Patent Publication Number: US-2023147254-A1

Title: Impeller attach mechanism

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to turbochargers and, more particularly, to turbochargers with a compressor impeller joint. 
     BACKGROUND 
     Internal combustion engines, for example, diesel engines, gasoline engines, or natural gas engines, employ turbochargers to deliver compressed air to combustion chambers within the engine. An increased supply of air enables increased fuel combustion within the combustion chambers of the engine, resulting in increased power output from the engine. 
     A typical turbocharger rotor includes a shaft extending between a compressor impeller (also referred to as a compressor wheel) and a turbine. Bearings typically support the shaft, and separate housings coupled together enclose the compressor impeller, the turbine, and the bearings. In operation, hot exhaust from the engine flows through the turbine housing and expands over the turbine, rotating the turbine and the shaft, which in turn rotates the compressor impeller. The compressor impeller receives cool air from ambient surroundings and forces compressed air into combustion chambers of the engine. Turbocharger rotors typically require attachment of the compressor impeller to a shaft system via a joint. This joint must align to the shaft system along an axis of rotation during rotor balancing and assembly installation, for example, with little to no variance from the balanced state in order to maintain balance and remain secure throughout the service life of the turbocharger rotor. 
     Although small turbochargers can utilize a simple screw-type shaft to attach to the compressor impellers, larger compressor impellers (such as those found in locomotives, for example) typically require a tensioning element and tool access to a nose of the compressor impeller, in order to tighten the tensioning element. In other arrangements, separate tension elements, such as an integral extension to the shaft system, may be utilized, but these elements may require large torque application or tensioning via hydraulic means. In addition, complicated torque transmission features such as splines or keys take up space that increases the corresponding bore diameter along the length of the compressor impeller thereby compromising overall strength and ultimately fatigue life. 
     U.S. Pat. No. 9,835,164 (“the &#39;164 patent”) discloses an impeller assembly that aims to simplify manufacturing and assembly. In particular, the &#39;164 patent discloses a turbocharger rotor that has a turbine wheel and shaft, a compressor impeller, an insert and a stud. The stud includes a first threaded portion that engages a threaded portion of the insert, while a second threaded portion engages a threaded portion of the shaft. The first and second threaded portions are spaced apart axially, allowing the second threaded portion, for example, to extend deeper into the shaft. While the system of the &#39;164 patent achieves a desired simplification of manufacturing and assembly, there is still a need for a compressor impeller assembly that also maintains alignment and minimizes rocking movement during operation of the turbocharger. 
     The compressor impeller assembly of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art. 
     SUMMARY 
     In accordance with one aspect of the present disclosure, an impeller attach mechanism for a turbocharger is disclosed. The impeller attach mechanism may include a stud extending from a central bore of a compressor impeller toward a turbine wheel. The stud may have a first threaded region and a second threaded region. The impeller attach mechanism may also include a shaft coupled to the turbine wheel and extending toward the compressor impeller, and may have a leading portion with a threaded interior configured to engage the second threaded region of the stud. An insert may include an internal portion and an external portion. The internal portion may have a threaded external surface to engage the compressor impeller, and may also have a threaded internal surface to engage the first threaded region of the stud. The external portion may be configured to surround the leading portion of the shaft. 
     In accordance with another aspect of the present disclosure, an impeller attach mechanism for a turbocharger is disclosed. The impeller attach mechanism may include a stud, a shaft, an insert, a thrust washer, and an impeller collar. The stud may extend from a central bore of a compressor impeller, and may have a first threaded region and a second threaded region. The shaft may be coupled to the turbine wheel, and may have a leading portion with a threaded interior configured to engage the second threaded region of the stud. The insert may have an internal portion and an external portion, with the internal portion housed within the compressor impeller. The internal portion may also have a threaded internal surface to engage the first threaded region of the stud, and the external portion may be configured to engage an external surface of the leading portion of the shaft. The thrust washer may have a washer bore, and the impeller collar may have a turbine side extension radially disposed in the washer bore between the shaft and the thrust washer. 
