Abstract:
An electrically assisted turbocharger ( 10 ) includes an electric motor ( 70 ) having a rotor ( 72 ) and a stator ( 74 ). The rotor ( 72 ) rotates in response to operation of the turbocharger ( 10 ) and the stator ( 74 ) is fixed relative to the rotor ( 72 ). A component ( 40, 48, 24 ) rotates in unison with the rotor ( 72 ) and includes a plurality of features ( 80, 84, 86, 90 ). To control timing of phase excitation of the electric motor ( 70 ), a position sensor ( 82 ) is mounted to the turbocharger ( 10 ) to detect the plurality of features ( 80,   84, 86, 90 ) on the rotating component ( 40, 48, 24 ) to determine a rotational position of the rotor ( 72 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and all the benefits of U.S. Provisional Application No. 61/600,126, filed on Feb. 17, 2012, and entitled “Position Sensor Placement For Electrically Assisted Turbocharger.” 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to an electrically assisted turbocharger for an internal combustion engine. More particularly, this invention relates to a method of sensing rotor position in an electrically assisted turbocharger. 
         [0004]    2. Description of Related Art 
         [0005]    A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine&#39;s horsepower without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment. 
         [0006]    Turbochargers typically include a turbine housing connected to the engine&#39;s exhaust manifold, a compressor housing connected to the engine&#39;s intake manifold, and a center bearing housing coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines an axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow, density and air pressure delivered to the engine&#39;s cylinders via the engine&#39;s intake manifold. 
         [0007]    To further improve engine efficiency, it is known to integrate an electric motor into the shaft of the turbocharger. This type of turbocharger is referred to as an electrically assisted turbocharger. In such a configuration, the motor is energized at low engine speeds to impart additional rotation to the shaft, which increases rotation of the compressor impeller in order to minimize turbo lag. The electric motor can also be used as a generator, which converts shaft work into electrical power. The electrical power produced by the generator can be used to run auxiliary electrical components or to run a motor mounted on the engine crankshaft, recovering otherwise wasted energy in the exhaust gas. 
         [0008]    One example of an electric motor that is integrated into the shaft of the turbocharger is a switched reluctance motor (SRM). The principles of operation of SRMs are simple, well known, and based on reluctance torque. SRMs have a stator with concentrated windings and a rotor with no winding. In the electrically assisted turbocharger, the rotor is incorporated with the shaft of the turbocharger and the stator surrounds the rotor. A typical SRM may have six stator poles and four rotor poles, denoted as a “6/4 SRM.” The 6/4 SRM has three phases, each phase consisting of two windings on opposite stator poles. The windings in one phase are simultaneously energized and generate a magnetic flux. The magnetic flux created by the windings follows the path of least magnetic reluctance, meaning the flux will flow through the rotor poles that are closest to the energized stator poles, thereby magnetizing those rotor poles and causing the rotor to align itself with the energized stator poles. Electromagnetic torque is produced by the tendency of the rotor poles to align with the energized stator poles. As the rotor turns, different phases will be sequentially energized to keep the rotor turning. For use as a generator, the phases are energized when the stator poles and rotor poles are separating, rather than when they are approaching. Thus, controlling the timing of phase excitation, whether as a motor or generator, is important to the operation of the electrically assisted turbocharger. 
         [0009]    In order to properly control the timing of phase excitation, accurate position sensing of the rotor relative to the stator is required. It is desirable, therefore, to provide an electrically assisted turbocharger having simple and accurate position sensing for a rotor of an electric motor. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one aspect of the invention, an electrically assisted turbocharger includes a turbine wheel mounted on one end of a shaft and a compressor impeller mounted on an opposite end of the shaft. The shaft and compressor impeller rotate in response to rotation of the turbine wheel. A rotor of an electric motor is fixed to the shaft between the turbine wheel and the compressor impeller and rotates with the shaft. A stator of the electric motor is fixed relative to the rotor. A component, such as a compressor nut, flinger sleeve, or the compressor impeller, rotates with the shaft and includes a plurality of features such as flats, lobes, or scallops. A position sensor is mounted to the turbocharger and arranged to detect the plurality of features on the rotating component which is used to determine a rotational position of the rotor in order to control timing of phase excitation in the electric motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0012]      FIG. 1  is a cross-sectional view of an electrically assisted turbocharger including an electric motor; 
           [0013]      FIG. 2  is a cross-sectional view of a rotor of the electric motor mounted on a shaft of a turbine wheel; 
           [0014]      FIG. 3A  is a perspective view of a compressor nut including a plurality of features according to one embodiment of the invention; 
           [0015]      FIG. 3B  is an end view of the compressor nut shown in  FIG. 3A  illustrating one location for a position sensor; 
           [0016]      FIG. 4A  is a partially cut-away cross-sectional view of a flinger sleeve including a plurality of features and an insert according to another embodiment of the invention illustrating another location for the position sensor; 
           [0017]      FIG. 4B  is an end view of the flinger wheel shown in  FIG. 4A ; 
           [0018]      FIG. 5A  is a partially cut-away cross-sectional view of a compressor impeller including a plurality of features according to yet another embodiment of the invention illustrating another location for the position sensor; 
           [0019]      FIG. 5B  is a back end view of the compressor impeller shown in  FIG. 5A ; and 
           [0020]      FIG. 6  is a front end view of the compressor impeller including a plurality of scallop cuts according to still another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0021]    Referring to the Figures, a turbocharger is illustrated generally at  10  in  FIG. 1 . The turbocharger  10  includes a housing assembly  12  consisting of a turbine housing  14 , a bearing housing  16 , and a compressor housing  18  that are connected to each other. A turbine wheel  20  is disposed in the turbine housing  14  and is rotatably driven by an inflow of exhaust gas supplied from an engine exhaust manifold. After driving the turbine wheel  20 , the exhaust gas is discharged from the turbine housing  14  through a central exit pipe or exducer  21 . A shaft  22  that is rotatably supported in the bearing housing  16  connects the turbine wheel  20  to a compressor impeller  24  in the compressor housing  18  such that rotation of the turbine wheel  20  causes rotation of the compressor impeller  24 . The shaft  22  connecting the turbine wheel  20  and the compressor impeller  24  defines an axis of rotation R 1 . As the compressor impeller  24  rotates, air is drawn into the compressor housing  18  through an inlet passage  25  and is compressed to be delivered at an elevated pressure to an engine intake manifold. 
         [0022]    The shaft  22  is rotatably supported in the bearing housing  16  by a pair of spaced apart journal bearings  26 ,  28 . The turbine wheel  20  is typically butt welded to one end of the shaft  22  directly adjacent to an enlarged shoulder portion  30  of the shaft  22 . The shaft  22  enters the bearing housing  16  though a piston ring bore  32  that is formed in a turbine side of the bearing housing  16 . The shoulder portion  30  is disposed in the piston ring bore  32 . A piston ring  34  is seated in a groove on the shoulder portion  30  and forms a seal between the shaft  22  and the bearing housing  16 . An opposite end of the shaft  22  has a reduced diameter portion  36  on which the compressor impeller  24  is mounted. A distal end  38  of the shaft  22  is threaded and a compressor nut  40  securely retains the compressor impeller  24  to the shaft  22 . Adjacent to the journal bearing  28 , the reduced diameter portion  36  of the shaft  22  carries a thrust washer  42  that cooperates with a stationary thrust bearing member  44  to handle axial loads in the turbocharger  10 . The reduced diameter portion  36  also carries an insert  46  and a flinger sleeve  48  that are located directly adjacent to a back-wall  50  of the compressor impeller  24 . The thrust washer  42 , thrust bearing member  44 , insert  46 , and flinger sleeve  48  are assembled into a thrust bearing pocket  52  which is formed in a compressor side of the bearing housing  16 . The insert  46  and flinger sleeve  48  cooperate to prevent oil from being sucked into the compressor housing  14  and to keep the compressed air from leaking into the bearing housing  16 . The flinger sleeve  48  includes an outer portion  54  that is adjacent to the compressor impeller  24  and an inner portion  56  that is adjacent to the thrust washer  42 , best seen in  FIG. 4A . The shaft  22  exits the bearing housing  16  through a piston ring bore  58  that is formed in the insert  46 . The flinger sleeve  48  rotates with the shaft  22  and the outer portion  54  thereof is disposed in the piston ring bore  58 . A piston ring  60  is seated in a groove on the outer portion  54  of the flinger sleeve  48  and forms a seal between the flinger sleeve  48  and an inner circumference of the insert  46 . An O-ring  62  is seated in a groove on an outer circumference of the insert  46  and forms a seal between the insert  46  and the bearing housing  16 . A snap ring  64  secures the insert  46  in place. The inner portion  56  of the flinger sleeve  48  is disposed in a bore of the thrust bearing member  44 . The flinger sleeve  48  also includes a lip  66  between the outer and inner portions  54 ,  56  having a circumference that is larger than the circumference of each of the outer and inner portions  54 ,  56 . The lip  66  is disposed between the insert  46  and the thrust bearing member  44 . 
