Abstract:
The method for turbocharging an engine of a locomotive in which the engine is operable at a plurality of discrete operating power levels includes controlling at least one of energy to a motor-assisted turbocharger at a plurality of discrete energy levels and air pressure from the motor-assisted turbocharger to the engine at a plurality of discrete air pressure levels above ambient air pressure based on at least some of the plurality of discrete operating power levels (e.g., low power levels) of the engine. Desirably, the method also includes controlling generation of electrical energy from the motor-assisted turbocharger at some of the plurality of discrete operating power levels (e.g., high power levels) of the engine. Apparatus for turbocharging a diesel engine of a locomotive incorporating the above methods are also disclosed.

Description:
BACKGROUND OF INVENTION 
     This invention relates generally to turbochargers, and more specifically, to motor-assisted turbochargers for locomotives. 
     Conventionally, turbochargers are operably connected to an internal combustion engine in which exhaust gas from the engine is utilized to increase the pressure of air above ambient to the engine. Typically, the turbocharger includes a shaft, a driving turbine or expander attached at one end of shaft, and a compressor attached to the other end of the shaft. The expander is attached to the engine to receive exhaust gases from the engine and the compressor is attached to an air intake manifold of the engine. 
     During operation, the expander receives exhaust gas which causes the shaft to rotate, which in turn, causes the compressor to rotate and supply air to the air intake manifold of the engine at an increased pressure, i.e., at a pressure greater than ambient air pressure. 
     Some turbocharger systems have incorporated a separate electric motor/alternator connected to the shaft to increase the rotational speed of the shaft in a continuous manner relative to and in response to the speed of the engine, to increase the rotational speed of the shaft to overcome “turbo lag” (i.e., the short period of time after increased power demand is first sensed until the rotary compressor driven by the exhaust gas turbine reaches its full power capacity), and also to extract electrical energy from the exhaust gas. 
     In normal operation, the propulsion system of diesel electric locomotives is typically controlled to establish a balanced steady state condition wherein a diesel engine driven alternator produces, for each discrete position of a throttle handle, a substantially constant amount of electrical power for the traction motors. The throttle typically has eight positions or notches with notch  1  being a low power level and notch  8  being maximum power level. 
     There is a need for a motor-assisted turbocharger for tailoring the turbocharging of a diesel engine of a diesel electric locomotive to increase engine performance and to provide auxiliary electrical power for auxiliary devices over a range of discrete power levels. 
     SUMMARY OF INVENTION 
     The above-mentioned need is met by the present invention which provides, in a first aspect, a method for turbocharging an engine of a locomotive in which the engine is operable at a plurality of discrete operating power levels. The method includes controlling at least one of electrical energy to a motor-assisted turbocharger at a plurality of discrete energy levels and air pressure from the motor-assisted turbocharger to the engine at a plurality of discrete air pressure levels above ambient air pressure based on at least some of the plurality of discrete operating power levels of the engine. 
     In a second aspect, a method for operating an engine of a locomotive in which the engine is operable at a plurality of discrete operating power levels includes controlling at least one of electrical energy to a motor-assisted turbocharger at a plurality of discrete energy levels and air pressure from the motor-assisted turbocharger to the engine at a plurality of discrete air pressure levels above ambient air pressure based on at least some of the plurality of discrete operating power levels of the engine, and controlling generation of electrical energy from the motor-assisted turbocharger at some of the plurality of discrete operating power levels of the engine. 
     In a third aspect, an apparatus for turbocharging an engine of a locomotive having a plurality of discrete operating power levels includes a motor-assisted turbocharger for increasing air pressure above ambient air pressure to the engine, and a controller for controlling at least one of electrical energy to a motor-assisted turbocharger at a plurality of discrete energy levels and air pressure from the motor-assisted turbocharger to the engine at a plurality of discrete air pressure levels above ambient air pressure based on at least some of the plurality of discrete operating power levels of the engine. 