     In accordance with yet another aspect of the present disclosure, a turbocharger is disclosed. The turbocharger may include a turbine wheel, a compressor impeller, a stud, a shaft, and an insert. The compressor impeller may have a central bore and a hub extension protruding toward the turbine wheel. The stud may extend from the central bore of the compressor impeller and may have a first threaded region and a second threaded region. The shaft may be coupled to the turbine wheel, and may have a leading portion. The leading portion may have a threaded interior configured to engage the second threaded region of the stud. The insert may have an internal portion and an external portion. The internal portion may have a threaded internal surface to engage the first threaded region of the stud, and may be dimensioned to radially encase the first threaded region of the stud. In addition, the hub extension may be dimensioned to radially encase the internal portion of the insert, the leading portion of the shaft may be dimensioned to radially encase the second threaded region of the stud, and the external portion of the insert may be dimensioned to configured to radially encase the leading portion of the shaft. 
     These and other aspects and features of the present disclosure will be better understood upon reading the following detailed description, when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic illustration of an engine system including a turbocharger, in accordance with an embodiment of the present disclosure; 
         FIG.  2    is a perspective view of the turbocharger of  FIG.  1   , in accordance with an embodiment of the present disclosure; 
         FIG.  3    is a longitudinal cross-sectional view of the turbocharger rotor within the turbocharger of  FIG.  1   , in accordance with an embodiment of the present disclosure; 
         FIG.  4    is an enlarged cross-sectional view of a portion of the turbocharger of  FIG.  1   , in accordance with an embodiment of the present disclosure; 
         FIG.  5    is an enlarged cross-sectional view of a portion of the turbocharger rotor of  FIG.  3   , in accordance with an embodiment of the present disclosure; and 
         FIG.  6    is a perspective view of an exemplary disclosed anti-rotation feature of the turbocharger rotor of  FIG.  3   , in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. 
     Referring now to  FIG.  1   , an exemplary power system  10  is illustrated schematically. The power system  10  includes an internal combustion engine  12 , an integrated turbocharger  14 , an air induction system  16 , and an exhaust system  18 . For the purposes of this disclosure, the engine  12  may be a two-stroke diesel engine, although one skilled in the art will recognize that the engine may be any other type of internal combustion engine such as, for example, a four-stroke diesel engine or a two- or four-stroke gasoline or gaseous fuel-powered engine. Further, the engine  12  may find applications in mobile machines (not shown) such as, but not limited to, locomotives, vehicles, heavy mechanical equipment, large tractors, on-road vehicles, off-road vehicles, marine vessels and the like, as well as in stationary machines (not shown) such as generator sets and pumps. 
     The engine  12  may include an engine block  20  that at least partially defines a plurality of cylinders  22 . A piston (not shown) may be slidably disposed within each cylinder  22  to reciprocate between a top-dead-center position and a bottom-dead-center position, and a cylinder head (not shown) may be associated with each cylinder. Each cylinder  22 , piston, and cylinder head may, together, at least partially define a combustion chamber. In the embodiment illustrated in  FIG.  1   , the engine  12  includes six cylinders  22  arranged in an inline configuration. However, it is contemplated that the engine  12  may include a greater or lesser number of cylinders  22 , and that the cylinders may be arranged in a V-configuration (i.e., a configuration having first and second banks or rows of cylinders), an opposing-piston configuration, or another configuration as will be apparent to those skilled in the art. Combustion of a fuel and air mixture in each cylinder  22  generates motive power that rotates an engine output shaft  24 , and a resultant exhaust gas is produced, as is known in the art. 
     The engine  12  may further include an air intake manifold  26  and an exhaust manifold  28  that are selectively in fluid communication with each compression cylinder  22 . The air intake manifold  26  may provide compressed intake air to the compression cylinders  22  from the air induction system  16 , which draws air from the ambient atmosphere surrounding the engine  12  and any machine in which the engine is installed. Compressed air from the air intake manifold  26 , along with fuel from a fuel tank (not shown), forms a combustible mixture that ignites when compressed, such as in each cylinder  22 , or in the presence of a spark, for example. Combustion byproducts are evacuated from each cylinder  22  through the exhaust manifold  28 , to one of the exhaust system  18  and the turbocharger  14 . At least a portion of the exhaust gases may be transmitted to the exhaust system  18  for after-treatment prior to being released back into the atmosphere. Another portion of the exhaust gases may be transmitted to the turbocharger  14 , and, more specifically, to a turbine wheel  30  via a high pressure exhaust gas line  32 , for example. 
