System for controlling engine exhaust temperature

Information

  • Patent Grant
  • 6550464
  • Patent Number
    6,550,464
  • Date Filed
    Wednesday, January 31, 2001
    23 years ago
  • Date Issued
    Tuesday, April 22, 2003
    21 years ago
Abstract
A system is provided for limiting engine exhaust temperature to a maximum temperature limit. The system is operable to limit either a first or a second fueling parameter in accordance with an engine exhaust temperature estimation model. An engine exhaust temperature-limited fueling command is computed from the respective fueling parameter, and fuel supplied to the engine is limited thereby in order to maintain the actual engine exhaust temperature below the maximum temperature limit. In one embodiment, the engine exhaust temperature model is based on current values of engine speed, intake manifold temperature, mass charge flow, default fuel command parameters, and a first set of model constants. In an alternative embodiment, the engine exhaust temperature model is based on current values of engine speed, intake manifold temperature, intake manifold pressure, mass charge flow, default fueling parameters, and a second set of model constants including a lower heating value of fuel constant.
Description




FIELD OF THE INVENTION




The present invention relates generally to fuel limiting strategies for internal combustion engines, and more specifically to such systems for controlling engine exhaust temperatures during engine operation.




BACKGROUND OF THE INVENTION




When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NO


X


). This problem is aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.




One known technique for reducing unwanted emissions such as NO


X


involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NO


X


. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold. valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.




While EGR systems of the foregoing type are generally effective in reducing unwanted emissions resulting from the combustion process, a penalty is paid thereby in the form of a resulting loss in engine efficiency. A tradeoff thus exists in typical engine control strategies between the level of NO


X


production and engine operating efficiency, and difficulties associated with managing this tradeoff have been greatly exacerbated by the increasingly stringent requirements of government-mandated emission standards.




In order to achieve the dual, yet diametrically opposed, goals of limiting the production of NO


X


emissions to acceptably low levels while also maximizing engine operational efficiency under a variety of load conditions, substantial effort must be devoted to determining with a high degree of accuracy the correct proportions of air, fuel and exhaust gas making up the combustion charge. To this end, accurate, real-time values of a number of EGR system-related operating parameters must therefore be obtained, preferably at low cost. Control strategies must then be developed to make use of such information in accurately controlling the engine, EGR system and/or turbocharger. The present invention is accordingly directed to techniques for controlling engine operation to maintain engine exhaust temperatures within desired operating limits.




SUMMARY OF THE INVENTION




The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for controlling exhaust temperature of an internal combustion engine comprises a temperature sensor producing a temperature signal corresponding to a temperature of an intake manifold of an internal combustion, an engine speed sensor producing an engine speed signal corresponding to a rotational speed of the engine, means for determining a charge flow value corresponding to a mass flow of charge entering the intake manifold, and a control circuit producing a fueling command for fueling the engine, the control circuit controlling engine exhaust temperature by limiting the fueling command based on the temperature signal, the engine speed signal and the charge flow value.




In accordance with another aspect of the present invention, a method for controlling exhaust temperature of an internal combustion engine comprises determining a temperature of an intake manifold of an internal combustion engine, determining a rotational speed of the engine, determining a mass flow of charge entering the intake manifold, and controlling engine exhaust temperature by limiting a fueling command for fueling the engine based on current values of the temperature, the rotational speed and the mass flow of charge.




One object of the present invention is to provide a virtual sensor operable to estimate engine exhaust temperature based on existing engine operational information.




Another object of the present invention is to provide a strategy for controlling engine exhaust temperature relative to an exhaust gas temperature limit by limiting at least one engine fueling parameter forming part of the engine exhaust temperature estimate.




These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a diagrammatic illustration of one preferred embodiment of a system for controlling engine exhaust temperature, in accordance with the present invention.





FIG. 2

is a diagrammatic illustration of one preferred embodiment of a technique for determining a charge flow parameter for use by the exhaust temperature fueling limiter block of FIG.


1


.





FIG. 3

is a diagrammatic illustration of one preferred embodiment of the exhaust temperature fueling limiter block of

FIG. 1

, in accordance with the present invention.





FIG. 4

is a flowchart illustrating one preferred embodiment of a software algorithm for controlling exhaust gas according to the exhaust temperature fueling limiter embodiment shown in FIG.


3


.





FIG. 5

is a diagrammatic illustration of an alternate embodiment of the exhaust temperature fueling limiter block of

FIG. 1

, in accordance with the present invention.





FIG. 6

is a flowchart illustrating one preferred embodiment of a software algorithm for controlling exhaust gas according to the exhaust temperature fueling limiter embodiment shown in FIG.


5


.





FIG. 7

is a flowchart illustrating one preferred embodiment of a software algorithm for estimating engine exhaust temperature, in accordance with the present invention.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




For the purposes of promoting an understanding of the principles of the invention, reference will now be made to a number of preferred embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated embodiments, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.




