U.S. patent application number 10/678024 was filed with the patent office on 2004-03-11 for method and system for controlling partial pressure of air in an intake manifold of an engine.
Invention is credited to Kolmanovsky, Ilya V., Stotsky, Alexander Anatoljevich.
Application Number | 20040045526 10/678024 |
Document ID | / |
Family ID | 21692426 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040045526 |
Kind Code |
A1 |
Kolmanovsky, Ilya V. ; et
al. |
March 11, 2004 |
Method and system for controlling partial pressure of air in an
intake manifold of an engine
Abstract
A method for controlling partial air pressure in an intake
manifold of an engine. The engine has an intake throttle device for
controlling a flow of air to the intake manifold. An EGR valve is
provided for controlling a flow of exhaust gas from the engine to
the intake manifold downstream of the intake throttle. The engine
has at least one cylinder fed a flow comprising air passing through
the throttle to the intake manifold and exhaust products passing
through the EGR valve to the intake manifold. Both the air through
the throttle and the exhaust gas products in the intake manifold
are passed as a combined flow to the intake manifold and then to
the at least one cylinder. The method includes: specifying a
dynamic reference model for the desired partial pressure of the air
as a function of time; and controlling the flow through the intake
throttle device in accordance with an estimated EGR flow obtained
by a dynamic observer and an estimate of partial air fraction in
the exhaust gas products. In one embodiment, the partial air
fraction is estimated in accordance with intake to exhaust delay
and fuel injection to exhaust delay. In one embodiment the dynamic
observer does not require information of engine exhaust
temperature, engine exhaust pressure, or EGR valve position.
Inventors: |
Kolmanovsky, Ilya V.;
(Ypsilanti, MI) ; Stotsky, Alexander Anatoljevich;
(Gothenburg, SE) |
Correspondence
Address: |
DALY, CROWLEY & MOFFORD, LLP
SUITE 101
275 TURNPIKE STREET
CANTON
MA
02021-2310
US
|
Family ID: |
21692426 |
Appl. No.: |
10/678024 |
Filed: |
October 2, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10678024 |
Oct 2, 2003 |
|
|
|
10000648 |
Nov 1, 2001 |
|
|
|
6651492 |
|
|
|
|
Current U.S.
Class: |
123/399 |
Current CPC
Class: |
Y02T 10/40 20130101;
F02D 11/105 20130101; F02D 2200/0406 20130101; F02D 2041/0017
20130101; F02D 41/0072 20130101; F02D 37/02 20130101; F02D
2200/0414 20130101; F02D 41/187 20130101; F02D 2041/1416 20130101;
F02D 2011/102 20130101; Y02T 10/47 20130101 |
Class at
Publication: |
123/399 |
International
Class: |
F02D 001/00 |
Claims
What is claimed is:
1. A method for determining partial air pressure in an intake
manifold of an engine, such engine having an intake throttle device
for controlling a flow of air to the intake manifold, an EGR valve
for controlling a flow of exhaust gas from the engine to the intake
manifold downstream of the intake throttle, at least one cylinder
fed a flow comprising air passing through the throttle to the
intake manifold and exhaust products passing through the EGR valve
to the intake manifold, both the air through the throttle and the
exhaust gas products in the intake manifold passing as a combined
flow to the intake manifold and then to the at least one cylinder,
such method comprising: estimating the flow of exhaust gas products
passing through the EGR valve to the intake manifold; determining
intake manifold pressure; determining air flow through the throttle
device to the intake manifold; estimating the air fraction in the
portion of the exhaust gas products passing to the intake manifold;
combining the estimated flow of gas products, the determined intake
manifold pressure, with the estimated air fraction to determine the
partial air pressure in the intake manifold.
2. The method recited in claim 1 wherein the estimate of the air
fraction comprises using an open loop estimator.