     A turbocharger housing  34  may be configured to direct the pressurized exhaust gas toward the turbine wheel  30 , which may be mounted opposite a compressor impeller  36  on a shaft  38  within the turbocharger housing. In an exemplary embodiment, the shaft  38  may be made of a metal, such as steel. The compressor impeller  36  may be mounted on the shaft  38 , and configured for rotation with the shaft and turbine wheel  30 . When the temperature and pressure of the exhaust gas from the engine  12  are sufficient, exhaust torque generated by the exhaust gas drives the turbine wheel  30 , which causes rotation of the shaft  38  and, ultimately, the compressor impeller  36 . The rotating compressor impeller  36  thereby compresses air received from the air induction system  16 , and outputs compressed air to the air intake manifold  26 , where the compressed air is mixed with air provided by the air induction system. After powering the turbine wheel  30 , spent exhaust gas is discharged to the exhaust system  18  via, for example, a low pressure exhaust gas return line  40 . 
     During some operating conditions of the engine  12 , it may be desirable to drive the turbine wheel  30  of the turbocharger  14  even though a temperature and pressure of the exhaust gas may be insufficient to rotate the turbine wheel at a desired speed. For example, at low engine speeds, such as when the engine  12  is idling, emissions of pollutants such as nitrous oxides (NOx) can increase and low exhaust temperatures can make exhaust after treatment systems in the exhaust system  18  ineffective. In one exemplary embodiment, to selectively provide direct drive to the turbocharger  14  by the engine  12  when the operating conditions dictate, the engine output shaft  24  may drive the shaft  38  when the exhaust gas will not drive the turbine wheel  30 , and may be disengaged when the exhaust gas will create sufficient torque and rotate the turbine wheel and the compressor impeller  36  at sufficient speeds so that direct drive by the engine is unnecessary. 
     For example, in one embodiment, a carrier shaft  44  may be operatively coupled to the turbine wheel  30  and may have a carrier drive gear  46  mounted thereon and rotatable therewith. An operative connection between the engine  12  may be provided by a turbocharger drive gear  48  connected to a gear train or transmission  52  that is driven by the engine output shaft  24 . The turbocharger drive gear  48  may be operatively connected to the carrier drive gear  46  by one or more idler gears  50  so that the carrier shaft  44  will spin at a desired speed and direction relative to the engine output shaft  24 . In other embodiments, other appropriate drive mechanisms and arrangements may be utilized to drive the turbine wheel  30  and compressor impeller  36 . 
     With reference to  FIG.  2   , and continued reference to  FIG.  1   , an exemplary embodiment of the turbocharger  14  is illustrated. The turbocharger housing  34  includes both a compressor housing  54  and a turbine housing  56 . In operation, air may enter the compressor housing  54  from the air induction system  16  via a compressor inlet  58 , and may exit the compressor housing toward the air intake manifold  26  via a compressor outlet  60 . Similarly, exhaust gases may enter the turbine housing  56  from the exhaust manifold  28  via a turbine inlet  64 , and may exit the turbine housing toward the exhaust system  18  via a turbine exhaust duct  62 . 
     Referring now to  FIG.  3   , an exemplary embodiment of a compressor impeller assembly  66  is illustrated. The compressor impeller assembly  66  may be comprised of various components, including the compressor impeller  36 , an insert  68 , an impeller collar  70 , a thrust washer  72 , a stud  74  and the shaft  38 , all of which may be disposed around a rotational axis  76 . The compressor impeller  36  may include a nose  78 , a hub extension  80 , and blades  82 . The nose  78  may be disposed adjacent a front end  84  of the compressor impeller  36 , and the hub extension  80  may be disposed adjacent a rear end  86  of the compressor impeller  36 . The rear end  86  may be disposed opposite the front end  84 . The blades  82  may be disposed between the nose  78  and the hub extension  80 . In an exemplary embodiment, the compressor impeller  36  may be made of metal, such as aluminum or an aluminum alloy material. 
