Abstract:
A method of operating an internal combustion engine, includes the steps of: detecting an operating speed reduction of the internal combustion engine; determining if the operating speed reduction is caused by an external load; and controlling operation of a fuel supply system to increase an output of fuel above a normal maximum fuel output, when the operating speed reduction is caused by the external load.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to internal combustion engines, and, more particularly, to power boost techniques for such engines.  
       BACKGROUND OF THE INVENTION  
       [0002]     The step load response of an internal combustion (IC) engine in transient after a load impact is a feature mostly influenced by the engine displacement, the hardware of the engine (e.g., whether it has a standard turbocharger, a turbocharger with waste gate or variable geometry, etc.), and by the software strategy for driving the air and fuel actuators (e.g., exhaust gas recirculation, turbocharger with variable geometry turbine (VGT), fuel injector configuration, etc.) with respect to the requirements of emissions legislation (e.g., visible smoke, NOx, etc.), noise or vibrations.  
         [0003]     Engine systems as a whole react in a linear manner during the application of a transient external load. Initially, the load is applied to the drive shaft of the IC engine. The IC engine speed decreases when the load increases. The engine speed drop is influenced by whether the governor is isochronous or has a speed drop. The air flow is increased to provide additional air to the IC engine by modifying the air actuators. A time delay is necessary to achieve the new air flow set point. The fuel injection quantity, which is nearly immediate, is increased with respect to both the smoke limit and maximum allowable fuel quantity. The engine then recovers to the engine speed set point. The parameters associated with an engine step load response in transient after a load impact are the speed drop and the time to recover to the engine set point.  
         [0004]     With conventional IC engine systems, a fuel injection system under the control of an electronic control module (ECM) provides fuel to the combustion cylinders. The maximum mechanical torque output from the engine is a limiting factor on the normal maximum fuel level which is provided to the combustion cylinders. Under a high external transient load as described above, the fuel level remains limited to the normal maximum fuel level supplied to the combustion cylinders, and the engine speed drop and recovery time can be excessive.  
         [0005]     What is needed in the art is a power boost method for an IC engine which improves engine speed drop and recovery time.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides and internal combustion engine with a power boost which is dependent upon a sensed external load.  
         [0007]     The invention comprises, in one form thereof, a method of operating an internal combustion engine, including the steps of: detecting an operating speed reduction of the internal combustion engine; determining if the operating speed reduction is caused by an external load; and controlling operation of a fuel supply system to increase an output of fuel above a normal maximum fuel output, when the operating speed reduction is caused by the external load.  
         [0008]     The invention comprises, in another form thereof, a method of operating an internal combustion engine, including the steps of: sensing an operating speed of the internal combustion engine; detecting an operating speed reduction using the sensed operating speed; comparing a difference between a desired operating speed and the sensed operating speed with a boost on threshold value; determining if the operating speed reduction is caused by an external load; and controlling operation of a fuel supply system to increase an output of fuel above a normal maximum fuel output, dependent upon each of the comparing and determining steps.  
         [0009]     An advantage of the present invention is that the IC engine experiences faster speed recovery when an external high inertia load is applied.  
         [0010]     Another advantage is that the maximum fueling level can be temporarily increased above a normal maximum fueling level during a period of high external load, and then returned to normal torque curve fueling for normal operation.  
         [0011]     Yet another advantage is that the IC engine has a more constant operating speed, resulting in better operator control of hydraulically driven loads.  
         [0012]     A further advantage is that the tendency for IC engine stalling is reduced when engaging high inertia loads.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic illustration of an embodiment of an IC engine of the present invention, which may be used with the method of operating an IC engine of the present invention;  
         [0014]      FIG. 2  is a flow chart of an embodiment of the method of operating an IC engine of the present invention;  
         [0015]      FIG. 3  is a comparative graphical illustration of fueling levels for the method of operating an IC engine of the present invention versus standard torque curve fueling levels; and  
         [0016]      FIG. 4  is a comparative graphical illustration of IC engine operating speed recovery for the method of operating an IC engine of the present invention versus standard torque curve operation. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Referring now to the drawings, and, more particularly to  FIG. 1 , there is shown an embodiment of an IC engine system  10  of the present invention, which may be used with the method of operating an IC engine of the present invention. IC engine system  10  generally includes an IC engine  12 , an electrical processing circuit in the form of an ECM  14 , an external load indicator  16 , a fuel system  18 , a flywheel  20 , and a speed sensor  22 .  
