Abstract:
An electric machine including an engine, generator, and motor. The electric grid is positioned between an input passage and output passage of an exhaust system of the engine. While in retard mode, excess electric power is dumped to the electric grid. Continuous airflow from the engine through the exhaust system removes the energy, in the form of heat, away from the electric grid.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to electric drive systems for propelled machines, and more particularly to electric grids for machines having an electric drive. 
       BACKGROUND 
       [0002]    Conventional propelled machines generally include an internal combustion engine that is mechanically coupled through a transmission assembly and drive train to driven wheels or sprockets of the machine. In contrast, propelled machines having electric drive systems including an internal combustion engine that is mechanically coupled to a generator, which creates electrical power. A motor that is mechanically coupled to drive the wheels of the propelled machine then consumes the power from the generator. Accordingly, the generator and motor of the electric drive systems replace the mechanical transmission and drive train of conventional internal combustion engine driven machines. This may result in a propelled machine with superior drive train efficiency and improved propulsion performance, which correlates to a machine having greater fuel economy and reduced emissions. 
         [0003]    To retard the machine, the motor acts as a generator and the generator acts as a motor to drive the engine. In many situations, however, excess energy must be dissipated through a retarding grid. On machines where space is limited, proper placement of the retarding grid is difficult. 
         [0004]    European Patent 0 603 907, filed Dec. 23, 1992, entitled Motor vehicle, particularly city-bus, with a diesel engine/generator unit, teaches an electric drive bus with a particle filter enclosed within an exhaust duct of the diesel engine. Electric leads from the generator, which provides power to the motor, provide energy to heating elements within the particle filter. The heating elements draw power from the generator at predetermined times to provide heat to regenerate the particle filter. 
         [0005]    The present disclosure is directed to overcoming some or all of the shortcomings in the prior art. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect, an exhaust system is provided. The exhaust system includes an inlet passage adapted to receive a flow of exhaust from an engine, an outlet passage adapted to expel the exhaust, and an electric grid, adapted to receive excess power during a retarding moment, positioned between the inlet passage and the outlet passage, in direct communication with the exhaust. 
         [0007]    According to another aspect, an electric machine is provided. The electric machine includes an engine having an exhaust system, a generator connected to the engine, and an electric grid electrically connected to the generator. The electric retarding grid is positioned substantially within the exhaust system in direct communication with air traveling through the exhaust system. The power electronics direct excess energy during a retarding moment to the electric retarding grid. 
         [0008]    According to yet another aspect, a method of cooling an electric grid of an electric machine having an engine, a generator, and an exhaust system, is provided. The method includes the steps of determining when a retarding condition is present, causing the generator to motor the engine, dumping excess electrical power from the generator to the electric grid within the exhaust system, and passing air from the engine through the exhaust system into direct communication with the electric grid. 
         [0009]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
           [0011]      FIG. 1  illustrates an electric machine according to one embodiment of the present disclosure; and 
           [0012]      FIG. 2  illustrates a schematic drawing of an electric retarding system according to another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Reference will now be made in detail to embodiments or features of the invention. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
         [0014]      FIG. 1  provides a diagrammatic perspective view of a work machine  10  according to an exemplary disclosed embodiment. While work machine  10  is illustrated as a mining vehicle, work machine  10  may also be any type of work machine that includes one or more electric motors. For example, work machine  10  may include on-highway vehicles, automobiles, tractors, wheel loaders, excavators, skid steers, and other types of machinery. 
         [0015]    The work machine  10  includes a power source  12  configured to provide a power output for powering various operations of the work machine  10 . The power source  12  may be an internal combustion engine that operates using diesel fuel, gasoline, natural gas, or other type of fuel. 
         [0016]    Referring to  FIG. 2 , the electric drive  12  includes a generator  18  connected to the engine  14 , power electronics  20  connected to the generator  18 , and at least one motor  22  connected to the power electronics  20 . 
