Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2002-07-30
2004-11-09
Solis, Erick (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S681000, C701S109000
Reexamination Certificate
active
06814067
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a control system for a plant, which uses a self-tuning regulator, and also relates to an air-fuel ratio control system for controlling, to a target value, an air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine.
An example of a control system for a plant, which uses a self-tuning regulator is described in Japanese Patent Laid-open No. 11-73206.
FIG. 15
is a block diagram showing a general configuration of a control system using a self-tuning regulator
104
as shown in this publication. The self-tuning regulator
104
includes a parameter adjusting mechanism
105
and an inverse transfer function controller
106
. The parameter adjusting mechanism
105
identifies model parameters (which will be hereinafter referred to also as “self-tuning parameters”) of a controlled object model obtained by modeling a controlled object (an engine system). The inverse transfer function controller
106
calculates a self-tuning correction coefficient KSTR by an inverse transfer function of a transfer function of the controlled object model by using the model parameters identified by the parameter adjusting mechanism
105
. An air-fuel ratio detected by an air-fuel ratio sensor
17
is converted into a detected equivalent ratio KACT by a converting section
103
, and the detected equivalent ratio KACT is supplied to the self-tuning regulator
104
.
A target value calculating section
102
calculates a target air-fuel ratio coefficient KCMD (target equivalent ratio) corresponding to a target air-fuel ratio, and inputs the target air-fuel ratio coefficient KCMD into a fuel amount calculating section
101
and the inverse transfer function controller
106
. The parameter adjusting mechanism
105
identifies the model parameters according to the detected equivalent ratio KACT and the self-tuning correction coefficient KSTR. The inverse transfer function controller
106
calculates a present value of the self-tuning correction coefficient KSTR according to the target equivalent ratio KCMD, the detected equivalent ratio KACT, and past values of the self-tuning correction coefficient KSTR. The self-tuning correction coefficient KSTR and the target equivalent ratio KCMD are input to the fuel amount calculating section
101
. The fuel amount calculating section
101
calculates a fuel amount TOUT, that is, an amount of fuel to be supplied to an internal combustion engine (which will be hereinafter referred to also as “engine”)
1
, using the target air-fuel ratio coefficient KCMD, the self-tuning correction coefficient KSTR, and other correction coefficients.
More specifically, the engine system as a controlled object is modeled into a controlled object model (DARX model (delayed autoregressive model with exogenous input)) defined by Eq. (1) shown below:
KACT
(
k
)=b
0
×
KSTR
(
k−
2)+r
1
×
KSTR
(
k−
3)+r
2
×
KSTR
(
k−
4)+r
3
×
KSTR
(
k−
5)+s
0
×
KACT
(
k−
2) (1)
where b
0
, r
1
, r
2
, r
3
, and s
0
are the model parameters identified by the parameter adjusting mechanism
105
. When a model parameter vector &thgr;(k) having the model parameters as elements is defined by Eq. (2), shown below, the model parameter vector &thgr;(k) is calculated from Eq. (3) shown below:
&thgr;(
k
)
T
=[b
0
, r
1
, r
2
, r
3
, s
0
] (2)
&thgr;(
k
)=
EPS &thgr;
(
k−
1)+
KP
(
k
)
ide
(
k
) (3)
where KP(k) is a gain coefficient vector defined by Eq. (4) shown below, and ide(k) is an identification error defined by Eq. (5), shown below. Further, EPS is a forgetting coefficient vector defined by Eq. (6), shown below. In Eq. (6), &egr; is a forgetting coefficient which is set to a value between “0” and “1”:
K
P
(
k
)
=
P
ζ
(
k
)
1
+
ζ
T
(
k
)
P
ζ
(
k
)
(
4
)
ide
(
k
)=
KACT
(
k
)−&thgr;(
k−
1)
T
(
k
) (5)
EPS
=[1, &egr;, &egr;, &egr;, &egr;] (6)
In Eq. (4), P is a square matrix wherein the diagonal elements are constants and all the other elements are “0”. In Eqs. (4) and (5), &zgr;(k) is a vector defined by Eq. (7), shown below, and having a control output (KACT) and control inputs (KSTR) as elements.
&zgr;(
k
)
T
=[KSTR
(
k−
2),
KSTR
(
k−
3),
KSTR
(
k−
4),
KSTR
(
k−
5),
KACT
(
k−
2)] (7)
Further, the inverse transfer function controller
106
determines the control input KSTR(k) so that Eq. (8), shown below, holds:
KCMD
(
k
)=
KACT
(
k+
2) (8)
By applying Eq. (1) to Eq. (8), the right side of Eq. (8) becomes:
KACT
(
k+
2)=b
0
×
KSTR
(
k
)+r
1
×
KSTR
(
k−
1)+r
2
×
KSTR
(
k−
2)+r
3
×
KSTR
(
k−
3)+s
0
×
KACT
(
k
) (8a)
Accordingly, the following equation (9), shown below is obtained from Eqs. (8) and (8a). The control input KSTR(k) is calculated from Eq. (9):
KSTR
(
k
)=(1/b
0
)[
KCMD
(
k
)−r
1
×
KSTR
(
k−
1)−r
2
×
KSTR
(
k−
2)−r
3
×
KSTR
(
k−
3)−s
0
×
KACT
(
k
)] (9)
That is, the inverse transfer function controller
106
calculates the control input KSTR(k) so that a deviation e(k) between a future equivalent ratio KACT(k+2) which will be detected two control cycles later, and the present value KCMD(k) of the target equivalent ratio, becomes “0”. The deviation e(k) is defined by Eq. (10), shown below:
e
(
k
)=
KACT
(
k+
2)−
KCMD
(
k
) (10)
The characteristic of the controlled object model defined by Eq. (1) does not completely coincide with the characteristic of the actual controlled object, but includes a modeling error (the difference between the characteristic of the controlled object model and the characteristic of the actual controlled object). Further, the parameter adjusting mechanism
105
adopts a fixed gain algorithm. Accordingly, when the target equivalent ratio KCMD changes stepwise as shown in
FIG. 16
, the detected equivalent ratio KACT is influenced by the identification behavior of the model parameters due to the modeling error and the fixed gain algorithm, which sometimes results in an overshoot of the detected equivalent ratio KACT with respect to the target equivalent ratio KCMD.
Such overshoot causes a reduction in the purification rate of a catalyst provided in an exhaust system of the engine. This results in a deterioration of exhaust characteristics. Furthermore, depending on engine operating conditions, there is a possibility of causing an engine output surge wherein the engine driving force fluctuates.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a control system for a plant, wherein a plant such as the above-described engine system is properly controlled, using a self-tuning regulator. As a result, an output from the plant accurately coincides with a control target value even when the control target value changes stepwise.
It is another object of the present invention to provide an air-fuel ratio control system for an internal combustion engine which can properly control the air-fuel ratio of an air-fuel mixture to be supplied to the engine. As a result, the actual air-fuel ratio detected in an exhaust system of the engine accurately coincides with a target value even when the target value changes stepwise, thereby preventing a deterioration in the exhaust characteristic and the engine output surge.
To attain the first object, the present invention provides a control system for a plant, including identifying means (
54
) and control means (
55
). The identifying means (
54
) identifies model parameters (b
0
, r
1
, r
2
, r
3
, s
0
) of a controlled object model obtained by modeling the plant. The control means (
55
) calculates a control input (KSTR) to the
Iwaki Yoshihisa
Yasui Yuji
Honda Giken Kogyo Kabushiki Kaisha
Solis Erick
Squire Sanders & Dempsey LLP
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