U.S. patent application number 10/895335 was filed with the patent office on 2005-02-03 for combustion control system of internal combustion engine.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Kitahara, Yasuhisa.
Application Number | 20050022513 10/895335 |
Document ID | / |
Family ID | 34101094 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050022513 |
Kind Code |
A1 |
Kitahara, Yasuhisa |
February 3, 2005 |
Combustion control system of internal combustion engine
Abstract
In an internal combustion engine equipped with a fuel injection
system and an exhaust purifying device, such as NOx trap catalyst
and/or diesel particulate filter (DPF), a control unit is provided.
The control unit controls the fuel injection system to permit the
engine to have a predetermined combustion mode in which, under a
predetermined condition of the exhaust purifying device, the fuel
injection system causes the engine to carry out a main combustion
to produce a torque and at least one preliminary combustion prior
to the main combustion. The at least one preliminary combustion is
effected at a timing in the vicinity of top dead center of
compression stroke, and the main combustion is effected at a first
timing after completion of the preliminary combustion. The control
unit further controls the fuel injection system in such a manner
that upon switching of the engine operation from a previous
combustion mode to the predetermined combustion mode, the main
combustion that takes place after completion of the preliminary
combustion is effected at a second timing that is retarded as
compared with the first timing.
Inventors: |
Kitahara, Yasuhisa;
(Yokohama, JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
34101094 |
Appl. No.: |
10/895335 |
Filed: |
July 21, 2004 |
Current U.S.
Class: |
60/285 ;
60/301 |
Current CPC
Class: |
F02D 41/107 20130101;
F01N 3/0821 20130101; Y02T 10/40 20130101; F02D 41/403 20130101;
F02D 41/3011 20130101; Y02T 10/12 20130101; F01N 3/0842 20130101;
Y02T 10/24 20130101; F01N 3/0814 20130101; F02B 37/00 20130101;
Y02T 10/44 20130101 |
Class at
Publication: |
060/285 ;
060/301 |
International
Class: |
F01N 003/00; F01N
003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2003 |
JP |
2003-284311 |
Claims
What is claimed is:
1. A combustion control system of an internal combustion engine,
comprising: a fuel injection system provided at an intake system of
the engine; an exhaust purifying device provided at an exhaust
system of the engine; and a control unit that controls the fuel
injection system to permit the engine to have a predetermined
combustion mode, the predetermined combustion mode being a mode in
which, under a predetermined condition of the exhaust purifying
catalyst, the fuel injection system causes the engine to carry out
a main combustion to produce a torque and at least one preliminary
combustion prior to the main combustion, the at least one
preliminary combustion being effected at a timing in the vicinity
of top dead center of compression stroke, the main combustion being
effected at a first timing after completion of the preliminary
combustion, wherein the control unit further controls the fuel
injection system in such a manner that upon switching of the engine
operation from a previous combustion mode to the predetermined
combustion mode, the main combustion that takes place after
completion of the preliminary combustion is effected at a second
timing that is retarded as compared with the first timing.
2. A combustion control system as claimed in claim 1, in which the
second timing for the main combustion is controlled to have a value
that gradually reaches a target value.
3. A combustion control system as claimed in claim 2, in which a
fuel injection timing for the main combustion is gradually retarded
to have a target fuel injection timing.
4. A combustion control system as claimed in claim 1, in which the
main combustion after completion of the preliminary combustion is
carried out after a fluctuation of the intake system, that is
induced by the switching to the predetermined combustion mode from
the previous combustion mode, subsides.
5. A combustion control system as claimed in claim 1, in which a
fuel injection quantity for the preliminary combustion is
determined to a quantity that permits an incylinder temperature at
the second timing of fuel injection for the main combustion to be
higher than a temperature that enables a self ignition of the main
combustion.
6. A combustion control system as claimed in claim 1, in which a
combustion start timing of the main combustion is retarded from a
combustion start timing of the preliminary combustion by over 20
degrees in crank angle.
7. A combustion control system as claimed in claim 1, in which the
main combustion is completed at a timing of over 50 degrees in
crank angle after top dead center of compression stroke.
8. A combustion control system as claimed in claim 1, in which the
exhaust temperature of the engine is controlled by controlling a
fuel injection timing for the main combustion.