         [0018]     IC engine system  10  may be incorporated into any suitable application, such as an off road vehicle (e.g., agricultural tractor or combine), on road vehicle (e.g., heavy truck), or stationary power set (e.g., electrical generator set).  
         [0019]     IC engine  12  is also coupled with an external load  24 . In the case that IC engine  12  is part of an agricultural combine, external load  24  may be, e.g., an engagement of a grain separating cylinder or unloading auger. In the case IC engine  12  is part of a stationary generator set, external load  24  may be in the form of an energized electrical load. In other exemplary applications, IC engine  12  and external load  24  may be part of a hydraulic excavator, a tree harvester, or other applications where a high energy inertial load is engaged.  
         [0020]     IC engine system  10  may be incorporated into any suitable application, such as an off road vehicle (e.g., agricultural tractor or combine), on road vehicle (e.g., heavy truck), or stationary power set (e.g., electrical generator set).  
         [0021]     ECM  14  is coupled with sensor  22 , external load indicator  16  and fuel system  18 . In the embodiment shown, ECM  14  receives input signals from sensor  22  and external load indicator  16 , and provides output signals to fuel system  18 . Further, ECM  14  is coupled via electrical wires with sensor  22 , external load indicator  16  and fuel system  18 , but could also be coupled via suitable wireless connections depending upon the application.  
         [0022]     Although the electrical processing circuit associated with IC engine  12  is in the form of an ECM, it should be apparent to those skilled in the art that any suitable configuration of digital and/or analog circuitry may be used.  
         [0023]     Fuel system  18  may be any suitable controllably actuated fuel system. In the embodiment shown, fuel system  18  is in the form of a fuel injection system under the control of ECM  14 . Other suitable controllably actuated fuel systems may be used, depending upon the specific application.  
         [0024]     Sensor  22  is positioned in association with flywheel  20  and detects an operating speed of IC engine  12 . Sensor  22  may be an optical, proximity, inductive or other suitable sensor for detecting the rotational speed of flywheel  20 . Sensor  22  provides an output signal to ECM  14  corresponding to the sensed rotational speed.  
         [0025]     External load indicator  16  provides a signal to ECM  14  indicating whether a drop in engine speed is a result of the application of an external load, or some other factor not related to the application of an external high inertial load. For example, external load indicator  16  can be a sensor associated with an operator controlled throttle. If ECM  14  receives a signal from sensor  22  indicating that the engine speed has dropped, and concurrently ECM receives a signal from the throttle sensor indicating that the user just throttled down, then ECM determines that the engine speed drop is not a result of an external load.  
         [0026]     As another example, external load indicator  16  can be a sensor associated with a fuel line and providing a fault signal indicating that a fuel line is plugged. The drop in engine speed is thus likely a result of inadequate fuel flow, and ECM  14  determines that the engine speed drop is not the result of an external load.  
         [0027]     As yet another example, external load indicator  16  can be a sensor associated with an air filter and providing a fault signal indicating that an air filter is plugged. The drop in engine speed is thus likely a result of inadequate air flow, and ECM  14  determines that the engine speed drop is not the result of an external load.  
         [0028]     From the foregoing examples, it is apparent that ECM  14  provides a logical boolean combining of signals from speed sensor  22  and external load indicator  16  to determine if an engine speed drop is a result of an external load or some other factor not related to an external load.  
         [0029]      FIG. 3  illustrates a graphical comparison of fueling levels for the method of operating an IC engine of the present invention versus standard torque curve fueling levels. Under normal operating and load conditions, the maximum fuel level corresponds to the maximum torque output of IC engine  12 . The torque curve fueling level in  FIG. 3  is represented in %, and therefore the normal maximum fuel level is 100%. On the other hand, when an engine speed reduction is caused by an external load, the engine speed drop causes the engine not to provide a maximum output torque. Therefore, the fuel level can be temporarily increased above the normal maximum fuel level until the engine speed recovers to at or near an operating speed set point.  