Referring now to

FIG. 1

, one preferred embodiment of a system


10


for controlling engine exhaust temperature, in accordance with the present invention, is shown. System


10


includes an internal combustion engine


12


having an intake manifold


14


coupled thereto. An intake manifold temperature sensor


16


is disposed within, or otherwise disposed in fluid communication with, manifold


14


. Sensor


16


is preferably a temperature sensor of known construction that is operable to sense the temperature within the intake manifold


14


and produce an intake manifold temperature (IMT) signal corresponding thereto. Manifold


14


may optionally include an intake manifold pressure sensor


18


is disposed therewithin, or otherwise disposed in fluid communication therewith, wherein sensor


16


is preferably of known construction and operable to sense a pressure within manifold


14


and produce an intake manifold pressure (IMP) signal corresponding thereto.




Engine


12


includes an engine speed sensor


26


operable to sense rotational speed of the engine


12


and produce an engine speed (ESP) signal corresponding thereto. Preferably, sensor


26


is of known construction, and in one embodiment sensor


26


is a Hall effect sensor operable to sense passage thereby of a number of teeth forming part of a gear or tone wheel. Alternatively, sensor


26


may be a variable reluctance sensor or other known speed sensor, and in any case sensor


26


is operable to produce an engine speed signal indicative of engine rotational speed.




Engine


12


further includes a fuel system


40


responsive to one or more final fuel commands (FFC) to supply fuel to engine


12


. Fuel system


40


is preferably an electronically controlled fuel system of known construction, wherein the operation thereof is generally known in the art.




Central to system


10


is a control circuit


20


that is preferably microprocessor-based and is generally operable to control and manage the overall operation of engine


12


. Control circuit


20


includes a memory unit


22


as well as a number of inputs and outputs for interfacing with various sensors and systems coupled to engine


12


, such as those just described hereinabove. Control circuit


20


, in one embodiment, may be a known control unit sometimes referred to as an electronic or engine control module (ECM), electronic or engine control unit (ECU) or the like, or may alternatively be any control circuit capable of operation as will be described in greater detail hereinafter. In any case, control circuit


20


includes a default fueling block


34


receiving the engine speed signal (ESP) from engine speed sensor


26


via signal path


28


, as well as a number of additional input signals


36


. Block


34


is responsive to the ESP signal on signal path


28


as well as one or more of the additional signals


36


to compute a default fueling command (DFC) in accordance with techniques well-known in the art. The default fueling command DFC may be an unrestricted fueling command that is used as the final fueling command FFC produced on any number, M, of signal paths


42


for controlling fuel system


40


, wherein M may be any positive integer. As it relates to the present invention, however, the default fueling determination block


34


may alternatively or additionally include one or more fuel limiting algorithms designed to achieve certain engine operational goals, wherein the default fueling command DFC produced by block


34


represents an unrestricted fueling command that has been limited by one or more such fuel limiting algorithms.




In accordance with the present invention, control circuit


20


further includes an exhaust temperature fueling limiter block


24


receiving the engine speed signal (ESP) from engine speed sensor


26


via signal path


28


, the intake manifold temperature signal (IMT) from the intake manifold temperature sensor


16


via signal path


30


, optionally the intake manifold pressure signal (IMP) from intake manifold pressure sensor


18


via signal path


32


, and the default fueling command (DFC) from the default fueling determination block


34


. In a general sense, the default fueling command (DFC) typically includes timing information relating to the start-of-injection (SOI) and fuel quantity information relating to mass fuel flow (FF), as these terms are understood to those skilled in the art. In one preferred embodiment, the default fueling determination block


34


is configured to supply the exhaust temperature fueling limiter block


24


with the default fueling command (DFC), and block


24


is operable to determine from DFC the values of SOI and FF in a manner known in the art. Alternatively, the default fueling determination block


34


may be configured to supply the exhaust temperature fueling limiter block


24


with the SOI and/or FF values directly, wherein block


24


is operable to process either one, or both, of these values in a manner to be more fully described hereinafter.




In addition to the fueling information supplied by the default fueling determination block


34


, the engine speed signal (ESP), the intake manifold temperature signal (IMT), and optionally the intake manifold pressure signal (IMP), the exhaust temperature fueling limiter block


24


is configured to receive a mass charge flow value (ECF). In one preferred embodiment, the mass charge flow value (ECF) is supplied by a known software algorithm operable to compute a charge flow estimate based on certain engine operating parameter values, although the present invention contemplates that intake manifold


14


may alternatively include a mass air flow sensor (MAF)


44


of known construction supplying a charge flow value to block


24


as shown in phantom. In cases where the charge flow value (ECF) is estimated in accordance with a known estimation algorithm, one preferred embodiment of control circuit


20


includes a charge flow determination block of the type illustrated in FIG.


2


.