3. A method for controlling partial air pressure in an intake
manifold of an engine, such engine having an intake throttle device
for controlling a flow of air to the intake manifold, an EGR valve
for controlling a flow of exhaust gas from the engine to the intake
manifold downstream of the intake throttle, at least one cylinder
fed a flow comprising air passing through the throttle to the
intake manifold and exhaust products passing through the EGR valve
to the intake manifold, both the air through the throttle and the
exhaust gas products in the intake manifold passing as a combined
flow to the intake manifold and then to the at least one cylinder,
such method comprising: estimating the flow of exhaust gas products
passing through the EGR valve to the intake manifold from engine
operating parameters; estimating the air fraction in the estimated
flow of exhaust gas products passing through the EGR valve to the
intake manifold; determining the partial pressure of air in the
intake manifold from such estimate of the flow of exhaust gas
products and such estimate of the air fraction; and, adjusting the
intake throttle device in accordance with a difference between a
desired partial pressure of the air in the intake manifold and the
determined partial pressure of air in the intake manifold.
4. The method recited in claim 1 wherein the estimate of the flow
of gas products passing through the EGR valve comprises providing
such estimate in accordance with an open loop estimator.
5. A method for controlling partial pressure of air in an intake
manifold of an engine, such engine having an intake throttle device
for controlling a flow of air to the intake manifold, an EGR valve
for controlling a flow of exhaust gas from the engine to the intake
manifold downstream of the intake throttle, at least one cylinder
fed a flow comprising air passing through the throttle to the
intake manifold and exhaust products passing through the EGR valve
to the intake manifold, both the air through the throttle and the
exhaust gas products in the intake manifold being passed as a
combined flow to the intake manifold and then to the at least one
cylinder, such method comprising: specifying a dynamic reference
model for the desired partial pressure of the air as a function of
time; and controlling the flow through the intake throttle device
in accordance with an estimated EGR flow obtained by a dynamic
observer and an estimate of partial air fraction in the exhaust gas
products to force the estimated partial pressure of air in intake
manifold to follow the desired partial pressure of air provided by
the reference model.
6. The method recited in claim 3 wherein the partial air fraction
is estimated in accordance with intake to exhaust delay and fuel
injector to exhaust delay.
7. The method recited in claim 4 wherein the dynamic observer is
void of information of engine exhaust temperature.
8. The method recited in claim 4 wherein the dynamic observer is
void of information of engine exhaust pressure.
9. The method recited in claim 6 wherein the dynamic observer is
void of information of engine exhaust temperature.
10. The method recited in claim 6 wherein the dynamic observer is
void of information of engine exhaust pressure.
11. The method recited in claim 3 wherein the dynamic observer is 9
( t k + 1 ) = ( t k ) + dT ( - ( t k ) - R T ^ ( t k ) V IM ( W th
( t k ) - W ^ cyl ( t k ) ) + 2 p ( t k ) ) where : {circumflex
over ( )} denotes an estimated value; t.sub.k is the time of a
sample of the parameter; dT is the period between samples of the
parameter; T, is the temperature in the engine intake manifold;
W.sub.th is the mass air flow measured through the engine intake
throttle; W.sub.th is the total flow into the cylinder of the
engine; V.sub.IM is intake manifold volume; R is the gas constant;
.lambda. is adjusted to provide a desired shape of engine torque
response; and p=p.sub.air+p.sub.bg (where p.sub.air is the total
pressure in the intake manifold and p.sub.bg is the partial
pressure of burnt gas in the intake manifold).
12. A method for controlling partial air pressure in an intake
manifold of an engine, such engine having an intake throttle device
for controlling a flow of air to the intake manifold, an EGR valve
for controlling a flow of exhaust gas from the engine to the intake
manifold downstream of the intake throttle, and, at least one
cylinder fed a flow comprising air passing through the throttle to
the intake manifold and exhaust gas in the intake manifold passing
through the EGR valve to the at least one cylinder, such method
comprising: determining engine operating parameters comprising: the
flow to the cylinder, the flow of air through the intake throttle,
and intake manifold pressure; providing an estimate of the flow
through the EGR valve from the determined engine operating
parameters; and determining an estimate of the air fraction on the
exhaust gas passed through the EGR to the intake manifold; and
adjusting the intake throttle in accordance with a desired partial
pressure of the air in the intake manifold and the estimated flow
through the EGR valve.
13. A method for controlling partial air pressure in an intake
manifold of an engine, such engine having an intake throttle device
for controlling a flow of air to the intake manifold, an EGR valve
for controlling a flow of exhaust gas from the engine to the intake
manifold downstream of the intake throttle, and at least one
cylinder fed a flow comprising air passing through the throttle to
the intake manifold and exhaust products passing through the EGR
valve to the intake manifold, both the air through the throttle and
the exhaust gas products in the intake manifold passing as a
combined flow to the intake manifold and then to the at least one
cylinder, such method comprising: calculating the desired partial
pressure of air dynamically, as a function of time in accordance
with a reference model; estimating the flow of exhaust gas products
passing through the EGR valve to the intake manifold from engine
operating parameters; estimating the air fraction in the estimated
flow of exhaust gas products passing through the EGR valve to the
intake manifold; determining the partial pressure of air in the
intake manifold from such estimate of the flow of exhaust gas
products and such estimate of the air fraction; and, adjusting the
intake throttle device in accordance with a difference between a
desired partial pressure of the air in the intake manifold and the
determined partial pressure of air in the intake manifold.
14. A method for controlling partial air pressure in an intake
manifold of an engine, such engine having an intake throttle device
for controlling a flow of air to the intake manifold, an EGR valve
for controlling a flow of exhaust gas from the engine to the intake
manifold downstream of the intake throttle, and, at least one
cylinder fed a flow comprising air passing through the throttle to
the intake manifold and exhaust gas in the intake manifold passing
through the EGR valve to the at least one cylinder, such method
comprising: estimating partial air pressure in intake manifold
based on open loop observer and estimated partial air fraction in
the flow of exhaust to the intake manifold.
15. An engine control unit programmed to execute the following:
storing in a memory of such unit a specified dynamic reference
model for a desired partial pressure of the air as a function of
time; and controlling a flow through an intake throttle device in
accordance with an estimated exhaust gas recirculation flow
obtained by a dynamic observer and an estimate of partial air
fraction in exhaust gas products.
16. An engine control unit programmed to execute the following:
calculate a desired partial pressure of air dynamically, as a
function of time in accordance with a reference model; estimate the
flow of exhaust gas products passing through an emission gas
recirculation to an intake manifold from engine operating
parameters; estimate the air fraction in the estimated flow of
exhaust gas products passing through an EGR valve to the intake
manifold; determine the partial pressure of air in the intake
manifold from such estimate of the flow of exhaust gas products and
such estimate of the air fraction; and, adjust the intake throttle
device in accordance with a difference between a desired partial
pressure of the air in the intake manifold and the determined
partial pressure of air in the intake manifold.
17. An engine control unit programmed to execute the following:
estimate partial air pressure in an intake manifold based on open
loop observer and estimated partial air fraction in a flow of
exhaust to the intake manifold.
Description
TECHNICAL FIELD
[0001] This invention relates generally to methods and systems for
controlling the partial pressure of air in an intake manifold of an
engine.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] As is known in the art, the mass of air, or cylinder air
charge, inducted into each cylinder of an internal combustion
engine must be known as precisely as possible in order to match the
air mass with an appropriate mass of metered fuel. Placing sensors
at the intake port of each cylinder is technically very difficult
and expensive. Instead, a sensor is typically located either inside
the intake manifold or at the throttle opening into the intake
manifold. A physics model is then used to estimate the air mass
propagation through the intake manifold into each cylinder.
[0003] Two types of the above-described sensors are typically
employed in internal combustion engines. One type is a manifold
absolute pressure (MAP) sensor. An estimation algorithm treats the
manifold pressure as an input to the system and uses mapped engine
data and engine speed to estimate air flow into the engine
cylinders. The other type of sensor is a relatively expensive mass
air flow (MAF) sensor used to directly measure mass air flow at the
throttle body. For the MAF based system, fresh air from the
throttle is directly measured. EGR gas content is left out of the
cylinder port air charge estimation. Other air flows not from the
throttle (via vacuum lines from the brakes, canister purge system,
etc.) are not accounted for by the MAF measurement and must be
accounted for by other means.
[0004] The MAP sensor measures the absolute pressure in the intake
manifold and thus incorporates the air flow from all sources.
Difficulties arise, however, when gases other than air are
introduced into the intake manifold. For the MAP based system
(often referred to as a speed density system), gases other than
air, such as the deliberately introduced exhaust gas (referred to
as EGR or exhaust gas recirculation), increase the manifold
pressure. These gases should not be matched by fuel. However, the
MAP sensor cannot distinguish between fresh air and EGR. Thus, EGR
mass in the intake manifold must be measured or estimated.
[0005] More particularly, control of the partial pressure of air
has to be achieved under uncertainties in the EGR flow. These
uncertainties are due to the soot deposits in the EGR valve conduit
and the fact that the exhaust pressure and temperature are not
measured. Additionally, air is present in the EGR flow during lean
operation and this air needs to be accounted for in the partial
pressure of air estimate.
[0006] In accordance with the present invention, a method is
provided for controlling partial pressure of air in an intake
manifold of an engine. The engine has an intake throttle device for
controlling a flow of air to the intake manifold. An EGR valve is
provided for controlling a flow of exhaust gas from the engine to
the intake manifold downstream of the intake throttle. The engine
has at least one cylinder fed a flow comprising air passing through
the throttle to the intake manifold and exhaust products passing
through the EGR valve to the intake manifold. Both the air through
the throttle and the exhaust gas products in the intake manifold
are passed as a combined flow to the intake manifold and then to
the at least one cylinder. The method includes: specifying a
dynamic reference model for the desired partial pressure of the air
as a function of time; and controlling the flow through the intake
throttle device in accordance with an estimated EGR flow obtained
by a dynamic observer and an estimate of partial air fraction in
the exhaust gas products.
[0007] In one embodiment, the partial air fraction is estimated in
accordance with intake to exhaust delay and fuel injection to
exhaust delay.
[0008] In one embodiment the dynamic observer does not require
information of engine exhaust temperature, engine exhaust pressure,
or EGR valve position.
[0009] According to the present invention, there is provided a
method controlling partial air pressure in an intake manifold of an
engine. The engine has an intake throttle device for controlling a
flow of air to the intake manifold. An EGR valve is provided for
controlling a flow of exhaust gas from the engine to the intake
manifold downstream of the intake throttle. The engine has at least
one cylinder fed a flow comprising air passing through the throttle
to the intake manifold and exhaust products passing through the EGR
valve to the intake manifold. Both the air through the throttle and
the exhaust gas products in the intake manifold are passed as a
combined flow to the intake manifold and then to the at least one
cylinder. The method includes: calculating the desired partial
pressure of air dynamically, as a function of time in accordance
with a reference model, estimating the flow of exhaust gas products
passing through the EGR valve to the intake manifold from engine
operating parameters; estimating the air fraction in the estimated
flow of exhaust gas products passing through the EGR valve to the
intake manifold; determining the partial pressure of air in the
intake manifold from such estimate of the flow of exhaust gas
products and such estimate of the air fraction; and, adjusting the
intake throttle device in accordance with a difference between a
desired partial pressure of the air in the intake manifold and the
determined partial pressure of air in the intake manifold.
[0010] In a preferred embodiment of the invention, the estimate of
the flow of gas products passing through the EGR valve comprises
providing such estimate in accordance with an open loop
estimator.
[0011] In accordance with the present invention, a method is
provided for controlling partial air pressure in an intake manifold
of an engine. The method includes estimating partial air pressure
in intake manifold based on open loop observer and estimated
partial air fraction in the flow of exhaust to the intake
manifold.
[0012] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0013] The single figure is a schematic diagram of an engine system
having control of partial air pressure at an intake manifold
thereof.
DETAILED DESCRIPTION
[0014] Referring now to FIG. 1, a gasoline engine system 10 is
shown to include an engine block 16 is shown having for example,
four cylinders 18. Each of the combustion chambers 18 includes here
for example direct-injection fuel injectors 20. The duty cycle of
the fuel injectors 20 is determined by the engine control unit
(ECU) 24 and transmitted along signal line 22.
[0015] The engine system 10 has an intake throttle device 49 for
controlling a flow of air to an intake manifold 26. An EGR valve 12
is provided for controlling a flow of a portion of exhaust gas
(shown by arrow 31) passing from the engine to the intake manifold
26 downstream of the intake throttle 49. The portion of the exhaust
gas passing through the EGR valve 12 is indicated by arrow 32. The
cylinders 18 are thus fed a flow comprising air passing through the
intake throttle device 49 to the intake manifold 26 and the portion
of the exhaust gas products passing through the EGR valve 12 to the
intake manifold 26. Both the air through the throttle 49 and the
exhaust gas products in the intake manifold are passed as a
combined flow to the cylinders 18, such combined flow being
indicated by the arrow 35.
[0016] The EGR system is provided to reduce the level of NOx
emissions. The EGR system comprises the EGR valve 12 disposed in a
conduit 33 connecting the exhaust manifold 28 to the intake
manifold 26. This allows a portion of the exhaust gases to be
circulated from the exhaust manifold 28 to the intake manifold 26
as described above. It is noted that the flow of exhaust gas though
the EGR valve 12 is a function of the pressure across such valve 12
in addition to the electrical signal provided to the valve on line
46 from the ECU 24. Here, there is no pressure sensor at the input
to the EGR valve 34 (i.e., in the exhaust manifold 28). The
electrical signal on line 46 is produced by the ECU 24 from
relationships stored a priori in the ECU 24 in accordance with a
computer program stored in a memory 25 in the ECU 24.
[0017] All of the engine systems, including the EGR valve 12, fuel
injectors 20, intake throttle device 49 are controlled by the ECU
24. For example, signal 46 from the ECU 24 regulates the EGR valve
12 position and a signal on line 47 controls the position of the
intake throttle device 49.
[0018] In the ECU 24, the command signal 47 to the intake throttle
device 49 will be described in detail below. Suffice it to say
here, however, that the signal on line 47 for the intake throttle
device 49 is produced by the ECU 24 to provide a desired partial
air pressure in the intake manifold 26. Additional sensory inputs
are also received by the ECU 24 via lines 62 along with: engine
intake manifold temperature, TEMP, as measured by temperature
sensor 50 which produces a signal on line 52; mass air flow, MAF,
to the intake throttle device 49 as measured by flow sensor 59
which produces a signal on line 61; mass air pressure (MAP) as
measured by intake manifold pressure sensor 58 which produces a
signal on line 52; and engine speed which is fed to the ECU 24 as
the signal, n.sub.e, etc. Additional operator inputs 68 are
received along signal 70 such as the accelerator pedal
position.
[0019] As will be described in more detail below, a set of control
instructions or code are stored in a memory 25 in the ECU 24.
Execution of the stored code by the ECU 24 results in a method
being performed which estimates the flow of exhaust gas products
passing through the EGR valve 12 to the intake manifold 26 from
engine operating parameters; estimates the air fraction in the
estimated flow of exhaust gas products passing through the EGR
valve 12 to the intake manifold; determines the partial pressure of
air in the intake manifold 26 from such estimate of the flow of
exhaust gas products and such estimate of the air fraction; and,
adjusts the intake throttle device 49 position in accordance with a
difference between a desired partial pressure of the air in the
intake manifold and the determined partial pressure of air in the
intake manifold. The estimate of the flow of gas products passing
through the EGR valve 12 provides such estimate in accordance with
an open loop estimator to be described.
[0020] It should first be noted that the following notation is used
herein, reference being made to FIG. 1:
[0021] {circumflex over ( )} denotes an estimated value of an
engine operating parameter;
[0022] t.sub.k is the time of a sample of the parameter;
[0023] dT is the period between samples of the parameter;
[0024] T, is the temperature measured in the engine intake manifold
(i.e., the signal TEMP on line 60);
[0025] W.sub.th is the mass air flow measured through the engine
intake throttle (i.e., the signal MAF on line 61);
[0026] W.sub.cyl is the total flow into a cylinder of the
engine;
[0027] W.sub.cyl,air is the partial flow of air into a cylinder of
the engine (estimated in a manner to be described below);
[0028] W.sub.egr is the exhaust gas recirculation (EGR) flow
(estimated in a manner to be described below);
[0029] .chi. is the air fraction in the exhaust gas of the engine
(estimated in a manner to be described below);
[0030] V.sub.IM is a priori measured intake manifold volume;
[0031] V.sub.d is a priori measured cylinder displacement;
[0032] P.sub.air is the partial pressure of air measured in the
intake manifold (i.e., the MAP signal on line 52);
[0033] P.sub.air,d is the desired partial pressure in the intake
manifold 26;
[0034] P=p.sub.air+P.sub.bg (where p.sub.air is the total pressure
in the intake manifold and p.sub.bg is the partial pressure of
burnt gas in the intake manifold);
[0035] n.sub.e is measured engine speed in revolutions per
second;
[0036] .eta..sub.v is engine volumetric efficiency;
[0037] .DELTA..sub.fi is fuel injection to exhaust delay
[0038] .DELTA..sub.io is intake to exhaust delay
[0039] R is the gas constant
[0040] To maintain good engine performance it is desirable to have
a well-controlled partial pressure of air response in the intake
manifold 26. The desired response for the partial pressure of air
is here defined by a reference model, here a first order
system:
p.sub.air(t.sub.k+1)=p.sub.air(t.sub.k)+dT(-.lambda..multidot.(p.sub.air(t-
.sub.k)-p.sub.air,d)) (1)
[0041] where;
[0042] p.sub.air is the actual partial pressure in the intake
manifold 26; and
[0043] p.sub.air,d is the desired behavior of partial pressure of
air in the reference model, as presented above in equation (1).
[0044] In order to achieve this desired partial pressure,
p.sub.air,d, the intake throttle 49 is adjusted to provide the
following air flow through such throttle 49: 1 W th , d ( t k ) = -
( p ^ air ( t k ) - p air , d ) V IM R T ^ ( t k ) + W ^ cyl , air
( t k ) - ^ ( t k ) W ^ egr ( t k ) ( 2 )
[0045] In order to determine W.sub.th,d(tk) from equation (2),
while the following parameters are known: V.sub.IM, R, T and, as
will be described, .lambda., an estimate of W.sub.cyl,air, .chi.,
W.sub.egr. and p.sub.air are determined as described below.
[0046] Given this desired flow rate of air through the throttle,
W.sub.th,d we backtrack the desired throttle device 49 position to
provide this flow and set the throttle device 49 to that position
via the signal on line 47.
[0047] The parameter .lambda. is adjusted to ensure the desired
shape of the engine torque response. A larger .lambda. provides
faster torque response; however, very large .lambda. s should not
be used since fast torque response may cause driveline oscillations
and other driveability problems and also may cause the estimators
employed throughout perform poorly (i.e., not be able to track or
catch up with a fast engine behavior).
[0048] The estimates of W.sub.cyl,air, .chi., W.sub.egr. and
p.sub.air are determined as follows:
[0049] (1) Determine throttle flow, W.sub.th, by estimates thereof
or by measuring the mass air flow (MAF) with MAF sensor 59, as
indicated in FIG. 1
[0050] (2) Estimate or measure the intake manifold pressure p(t)
with a MAP sensor 50 as indicated in FIG. 1;
[0051] (3) Estimate cylinder flow W.sub.cyl(t.sub.k) at the present
sampling time instant, t.sub.k, in accordance with: 2 W ^ cyl ( t k
) = v ( t k ) n e ( t k ) 2 V d p ( t k ) T ^ ( t k )
[0052] where:
[0053] .eta..sub.n(t.sub.k)=.eta..sub.n(.eta..sub.e(t.sub.k),
p(t.sub.k)) is volumetric efficiency obtained from a look-up table
or a regression equation
[0054] (4) Determine the estimate of the EGR flow in accordance
with the following:
[0055] It is first noted from FIG. 1 that the amount of air flow in
the exhaust gas returned to the intake manifold through the EGR
valve is .chi..multidot.W.sub.egr, where, as noted above, W.sub.egr
is the total exhaust gas recirculation flow and .chi. is air
fraction in the exhaust gas. Here, estimates are made of the air
fraction in the exhaust gases by making estimates of .chi. and
W.sub.egr in accordance with: 3 ^ ( t k ) = max { W ^ cyl , air ( t
k - io ) - W f ( t k - fi ) ( A / F ) s , 0 } W ^ cyl ( t k - io )
+ W f ( t k - fi )
[0056] where:
[0057] (A/F)s is the stoichiometric air-to-fuel ratio (approx.
14.64), and 4 W ^ egr ( t k ) = V IM R T ^ ( t k ) ( ( t k ) - p (
t k ) ) ,
[0058] respectively,
[0059] where .epsilon. is an open loop estimator state which is
updated in accordance with: 5 ( t k + 1 ) = ( t k ) + dT ( - ( t k
) - R T ^ ( t k ) V IM ( W th ( t k ) - W ^ cyl ( t k ) ) + 2 p ( t
k ) )
[0060] The estimate of the partial pressure of air in the intake
manifold is given by: 6 p ^ air ( t k + 1 ) = p ^ air ( t k ) + dT
( R T ^ ( t k ) V IM ( W th ( t k ) + W ^ egr ( t k ) ^ ( t k ) - W
^ cyl , air ( t k ) ) )
[0061] Having determined the desired throttle flow, W.sub.th,d as
function of p.sub.air,d in accordance with equation (2), the intake
throttle device 49 position signal on line 47 is set as a function
of p(t.sub.k)/p.sub.amb and W.sub.th,d to match W.sub.th,d 7 th = A
- 1 ( W th , d / f th ( p ( t k ) p amb ) / p amb T amb ) ,
[0062] where A is the throttle position to throttle effective flow
area (geometric flow area times the discharge coefficient) map,
A.sup.-1 is its inverse, .alpha..sub.th is the throttle position,
T.sub.amb is the ambient temperature, p.sub.amb is ambient pressure
and 8 f th ( x ) = { 0.5 ( 2 + 1 ) + 1 2 ( - 1 ) , x 0.5 , x 1 { 2
- 1 [ 1 - x - 1 ] } 1 2 , x 0.5
[0063] where .gamma.=1.4
[0064] The EGR flow is controlled with EGR valve 12 via the signal
on line 46 while the fuel and spark are adjusted as desired with
the remainder of the control system.
[0065] In summary, the method described above combines an estimator
for the EGR flow that uses intake manifold pressure and throttle
flow measurements, with an open-loop estimator for the air fraction
in the exhaust gas. This EGR flow estimator provides a robust way
of estimating the EGR flow in presence of significant uncertainties
in the EGR valve conduit. The controller for the electronic intake
throttle device is then developed to enforce the desired response
of the partial pressure of air estimate.
[0066] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
* * * * *