U.S. patent application number 11/112444 was filed with the patent office on 2006-10-26 for intake oxygen estimator for internal combustion engine.
Invention is credited to Anupam Gangopadhyay.
Application Number | 20060241849 11/112444 |
Document ID | / |
Family ID | 37037365 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060241849 |
Kind Code |
A1 |
Gangopadhyay; Anupam |
October 26, 2006 |
INTAKE OXYGEN ESTIMATOR FOR INTERNAL COMBUSTION ENGINE
Abstract
An internal combustion engine system includes an intake
manifold, a combustion chamber, an exhaust manifold and exhaust gas
recirculation apparatus for recirculating a portion of the
exhausted gases from the exhaust manifold to the intake manifold.
An estimate intake manifold oxygen concentration is determined from
the air fraction within the intake manifold which is determined
from an engine system model that provides interdependent air mass
fractions at various locations within the engine system.
Inventors: |
Gangopadhyay; Anupam; (Troy,
MI) |
Correspondence
Address: |
GENERAL MOTORS CORPORATION;LEGAL STAFF
MAIL CODE 482-C23-B21
P O BOX 300
DETROIT
MI
48265-3000
US
|
Family ID: |
37037365 |
Appl. No.: |
11/112444 |
Filed: |
April 22, 2005 |
Current U.S.
Class: |
701/108 |
Current CPC
Class: |
F02D 2200/0406 20130101;
F02D 41/0072 20130101; F02B 37/24 20130101; F02D 41/1454 20130101;
F02D 2200/0814 20130101; F02D 41/0007 20130101; F02D 41/1401
20130101; F02D 41/182 20130101; F02D 2200/0402 20130101 |
Class at
Publication: |
701/108 |
International
Class: |
F02D 41/00 20060101
F02D041/00 |
Claims
1. Method for estimating oxygen concentration at points within an
internal combustion engine system including a combustion chamber,
an exhaust manifold, an intake manifold and exhaust gas
recirculation apparatus for variable recirculation of exhaust gases
from the exhaust manifold to the intake manifold, comprising
reticulating the engine system into a plurality of interconnected
engine sub-systems; modeling the interconnected engine sub-systems
to provide interdependent air mass fractions at predetermined
points within the internal combustion engine; and estimating oxygen
concentration at said predetermined points within the internal
combustion engine as a function of the respective modeled air mass
fractions at said predetermined points.
2. The method for estimating oxygen concentration as claimed in
claim 1 wherein modeling interdependent air mass fractions at
predetermined points within the internal combustion engine includes
modeling the air mass fraction at the combustion chamber exhaust
mass flow from an empirically determined data set correlating
combustion chamber air mass fraction to a plurality of engine
operating parameters.
3. The method for estimating oxygen concentration as claimed in
claim 2 wherein said plurality of engine operating parameters
comprises engine speed, fuel mass flow, combustion timing, intake
manifold pressure, exhaust manifold pressure, intake manifold
temperature and intake manifold air fraction.
4. Method for estimating oxygen concentration in an intake manifold
of an internal combustion engine system including an exhaust
manifold and exhaust gas recirculation apparatus for variable
recirculation of exhaust gases from the exhaust manifold to the
intake manifold, comprising reticulating the engine system into a
plurality of interconnected engine sub-systems including an intake
manifold, an exhaust manifold, an exhaust gas recirculation
apparatus and combustion chambers; identifying all significant mass
flows corresponding to said engine sub-systems including combustion
chamber exhaust mass flow; identifying all significant pressure
nodes corresponding to said engine sub-systems including the intake
manifold and exhaust manifold; modeling interdependent air mass
fractions at a) the identified pressure nodes including the air
mass fraction at the intake manifold, and b) the combustion chamber
exhaust mass flow; and estimating oxygen concentration in the
intake manifold as a function of the modeled air mass fraction at
the intake manifold.
5. The method for estimating oxygen concentration as claimed in
claim 4 wherein engine sub-systems include intake pressure boost
apparatus.
6. The method for estimating oxygen concentration as claimed in
claim 4 wherein: modeling interdependent air mass fractions at the
identified pressure nodes includes modeling the air mass fraction
at the exhaust manifold; and modeling the air mass fraction at the
intake manifold includes determining recirculated exhaust gas mass
flow and determining recirculated exhaust gas air mass flow based
on the recirculated exhaust gas mass flow and the air mass fraction
at the exhaust manifold.
7. The method for estimating oxygen concentration as claimed in
claim 4 wherein: modeling the air mass fraction at the combustion
chamber exhaust mass flow includes factoring a combustion transport
delay.
8. The method for estimating oxygen concentration as claimed in
claim 6 wherein: determining recirculated exhaust gas mass flow
includes factoring an exhaust gas recirculation transport
delay.
9. The method for estimating oxygen concentration as claimed in
claim 6 wherein: modeling the air mass fraction at the combustion
chamber exhaust mass flow includes factoring a combustion transport
delay; and determining recirculated exhaust gas mass flow includes
factoring an exhaust gas recirculation transport delay.
10. Control system for an internal combustion engine including a
combustion chamber, an exhaust manifold, an intake manifold and
exhaust gas recirculation apparatus for variable recirculation of
exhaust gases from the exhaust manifold to the intake manifold,
comprising: means for providing respective measures of a plurality
of engine operating parameters; a microprocessor based controller
including computer code stored in a storage medium for applying the
engine operating parameter measures to a model to estimate
interdependent air mass fractions at locations within the internal
combustion engine; and at least one actuator controlled in response
to at least one of said interdependent air mass fractions.
11. The control system as claimed in claim 10 wherein one of said
interdependent air mass fractions is estimated at the intake
manifold and said at least one actuator comprises an intake boost
control actuator.
12. The control system as claimed in claim 10 wherein one of said
interdependent air mass fractions is estimated at the intake
manifold and said at least one actuator comprises an exhaust gas
recirculation actuator.
13. The control system as claimed in claim 11 wherein said intake
boost control actuator comprises a variable geometry turbocharger
actuator.
14. The control system as claimed in claim 11 wherein said intake
boost control actuator comprises a variable nozzle turbocharger
actuator.
Description
TECHNICAL FIELD
[0001] The present invention is related to lean burn internal
combustion engines. More particularly, the invention is concerned
with estimations of intake manifold gas composition.
BACKGROUND OF THE INVENTION
[0002] Most of the time a diesel engine operates significantly lean
of stoichiometry wherein gases expelled from the combustion
chambers are characterized by excess oxygen. Richer air/fuel ratios
may be controlled during brief periods for the purposes of
particulate or oxides of nitrogen (NOx) trap regenerations where
such apparatus are utilized as part of the engine emission control
system. Diesel engines may also use exhaust gas recirculation (EGR)
in the emission controls to reduce the NOx produced in the diesel
engine's combustion process by lowering the effective combustion
temperature and reducing the oxygen component of the cylinder
charge.
[0003] Oxygen concentration in the intake manifold is a key
parameter in controlling the make up of the exhaust gases expelled
from a combustion chamber. Exhaust gases recirculated back into the
intake manifold will vary the oxygen concentration in the intake
manifold and, in turn, the oxygen concentration in the intake
manifold will affect the oxygen concentration in the combustion
chambers established during cylinder filling periods. Therefore,
the total pre-combustion trapped charge within the combustion
chamber may contain different amounts of oxygen depending on the
prevailing intake concentration of oxygen during the cylinder
filling period. The amount of oxygen affects both the amount of
fuel that can be injected before unacceptable levels of particulate
emissions (i.e. smoke) are produced and the level of NOx
production.
[0004] Combustion controls which rely upon post-combustion oxygen
sensing are generally satisfactory for managing steady state or
slowly varying oxygen levels. EGR dynamics are therefore limited by
the effectiveness of such controls in accounting for rapid changes
in EGR levels. Additional factors including intake temperature and
pressure also affect the oxygen levels. Intake boosting, such as by
turbocharging or supercharging, also have limited dynamics in
accordance with the effectiveness of such controls in accounting
for rapid changes in boost levels.
[0005] Ideally, pre-combustion oxygen sensing in the intake
manifold would alleviate much of the dynamic limitations mentioned
by providing substantially instantaneous intake oxygen
concentration measurements thus accounting for rapid changes in EGR
concentrations and intake boost pressures. However, known wide
range oxygen sensing technologies are effective at substantially
elevated temperatures. Whereas they work well in a high temperature
exhaust environment, substantial heat would need to be added
thereto to achieve light-off in the much cooler intake environment.
A supplemental electrical heater would likely result in an
unacceptably high power consumption penalty. Also, known wide range
oxygen sensing technologies are effective at substantially ambient
pressure levels and require proper pressure compensation to produce
accurate oxygen concentration information.
SUMMARY OF THE INVENTION
[0006] This invention enables the estimation of instantaneous
levels of oxygen at various locations within an internal combustion
engine system that uses exhaust gas recirculation, including within
the intake manifold. A real-time, transient-responsive model of the
internal combustion engine includes interdependent sub-system
models effective to estimate air or oxygen fractions at various
locations within the system including at combustion chamber exhaust
ports and intake and exhaust manifolds.
[0007] An internal combustion engine system includes a combustion
chamber, an exhaust manifold, an intake manifold and exhaust gas
recirculation apparatus for variable recirculation of exhaust gases
from the exhaust manifold to the intake manifold. A method for
estimating oxygen concentration at points within the internal
combustion engine system includes reticulating the engine system
into a plurality of interconnected engine sub-systems. The
interconnected engine sub-systems are modeled to provide
interdependent air mass fractions at predetermined points within
the internal combustion engine. Oxygen concentration at the
predetermined points within the internal combustion engine are then
estimated as a function of the respective modeled air mass
fractions at said predetermined points. Preferably, an empirically
determined data set correlating combustion chamber air mass
fraction to a plurality of engine operating parameters is used to
model the air mass fraction at the combustion chamber exhaust port.
Engine speed, fuel mass flow, combustion timing, intake manifold
pressure, exhaust manifold pressure, intake manifold temperature
and intake manifold air fraction are among the engine operating
parameters used in the empirical determination of the data set.
[0008] A method for estimating oxygen concentration in the intake
manifold of an internal combustion engine includes reticulating the
engine system into a plurality of interconnected engine sub-systems
including an intake manifold, an exhaust manifold, an exhaust gas
recirculation apparatus and combustion chambers. All significant
mass flows corresponding to the engine sub-systems are identified,
including combustion chamber exhaust mass flows. Similarly, all
significant pressure nodes corresponding to the engine sub-systems
are identified, including the intake manifold and the exhaust
manifold. Interdependent air mass fractions at the identified
pressure nodes, including at the intake manifold, and at the
combustion chamber exhaust mass flow are modeled. Oxygen
concentration in the intake manifold is then estimated as a
function of the modeled air mass fraction at the intake manifold.
The engine sub-systems may further include intake pressure boost
apparatus such as turbochargers and superchargers. The modeling of
the interdependent air mass fractions at the identified pressure
nodes may further include modeling of the air mass fraction at the
exhaust manifold and the modeling of the air mass fraction at the
intake manifold may include determining recirculated exhaust gas
mass flow and determining recirculated exhaust gas air mass flow
based on the recirculated exhaust gas mass flow and the air mass
fraction at the exhaust manifold. Combustion transport delay is
preferably accounted for in the modeling of the air mass fraction
at the combustion chamber exhaust mass flow, and exhaust gas
recirculation transport delay is preferably accounted for in the
determination of recirculated exhaust gas mass flow.
[0009] A control system for an internal combustion engine includes
means for providing respective measures of a plurality of engine
operating parameters and a microprocessor based controller includes
computer code stored in a storage medium for applying the engine
operating parameter measures to a model to estimate interdependent
air mass fractions at locations within the internal combustion
engine. The control system further includes at least one actuator
controlled in response to at least one of the interdependent air
mass fractions. One of the interdependent air mass fractions is
estimated at the intake manifold and an actuator may comprise an
intake boost control actuator (e.g. variable geometry turbocharger,
variable nozzle turbocharger) or an exhaust gas recirculation
actuator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0011] FIG. 1 is a schematic illustration of an internal combustion
engine system and engine controller in accordance with one
embodiment of the present invention;
[0012] FIG. 2 is a schematic illustration of a model the engine
system shown in FIG. 1 reticulated into engine sub-systems;
[0013] FIG. 3A is a schematic illustration of an exhaust manifold
sub-system model including inputs and outputs in accordance with
the present invention;
[0014] FIG. 3B is a schematic illustration of a combustion chamber
sub-system model including inputs and outputs in accordance with
the present invention;
[0015] FIG. 3C is a schematic illustration of an intake manifold
sub-system model including inputs and outputs in accordance with
the present invention;
[0016] FIG. 3D is a schematic illustration of an EGR and cooler
sub-system model including inputs and outputs in accordance with
the present invention;
[0017] FIG. 3E is a schematic illustration of a turbocharger and
intercooler sub-system model including inputs and outputs in
accordance with the present invention;
[0018] FIG. 4 is a proportional-integral control for providing a
closed loop correction term to the EGR and cooler model in
accordance with the present invention; and
[0019] FIG. 5 is a proportional-integral control for providing a
closed loop correction term to the combustion chamber model in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] A preferred embodiment will now be described in conjunction
with application of the present invention to a turbocharged diesel
engine system, generally labeled 10 in FIG. 1. The diesel engine
system includes engine 11 having intake manifold 13 and exhaust
manifold 15, each of which includes a plurality of runners (not
separately labeled) corresponding in number to the number of
individual cylinders of the engine 11. Intake air at substantially
atmospheric pressure is ingested at intake 33. Conventional mass
airflow sensor (MAF) 31 is coupled to the flow of ingested air
upstream from air-cooled turbocharger 29 for providing a signal
indicative of the mass flow rate of inducted air. Turbocharger 29
is adapted to provide a variable boost pressure for a given exhaust
flow in accordance with well known variable vane geometry or
variable nozzle geometry, commonly referred to as variable geometry
turbocharger (VGT) and variable nozzle turbocharger (VNT),
respectively. Further reference to turbocharger is consistent with
VNT 29 and the particular embodiment of the invention utilizing a
variable nozzle turbocharger. Other boost technologies, including
conventional and wastegate turbochargers, compounded and two-stage
turbochargers and superchargers, for example, may be used in
practicing the present invention. The airflow is compressed by
turbocharger 29 and provided to intercooler 25. Further downstream
is conventional electrically controllable intake throttle valve
(ITV) which may take the form of a stepper motor controlled
butterfly valve or other actuator/valve combination adequate for
varying the intake restriction. Continuing downstream is
conventional manifold absolute pressure (MAP) sensor 17 for
providing a pressure signal therefrom. Exhaust gases are expelled
from individual cylinders to a corresponding plurality of runners
(not separately labeled) and into exhaust-manifold 15. Exhaust
gases are channeled from the exhaust manifold to drive the turbine
of turbocharger 29 and thereafter finally exhausted through exhaust
line 27 to atmosphere subsequent to passing through exhaust gas
after treatment devices 28 such as NOx traps, catalytic treatment
devices, particulate filters and various combinations thereof.
Downstream of the turbine is conventional wide range air-fuel
(WRAF) sensor 30 for providing an oxygen content signal therefrom.
Also, after the exhaust manifold but preceding the turbocharger, a
portion of exhaust gas flow is directed through an exhaust gas
recirculation path to conventional exhaust gas cooler 21 and
electrically controllable exhaust gas recirculation (EGR) valve 19,
typically but not necessarily, a solenoid-actuated pintle valve or
a DC motor driven valve. The flow through the exhaust gas
recirculation path continues downstream of EGR valve 19 to be mixed
with the fresh intake air flow to establish the ingested cylinder
charge gas mix.
[0021] Integral to the implementation of the present invention and
the engine system is a conventional microprocessor based engine or
powertrain control module (ECM) 12 comprising such common elements
as microprocessor, read only memory ROM, random access memory RAM,
electrically programmable read only memory EPROM, high speed clock,
analog to digital (A/D) and digital to analog (D/A) circuitry,
input/output circuitry and devices (I/O), and appropriate signal
conditioning and buffer circuitry. ECM 12 is shown in FIG. 1 having
a plurality of sensor inputs utilized in the present invention and
which may be used in other engine control routines including engine
speed (N.sub.eng), turbocharger shaft speed (.omega..sub.shaft),
mass airflow (MAFI), manifold absolute pressure (MAP), EGR valve
position (EGR.sub.pos), VNT position (VNT.sub.pos), ambient air
temperature (T.sub.amb), ambient pressure (P.sub.amb) from
barometric pressure sensor (BARO), engine coolant temperature
(T.sub.engcoolant) and oxygen content from WRAF sensor.
[0022] ECM 12 includes non-volatile memory storing program
instruction code for implementing the present invention including
code for implementing the engine system model comprising the
various sub-system models. The model determines, in accordance with
the present invention, the oxygen concentration at predetermined
points within the internal combustion engine system. One such point
within the system having particular utility is at the intake to the
combustion chamber. The oxygen concentration within the intake
manifold substantially approximates the intake oxygen concentration
assuming reasonably homogenous mixing of intake mass flows and
volume displacement intake runner dynamics. The intake manifold
oxygen concentration is used in conjunction with known intake boost
controls (VNT position) or EGR controls (EGR position) to maintain
the trapped oxygen to predetermined set-points.
[0023] Having thus described a preferred engine system for
implementation of the present invention, additional reference is
now made to the remaining FIGS. 2 through 5. Generally, the engine
system 10 is reticulated into interconnected sub-systems in
establishing system model 50 as shown in FIG. 2. System model 50
comprehends, at a minimum, sub-system models of the intake manifold
51, combustion chambers 53, exhaust manifold 55 and exhaust gas
recirculation apparatus 57. Additionally as appropriate, sub-system
modeling of intake boost apparatus such as the turbocharger and
intercooler 59 is comprehended in the system model 50.
Interconnections between the various sub-system models 51-59 are
shown by solid lines and correspond to various model interactions
and interdependencies of model parameters related to sub-system
pressures, temperatures and mass flows, for example.
[0024] The specific sub-system models corresponding to the
reticulated engine system 10 are now presented in the various FIGS.
3A through 3E. Beginning first with the exhaust manifold model 55,
FIG. 3A illustrates along the left side of the model block a
plurality of model inputs. Graphically, model inputs that are not
provided by other model interdependencies are designated by a
diamond and may include, for example, various sensed, derived or
control quantities of utility in engine controls such as shaft
speeds, actuator positions, temperatures, etc. Other quantities
used by the models include various calibrations and constants which
may appear in more detail in the various modeling equations set
forth in further detail herein below. However, such calibrations
and constants are not generally shown in the corresponding model
figures. FIG. 3A also illustrates along the top side of the model
block a plurality of model outputs. The model outputs provide
inputs to other of the sub-system models as will become apparent
with additional description and reference to additional figures.
The exhaust manifold is a significant pressure node in the engine
system characterized by significant volume and significant mass
flows into and out of the manifold. The exhaust manifold model 55
utilizes the significant mass flows associate with the exhaust
manifold and thermal inputs in describing the temperature and
pressure associated with the exhaust manifold gas mass. The
significant mass flows are identified as those into the exhaust
manifold from the combustion chamber exhaust, and those out of the
exhaust manifold comprising the EGR flow and the remainder
exhausted to atmosphere. In the present example, the remainder
exhausted to atmosphere is the turbocharger turbine mass flow used
to drive the turbocharger. The following algebraic and differential
modeling equations describe the exhaust manifold: d m em d t = m
.cndot. ex - m .cndot. egr - m .cndot. t ( 1 ) d P em d t = R em c
v em .times. V em .function. [ m .cndot. ex .times. T ex .times. c
p ex - ( m .cndot. egr + m .cndot. t ) .times. T em .times. c p em
- Q .cndot. em ] ( 2 ) Q .cndot. em = h tem .times. A em .function.
( T em - T amb ) ( 3 ) T em = P em .times. V em m em .times. R em (
4 ) ##EQU1## [0025] where m.sub.em is the resident mass in the
exhaust manifold, [0026] .sub.ex is the exhaust mass flow from the
combustion chambers, [0027] .sub.egr is the EGR mass flow, [0028]
.sub.t is the turbocharger turbine mass flow, [0029] P.sub.em is
the exhaust manifold pressure, [0030] R.sub.em is the gas constant
for exhaust manifold conditions, [0031] c.sub.v.sub.em is the
specific heat at constant volume for the exhaust manifold, [0032]
V.sub.em is the exhaust manifold volume, [0033] T.sub.ex is the
mass averaged exhaust port flow temperature, [0034] c.sub.p.sub.ex
is the specific heat at constant pressure exhaust port flow
conditions, [0035] T.sub.em is the exhaust manifold temperature,
[0036] c.sub.p.sub.em is the specific heat at constant pressure
exhaust manifold conditions, [0037] .sub.em is the exhaust manifold
heat loss rate, [0038] h.sub.tem is the heat transfer coefficient
for the exhaust manifold, [0039] A.sub.em is the heat transfer area
for the exhaust manifold, and [0040] T.sub.amb is the ambient
temperature. The ambient temperature, T.sub.amb, is preferably
provided by conventional temperature sensing apparatus adapted to
provide a measure of outside air temperature.
[0041] The exhaust manifold is more particularly described in
accordance with air mass fractions as described in the following
algebraic and differential modeling equations: d m em air d t = m
.cndot. ex .times. f air ex - ( m .cndot. t + m .cndot. egr )
.times. f air em ( 5 ) f air em = m em air m em ( 6 ) ##EQU2##
[0042] where m em air ##EQU3## [0043] is the resident air mass in
the exhaust manifold, f air ex ##EQU4## [0044] is the fraction of
air in the combustion chamber exhaust port flow, and f air em
##EQU5## [0045] is the fraction of air in the exhaust manifold.
[0046] The combustion chamber model 53 is illustrated in FIG. 3B
wherein a plurality of model inputs appear along the left side of
the model block and a plurality of model outputs are illustrated
along the top side of the model block. The combustion chambers are
pumping apparatus for effecting mass flow by way of the combustion
forces produced therein and a source of heat added to the exhausted
gases. Combustion chamber model 53 utilizes mass flows associated
with the combusted fuel, thermal input associated with the ingested
intake gases, pressures associated with the intake and exhaust
manifolds and combustion timing in describing the intake and
exhaust port mass flows and the temperature associated with the
exhaust manifold gas mass. The following modeling equations
describe the combustion chambers:
=F.sub.engflow(N,,P.sub.im,T.sub.im,P.sub.em) (7)
.sub.ex=(.sub.o+.sub.f)(t-.tau..sub.comb) (8)
T.sub.ex=F.sub.engtemp(N,.sub.f,SOI,P.sub.im,T.sub.im,P.sub.em) (9)
[0047] where .sub.o is the mass flow into the combustion chambers,
[0048] F.sub.engflow(.circle-solid.) is a map modeling volumetric
efficiency, [0049] N is engine rotational speed, [0050] .sub.f is
fuel flow rate, [0051] P.sub.im is the intake manifold pressure,
[0052] T.sub.im is the intake manifold temperature, [0053] P.sub.em
is the exhaust manifold pressure, [0054] .sub.ex is the exhaust
mass flow from the combustion chambers, [0055] t is time, [0056]
.tau..sub.comb is the combustion cycle delay, [0057] T.sub.ex is
the mass averaged exhaust port flow temperature, [0058]
F.sub.engtemp(.circle-solid.) is a map modeling engine temperature
rise, and [0059] SOI is the fuel injector timing. The fuel flow
rate, .sub.f, is provided by the ECM in accordance with it engine
control routines. The maps modeling volumetric efficiency,
F.sub.engflow(.circle-solid.), and engine temperature rise,
F.sub.engtemp(.circle-solid.), are preferably provided in stored
data sets within the engine controller and are constructed using
empirically determined data from conventional dynamometric engine
testing over a variety of speed and load points of interest for
fuel and emission economy and across the variety of parameters or
variables represented in the mapping. The fuel injector timing,
SOI, is also provided by the ECM in accordance with it engine
control routines.
[0060] It is noted that the modeling equation for exhaust mass flow
from the combustion chambers, .sub.ex, additionally accounts for
combustion transport or cycle delay as represented in the model
equation (8) temporal term set forth as (t-.tau..sub.comb).
[0061] The combustion chambers are more particularly described in
accordance with the exhausted air mass fractions as described in
the following modeling equation: f air eng = F engair .function. (
N , m .cndot. f , SOI , P im , T im , P em , f air im ) ( 10 )
##EQU6## [0062] where f air eng .times. ##EQU7## [0063] is the
dynamically predicted air fraction of the combustion chamber
exhaust, [0064] F.sub.engair (.circle-solid.) is a map modeling the
air content of the combustion chamber exhaust, and f air im
##EQU8## [0065] is the fraction of air in the intake manifold. The
map modeling combustion chamber exhaust,
F.sub.engair(.circle-solid.), is preferably provided in stored data
sets within the engine controller and are constructed using
empirically determined data from conventional dynamometric engine
testing.
