Abstract:
A transient response system includes a power source operable to generate a power output and a transmission operatively coupled to the power source. The transient response system also includes a generator operatively coupled to the power source and a controller in communication with the generator and at least one of the power source and the transmission. The controller is operable to receive at least one input having a value indicative of a change in load on the power source and operable to cause the generator to remove power from the power output at a rate corresponding to the value of the at least one input.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to a transient response system, and more particularly to transient response system having a motor/generator.  
       BACKGROUND  
       [0002]     Work machines, including on-highway trucks and other types of heavy machinery, are used for a variety of tasks. These work machines may include a transmission coupled to an engine such as, for example, a diesel engine, a gasoline engine, or a natural gas engine that provides the power to complete these tasks. The transmission may be a mechanical, hydro-mechanical, hydraulic, or electric transmission that transmits engine power to a traction device. A power load placed on the transmission by the traction device is transmitted to the engine. Power load changes, either requiring additional power or less power, may cause the engine to deviate from a desired operating range. Deviations from the desired speed range may result in poor efficiency, less production, increased wear on the engine, and operator dissatisfaction.  
         [0003]     Work machines may include a flywheel to minimize the variations in engine speed caused by a change in the power load. The magnitude of the speed changes may be minimized by increasing the inertia of the flywheel. However, as flywheel inertia increases, responsiveness of the engine decreases. A conventional flywheel may be inefficient at providing a balance between minimizing engine speed fluctuations and allowing the engine to respond quickly to desired power changes. A range of flywheel sizes may be provided for a particular engine application to allow selection of flywheel size based on expected load changes. Unfortunately, this may result in increased parts, tooling, and production cost.  
         [0004]     In an attempt to provide a flywheel offering improved response to a wider range of load changes, at least one variable inertial mass flywheel has been proposed. For example, U.S. Pat. No. 5,007,303 (the &#39;303 patent) issued to Okuzumi on Apr. 16, 1991, describes a variable inertial mass flywheel having a main flywheel member coupled to an engine crankshaft and a sub-flywheel member separated from the main flywheel member by electrorheological fluid. The viscosity of an electrorheolgical fluid is proportional to the intensity of an electric field applied to the fluid. During power load fluctuations, the intensity of the electric field is changed to change the viscosity of the electorheological fluid. As a result, the change in viscosity increases or decreases friction between the main flywheel and the sub-flywheel. During accelerations or decelerations, the intensity of the field is set low to minimize friction between the main flywheel and the sub-flywheel, thereby creating a low inertia flywheel that may respond quickly. During power load changes of high magnitude, the intensity of the field is set high to increase friction between the main flywheel and the sub-flywheel, thereby creating a high inertia flywheel that may offset the high magnitude changes in power load.  
         [0005]     While, the variable inertial mass flywheel of the &#39;303 patent may offer an improved response to a wider range of load changes, as compared to traditional fixed-mass flywheels, the flywheel of the &#39;303 patent may be problematic. For example, the variable inertial mass flywheel may not efficiently use and/or dissipate the energy absorbed by the flywheel.  
         [0006]     The present invention is directed to overcoming one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0007]     In one aspect, the present disclosure is directed to a transient response system that includes a power source operable to generate a power output and a transmission operatively coupled to the power source. The transient response system also includes a generator operatively coupled to the power source and a controller in communication with the generator and at least one of the power source and the transmission. The controller is operable to receive at least one input having a value indicative of a change in load on the power source and operable to cause the generator to remove power from the power output at a rate corresponding to the value of the at least one input.  
         [0008]     In another aspect, the present disclosure is directed to a method of operating a transient response system. The method includes driving a transmission with a power source, the power source operable to produce a power output. The method also includes sensing a load on the power source and identifying a change in the load on the power source. The method further includes controlling a generator to remove power from the power output at a rate corresponding to the value associated with the change in load on the power source. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a diagrammatic illustration of a work machine having a transient response system according to an exemplary embodiment of the present invention;  
         [0010]      FIG. 2  is a schematic illustration of a transient response system according to an exemplary embodiment of the present invention;  
         [0011]      FIG. 3  is a flowchart illustrating a method of operation of the transient response system according to an exemplary embodiment of the present invention; and  
         [0012]      FIG. 4  is a graph comparing the response of the transient response system with conventional flywheels. 
     
    
     DETAILED DESCRIPTION  
       [0013]      FIG. 1  illustrates an exemplary embodiment of a transient response system  10  for a work machine  12  having a housing  13 . The transient response system  10  is intended for use with an engine  16  and a transmission  14  connected to a traction device  18  of the work machine  12 . Engine  16  may be a diesel engine, a gasoline engine, a natural gas engine, or any other engine readily apparent to one skilled in the art. Transmission  14  may be a mechanical, hydro-mechanical, electric, or any other transmission known in the art.  
         [0014]     As illustrated in  FIG. 2 , the transient response system  10  may include a motor/generator  20 , a drive inverter  22 , a power storage device  24 , and a control system  26 . Transient response system  10  may replace a conventional flywheel of engine  16 . Alternately, transient response system  10  may also be used in conjunction with a conventional flywheel.  
         [0015]     Motor/generator  20  may include a motor and a generator in a single unit. Alternatively, the motor and generator may be separated from one another. The motor/generator  20  may be connected to engine  16  by a crankshaft  28  of engine  16 , or in any other manner known in the art. Motor/generator  20  may be configured to both drive engine  16  and be driven by engine  16 . Motor/generator  20  may include a conventional starter/generator that is configured to drive engine  16  when engine  16  is already running as well as during a starting sequence.  
         [0016]     It is also contemplated that the motor/generator may be absent and only a generator (not shown) included in transient response system  10 . The generator may be connected to engine  16  by a crankshaft  28  of engine  16 , or in any other manner known in the art. The generator may be configured to be driven by engine  16  to generate power.  
         [0017]     Drive inverter  22  may be connected to motor/generator  20  via power lines  30 . Drive inverter  22  may include various components including insulated gate bipolar transistors (IGBTs), microprocessors, capacitors, memory storage devices, and any other components that may be used for operating motor/generator  20 . Other components that may be associated with drive inverter  22  include power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others.  
         [0018]     Drive inverter  22  may direct power, generated by motor/generator  20 , to power storage device  24  and to other power consuming devices  32  via power lines  34 . Power storage device  24  may be any device (such as a battery) for storing power. Power consuming devices  32  may include, for example, one or more of an air conditioning unit, a heating unit, a resistive grid, lights, appliances, personal electronics, pumps, motors, and other electronic engine components and accessories known in the art.  
         [0019]     Control system  26  may be in communication with engine  16 , transmission  14 , and drive inverter  22  via communication lines  36 ,  38 , and  40  respectively. Control system  26  may include a controller  42 , which may include components such as a memory, a secondary storage device, a processor, and any other component that may be used for running applications. Controller  42  may contain other components including power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other appropriate circuitry known in the art.  
         [0020]     A flow chart  52  illustrated in  FIG. 3  depicts the operation of the transient response system  10 . A graph  44 , illustrated in  FIG. 4 , depicts a response time comparison of transient response system  10  and conventional flywheels. These figures will be discussed in the following section to further illustrate the disclosed system and its operation.  
       INDUSTRIAL APPLICABILITY  
       [0021]     The disclosed system may be applicable to any engine that requires dampening of transient power loads applied to the engine to minimize or prevent engine deviations outside of a desired operating range. For purposes of this disclosure, the term “desired operating range” includes those operating conditions that the work machine operator and/or work machine control system wants to achieve and/or maintain such as, for example, engine speed. Deviations from this desired operating range may result in, for example, increased fuel consumption, increased exhaust emissions, increased engine temperatures, decreased machine productivity, operator dissatisfaction, and/or decreased responsiveness.  
         [0022]     Deviations from the desired operating range may be experienced when sudden changes in power load experienced by traction device  18  are transferred by transmission  14  or other engine powered devices to engine  16 . Engine  16  may include various systems (not shown) working in combination with each other to respond to the power load. Such systems may include, for example, fuel delivery systems, air induction systems, control systems, combustion systems, and others known in the art. Each of these systems may have an associated response time lag. The combined response time lags of each system result in a total response time lag of engine  16 . The response time lag of engine  16  is a factor that may determine whether power load changes cause deviations from the desired operating range to occur.  
         [0023]     Work machine  12 , as illustrated in  FIG. 1 , may utilize transient response system  10  to dampen sudden changes in power load transmitted to engine  16  from transmission  14  or other engine powered devices. Transient response system  10  may determine a change in the power load placed on the engine  16  and operate motor/generator  20  to change the power output of engine  16  in response to the sudden change in power load. While motor/generator  20  is responding to the change in power load, another power source (not shown) may supply the electrical requirements of work machine  12 . Transient response system  10  may enable engine  16  to respond more quickly to a sudden change in power load than if engine  16  included only a traditional flywheel. Transient response system  10  may, therefore, decrease the likelihood of engine  16  deviating from the desired operating range.  
         [0024]     Flow chart  52  of  FIG. 3  depicts the operation of transient response system  10 . At step  54 , controller  42  senses the power load applied to engine  16 . Controller  42  may monitor the change in power load that transmission  14  has transmitted or will transmit to engine  16 . For example, controller  42  may sense a change in fluid pressure within a hydraulic transmission or a change in a speed command signal sent to an electric transmission. Sensing the fluid pressure or speed command signal in transmission  14  may indicate a change in power load before the change is transmitted to engine  16 . Controller  42  may also sense an engine speed deviation, which may be an indication that a change in power load has already been transmitted to engine  16 .  