Referring to

FIG. 2

, a system


50


is shown for estimating charge, flow; i.e., the mass flow of charge supplied to intake manifold


14


, wherein the term “charge”, as used herein, is defined as a composition of fresh air and recirculated exhaust gas. In any case, system


50


includes several components in common with system


10


of

FIG. 1

, and like numbers are therefore used to identify like components.




System


50


includes an internal combustion engine


12


having an intake manifold


14


fluidly coupled to an intake conduit


16


, wherein intake manifold


14


receives fresh air via conduit


16


. In exhaust manifold


58


of engine


12


expels exhaust gas to ambient via exhaust conduit


56


, and an EGR valve


60


is disposed in fluid communications with the intake and exhaust conduits


16


and


58


respectively via conduit


54


. A ΔP sensor


62


is positioned across the EGR valve


60


and is electrically connected to a charge flow determination block


68


of control circuit


20


via signal path


70


, and an engine speed sensor


28


electrically connected to block


68


via signal path


28


. An intake manifold temperature sensor (IMT)


16


is disposed in fluid communication with the intake manifold


14


of engine


12


, and is electrically connected to the charge flow determination block


68


of control circuit


20


via signal path


30


. Intake manifold


14


also includes an intake manifold pressure sensor (IMP)


18


in fluid communication therewith and electrically connected to the charge flow determination block


68


of control circuit


20


via signal path


32


. Optionally, as will be described in greater detail hereinafter, system


50


may include an exhaust pressure sensor (EP)


72


disposed in fluid communication with the exhaust manifold


58


or an exhaust pressure sensor (EP)


74


disposed in fluid communication with exhaust conduit


56


as shown in phantom in FIG.


2


.




In one preferred embodiment, the charge flow determination block


68


of the control circuit


20


is operable to compute an estimate of the mass charge flow (ECF) into intake manifold


14


by first estimating the volumetric efficiency (η


v


) of the charge intake system, and then computing ECF as a function of η


v


using a conventional speed/density equation. Any known technique for estimating η


v


may be used, and in one preferred embodiment of block


68


η


v


is computed according to a known Taylor mach number-based volumetric efficiency equation given as:






η


v




=A




1


*{(Bore/


D


)


2


*(stroke*


ESP


)


B


/sqrt(γ*


R*IMT


)*[(1+


EP/IMP


)+


A




2




]}+A




3


,






where,




A


1


, A


2


, A


3


and B are all calibratable parameters preferably fit to the volumetric efficiency equation based on mapped engine data,




Bore is the intake valve bore length,




D is the intake valve diameter,




stroke is the piston stroke length, wherein Bore, D and stroke are generally dependent upon engine geometry,




γand R are known constants (γ*R=387.414 KJ/kg/deg K),




ESP is engine speed,




IMP is the intake manifold pressure,




EP is the exhaust pressure, where EP=IMP+ΔP, and




IMT=intake manifold temperature.




From the foregoing equation, it should be apparent that system


50


may substitute an exhaust pressure sensor


72


or


74


, as shown in phantom in

FIG. 2

, for the ΔP sensor


62


, although commercially available exhaust pressure sensors that are capable of withstanding harsh environments associated with the exhaust manifold


58


and/or exhaust conduit


56


are not typically available. For purposes of the present invention, a ΔP sensor


62


is therefore preferably used.




With the volumetric efficiency value η


v


estimated according to the foregoing equation, the estimate charge flow value ECF is preferably computed according to the equation:








ECF=η




v




*V




DIS




*ESP*IMP


/(2


*R*IMT


),






where,




η


v


is the estimated volumetric efficiency,




V


DIS


is engine displacement and is generally dependent upon engine geometry,




ESP is engine speed,




IMP is the intake manifold pressure,




R is a known gas constant (R=54), and




IMT is the intake manifold temperature.




Referring again to

FIG. 1

, the exhaust temperature fueling limiter block


24


preferably includes a model for estimating engine exhaust temperature (ETE), in accordance with one aspect of the present invention, wherein the engine exhaust temperature estimate is preferably a function of at least the ESP, IMT, ECF and DFC (or SOI and FF) values, and optionally the IMP value. While the engine exhaust temperature model is preferably provided in the form of an equation stored within block


24


or memory unit


22


, the present invention contemplates that the model may alternatively be provided in the form of one or more graphical representations, tables, and/or the like. In any case, the exhaust temperature fueling limiter block


24


is preferably operable to compute a model-based engine exhaust temperature estimate (ETE) for use in accordance with other aspects of the present invention, and/or for use by other algorithms and/or control strategies within control circuit


20


.




In accordance with another aspect of the present invention, the exhaust temperature fueling limiter block


24


is further operable to compute an engine exhaust temperature-limited fueling command value (FC


ETL


) as a function of the engine exhaust temperature estimation model. The exhaust temperature-limited fueling command FC


ETL


is preferably a function of the default fueling command (DFC) that is limited by block


24


as a function of an imposed maximum exhaust temperature limit (T


EL


) according to the exhaust temperature estimation model of the present invention, as will be described in greater detail hereinafter. In any case, the default fueling command (DFC) produced by the default fueling determination block


34


and the engine exhaust temperature-limited fueling command FC


ETL


produced by the exhaust temperature fueling limiter block


24


are both provided to a MIN block


38


operable to produce as the final fueling command FFC on signal path


42


a minimum value thereof.