         [0017]    Electrical energy produced by the generator  18  may be used to drive the electric motor  22 . For example, the generator  18  may be configured to provide a three-phase output of a desired voltage level (e.g., 480 V or any other suitable level) and supply this output to the power electronics  20 . The power electronics  20  includes a generator power converter  19  and a motor power converter  21 . The generator power converter  19  may convert the three-phase voltage to a DC voltage of another desired level (e.g., 615 V or any other suitable level). The motor power converter  21  may be configured to receive the voltage supplied by the generator power converter  19  and to provide a variable voltage, three-phase, AC voltage to drive the motor  22 . 
         [0018]    The generator  18  electrically communicates with an electric grid  24 , positioned at any location within an exhaust system  26  of the engine  14 . Specifically, the electric grid  24  is positioned downstream from the engine exhaust ports  27 , before or after a particulate filter  29 , or before or after other devices, such as, for example, a catalytic converter  31  or muffler  33 . 
         [0019]    The electric motor  22  may be mechanically coupled to a final drive assembly  30 , a transmission (not shown), a differential (not shown) or other torque-transmitting device to provide a driving force to the driven elements  16  of the machine  10 . 
         [0020]    A control unit  35  electrically communicates with the engine  14 , the generator  18 , the power electronics  20 , and the electric motor  22 . The control unit  35  continuously monitors conditions of the machine  10  to send and receive speed and torque commands, desired speed commands, actual speed signals, etc. When the actual speed exceeds a desired speed the control unit  35  commands the machine  10  into a retarding mode. 
         [0021]    While in retarding mode, the power electronics  22  provide reverse power capability to enable the generator  18  to operate as an electric motor for powering the internal combustion engine  14  while operating in retard mode, or during a retarding moment. Excess electricity is sent to the electric grid  24 . 
         [0022]    The electric grid  24  converts the excess electricity into heat by, for example, controlling the current across a heat-emitting element  28 , such as a power resistor, or a plurality of power resistors arranged in series and/or parallel form. In one embodiment, the power resistor(s)  28  is/are configured to receive between 50 and 500 kilowatts of excess energy during a retarding moment. It is noted that the electric grid  24  may be configured to receive more energy under transient conditions where the excess energy is momentarily “pulsed” to the electric grid  24 , rather than continuously applied. 
       INDUSTRIAL APPLICABILITY 
       [0023]    During propulsion of the machine  10  the internal combustion engine  14  combusts fuel to drive the generator  18 . The generator  18 , in turn, produces electrical power that is provided to the power electronics  16  and to the electric motor  22  to drive the driven elements  16 . 
         [0024]    While in retard mode, the driven elements  16  drive the motor  22 , acting as a generator, to create electrical power. The retarding condition, or retarding moment, is detected when the control unit  35  detects that the desired speed is less than the actual speed, or when the machine is attempting to move in a direction faster than the desired speed. The electrical power travels through the power electronics  20  to drive the generator  18 , now acting as a motor. The generator/motor power electronics allow the motor  22  to drive the engine  14 , relying on friction and parasitic losses to create loads on the generator/motor to slow the machine. Excess electrical power, or energy, is dissipated to the electric grid  24  located within the exhaust system  26 . The control unit may be configured to predetermine a maximum amount of retarding available from the engine, or other parasitic devices, such as a pump, air conditioning system, etc. It is understood that the terms “energy” and “power” are referred to herein interchangeably. 
         [0025]    The power electronics of the generator  18  control the amount of energy used to retard the engine  14 . When the engine  14  reaches a maximum retarding capability, the excess energy passes to the electric grid  24  and converts to heat. Exhaust gases exiting the engine  14  through the exhaust ports, and traveling through the exhaust system  26 , provides relatively cool gas over the electric grid  24  to remove the heat therefrom. 
         [0026]    It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed system and method without departing from the scope or spirit of the embodiments of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only.