terminate in an end block  724 . The method  700  optionally includes another balancing block wherein the compressor wheel and operational shaft are balanced as an assembly. In an alternative, the exemplary shaft is used in a balancing process for an exemplary compressor wheel. 
   The exemplary method  700  and/or portions thereof are optionally performed using hardware and/or software. For example, the method and/or portions thereof may be performed using robotics and/or other computer controllable machinery. 
   As described herein such an exemplary method or steps thereof are optionally used to produce a balanced compressor wheel. Various exemplary compressor wheels disclosed herein include a proximate end, a distal end, an axis of rotation, a z-plane positioned between the proximate end and the distal end, and an extension having an axis coincident with the axis of rotation. An exemplary shaft includes a complimentary joint to receive the extension, at least partially therein. An exemplary shaft joint may include a contoured end surface optionally having an elliptical cross-section (e.g., radius to height ratio of approximately 3:1, etc.). An exemplary compressor wheel optionally includes titanium, titanium alloy (e.g., Ti6-4, etc.) or other material having same or similar mechanical properties. Such a compressor wheel optionally has a peak principle operational stress less than that of a conventional boreless compressor wheel. Various exemplary compressor wheels are optionally part of an assembly (e.g., a balancing assembly, a turbocharger assembly, a compressor assembly, etc.). An exemplary assembly includes an exemplary compressor wheel and an exemplary operational shaft. 
   Conclusion 
   Although some exemplary methods, devices, systems, etc., have been illustrated in the accompanying Drawings and described in the foregoing Description, it will be understood that the methods, devices, systems, etc., are not limited to the exemplary embodiments disclosed, but are capable of numerous rearrangements, modifications and substitutions without departing from the spirit set forth and defined by the following claims.