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Claims  |
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The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. An engine--powertrain--controller combination, comprising:
a powertrain receiving power from said engine and including a transmission;
means for determining measures of a set of engine parameters and for
providing measurement signals indicative of said measures; and
a microprocessor control unit, including (i) means for receiving the
measurement signals, (ii) means for predicting a prediction set including
at least one predicted value of a desired engine state, and (iii) means
for controlling the vehicle engine--powertrain in response to the
prediction set, providing improved control of an engine--powertrain
parameter comprising: air-fuel ratio, engine idle speed, engine speed,
spark timing, or transmission gear selection, wherein
the microprocessor control unit iteratively (i) determines the prediction
set in response to (a) the measurement signals, (b) a linear model
comprising a set of fixed predetermined model parameters, and (c) an
estimation set including at least one estimated value of the desired
engine state, and (ii) determines the estimation set in response to (a) a
present measure of the desired engine state, (b) the prediction set, and
(c) a correction set of fixed predetermined correction coefficients
wherein the predicted value of the desired engine state is a substantially
accurate prediction of the desired engine state's future value.
2. The control system of claim 1 wherein the desired engine state is one
state of a set consisting of: manifold absolute pressure, engine speed,
and mass air flow.
3. The control system of claim 1 wherein the prediction set includes (i) a
predicted value of the desired engine state for one engine event in the
future and (ii) a predicted value of the desired engine state for R engine
events in the future, where R is at least 1 and wherein the controlling
means controls the vehicle engine--powertrain in response to the predicted
value of the desired engine state for R engine events in the future.
4. The control system of claim 3, wherein the controlling means controls
fueling of the engine by developing a fuel command in response to the
predicted value of the desired engine state R engine events in the future
and outputting the fuel command to a fuel injection control unit, which
fuels the engine in response to the fuel command, thereby improving engine
air-fuel ratio control.
5. The control system of claim 1, wherein the controlling means controls
fueling of the engine by developing a fuel command in response to the
predicted value of the desired engine state and outputting the fuel
command to a fuel injection control unit, which PG,45 fuels the engine in
response to the fuel command, thereby improving engine air-fuel ratio
control.
6. The control system of claim 4 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
7. The control system of claim 5 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
8. The control system of claim 1, wherein the controlling means controls
engine spark through spark timing and dwell commands, output to a spark
timing control module, by developing the spark timing and dwell commands
in response to the predicted value of the desired engine state and
outputting the spark timing and dwell commands to the spark timing control
module.
9. The control system of claim 3, wherein the controlling means controls
engine spark through spark timing and dwell commands, output to a spark
timing control module, by developing the spark timing and dwell commands
in response to the predicted value of the desired engine state R engine
events in the future and outputting the spark timing and dwell commands to
the spark timing control module.
10. The control system of claim 8 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
11. The control system of claim 9 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
12. The control system of claim 1, wherein the controlling means controls
an idle air control valve through an idle air control valve command, by
developing the idle air control valve command in response to the predicted
value of the desired engine state and outputting the idle air control
valve command to the idle air control valve.
13. The control system of claim 3, wherein the controlling means controls
an idle air control valve through an idle air control valve command, by
developing the idle air control valve command in response to the predicted
value of the desired engine state R engine events in the future and
outputting the idle air control valve command to the idle air control
valve.
14. The control system of claim 12 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
15. The control system of claim 13 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
16. The control system of claim 1, wherein the controlling means controls
the transmission, through a transmission gear signal, by developing the
transmission gear signal in response to the predicted value of the desired
engine state and outputting the transmission gear signal to the
transmission.
17. The control system of claim 3, wherein the controlling means controls
the transmission, through a transmission gear signal, by developing the
transmission gear signal in response to the predicted value of the desired
engine state and outputting the transmission gear signal to the
transmission.
