Abstract:
A turbocharger includes a housing and a rotary assembly disposed within the housing and including a turbine wheel and a compressor wheel attached to one another by a shaft. A bearing is disposed in the housing and rotatably supports the shaft. The bearing includes a pair of inner bearing surfaces that engage opposite ends of the shaft and a pair of outer bearing surfaces that engage the housing. The pair of inner bearing surfaces have a first axial dimension and the pair of outer bearing surfaces have a second axial dimension that is smaller than the first axial dimension.

Description:
FIELD 
       [0001]    The present disclosure relates to turbochargers and more particularly to a bearing system with improved durability and noise reduction. 
       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 boosting 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 is supported by one or more bearings and 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]    Sub synchronous frequency vibration noise can be a concern in a turbocharger. The semi-floating or fully floating bearing according to the principles of the present disclosure is designed to minimize sub synchronous vibration. In conventional bearings as shown in  FIG. 4 , the bearing  1  includes a pair of inner bearing surfaces  2  that engage the turbocharger shaft  3  and a pair of outer bearing surfaces  4  that contact the turbocharger housing. The inner bearing surfaces  2  of the conventional bearing  1  have an axial dimension DI that is smaller than an axial dimension DO of the pair of outer bearing surfaces  4 . 
         [0007]    However, it is a discovery of the present application that a reduced outer bearing surface axial dimension relative to the inner bearing surface axial dimension can decrease sub-synchronous frequency vibrations. Accordingly, the present disclosure provides a turbocharger including a housing and a rotary assembly disposed within the housing and including a turbine wheel and a compressor wheel attached to one another by a shaft. A bearing is disposed in the housing and rotatably supports the shaft. The bearing includes a pair of inner bearing surfaces that engage opposite ends of the shaft and a pair of outer bearing surfaces that engage the housing. The pair of inner bearing surfaces have a first axial dimension and the pair of outer bearing surfaces have a second axial dimension that is smaller than the first axial dimension. 
         [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 schematic cross-sectional illustration of the turbocharger shown in  FIG. 1 ; 
           [0012]      FIG. 3  is a cross-sectional view of the turbocharger bearing according to the principles of the present disclosure; 
           [0013]      FIG. 4  is a cross-sectional view of a conventional turbo charger bearing; and 
           [0014]      FIG. 5  is a spring and damper model diagram of the turbocharger bearing. 
       
    
    
       [0015]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0016]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0017]    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. 
         [0018]    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. 
         [0019]    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. 
         [0020]    Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
         [0021]    Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
         [0022]    An engine assembly  10  is illustrated in  FIG. 1  and may include an engine structure  12  defining a plurality of cylinders  14  and intake and exhaust ports  16 ,  18  in communication with the cylinders  14 . An intake manifold  20  is in communication with the intake ports and an exhaust manifold  22  is in communication with the exhaust ports  18 . A throttle valve  24  and a turbocharger  26  are provided in an intake passage that is connected to the intake manifold  20  and the turbocharger  26  is also in communication with an exhaust passage connected to the exhaust manifold  22 . The engine assembly  10  is illustrated as an in-line 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. 
         [0023]    As shown in  FIG. 2 , the turbocharger  26  includes a shaft  28  having a first end  30  and a second end  32 . A turbine wheel  36  is mounted on the shaft  28  proximate to the first end  30  and configured to be rotated by combustion exhaust gasses emitted from the cylinders  14 . The turbine wheel  36  is typically formed from a temperature and oxidation resistant material, such as a nickel-chromium-based “inconel” super-alloy to reliably withstand temperatures of the combustion exhaust gasses which in some engines may approach 2,000 degrees Fahrenheit. The turbine wheel  36  is disposed inside a turbine housing  38  that includes a volute or scroll  40 . The scroll  40  receives the combustion exhaust gases and directs the exhaust gases to the turbine wheel  36 . 
         [0024]    As further shown in  FIG. 2 , the turbocharger  26  also includes a compressor wheel  42  mounted on the shaft  28  proximate to the second end  32 . The compressor wheel  42  is configured to pressurize the airflow being received from the ambient for eventual delivery to the cylinders  14 . The compressor wheel  42  is disposed inside a compressor cover  44  that includes a volute or scroll  46 . The scroll  46  receives the airflow and directs the airflow to the throttle valve  24  and the intake manifold  20 . Accordingly, rotation is imparted to the shaft  28  by the combustion exhaust gases energizing the turbine wheel  36 , and is in turn communicated to the compressor wheel  42 . 
         [0025]    With continued reference to  FIG. 2 , the shaft  28  is supported for rotation via a bearing  48 . The bearing  48  is mounted in a bore  50  of a bearing housing  52  and is lubricated and cooled by a supply of pressurized engine oil. As shown in  FIG. 3 , the bearing  48  includes a pair of inner bearing surfaces  54  that contact the shaft  28  and a pair of outer bearing surfaces  56  that contact the bore  50  of the housing  52 . The pair of inner bearing surfaces  54  have an axial dimension D 1  and the outer bearing surfaces  56  have an axial dimension D 2  which is smaller than the axial dimension D 1 . The axial dimension D 2  of the outer bearing surfaces  56  can preferably be 90 percent or smaller of the axial dimension D 1  of the inner bearing surfaces  54 . The bearing  48  can be a semi-floating (non-rotating) or fully floating (rotating) type. 
         [0026]    The effect of the relative reduced axial dimension D 2  of the outer bearing surfaces  56  of the bearing  48  can be modeled by a mass-spring-damper system as illustrated in  FIG. 5 . In the diagram of  FIG. 5 , the bearing  48  is shown with a spring and damper system representing an oil film  58  between the bearing  48  and the housing  52  and with a spring and damper system representing the oil film  60  between the bearing  48  and the shaft  28 . The spring and damper systems  58 ,  60  are represented by spring constants k 1 , k 2  and damping coefficients c 1 , c 2 . When the turbocharger  26  does a speed ramp-up, the self-induced oil whirl in the inner film  60  will excite the rotor-dynamic natural frequency (called sub-2 conical model), the magnitude of the vibration X 2  and force F 1  depends on the interaction between the spring constants and damping coefficients k 1 , c 1  and k 2 , c 2  which are governed by the bearing design. The reduced axial dimension of the outer film  58  reduces the k 1 , c 1  and numerically proves to be able to significantly reduce the vibration of the shaft and the interaction force between the bearing  48  and the shaft  28 . 
         [0027]    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.