Abstract:
A turbocharger internal heat shield ( 1 ) is provided having axial flow turning vanes ( 2 ). Additionally, the heat shield may have a volute divider wall extender ( 5 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a turbocharger for an internal combustion engine. More particularly, this invention relates to turbocharger having an axial flow turbine wheel and an internal heat shield having turning vanes. Optionally, for a twin exhaust gas volute the heat shield may have a divider wall extender. 
         [0003]    2. Description of Related Art 
         [0004]    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. 
         [0005]    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. 
         [0006]    In a turbocharger, the turbine wheel may be either a radial flow wheel in which the exhaust gas is directed along the radius of the wheel, or an axial flow wheel in which the exhaust gas is directed along the axis of the turbine wheel. Frequently, the bearing housing is shielded from the heat of the exhaust gases by a heat shield which is placed between the turbine wheel and the bearing housing. 
         [0007]    U.S. Pat. No. 7,631,497 relates to a turbocharger with a heat shield positioned between the turbine wheel and the bearing housing, wherein the heat shield defines a gap between the turbine wheel. and the heat shield and is provided with at least one rib extending into the gap. In this gap, in the case of a conventional flat heat shield, the turbine wheel backface may act in the manner of a centrifugal pump, pumping gas out from within the gap, creating a region of reduced pressure adjacent the outboard side of the turbine shaft bearing, and drawing oil out the shaft bearing and into the space between the turbine wheel backface and the heat shield. The inventive heat shield has raised structures designed to interfere with the rotational and centrifugal flow of gas in the gap between heat shield and turbine wheel backface, thus prevent oil bypass. 
         [0008]    U.S. Pat. No. 6,739,134 relates to an exhaust-gas turbocharger for an internal combustion engine having a turbine in the exhaust-gas tract and a compressor, driven by the turbine, in the intake tract, the turbine having a flow channel with a radial flow-inlet cross-section and a semi-axial flow-inlet cross-section, and a flow ring being provided which limits the two flow-inlet cross-sections. The turbine is furnished with variable turbine geometry for the changeable adjustment of the flow-inlet cross-section. To improve efficiency, the position of the flow ring in the housing of the exhaust-gas turbocharger is variably adjustable. 
       SUMMARY OF THE INVENTION 
       [0009]    In many turbochargers the exhaust gas volute conveys the exhaust gas to the turbocharger in a direction which is radial to the turbine wheel. In turbochargers having an axial turbine wheel, it is necessary to turn the exhaust gas to the axial direction before it gets to the turbine wheel. It has been discovered that a heat shield having turning vanes may be used to redirect or guide the exhaust gas before it gets to the turbine wheel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    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: 
           [0011]      FIG. 1  shows a heat shield with turning vanes; 
           [0012]      FIG. 2  shows a heat shield with turning vanes and a volute divider wall extender; and 
           [0013]      FIG. 3  shows a heat shield, and a volute having a divider and a divider wall extender. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0014]      FIG. 1  shows a heat shield ( 1 ) with turning vanes ( 2 ). 
         [0015]      FIG. 2  shows a heat shield ( 3 ) with turning vanes ( 4 ) and a volute divider wall extender ( 5 ). 
         [0016]      FIG. 3  shows a heat shield ( 6 ), a volute ( 7 ), with a divider wall ( 8 ) and a volute divider wall extender ( 9 ). 
         [0017]    The exhaust gas from the engine is conducted to the turbine housing by the exhaust gas volute ( 7 ). The exhaust gas volute ( 7 ) allows the exhaust gas to enter the turbine housing in a direction which is radial to the turbine wheel. If an axial turbine wheel is being used, the gas must be turned to an axial direction before it arrives at the turbine wheel. Exhaust gas directed toward a flat bearing housing face will turn to the axial direction. Often a heat shield ( 1 ) and ( 3 ) is placed over the wall of the bearing housing to shield the bearing housing from the hot exhaust gases. Exhaust gases directed toward the heat shield ( 1 ) and ( 3 ) will turn to the axial direction. However, it has now been discovered that vanes ( 2 ) and ( 4 ) in the heat shield ( 1 ) and ( 3 ) wall will efficiently redirect the exhaust gas from the radial to the axial direction. The vanes ( 2 ) and ( 4 ) guide the exhaust gas along the wall of the heat shield ( 1 ) and ( 3 ) and thereby optimize the angle of incidence on the turbine wheel blades&#39; leading edges. Instead of relying on the natural vectors of the gas leaving the housing volute and the turning vector imposed by the heat shield surface, addition of the turning vanes ( 2 ) and ( 4 ) can force the gas incidence angle to be more optimized for what the wheel blade angles are expecting. By better organizing the flow into a more specific flow vector, improved efficiency is achieved. The number of vanes can vary. Four to eight turning vanes has been found to be satisfactory. 
         [0018]    In multi-cylinder engines, cylinders from opposing banks fire alternatively. In the case of a “V” engine the banks are separated across the engine. In the case of an inline engine, the banks could simply be the front half of cylinders versus the back half of cylinders. The exhaust gas is conducted to turbine housing in separated portions of the volute. The separate gas streams serve to preserve the pulse of pressure which occurs when the exhaust gas is released from the cylinder. The preservation of the pulses is desirable because the extra pulse of pressure can start the turbine moving faster. This is helpful in reducing turbo lag. In the region where the exhaust gases are admitted to the turbine housing, a separator or divider wall ( 8 ) between the two halves of the volute can help preserve the separation between exhaust gases from each cylinder bank, and thus maintain the pressure pulses. A drawback of using an axial flow wheel and a heat shield in a turning arrangement is that the wheel is now spaced far away from the turbine housing, and hence far away from the housing divider wall ( 8 ) and the pulse separation. By adding a divider wall extension ( 5 ) and ( 9 ) to the heat shield, the preservation of pulses can be maintained all the way downstream to the wheel inlet. 
         [0019]    While the invention has been shown and described with respect to the particular embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the present invention as defined in the following claims.