Abstract:
A turbocharger for an internal combustion engine, particularly suitable for use in a work machine, is provided with a turbine having a low pressure region of minimum static pressure. A compressor has a high pressure region of maximum dynamic pressure. A conduit fluidly interconnects the high pressure region with the low pressure region. A valve is associated with the conduit for opening and closing the conduit. Compressed air or a fuel/air mixture may be bled from the compressor to the turbine over a wider arrange of operating conditions, even at low load operating conditions.

Description:
TECHNICAL FIELD 
     The present invention relates to a turbocharger for use in an internal combustion engine, and, more particularly, to a turbocharger including a multi-stage compressor. 
     BACKGROUND 
     An internal combustion engine may include one or more turbochargers for compressing a fluid which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor which is driven by the turbine. The compressor receives the fluid to be compressed and supplies the fluid to the combustion chambers. The fluid which is compressed by the compressor may be in the form of combustion air or a fuel/air mixture. 
     The operating behavior of a compressor within a turbocharger may be graphically illustrated by a “compressor map” associated with the turbocharger in which the pressure ratio (compression outlet pressure divided by the inlet pressure) is plotted on the vertical axes and the flow is plotted on the horizontal axes. In general, the operating behavior of a compressor wheel is limited on the left side of the compressor map by a “surge line” and on the right side of the compressor map by a “choke line”. The surge line basically represents “stalling” of the air flow in the compressor. With too small a volume flow and too high a pressure ratio, the flow will separate from the suction side of the blades on the compressor wheel, with the result that the discharge process is interrupted. The air flow through the compressor is reversed until a stable pressure ratio by positive volumetric flow rate is established, the pressure builds up again and the cycle repeats. This flow instability continues at a substantially fixed frequency and the resulting behavior is known as “surging”. The choke line represents the maximum centrifugal compressor volumetric flow rate, which is limited for instance by the cross-section at the compressor inlet. When the flow rate at the compressor inlet or other location reaches sonic velocity, no further flow rate increase is possible and choking results. Both surge and choking of a compressor should be avoided. 
     U.S. Pat. No. 3,044,683 (Woollenweber) discloses a fluid passage extending from the high pressure side of the compressor to the inlet side of a turbine. A spring loaded valve is disposed within the fluid passage and opens upon a high pressure condition within the compressor. The spring loaded valve thus merely acts to bypass some of the high pressure gas on an over pressure condition to the turbine of the turbocharger. 
     U.S. Pat. No. 5,724,813 (Fenelon et al.) assigned to the assignee of the present invention, discloses a turbocharger having a single stage compressor. A portion of the compressed gas from the single stage compressor may be recirculated to the outlet side of the turbine using controllably actuated valves. The control scheme utilizes only a single stage compressor. 
     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 having a low pressure region of minimum static pressure. A compressor has a high pressure region of maximum dynamic pressure. A conduit fluidly interconnects the high pressure region with the low pressure region. A valve is associated with the conduit for opening and closing the conduit. 
     In 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 coupled with a compressor; driving the turbine with exhaust gas from an exhaust manifold of the internal combustion engine, rotatably driving the compressor with the turbine; transporting combustion air through a high pressure region of maximum dynamic pressure within the compressor; transporting exhaust gas through a low pressure region of minimum static pressure within the turbine; fluidly interconnecting a conduit between the high pressure region and the low pressure region; and operating a valve associated with the conduit to selectively open and close the conduit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of an embodiment of a turbocharger of the present invention for use with an internal combustion engine. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawing, there is shown an embodiment of a turbocharger  10  for use with an internal combustion engine  12 . Internal combustion engine  12  generally includes a plurality of combustion cylinders  14 , only three of which are shown for simplicity sake in the drawing. The particular number of combustion cylinders  14  within internal combustion engine  12  may vary, depending upon the particular application. Internal combustion engine  12  also includes an exhaust manifold  16  and an inlet manifold  18 . Inlet manifold  18  provides air or a fuel/air mixture to combustion cylinders  14 . Exhaust manifold  16  receives exhaust gas from combustion cylinders  14 . Exhaust manifold  16  and inlet manifold  18  are shown with a single part construction for simplicity sake in the drawing. However, it is to be understood that exhaust manifold  16  and/or inlet manifold  18  may be constructed as multiple-part manifolds, depending upon the particular application. 