9. A combustion control system as claimed in claim 1, in which the
exhaust purifying device is a PM filter that collects particulate
matter in the exhaust gas, and in which under a predetermined
condition of the filter, the control unit controls the fuel
injection system in a manner to increase the exhaust temperature
for burning the particulate matter accumulated on the filter.
10. A combustion control system as claimed in claim 1, in which the
exhaust purifying device is a NOx trap catalyst that traps NOx in
the exhaust gas when the exhaust air/fuel ratio is lean, and in
which under a predetermined condition of the NOx trap catalyst, the
control unit controls the fuel injection system in a manner to make
the exhaust air/fuel ratio richer thereby to release the trapped
NOx from the catalyst.
11. A combustion control system as claimed in claim 1, in which the
exhaust purifying device is a NOx trap catalyst that traps NOx in
the exhaust gas when the exhaust air/fuel ratio is lean, and in
which under a predetermined condition of the NOx trap catalyst, the
control unit controls the fuel injection system in a manner to
increase the exhaust temperature to release a sulfur poisoning from
the catalyst.
12. A combustion control system as claimed in claim 1, in which the
predetermined condition of the exhaust purifying device is a
condition wherein the exhaust purifying device is under
inactivation condition.
13. A combustion control system as claimed in claim 1, in which the
combustion of the previous combustion mode contains mainly a
diffusive combustion that is produced when a main fuel injection is
effected during a combustion induced by a pilot fuel injection.
14. In an internal combustion engine that is equipped at an intake
system with a fuel injection system and at an exhaust system with
an exhaust purifying device, a method for controlling the engine,
comprising: controlling the fuel injection system to permit the
engine to have a predetermined combustion mode in which, under a
predetermined condition of the exhaust purifying device, the fuel
injection system causes the engine to carry out a main combustion
to produce a torque and at least one preliminary combustion prior
to the main combustion; controlling the fuel injection system in
such a manner that the at least one preliminary combustion is
effected at a timing in the vicinity of top dead center of
compression stroke, and the main combustion is effected at a first
timing after completion of the preliminary combustion; and
controlling the fuel injection system in such a manner that upon
switching of the engine operation from a previous combustion mode
to the predetermined combustion mode, the main combustion that
takes place after completion of the preliminary combustion is
effected at a second timing that is retarded as compared with the
first timing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates in general to a control system
for controlling operation of an internal combustion engine, and
more particularly to a combustion control system for controlling
combustion of an internal combustion engine that is equipped at an
exhaust system thereof with an exhaust purifying device.
[0003] 2. Description of the Related Art
[0004] In order to clarify the task of the present invention, a
known combustion control system of an internal combustion engine
will be briefly discussed prior to describing the detail of the
present invention, with the aid of the disclosure of Laid-open
Japanese Patent Application (Tokkai) 2000-320386.
[0005] Disclosed by the publication is a combustion control system
of a diesel engine that has an exhaust purifying device installed
in an exhaust system thereof. Upon need of increasing the
temperature of the exhaust purifying device, the combustion control
system controls a fuel injection device in such a manner that each
fuel injector injects a reference quantity of fuel, that meets the
torque needed by the engine, into a corresponding cylinder at a
timing in the vicinity of TDC (viz., top dead center) of
compression stroke while splitting the fuel injection by three,
that is, first, second and third fuel injection shots.
SUMMARY OF THE INVENTION
[0006] In the combustion control system of the publication, the
split fuel injection is so controlled as to keep the combustion of
fuel that has been injected into the cylinder in the fuel splitting
manner. In such control, the second or third fuel shot is directed
to a flame of the combustion of fuel that has been injected by the
first or second fuel shot, and thus the fuel injected by the second
and third shots is subjected to a combustion that includes mainly a
diffusion combustion. If, under this combustion condition, the
exhaust air/fuel ratio is made richer, deterioration of emission
characteristic, particularly smoke characteristic, becomes
severe.
[0007] Accordingly, the present invention is provided by taking the
above-mentioned fact into consideration and aims to provide a
combustion control system of an internal combustion engine equipped
at an exhaust system with an exhaust purifying device, that can
suppress or at least minimize the deterioration of emission
characteristic even when the exhaust air/fuel ratio is turned rich
for increasing the temperature of the exhaust purifying device and
that can, upon switching of a combustion mode of the engine, induce
a desired exhaust air/fuel ratio without inducing undesirable
torque fluctuation.
