U.S. patent application number 10/713355 was filed with the patent office on 2004-07-01 for sulfur poisoning elimination of diesel engine catalyst.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Inoue, Takao, Tabata, Munehiro.
Application Number | 20040123590 10/713355 |
Document ID | / |
Family ID | 32463587 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040123590 |
Kind Code |
A1 |
Tabata, Munehiro ; et
al. |
July 1, 2004 |
Sulfur poisoning elimination of diesel engine catalyst
Abstract
A NOx catalyst (10) traps nitrogen oxides in the exhaust gas of
a diesel engine (40), and particulate matter is trapped by a filter
(41). The sulfur poisoning of the NOx catalyst (10) is eliminated
using exhaust gas corresponding to a rich air-fuel ratio. The
exhaust gas composition is changed over to a lean air-fuel ratio
according to an increase of a particulate matter collection amount
during the elimination of sulfur poisoning so that the particulate
matter collection amount in the filter (41) does not increase. As a
result, when the particulate matter collection amount decreases due
to combustion of collected particulate matter, elimination of
sulfur poisoning again proceeds using exhaust gas corresponding to
a rich air-fuel ratio.
Inventors: |
Tabata, Munehiro;
(Isehara-shi, JP) ; Inoue, Takao; (Yokohama-shi,
JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
32463587 |
Appl. No.: |
10/713355 |
Filed: |
November 17, 2003 |
Current U.S.
Class: |
60/295 ; 60/285;
60/297 |
Current CPC
Class: |
F02D 41/029 20130101;
F02D 41/028 20130101; Y02A 50/20 20180101; F01N 3/0814 20130101;
Y02A 50/2344 20180101; F01N 2250/14 20130101; F02B 37/00 20130101;
F02M 26/05 20160201; F01N 9/002 20130101; Y02T 10/12 20130101; F02B
29/0406 20130101; F01N 13/009 20140601; F01N 2570/14 20130101; F01N
2250/12 20130101; F01N 2250/02 20130101; Y02T 10/24 20130101; F01N
2260/04 20130101; F01N 3/0842 20130101; F02M 26/10 20160201 |
Class at
Publication: |
060/295 ;
060/285; 060/297 |
International
Class: |
F01N 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2002 |
JP |
2002-377232 |
Claims
What is claimed is:
1. A purification device for an exhaust gas of a diesel engine,
comprising: a catalyst which traps nitrogen oxides in the exhaust
gas but decreases a nitrogen oxides trapping performance when
poisoned by sulfur oxides in the exhaust gas, the sulfur oxides
poisoning the catalyst being eliminated by contact with an exhaust
gas corresponding to a rich air-fuel ratio; a filter which traps
particulate matter in the exhaust gas and burns a trapped
particulate matter by contact with an exhaust gas corresponding to
a lean air-fuel ratio; an air-fuel ratio regulating mechanism which
varies an exhaust gas composition of the engine between a
composition corresponding to the lean air-fuel ratio and a
composition corresponding to the rich air-fuel ratio; a sensor
which detects a particulate matter trap amount of the filter; and a
programmable controller programmed to: control the air-fuel ratio
regulating mechanism to cause the exhaust gas composition of the
engine to be in a state corresponding to the rich air-fuel ratio;
determine whether or not the particulate matter trap amount has
reached a predetermined amount while the exhaust gas composition is
in a state corresponding to the rich air-fuel ratio; control the
mechanism to cause the exhaust gas composition to be in a state
corresponding to the lean air-fuel ratio, when the particulate
matter trap amount has reached the predetermined amount during a
period when the exhaust gas composition is in a state corresponding
to the rich air-fuel ratio; determine whether or not the
particulate matter trap amount has reached a predetermined decrease
state during a period when the exhaust gas composition is in the
state corresponding to the lean air-fuel ratio; and control the
mechanism to cause the exhaust gas composition to be in a state
corresponding to the rich air-fuel ratio, when the particulate
matter trap amount has reached the predetermined decrease state
during the period when the exhaust gas composition is in the state
corresponding to the lean air-fuel ratio.
2. The purification device as defined in claim 1, wherein the
sensor comprises a sensor which detects a differential pressure
between an inlet and an outlet of the filter.
3. The purification device as defined in claim 1, wherein the state
of the exhaust gas composition corresponding to the rich air-fuel
ratio, corresponds to an exhaust gas produced by combustion of an
air-fuel mixture wherein an excess air factor is within the range
0.95 to 1.0.
4. The purification device as defined in claim 1, wherein the state
of the exhaust gas composition corresponding to the lean air-fuel
ratio, corresponds to an exhaust gas produced by combustion of an
air-fuel mixture wherein an excess air factor is within the range
1.05 to 1.1.
5. The purification device as defined in claim 1, wherein the
air-fuel ratio regulating mechanism comprises an intake throttle
which regulates an intake air amount of the engine.
6. The purification device as defined in claim 1, wherein the air
-fuel ratio regulating mechanism comprises a fuel injector which
injects fuel into the exhaust gas of the engine.
7. The purification device as defined in claim 1, wherein the
engine comprises an exhaust gas recirculation passage which
recirculates part of the exhaust gas into an intake air according
to an exhaust gas pressure of the engine, and the air-fuel ratio
regulating mechanism comprises an exhaust throttle which regulates
the exhaust gas pressure.