         [0023]    Oil circulates through the bearing housing  16  to provide lubrication to the journal bearings  26 ,  28  and to remove heat that comes from the turbine housing  14 . The exhaust gas is prevented from entering the bearing housing  16  on the turbine side by the piston ring  34 . Similarly, the compressed air is prevented from entering the bearing housing  16  on the compressor side by the piston ring  60 . On the turbine side, oil leaving the journal bearing  26  is picked up by a face  68  of the shoulder portion  30 , best seen in  FIG. 2 , as the shaft  22  rotates and is directed into a first slot which opens into an oil drain cavity of the bearing housing  16 . On the compressor side, oil leaving the journal bearing  28  is picked up by the lip  66  of the flinger sleeve  48  as the shaft  22  rotates and is directed into a second slot which also opens into the oil drain cavity of the bearing housing  16 . 
         [0024]    An electric motor is incorporated into the turbocharger  10 . In the present embodiment, the motor is a switched reluctance motor (SRM), generally shown at  70 . It is appreciated, however, that the electric motor may be any suitable motor without varying from the scope of the invention. The SRM  70  is disposed in the bearing housing  16  generally between the spaced apart journal bearings  26 ,  28 . The SRM  70  includes a rotor  72  that rotates with the shaft  22  and a stator  74  with concentrated windings that is stationary and circumferentially surrounds the rotor  72 . In the present embodiment, the rotor  72  has four rotor poles and the stator  74  has six stator poles. A collar  76  on the turbine side is fixed to the shaft  22  and acts as a spacer between the journal bearing  26  and the rotor  72 . Similarly, a collar  78  on the compressor side is fixed to the shaft  22  and acts as a spacer between the journal bearing  28  and the rotor  72 . In order to properly control the timing of phase excitation in the SRM, accurate position sensing of the rotor  72  is required, as is well known to one skilled in the art. However, due to space constraints and extreme conditions in certain areas within the housing assembly  12 , there are relatively few locations for arranging a conventional position sensor to detect rotor position. Since the shaft  22  rotates in unison with the rotor  72 , accurate position sensing of the shaft  22  will satisfy this requirement. Likewise, any rotating component associated with the rotor  72  can be used to facilitate position sensing of the rotor  72 . Flats, lobes, scallops, or other features can be added to these rotating components for detection by a position sensor. It is contemplated that the position sensor may be any type of sensor that is suitable for monitoring these features, such as a magnetic pickup (Hall effect) sensor or a reflective type (optical) sensor. It is further contemplated that various factors will all play a role in the type of position sensor that is used. For example, whether the features are magnetic or non-magnetic, shape and size of the features, and the proximity of the position sensor relative to the features. 
         [0025]    In the present embodiment, it is convenient to add four features to a rotating component in the turbocharger  10  to correspond with the number of poles of the rotor  72  in order to simplify the control and electronics required for phase excitation of the SRM  70 . It is appreciated, however, that fewer or more features may be used without varying from the scope of the invention. Further, it may be desirable to orient or “clock” the features on the rotating component such that the features are aligned with the poles of the rotor  72 , however, such alignment of the features with the poles is not necessary. 
         [0026]    In one embodiment of the invention, shown in  FIGS. 3A and 3B , an outer periphery or circumference of the compressor nut  40  has four features  80  and a position sensor  82  is mounted within the inlet passage  25  of the compressor housing  18  to detect the features  80  during rotation of the shaft  22 . In the embodiment shown, the features  80  are flats, however, the features  80  may have some other form without varying from the scope of the invention. In addition, the features  80  are shown to be spaced equally around the circumference of the compressor nut  40 . In other words, the features  80  are spaced equally around the axis of rotation R 1 . However, it is not necessary for the features  80  to be spaced equally around the axis of rotation R 1 . 
         [0027]    In another embodiment of the invention, shown in  FIGS. 4A and 4B , an outer periphery or circumference of the flinger sleeve  48  has four features  84  and the position sensor  82  is affixed to the insert  46  to detect the features  84  during rotation of the shaft  22 . The features  84  are positioned adjacent to the thrust bearing member  44 . In the embodiment shown, the features  84  are lobes, however, the features  84  may have some other form without varying from the scope of the invention. More specifically, the features  84  extend radially outwardly from the lip  66  and arc shown to be spaced equally around the circumference of the lip  66 . In other words, the features  84  are spaced equally around the axis of rotation R 1 . However, it is not necessary for the features  84  to be spaced equally around the axis of rotation R 1 . 
         [0028]    In yet another embodiment of the invention, shown in  FIGS. 5A and 5B , an outer periphery of the compressor impeller  24 , adjacent to the back-wall  50  of the compressor impeller  24 , has four features  86  and the position sensor  82  is located in the compressor side of the bearing housing  16  to detect the features  86  during rotation of the shaft  22 . In the embodiment shown, the features  86  are lobes, however, the features  86  may have some other form without varying from the scope of the invention. In addition, the features  86  are shown to be spaced equally around the outer periphery of the compressor impeller  24 . In other words, the features  86  are spaced equally around the axis of rotation R 1 . However, it is not necessary for the features  86  to be spaced equally around the axis of rotation R 1 . It is contemplated that the features  86  may be located on a nose  88  of the compressor impeller  24  adjacent to the compressor nut  40 , on the back-wall  50  of the compressor impeller  24 , or on an outer periphery of the back-wall  50 , without varying from the scope of the invention. In such instances, the position sensor  82  is located within the turbocharger  10  in a manner to detect the features  86  accordingly. It is further contemplated that in addition to position sensing, the features  86  on or adjacent to the back-wall  50  of the compressor impeller  24  can be used for balance correction of the compressor impeller  24 . As such, the features  86  may not be equally sized. It is appreciated that the compressor impeller  24  is typically made from aluminum. As such, the position sensor  82  would be an optical sensor rather than a magnetic sensor. 
         [0029]    In still another embodiment of the invention, shown in  FIG. 6 , an outer periphery of the back-wall  50  of the compressor impeller  24  has four features  90  and the position sensor  82  is located generally in the compressor housing  18  and/or compressor side of the bearing housing  16  to detect the features  90  during rotation of the shaft  22 . The position sensor  82  may be positioned radially, axially, or at some angle therebetween. In the embodiment shown, the features  90  are scallop cuts, however, the features  90  may have some other form without varying from the scope of the invention. The features  90  are shown to be spaced equally around the outer periphery of the back-wall  50 . In other words, the features  90  are spaced equally-around the axis of rotation R 1 . However, it is not necessary for the features  90  to be spaced equally around the axis of rotation R 1 . It is contemplated that in addition to position sensing, the features  90  on the outer periphery of the back-wall  50  of the compressor impeller  24  can be used for balance correction of the compressor impeller  24 . As such, the features  90  may not be equally sized. 
         [0030]    The invention has been described here in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of words of description rather than limitation. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically enumerated within the description.