18. The control system of claim 16 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
19. The control system of claim 17 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
20. The control system of claim 3, wherein: the prediction set for a given
engine event comprises a vector X.sup.p (k) where k is the present engine
event, the measures of the set of engine parameters comprise a vector
U(k), the estimation set comprises a vector X.sup.e (k), and the set of
fixed predetermined model parameters comprises matrices A, B, and C, the
prediction set for one engine event in the future being determined by a
relation:
X.sup.p (k+1)=AX.sup.e (k)+BU(k)+C, and
the prediction set for R engine events in the future being determined by:
X.sup.p (k+R)=A.sup.R X.sup.e (k)+[A.sup.R-1 B+A.sup.R-2 B+ . . .
+AB+B]U(k)+[A.sup.R-1 +A.sup.R-2 + . . . +A+I]C; and ,
the correction set comprises a vector G, and X.sup.p (k) and X(k) represent
predicted and measured values of the desired engine state at event k,
respectively, the estimation set being determined by a relation:
X.sup.e (k)=X.sup.p (k)+G(X(k)-X.sup.p (k)).
21. The control system of claim 20 wherein the model parameters are
predetermined through statistical regression.
22. The control system of claim 20 wherein the model parameters are
scheduled according to two independent engine variables.
23. The control system of claim 1 wherein the correction coefficients are
predetermined through Kalman filtering.
24. The control system of claim 20 wherein the correction coefficients are
predetermined through Kalman filtering.
25. The control system of claim 1 wherein the set of engine parameters
includes throttle position and engine speed.
26. The control system of claim 20 wherein the set of engine parameters
includes throttle position and engine speed.
27. The control system of claim 20 wherein the set of engine parameters
also includes at least one member of a set comprising: manifold absolute
pressure, measured mass air flow, predicted mass air flow, idle air
control valve position, exhaust gas recirculation valve position,
atmospheric pressure and air temperature.
28. The control system of claim 25 wherein the set of engine parameters
also includes at least one member of a set comprising: manifold absolute
pressure, measured mass air flow, predicted mass air flow, idle air
control valve position, exhaust gas recirculation valve position,
atmospheric pressure and air temperature.
29. The control system of claim 26 wherein the set of engine parameters
also includes at least one member of a set comprising: manifold absolute
pressure, measured mass air flow, predicted mass air flow, idle air
control valve position, exhaust gas recirculation valve position,
atmospheric pressure and air temperature.
30. An engine--powertrain--controller combination, comprising:
an engine;
a powertrain receiving power from said engine and including a transmission;
means for determining, at successive time events, measures of a set of
engine parameters and for providing measurement signals indicative of said
measures; and
a microprocessor control unit, including (i) means for receiving the
measurement signals, (ii) means for predicting from engine information
available at event k, a prediction set including at least one predicted
value of a desired engine state at an event k+R, where R is at least 1,
and (iii) means for controlling the vehicle engine--powertrain in response
to the prediction set, providing improved control of an engine--powertrain
parameter comprising: air-fuel ratio, engine idle speed, engine speed,
spark timing, or transmission gear selection, wherein
the microprocessor control unit iteratively:
determines an estimation of the desired engine state in response to a
present measure of the desired engine state, a prediction of the desired
engine state at event k, and a set of fixed predetermined correction
coefficients;
determines the prediction of the desired engine state at an event k+1 in
response to information including (i) the measurement signals including
signals indicative of the measures of the set of engine parameters at
event k and previous events, (ii) the estimation of the desired engine
state, and (iii) a set of fixed predetermined model parameters; and
determines the predicted value of the desired engine state at event k+R in
response to information including (i) the measurement signals including
signals indicative of the measures of the set of engine parameters at
event k and previous events, (ii) the estimation of the desired engine
state, and (iii) the set of fixed predetermined model parameters, wherein
the predicted value of the desired engine state at event k+R is a
substantially accurate representation of a value of the desired engine
state at event k+R.
31. The control system of claim 30 wherein the desired engine state is one
state of a set consisting of: manifold absolute pressure, engine speed,
and mass air flow.