8. The purification device as defined in claim 1, wherein the
engine comprises a fuel injector which supplies fuel for
combustion, and the air-fuel ratio regulating mechanism comprises
the fuel injector set to perform a post-injection after fuel is
supplied for combustion.
9. The purification device as defined in claim 1, wherein the
controller is further programmed to determine that, when the
exhaust gas composition of the engine has continued to be in the
state corresponding to the lean air-fuel ratio for a predetermined
time, the particulate matter trap amount has reached the
predetermined decrease state.
10. The purification device as defined in claim 1, wherein the
predetermined amount corresponds to a state where the particulate
matter trap amount is saturated, and the predetermined decrease
state corresponds to a state where the particulate matter trap
amount is zero.
11. The purification device as defined in claim 1, wherein the
predetermined decrease state corresponds to a differential pressure
when the controller started to control the air-fuel ratio
regulating mechanism for the first time to cause the exhaust gas
composition of the engine to be in the state corresponding to the
rich air-fuel ratio.
12. A purification device for an exhaust gas of a diesel engine,
comprising: a catalyst which traps nitrogen oxides in the exhaust
gas but decreases a nitrogen oxides trapping performance when
poisoned by sulfur oxides in the exhaust gas, the sulfur oxides
poisoning the catalyst being eliminated by contact with an exhaust
gas corresponding to a rich air-fuel ratio; a filter which traps
particulate matter in the exhaust gas and burns a trapped
particulate matter by contact with an exhaust gas corresponding to
a lean air-fuel ratio; an air-fuel ratio regulating mechanism which
varies an exhaust gas composition of the engine between a
composition corresponding to the lean air-fuel ratio and a
composition corresponding to the rich air-fuel ratio; means for
detecting a particulate matter trap amount of the filter; means for
controlling the air-fuel ratio regulating mechanism to cause the
exhaust gas composition of the engine to be in a state
corresponding to the rich air-fuel ratio; means for determining
whether or not the particulate matter trap amount has reached a
predetermined amount while the exhaust gas composition is in a
state corresponding to the rich air-fuel ratio; means for
controlling the mechanism to cause the exhaust gas composition to
be in a state corresponding to the lean air-fuel ratio, when the
particulate matter trap amount has reached the predetermined amount
during a period when the exhaust gas composition is in a state
corresponding to the rich air-fuel ratio; means for determining
whether or not the particulate matter trap amount has reached a
predetermined decrease state during a period when the exhaust gas
composition is in the state corresponding to the lean air-fuel
ratio; and means for controlling the mechanism to cause the exhaust
gas composition to be in a state corresponding to the rich air-fuel
ratio, when the particulate matter trap amount has reached the
predetermined decrease state during the period when the exhaust gas
composition is in the state corresponding to the lean air-fuel
ratio.
13. A method for controlling a purification device for an exhaust
gas of a diesel engine, the device comprising a catalyst which
traps nitrogen oxides in the exhaust gas but decreases a nitrogen
oxides trapping performance when poisoned by sulfur oxides in the
exhaust gas, wherein the sulfur oxides poisoning the catalyst is
eliminated by contact with an exhaust gas corresponding to a rich
air-fuel ratio, a filter which traps particulate matter in the
exhaust gas and burns a trapped particulate matter by contact with
an exhaust gas corresponding to a lean air-fuel ratio, and an
air-fuel ratio regulating mechanism which varies an exhaust gas
composition of the engine between a composition corresponding to
the lean air-fuel ratio and a composition corresponding to the rich
air-fuel ratio, the method comprising: determining a particulate
matter trap amount of the filter; controlling the air-fuel ratio
regulating mechanism to cause the exhaust gas composition of the
engine to be in a state corresponding to the rich air-fuel ratio;
determining whether or not the particulate matter trap amount has
reached a predetermined amount while the exhaust gas composition is
in a state corresponding to the rich air-fuel ratio; controlling
the mechanism to cause the exhaust gas composition to be in a state
corresponding to the lean air-fuel ratio, when the particulate
matter trap amount has reached the predetermined amount during a
period when the exhaust gas composition is in a state corresponding
to the rich air-fuel ratio; determining whether or not the
particulate matter trap amount has reached a predetermined decrease
state during a period when the exhaust gas composition is in the
state corresponding to the lean air-fuel ratio; and controlling the
mechanism to cause the exhaust gas composition to be in a state
corresponding to the rich air-fuel ratio, when the particulate
matter trap amount has reached the predetermined decrease state
during the period when the exhaust gas composition is in the state
corresponding to the lean air-fuel ratio.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the elimination of sulfur
poisoning of a NOx trap catalyst that traps nitrogen oxides (NOx)
discharged by a diesel engine.
BACKGROUND OF THE INVENTION
[0002] JP06-272541A published by the Japanese Patent Office in
1992, discloses an exhaust gas purification device wherein a diesel
particulate filter (DPF) that traps particulate matter in the
exhaust gas of a diesel engine and a NOx trap catalyst that traps
NOx in the exhaust gas, are used.
[0003] The NOx trap catalyst also traps sulfur oxides (SOx)
contained in the diesel fuel. This is referred to as sulfur
poisoning. When sulfur poisoning occurs, the NOx trap ability of
the catalyst decreases.
[0004] In the prior art, the NOx trapped by the NOx trap catalyst
is first reduced, next, the DPF burns the trapped particulate
matter, and the reducing agent concentration in the exhaust gas is
then increased to eliminate the sulfur poisoning.
SUMMARY OF THE INVENTION
[0005] When the reducing agent concentration of the exhaust gas is
increased, a large amount of particulate matter is discharged.
Therefore, when a long time is spent on eliminating the sulfur
poisoning, a large amount of particulate matter collects in the DPF
by the time the sulfur poisoning has been eliminated.
[0006] In general, the diesel engine runs in a lean atmosphere. If
a large amount of particulate matter collects in the DPF when the
air-fuel ratio is returned to lean for the usual operation after
the sulfur poisoning is eliminated, a problem arises. Specifically,
if the temperature of the exhaust gas at this time is higher than
the self-ignition temperature of the particulate matter, the
particulate matter trapped by the DPF burns rapidly. As a result,
when the temperature of the DPF exceeds a preferable range for
performance, the particulate trap performance of the DPF
decreases.
[0007] It is therefore an object of this invention to eliminate the
sulfur poisoning of a NOx catalyst while preventing particulate
matter from collecting in the DPF.
[0008] In order to achieve the above object, this invention
provides a purification device for an exhaust gas of a diesel
engine, comprising a catalyst which traps nitrogen oxides in the
exhaust gas but decreases a nitrogen oxides trapping performance
when poisoned by sulfur oxides in the exhaust gas wherein the
sulfur oxides poisoning the catalyst is eliminated by contact with
an exhaust gas corresponding to a rich air-fuel ratio, a filter
which traps particulate matter in the exhaust gas and burns a
trapped particulate matter by contact with an exhaust gas
corresponding to a lean air-fuel ratio, an air-fuel ratio
regulating mechanism which varies an exhaust gas composition of the
engine between a composition corresponding to the lean air-fuel
ratio and a composition corresponding to the rich air-fuel ratio, a
sensor which detects a particulate matter trap amount of the
filter, and a programmable controller.
[0009] The controller is programmed to control the air-fuel ratio
regulating mechanism to cause the exhaust gas composition of the
engine to be in a state corresponding to the rich air-fuel ratio,
determine whether or not the particulate matter trap amount has
reached a predetermined amount while the exhaust gas composition is
in a state corresponding to the rich air-fuel ratio, control the
mechanism to cause the exhaust gas composition to be in a state
corresponding to the lean air-fuel ratio, when the particulate
matter trap amount has reached the predetermined amount during a
period when the exhaust gas composition is in a state corresponding
to the rich air-fuel ratio, determine whether or not the
particulate matter trap amount has reached a predetermined decrease
state during a period when the exhaust gas composition is in the
state corresponding to the lean air-fuel ratio, and control the
mechanism to cause the exhaust gas composition to be in a state
corresponding to the rich air-fuel ratio, when the particulate
matter trap amount has reached the predetermined decrease state
during the period when the exhaust gas composition is in the state
corresponding to the lean air-fuel ratio.
[0010] This invention also provides a method for controlling a
purification device for an exhaust gas of a diesel engine. The
purification device comprises a catalyst which traps nitrogen
oxides in the exhaust gas but decreases a nitrogen oxides trapping
performance when poisoned by sulfur oxides in the exhaust gas,
wherein the sulfur oxides poisoning the catalyst is eliminated by
contact with an exhaust gas corresponding to a rich air-fuel ratio,
a filter which traps particulate matter in the exhaust gas and
burns a trapped particulate matter by contact with an exhaust gas
corresponding to a lean air-fuel ratio, and an air-fuel ratio
regulating mechanism which varies an exhaust gas composition of the
engine between a composition corresponding to the lean air-fuel
ratio and a composition corresponding to the rich air-fuel
ratio.
[0011] The method comprises determining a particulate matter trap
amount of the filter, controlling the air-fuel ratio regulating
mechanism to cause the exhaust gas composition of the engine to be
in a state corresponding to the rich air-fuel ratio, determining
whether or not the particulate matter trap amount has reached a
predetermined amount while the exhaust gas composition is in a
state corresponding to the rich air-fuel ratio, controlling the
mechanism to cause the exhaust gas composition to be in a state
corresponding to the lean air-fuel ratio, when the particulate
matter trap amount has reached the predetermined amount during a
period when the exhaust gas composition is in a state corresponding
to the rich air-fuel ratio, determining whether or not the
particulate matter trap amount has reached a predetermined decrease
state during a period when the exhaust gas composition is in the
state corresponding to the lean air-fuel ratio, and controlling the
mechanism to cause the exhaust gas composition to be in a state
corresponding to the rich air-fuel ratio, when the particulate
matter trap amount has reached the predetermined decrease state
during the period when the exhaust gas composition is in the state
corresponding to the lean air-fuel ratio.
[0012] The details as well as other features and advantages of this
invention are set forth in the remainder of the specification and
are shown in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic diagram of a diesel engine exhaust gas
purification device according to this invention.
[0014] FIG. 2 is a flowchart describing a sulfur poisoning
elimination routine executed by a controller according to this
invention.
[0015] FIG. 3 is a flowchart describing an air-fuel ratio control
subroutine executed by the controller.
[0016] FIG. 4 is a flowchart describing an air-fuel ratio control
subroutine for regenerating a DPF executed by the controller.
[0017] FIGS. 5A-5E are timing charts that describe changes in an
excess air ratio lambda (.lambda.), a sulfur poisoning amount and a
particulate matter collection amount due to execution of the sulfur
poisoning elimination routine.
[0018] FIG. 6 is similar to FIG. 1, but showing a second embodiment
of this invention.
[0019] FIG. 7 is similar to FIG. 1, but showing a third embodiment
of this invention.
[0020] FIGS. 8A-8E are timing charts that describe changes in the
excess air ratio .lambda., the sulfur poisoning amount and the
particulate matter collection amount under the sulfur poisoning
elimination control according to a fifth embodiment of this
invention.
[0021] FIGS. 9A-9E are timing charts that describe changes in the
excess air ratio .lambda., the sulfur poisoning amount and the
particulate matter collection amount under the sulfur poisoning
elimination control according to a sixth embodiment of this
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Referring to FIG. 1 of the drawings, a diesel engine 40 for
vehicles rotates due to combustion of a gaseous mixture of air
aspirated from an intake pipe 21 via a throttle 41, and diesel fuel
injected from a fuel injector 44. The fuel is supplied to the fuel
injector 44 by a common rail fuel system.
[0023] The exhaust gas due to combustion is discharged via an
exhaust pipe 22. A part of the exhaust gas is recirculated to the
intake pipe 21 via an exhaust gas recirculation (EGR) passage
23.
[0024] An exhaust gas purification device 1 is installed midway in
the exhaust pipe 22.
[0025] The exhaust gas purification device 1 comprises a NOx trap
catalyst 10 which traps NOx (nitrogen oxides) in the exhaust gas,
and a diesel particulate filter (DPF) 20.
[0026] The NOx trap catalyst 10 contains a NOx trap agent that
traps NOx. As the NOx trap agent, barium (Ba), magnesium (Mg) or
cesium (Cs) can be used. The NOx trap catalyst 10 traps NOx
contained in the exhaust gas corresponding to a lean air-fuel ratio
due to the action of the trap agent. The trapped NOx is reduced by
reducing agent components contained in exhaust gas corresponding to
a rich air-fuel ratio, under the catalysis of the NOx trap catalyst
10, and is discharged.
[0027] The NOx trap catalyst 10 traps not only the NOx in the
exhaust gas, but also SOx (sulfur oxides) as previously stated.
When sulfur oxides collect in the NOx trap catalyst 10, the NOx
trap ability decreases. This state is called sulfur poisoning. To
eliminate the sulfur poisoning, it is necessary to increase the
reducing agent components contained in the exhaust gas. For this
purpose, it is necessary to make the exhaust gas composition
correspond to a rich air-fuel ratio.
[0028] The DPF 20 is installed downstream of the NOx trap catalyst
10. The DPF 20 comprises a ceramic porous filter. The DPF 20 traps
particulate matter in the exhaust gas. The trapped particulate
matter burns due to the temperature rise of the exhaust gas, and is
removed from the DPF 20. In the following description, the raising
of the exhaust gas temperature to burn particulate matter trapped
by the DPF 20 is referred to as the regeneration of the DPF 20. The
regeneration of the DPF 20 is performed using the high temperature
exhaust gas generated by the combustion of the air-fuel mixture at
a lean air-fuel ratio.
[0029] The elimination of the sulfur poisoning of the NOx trap
catalyst 10 and the regeneration of the DPF 20 are both performed
by controlling the air-fuel ratio of the burning air-fuel mixture.
The air-fuel ratio of the air-fuel mixture is determined by the air
amount aspirated via the intake throttle 41 and the fuel injection
amount of the fuel injector 44. The opening of the intake throttle
41 and the fuel injection amount of the fuel injector 44 are varied
according to signals output by a controller 50.
[0030] The controller 50 comprises a microcomputer comprising a
central processing unit (CPU), read-only memory (ROM), random
access memory (RAM) and input/output (I/O) interface. The
controller may also comprise plural microcomputers.
[0031] The controller 50 determines the fuel injection amount of
the fuel injector 44 according to the required load, i.e., for
example, according to a depression amount of an accelerator pedal
with which the vehicle is provided. In normal operation of the
engine 40, the controller 50 maintains the air-fuel ratio of the
burning air-fuel mixture at a predetermined lean air-fuel ratio by
increasing or decreasing the opening of the intake throttle 41
according to the fuel injection amount.
[0032] The controller 50, by controlling the air-fuel ratio to a
predetermined rich air-fuel ratio, eliminates the sulfur poisoning
of the NOx trap catalyst 10. During the elimination of sulfur
poisoning, however, the controller 50 occasionally controls the
air-fuel ratio to lean to perform the regeneration of the DPF 20
when the particulate matter collection amount has increased to a
certain degree, thereby preventing an increase in the particulate
matter collection amount of the DPF 20 due to the elimination of
sulfur poisoning. When the particulate matter collection amount of
the DPF 20 decreases as a result of the regeneration of the DPF 20,
the air-fuel ratio is again controlled to a predetermined rich
air-fuel ratio, and elimination of sulfur poisoning of the NOx trap
catalyst 10 is continued.
[0033] To perform the above air-fuel ratio control, detection
signals from various sensors are input to the controller 50.
[0034] These sensors include a differential pressure sensor 31 that
detects the pressure difference of the exhaust gas at the inlet and
outlet of the DPF 20, a .lambda. sensor 32 which detects an excess
air factor lambda (.lambda.) of the air-fuel mixture from the
oxygen concentration in the exhaust gas at the inlet of the NOx
trap catalyst 10, a temperature sensor 33 which detects the inlet
temperature of the DPF 20, and a temperature sensor 34 which
detects the outlet temperature of the DPF 20.
[0035] Next, referring to FIG. 2, a sulfur poisoning elimination
routine executed by the controller 50 will be described.
[0036] This routine is always executed during running of the diesel
engine 40. Specifically, when the controller 50 terminates the
routine, the following execution of the routine is started
immediately or after a predetermined time interval.
[0037] First, in a step S1, the controller 50 determines whether or
not the sulfur poisoning elimination of NOx trap catalyst 10 is
required. This determination is made not by directly detecting the
sulfur poisoning amount of the NOx trap catalyst 10, but based on
running data such as the vehicle travel distance, the fuel
consumption and the travel time after the latest sulfur poisoning
elimination. If it is determined that sulfur poisoning elimination
of the NOx trap catalyst 10 is not required, the routine is
terminated without further processing.
[0038] When it is determined that sulfur poisoning elimination of
NOx trap catalyst 10 is required, the controller 50 performs the
processing of a step S2 and further steps.
[0039] In the step S2, the controller 50 executes air-fuel ratio
control to eliminate sulfur poisoning by using a subroutine shown
in FIG. 3.
[0040] Referring to FIG. 3, the controller 50, in a step S21,
determines whether or not the excess air factor .lambda. of the
air-fuel mixture detected by the .lambda. sensor 32 is 1.0 or less.
If the excess air factor .lambda. of the air-fuel ratio is 1.0 or
less, it means that the air-fuel ratio is equal to or richer than
the stoichiometric air-fuel ratio.
[0041] If, as a result of this determination, the excess air factor
.lambda. is not 1.0 or less, i.e., the air-fuel ratio is lean, the
controller 50, in a step S22, decreases the excess air factor
.lambda.. This is done by decreasing the opening of the intake
throttle 41 by a fixed amount. After the processing of the step
S22, the controller 50 repeats the determination of the step S21.
Thus, the controller 50 repeats the processing of the steps S21 and
S22 until the excess air factor .lambda. becomes 1.0 or less.
[0042] When the excess air factor .lambda. becomes 1.0 or less, the
controller 50 performs the processing of a step S23.
[0043] In the step S23, the controller 50 determines whether or not
the excess air factor .lambda. is larger than 0.95. When, as a
result of this determination, the excess air factor .lambda. is not
larger than 0.95, the controller 50, in a step S24, increases the
excess air factor .lambda.. This is done by increasing the opening
of the intake throttle 41 by a fixed amount. After the processing
of the step S24, the controller 50 repeats the determination of the
step S23. Hence, the controller 50 repeats the processing of the
step S23 and S24 until the excess air factor .lambda. exceeds the
value of 0.95.
[0044] When the excess air factor .lambda. becomes larger than 0.95
in the step S23, the controller 50 terminates the subroutine.
[0045] Due to the execution of this subroutine, the excess air
factor .lambda. is controlled to within a range that is less than
1.0 and larger than 0.95.
[0046] Referring again to FIG. 2, after controlling the excess air
factor .lambda. to within a range that is less than 1.0 and larger
than 0.95 in the step S2, the controller 50, in a step S3,
determines whether or not regeneration of the DPF 20 is required.
This determination is performed by comparing the pressure
difference between the inlet and outlet of the DPF 20 detected by
the differential pressure sensor 31 with a first predetermined
value.
[0047] Particulate matter which has collected in the DPF 20 is an
obstacle to the flow of exhaust gas, and leads to pressure loss in
the exhaust gas energy. As a result, the pressure difference
between the inlet and outlet of the DPF 20 increases. The
controller 50 determines that when this difference exceeds the
first predetermined value, regeneration of the DPF 20 is
required.
[0048] This first predetermined value is a value that is a
predetermined amount larger than the pressure difference when the
determination result of the step S1 is affirmative for the first
time, i.e., the pressure difference when air-fuel ratio control to
eliminate sulfur poisoning starts.
[0049] When it is determined in the step S3 that regeneration of
the DPF 20 is not required, the controller 50 repeats the
processing of the step S2 and step S3 until regeneration of the DPF
20 is required. In other words, until it is determined in the step
S3 that regeneration of the DPF 20 is required, the excess air
factor .lambda. of the air-fuel mixture has a value within a range
less than 1.0 and larger than 0.95, which corresponds to a rich
air-fuel ratio.
[0050] As a result, sulfur oxides (SOx) which have collected in the
NOx trap catalyst 10 are oxidized by reducing agent components in
the exhaust gas increased by the rich air-fuel ratio, and
elimination of the sulfur poisoning of the NOx trap catalyst 10
takes place.
[0051] On the other hand, when the reducing agent concentration in
the exhaust gas increases, the particulate matter generation amount
also increases.
[0052] As a result, in the step S3, when it is determined that
regeneration of the DPF 20 is required, the controller 50, in a
step S4, performs air-fuel ratio control to regenerate the DPF 20
using a subroutine shown in FIG. 4.
[0053] Referring to FIG. 4, the controller 50, firstly in a step
S41, determines whether or not the excess air factor .lambda. is
larger than 1.05.
[0054] If the excess air factor .lambda. is not larger than 1.05,
in a step S42, the excess air factor .lambda. is increased. This
processing is performed by increasing the opening of the intake
throttle 41 by a fixed amount. After the processing of the step
S42, the controller 50 repeats the determination of the step S41.
In this way, the controller 50 repeats the processing of the steps
S41 and S42 until the excess air factor .lambda. is larger than
1.05.
[0055] When the excess air factor .lambda. becomes larger than
1.05, the controller 50 performs the processing of a step S43.
[0056] In the step S43, the controller 50 determines whether or not
the excess air factor .lambda. is less than 1.1.
[0057] If the excess air factor .lambda. is not less than 1.1 the
controller 50, in a step S44, decreases the excess air factor
.lambda.. This processing is performed by decreasing the opening of
the intake throttle 41 by a fixed amount. After the processing of
the step S44, the controller 50 repeats the determination of the
step S43.
[0058] In this way, the controller 50 repeats the processing of the
steps S43 and 44 until the excess air factor .lambda. becomes less
than 1.1.
[0059] When the excess air factor .lambda. becomes less than 1.1 in
the step S43, the controller 50 terminates the subroutine.
[0060] Due to the execution of this subroutine, the excess air
factor .lambda. is controlled to a range larger than 1.5 and less
than 1.1.
[0061] Referring again to FIG. 2, after the excess air factor
.lambda. is controlled to a range larger than 1.05 and less than
1.1 in the step S4, the controller 50, in a step S5, determines
whether or not regeneration of the DPF 20 is complete. This is done
by comparing the pressure difference between the inlet and outlet
of the DPF 20 detected by the differential pressure sensor 31 with
a second predetermined value.
[0062] When the particulate matter is burnt and is removed from the
DPF 20, the exhaust gas flow resistance of the DPF 20 decreases,
and the exhaust gas energy loss also decreases. As a result, the
pressure difference between the inlet and outlet of the DPF 20
decreases. When the pressure difference drops below the second
predetermined value, the controller 50 determines that regeneration
of the DPF 20 is complete. The second predetermined value is set
equal to the pressure difference when the determination result of
the step S1 is affirmative for the first time, i.e., the pressure
difference when air-fuel ratio control to eliminate sulfur
poisoning starts.
[0063] Here, the basic concept of setting the first predetermined
value and second predetermined value will be described. The
regeneration control of the DPF 20 performed during this routine
has the purpose of preventing increase of particulate matter
collected in the DPF 20 due to the sulfur poisoning elimination
control of the NOx trap catalyst 10. In other words, it is
different from the ordinary regeneration control of the DPF 20
which effectively makes the particulate matter collection amount
zero.
[0064] Therefore, the difference between the first predetermined
amount and second predetermined amount may be set to be narrower
than during ordinary regeneration control, and by burning
particulate matter a little at a time within a short interval,
excessive temperature rise of the DPF 20 is prevented.
[0065] If regeneration of the DPF 20 is not complete in the step
S5, the controller 50 repeats the processing of the steps S4 and
S5. In other words, the excess air factor .lambda. is maintained
within a range larger than 1.5 and less than 1.1, i.e.,
corresponding to a lean air-fuel ratio. As a result, the oxygen due
to the lean air-fuel ratio promotes combustion of the particulate
matter, and regeneration of the DPF 20 continues.
[0066] If it is determined in the step S5 that regeneration of the
DPF 20 is complete, the controller 50, in a step S6, determines
whether or not sulfur poisoning elimination is complete. This
determination is performed by determining whether or not the total
execution time of air-fuel ratio control for eliminating sulfur
poisoning from the starting of the routine, i.e., the total
continuation time of the air-fuel ratio state where the excess air
factor .lambda. is less than 1.0 and more than 0.95, has reached a
predetermined time.
[0067] If the elimination of sulfur poisoning is not complete, the
controller 50 repeats the processing of the steps S2-S6. When it is
determined that the elimination of sulfur poisoning is complete,
the controller 50 terminates the routine.
[0068] Next, referring to FIGS. 5A-5E, the variation of the excess
air factor .lambda., sulfur poisoning amount and particulate matter
collection amount due to execution of the above routine will be
described.
[0069] At a time t11, if it is determined in the step S1 that the
elimination of sulfur poisoning of the NOx trap catalyst 10 is
required, the air-fuel ratio control to eliminate sulfur poisoning
of the step S2 starts, and the excess air factor .lambda. of the
engine 40 is controlled to a rich air-fuel ratio region between
0.95 and 1.0 as shown in FIG. 5C. As a result, the sulfur poisoning
amount falls as shown in FIG. 5D, and as the particulate matter
discharge amount increases due to the rich air-fuel ratio, the
particular matter collection amount of the DPF 20 increases as
shown in FIG. 5E.
[0070] Here, FIGS. 5D and 5E respectively show the sulfur poisoning
amount of the NOx trap catalyst 10 and particulate matter
collection amount of the DPF 20 as percentages.
[0071] Regarding the sulfur poisoning amount, the poisoning amount
when it is determined that elimination of poisoning is required, is
taken as 100%, and the poisoning amount when the total execution
time of the air-fuel ratio control for eliminating sulfur poisoning
has reached the predetermined time, is taken as 0%.
[0072] Regarding the particulate matter collection amount, the
state where the particulate matter trap ability of the DPF 20 is
saturated, is taken as 100%, and the state where particulate matter
has not collected in the DPF 20, is taken as 0%.
[0073] At a time t12, when the particulate matter collection amount
has reached a value corresponding to the aforesaid first
predetermined value, it is determined in the step S3 that
regeneration of the DPF 20 is required. As a result, the air-fuel
ratio control to regenerate the DPF 20 of the step S4 is performed,
and the excess air factor .lambda. of the engine 40 is controlled
to a lean air-fuel ratio region where the excess air factor
.lambda. is between 1.05 and 1.1, as shown in FIG. 5C.
[0074] Due to this control, combustion of particulate matter which
has collected in the DPF 20 is promoted as shown in FIG. 5E, and
regeneration of the DPF 20 is performed. At a time t13, when the
particulate matter collection amount in the DPF 20 decreases to a
value corresponding to the aforesaid second predetermined value, it
is determined that regeneration of the DPF 20 in the step S5 is
complete. Next, it is determined whether or not elimination of
sulfur poisoning in the step S6 is complete.
[0075] At the time t13, the elimination of sulfur poisoning is not
complete as shown in FIG. 5D. Therefore, the air-fuel ratio control
to eliminate sulfur poisoning of the step S2 is repeated.
[0076] Due to the air-fuel ratio control to regenerate the DPF 20,
when the particulate matter collected in the DPF 20 burns, the
combustion heat is transmitted to the NOx trap catalyst 10, and the
temperature of the NOx trap catalyst 10 rises. This temperature
rise of the NOx trap catalyst 10 has a favorable effect when
promoting reduction of SOx in the NOx trap catalyst 10, on the next
occasion when air-fuel ratio control is performed to eliminate
sulfur poisoning.
[0077] In this way, by repeating air-fuel ratio control to
eliminate sulfur poisoning and air-fuel ratio control to regenerate
the DPF 20, the sulfur poisoning rate becomes zero, as shown in
FIG. 5D.
[0078] Each time air-fuel ratio control to regenerate the DPF 20 is
terminated, the controller 50 determines whether or not elimination
of sulfur poisoning in the step S6 is complete. At a time t14, when
it is determined that elimination of sulfur poisoning is complete,
the controller 50 terminates the routine.
[0079] The interval when sulfur poisoning elimination control is ON
from the time t11 to the time t14 of FIG. 5A, corresponds to the
effective routine execution period. Within the interval when sulfur
poisoning elimination control is ON, air-fuel ratio control to
eliminate sulfur poisoning and air-fuel ratio control to regenerate
the DPF 20 are repeatedly performed in alternation.
[0080] As a result, at the time t14, sulfur poisoning is completely
eliminated, and at the same time, the particulate matter collection
amount in the DPF 20 is maintained at substantially the same level
as at the time t11. Due to this control, sulfur poisoning
elimination is performed without increasing the particulate matter
collection amount.
[0081] The air-fuel ratio control to regenerate the DPF 20 shown in
FIGS. 5B and 5C is performed to prevent the particulate matter
collection amount of the DPF 20 from increasing due to elimination
of sulfur poisoning as described above. Ordinary regeneration
control of the DPF 20 is performed by a separate routine.
[0082] Next, referring to FIG. 6, a second embodiment of this
invention will be described.
[0083] The exhaust gas purification device according to this
embodiment comprises a fuel injector 42 upstream of the NOx trap
catalyst 10 in the exhaust pipe 22. The fuel injector 42 injects
fuel according to a signal from the controller 50 in an identical
way to the fuel injector 44. The remaining features of the
construction relating to the hardware of the exhaust gas
purification device are identical to those of the first embodiment
shown in FIG. 1.
[0084] As in the first embodiment, the controller 50 performs
elimination of sulfur poisoning of the NOx trap catalyst 10 by the
routine of FIG. 2 and the subroutines of FIGS. 3 and 4.
[0085] However, in this embodiment, the operation of decreasing the
excess air factor .lambda. in the step S22 of FIG. 3 and the step
S44 of FIG. 4, is performed by a fuel injection from the fuel
injector 42. By injecting fuel into the exhaust gas, reducing agent
components in the exhaust gas are increased, and as a result, the
same exhaust gas composition as when the excess air factor .lambda.
in the air-fuel mixture falls, is obtained.
[0086] In the same way, the operation of increasing the excess air
factor .lambda. in the step S24 of FIG. 3 and the step S42 of FIG.
4 is performed by stopping the fuel injection by the fuel injector
42. By stopping injection of fuel which was injected into the
exhaust gas, reducing agent components in the exhaust gas decrease,
and as a result, the same exhaust gas composition as when the
excess air factor .lambda. in the air-fuel mixture increases, is
obtained.
[0087] In this embodiment, by injecting fuel directly into the
exhaust gas, the reducing agent component concentration of the
exhaust gas can be more precisely controlled. The air-fuel ratio of
the air-fuel mixture supplied to the engine 40 is not changed, so
sulfur poisoning elimination control of the NOx trap catalyst 10
can be performed without affecting the combustion of the engine 40
and without causing any fluctuation of the output torque of the
engine 40.
[0088] Next, a third embodiment of this invention will be described
referring to FIG. 7.
[0089] The exhaust gas purification device according to this
embodiment comprises an exhaust throttle 43 downstream of the DPF
20 of the exhaust pipe 22. The exhaust throttle 43 has an opening
which can be varied according to a signal from the controller
50.
[0090] When the opening of the exhaust throttle 43 is decreased,
the exhaust gas pressure rises, and as a result, the EGR rate
increases. When the EGR rate increases, the proportion of fresh air
in the intake air amount of the engine 40 decreases, so the excess
air factor .lambda. decreases.
[0091] On the other hand, if the opening of the exhaust throttle 43
increases, the exhaust gas pressure decreases, and as a result, the
EGR rate decreases. When the EGR rate decreases, the proportion of
fresh air in the intake air amount of the engine 40 increases, so
the excess air factor .lambda. increases.
[0092] The remaining features relating to the hardware of the
exhaust gas purification device are identical to those of the first
embodiment shown in FIG. 1.
[0093] The controller 50, by repeating the routine of FIG. 2 and
the subroutines of FIGS. 3 and 4 as in the first embodiment,
performs elimination of the sulfur poisoning of the NOx trap
catalyst 10.
[0094] However, the operation of decreasing the excess air factor
.lambda. in the step S22 of FIG. 3 and the step S44 of FIG. 4 is
performed by decreasing the opening of the exhaust throttle 43. The
operation of increasing the excess air factor .lambda. in the step
S24 of FIG. 3 and the step S42 of FIG. 4 is performed by increasing
the opening of the exhaust throttle 43.
[0095] According to this embodiment, elimination of the sulfur
poisoning of the NOx trap catalyst 10 can be performed without
varying the fuel injection amount.
[0096] Next, a fourth embodiment of this invention will be
described.
[0097] The hardware construction of the exhaust gas purification
device according to this embodiment is identical to that of the
first embodiment, and the performing of the routine of FIG. 2 and
subroutines of FIGS. 3 and 4 is identical to the first
embodiment.
[0098] However, according to this embodiment, a post-injection is
performed by the fuel injector 44 after the fuel injection for
ordinary combustion. The operation of decreasing the excess air
factor .lambda. in the step S22 of FIG. 3 and the step S44 of FIG.
4 is performed by increasing the post-injection amount. The
operation of increasing the excess air factor .lambda. in the step
S24 of FIG. 3 and the step S42 of FIG. 4 is performed by decreasing
the post-injection amount.
[0099] In this way, by controlling the excess air factor .lambda.
by increasing or decreasing the post-injection amount, the control
response and precision can be improved.
[0100] Next, a fifth embodiment of this invention will be described
referring to FIGS. 8A-8E.
[0101] The hardware construction of the exhaust gas purification
device according to this embodiment is identical to that of the
first embodiment, and the performing of the routine of FIG. 2 and
subroutines of FIGS. 3 and 4 is identical to the first
embodiment.
[0102] However, according to this embodiment, the determination as
to whether or not regeneration of the DPF 20 is complete performed
in the step S5 of FIG. 2, is performed according to the
continuation time of the regeneration control of the DPF 20, i.e.,
the time from a time t22 to a time t23 in the figure, without
referring to the differential pressure detected by the differential
pressure sensor 31. When the continuation time of the regeneration
control of the DPF 20 reaches a predetermined time, the controller
50 determines that regeneration of the DPF 20 is complete.
[0103] According to this embodiment, if the predetermined time is
set to be long, the particulate matter collection amount of the DPF
20 can be reduced by a larger amount. During regeneration of the
DPF 20, sulfur poisoning of the NOx trap catalyst takes place, so
if the predetermined time is set to be long, it is preferred to set
the continuation time of the elimination of sulfur poisoning
overall, i.e., the time from a time t21 to a time t24, to be
long.
[0104] Next, referring to FIGS. 9A-9E, a sixth embodiment of this
invention will be described.
[0105] The hardware construction of the exhaust gas purification
device according to this embodiment is identical to that of the
first embodiment, and the routine of FIG. 2 and subroutines of
FIGS. 3 and 4, are identical to those of the first embodiment.
[0106] However, according to this embodiment, the determination of
whether or not to perform regeneration of the DPF 20 performed in
the step S3 of FIG. 2, and the determination as to whether or not
regeneration of the DPF 20 is complete performed in the step S5,
are different from the first embodiment.
[0107] Specifically, in the step S3, it is determined that
regeneration of the DPF 20 is required when the particulate matter
collection rate reaches 100%. When, in the step S5, the particulate
matter collection rate reaches 0%, it is determined that
regeneration of the DPF 20 is complete. These conditions are
equivalent to setting the first predetermined value to correspond
to 100% and the second predetermined value to correspond to 0% in
the first embodiment.
[0108] When the conditions of the step S3 and step S5 are set in
this way, the minimum occurrence of DPF regeneration is realized
during the routine execution period from the time t31 to the time
t34.
[0109] As a result, as shown in FIG. 9C, the variation frequency of
the excess air factor .lambda. is largely reduced compared to the
first embodiment, so the effect of sulfur poisoning elimination on
the running of the engine 40 can be reduced.
[0110] The contents of Tokugan 2002-377232, with a filing date of
Dec. 26, 2002 in Japan, are hereby incorporated by reference.
[0111] Although the invention has been described above by reference
to certain embodiments of the invention, the invention is not
limited to the embodiments described above. Modifications and
variations of the embodiments described above will occur to those
skilled in the art, within the scope of the claims.
[0112] For example, the second-fourth embodiments relating to the
means of increasing/decreasing the excess air factor .lambda., and
the fifth and sixth embodiments relating to criteria for
regenerating the DPF 20, may be performed in any combination.
[0113] The embodiments of this invention in which an exclusive
property or privilege is claimed are defined as follows:
* * * * *