     The hub extension  80  may extend toward the rear end  86  of the compressor impeller  36 , and may have a diameter smaller than an outer diameter of the blades  82 . The hub extension  80  may also have a generally cylindrically shaped outer surface. It is contemplated, however, that the outer surface may have an elliptical, polygonal, or any other shape known in the art. Compressor impeller  36  may accordingly have a first impeller bore  88 , which may be disposed within the hub extension  80  adjacent the rear end  86  of the compressor impeller. The first impeller bore  88  may extend the length of the hub extension  80 , and may have an internal thread. Compressor impeller  36  may also have a second impeller bore  90 , which may be disposed within the nose  78  adjacent the front end  84 . The second impeller bore  90  may be a stepped bore extending from the front end  84  toward the rear end  86 , and be dimensioned to house a drive feature  92  and at least a portion of the stud  74 . The drive feature  92  may both provide a seal at the front end  84  of the compressor impeller  36  from moisture intrusion, and also assist with securing the stud  74  within the compressor impeller  36 . Finally, the compressor impeller  36  may also have a third impeller bore  94  disposed between the front end  84  and the rear end  86 , and may be dimensioned to accommodate the stud  74 . 
     With reference to  FIGS.  4  and  5   , and with continued reference to  FIG.  2   , the insert  68  may have a first insert portion  96  that may be disposed within the first impeller bore  88  and a second insert portion  98  that may be disposed outside first impeller bore. The first insert portion  96  may have an exterior surface  100  that may be threaded, so as to matingly engage with the threaded interior surface of the first impeller bore  88  during installation of the insert  68  within the first impeller bore  88 . A portion  102  of an interior surface of the first insert portion  96  may also be threaded. This threaded portion  102  may have a first pitch, and may be configured to matingly engage with a first threaded exterior portion  104  of the stud  74 . As such, the threaded portion  102  of the first insert portion  96  may have the same pitch as the first threaded exterior portion  104  of the stud. In one embodiment, the threaded portion  102  and the first threaded exterior portion  104  may have a fine thread pitch, for example. 
     The impeller collar  70  may extend from a first collar end  106  to a second collar end  108 . In one exemplary embodiment, the first collar end  106  may be disposed adjacent the rear end  86  of compressor impeller  36 . The impeller collar  70  may have a cap portion  110  disposed at the first collar end  106 , and configured to form a cap bore  112  that may have a diameter such that the cap portion may be disposed around the outer surface of the hub extension  80 . In one exemplary embodiment, the cap portion  110  may engage with the outer surface of the hub extension via an interference fit, however, it is also contemplated that a clearance fit may be alternatively employed. 
     The impeller collar  70  may also include a stepped bore  114  having an insert region  116  and a shaft region  118 . The insert region  116  may have a larger diameter bore than the shaft region  118 . The insert region  116  of the impeller collar  70  may be dimensioned such that it may surround the second insert portion  98  disposed outside first impeller bore  88 , which may in turn surround a leading shaft portion  120  of the shaft  38 , which may in turn surround a second threaded exterior portion  132  of the stud  74 . 
     The shaft  38  may be coupled to, and extend from, the turbine wheel  30 . More specifically, the shaft  38  may include the leading shaft portion  120 , a mid-shaft portion  122 , and a trailing shaft portion  124 . The leading shaft portion  120  may be disposed within the second insert portion  98  of the insert  68 . The leading shaft portion  120  may have an exterior surface  126  which may engage with an interior surface  128  of the second insert portion  98  of the insert  68 . The exterior surface  126  may include an anti-rotation feature  170 , which will be discussed further below in reference to  FIG.  6   . An interior surface  130  of the leading shaft portion  120  may be threaded so as to matingly engage a second threaded exterior portion  132  of the stud  74 . As such, the threaded interior surface  130  of the leading shaft portion  120  may have the same pitch as the second threaded exterior portion  132  of the stud  74 . In an exemplary embodiment, the pitch of the second threaded exterior portion  132  may be coarse, such that the pitch of the first threaded exterior portion  104  may be finer than the pitch of the second threaded exterior portion. 