32. The control system of claim 31 wherein the set of engine parameters
includes throttle position and engine speed.
33. The control system of claim 32 wherein the set of engine parameters
also includes at least one member of a set comprising: manifold absolute
pressure, measured mass air flow, predicted mass air flow, idle air
control valve position, exhaust gas recirculation valve position,
atmospheric pressure and air temperature.
34. An engine--powertrain--controller combination, comprising:
an engine;
a powertrain receiving power from said engine and including a transmission;
means for determining, at successive time events, measures of a set of
engine parameters and for providing measurement signals indicative of said
measures; and
a microprocessor control unit, including (i) means for receiving the
measurement signals, (ii) means for predicting, from engine information
available at event k, a prediction set including at least one predicted
value of a desired engine state at an event k+R, where R is greater than
zero, and (iii) means for controlling the vehicle engine--powertrain in
response to the prediction set, providing improved control of an
engine--powertrain parameter comprising: air-fuel ratio, engine idle
speed, engine speed, spark timing, or transmission gear selection, wherein
the microprocessor control unit:
initializes a set of variables including the set of engine parameters for
events preceding time k; thereafter iteratively:
receives the measurement signals for event k;
determines an error signal in response to a difference between a measure of
the desired engine state at event k and a prediction of the desired engine
state for event k;
schedules a set of fixed predetermined correction coefficients in response
to two of the measurement signals representing independent engine
parameters;
determines a set of estimated values of the desired engine state in
response to the prediction set, the error signal, and the set of fixed
predetermined correction coefficients;
schedules a set of fixed model parameters in response to the two
measurement signals representing independent engine states;
determines the prediction set in response to the measurement signals for
event k and preceding events, the set of estimated values, and a set of
fixed predetermined model parameters, the prediction set including a
prediction of the desired engine state at event k+1; and
determines engine--powertrain control in response to the prediction set.
35. The control system of claim 34 wherein the set of model parameters and
the set of correction coefficients are scheduled from look-up tables
within control unit memory.
36. The control system of claim 34 wherein the desired engine state is one
state of a set of states consisting of: manifold absolute pressure, engine
speed, and mass air flow.
37. The control system of claim 34 wherein the set of engine parameters
includes throttle position and engine speed.
38. The control system of claim 37 wherein the set of engine parameters
also includes at least one member of a set comprising: manifold absolute
pressure, measured mass air flow, predicted mass air flow, idle air
control valve position, exhaust gas recirculation valve position,
atmospheric pressure and air temperature. |
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Claims |
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Description |
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This invention relates engine--powertrain control based on predicted engine
states.
The subject of this application is related to copending patent applications
U.S. Ser. No. 07/653,931, entitled "Software Air Meter", and U.S. Ser. No.
07/653,923, entitled "Method for Estimating and Correcting Bias Errors in
a Software Air Meter", both filed Feb. 12, 1991, concurrently with the
parent to this application and assigned to the assignee of this
application. The disclosures of patent applications Ser. Nos. 653,931 and
653,923 are hereby incorporated into this application by reference.
BACKGROUND OF THE INVENTION
The air-fuel ratio in a combustion engine affects both engine emissions and
performance. With strict modern emissions standards for automobiles, it is
necessary to accurately control the air-fuel ratio of the automobile
engine, requiring precise measurement of the mass airflow into the engine.
Currently, engine airflow is either measured with a mass airflow sensor or
calculated by the speed-density method. Improvements in both types of
systems have lead to improved air-fuel ratio control of engines, enabling
vehicle manufacturers to meet existing emissions standards. In general,
while mass airflow sensors are more accurate than speed-density systems,
they are also more expensive.
In an ideal speed-density system, sensor processing and fuel delivery occur
instantaneously to allow precise air-fuel ratio control. In reality,
however, it takes a finite amount of time to process sensor measurements
to compute proper fueling and a finite amount of time to physically
deliver the fuel. The delays in the fuel computation and delivery force
the fuel control system to compute the fuel to be delivered in a
particular cylinder before the actual delivery of the fuel.