Referring now to

FIG. 7

, a flowchart illustrating one preferred embodiment of a software algorithm


300


for estimating engine exhaust gas temperature (ETE), in accordance with the present invention, is shown. Algorithm


300


is preferably stored within limiter block


24


and is executable by control circuit


20


to produce the exhaust temperature estimate (ETE). Algorithm


300


begins at step


302


, and at step


304


, control circuit


20


is operable to determine current values of engine speed (ESP), intake manifold temperature (IMT) and model constants. In a first embodiment of the present invention, block


24


is operable to estimate engine exhaust temperature (ETE) according to the model:








ETE=IMT+A+


(


B*SOI


)+


C/


(


ECF/FF


)+(


D*SOI


)


/ESP+E/[


(


ESP*ECF


)


/FF]


  (1),






wherein the model constants determined at step


304


correspond to constants A, B, C, D and E in equation (1). In a second embodiment of the present invention, control circuit


20


is further operable at step


304


to determine a current value for the intake manifold pressure (IMP). In this second embodiment, block


24


is operable to estimate engine exhaust temperature (ETE) according to the model:








ETE=IMT+[


(


A*ESP


)+(


B*IMP


)+(


C*SOI


)+


D


)][(


LHV*FF


)/


ECF]


  (2),






wherein the model constants determined at step


304


correspond to constants A, B, C, and D in equation (2). In this embodiment, equation (2) includes an additional lower heating value of fuel (LHV) constant, which is a known constant depending upon the type of fuel used by engine


12


. Regardless of whether equation (1) or (2) is used, the model constants A-E of equation (1) or A-D of equation (2) are preferably obtained as a result of one or more known data fitting techniques operable to optimize a fit between available performance data and the respective model.




In any case, algorithm


300


advances from step


304


to step


306


where control circuit


20


is operable in each of the above-described embodiments to determine a mass charge flow value (ECF). In one preferred embodiment, ECF is obtained in accordance with a known charge flow estimation algorithm such as that described with respect to FIG.


2


. Alternatively, ECF may be obtained from an actual sensor such as the optional mass air flow sensor


44


shown in phantom in FIG.


1


. In either case, algorithm


300


advances from step


306


to step


308


where control circuit


20


is operable in each of the model embodiments illustrated in equations (1) and (2) to determine a default fueling command (DFC). In one preferred embodiment, DFC is provided by the default fueling determination block


34


, and block


24


is operable to determine start-of-injection (SOI) and mass fuel flow (FF) values therefrom in accordance with well-known techniques therefore. Alternatively, the default fueling determination block


34


is operable to provide the SOI and FF values directly to block


24


. In either case, algorithm execution advances from step


308


to step


310


where block


24


is operable to compute an estimate of the engine exhaust temperature (ETE) according to either equation (1) or equation (2). Thereafter, algorithm execution preferably loops back to step


304


for continuous determination of ETE, but may alternatively return from step


310


to another calling routine.




Exhaust temperature estimation equation (1) is, in accordance with the present invention, based on a statistical sensitivity approach, and is believed to provide sufficiently accurate results for many applications. Exhaust temperature estimation equation (2) is, in accordance with the present invention, based on a model that assumes that a fraction of the fuel energy is transferred to the engine exhaust. Test data has indicated that the engine exhaust temperature estimation model represented by equation (2) is more accurate, is less sensitive to uncertainties, and is less sensitive to deterioration effects than the model represented by equation (1).




Referring now to

FIG. 3

, one preferred embodiment


24


′ of the exhaust fueling determination block


24


of

FIG. 1

for producing an exhaust temperature-limited fueling command (FC


ETL


), in accordance with the present invention, is shown. In the embodiment of block


24


′ illustrated in

FIG. 3

, a fueling parameter limit determination block


80


receives input signals ESP and IMT (and optionally IMP) from associated sensors described with respect to FIG.


1


. Block


80


also receives the mass charge flow value ECF either from the estimation algorithm described with respect to

FIG. 2

or from a mass air flow sensor as described with respect to

FIG. 1

, and further receives either the default fueling command value (DFC) or the mass fuel flow value (FF) from the default fueling determination block


34


. In one preferred embodiment, block


80


is operable to determine the mass fuel flow value FF from the default fueling command DFC in accordance with known techniques, and in this embodiment block


80


is thus configured to receive DFC from block


34


. Alternatively, as shown in phantom in

FIG. 3

, block


34


may be configured to supply FF directly to block


80


in which case the default fueling command DFC need not be provided.




Block


24


′ further includes a model constants block


82


having the various model constants stored therein, wherein block


82


is operable to provide such constants to block


80


. In embodiments utilizing equation (1) as the engine exhaust temperature model, block


82


includes model constants A, B, C, D and E thereof, and in embodiments utilizing equation (2), block


82


includes model constants A, B, C and D, as well as the lower heating value of fuel constant LHV, thereof. Block


24


′ further includes an exhaust temperature limit block


84


having an exhaust temperature limit value (T


EL


) stored therein, wherein block


84


is operable to supply T


EL


to the fueling parameter limit determination block


80


. Preferably, T


EL


is a programmable value, and in any case represents a maximum aIlowable limit for the engine exhaust temperature.




In accordance with the present invention, the fueling parameter limit determination block


80


is responsive to the various input signals and values to compute a limited start-of-injection value (SOI


L


) based on either of the engine exhaust temperature estimation models represented in equations (1) and (2), and to provide the SOI


L


value along with the mass fuel flow value FF to a fueling determination block


86


. Fueling determination block


86


is responsive to the SOI


L


and FF values to compute an exhaust temperature-limited fueling command value (FC


ETL


), using known equations therefore, and to provide FC


ETL


to the MIN block


38


of FIG.


1


.




In the embodiment illustrated in

FIG. 3

, the exhaust temperature fueling limiter block


24


′ is operable to limit the default start-of-injection value SOI to a limited value SOI


L


, based on a desired exhaust temperature limit value T


EL


and on either of the engine exhaust temperature estimation models represented by equations (1) and (2). The SOI


L


value and the mass fuel flow value FF are then recombined at the fueling determination block


86


to produce the exhaust temperature-limited fueling command value FC


ETL


. The minimum value of the exhaust temperature-limited fueling command FC


ETL


and the default fueling command DFC is produced by control circuit


20


as the final fueling command FFC on signal path


42


. The fuel system


40


is responsive to the final fueling command FFC to correspondingly supply fuel to engine


12


, and the temperature of engine exhaust is thereby limited to a maximum value of T


EL


.




Referring now to

FIG. 4

, one preferred embodiment of a software algorithm


100


for carrying out the concepts illustrated and described with. respect to

FIG. 3

, is shown. Algorithm


100


begins at step


102


, and thereafter at step


104


the fueling parameter limit determination block


80


is operable to determine ESP and IMT (and optionally IMP) from the respective sensors, and to determine the model constants from block


82


. In embodiments utilizing the engine exhaust temperature estimate model of equation (1), the model constants preferably include constants A, B, C, D and E thereof. Conversely, in embodiments utilizing,the engine exhaust temperature estimate model of equation (2), the model constants preferably include constants A, B, C and D, as well as the lower heating value of fuel constant LHV thereof. In any case, algorithm execution advances from step


104


to step


106


where block


80


is operable to receive the mass charge flow value ECF either from a charge flow estimation algorithm such as that illustrated in

FIG. 2

, or from a mass air flow sensor such as sensor


44


shown in phantom in FIG.


1


. Algorithm execution advances from step


106


to step


108


where the fueling parameter limit determination block


800


is operable to determine the default mass fuel flow value FF. In one embodiment, block


80


is operable at step


106


to receive FF directly from the default fueling determination block


34


as shown in phantom in FIG.


3


. Alternatively, block


80


may be operable at step


106


to receive the default fueling value DFC from block


34


and compute FF therefrom using known techniques therefore. Thereafter at step


110


, the fueling parameter limit determination block


80


is operable to determine an exhaust temperature limit T


EL


, preferably by receiving T


EL


from block


84


.




Following step


110


, algorithm execution advances to step


112


where the fueling parameter limit determination block


80


is operable to determine the start-of-injection limit SOI


L


as a function of the various input signals and values thereto. In embodiments where the engine exhaust temperature is estimated in accordance with equation (1), the estimated exhaust temperature value ETE is preferably replaced with the exhaust temperature limit T


EL


, and equation (1) is solved for SOI


L


, resulting in the equation:








SOI




L




={T




EL




−IMT−A−C


/(


ECF/FF


)−


E/[ESP*


(


ECF/FF


)]}/(


B+D/ESP


)  (3).






In embodiments where the engine exhaust temperature is estimated in accordance with equation (2), the estimated exhaust temperature value ETE is preferably replaced with the exhaust temperature limit T


EL


, and equation (2) is solved for SOI


L


, resulting in the equation:








SOI




L


={[(


T




EL




−IMT


)/(


C*LHV


)]*(


ECF/FF


)}−(


A*ESP


)/


C−


(


B*IMP


)/


C−D/C


  (4).






In either case, algorithm execution advances from step


112


to step


114


where block


86


is operable to determine an exhaust temperature-limited fueling command FC


ETL


as a function of FF and SOI


L


, using known techniques therefore. Thereafter at step


116


, control circuit


20


is operable to limit the final fueling command FFC to a fueling command no greater than FC


ETL


to thereby limit the actual engine exhaust temperature to values no greater than T


EL


. Algorithm execution advances from step


116


to step


118


where algorithm


100


is returned to its calling routine.




As an alternative to controlling the final fueling command FFC as a function of a start-of-injection limit value SOI


L


as just described, the present invention contemplates instead limiting FFC as a function of a mass fuel flow limit value FF


L


. Referring to

FIG. 5

, an alternate embodiment


24


″ of the exhaust temperature fueling determination block


24


, in accordance with the present invention, is therefore shown wherein block


24


″ is operable to compute the exhaust temperature-limited fueling command FC


ETL


as a function of a mass fuel-flow limit FF


L


and of the default start-of-injection value SOI. In the embodiment of block


24


″ illustrated in

FIG. 5

, a fueling parameter limit determination block


150


receives input signals ESP and IMT (and optionally IMP) from associated sensors described with respect to FIG.


1


. Block


150


also receives the mass charge flow value ECF either from the estimation algorithm described with respect to

FIG. 2

or from a mass air flow sensor as described with respect to

FIG. 1

, and further receives either the default fueling command value (DFC) or the start-of-injection value (SOI) from the default fueling determination block


34


. In one preferred embodiment, block


150


is operable to determine the start-of-injection value SOI from the default fueling command DFC in accordance with known techniques, and in this embodiment block


150


is thus configured to receive DFC from block


34


. Alternatively, as shown in phantom in

FIG. 5

, block


34


may be configured to supply SOI directly to block


150


in which case the default fueling command DFC need not be provided.




Block


24


″ further includes a model constants block


152


having the various model constants stored therein, wherein block


152


is operable to provide such constants to block


150


. In embodiments utilizing equation (1) as the engine exhaust temperature model, block


152


includes model constants A, B, C, D and E thereof, and in embodiments utilizing equation (2), block


152


includes model constants A, B, C and D, as well as the lower heating value of fuel constant LHV, thereof. Like block


24


′ of

FIG. 3

, block


24


″ further includes an exhaust temperature limit block


154


having an exhaust temperature limit value (T


EL


) stored therein, wherein block


154


is operable to supply T


EL


to the fueling parameter limit determination block


150


. Preferably, T


EL


is a programmable value, and in any case represents a maximum allowable limit for the engine exhaust temperature.




In accordance with the present invention, the fueling parameter limit determination block


150


is responsive to the various input signals and values to compute a limited mass fuel flow value (FF


L


) based on either of the engine exhaust temperature estimation models represented in equations (1) and (2), and to provide the FF


L


value along with the default start-of-injection value SOI to a fueling determination block


156


. Fueling determination block


156


is responsive to the FF


L


and SOI values to compute an exhaust temperature-limited fueling command value (FC


ETL


), using known equations therefore, and to provide FC


ETL


to the MIN block


38


of FIG.


1


.




In the embodiment illustrated in

FIG. 5

, the exhaust temperature fueling limiter block


24


″ is operable to limit the default mass fuel flow value FF to a limited value FF


L


, based on a desired exhaust temperature limit value T


EL


and on either of the engine exhaust temperature estimation models represented by equations (1) and (2). The FF


L


value and the start-of-injection value SOI are then recombined at the fueling determination block


156


to produce the exhaust temperature-limited fueling command value FC


ETL


. The minimum value of the exhaust temperature-limited fueling command FC


ETL


and the default fueling command DFC is produced by control circuit


20


as the final fueling command FFC on signal path


42


. The fuel system


40


is responsive to the final fueling command FFC to correspondingly supply fuel to engine


12


, and the temperature of engine exhaust is thereby limited to a maximum value of T


EL


.




Referring now to

FIG. 6

, one preferred embodiment of a software algorithm


200


for carrying out the concepts illustrated and described with respect to

FIG. 5

, is shown. Algorithm


200


begins at step


202


, and thereafter at step


204


the fueling parameter limit determination block


150


is operable to determine ESP and IMT (and optionally IMP) from the respective sensors, and to determine the model constants from block


152


. In embodiments utilizing the engine exhaust temperature estimate model of equation (1), the model constants preferably include constants A, B, C, D and E thereof. Conversely, in embodiments utilizing the engine exhaust temperature estimate model of equation (2), the model constants preferably include constants A, B, C and D, as well as the lower heating value of fuel constant LHV thereof. In any case, algorithm execution advances from step


204


to step


206


where block


150


is operable to receive the mass charge flow value ECF either from a charge flow estimation algorithm such as that illustrated in

FIG. 2

, or from a mass air flow sensor such as sensor


44


shown in phantom in FIG.


1


. Algorithm execution advances from step


206


to step


208


where the fueling parameter limit determination block


150


is operable to determine the default start-of-injection value SOI. In one embodiment, block


150


is operable at step


206


to receive SOI directly from the default fueling determination block


34


as shown in phantom in FIG.


5


. Alternatively, block


150


may be operable at step


206


to receive the default fueling value DFC from block


34


and compute SOI therefrom using known techniques therefore. Thereafter at step


210


, the fueling parameter limit determination block


150


is operable to determine an exhaust temperature limit T


EL


, preferably by receiving T


EL


from block


154


.




Following step


210


, algorithm execution advances to step


212


where the fueling parameter limit determination block


150


is operable to determine the mass fuel flow limit FF


L


as a function of the various input signals and values thereto. In embodiments where the engine exhaust temperature is estimated in accordance with equation (1), the estimated exhaust temperature value ETE is preferably replaced with the exhaust temperature limit T


EL


, and equation (1) is solved for FF


L


, resulting in the equation:








FF




L




=[T




EL




−IMT−A−B/SOI−


(


D*SOI


)/


ESP]/[


(


C*ESP


)+


E]/ECF


  (5).






In embodiments where the engine exhaust temperature is estimated in accordance with equation (2), the estimated exhaust temperature value ETE is preferably replaced with the exhaust temperature limit T


EL


, and equation (2) is solved for FF


L


, resulting in the equation:








FF




L


=(


IMT*ECF


)


/T




EL


+[(


A*ESP


)+(


B*IMP


)+(


C*SOI


)+


D]


(


ECF*LHV


)/


T




EL


  (6).






In either case, algorithm execution advances from step


212


to step


214


where block


156


is operable to determine an exhaust temperature-limited fueling command FC


ETL


as a function of SOI and FF


L


, using known techniques therefore. Thereafter at step


216


, control circuit


20


is operable to limit the final fueling command FFC to a fueling command no greater than FC


ETL


to thereby limit the actual engine exhaust temperature to values no greater than T


EL


. Algorithm execution advances from step


216


to step


218


where algorithm


200


is returned to its calling routine.




While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only preferred embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. For example, while the invention has been illustrated and described as limiting a final engine fueling command (FFC) by computing either a start-of-injection limit (SOI


L


) or a mass fuel flow limit (FF


L


) and using the default value for the remaining parameter, the present invention contemplates embodiments of the present invention wherein FFC is limited. by computing both SOI


L


and FF


L


. As a specific example, an alternate embodiment of the present invention may use a default value for a third fueling parameter that goes into the final fueling calculation (e.g., peak cylinder pressure). In this case, two fuel limiting equations are then solved for the two unknown parameters SOI


L


and FF


L


.