     Turbocharger  10  includes a turbine  20  and a two stage compressor  22 . Turbine  20  is fluidly coupled with exhaust manifold  16  as indicated schematically by line  24 . Turbine  20  includes a turbine wheel  26  is rotatable about a longitudinal axis  28  of shaft  30 . More particularly, turbine  20  includes a volute section  32  which receives exhaust gas from exhaust manifold  16  via line  24 . Volute section  32  may be in the form of a single volute as shown, or may be in the form of a split volute or other configuration, depending upon the particular application. Exhaust gas enters volute section  32  and impinges against a plurality of vanes  34  of turbine wheel  26 . Turbine wheel  26  is thus rotatably driven by exhaust gas from exhaust manifold  16 . The spent exhaust gas flows to a muffler system (not shown) downstream from turbocharger  10 , as indicated by directional arrow  36 . 
     Two stage compressor  22  includes a first compressor  38  and a second compressor  40 . First compressor  38  and second compressor  40  each include a compressor wheel  42  and  44 , respectively. Two stage compressor  22  receives combustion air as indicated by arrow  46 . First compressor wheel  42  and second compressor wheel  44  compress the combustion air in a series manner to provide a desired total compression ratio. Second compressor wheel  44  discharges the compressed combustion air into a volute section  48  which is fluidly coupled with inlet manifold  18  as indicated schematically by line  50 . Two stage compressor  22  thus provides compressed combustion air to inlet manifold  18 . 
     According to an aspect of the present invention, a conduit  52  fluidly interconnects volute section  48  of two stage compressor  22  with volute section  32  of turbine  10 . A valve  54  is positioned within conduit  52 , and is controllably actuated to open and close conduit  52 . Conduit  52  fluidly couples with and extends in a radially outward direction from a radially outer portion of volute section  48 . Moreover, conduit  52  fluidly couples with a low static pressure region of volute section  32  of turbine  20 . Conduit  52  is disposed at an acute angle relative to a high velocity portion of volute section  32 . 
     A controller  56  is electrically coupled with valve  54  via line  58 . Controller  56  is also electrically coupled with one or more sensors  60  via an associated line  62  and receives an input signal therefrom. Sensor  60  senses an operating parameter associated with operation of turbocharger  10  and/or internal combustion engine  12  indicative of a surge condition within turbocharger  10 . 
     INDUSTRIAL APPLICABILITY 
     During use, internal combustion engine  12  operates in known manner using, e.g., the diesel principle of operation. Exhaust gas is transported from exhaust manifold  16  to volute section  32  of turbine  20  via line  24 . The exhaust gas impinges upon vanes  34  of turbine wheel  26  and rotatably drives turbine wheel  26 . Spent exhaust gas is discharged to a muffler system, as indicated by arrow  36 . Rotation of turbine wheel  26  in turn causes rotation of shaft  30  which drives first compressor wheel  42  and second compressor wheel  44 . Combustion air or a fuel/air mixture is drawn into first compressor  38 , as indicated by arrow  46 . The combustion air or fuel/air mixture is compressed in a series manner within two stage compressor  22  using first compressor wheel  42  and second compressor wheel  44 . The compressed combustion air or fuel/air mixture is discharged from volute section  48  of second compressor  40  to inlet manifold  18  via line  50 . 