[0008] According to the present invention, there is provided a
combustion control system of an internal combustion engine equipped
at an exhaust system with an exhaust purifying device, that, upon
sensing a given condition of the exhaust purifying device, starts a
predetermined combustion control for controlling the fuel injection
to the engine in a manner to cause the engine to carry out both at
least one preliminary combustion and a main combustion that follows
the preliminary combustion to produce a main torque, wherein the at
least one preliminary combustion is carried out at a timing in the
vicinity of TDC (viz., top dead center) of compression stroke and
the main combustion is forced to start after completion of the
preliminary combustion, and wherein upon switching to the
predetermined combustion control from a previous combustion
control, the switching to the main combustion after switching of
the preliminary combustion is retarded by a certain degree.
[0009] Because the main combustion is forced to start after
completion of the preliminary combustion, the main combustion can
include mainly a premixed combustion, so that deterioration of
emission characteristic, that would be caused by the enrichment of
exhaust air/fuel ratio, can be suppressed or at least
minimized.
[0010] Furthermore, since the incylinder temperature is increased
by means of the preliminary combustion, start timing of the main
combustion can be retarded and thus the exhaust temperature can be
increased.
[0011] Accordingly, by switching the combustion mode as mentioned
hereinabove, the regeneration of the exhaust purifying device, that
would be achieved by enrichment of the exhaust air/fuel ratio
and/or increase of the exhaust temperature, is assuredly carried
out without inducing deterioration of emission characteristic of
the engine.
[0012] If, upon switching to the predetermined combustion control
due to occurrence of the given condition of the exhaust purifying
device, a certain fluctuation is shown in the intake system, the
preliminary combustion that is effected at the timing in the
vicinity of TDC of compression stroke is hardly affected by such
fluctuation, and thus, the exhaust air/fuel ratio can be switched
to a target ratio instantly. While, since the main combustion that
is effected after the compression stroke is easily affected by such
intake system fluctuation, instant switching to the target air/fuel
ratio tends to induce unstable ignition and thus intends to induce
incomplete combustion of the mixture in the cylinder.
[0013] Accordingly, in the present invention, at first, the
preliminary combustion is carried out to produce a compression end
temperature that enables the main combustion, and then, switching
to the main combustion is carried out with a certain retardation.
With this, the switching to the main combustion is effected after
the intake system fluctuation has been reduced, and thus, the main
combustion can be stably effected establishing a smoothed switching
of the combustion control.
[0014] In accordance with a first aspect of the present invention,
there is provided a combustion control system of an internal
combustion engine. The combustion control system comprises a fuel
injection system provided an intake system of the engine; an
exhaust purifying device provided at an exhaust system of the
engine; and a control unit that controls the fuel injection system
to permit the engine to have a predetermined combustion mode, the
predetermined combustion mode being a mode in which, under a
predetermined condition of the exhaust purifying device, the fuel
injection system causes the engine to carry out a main combustion
to produce a torque and at least one preliminary combustion prior
to the main combustion, the at least one preliminary combustion
being effected at a timing in the vicinity of top dead center of
compression stroke, the main combustion being effected at a first
timing after completion of the preliminary combustion, wherein the
control unit further controls the fuel injection system in such a
manner that upon switching of the engine operation from a previous
combustion mode to the predetermined combustion mode, the main
combustion that takes place after completion of the preliminary
combustion is effected at a second timing that is retarded as
compared with the first timing.
[0015] In accordance with a second aspect of the present invention,
there is provided a method for controlling an internal combustion
engine that is equipped at an intake system with a fuel injection
system and at an exhaust system with an exhaust purifying device.
