Abstract:
An internal combustion engine is provided with a turbocharger having a compressor section and a turbine section. The turbine section is in communication with an exhaust manifold of the engine. The compressor section includes an exhaust gas recirculation passage in communication with the exhaust gas recirculation line and a variable inlet in communication with the exhaust gas recirculation passage that provides the turbocharged engine with a wider operating range and improved efficiency.

Description:
FIELD 
       [0001]    The present disclosure relates to a turbocharged engine and more particularly to a turbocharger having a variable inlet duct. 
       BACKGROUND AND SUMMARY 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    Internal combustion engines are used to generate considerable levels of power for prolonged periods of time on a dependable basis. Many such engine assemblies employ a supercharging device, such as an exhaust gas turbine driven turbocharger, to compress the airflow before it enters the intake manifold of the engine in order to increase power and efficiency. 
         [0004]    Specifically, a turbocharger utilizes a centrifugal gas compressor that forces more air and, thus, more oxygen into the combustion chambers of the engine than is otherwise achievable with ambient atmospheric pressure. The additional mass of oxygen-containing air that is forced into the engine improves the engine&#39;s volumetric efficiency, allowing it to burn more fuel in a given cycle, and thereby produce more power. 
         [0005]    A typical turbocharger employs a central shaft that transmits rotational motion between an exhaust-driven turbine wheel and an air compressor wheel. Both the turbine and compressor wheels are fixed to the shaft, which in combination with various bearing components constitute the turbocharger&#39;s rotating assembly. 
         [0006]    A recirculation passage is commonly provided in a compressor stage and allows for high pressure flow to bypass the wheel so as to prevent surge and choke. The operating range of a turbocharger is limited based upon its map width. In particular, the map width is the operating range of the mass air flow and pressure range for the turbocharged engine. For example, while a turbocharger design may operate without surge at high RPMs, the same turbocharger can experience surge or choke at low RPMs. 
         [0007]    Surge margin is maximized if the walls of the passage redirect the flow back into the wheel. Redirecting flow requires a small opening between the end of the inlet duct to the compressor shroud. However, choke margin is maximized if this opening to the recirculation passage is large. The present disclosure alters the compressor map for a turbocharger by altering an opening of the recirculation passage so that a wider compressor map can be achieved. Accordingly, as engine RPM increases, air flow can be controlled for the appropriate situation, resulting in the use of a more efficient map. 
         [0008]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0009]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0010]      FIG. 1  is a schematic illustration of an engine assembly according to the present disclosure; 
           [0011]      FIG. 2  is a cross-sectional view of a turbocharger having a variable inlet duct according to the principles of the present disclosure; 
           [0012]      FIG. 3  is a partial cross-sectional view of a compressor section of a turbocharger having a variable inlet duct according to the principles of the present disclosure; and 
           [0013]      FIG. 4  is a graph of a turbo map in which the pressure ratio versus air flow curve is shown with two effective map ranges superimposed thereon. 
       
    
    
       [0014]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0015]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0016]    Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
         [0017]    The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0018]    When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0019]    An engine assembly  10  is illustrated in  FIG. 1  and may include an engine structure  12  defining cylinders  14  and intake and exhaust ports  16 ,  18  in communication with the cylinders  14 , an intake manifold  20 , exhaust manifold  22 , a throttle valve  24  and a turbocharger  26 . The engine assembly  10  is illustrated as an inline four cylinder arrangement for simplicity. However, it is understood that the present teachings apply to any number of piston-cylinder arrangements and a variety of reciprocating engine configurations including, but not limited to, V-engines, inline engines, and horizontally opposed engines, as well as both overhead cam and cam-in-block configurations. The engine assembly include a piston  28  in each cylinder that are each drivingly connected to a crankshaft  30  as is well known in the art. An engine speed sensor  32  can be provided for detecting a rotational speed of the crankshaft or another component of the engine. 
         [0020]    The turbocharger  26  includes a housing  34  defining a turbine section  36  and a compressor section  38 . The turbine section  36  has an inlet  40  connected to the exhaust passage  42  and includes an exhaust outlet  44 . The compressor section  38  includes an air inlet  46  and an air outlet  48  can provide compressed air to the air intake passage  50 . 
         [0021]    With reference to  FIG. 2 , the turbocharger  26  includes a turbine wheel  56  provided within a turbine chamber  57  of the turbine section  36  and a compressor wheel  58  within a compressor chamber  59  of the compressor section  38 . The turbine wheel  56  and the compressor wheel  58  can be connected to one another by a shaft  60 . Exhaust gases pass through the exhaust passage  42  and thus the turbine section  36  can drive the turbine wheel  56  which in turn drives the shaft  60  and compressor wheel  58 . As the compressor wheel  58  is turned, the intake air from an air inlet  46  is compressed and delivered to the air outlet  48  so that the compressed air is delivered through the air intake passage  50  through the throttle valve  24  and intake manifold  20 . 
         [0022]    With reference to  FIG. 3 , a recirculation passage  60  is provided within the compressor section  38 . The recirculation passage includes an intermediate passage  62  that extends from the compressor chamber  59  and communicates with the compressor wheel  58 . The recirculation passage also includes an upstream inlet duct  66  that communicates with the compressor chamber  59 . A variable extender  68  is located upstream of the compressor wheel and is movable to change the size of the upstream inlet duct  66  to modify the exhaust gas recirculation flow in and out of the recirculation passage  60 . 
         [0023]    A control unit  70  is provided to control the operation of an actuator  72  for moving the variable extender  68 . The actuator  72  can take on various forms including a linear actuator, a rotary to linear actuator, a cam and groove actuator just to name a few. A cam lens type extender can be particularly suited for variable positioning of the variable extender  68 . The variable extender  68  can be in the form of a cylindrical wall. At low engine speeds control unit  70  can control the actuator  72  to cause the variable extender  68  to extend closer to the recirculation passage  54  for increasing the surge margin. At high engine speed, the variable extender  68  can be retracted away from the recirculation passage  54  in order to recover performance at high engine speeds with more choke margin. In other words, by changing the position of the variable extender  68  in front of the turbo compressor the control unit  70  can change the air flow in and out of the recirculation passage  60  and a wider map width can be obtained. Effectively, the variable inlet duct can enable one turbo design to act as if it was changing between two compressor wheel designs, each with different tradeoffs. 
         [0024]    As shown in  FIG. 4 , a graph of a turbo map is shown in which the pressure ratio versus air flow curve  100  is shown with two effective map ranges superimposed thereon. The first map range  102  having a closed inlet duct  66  shows that the curve  100  is within the first map range  102  at low engine speeds and that at high engine speeds, the curve  100  exceeds the map range  102 . The second map range  104  illustrates an open inlet duct  66  wherein the curve  100  is close to the edge range at low engine speeds but well within the second map range  104  at high engine speeds. The primary benefit is to eliminate surge choke events by actively changing the range of operation of the turbocharger. At low engine speeds the variable extender is moved closer to the recirculation passage  66  for more surge margin. However, in this position, performance is lost at high engine speeds. At high engine speeds, the variable extender  68  can be retracted away from the recirculation passage in order to recover performance at high engine speeds, with more choke margin. In addition, the present disclosure provides the added benefit of optimizing the compressor efficiency. 
         [0025]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.