Abstract:
A turbocharger component cooling system employs an ejector using energizing gas from the turbocharger system to draw cooling fluid through a plenum around the component to be cooled into the secondary inlet of the ejector and dumping the combined energizing and cooling gas flows into a low pressure dump. Energizing gas is drawn from the high pressure side of the compressor or turbine flows in the turbocharger and returned to the low pressure side in the same flow.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of cooling of components in turbocharger systems and, more particularly, to an ejector entrainment arrangement for drawing cooling air through components of the turbocharger for operating temperature reduction. 
     2. Description of the Related Art 
     Turbocharger systems are rapidly evolving for higher performance. Novel bearing systems such as air bearings and supplemental energy devices such as electrical motor systems for accelerating turbine and compressor rotors in low exhaust energy states are being developed for increasing range and performance of current turbochargers. These systems often require temperature regulation for efficient operation. The relatively high operating temperatures of turbocharger components provide minimal availability of conductive heat reduction. Water jacketing systems have been used with some success in reducing operating temperatures of conventional bearings, however, liquid cooling systems require complex casting, machining and sealing technologies for implementation. In addition, current engine systems are operating at the upper limits of heat load rejection without undesirable increases in sizing of cooling heat exchanger components and addition of more cooling requirements may not optimize the overall engine cooling system. 
     It is therefore desirable to provide alternative cooling methods for new turbocharger components which limit operational impact on current engine heat exchanger components. 
     Additionally, a system for providing cooling flow to a turbocharger device is desirable with the ability to support compressor operation all the way from choke to surge, and from low to high shaft speeds. 
     Further, cleanliness of the provided cooling flow is required to avoid any possible harmful contamination or startup problems and a compact system with minimum impact on the engine overall performance is desirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a turbocharger component cooling system using an ejector having a primary inlet, a secondary inlet and an outlet. An energizing gas conduit connects a first bleed port from a high energy gas source and the primary inlet of the ejector. A cooling gas conduit connects a coolant inlet to a component cooling plenum and then connects the cooling plenum to the secondary inlet of the ejector. An outlet gas conduit connects the ejector outlet to a low pressure dump. In one embodiment, the energizing gas source is the output of the turbocharger compressor while in a first alternative embodiment, the energizing gas source is the exhaust gas inlet to the turbocharger. For these embodiments, the low pressure dump is the compressor inlet and the turbine exhaust gas outlet, respectively. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
     FIG. 1 is a schematic block diagram of a turbocharger system employing an ejector cooling entrainment system according to the present invention using compressor outlet bleed flow as a source of high energy gas for the primary ejector flow; 
     FIG. 2 is a sectioned elevation view of an embodiment of the ejector for use in the system shown in FIG. 1; 
     FIG. 3 is a schematic block diagram of a turbocharger system employing an ejector cooling entrainment system using turbine inlet flow as the source of high energy gas for the primary ejector flow; 
     FIG. 4 shows an exemplary embodiment of a cooling flow path in a center housing of a turbocharger employing an air bearing; and 
     FIG. 5 shows an exemplary embodiment of a cooling flow path in a center housing of a turbocharger employing an electric motor stator and rotor for electrically assisting operation of the turbocharger. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, FIG. 1 schematically demonstrates an embodiment of the present invention for cooling bearing components in the center housing of turbocharger  10  having a turbine  12  and a compressor  14  interconnected by a shaft  16 . The shaft is supported by a bearing system  18  which is mounted within the center housing as will be described in greater detail subsequently. The turbocharger operates in a conventional fashion with the turbine receiving exhaust gas from the engine  20  through exhaust manifold  22 . Charge air for the engine is provided from an air intake through an air filter  24  to the inlet of the compressor. After compression the charge air flows through an intercooler  26  through the inlet manifold  28  to the intake of the engine. In the embodiment shown for a diesel engine, a crankcase breather  30  is connected to the inlet conduit for the compressor. 
     An ejector  32  receives high energy air, in the embodiment of FIG. 1, as bleed flow from the compressor discharge through a bleed port  34  and conduit  36 . The ejector, best seen in FIG. 2 in an exemplary embodiment, directs the high energy bleed flow into the ejector primary flow inlet  38  through a nozzle  40  increasing the velocity of the bleed flow as the primary gas stream generally designated “A”. In the embodiment shown the nozzle is converging; however, in alternative embodiments, a converging-diverging nozzle is employed for obtaining desired flow velocity and pressure. An annular slot  42  in the ejector downstream of the nozzle provides the inlet for entrainment of the secondary gas stream entering the ejector through one or more secondary flow inlet ports  44 . The secondary gas stream generally designated “B” constitutes the coolant which is drawn into the low pressure nozzle exit  46  of the ejector for entrainment and mixing with the primary gas flow. The mixed stream generally designated “AB” then passes through a diffuser  48  to the outlet of the ejector  50  in the embodiment shown in the drawings. 
     Returning to FIG. 1, the coolant flow for entrainment in the ejector is drawn as a bleed flow from the compressor inlet through a second bleed port  52 . The cooling air is bled downstream of the engine air-filter and any air flow-meter the engine may have, but upstream of the crankcase breather (if connected to the compressor inlet as shown in FIG. 1) to eliminate any need for further filtering devices. The coolant flows through first coolant conduit  54  to a plenum associated with the component to be cooled, in the case of FIG. 1 the bearing system, and through a second coolant conduit  56  to the secondary flow inlet ports of the ejector. The mixed stream from the ejector is then returned through conduit  58  to be dumped in the low energy flow at the compressor inlet. Reintroduction of the mixed flow from the ejector into the charge air is accomplished through a “Y” or annular mixer generally designated  60  adjacent the inlet of the compressor. 
     The high flow density at compressor discharge bleed port allows the ejector to be very compact. Impact of the bleed flow on engine performance is minimized by rematching the turbocharger to the engine under the bleed conditions, or by changing the positioning of the vanes in Variable Nozzle Turbine turbochargers, or both where possible. In addition, using this embodiment, there is no need for any additional engine control related flow metering to account for the bled compressor discharge flow that is not getting to the engine since all the flow that is bled from the compressor is dumped back into the compressor inlet, and all manipulation of the flow is all occurring downstream of where the airflow meter  62  on the engine is typically located, therefore, all of the amount of airflow measured by the airflow meter gets to the engine cylinders. The system matching for the ejector cooling system in the present invention is ideal in that the energy of the compressor discharge gas is dependent on the rotational speed of the turbocharger. Higher rotational speed implies higher bearing and component temperatures; however, the higher energy of the discharge bleed gas for the primary ejector flow allows pumping of a larger volume of cooling gas through the ejector secondary flow. 
     An alternative embodiment of the present invention using bleed flow from the engine exhaust gas inlet to the turbine as the high energy primary flow for the ejector is shown in FIG.  3 . The primary components of the system are comparable to those described with respect to FIG. 1; however, the high energy gas stream is provided through a first bleed port  64  in the exhaust manifold upstream of the turbine inlet. The mixed flow from the ejector is dumped into the low pressure exhaust gas stream through a “Y”  66  or, alternatively, an annular mixer downstream of the turbine outlet for treatment with the main exhaust gas stream from the turbocharger. 
     Cooling flow provided by the present invention is employed in several exemplary embodiments shown in FIGS. 4 and 5. FIG. 4 demonstrates a system employing the combined components of the invention for cooling an air bearing  68  in the turbocharger center housing  70 . The air bearing supports the shaft  16  which interconnects the turbine and compressor. The cooling air flow is drawn from the first coolant conduit  54  through the center housing coolant inlet  72  for circulation in the plenum  74  surrounding the air bearing. Details of the plenum and flow configuration of the coolant are dependent on the air bearing configuration. The cooling air is exhausted from the center housing through coolant outlet  76  to which the second coolant conduit  56  is attached for carrying the coolant flow to the ejector. 
     FIG. 5 shows a second application of the invention for cooling the stator  78  and rotor  80  of an electric motor in an electrically assisted turbocharger. The rotor is integral to or mounted on the shaft of the turbocharger. The stator is mounted in the center housing concentric to the shaft. In the embodiment shown in the drawing, the cooling air flow is drawn from the first coolant conduit  54  through the center housing coolant inlet  82  for circulation in the plenum  84  surrounding the stator and rotor. The cooling air is exhausted from the center housing through coolant outlet  86  to which the second coolant conduit  56  is attached for carrying the coolant flow to the ejector. 
     Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.