     Finally, the mid-shaft portion  122  may have a generally cylindrical exterior shape. In an alternative embodiment, however, it is contemplated that the exterior surface of the mid-shaft portion  122  may have an elliptical, polygonal or any other shape known in the art. The mid-shaft portion  122  may engage with a portion of the impeller collar  70  via a clearance fit or an interference fit. The trailing shaft portion  124  may also have a generally cylindrical outer surface  182 , and may generally have a diameter larger than a diameter the mid-shaft portion  122 , creating a shoulder  134  on the shaft  38 . The thrust washer  72  may be disposed axially between an end shoulder  136  of the impeller collar  70  and the shoulder  134  of the shaft  38 . Similarly, the thrust washer  72  may be radially disposed to surround an exterior surface of a turbine side extension  138  of the impeller collar  70  via, for example an interference or clearance fit. The turbine side extension  138  of the impeller collar  70 , therefore, may be radially disposed between the shaft  38  and the thrust washer  72 . Two pilots may be formed by this arrangement. A first pilot  140  may be formed at a distal end  144  of the turbine side extension  138  of the impeller collar  70 , and a second pilot  142  may be formed at a proximal end  146  of the turbine side extension of the impeller collar. 
       FIG.  6    illustrates a cutaway perspective view of the anti-rotation feature  170  formed by the external geometry of the shaft  38  at the leading shaft portion  120  and the mid-shaft portion  122  (see e.g.  FIG.  5   ). As illustrated, the external geometry of the shaft  38  along the leading shaft portion  120  and the mid-shaft portion  122  may have a three-lobed polygonal shape. A bore of the impeller collar  70  may also have a three-lobed polygonal shape corresponding to the shape of outer surface of the shaft. The anti-rotation feature  170  may help prevent relative rotational motion between the insert  68  and impeller collar  70 . Similarly, the anti-rotation feature  170  may also assist with centering the stud  74  to ensure the stud, the shaft  38 , the insert  68  and the impeller collar  70  remain concentric with each other during installation and operation. 
     INDUSTRIAL APPLICABILITY 
     In practice, the teachings of the present disclosure may find applicability in many industries including, but not limited to, the railroad, marine, power generation, mining, construction, and farming industries, as well as other industries known in the art. More specifically, the present disclosure may be beneficial to locomotives, other vehicles, and any other machine utilizing a turbocharger. 
     Traditionally, turbocharger rotors require attachment of the compressor impeller to the shaft system via a joint. This joint must align to the shaft system along its axis and rotationally during rotor balancing and assembling installation with little to no variance from the balanced state in order to maintain secure throughout the rotor service life. Repeated assembly and disassembly, for example, should not alter the balance consistency. Further, the joint should only require simple tools and methods of construction to minimize assembly duration and provide similar benefits during remanufacture of the entire assembly. 
     In contrast to other joints, the present impeller attach mechanism employs a novel means of alignment, attachment, torque transmission and fastening. For example, the shaft pilots  140 ,  142  align both the compressor impeller  36  and the thrust washer  72  via the impeller collar  70 . The shoulder  134  of the shaft  38  transmits aerodynamic thrust through the thrust washer  72 . Further, in one embodiment illustrated in  FIG.  6   , two identical alignment and torque transmission three-lobed polygons formed by the external geometry of the shaft  38  at the leading shaft portion  120  and the mid-shaft portion  122  may interface with the impeller collar  70  and the insert  68 . Finally, a hollow section  148  formed by the shaft minimized wall thickness to allow stretch for joint fixity while providing bending stiffness. 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and assemblies without departing from the scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof. 
     It should also be understood that, unless a term was expressly defined herein, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to herein in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning.