U.S. patent application number 11/264359 was filed with the patent office on 2006-06-01 for exhaust emission control device of internal combustion engine.
This patent application is currently assigned to Mitsubishi Fuso Truck and Bus Corporation. Invention is credited to Susumu Kohketsu, Shinji Nakayama, Daisuke Sunohara, Keiki Tanabe.
Application Number | 20060112681 11/264359 |
Document ID | / |
Family ID | 35658964 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060112681 |
Kind Code |
A1 |
Nakayama; Shinji ; et
al. |
June 1, 2006 |
Exhaust emission control device of internal combustion engine
Abstract
An exhaust emission control device of an internal combustion
engine includes a fuel supply unit provided in a fuel supply
passage, for supplying a reducing agent directly to a NOx trap
catalytic converter; an addition pressure detection unit for
detecting the supply pressure of the reducing agent supplied by the
fuel supply unit; and a controller for calculating the amount of
NOx adsorbed by the catalytic converter. When the supply pressure
of the reducing agent is almost zero, the controller prohibits
calculation of NOx adsorption amount depending on the supply of the
reducing agent, creates a rich state in a cylinder, carries out
calculation of NOx adsorption amount depending on the created rich
state, and causes release and reduction of the adsorbed NOx.
Inventors: |
Nakayama; Shinji; (Tokyo,
JP) ; Kohketsu; Susumu; (Tokyo, JP) ; Tanabe;
Keiki; (Tokyo, JP) ; Sunohara; Daisuke;
(Tokyo, JP) |
Correspondence
Address: |
ROSSI, KIMMS & McDOWELL LLP.
P.O. BOX 826
ASHBURN
VA
20146-0826
US
|
Assignee: |
Mitsubishi Fuso Truck and Bus
Corporation
Minato-ku
JP
|
Family ID: |
35658964 |
Appl. No.: |
11/264359 |
Filed: |
November 1, 2005 |
Current U.S.
Class: |
60/286 ; 60/295;
60/301 |
Current CPC
Class: |
F02D 41/405 20130101;
F01N 3/206 20130101; F01N 2430/085 20130101; F02D 41/1441 20130101;
Y02T 10/44 20130101; Y02T 10/24 20130101; F01N 3/0807 20130101;
F02D 41/0275 20130101; F02D 41/3836 20130101; Y02T 10/12 20130101;
Y02T 10/47 20130101; F01N 3/0842 20130101; F01N 11/00 20130101;
F01N 2550/05 20130101; Y02T 10/40 20130101; F02D 41/22 20130101;
F01N 2430/06 20130101 |
Class at
Publication: |
060/286 ;
060/295; 060/301 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2004 |
JP |
2004-320847 |
Claims
1. An exhaust emission control device of an internal combustion
engine, comprising: an exhaust passage connected with a cylinder of
the engine, a NOx trap catalytic converter provided in the passage,
capable of adsorbing NOx contained in exhaust in lean operation and
releasing and reducing the adsorbed NOx in rich operation, a supply
means provided in the passage, for supplying a reducing agent
directly to the catalytic converter, a detection means for
detecting the supply pressure of the reducing agent supplied by the
supply means, and a controller for calculating the amount of NOx
adsorbed by the catalytic converter, wherein when the supply
pressure of the reducing agent is almost zero, the controller
prohibits calculation of NOx adsorption amount depending on the
supply of the reducing agent, creates a rich state in the cylinder,
carries out calculation of NOx adsorption amount depending on the
created rich state, and causes release and reduction of the
adsorbed NOx.
2. The exhaust emission control device of the internal combustion
engine according to claim 1, wherein when the supply pressure of
the reducing agent is almost zero, the controller treats the amount
of NOx emitted by the supply of the reducing agent, as zero, to
negate it in the calculation of the amount of adsorbed NOx.
3. The exhaust emission control device of the internal combustion
engine according to claim 1, wherein when the supply pressure of
the reducing agent is almost zero, the controller performs rich
spike by post injection under specific restrictions.
4. The exhaust emission control device of the internal combustion
engine according to claim 3, wherein the number of times that the
rich spike by post injection is performed or the accumulated time
of the rich spike by post injection is restricted to the number of
times or the time which does not cause lubricating oil for the
engine to exceed a dilution limit.
5. The exhaust emission control device of the internal combustion
engine according to claim 3, wherein the rich spike by post
injection is restricted to the engine operation with medium load or
lower.
6. An exhaust emission control device of an internal combustion
engine, comprising: an exhaust passage connected with a cylinder of
the engine, a NOx trap catalytic converter provided in the passage,
capable of adsorbing NOx contained in exhaust in lean operation and
releasing and reducing the adsorbed NOx in rich operation, a supply
means provided in the passage, for supplying a reducing agent
directly to the catalytic converter, a detection means for
detecting the supply pressure of the reducing agent supplied by the
supply means, and a controller for calculating the amount of NOx
adsorbed by the catalytic converter, wherein when the supply
pressure of the reducing agent is less than a specific pressure,
the controller calculates the amount of the reducing agent
supplied, on the basis of the detected supply pressure, carries out
calculation of NOx adsorption amount depending on the supply of the
reducing agent, and causes release and reduction of the adsorbed
NOx.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an exhaust emission control device
suitable for an internal combustion engine designed to cause
release and reduction of NOx adsorbed by a NOx trap catalyst, by
rich spike by out-of-cylinder rich operation.
[0003] 2. Description of the Related Art
[0004] Generally, the NOx trap catalyst adsorbs NOx (nitrogen
oxide) contained in exhaust when the exhaust air-fuel ratio is
lean, and releases and reduces the adsorbed NOx when the exhaust
air-fuel ratio is rich. Specifically, this catalyst has a
characteristic that it adsorbs NOx contained in exhaust in the form
of nitrate salt in an oxygen excess state (oxidation atmosphere),
and reduces the adsorbed NOx to nitrogen in a carbon-monoxide
excess state (reduction atmosphere).
[0005] In an engine provided with this catalyst, rich spike, that
is, cyclic changeover to rich operation before NOx adsorbed reaches
an amount that saturates the catalyst, is carried out to suppress
the performance degradation of the catalyst caused by increase in
NOx adsorbed. By this, the catalyst is regenerated, so that the
exhaust is purified satisfactorily.
[0006] Rich spike is performed by in-cylinder rich operation or by
out-of-cylinder rich operation. Specifically, in-cylinder rich
operation is performed by recirculating a large amount of exhaust
to cause imperfect combustion and utilizing carbon monoxide (CO)
discharged from the cylinder due to the imperfect combustion, as a
reducing agent, or by supplying unburned fuel (HC) as a reducing
agent into the cylinder in exhaust stroke by post (after)
injection. Meanwhile, out-of-cylinder rich operation is performed
by adding HC to an exhaust passage, or in other words, supplying
fuel directly to the catalyst (Japanese Unexamined Patent
Publication No. 2002-242780).
[0007] In this technique, pressure in a fuel addition line, namely
a line through which HC is supplied directly to the catalyst is
detected. If there is trouble such as malfunction of a fuel pump
for supplying HC or fuel leakage, a controller sends out a signal
for stopping the supply of HC and a signal for displaying a warning
for a driver.
[0008] However, only by stopping the supply of HC and displaying a
warning, error in the controller's calculation of the amount of
adsorbed NOx cannot be prevented. Further, there remains concern
that NOx in exhaust may not be reduced and discharged into the
atmosphere as NOx, since the controller gives an instruction for
the next release and reduction of NOx on the basis of an incorrect
amount of NOx adsorbed. Thus, this technique has a problem to be
solved in respect of the case where a reducing agent fails to be
added to the catalyst.
SUMMARY OF THE INVENTION
[0009] An object of this invention is to provide an exhaust
emission control device of an internal combustion engine that can
produce satisfactory effects even when a reducing agent fails to be
added to a NOx trap catalyst (fail-safe).
[0010] An exhaust emission control device of an internal combustion
engine according to this invention comprises an exhaust passage
connected with a cylinder of the engine; a NOx trap catalytic
converter provided in the exhaust passage, capable of adsorbing NOx
contained in exhaust in lean operation and releasing and reducing
the adsorbed NOx in rich operation; a supply means provided in the
exhaust passage, for supplying a reducing agent directly to the NOx
trap catalytic converter; a detection means for detecting the
supply pressure of the reducing agent supplied by the supply means;
and a controller for calculating the amount of NOx adsorbed by the
catalytic converter, wherein when the supply pressure of the
reducing agent is almost zero, the controller prohibits calculation
of NOx adsorption amount depending on the supply of the reducing
agent, creates a rich state in the cylinder, carries out
calculation of NOx adsorption amount depending on the created rich
state, and causes release and reduction of the adsorbed NOx.
[0011] Thus, in the exhaust emission control device according to
this invention, while the NOx trap catalytic converter is caused to
release and reduce NOx basically by out-of-cylinder rich operation,
supply pressure in the fuel addition line is detected. When the
supply pressure is almost zero, that is, the reducing agent is not
added to the NOx trap catalytic converter, calculation of NOx
adsorption amount depending on out-of-cylinder rich operation is
prohibited. At the same time, according to a rich spike instruction
given for the NOx trap catalytic converter, in-cylinder rich
operation is performed to regenerate the NOx catalytic converter.
Thus, when the reducing agent fails to be added to the NOx trap
catalytic converter, appropriate alternative operation is performed
to avoid increase in NOx (fail-safe). Consequently, reliability of
the exhaust emission control device further improves.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus, are
not limitative of the present invention, and wherein:
[0013] FIG. 1 is a diagram showing structure of an engine system to
which an exhaust emission control device of an internal combustion
engine as an embodiment of the present invention is applied;
[0014] FIG. 2 is a block diagram showing control in the exhaust
emission control device of FIG. 1; and
[0015] FIG. 3 is a block diagram showing control in another
embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Referring to the drawings, embodiments of this invention
will be described below.
[0017] FIG. 1 is a diagram showing structure of an engine system.
This system includes a diesel engine (hereinafter referred to
simply as "engine") 1 to which an exhaust emission control device
as an embodiment of this invention is applied. As shown in this
figure, a fuel supply line 16, an intake passage 8 and an exhaust
passage 20 are connected to each cylinder 2 of the engine 1. The
line 16 includes a fuel injection unit, the passage 8 is the one
through which fresh air is sent to a combustion chamber 4 when an
intake valve 6 is opened, and the passage 20 is the one through
which exhaust is sent from the combustion chamber 4 when an exhaust
valve 18 is opened.
[0018] In the intake passage 8, on the upstream side, a
supercharger 14 is provided. An air cleaner (not shown) is
connected to the passage 8 near the upstream end thereof. An intake
throttle 10 and an inter-cooler 12 are also provided in the passage
8. The intake throttle 10 adjusts the flow passage area of the
passage 8, and the inter-cooler 12 cools fresh air flowing through
the passage 8 to increase volumetric efficiency.
[0019] In the exhaust passage 20, on the downstream side, a NOx
trap catalytic converter 22 is provided. The catalytic converter 22
adsorbs NOx contained in exhaust when the exhaust air-fuel ratio is
lean, namely greater than the stoichiometric air-fuel ratio, and
releases and reduces the adsorbed NOx when the exhaust air-fuel
ratio is rich and the exhaust contains unburned fuel (HC) and/or
carbon monoxide (CO) serving as a reducing agent. The catalytic
converter 22 has a known structure.
[0020] From the exhaust passage 20 extends an EGR passage 24. At
the forward end, the passage 24 is connected with the intake
passage 8. An EGR cooler 26 and an EGR valve 28 are provided in the
passage 24. The valve 28 is electrically connected to an electronic
control unit (ECU) 50 and adjusts the flow passage area of the
passage 24.
[0021] Fresh air from the air cleaner flows through the
supercharger 14 into the intake passage 8, then reaches the cooler
12, then is adjusted by the throttle 10, and then flows into the
combustion chamber 4 of each cylinder 2. Combustion of fuel
supplied through the line 16 causes a crank shaft 46 and a flywheel
48 to operate. After the combustion ends, exhaust is discharged
into the exhaust passage 20 and sent to the catalytic converter
22.
[0022] In the exhaust passage 20, a NOx sensor 30 and an exhaust
temperature sensor 34 are provided at appropriate positions
upstream of the catalytic converter 22. The sensor 30 detects NOx
concentration, or in other words, NOx amount upstream of the
catalytic converter 22, from output voltage. The sensor 34 detects
exhaust temperature T.sub.E in the passage 20. Further, a NOx
sensor 32 and a catalyst temperature sensor 36 are provided at
appropriate positions downstream of the catalytic converter 22. The
sensor 32 detects NOx amount downstream of the catalytic converter
22, and the sensor 36 detects temperature Tc of the catalytic
converter 22. These sensors 30, 32, 34 and 36 are electrically
connected to the ECU 50.
[0023] In the exhaust passage 20, at an appropriate position
upstream of the catalytic converter 22, an addition injector
(supply means) 38 for supplying HC directly to the catalytic
converter 22 is provided. The injector 38 is connected with a pump
40 by a fuel addition line 39. Pressure in the line 39 is detected
by a fuel pressure sensor (detection means) 42. Also the sensor 42
is electrically connected to the ECU 50.
[0024] To the input side of the ECU 50, various sensors for
detecting the operating state of the engine 1 such as a crank angle
sensor 44 are electrically connected, in addition to the
above-mentioned sensors 30, 32, 42, etc. To the output side of the
ECU 50, various actuators such as an actuator for the injector 38
are electrically connected, in addition to the above-mentioned line
16, throttle 10, valve 28 and pump 40.
[0025] The catalytic converter 22 adsorbs NOx contained in exhaust
when it has an oxidizing atmosphere, and the ECU 50 carries out
rich operation periodically. In this embodiment, rich operation is
carried out basically in the form of out-of-cylinder rich
operation. Specifically, according to a rich spike instruction, HC
forced by the pump 40 is supplied directly into exhaust through the
injector 38 provided to the passage 20 to create conditions for
rich operation. When the conditions for rich operation are created,
NOx is released and reduced.
[0026] More specifically, as shown in FIG. 2, the ECU 50 includes
an adsorption amount operation unit (OU) 52 and a combustion
monitor unit (MU) 54. The MU 54 monitors the pressure in the line
39 on the basis of a detection signal from the sensor 42, and sends
out a signal to the OU 52 when the HC supply pressure is almost
zero. The HC supply pressure being almost zero is thought to
indicate fuel leakage from the line 39, malfunction of the pump 40,
etc.
[0027] The OU 52 estimates the amount of NOx adsorbed by the
catalytic converter 22. Specifically, first on the basis of output
signals from the sensors 30, 32, NOx amount on the inlet side of
the catalytic converter 22 and NOx amount on the outlet side
thereof are obtained, and the amount of NOx adsorbed (referred to
as "adsorption amount") is calculated. Then, by subtracting the
amount of NOx released and reduced by rich spike (referred to as
"emission amount by rich spike") from the calculated adsorption
amount, the current adsorption amount is estimated.
[0028] As understood from the above, as the emission amount by rich
spike, basically the amount of NOx emitted by out-of-cylinder rich
operation (referred to as "emission amount by out-of-cylinder rich
operation"), namely the amount of NOx released and reduced by
adding HC through the injector 38 is used. The emission amount by
out-of-cylinder rich operation is obtained in advance, for example,
from maps that are prepared depending on temperature T.sub.C of the
catalytic converter 22, temperature T.sub.E of the passage 20, flow
rate of exhaust SV, etc. and stored in the ECU 50.
[0029] When a rich spike instruction is given depending on signals
from the sensors 30, 32, 34, 36, etc., the emission amount by
out-of-cylinder rich operation is set and used for estimating the
current adsorption amount.
[0030] However, when the sensor 42 detects the HC supply pressure
which is almost zero so that the MU 54 sends out a signal to the OU
52, the OU 52 prohibits the calculation of the adsorption amount
depending on out-of-cylinder rich operation. Specifically, an
emission amount change unit 56 changes the emission amount by
out-of-cylinder rich operation to zero to negate it in the
estimation of the current adsorption amount.
[0031] Thus, when the HC supply pressure is almost zero, the amount
of NOx released and reduced by out-of-cylinder rich operation is
treated as zero. However, if nothing is done, NOx is not easily
released and reduced. Hence, in the present embodiment, as one type
of in-cylinder rich operation, post injection in which HC is
supplied into the cylinders 2 in exhaust stroke is used,
calculation of the adsorption amount depending on this post
injection is carried out, and release and reduction of the adsorbed
NOx is caused.
[0032] Specifically, when a rich spike instruction is given, the
amount of NOx emitted by post injection (referred to as "emission
amount by post injection") is set on the basis of output values
from the sensors 30, 32, 34, 36, and supplied to a rich spike
change unit 58. Also the emission amount by post injection is
obtained in advance from maps stored in the ECU 50.
[0033] When the MU 54 sends out a signal, the change unit 58
chooses the emission amount by post injection. Then, the OU 52
estimates the current adsorption amount by subtracting the emission
amount by post injection from the adsorption amount calculated on
the basis of the output signals from the NOx sensors 30 and 32.
[0034] For the post injection as in the present embodiment, various
restrictions are provided. Specifically, the number of times that
rich spike by post injection is performed and the accumulated time
of rich spike by post injection are restricted to the number of
times and the time which does not cause lubricating oil for the
engine 1 to exceed its dilution limit. This is because the fuel
supplied by post injection does not contribute to power generated
by the engine 1, and hence, it can dilute lubricating oil held in a
crank case along the cylindrical wall of the combustion chamber 4,
etc. By providing the above restrictions, dilution of the
lubricating oil is prevented.
[0035] Further, post injection is restricted to the engine 1
operation with medium load or lower. This is because when the
engine is operating with high load, post injection leads to
increase in NOx in exhaust. By providing this restriction, the
number of times that post injection is performed is reduced, NOx
contained in exhaust is reduced, and the necessity of immediately
stopping the engine 1 can be avoided.
[0036] As described above, the present embodiment is designed to
perform alternative operation when the line 39, etc. are out of
order (fail-safe).
[0037] While the catalytic converter 22 is caused to release and
reduce NOx basically by out-of-cylinder rich operation, the sensor
42 for detecting the supply pressure in the line 39 is provided and
the MU 54 monitors this pressure. When this pressure is almost
zero, that is, HC is not added to the catalytic converter 22, the
OU 52 prohibits the calculation of the adsorption amount depending
on out-of-cylinder rich operation. At the same time, by the
operation of the change unit 58, post injection is performed to
regenerate the catalytic converter 22. Thus, when HC fails to be
added to the catalytic converter 22, appropriate alternative
operation is performed, so that increase in NOx is avoided
(fail-safe). Consequently, reliability of the exhaust emission
control device further improves.
[0038] Further, when the HC supply pressure is almost zero, the
change unit 56 sets the emission amount by out-of-cylinder rich
operation to zero. Hence, unlike the conventional case, incorrect
estimation of the adsorption amount on the assumption that HC is
property supplied is not continued. Thus, the accuracy of
estimation of the adsorption amount improves, compared with the
conventional case.
[0039] Further, while rich spike by post injection is performed as
alternative operation, various restrictions are provided for the
post injection. Thus, adverse effects of the post injection are
minimized.
[0040] The above is the description of one embodiment of the
present invention. The present invention is, however, not limited
to the above embodiment.
[0041] For example, in the above embodiment, alternative operation
is performed by changing the way of rich spike from out-of-cylinder
rich operation to in-cylinder rich operation. However, appropriate
alternative operation can be performed using only out-of-cylinder
rich operation. As shown in FIG. 3, in this embodiment, the
emission amount by out-of-cylinder rich operation is used.
[0042] In the embodiment shown in FIG. 3, the OU 52 obtains NOx
amount on the inlet side of the catalytic converter 22 and NOx
amount on the outlet side thereof on the basis of output signals
from the sensors 30, 32, and calculates the adsorption amount.
Then, when a rich spike instruction is given depending on signals
from the sensors 30, 32, 34, 36, etc., the emission amount by
out-of-cylinder rich operation is set referring to the maps.
[0043] Here, if the HC supply pressure detected by the sensor 42 is
not zero but less than a desired supply pressure, the MU 54 sends
out a signal to the OU 52. The OU 52 sets a coefficient depending
on the HC supply pressure detected. The coefficient is an index of
what proportion of the fuel injected when the line 39, etc. are in
order is actually injected into exhaust through the injector 38.
The emission amount by out-of-cylinder rich operation, set in
advance referring to the maps, is corrected by being multiplied by
this coefficient. The amount of NOx actually emitted (released and
reduced) by out-of-cylinder rich operation is calculated this way,
and the current adsorption amount is estimated.
[0044] Thus, in this embodiment, although the rich spike cycle may
be shortened, appropriate alternative operation is performed when
HC fails to be added to the catalytic converter 22, so that
increase in NOx is avoided. Consequently, also in this embodiment,
reliability of the exhaust emission control device further improves
(fail-safe).
[0045] The exhaust emission control device can be a combination of
FIGS. 2 and 3. Specifically, first, when the HC supply pressure
detected by the sensor 42 is less than a desired supply pressure,
the OU 52 calculates the amount of NOx actually emitted (released
and reduced), by correcting the emission amount by out-of-cylinder
rich operation, using the coefficient, and estimates the current
adsorption amount.
[0046] Next, when the HC supply pressure detected by the sensor 42
is almost zero, that is, HC is not added to the catalytic converter
22, the OU 52 uses the emission amount by out-of-cylinder rich
operation which has been set to zero by the change unit 56. After
this, as long as the HC supply pressure remains almost zero, when a
rich spike instruction is given, post injection is performed and
the current adsorption amount is estimated by subtracting the
emission amount by post injection. In this embodiment, more
appropriate alternative operation is performed.
[0047] Although in the above-described embodiments, the MU 54
monitors the value detected by the fuel pressure sensor 42, the MU
54 may monitor the value detected by the flow rate sensor. Further,
although the change unit 58 changes out-of-cylinder rich operation
to post injection, out-of-cylinder rich operation may be changed to
in-cylinder rich operation using CO emitted due to imperfect
combustion caused by recirculating a large amount of exhaust and
utilizing the valve 28 and the throttle 10.
[0048] Further, the engine is preferably a diesel engine but not
limited to it. The exhaust emission control device according to
this invention is applicable to all the engine systems that have a
NOx trap catalytic converter in an exhaust passage and are capable
of rich operation.
[0049] The invention thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *