Abstract:
An internal combustion engine incorporating a turbo-generator and one or more variably activated exhaust valves. The exhaust valves are adapted to variably release exhaust gases from a combustion cylinder during a combustion cycle to an exhaust system. The turbo-generator is adapted to receive exhaust gases from the exhaust system and rotationally harness energy therefrom to produce electrical power. A controller is adapted to command the exhaust valve to variably open in response to a desired output for the turbo-generator.

Description:
[0001]    This invention was made with Government support under contract DE-FC26-05NT42422 awarded by the Department of Energy. The United States Government has certain rights in this invention 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention related to control of an internal combustion engine having a turbo-generator, and more specifically, to the allocation of combustion energy between the engine and turbo-generator. 
       BACKGROUND OF THE INVENTION 
       [0003]    Internal combustion (IC) engines are widely used to provide mechanical power in mobile and stationary applications. It is common for engines to use turbochargers to harness residual energy from the engine exhaust gases with a turbine driving a compressor to boost airflow to the engine. It is also known to use a power-turbine to harness additional mechanical power, or to drive an electrical generator. The later configuration is known as a turbo-generator. 
         [0004]    Traditionally, turbochargers and turbo-generators were employed as a way of extracting waste energy that was otherwise released to the atmosphere, thereby improving the overall efficiency of the power unit. However, the control strategies employed with these power units focus primarily on the output of the internal combustion engine, with output of the turbo systems subject to the default amount of energy available in the exhaust gases. However, this strategy leaves turbo-generator systems unable to provide consistent electrical power to meet demand. In some cases it is more energy efficient to expand the cylinder gases from late in the expansion stroke with the turbine since it has a larger expansion ratio. 
       SUMMARY OF THE INVENTION 
       [0005]    Described herein is a system for controlling the output of an IC engine incorporating a turbo-generator. The system employs variable valve actuation (VVA) technology to variably adjust the exhaust valve timing to begin opening at points within the expansion stroke of the IC engine combustion cycle. The early release of exhaust gases allocates additional energy to the turbo-generator in order to meet changing electrical loads. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic illustration showing an embodiment of an internal combustion engine of the present invention having a turbo-generator developing electrical power; and 
           [0007]      FIG. 2  is a graphical illustration showing a shift in time for the exhaust valve opening using the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]    Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a portion of a power unit  6  including a frame  8  which carries an IC engine  10 . Power unit  6  can be in the form of a work vehicle such as an agricultural or construction tractor, or an electrical generator set. Thus, it should be clear that the desired output from power unit  6  can be either mechanical or electrical power. 
         [0009]    IC engine  10  includes a turbo-generator  12  developing electrical power, and an electronic controller unit (ECU)  14  for monitoring and controlling the engine  10 . The engine  10  includes a cylinder block  20 , a cylinder head  22 , an intake system  24 , an exhaust system  26 , and a turbocharger  28 . The turbo-generator  12  includes a power-turbine  30  coupled to an electrical generator  32 . The engine  10  develops mechanical power under combustion cycles generally known in the art, while the turbo-generator  12  and turbocharger  28  harness residual energy from the engine exhaust system  26  under turbine cycles generally known in the art. 
         [0010]    The cylinder block  20  includes one or more combustion cylinders  40  and a crankshaft  42  coupled to a flywheel  44 . A piston  46  slides within each cylinder  40 , to transmit energy from the combustion cycle to the crankshaft  42  via a connecting rod  48 . The cylinder head  22  includes intake ports  50  that channel intake air from the intake system  24  into each cylinder  40  via one or more intake valves  52 . The cylinder head  22  also includes exhaust ports  54  that channel exhaust gases from each cylinder  40  into the exhaust system  26  via one or more exhaust valves  56 . The turbocharger  28  includes a power-turbine  60  that is placed downstream of the exhaust system  26 , coupled via a rotating drive shaft with a compressor  62  that is placed upstream of the intake system  28 . The power turbine  60  harnesses waste energy from the engine exhaust system  26  in order to boost airflow in the intake system  28 . 
         [0011]    The ECU  14  may take the form of any combination of electronic hardware and/or software typical in the art for monitoring and controlling engine  10  and vehicles systems. In this embodiment, the ECU  14  monitors a crankshaft sensor  70  indicating crank-angle or rotational speed of the crankshaft  42 , and a turbo-generator output sensor  72  indicating rotational speed or electrical current of the turbo-generator  12 . The ECU  14  normally controls the timing and quantity of fuel delivered to each combustion cylinder  40 . In this embodiment, the ECU  14  also controls the timing and duration of the intake valve  52  and the exhaust valve  56  with VVA technology that has recently become known in the art. 