In speed-density systems, airflow estimates are based on measures of
manifold absolute pressure. The aforementioned delays force speed-density
systems to read manifold absolute pressure prior to the theoretically
optimal time, which would be during the intake event for the cylinder to
be fueled. A typical value for this delay is two to three engine events.
Because of the dynamic characteristics of engines, the manifold absolute
pressure, and hence airflow, can change dramatically between the time
manifold absolute pressure is read (and the fuel computed) and the intake
event for the cylinder being fueled. Therefore, in speed-density systems,
the lag between the calculated airflow and the actual airflow is
prominent. Speed-density calculations are most accurate during static
situations. During dynamic situations, when the mass airflow into the
engine is changing, the calculated mass airflow into the engine lags the
actual mass airflow. This increases the difficulty of properly controlling
the air-fuel ratio during transient conditions.
What is desired is a method of achieving increased accuracy in the
determination of proper air-fuel ratio for the vehicle engine in vehicles
with or without mass airflow meters to enable vehicle manufacturers to
meet increasingly tightening emissions standards.
SUMMARY OF THE PRESENT INVENTION
Increased accuracy in speed-density systems can be achieved by using
accurate predictions of manifold absolute pressure for the time air and
fuel actually enter the engine cylinder, instead of using a value of
manifold absolute pressure measured at a time before the cylinder intake
valve(s) open. This invention provides an engine--powertrain--controller
combination for predicting vehicle engine states and controlling the
vehicle engine--powertrain in response to the engine state predictions.
Vehicle engine states as referred to in this specification encompass
engine parameters that can be mathematically modeled in relation to other
engine variables, examples include manifold absolute pressure (MAP), mass
airflow into the engine (MAF), and engine speed (RPM). An example of an
engine parameter that is not a state is throttle position, which is
strictly a function of accelerator pedal position (for conventional
systems). Implementation of this invention enables increased accuracy in
calculations of proper fuel distribution so that the proper air-fuel ratio
at the time of actual combustion can be achieved. Additionally,
predictions of engine states such as manifold absolute pressure may be
used to control engine spark timing, engine idle air flow, engine idle
speed, engine speed and transmission gear selection for electronically
controlled transmissions.
The method of predicting vehicle engine states of this invention is an
extension of the technique of prediction and estimation as implemented in
state observers. The prediction-estimation technique is a two step
process: (1) model-based prediction, and (2) measurement-based correction
(estimation). In the prediction step, past and present measures of a set
of engine parameters, and previous estimations of the desired parameter
are used to determine future predictions of the desired state. The number
of engine events in the future for which the prediction is made may vary
from system to system (note that in this specification engine event is
used as the time variable, e.g., two engine events in the future refers to
two time events in the future). In the estimation, or measurement-based
correction step, the error in the prediction of the present engine event
value of the desired state is used in combination with a set of estimator
correction coefficients to determine the estimation of the desired state.
The method is iteratively executed by a computer-based controller and may
be used several times in the controller to predict more than one engine
state (e.g., manifold absolute pressure and engine speed may both be
predicted). For each state being predicted, a separate set of model
parameters and correction coefficients is used. The prediction results are
used to control the engine--powertrain of the vehicle.
The model parameters may be determined through statistical reduction of
data taken from a test vehicle. The estimator correction coefficients are
preferably determined through statistical optimization.
Use of the present invention to predict manifold pressure at the time air
and fuel enter the engine cylinder allows precise air-fuel ratio control.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing an engine--powertrain assembly,
sensors, and control unit in which the invention may be implemented.
FIG. 2 is an example control unit of the type shown in FIG. 1.
FIG. 3 is an engine timing diagram.
FIG. 4 is a schematic diagram showing the prediction-estimation method
implemented by the present invention.
FIGS. 5, 6, and 7 are flow diagrams for computer implementations of the
present invention.
FIG. 8 is a flow diagram for a computer implementation of a method for
estimating and correcting bias errors in parameter measurements.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 the engine--powertrain assembly shown includes the
engine 44, transmission 45, fuel injectors 42, spark plugs 41 and 43, air
intake manifold 40, throttle 32, exhaust gas recirculation (EGR) valve 36,
idle air control (IAC) valve 28, and exhaust gas manifold 21. The throttle
is controlled by accelerator pedal 30 as shown by dotted line 18 and the
transmission 45, IAC valve 28, EGR valve 36, spark plugs 41 and 43, and
fuel injectors 42 are controlled by controller 12 through lines 49, 16,
14, 23, 25 and 24.
The engine assembly includes means for determining at each time event
measures of a set of engine parameters and providing a signal indicative
of the measurements to the control unit 12 to be used in the engine state
predictions. For example, air temperature and atmospheric pressure are
sensed by sensors (not shown) and input into the controller 12 through
lines 13 and 15. The positions of the IAC valve 28 and the EGR valve 36
are determined from the commands on command lines 16 and 14, or they may
be measured directly using position sensors (not shown). The throttle
position and manifold pressure are sensed by sensors 34 and 38 and input
into the control unit 12 through lines 20 and 22. Engine speed is measured
through the sensor 48, which detects the rotations of output shaft 46, and
input into the control unit 12 through line 26. The engine coolant
temperature is sensed by a sensor (not shown) and the oxygen content of
the exhaust gas is sensed by sensor 19 and both measurements are input
into the control unit 12 through lines 11 and 17. The sensors mentioned
above are all standard sensors, a variety of which are readily available
to those skilled in the art.
The control unit 12 is a standard control unit easily implemented by one
skilled in the art and an example control unit 12 is shown in FIG. 2. The
example control unit 12 shown includes microprocessor 310, clock 312, I/O
unit 325, interfaces 314, 316, 318 and 320 for controlling engine spark
timing, fuel injection, IAC valve position and EGR valve position in
response to microprocessor 310. Microprocessor 310 executes an engine
control program implementing this invention with standard engine control
functions. The control program is stored in ROM 332 and RAM 334 is used
for temporary storage of program variables, parameter measurements and
other data. Microprocessor 310 sends commands to I/O unit 325, ROM 332,
RAM 334 and timer 336 through bus 322 and transfers information between
the various units through bi-directional data bus 324.
The I/O unit 325 and the timer unit 336 comprise means for receiving the
measurement signals for the measured engine parameters. Engine speed data
from sensor 48 is fed, through line 26, to counter 338, which counts the
rotations of the engine output shaft 46. The counter 338 provides the
count information to timer 336 through lines 340. From the information
provided by counter 338 and timer 336, microprocessor 310 can easily
compute the engine speed (RPM) and store the information in RAM 334.
Various other input signals are provided through the I/O unit 325.
Equivalent functions to those of microprocessor 310, I/O unit 325, ROM
332, RAM 334 and timer 336, all shown within box 309, can be performed by
a single chip microcomputer, such as Motorola.TM. microcomputer No.
MC68HC11.
Spark timing and dwell commands may be determined by the microprocessor 310
(in accordance with this invention as described below) and those commands
are provided to a standard spark timing module 14 through bus 326. Spark
timing module 314 also receives engine position reference signals from a
standard reference pulse generator 327 and controls the engine spark plugs
through lines 23-25.
Buses 328, 329 and 330 provide commands from microprocessor 310 to
interface units 316, 318 and 320, which are standard drivers for the
engine fuel injection, idle air control valve and exhaust gas
recirculation valve.
This invention can be used to predict various engine states at future
engine events. The predicted engine states, such as manifold absolute
pressure, mass air flow and engine speed are determined in response to a
variety of engine parameters. The predicted values for these states may be
used in place of measured values in conventional engine--powertrain
controls to provide improved engine--powertrain control.
