Patent Publication Number: US-6655142-B2

Title: Separate shaft turbocharger

Description:
TECHNICAL FIELD 
     The present invention relates to turbochargers for use in internal combustion engines, and, more particularly, to a turbocharger having two or more compressor stages driven by one turbine. 
     BACKGROUND 
     A limiting factor in the performance of an internal combustion engine is the amount of combustion air that can be delivered to the intake manifold for combustion in the engine cylinders. Atmospheric pressure is often inadequate to supply the required amount of air for proper operation of an engine. 
     An internal combustion engine, therefore, may include one or more turbochargers for compressing air to be supplied to one or more combustion chambers within corresponding combustion cylinders. The turbocharger supplies combustion air at a higher pressure and higher density than existing atmospheric pressure and ambient density. The use of a turbocharger can compensate for lack of power due to altitude, or to increase the power that can be obtained from an engine of a given displacement, thereby reducing the cost, weight and size of an engine required for a given power output. 
     Each turbocharger typically includes a turbine driven by exhaust gases from the engine, and a compressor driven by the turbine. The compressor receives the air to be compressed and supplies the air to the combustion chamber. It is known to drive the compressor via a shaft carrying both the compressor wheel and the turbine wheel. 
     It is known to provide higher compression levels through the use of a multi-stage turbocharger. A known multi-stage turbocharger includes a turbine section and two or more compressor sections. A common shaft interconnects the turbine wheel of the turbine section with compressor wheels in the compressor sections. A stream of exhaust gases from the engine is conducted from the exhaust manifold to the turbine section of the turbocharger The stream of exhaust gases passing through the turbine section causes the turbine wheel to rotate, thereby turning the common shaft interconnecting the turbine wheel and the compressor wheels and rotating the compressor wheels. 
     Ambient air to be used for combustion in the internal combustion engine is brought into an inlet for the first compressor section. The air is compressed by the first compressor wheel, and passes from the first compressor section through a first compressor section outlet to the inlet of the second compressor section, for further compression. An interstage duct is used to conduct the compressed air from the first compressor section outlet to the inlet of the second compressor section. The out flow from the second compressor section exits the turbocharger at the second compressor section outlet, and is directed to the inlet manifold of the internal combustion engine. 
     U.S. Pat. No. 4,344,289 (Curiel et al.) discloses a supercharger with a two-stage compressor having two compressor wheels which are disposed in a back-to-back orientation relative to each other and carried by a common shaft. It is also known to provide two compressors operating to separately compress volumes of air supplied to a common duct. U.S. Pat. No. 5,157,924 (Sudmanns) discloses compressor wheels disposed in a face-to-face manner relative to each other, and which are carried by a common shaft. 
     Several problems are experienced with previously known constructions for turbochargers as described above. Providing a common shaft carrying the turbine wheel and two or more compressor wheels for separate compressor stages results in an undesirably large structure, difficult to arrange in an engine compartment. The combined mass of the turbine wheel and compressor wheels, even though positioned at different locations along the shaft, can cause shaft deflections. It is difficult to mount bearings accurately, and premature wear can be a problem. Further, since the compressor wheels are mounted directly on a single shaft, it has not been possible to optimize all compressor wheel speeds for optimum turbocharger performance. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a turbocharger for an internal combustion engine is provided with a turbine including a turbine shaft, a turbine wheel carried by the turbine shaft, and a drive gear carried by the turbine shaft. A compressor includes a compressor shaft, a compressor wheel carried by the compressor shaft, and a driven gear carried by the compressor shaft. The driven gear is operatively engaged with the drive gear. 
     In another aspect of the invention, an internal combustion engine is provided with a plurality of combustion cylinders, an intake manifold fluidly coupled for supplying combustion gas to the plurality of combustion cylinders, and an exhaust manifold fluidly coupled to receive a flow of exhaust gases from the plurality of combustion cylinders. A turbocharger includes a turbine having a rotatable turbine shaft, a turbine wheel carried by the turbine shaft, a drive gear carried by the turbine shaft and a turbine inlet and a turbine outlet associated with the turbine wheel. The turbine inlet is connected in flow communication with the exhaust manifold. A first compressor includes a first compressor shaft, a first compressor wheel carried by the first compressor shaft, a first driven gear carried by the first compressor shaft, and a first compressor inlet and a first compressor outlet associated with the first compressor wheel. The first driven gear is operatively engaged with the drive gear, and the first compressor outlet is connected in flow communication with the intake manifold. 
     In yet another aspect of the invention, a method of operating a turbocharger in an internal combustion engine is provided, with the steps of providing a turbine including a turbine shaft, a turbine wheel carried by the turbine shaft, and an inlet and an outlet associated with the turbine wheel; providing a first compressor including a first compressor shaft, a first compressor wheel carried by the first compressor shaft, and a first compressor inlet and a first compressor outlet associated with the first compressor wheel; providing driving engagement of the first compressor shaft with turbine shaft; circulating a fluid stream to the turbine inlet and through the turbine to the turbine outlet, and rotating the turbine wheel and the turbine shaft thereby; and rotating the first compressor shaft and the first compressor wheel through the driving engagement of the first compressor shaft and the turbine shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an internal combustion engine having a separate shaft turbocharger embodying the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, an internal combustion engine  10  is shown having an exhaust gas recirculation (EGR) system  12 , and a turbocharger  14  in which the present invention for a separate shaft turbocharger may be used advantageously. 
     Internal combustion engine  10  includes a plurality of combustion cylinders  16 , and as shown in FIG. 1, includes six combustion cylinders  16 . Each combustion cylinder  16  is coupled with an intake manifold  18  and with an exhaust manifold  20 . While a single intake manifold  18  is shown, it should be understood that more than one intake manifold may be used, with each intake manifold  18  coupled to a plurality of combustion cylinders  16 , for providing an air mixture to each combustion cylinder  16 . Further, while a single exhaust manifold  20  is shown, it should be understood that more than one exhaust manifold could be provided, with each exhaust manifold coupled to a different plurality of combustion cylinders  16 . A fuel, such as diesel fuel, is introduced into each combustion cylinder and combusted therein, in a known manner. 
     Turbocharger  14  includes a turbine  22 , a first compressor  24  and a second compressor  26 . Turbine  22  includes a turbine casing  28  defining a turbine inlet  30  and a turbine outlet  32 . Turbine inlet  30  is connected in flow communication with exhaust manifold  20  via a fluid conduit  34 . Turbine outlet  32  is connected to a further exhaust system (not shown) of engine  10 , which may include one or more mufflers, with subsequent discharge to an ambient environment. 
     Turbine  22  further includes a turbine shaft  36  rotatably disposed in turbine casing  28 . A turbine wheel  38  is carried by turbine shaft  36 , near one end turbine shaft  36 . A drive gear  40  is also carried by turbine shaft  36 , near the opposite end of turbine shaft  36  from turbine wheel  38 . Turbine inlet  30  and turbine outlet  32  are each associated with turbine wheel  38 , in known manner, such that a flow of fluid from exhaust manifold  20  enters turbine inlet  30  and flows past turbine wheel  38  to turbine outlet  32 , causing rotation of turbine wheel. 
     First compressor  24  includes a first compressor casing  50  defining a first compressor inlet  52  and a first compressor outlet  54 . First compressor inlet  52  receives combustion gas from a source such as ambient air, and first compressor outlet  54  supplies compressed combustion gas to engine  10 , as will be described hereinafter. 
     First compressor  24  further includes a first compressor shaft  56  rotatably disposed in first compressor casing  50 . A first compressor wheel  58  is carried by first compressor shaft  56 , near one end of first compressor shaft  56 . A first driven gear  60  is also carried by first compressor shaft  56 , near the opposite end of first compressor shaft  56  from first compressor wheel  58 . First driven gear  60  is drivingly coupled with drive gear  40  on turbine shaft  36 , such that rotation of drive gear  40  by turbine shaft  36  causes rotation of first compressor shaft  56  and first compressor wheel  58 . First compressor inlet  52  and first compressor outlet  54  are each associated with first compressor wheel  58 , in known manner, such that fluid, such as ambient air, entering first compressor  24  through first compressor inlet  52  is compressed by first compressor wheel  58  in first compressor casing  50 , while flowing to first compressor outlet  54 . 
     Second compressor  26  includes a second compressor casing  70  defining a second compressor inlet  72  and a second compressor outlet  74 . Second compressor  24  further includes a second compressor shaft  76  rotatably disposed in second compressor casing  70 . A second compressor wheel  78  is carried by second compressor shaft  76 , near one end of second compressor shaft  76 . A second driven gear  80  is also carried by second compressor shaft  76 , near an opposite end of second compressor shaft  76  from second compressor wheel  78 . Second driven gear  80  is drivingly coupled with drive gear  40  on turbine shaft  36 , such that rotation of drive gear  40  by turbine shaft  36  causes rotation of second compressor shaft  76  and second compressor wheel  78 . Second compressor inlet  72  and second compressor outlet  74  are each associated with second compressor wheel  78 , in known manner, such that fluid entering second compressor  24  through second compressor inlet  72  is compressed by second compressor wheel  78  in second compressor casing  70 , while flowing to second compressor outlet  74 . 
     Second compressor inlet  72  may receive combustion gas from a source such as ambient air, if first compressor  24  and second compressor  26  are operated in parallel, to each separately compress separate volumes of fluid. Alternatively, first compressor  24  and second compressor  26  can be operated in series, to sequentially compress fluid such as combustion gas. As illustrated in FIG. 1, an interstage duct  82  is provided, establishing flow communication between first compressor outlet  54  and second compressor inlet  72 . For more efficient operation of second compressor  26 , an optional interstage cooler  84  is provided in interstage duct  82 , to cool the air compressed in first compressor  24  before second stage compression occurs in second compressor  26 . 
     Second compressor outlet  74  is connected to a mixer  86  via a fluid conduit  88 . An optional aftercooler  90  may be provided in conduit  88 , to reduce the temperature of the compressed combustion air supplied from turbocharger  14 . 
     EGR system  12  includes an EGR duct  92  receiving exhaust gas from exhaust manifold  20 , to direct the exhaust gas to intake manifold  18 . EGR duct  92  includes a valve  94  for controlling the flow of exhaust gas through duct  92 . An EGR cooler  96  may be provided in duct  92 , to lower the temperature of exhaust gas provided to intake manifold  18 . 
     EGR duct  92  also is fluidly coupled to mixer  86 . Mixer  86  controls the mixture of compressed combustion gas from turbocharger  14  with exhaust gas recirculated from EGR system  12 , providing a mixture thereof to intake manifold  18  through a fluid conduit  98 . 
     Industrial Applicability 
     During use of engine  10 , a fuel, such as diesel fuel, is injected into combustion cylinders  16  and combusted when a piston (not shown) disposed within each combustion cylinder  16  is at or near a top dead center position. Exhaust gas is transported from each combustion cylinder  16  to exhaust manifold  20 . Some of the exhaust gas within exhaust manifold  20  is transported to conduit  34  and inlet  30 , for rotatably driving turbine wheel  38 . The spent exhaust gas is discharged from turbine  22  to the ambient environment through turbine outlet  32 . 