[0066] Preferably for model robustness accounting for such factors
as engine system aging, manufacturing variation and modeling
errors, a correction term 54 is applied to the predicted air
fraction of the combustion chamber exhaust, f.sub.air.sub.eng, from
the combustion chamber model 53. A conventional closed-loop,
proportional-integral operation 52 is performed as shown in
additional detail in FIG. 5 utilizing the signal from wide range
air-fuel sensor 30, WRAF, and the fraction of air in the exhaust
manifold, f.sub.air.sub.em, from the exhaust manifold model 55. The
PI control is set forth below in equation form for convenience: f
air ex = f air eng + K p .function. ( WRAF air - f air em ) + K i
.times. .intg. ( WRAF air - f air em ) .times. d t ( 11 ) ##EQU9##
[0067] where f air ex ##EQU10## [0068] is the fraction of air in
the exhaust port flow, f air eng ##EQU11## [0069] is the
dynamically predicted air content in the combustion chamber
exhaust, [0070] K.sub.p is the proportional gain term, [0071]
WRAF.sub.air is sensed air (calculated from oxygen) in the exhaust
manifold, f air em ##EQU12## [0072] is the fraction of air in
exhaust manifold, and [0073] K.sub.i is the integral gain term.
[0074] The intake manifold model 51 is illustrated in FIG. 3C
wherein a plurality of model inputs appear along the left side of
the model block and a plurality of model outputs are illustrated
along the top side of the model block. The intake manifold is a
significant pressure node in the engine system characterized by
significant volume and significant mass flows into and out of the
manifold. The intake manifold model 51 utilizes the significant
mass flows associate with the intake manifold and thermal inputs in
describing the temperature and pressure associated with the intake
manifold gas mass. The significant mass flows are identified as
those into the combustion chamber from the intake manifold, and
those into the intake manifold comprising the EGR flow and the
fresh air intake. In the present example, the fresh air intake is
the turbocharger boosted compressor mass flow. The following
algebraic and differential modeling equations describe the intake
manifold: d m im d t = m .cndot. thr + m .cndot. egr - m .cndot. o
( 12 ) d P im d t = R im c v im .times. V im .function. [ m .cndot.
thr .times. T thr .times. c p im + m .cndot. egr .times. T egr
.times. c p egr - m .cndot. o .times. T im .times. c p im ] ( 13 )
T im = P im .times. V im R im .times. m im ( 14 ) ##EQU13## [0075]
where m.sub.im is the resident mass in the intake manifold, [0076]
.sub.thr is the throttle mass flow, [0077] .sub.egr is the EGR mass
flow, [0078] .sub.o is the mass flow into the cylinders, [0079]
P.sub.im is intake manifold pressure, [0080] R.sub.im is the gas
constant for standard atmospheric conditions, [0081] c.sub.v.sub.im
is the specific heat at constant volume for the intake manifold,
[0082] V.sub.im is the intake manifold volume, [0083] T.sub.thr is
throttle downstream flow temperature, [0084] T.sub.egr is the EGR
inlet temperature for the intake manifold, [0085] c.sub.p.sub.egr
is the specific heat at constant pressure of downstream EGR flow,
[0086] T.sub.im is the intake manifold temperature, and [0087]
c.sub.p.sub.im is the specific heat at constant pressure for the
intake manifold. It is presently assumed that throttle valve
dynamics are limited and hence approximate static conditions.
Therefore, the throttle mass flow, {dot over (m)}.sub.thr, is
obtained in the present embodiment from the mass airflow sensor,
MAF. The same throttle valve dynamics assumption allows for setting
the throttle downstream flow temperature, T.sub.thr, to the
intercooler outlet temperature, T.sub.ic.sub.out, in the present
embodiment.
[0088] The intake manifold is more particularly described in
accordance with air mass fractions as described in the following
algebraic and differential modeling equations: d m im air d t = m
.cndot. thr + m .cndot. egr air - f air im .times. m .cndot. o ( 15
) f air im = m im air m im ( 16 ) ##EQU14## [0089] where m im air
##EQU15## [0090] is the resident air mass in the intake manifold,
[0091] .sub.egr.sub.air is the EGR airflow, and f air im ##EQU16##
[0092] is the fraction of air in the intake manifold. In the
present embodiment, the quantity, .sub.egr.sub.air, which
represents the air mass in the EGR flow to the intake manifold, is
provided by the EGR and cooler model 57 as set forth in further
detail herein below.
[0093] The EGR and cooler model 57 is illustrated in FIG. 3D
wherein a plurality of model inputs appear along the left side of
the model block and a plurality of model outputs are illustrated
along the top side of the model block. The EGR is a controllably
restrictive apparatus for affecting mass flow and the cooler is a
heat transfer apparatus for removing heat from the mass flow. EGR
and cooler model 57 utilizes pressures associated with the intake
and exhaust manifolds, thermal input associated with the exhaust
manifold gases and the cooler coolant in describing the temperature
associated with the EGR into the intake manifold and the EGR mass
flows into the intake manifold. The following modeling equations
describe the EGR and cooler: m .cndot. egr = C d egr .times. A egr
.times. P em R egr .times. T egr up .times. .PHI. .function. ( P im
P em ) ( 17 ) where .times. .times. .times. .PHI. .function. ( x )
= { ( 2 .gamma. egr up - 1 ) .function. [ x 2 .gamma. egr up - x
.gamma. egr up + 1 .gamma. egr up ] } 0.5 .times. .times. for
.times. .times. x > ( 2 .gamma. egr up + 1 ) .gamma. egr up
.gamma. egr up - 1 = { .gamma. egr up .function. [ 2 .gamma. egr up
+ 1 ] .gamma. egr up + 1 .gamma. egr up - 1 } .times. .times. for
.times. .times. x .ltoreq. ( 2 .gamma. egr up + 1 ) .gamma. egr up
.gamma. egr up - 1 ( 18 ) T egr up = .eta. egrcooler .function. ( T
egrcoolant i .times. .times. n - T em ) + T em ( 19 ) T egr down =
F egr .function. ( T egr up , P im P em ) ( 20 ) ##EQU17## [0094]
where .sub.egr is the EGR mass flow, C d egr ##EQU18## [0095] is a
EGR valve discharge coefficient, [0096] A.sub.egr is EGR valve
geometric opening area, [0097] P.sub.em is the exhaust manifold
pressure, [0098] R.sub.egr is the gas constant for EGR, T egr up
##EQU19## [0099] is EGR temperature at the cooler outlet, [0100]
T.sub.egr.sub.down is EGR temperature downstream of the EGR valve
at the inlet to the intake manifold, [0101] P.sub.im is intake
manifold pressure, [0102] .phi. is the pressure ratio effect in
compressible flow equation, [0103] .gamma..sub.egr.sub.up is the
ratio of specific heats for EGR flow upstream, [0104]
.eta..sub.egrcooler is the EGR cooler efficiency, T egr coolantin
##EQU20## [0105] is the EGR coolant inlet temperature, [0106]
T.sub.em is the exhaust manifold temperature, and [0107]
F.sub.egr(.circle-solid.) is a function that models the EGR
downstream temperature. The EGR valve geometric opening area,
A.sub.egr, is determined as a function of EGR valve position
(EGR.sub.pos). The EGR coolant inlet temperature,
T.sub.egr.sub.coolanin, is determined as a function of the engine
coolant temperature T.sub.engcoolant. Alternatively, T egr
coolantin ##EQU21## may be approximated as a constant. The function
modeling EGR downstream temperature, F.sub.egr(.circle-solid.), is
preferably provided in stored data sets within the engine
controller and are constructed using empirically determined data
from conventional dynamometric engine testing.
[0108] The EGR and cooler are more particularly described in
accordance with air mass fractions of the EGR mass flow as
described in following modeling equation: m . egr air = m . egr
.times. f air em .function. ( t - .tau. egr ) ( 21 ) ##EQU22##
[0109] where m . egr air ##EQU23## [0110] is the EGR airflow,
[0111] f.sub.air.sub.em is the fraction of air in exhaust manifold,
[0112] t is time, and [0113] .tau..sub.egr is the EGR transport
delay. As previously mention herein above with respect to the
intake manifold model 51, it is recognized that the air mass in the
EGR flow to the intake manifold, {dot over (m)}.sub.egr.sub.air, is
provided by the EGR and cooler model 57. This is preferred due to
the additional accounting performed in the EGR and cooler model for
EGR transport delay as represented in the model equation (21)
temporal term set forth as (t-.tau..sub.egr).
[0114] Preferably for model robustness accounting for such factors
as engine system aging, manufacturing variation and modeling
errors, a correction term 56 is applied to the EGR temperature
downstream of the EGR valve, T.sub.egr.sub.down, from the EGR and
cooler model 57. A conventional closed-loop, proportional-integral
operation 58 is performed as shown in additional detail in FIG. 4
utilizing the signal from manifold absolute pressure sensor 17,
MAP, and the intake manifold pressure, P.sub.im, from the intake
manifold model 51. The PI control is set forth below in equation
form for convenience:
T.sub.egr=T.sub.egr.sub.down+K.sub.p(MAP-P.sub.im)+K.sub.i.intg.(MAP-P.su-
b.im)dt (22) [0115] where T.sub.egr is the EGR inlet temperature
for the intake manifold, T egr down ##EQU24## [0116] is the
estimated EGR inlet temperature, [0117] K.sub.p is the proportional
gain term, [0118] MAP is sensed manifold pressure, [0119] P.sub.im
is the intake manifold pressure, and [0120] K.sub.i is the integral
gain term.
[0121] The turbocharger and intercooler model 59 is illustrated in
FIG. 3E wherein a plurality of model inputs appear along the left
sides of the respective sub-model blocks 59A and 59B and a
plurality of model outputs are illustrated along the top side of
the respective sub-model blocks. The turbocharger is a pumping
apparatus for effecting mass flow by way of exhaust gas forces
operating upon a turbine/compressor combination and the intercooler
is considered to be a heat transfer apparatus for removing heat
from the mass flow. Turbocharger and intercooler model 59 utilizes
pressures associated with the intake and exhaust manifolds, thermal
input associated with the ambient air source and the intercooler
coolant in determining the exhaust mass flow driving the
turbocharger and the temperature associated with the boosted mass
flow to the intake manifold. The following modeling equations
describe the EGR and cooler: m . c = F compflow .function. (
.omega. shaft , P compout P amb ) ( 23 ) .eta. c = F compeff
.function. ( .omega. shift , P compout P amb ) ( 24 ) m . t = F
turbflow .function. ( .omega. shaft , P em P amb , VNT pos ) ( 25 )
.eta. t = F turbeff .function. ( .omega. shaft , P em P amb , VNT
pos ) ( 26 ) T q comp = m . c .times. c p .times. T amb .eta. c
.times. .omega. shaft .times. { ( P compout P amb ) .gamma. - 1
.gamma. - 1 } ( 27 ) T q turb = m . t .times. c pem .times. T amb
.eta. t .times. .omega. shaft .times. { 1 - ( P amb P em ) .gamma.
em - 1 .gamma. em } ( 28 ) I tc .times. .omega. . shaft = T q ,
turb - T q , comp ( 29 ) T ic out = .eta. IC .function. ( T
iccoolant .times. in - T c ) + T c ( 30 ) P compout = F ICdelP
.function. ( m . c ) + P im ( 31 ) ##EQU25## [0122] where .sub.c is
compressor mass flow, [0123] F.sub.compflow(.circle-solid.) is a
two dimensional map modeling compressor mass flow, [0124]
.omega..sub.shaft is turbocharger shaft speed, [0125] P.sub.compout
is compressor outlet pressure, [0126] P.sub.amb is ambient
pressure, [0127] .eta..sub.c is compressor efficiency, [0128]
F.sub.compeff(.circle-solid.) is a two dimensional map modeling
compressor efficiency, [0129] is the turbine mass flow, [0130]
F.sub.turbflow(.circle-solid.) is a three dimensional map modeling
turbine mass flow, [0131] P.sub.em is the exhaust manifold
pressure, [0132] VNT.sub.pos is the VNT valve position, [0133]
.eta..sub.t is turbine efficiency, [0134]
F.sub.turbeff(.circle-solid.) is a three dimensional map modeling
turbine efficiency, [0135] T.sub.q.sub.comp is compressor torque,
[0136] c.sub.p is the specific heat at constant pressure for
standard atmospheric conditions, [0137] T.sub.amb is ambient
temperature, [0138] .gamma. is the ratio of specific heats for
ambient conditions, [0139] T.sub.q.sub.turb is turbine torque,
[0140] c.sub.pem is the specific heat at constant pressure for
exhaust manifold conditions, [0141] .gamma..sub.em is the ratio of
specific heats for exhaust manifold conditions, [0142] I.sub.tc is
turbocharger inertia, [0143] T.sub.ic.sub.out is the intercooler
outlet temperature, [0144] .eta..sub.IC is the intercooler
efficiency, [0145] T.sub.iccoolant.sub.in is the intercooler
coolant inlet temperature, [0146] T.sub.c is the temperature of the
compressor outlet, [0147] F.sub.ICdelP(.circle-solid.) is a
correlation function that relates pressure drop along the
intercooler to mass flow rates, and [0148] P.sub.im is intake
manifold pressure. The ambient temperature, T.sub.amb, is provided
by the ambient air temperature sensor. The ambient pressure,
P.sub.amb, is provided by the BARO sensor. The intercooler coolant
inlet temperature, T.sub.iccoolant.sub.in, is a function of the
ambient air temperature in the present embodiment as provided by
the ambient temperature sensor, T.sub.amb. Alternately, the
intercooler coolant inlet temperature, T.sub.iccoolant.sub.in, may
be may be approximated as a constant. The intercooler efficiency,
.eta..sub.IC, is a regression based on engine data. The two
dimensional map modeling compressor mass flow,
F.sub.compflow(.circle-solid.), is preferably provided in stored
data sets within the engine controller and are constructed using
empirically determined data from a flow test bench of the
turbocharger. The two dimensional map modeling compressor
efficiency, F.sub.compeff(.circle-solid.), is preferably provided
in stored data sets within the engine controller and are
constructed using empirically determined data from a flow test
bench of the turbocharger. The three dimensional map modeling
turbine mass flow, F.sub.turbflow(.circle-solid.), is preferably
provided in stored data sets within the engine controller and are
constructed using empirically determined data from a flow test
bench of the turbocharger. The three dimensional map modeling
turbine efficiency, F.sub.turbeff(.circle-solid.), is preferably
provided in stored data sets within the engine controller and are
constructed using empirically determined data from a flow test
bench of the turbocharger. The correlation function that relates
pressure drop along the intercooler to mass flow rates,
F.sub.ICdelP(.circle-solid.), is preferably provided in stored data
sets within the engine controller and are constructed using
empirically determined data from conventional dynamometric engine
testing over a variety of speed and load points of interest for
fuel and emission economy.
[0149] The engine system model comprising the interconnected
sub-system models as set forth herein above thus identifies the
significant mass flows and pressure nodes within the engine system.
Interdependent air mass fractions are modeled at the intake and
exhaust manifolds and at the combustion cylinder exhaust port. The
oxygen concentration at any point within the system can be
determined by applying a simple gain to the air mass fraction at
the point of interest. The gain corresponds to the volumetric
fraction of oxygen in air and is substantially 0.21. Therefore, the
oxygen concentration in the intake manifold is determined by
applying this gain to the air mass fraction at the intake
manifold.
[0150] While the present invention has been described with respect
to certain preferred embodiments and particular applications, it is
understood that the description set forth herein above is to be
taken by way of example and not of limitation. Those skilled in the
art will recognize various modifications to the particular
embodiments are within the scope of the appended claims. Therefore,
it is intended that the invention not be limited to the disclosed
embodiments, but that it has the full scope permitted by the
language of the following claims.
* * * * *