         [0012]    Referring now to  FIG. 2 , during normal operation of the engine  10 , fuel and intake air is compressed and ignited within the cylinder  40  when the piston  46  is at or near the top of the cylinder  40 . The combustion releases energy, increasing temperature and pressure within the cylinder  40 . This in turn forces the piston  46  downward, transferring mechanical power to the crankshaft  42  in what is commonly called the expansion or power stroke. This process continues until the piston  46  reaches the bottom of the cylinder  40 , at which point the ECU  14  senses the crank-angle in the combustion cycle and commands the exhaust valve  56  to open at the beginning of the exhaust stroke (line A in  FIG. 2 ). The piston  46  then begins to travel upward in the cylinder  40  due to the momentum of the flywheel  44 , forcing the exhaust gases from the cylinder  40  into the exhaust system  26  in what is commonly called the exhaust stoke. This process continues until the piston  46  reaches the top of the cylinder  40 , at which point the ECU  14  senses the crank-angle in the combustion cycle and commands the exhaust valve  56  to close (at the right of line A). The four stroke combustion cycle then repeats in known manner. 
         [0013]    Once in the exhaust system  26 , the residual energy of the exhaust gas is available for the turbocharger  28  and turbo-generator  12  to harness for additional work. According to an aspect of the present invention, to increase this residual energy, and thereby provide for greater electrical output from the turbo-generator  12 , the ECU  14  is adapted to command the exhaust valve  56  to begin opening earlier than normal, at some point during and before the end of the expansion stroke (as shown by the dashed line portion of line B in  FIG. 2 ). In one embodiment, a desired rotational speed for the turbo-generator  12  is determined from an output signal from speed sensor  33 , preferably within a range at which the turbo-generator  12  is most efficient at harnessing residual energy from the exhaust system  26 . The ECU  14  then monitors the speed of the turbo-generator  12  for deviation from the desired speed, and adjusts the timing of the exhaust valve  56  to increase or reduce the residual energy available. 
         [0014]    For example, when the turbo-generator  12  is under little to no electrical load, the exhaust valve  56  is commanded to begin opening normally at or near the beginning of the exhaust stroke. As electrical load increases above turbo generator output, the voltage drops. ECU  14  senses the voltage drop, and commands the exhaust valve  56  to begin opening progressively earlier in the expansion stroke, advancing the timing until the residual energy in the exhaust system  26  increases to a point where the turbo-generator  12  is able to attain the desired voltage. Conversely, as electrical load decreases, the ECU  14  senses the voltage of the turbo-generator  12  increasing, and will command the exhaust valve  56  to begin opening progressively later in the expansion stroke, retarding the timing until the residual energy in the exhaust system  26  is reduced to a point where the turbo-generator  12  is able to attain the desired speed. 
         [0015]    During the foregoing events, where the ECU  14  is commanding the opening of the exhaust valve  56  to compensate for variable electrical load on the turbo-generator  12 , power output of the engine  10  is preferably regulated by the ECU  14  with a governed-speed algorithm commonly known in the art. In one embodiment of this algorithm, a desired speed for the crankshaft  42  is determined, usually from a sloping governor curve that is defined by an initial speed command selected by an operator. The ECU  14  then monitors the speed of the crankshaft  42  for deviation from the desired speed, and adjusts fuel quantity and timing to increase or reduce the mechanical power output of the engine  10  until the desired speed is attained. 
         [0016]    Several additional embodiments of the foregoing system will be apparent to one of ordinary skill in the art. For example, the combustion cycle could be a 2-stroke or 4-stroke cycle, or of an Otto or Diesel type. The engine  10  may be of a port injected, directed injected, or spark ignited configuration, or any combination thereof. The intake system  24  may include an intake manifold, a throttle valve, a charge air cooler, an EGR valve, and so forth. The exhaust system  26  may include an exhaust manifold, an EGR passage, an EGR cooler, and so on. Furthermore, the turbocharger  28  may be of a fixed geometry type, a variable geometry type (VGT), or equipped with a wastegate bypass valve. 
         [0017]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.