Claims
  • 1. A system for controlling exhaust temperature of an internal combustion engine, comprising:a temperature sensor producing a temperature signal (IMT) corresponding to a temperature of an intake manifold of said engine; an engine speed sensor producing an engine speed signal (ESP) corresponding to a rotational speed of said engine; means for determining a charge flow value (ECF) corresponding to a mass flow of charge entering said intake manifold; and a control circuit producing a fueling command for fueling said engine, said control circuit controlling engine exhaust temperature (TE) by limiting said fueling command based on said temperature signal, said engine speed signal and said charge flow value.
  • 2. The system of claim 1 further including a memory unit having a maximum exhaust temperature limit (TEL) stored therein;and wherein said control circuit is operable limit said fueling command further based on said maximum exhaust temperature limit so as to maintain engine exhaust temperature below said maximum exhaust temperature limit.
  • 3. The system of claim 2 wherein said control circuit is operable to determine start of injection (SOI) and mass fuel flow (FF) values corresponding to said fueling command;and wherein said control circuit is operable to limit said fueling command by limiting said start of injection value further based on said mass fuel flow value.
  • 4. The system of claim 3 wherein said memory unit further includes a number of model constants stored therein;and wherein said control circuit is operable to limit said fueling command further based on said model constants.
  • 5. The system of claim 4 wherein said control circuit is operable to compute a limited start of injection value (SOIL) according to:SOIL={TEL−IMT−A−C/(ECF/FF)−E/[ESP*(ECF/FF)]}/(B+D/ESP); wherein A, B, C, D and E correspond to said model constants.
  • 6. The system of claim 5 wherein said control circuit is operable to limit said fueling command by producing an exhaust temperature-limited fueling command based on said limited start of injection value and on said mass fuel flow value.
  • 7. The system of claim 6 further including a fuel system responsive to said exhaust temperature-limited fueling command to supply fuel to said engine.
  • 8. The system of claim 2 wherein said control circuit is operable to determine start of injection (SOI) and mass fuel flow (FF) values corresponding to said fueling command;and wherein said control circuit is operable to limit said fueling command by limiting said mass fuel flow value further based on said start of injection value.
  • 9. The system of claim 8 wherein said memory unit further includes a number of model constants stored therein;and wherein said control circuit is operable to limit said fueling command further based on said model constants.
  • 10. The system of claim 9 wherein said control circuit is operable to compute a limited mass fuel flow value (FFL) according to:FFL=[TEL−IMT−A−B/SOI−(D*SOI)/ESP]/[(C*ESP)+E]/ECF; wherein A, B, C, D and E correspond to said model constants.
  • 11. The system of claim 10 wherein said control circuit is operable to limit said fueling command by producing an exhaust temperature-limited fueling command based on said limited mass fuel flow value and on said start of injection value.
  • 12. The system of claim 11 further including a fuel system responsive to said exhaust temperature-limited fueling command to supply fuel to said engine.
  • 13. The system of claim 1 further including a pressure sensor producing a pressure signal (IMP) corresponding to intake manifold pressure;and wherein said control circuit is operable to control engine exhaust temperature by limiting said fueling command further based on said pressure signal.
  • 14. The system of claim 13 further including a memory unit having a maximum exhaust temperature limit (TEL) stored therein;and wherein said control circuit is operable limit said fueling command further based on said maximum exhaust temperature limit so as to maintain engine exhaust temperature below said maximum exhaust temperature limit.
  • 15. The system of claim 14 wherein said control circuit is operable to determine start of injection (SOI) and mass fuel flow (FF) values corresponding to said fueling command;and wherein said control circuit is operable to limit said fueling command by limiting said start of injection value further based on said mass fuel flow value.
  • 16. The system of claim 15 wherein said memory unit further includes a number of model constants and a lower heating value of fuel constant (LHV) stored therein;and wherein said control circuit is operable to limit said fueling command further based on said model constants and on said lower heating value of fuel constant.
  • 17. The system of claim 16 wherein said control circuit is operable to compute a limited start of injection value (SOIL) according to:SOIL={[(TEL−IMT)/(C*LHV)]*(ECF/FF)}−(A*ESP)/C−(B*IMP)/C−D/C; wherein A, B, C and D correspond to said model constants.
  • 18. The system of claim 17 wherein said control circuit is operable to limit said fueling command by producing an exhaust temperature-limited fueling command based on said limited start of injection value and on said mass fuel flow value.
  • 19. The system of claim 18 further including a fuel system responsive to said exhaust temperature-limited fueling command to supply fuel to said engine.
  • 20. The system of claim 14 wherein said control circuit is operable to determine start of injection (SOI) and mass fuel flow (FF) values corresponding to said fueling command;and wherein said control circuit is operable to limit said fueling command by limiting said mass fuel flow value further based on said start of injection value.
  • 21. The system of claim 20 wherein said memory unit further includes a number of model constants and a lower heating value of fuel constant stored therein;and wherein said control circuit is operable to limit said fueling command further based on said lower heating value of fuel constant and on said model constants.
  • 22. The system of claim 21 wherein said control circuit is operable to compute a limited mass fuel flow value (FFL) according to:FFL=(IMT*ECF)/TEL+[(A*ESP)+(B*IMP)+(C*SOI)+D](ECF*LHV)/TEL; wherein A, B, C, D and E correspond to said model constants.
  • 23. The system of claim 22 wherein said control circuit is operable to limit said fueling command by producing an exhaust temperature-limited fueling command based on said limited mass fuel flow value and on said start of injection value.
  • 24. The system of claim 11 further including a fuel system responsive to said exhaust temperature-limited fueling command to supply fuel to said engine.
  • 25. A method for controlling exhaust temperature of an internal combustion engine, comprising:determining a temperature of an intake manifold of said engine; determining a rotational speed of said engine; determining a mass flow of charge entering said intake manifold; and controlling engine exhaust temperature by limiting a fueling command for fueling said engine based on current values of said temperature, said rotational speed and said mass flow.
  • 26. The method of claim 25 further including the step of determining a start of injection value and a mass fuel flow value corresponding to said fueling command.
  • 27. The method of claim 26 wherein the controlling step further includes limiting said fueling command based on said mass fuel flow value;and wherein the controlling step further includes limiting said fueling command by limiting said start of injection value.
  • 28. The method of claim 26 wherein the controlling step further includes limiting said fueling command based on said start of injection value;and wherein the controlling step further includes limiting said fueling command by limiting said mass fuel flow value.
  • 29. The method of claim 25 further including the step of determining a pressure within said intake manifold;and wherein the controlling step further includes limiting said fueling command based on a current value of said pressure.
  • 30. The method of claim 29 further including the step of determining a start of injection value and a mass fuel flow value corresponding to said fueling command.
  • 31. The method of claim 30 wherein the controlling step further includes limiting said fueling command based on said mass fuel flow value;and wherein the controlling step further includes limiting said fueling command by limiting said start of injection value.
  • 32. The method of claim 30 wherein the controlling step further includes limiting said fueling command based on said start of injection value;and wherein the controlling step further includes limiting said fueling command by limiting said mass fuel flow value.
  • 33. The method of claim 25 wherein the step of controlling engine exhaust temperature includes limiting said fueling command further based on a maximum engine exhaust temperature limit so as to maintain said engine exhaust temperature below said maximum engine exhaust temperature limit.
  • 34. The method of claim 33 further including the step of retrieving said maximum engine exhaust temperature limit from a memory unit.
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