In one implementation of the invention to predict manifold absolute
pressure, the control unit determines the measures of the engine
parameters such as EGR valve position, IAC valve position, manifold
pressure, engine speed, temperature, and atmospheric pressure and uses the
measurements in the prediction-estimation process to determine an accurate
prediction of manifold pressure at the time air and fuel enter the engine
44. Once an accurate prediction of manifold pressure at the time air and
fuel enter the engine 44 is determined, the measure of mass airflow into
the engine can be calculated through standard speed-density calculations.
With the mass airflow calculated using the predicted manifold pressure,
the fuel injectors 42 can be controlled through lines 24 so that a proper
air-fuel ratio enters the engine 44. The mass airflow into the engine can
also be used together with other engine parameters to determine the
ignition timing for spark plugs 41 and 43.
Many engines do not have an IAC valve 28 or an EGR valve 36, but as will be
explained below, their presence is not necessary for the successful
implementation of the invention. Furthermore, the specific engine
parameters that need to be taken into account for successful
implementation of this invention vary depending upon which state this
invention is being implemented to predict. For example, if manifold
absolute pressure is being predicted, at least throttle position and
manifold absolute pressure must be taken into account in calculating the
predictions. Including other engine parameters in the calculations
improves the accuracy of the predicted manifold absolute pressure
measurement.
A more detailed description of a typical engine timing scheme can be
understood with reference to the timing diagram shown in FIG. 3. The
timing diagram shown is for a V6 engine. The times labeled TDC.sub.4,
TDC.sub.5, TDC.sub.6, TDC.sub.1, and TDC.sub.2 correspond to the times
when the fourth, fifth, sixth, first, and second cylinders achieve top
dead center position, respectively. In the example shown, each top dead
center occurs 120 degrees of engine output shaft rotation after the
previous cylinder achieves the top dead center position. In one
implementation, each engine event may correspond to a cylinder achieving
top dead center position. For example, if at the present engine event, k,
cylinder 5 is at the top dead center position (TDC.sub.5), then TDC.sub.4
occurred at event k-1, TDC.sub.6 will occur at event k+1, TDC.sub.1 will
occur at event k+2, TDC.sub.2 will occur at event k+3, etc. Alternatively,
any fixed point in the engine cycle may be chosen to correspond to the
occurrence of an engine event. Blocks 210, 212, and 214 represent the
power stroke, exhaust stroke, and intake stroke, respectively, for
cylinder one.
In order to account for the computation and fuel delivery delays, each
cylinder's fuel requirement must be calculated when the second preceding
cylinder achieves the top dead center position, e.g., the fuel requirement
for cylinder one must be calculated at the top dead center position of
cylinder five. Using the computation of fuel for cylinder one as an
example, the sensor measurements required to calculate the fuel for
cylinder one are taken at TDC.sub.5, the present engine event k. The fuel
and air are delivered to cylinder one during the intake stroke 214. To
compensate for the delays in this V6 system, manifold pressure is ideally
predicted somewhere between 2 and 3 engine events in advance. Although in
theory an optimal prediction point exists, it is difficult to determine.
However, depending upon the characteristics of the system, it may be
preferable to approximate and predict manifold pressure based on a
weighted average of the predictions 2 and 3 engine events in advance, or
in other systems a prediction 2 engine events in the future may be
optimal.
Implementation of the prediction-estimation method for predicting future
values of an engine state can be further explained with reference to FIG.
4. Block 66 represents the engine assembly whose parameters are measured
by sensors 68 and used by the predictor-estimator 78. As can be seen by
the arrangement of blocks 70, 72, and 76, the prediction-estimation method
operates in a loop.
As will be explained, the prediction-estimation method is a dynamic process
whose output depends upon previous measurements and estimations. For this
reason, various parameters of the system must be initialized, during
vehicle start-up or system reset. After initialization, estimations of the
desired engine state, X.sup.e (X here represents the general engine state
to be predicted, X.sup.e denoted an estimation of X and X.sup.p represents
a prediction of X), are computed through blocks 70 and 72 in response to
previously predicted values of the desired engine state, X.sup.p (k), and
a weighted comparison of a previously predicted value of the desired
engine state with an actual measured value of the desired engine state, X.
New predictions of the desired engine state at the next engine event and R
engine events ahead, X.sup.p (k+1) and X.sup.p (k+R), are determined at
block 76 in response to the estimates at block 72, the measured engine
parameters, and a set of fixed predetermined model parameters.
The number of engine events ahead, R, that is used depends on the specific
engine state being predicted, and the specific engine system. For example,
if manifold absolute pressure is predicted, typical values for R might
include 1, 2, 3 and 4 depending upon the specific engine system.
The prediction of the desired state at R engine events in the future,
X.sup.p (k+R), is the desired prediction result. The prediction of the
desired state at the next engine event, Xp(k+1), is for use in the
estimation step to correct for error tendencies in the prediction model.
The coefficients used in the weighted comparison in block 70 are
predetermined in block 62 in a test vehicle through a statistical
optimization process such as Kalman filtering and scheduled, based upon
two independent engine parameters, e.g., measured manifold absolute
pressure and engine speed, at block 61. After the estimator correction
coefficients are retrieved, they are used at block 70 in the weighted
comparison of the predicted value of the desired engine state for engine
event k and the measured value of the state. The weighted comparison may
be done either as a separate step from determining the estimations or as
part of the estimation determination step. The weighted comparison for the
example where manifold absolute pressure is predicted can be described as
the following function:
G.sub.f (X.sup.err),
where X.sup.err =X(k)=X.sup.p (k). The model parameters are predetermined
through statistical reduction of data taken from a test vehicle and
scheduled at box 75.
Both the model parameters and correction coefficients are fixed and
predetermined in a test vehicle. Because of the nonlinearity of the
engine, the model parameters and correction coefficients are scheduled.
The predetermination of the parameters and correction coefficients along
with the scheduling of the same allows for the control system to have fast
response to changing engine states. This is because when the engine
changes states, new model parameters and correction coefficients are
simply looked up from computer memory or interpolated from values in
computer memory, eliminating the need for adaptive predictions and the
slower response time accompanying adaptive systems (typically at least
200-300 events).
FIG. 5 represents a computer flow diagram of a generic implementation of
this invention to predict an engine state X, where X(k) is the measure of
the engine state X at time k and X.sup.p (k+R) is the prediction of the
engine state X at time (k+R). Blocks 100, 102, 104, and 106 startup the
system and initialize the variables. At block 108, the system checks for
an interrupt signal, which is produced by the engine controller whenever
it requires a new prediction. If there is an interrupt, the program
proceeds into the prediction-estimation loop starting at block 110, where
the set of engine parameters used in the prediction is determined through
input from the measurement means and/or calculation as described above.
The set of engine parameters used in the prediction comprises a vector
U(k), where
##EQU1##
where u.sub.1 (k) . . . u.sub..epsilon. (k) are the past and present
engine parameter measurements determined at block 110 and in computer
memory. For example, u.sub.1 (k)=TPS(k), u.sub.2 (k)=TPS(k-1), etc., where
TPS(k) is a measure of throttle position at event k and TPS(k-1) is a
measure of throttle position at event k-1.
At block 112, the computer computes a value for predicted state error,
X.sup.err. At block 114 the estimator correction coefficients are
scheduled and retrieved.
The estimator correction coefficients may be represented by a vector G,
such that:
##EQU2##
Implementation of statistical optimization of the estimator correction
coefficients reveals that the coefficients G for a given engine operating
point eventually achieve a virtual steady state. This allows the
determination of G to be done off line, e.g., in a test vehicle, and the
values for G to be program | | |