         [0025]     In step  56 , controller  42  may determine whether a change in power load has occurred or will occur. If a change in power load has occurred or will occur, control continues to step  58  where controller  42  determines whether the change in power load is an increase or a decrease in power load.  
         [0026]     If the change in power load is an increase, control continues in step  62 , where controller  42  determines the mode in which motor/generator  20  is currently operating. If motor/generator  20  is operating in a motoring mode (i.e., adding power to the power output by driving engine  16 ), control commences to step  64 , where motoring of motor/generator  20  is increased to add power supplied to the power output of engine  16 . If motor/generator  20  is deactivated (i.e., neither absorbing nor adding substantial power with motor/generator  20 ), control commences to step  66 , where motor/generator  20  is caused to enter the motoring mode to supply power to the power output of engine  16 . If motor/generator  20  is operating in a generating mode (i.e., absorbing power from the power output by driving motor/generator  20  with engine  16 ), control commences to step  68 , where the generating function of motor/generator  20  decreases to reduce the power diverted from the power output of engine  16 . As a result of each of steps  64 ,  66 , and  68 , power may be added to the power output of engine  16  to offset the increase in power load.  
         [0027]     The motoring mode and generating mode of motor/generator  20  will now be explained in further detail. When in the motoring mode, power from energy storage device  24 , for example, may be directed to motor/generator  20  to cause motor/generator  20  to apply torque to engine crankshaft  28 , thereby adding power to the power output of engine  16 . The power directed to motor/generator  20  may also be supplied by another power source (not shown), such as an auxiliary engine. In the motoring mode, motor/generator  20  may be used to crank engine  16  when starting or to add power to crankshaft  28  when engine  16  is already running.  
         [0028]     In the generating mode motor/generator  20  may be driven by engine  16  to generate power for various purposes. When in the generating mode, a portion of the mechanical power output of engine  16  may be converted by motor/generator  20  to electrical power. The generated electrical power may be directed to energy storage device  24  and to other power consuming devices  32  such as, for example, an air-conditioner, heating unit, resistive grid, lights, appliances, personal electronics, and other accessories. When motor/generator  20  is in the generating mode, power from the power output of engine  16  may be diverted from transmission  14  by motor/generator  20 .  
         [0029]     After steps  64 ,  66 , or  68 , control continues to step  70 , where controller  42  determines if the actions of steps  64 ,  66 , or  68  were sufficient to accommodate the increase in power load. This may be accomplished by monitoring the inputs from the transmission and engine in the same manner as step  54  described above. If the actions of steps  64 ,  66 , or  68  were insufficient, control loops back to step  62 . If the actions of steps  64 ,  66 , or  68  were sufficient, control loops back to step  54 .  
         [0030]     Returning to step  58 , if controller  42  determines that the change in power load is a decrease, control continues to step  74 . During step  74 , as described above for step  62 , controller  42  determines which mode motor/generator  20  is operating in.  
         [0031]     If motor/generator  20  is operating in a motoring mode, control commences to step  76 , where motoring of motor/generator  20  decreases and less power is supplied to the power output of engine  16 . If motor/generator  20  is deactivated, control commences to step  78 , where motor/generator  20  is caused to enter the generating mode to divert power from transmission  14  to motor/generator  20 . If motor/generator  20  is operating in a generating mode, control commences to step  80 , where generating by motor/generator  20  increases to increase the power diverted from transmission  14  by motor/generator  20 . As a result of steps  76 ,  78 , and  80 , the power output of engine  16  directed to transmission  14  prior to the power load decreases, thereby offsetting the decrease in power load.  
         [0032]     After steps  76 ,  78 , or  80 , control continues to step  82 , where controller  42  determines if the actions of steps  76 ,  78 , or  80  were sufficient to accommodate the decrease in power load. This may be accomplished by monitoring the inputs from the transmission and engine in the same manner as step  54  described above. If the actions of steps  76 ,  78 , or  80  were insufficient, control loops back to step  74 . If the actions of steps  76 ,  78 , or  80  were sufficient, control loops back to step  54 .  
         [0033]      FIG. 4  illustrates the performance of transient response system  10  relative to conventional flywheels. A curve  46  represents the response time of transient response system  10 . A curve  48  represents the response time a high-inertia flywheel. A curve  50  represents the response time of a low-inertia flywheel. As illustrated in  FIG. 4 , transient response system  10  may cause engine  16  to deviate less from the desired operating range than a high inertia flywheel. As further illustrated in  FIG. 4 , transient response system  10  responds more quickly than a low inertia flywheel. The stability and responsiveness that transient response system  10  may add to engine  16  can improve efficiency, production, and life of both engine  16  and work machine  12 .  
         [0034]     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed transient response system without departing from the scope 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 invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.