         [0030]      FIG. 4  illustrates a graphical comparison of IC engine operating speed recovery for the method of operating an IC engine of the present invention versus standard torque curve operation. In the example shown, without use of the present invention, the recovery time for returning to an engine operating speed set point of 1800 RPM is approximately 17 seconds. On the other hand, with the use of the present invention, the recovery time for returning to an engine operating speed set point of 1800 RPM is approximately 10 seconds. This results in better operability and fuel savings of IC engine  12 .  
         [0031]     Referring now again to  FIGS. 1 and 2  conjunctively, the operation of IC engine system  10  will be described in greater detail. ECM  14  normally controls fuel injection system  18  to provide a fuel level corresponding to a standard torque curve fueling level. The normal maximum fuel injected by fuel injection system  18  thus corresponds to the maximum torque level on the standard torque fueling curve. Sensor  22  senses an operating speed of flywheel  20  and provides output signals to ECM  14  representing the sensed operating speed. ECM  14  compares the measured speed value with a desired speed value and determines if a speed reduction has occurred ( FIG. 2 , block  30 ). In one embodiment, ECM  14  subtracts the measured speed value from the desired value to obtain a difference. The difference between the desired speed and the measured speed is then compared with a “boost on” threshold value. If the difference is greater than the value of the “boost on” threshold value, then an undesired drop in speed has occurred (block  32 ). This approach allows an incremental drop in engine speed to be used to determine if an undesirable engine speed reduction has occurred, regardless of the engine speed set point.  
         [0032]     As another option, it may be possible to use an actual value of the desired speed and measured speed to determine if an undesirable engine speed reduction has occurred. For example, a throttle sensor can provide an output signal representing an operator selected desired engine speed. The difference between the actual values of the desired engine speed and sensed engine speed can be compared with a “boost on” threshold value representing an actual operating speed to determine if an undesirable engine speed reduction has occurred. For example, if the desired operating speed is at 1800 RPM and the sensed speed drops to 1600 RPM, then an unacceptable engine speed reduction has occurred. This technique would likely require a look-up table or a boost on threshold value taken as a percentage of the desired operating speed.  
         [0033]     If ECM  14  detects a speed reduction as a result of the input signals from speed sensor  22 , then ECM  14  also checks for an input signal from external load indicator  16  indicating an operator requested a speed reduction or some other type of fault signal (block  34 ). If ECM  14  determines that the speed reduction is a result of an external load, then ECM  14  controls fuel injection system  18  to provide a maximum fuel injection level which is above the normal maximum fuel level (block  36 ). It is not desirable to maintain the fuel injection level above the normal maximum fuel injection level when IC engine  12  recovers to a speed at or near an operating set speed (which might cause IC engine to have an output exceeding maximum torque output), so ECM  14  continues to receive signals from speed sensor  22  (block  38 ). As the sensed speed approaches the desired operating speed, the difference between the sensed speed and the desired operating speed becomes smaller. When this difference is less than a “boost off” threshold value (block  40 ), then ECM  14  controls fuel system  18  to provide a fuel level which is at or below the normal maximum fuel output level (block  42 ).  
         [0034]     In the embodiment of the invention described above and shown in  FIG. 2 , the determination as to whether an engine speed reduction is caused by an external load includes determining whether an operator throttled down the speed of the engine or whether some other fault condition occurred which could have caused the engine speed reduction. These determinations for causes of an engine speed reduction other than an external load are represented in box  34  of  FIG. 2 . In another embodiment, it is also possible to check only for a fault condition in box  34 , and accommodate an operator initiated throttling down of the engine in box  32 . In other words, when the operator throttles down, the new operator initiated throttle speed becomes the new desired engine speed in box  32 , and the difference between the new desired speed and measured speed is compared to the boost on threshold value. Under this control scenario, then only a determination for another engine fault condition is made in box  34 .  
         [0035]     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.  
       ASSIGNMENT  
       [0036]     The entire right, title and interest in and to this application and all subject matter disclosed and/or claimed therein, including any and all divisions, continuations, reissues, etc., thereof are, effective as of the date of execution of this application, assigned, transferred, sold and set over by the applicant(s) named herein to Deere &amp; Company, a Delaware corporation having offices at Moline, Ill. 61265, U.S.A., together with all rights to file, and to claim priorities in connection with, corresponding patent applications in any and all foreign countries in the name of Deere &amp; Company or otherwise.