Power plants – Internal combustion engine with treatment or handling of... – Material from exhaust structure fed to engine intake
Reexamination Certificate
2001-07-10
2003-01-14
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Material from exhaust structure fed to engine intake
C060S274000, C060S285000, C123S406480
Reexamination Certificate
active
06505465
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for controlling an internal combustion engine by using a NOx purifying catalyst to reduce NOx (nitrogen oxides) in the exhaust gas. More particularly, the invention relates to a device for controlling an internal combustion engine capable of estimating the amount of NOx emission within short periods of time maintaining high precision and realizing improved control performance without increasing the cost that results when a memory having a large capacity is used.
2. Prior Art
Devices for controlling internal combustion engines of this kind have heretofore been provided with NOx amount estimating means for estimating the amount of NOx adsorbed by a NOx adsorbing agent as taught in, for example, Japanese Patent No. 2586739.
FIG. 3
is a block diagram illustrating the constitution of a conventional device that is adapted to a gasoline engine.
To avoid complexity, here, the description deals with one cylinder only. It should, however, be noted that the same constitution applies to plural cylinders.
In
FIG. 3
, an internal combustion engine
1
includes a piston
2
, a combustion chamber
3
, a spark plug
4
, an intake valve
5
, an intake port
6
, an exhaust valve
7
and an exhaust port
8
.
The intake port
6
is coupled to a surge tank
10
through a corresponding intake pipe
9
which is provided with a fuel injection valve
11
for injecting fuel into the intake port
6
.
The surge tank
10
is coupled to an air cleaner
13
through an intake duct
12
in which a throttle valve
14
is disposed. The intake duct
12
is further provided with an air flow sensor (not shown) for detecting the amount of the air taken in.
On the other hand, the exhaust port
8
is connected, through an exhaust manifold
15
and an exhaust pipe
16
, to a casing
18
in which a NOx adsorbing agent
17
is contained.
The NOx adsorbing agent
17
adsorbs NOx in the exhaust gas and works as a NOx purifying catalyst.
An electronic control unit (ECU)
30
comprises a digital computer which includes a ROM
32
, a RAM
33
, a CPU
34
, an input port
35
and an output port
36
which are connected to each other through a bidirectional bus
31
, as well as A/D converters
37
,
38
inserted on the input side of the input port
35
and drive circuits
39
inserted on the output side of the output port
36
.
A pressure sensor
19
is mounted in the surge tank
10
to generate an output voltage in proportion to an absolute pressure in the surge tank
10
. An output voltage of the pressure sensor
19
is fed to the input port
35
through the A/D converter
37
.
An air-fuel ratio sensor
25
is mounted on the exhaust pipe
16
. An output voltage of the air-fuel ratio sensor
25
is fed to the input port
35
through the A/D converter
38
.
Further, a known EGR pipe (not shown) is provided between the exhaust pipe
16
and the intake pipe
9
to recirculate part of the exhaust gas. The EGR pipe is provided with an EGR valve for adjusting the EGR amount.
An idle switch
20
is attached to the throttle valve
14
to detect the idle opening degree of the throttle valve
14
. An output signal of the idle switch
20
is input to the input port
35
. Similarly, an output signal (engine rotational speed Ne) of a rotational speed sensor
26
is fed to the input port
35
.
The operation of the conventional device shown in
FIG. 3
will be briefly described below with reference to
FIGS. 4 and 5
. The control operation of the conventional device is as disclosed in detail in the above-mentioned patent publication, and is not described here.
The CPU
34
in the ECU
30
constitutes NOx amount estimating means in cooperation with the ROM
32
and RAM
33
, and estimates the amount of NOx adsorbed by the NOx adsorbing agent
17
.
It is difficult to directly detect the amount of NOx adsorbed by the NOx adsorbing agent
17
. Therefore, the amount of NOx in the exhaust gas emitted from the engine
1
is found to estimate the amount of NOx adsorbed by the NOx adsorbing agent
17
from the amount of NOx in the exhaust gas.
In general, the amount of the exhaust gas emitted from the engine
1
per a unit time increases with an increase in the engine rotational speed Ne. Accordingly, the amount of NOx emitted from the engine
1
per a unit time increases with an increase in the engine rotational speed Ne.
Further, as the engine load increases (i.e., as the absolute pressure PM in the surge tank
10
increases), the amount of the exhaust gas emitted from the combustion chamber
3
increases and the combustion temperature increases. As the engine load increases (absolute pressure PM in the surge tank
10
increases), therefore, the amount of NOx emitted from the engine
1
per a unit time increases.
FIG. 4
is a diagram illustrating the amount of NOx emitted from the engine
1
per a unit time, and wherein the values found through experiment are related to the absolute pressure PM (ordinate) in the surge tank
10
and the engine rotational speed Ne (abscissa).
In
FIG. 4
, the continuous curves represent the same amounts of NOx.
As shown in
FIG. 4
, the amount of NOx emitted from the engine
1
per a unit time increases with an increase in the absolute pressure PM in the surge tank
10
and with an increase in the engine rotational speed Ne.
The amounts of NOx shown in
FIG. 4
have been stored in advance in the ROM
32
in the form of map data N
11
to Nij shown in FIG.
5
.
The map data shown in
FIG. 5
vary depending upon other various operating conditions. When it is attempted to correctly find the amount of NOx by operating the map, a large amount of memory capacity is necessary driving up the cost.
According to the conventional device of controlling the internal combustion engine as described above, the data used by the NOx amount estimating means in the ECU
30
are stored as map data N
11
to Nij as shown in FIG.
5
. Therefore, the map data must be formed for every operating condition of the engine
1
and must be stored in the ROM
32
, requiring laborious work and extended periods of time and driving up the cost.
SUMMARY OF THE INVENTION
The present invention was accomplished in order to solve the above-mentioned problem, and has an object of providing a device for controlling an internal combustion engine by estimating the amount of NOx emission within short periods of time maintaining high precision and improving control performance without the need of storing great amounts of map data in the ROM and, hence, without driving up the cost.
A device for controlling an internal combustion engine according to the present invention comprises:
an air flow sensor provided in an intake pipe of the internal combustion engine to detect the amount of the intake air;
temperature detector means and pressure detector means for detecting the temperature and the pressure of the air taken in by the internal combustion engine;
air-fuel ratio detector means provided in the exhaust pipe of the internal combustion engine and for detecting the air-fuel ratio in the exhaust gas;
EGR rate detector means for detecting the EGR rate of the exhaust gas recirculated into the intake air;
a NOx purifying catalyst provided in the exhaust pipe of the internal combustion engine;
NOx operation means for estimating the amount of NOx in the exhaust gas from a theoretical formula and an empirical formula based upon the amount of the intake air, temperature and pressure of the intake air, air-fuel ratio and EGR rate; and
control means for controlling at least either the NOx purifying catalyst or the combustion state in the internal combustion engine in order to lower the amount of NOx emission.
In the device for controlling an internal combustion engine according to the present invention, the theoretical formula and the empirical formula contain a correction coefficient that varies depending upon at least either the model of the internal combustion engine or the combustion mode.
In the device for controlling an internal combustion engine according to the present i
Kanazawa Yukiko
Katashiba Hideaki
Kawajiri Kazuhiko
Yonezawa Takashi
Denion Thomas
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Tu M.
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