     Sensor  60  senses one or more operating parameters associated with internal combustion engine  12  and/or turbocharger  10  indicative of a surge condition within turbocharger  10  and provides an output signal to controller  56  via line  62 . For example, one or more sensors  60  may be provided to sense engine speed, fuel consumption rate, ambient temperature, air temperature at the inlet to first compressor  38 , air flow through two stage compressor  22 , temperature of compressed air at the outlet of first compressor  38 , rotational speed of shaft  30 , engine inlet manifold temperature, engine inlet manifold pressure, ratio of air-to-fuel in inlet manifold  18 , and/or oxygen in exhaust manifold  16 . Of course, the exact placement location of sensor  60  within internal combustion engine  12  and/or turbocharger  10  will vary, dependent upon the specific operating parameter being sensed. For example, sensor  60  may be positioned adjacent to a crankshaft (not shown) of internal combustion engine  12  for sensing the engine speed; or may be positioned within the inlet to first compressor  38  or the outlet from second compressor  40  for sensing air flow through two stage compressor  22 . If configured to sense air flow, sensor  60  may be configured as a hot wire annemometer. Controller  56  determines the onset or existence of a surge condition within turbocharger  10  and controllably actuates valve  54  by outputting a signal over line  58 . When valve  54  is in an open state, compressed combustion air or a compressed fuel/air mixture within volute section  48  is bled through conduit  52  to volute section  32  of turbine  20 . Rather than bleeding to the ambient environment, the compressed combustion air or fuel/air mixture is transported to volute section  32  of turbine  20  to utilize some of the energy within the compressed air or fuel/air mixture. 
     Dependent upon the particular operating conditions of internal combustion engine  12 , it is not possible with conventional turbochargers to bleed air from a compressor to a turbine. For example, under a low load condition the rotational speed of shaft  30  is not high enough to sufficiently compress the combustion air or fuel/air mixture drawn into two stage compressor  22 . Thus, the pressure of exhaust gas within volute section  32  of turbine  20  may be higher than the pressure of the compressed air or fuel/air mixture within volute section  48 . If valve  54  is opened by controller  56  under such operating circumstances, flow actually is reversed and exhaust gas flows from volute section  32  of turbine  20  to volute section  48  of two stage compressor  22 . 
     To ensure that a positive pressure differential exists between two stage compressor  22  and turbine  20 , conduit  52  is coupled with two stage compressor  22  at a location of maximum total pressure, and is coupled with turbine  20  at a location of minimum static pressure. According to principals of fluid dynamics, the total pressure at any location within two stage compressor  22  or turbine  20  is the sum of both the dynamic pressure and the static pressure. The dynamic pressure is a function of the square of the flow velocity at any selected location. Thus, the faster the flow velocity the greater the dynamic pressure and the smaller the static pressure. For example, flow transported through a venturi section increases in velocity resulting in an increased dynamic pressure and decreased static pressure. Conduit  52  is coupled with two stage compressor  22  and turbine  20  to take advantage of these differing pressure components making up the total pressure within either two stage compressor  22  or turbine  20 . Conduit  52  is coupled with two stage compressor  22  at a location of maximum total pressure and is coupled with turbine  20  at a location of minimum static pressure so that compressed air or a fuel/air mixture can be bled from two stage compressor  22  to turbine  20  over the widest range of operating conditions. 
     In the embodiment shown, conduit  52  is coupled with volute section  48  of second compressor  40  at the radially outer portion of volute section  48 . At the radially outer portion of volute section  48  the flow velocity is the lowest resulting in the maximum static pressure. By connecting conduit  52  with an end receiving the high static pressure flow, the compressed air or fuel/air mixture is blown into conduit  52  which allows bleeding to occur over a wider range of operating conditions. Conduit  52  is also coupled with turbine  20  at the radially outer portion of volute section  32 . The dynamic pressure is at a maximum which results in a minimum static pressure. However, conduit  52  opens generally perpendicular to rather than in the flow of the exhaust gas. This means that conduit  52  is exposed principally to the low static pressure in volute section  32  rather than the high dynamic pressure. Compressed air or a fuel/air mixture may thus be bled from two stage compressor  22  to turbine  20  over a broader range of operating conditions. As an alternative, it is also possible to connect conduit  52  with turbine  20  at a venturi section where the flow is at an increased velocity and decreased static pressure. For example, volute section  32  may be configured with a flow constriction causing a local increase in velocity and decrease in static pressure. 
     The present invention allows more effective bleeding of compressed combustion air or a fuel/air mixture from a compressor to a turbine over a wider range of operating conditions. The bleeding may occur over normal operating conditions, or under low load conditions. The on-set or existence of a surge condition is sensed and the bleeding is automatically effected to prevent or eliminate surging within the turbocharger. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.