     Rotation of turbine wheel  38  by the flow of exhaust gases through turbine  22  rotates turbine shaft  36  and drive gear  40  carried by turbine shaft  36 . Drive gear  40  is drivingly coupled with each first driven gear  60  and second driven gear  80 , so that rotation of drive gear  40  rotates each first driven gear  60  and second driven gear  80 . First driven gear  60  and second driven gear  80 , being carried on first compressor shaft  56  and second compressor shaft  76 , respectively, rotate the respective shaft by which they are carried. First compressor wheel  58  and second compressor wheel  78 , similarly carried by first compressor shaft  56  and second compressor shaft  76 , respectively, are rotatably driven together with first driven gear  60  and second driven gear  80 , respectively. In this manner, turbine  22  drives each first compressor  24  and second compressor  26 . 
     First compressor  24 , driven by turbine  22  via turbine shaft  36  and first compressor shaft  56 , draws combustion air into first compressor inlet  52 . The combustion air is compressed within first compressor  24  and is discharged from compressor  24  through first compressor outlet  54 . The compressed combustion air is conducted to second compressor inlet  72  via interstage duct  82 , passing first through interstage cooler  84 . Second compressor  26 , driven by turbine  22  via turbine shaft  36  and second compressor shaft  76 , further compresses the combustion air, discharging the now high pressure combustion air through second compressor outlet  74 . The highly compressed combustion air flows through conduit  88  to mixer  86 , first being cooled in aftercooler  90 . 
     Exhaust gas is recirculated from exhaust manifold  20  to intake manifold  18  via EGR duct  92 , mixer  86  and fluid conduit  98 . Exhaust gas flow through EGR duct  92  is controlled by valve  94 , with the exhaust gases being cooled by EGR cooler  96 . 
     Mixer  86  combines fluid flow supplied by EGR system  12  through EGR duct  92  with compressed combustion air supplied by turbocharger  14  through fluid conduit  88 . The mixture of the combined fluids is provided to intake manifold  18  through fluid conduit  98 , for combustion in cylinders  16 . 
     As shown in FIG. 1, first compressor shaft  56  and second compressor shaft  76  extend in opposite directions away from first driven gear  60  and second driven gear  80  carried, respectively, thereon. First compressor shaft  56  and turbine shaft  36  extend in the same direction away from first driven gear  60  and drive gear  40 , respectively. Through the use of parallel, separate shafts for each turbine  22 , first compressor  24  and second compressor  26 , and with the proper selection of drive gear  40 , first driven gear  60  and second driven gear  80 , a variety of compact arrangements for turbocharger  14  are possible. 
     Each turbine shaft  36 , first compressor shaft  56  and second compressor shaft  76  can be relatively short, and carries only a single wheel and gear thereon. Problems associated with a single shaft carrying several wheels thereon are reduced significantly. Further, with each first compressor wheel  58  and second compressor wheel  78  carried on and driven by separate shafts, the response of each to speed change is enhanced, and operating each at optimum speed is facilitated. 
     The separate shaft turbocharger of the present invention provides the capability of independent compressor wheel speeds. Through the selection of drive gear  40 , first driven gear  60  and second driven gear  80 , each of first compressor wheel  58  and second compressor wheel  78  can be caused to rotate within an optimal range of speeds for the design of the compressor wheel. It is no longer required that each first compressor wheel  58  and second compressor wheel  78  operate at the same speed, as is required when both are carried on a common shaft with the turbine wheel. Through the selection of gear ratios, each can be driven within an optimal range, and compressor wheel designs having efficiencies in different operating speed ranges now can be used in the same turbocharger. 
     While the present invention has been described for a turbocharger having two compressors, separate parallel shafts can be used also for a turbocharger having only one compressor associated with the turbine, or for a turbocharger having more than two compressors associated with the turbine. Further, while direct drives using gears drivingly engaged are preferred, it should be understood that other types of drive couplings, including belts and/or chains, also can be used. Those skilled in the art will readily understand the manner in which such alternative driving engagements can be used between turbine shaft  36  and first and second compressor shafts  56  and  76 . 
     The turbocharger of the present invention provides a compact arrangement for a multistage turbocharger, with increased turbocharger performance through the optimization of speeds. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.