     In a fourth aspect, an apparatus for turbocharging an engine of a locomotive having at a plurality of discrete operating power levels includes a motor-assisted turbocharger for increasing air pressure above ambient air pressure to the engine, and a controller for controlling at least one of electrical energy to a motor-assisted turbocharger at a plurality of discrete energy levels and air pressure from the motor-assisted turbocharger to the engine at a plurality of discrete air pressure levels above ambient air pressure based on at least some of the plurality of discrete operating power levels of the engine, and the controller being operable to control generation of electrical energy from the motor-assisted turbocharger at some of the plurality of discrete operating power levels of the engine. 
     In another aspect, a portion of a power plant for a locomotive includes a diesel engine and the apparatus as described above for turbocharging the diesel engine. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic illustration of one embodiment of a power plant system of a diesel electric locomotive incorporating a motor-assisted turbocharger system according to the present invention; 
     FIG. 2 is an enlarged cross-sectional view of the motor-assisted turbocharger system of FIG. 1; 
     FIG. 3 is a graph of the increased air pressure provided by the turbocharger system of FIG. 1; and 
     FIG. 4 is a graph of the electrical energy supplied to the motor-assisted turbocharger relative to the notch position of the locomotive power system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 diagrammatically illustrates a power plant system  10  of a diesel electric locomotive according to one embodiment of the present invention. Power plant system  10  generally includes, for example, a diesel engine  12  having a drive shaft  14  coupled to a generator or alternator  16 . Alternator  16  provides electric power to one or more traction motors  18  for propelling the locomotive. 
     A throttle  20  operably connects to a controller  30  such as the locomotive&#39;s elaborate control system for controlling the operation of diesel engine  12 . Throttle  20  typically includes eight positions or notches plus idle and shutdown. Notch  1  corresponds to a minimum desired engine speed (power), while notch  8  corresponds to maximum speed and full power. In operation, the propulsion system of the diesel electric locomotive is controlled, e.g., by controller  30 , to establish a balanced steady state condition wherein the engine driven alternator produces, for each discrete position of a throttle handle, a substantially constant amount of electrical power for the traction motors. 
     In this embodiment, power plant system  10  also includes a motor-assisted turbocharger system  40  for increasing the air pressure above ambient air pressure to an intake manifold of diesel engine  12 . Motor-assisted turbocharger system  40  includes a single rotatable shaft  42  which is attached at one end to a driving turbine or expander  44  and at the other end to a compressor turbine or compressor  46 . Expander  44  is operably connected to an exhaust outlet of diesel engine  12  and compressor  46  is operably connected an air intake of diesel engine  12 . A rotary electric machine such as a motor/alternator  50  is attached to shaft  42  adjacent to an inlet side  48  of compressor  46 . As best shown in FIG. 2, positioning motor/alternator  50  adjacent to the relatively cool inlet side  45  of compressor  46  reduces the need to thermally insulate motor/alternator  50  from the high temperature expander compared to positioning the motor/alternator between the expander and compressor or to the end of the shaft extending from the expander. With reference again to FIG. 1, motor/alternator  50  is also operably connected to alternator  16  for suppling electrical energy to energize motor/alternator  50  and to a battery  60  for storing electrical energy generated by motor/alternator  50  as described below. 
     Motor-assisted turbocharger  40  benefits from both low and high engine power operation. For example, the locomotive in the low power region of operation, e.g., notches  1 ,  2  and  3 , controller  30  controls the supply of electrical energy from alternator  16  to motor/alternator  50  to rotate or spin compressor  48  faster than compressor  48  would normally be spun due to the low volume of exhaust gas from diesel engine  12  to expander  44  to provide a generally constant increased level of air pressure above ambient air pressure to diesel engine  12 . For each notch position in the lower power regions of operation, motor/alternator  50  is desirably operated in discrete constant modes, e.g., resulting in a constant speed and/or constant increased air pressure level above ambient air pressure for each of the notch levels. Increasing the speed of the rotation of shaft  42  of turbocharger  40  results in an increase in the intake air pressure and mass flow rate to diesel engine  12  thereby reducing emissions such as smoke, unburned hydrocarbons, and carbon monoxide, and improving fuel economy, and increasing engine power output. 
     FIG. 3 graphically illustrates the plurality of discrete generally constant discrete increased air pressure levels above ambient air pressure, e.g., as detected by pressure sensor  49  operably connected to controller  30 , for the notch positions of the throttle of the locomotive. FIG. 4 graphically illustrates the relative constant discrete energy levels supplied to motor/alternator  50  for notch positions, idle,  1 ,  2 , and  3 . As illustrated in FIG. 4, the amount of electrical energy required to power motor/alternator  50  decreased when going from idle to notch  4 . 
     When increasing the operating power level of the locomotive, e.g., moving throttle  20  from, for example, from idle to notch  1 , from notch  1  to notch  2 , or from notch  1  to notch  3 , motor/alternator  50  can be controllably energized, e.g., by controller  30 , until diesel engine  12  reaches equilibrium at the selected notch position. When decreasing the operating power level of the locomotive, e.g., moving throttle  20  from, for example, notch  4  to notch  3 , from notch  3  to notch  2 , or from notch  3  to notch  1 , motor/alternator  50  can be controlled, e.g., by controller  30 , to generate power and act as a brake to reduce the likelihood of undesirable surge of the turbocharger compressor, i.e., turbo overspeed. 
     In the high power region of operation of the locomotive, e.g., notches  5 ,  6 ,  7 , and  8 , the exhaust gas from diesel engine  12  to expander  44  is more than sufficient to power compressor  46  to supply pressurized air to diesel engine  12 . In the high power region of operation, motor-assisted turbocharger system  40  is used to extract energy from the exhaust gas, generate electrical energy and desirably maintain discrete increased levels of air pressure above atmospheric air to the engine (see FIG.  3 ). For example, controller  30  operably controls the operation of motor/alternator  50  to generate electrical power which is supplied to battery  60  and to auxiliary electrical devices  70  of the locomotive, e.g., for use in lighting. The generated electrical energy may also be supplied to the main propulsion system of the locomotive. In addition, in this region of operation the motor/alternator is used to control the speed of the turbocharger and act as a brake as noted above, and to avoid undesirable critical speed ranges, e.g., speed ranges where vibrations get too high, thereby improving fatigue life of various components of the motor-assisted turbocharger system. 
     In both the low and high power regions of operation of the locomotive, the motor-assisted turbocharger desirably provides an increase in the performance of the diesel engine and a reduction in emissions from the diesel engine. From the present description, it will be appreciated by those skilled in the art that where the combination of expander  44  and compressor  46  alone is insufficient to provide the necessary pressurized air for proper operation of diesel engine  12  at substantially maximum power levels, e.g., at low ambient air pressures such as at high altitudes, controller  30  may control the energizing of motor/alternator  50  to increase the speed of shaft  42  thereby increasing the pressure of air supplied to the air intake of diesel engine  12 . 
     Expander  44  and compressor  46  are desirably compactly configured and designed to supply sufficient pressurized air to the diesel engine at the mid operating power levels without the need for energizing the motor/alternator of the motor-assisted turbocharger. In addition, the diesel engine is desirably compactly designed and requires an increased air pressure above ambient air pressure at the low power levels for optimum performance. While a waste gate is not necessary to avoid overcharging the engine, desirably a safety gate is provided to prevent overcharging of the engine in the event the breaking effect of the motor/alternator is not sufficient to prevent overcharging of the engine. 
     From the present description, it will also be appreciated by those skilled in the art that while motor/alternator  50  is illustrated as being attached to inlet side  48  of the compressor  46 , it will be appreciated that a motor/alternator may be attached or connected between expander and compressor, or to an end of a rotatable shaft extending from the expander. 
     It will also be appreciated by those skilled in the art that the motor may be a hydraulically operated motor, pneumatically operated motor, or other suitable type of motor for assisting in the rotation or increasing the rotational speed of the exhaust-driven turbocharger shaft. In addition, the rotor of the motor need not be integral with the turbocharger shaft but may instead be connected by mechanical devices such as pulleys and belts, a chain, or a gear set. 
     Thus, while various embodiments of the present invention have been illustrated and described, it will be appreciated to those skilled in the art that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.