Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
1999-12-08
2002-02-12
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000
Reexamination Certificate
active
06345498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purifier for an internal combustion engine.
2. Description of the Prior Art
FIG. 19
is a structural diagram of an exhaust gas purifier for an internal combustion engine
1
disclosed by Japanese Laid-open Patent Application No. 8-232644. In
FIG. 19
, reference numeral
1
denotes an internal combustion engine,
2
a piston,
3
a combustion chamber,
4
a spark plug,
5
an inlet valve,
6
an inlet port,
7
an exhaust valve, and
8
an exhaust port. The inlet port
6
is connected to a surge tank
10
via a branch pipe
9
, and a fuel injection valve
11
for injecting fuel into the inlet port
6
is disposed in the branch pipe
9
. The surge tank
10
is connected to an air cleaner
13
via an inlet duct
12
, and a throttle valve
14
is arranged in the inlet duct
12
. The exhaust port
8
is connected to a casing
17
incorporating an NOx absorber catalyst
18
via an exhaust manifold
15
and an exhaust pipe
16
.
An electronic control unit
30
is a digital computer which comprises a ROM (read only memory)
32
, a RAM (random access memory)
33
, a CPU (microprocessor)
34
, a back-up RAM
35
which is always connected to a power source, an input port
36
, an output port
37
, AD converters
38
and drive circuits
39
all of which are connected to one another by a bilateral bus
31
. A pressure sensor
19
for outputting an output voltage proportional to the absolute pressure of the surge tank
10
is placed in the surge tank
10
, and the output voltage of the pressure sensor
19
is applied to the input port
36
through the corresponding AD converter
38
. A switching type air-fuel ratio sensor
20
called “O
2
sensor” is installed in the exhaust manifold
15
at an upstream of the NOx absorber catalyst
18
, and the output of the air-fuel ratio sensor
20
is applied to the input port
36
through the corresponding AD converter
38
. Another switching type air-fuel ratio sensor
22
called “O
2
sensor” is installed in the exhaust pipe
21
at a downstream of the NOx absorber catalyst
18
, and the output of the air-fuel ratio sensor
22
is applied to the input port
36
through the corresponding AD converter
38
. A revolution sensor
23
for generating an output pulse indicative of an engine speed N and a car speed sensor
24
for generating an output pulse indicative of a car speed are connected to the input port
36
. The output port
37
is connected to the spark plug
4
and the fuel injection valve
11
via the respective drive circuits
39
.
A description is subsequently given of the operation of the prior art device. A mixture having a lean air-fuel ratio (to be referred to as “lean mixture” hereinafter) is generally burnt in a combustion chamber
3
. When the amount of nitrogen oxide NOx absorbed by the NOx absorber catalyst
18
exceeds a predetermined amount, the NOx discharge function of the NOx absorber catalyst
18
is started by controlling such that the air-fuel ratio of exhaust gas flowing into the NOx absorber catalyst
18
becomes rich.
SUMMARY OF THE INVENTION
However, the deterioration of the NOx absorber catalyst is roughly divided into two types: (1) deterioration such as thermal deterioration by which the catalyst cannot restore its NOx absorbing capability and (2) deterioration such as sulfur poisoning from which the NOx absorber catalyst can restore its NOx absorbing capability to a certain extent by some regeneration treatment. In the exhaust gas purifier for an internal combustion engine
1
disclosed by the aforementioned Japanese Laid-open Patent Application No. 8-232644, the above two different types of deterioration are handled in the same manner and the permissible amount of absorbed NOx is set based on the NOx absorbing capacity after judgment on deterioration. Since rich operation for judging the deterioration of the NOx absorber catalyst is carried out based on the air-fuel ratio A/F set as one pattern in the above publication, as shown in
FIG. 20
, when the air-fuel ratio for judgment is rich, a difference in deterioration is small whereas, as shown in
FIG. 21
, when the air-fuel ratio is not so rich, the difference becomes large but rich operation for judgment lasts for a long time, which is disadvantageous from the view point of fuel cost.
The NOx absorber catalyst
18
deteriorates gradually while it is used. The NOx absorbing capability of the NOx absorber catalyst
18
degrades as it deteriorates and the catalyst cannot absorb NOx in the end. Therefore, when the NOx absorber catalyst
18
is used, it is necessary to detect how much the NOx absorber catalyst
18
deteriorates. When the air-fuel ratio of exhaust gas flowing into the NOx absorber catalyst
18
is made rich, the air-fuel ratio of exhaust gas flowing out from the NOx absorber catalyst
18
becomes slightly lean while the NOx discharge function of the NOx absorber catalyst
18
is executed. When the NOx discharge function of the NOx absorber catalyst
18
is completed, it is found that the air-fuel ratio of exhaust gas flowing out from the NOx absorber catalyst
18
becomes rich. In this case, as the amount of NOx absorbed by the NOx absorber catalyst
18
is smaller, a time elapsed from the time when the air-fuel ratio of exhaust gas flowing into the NOx absorber catalyst
18
is made rich to the time when the air-fuel ratio of the exhaust gas flowing out from the NOx absorber catalyst
18
becomes rich is shorter. Therefore, the deterioration degree of the NOx absorber catalyst
18
can be detected from the above time elapsed.
It is an object of the present invention which has been made to solve the above problems to provide an exhaust gas purifier for an internal combustion engine which is capable of detecting the deterioration degree of an NOx absorber catalyst making use of a time elapsed from the time when the air-fuel ratio of exhaust gas flowing into the NOx absorber catalyst is made rich to the time when the air-fuel ratio of exhaust gas flowing out from the NOx absorber catalyst becomes rich.
According to a first aspect of the present invention, there is provided an exhaust gas purifier for an internal combustion engine which comprises an NOx absorber catalyst, air-fuel ratio sensor, first NOx estimating means, decision means, air-fuel switching means, second NOx estimating means and deterioration judging means, wherein the NOx absorber catalyst absorbs NOx when the air-fuel ratio of inflow exhaust gas is lean and purifies and discharges its absorbed NOx when the air-fuel ratio of inflow exhaust gas is rich, the air-fuel ratio sensor detects the concentration of oxygen contained in exhaust gas at a downstream of the NOx absorber catalyst, the first NOx estimating means obtains a first estimated amount of NOx estimated to be absorbed by the NOx absorber catalyst, the judging means judges whether the first NOx estimated amount obtained by the first NOx estimating means exceeds a decision level for judging that the first NOx estimated amount becomes the NOx maximum permissible amount of the NOx absorber catalyst, the air-fuel ratio switching means switches the air-fuel ratio of the exhaust gas from lean to rich to discharge NOx from the NOx absorber catalyst when the judging means judges that the first NOx estimated amount exceeds the above decision level, the second NOx estimating means obtains a second estimated amount of NOx from the length of a time elapsed from the time when the air-fuel ratio switching means switches the air-fuel ratio of exhaust gas from lean to rich to the time when the output of the air-fuel ratio sensor is changed to an output level corresponding to a rich air-fuel ratio, and the deterioration judging means judges the deterioration degree of the NOx absorber catalyst by comparing the second estimated amount of NOx obtained by the second NOx estimating means with the first estimated amount of NOx obtained by the first NOx estimating means. The deterioration judging means judges the deterioration degree of the NOx absorbe
Katashiba Hideaki
Ohuchi Hirofumi
Wachi Satoshi
Yonekura Tosiaki
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