The method comprises controlling the fuel injection system to
permit the engine to have a predetermined combustion mode in which,
under a predetermined condition of the exhaust purifying catalyst,
the fuel injection system causes the engine to carry out a main
combustion to produce a torque and at least one preliminary
combustion prior to the main combustion; controlling the fuel
injection system in such a manner that the at least one preliminary
combustion is effected at a timing in the vicinity of top dead
center of compression stroke, and the main combustion is effected
at a first timing after completion of the preliminary combustion;
and further controlling the fuel injection system in s such a
manner that upon switching of the engine operation from a previous
combustion mode to the predetermined combustion mode, the main
combustion that takes place after completion of the preliminary
combustion is effected at a second timing that is retarded as
compared with the first timing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic diagram of a combustion control system
of an internal combustion engine, according to the present
invention;
[0017] FIG. 2 is a general flowchart showing the entire operation
steps executed by a control unit employed in the present invention
for effecting a combustion control;
[0018] FIG. 3 is a flowchart of a first branch extending from the
general flowchart, showing operation steps of "DPF regeneration
mode" executed by the control unit;
[0019] FIG. 4 is a flowchart of a second branch extending from the
general flowchart, showing operation steps of "sulfur poisoning
recovery mode" executed by the control unit;
[0020] FIG. 5 is a flowchart of a third branch extending from the
general flowchart, showing operation steps of "rich spike mode"
executed by the control unit;
[0021] FIG. 6 is a flowchart of a fourth branch extending from the
general flowchart, showing operation steps of "melt down
suppression mode" executed by the control unit;
[0022] FIG. 7 is a flowchart of a fifth branch extending from the
general flowchart, showing operation steps executed by the control
unit for determining the order of priority of regeneration in case
of presence of request for DPF regeneration;
[0023] FIG. 8 is a flowchart of a sixth branch extending from the
general flowchart, showing operation steps executed by the control
unit for determining the order of priority of regeneration in case
of presence of request for sulfur poisoning recovery;
[0024] FIG. 9 is a flowchart of a seventh branch extending from the
general flowchart, showing operation steps executed by the control
unit for turning "rq-DPF-flag" to 1;
[0025] FIG. 10 is a flowchart of an eighth branch extending from
the general flowchart, showing operation steps executed by the
control unit for turning "rq-desul-flag" to 1;
[0026] FIG. 11 is a flowchart of a ninth branch extending from the
general flowchart, showing operation steps executed by the control
unit for turning "rq-sp-flag" to 1;
[0027] FIG. 12 is a flowchart of a tenth branch extending from the
general flowchart, showing operation steps of "catalyst activation
promotion mode" executed by the control unit;
[0028] FIG. 13 is a time chart showing a combustion condition
exhibited by a first reference (1);
[0029] FIG. 14 is a time chart showing a combustion condition
exhibited by a second reference (2);
[0030] FIG. 15 is a time chart showing a combustion condition
exhibited by the present invention (3);
[0031] FIG. 16 is a graph showing a comparison of emission
characteristics effected by the first and second references ((1),
(2)) and the present invention (3);
[0032] FIGS. 17A, 17B, 17C and 17D are graphs showing a relation
between a main fuel injection timing and the emission
characteristic;
[0033] FIG. 18 is a map showing a target fuel injection timing for
a preliminary combustion;
[0034] FIG. 19 is a map showing a target fuel injection quantity
for the preliminary combustion;
[0035] FIG. 20 is a graph showing a target fuel injection timing
for a main combustion;
[0036] FIG. 21 is a time chart similar to FIG. 15, but showing
another combustion condition exhibited by the present
invention;
[0037] FIGS. 22A and 22B are flowcharts of two types of switching,
each showing operation steps executed by the control unit for
switching to a split retard combustion mode (SRCM);
[0038] FIG. 23 is a graph showing a relation between PM
accumulation quantity and a target ".lambda." during
regeneration;
[0039] FIG. 24 is a map used for looking up a target intake air
quantity for an engine operation of ".lambda.=1";
[0040] FIG. 25 is a graph showing a relation between a main fuel
injection timing and a torque correction factor "K1";
[0041] FIG. 26 is a graph showing a relation between the target
".lambda." and a torque correction factor "K2";
[0042] FIG. 27 is a map used for looking up a target intake air
quantity for a rich spike operation; and
[0043] FIG. 28 is a graph showing an area where both DPF
regeneration and sulfur poisoning recovery are possible.
DETAILED DESCRIPTION OF THE INVENTION
[0044] In the following, the present invention will be described in
detail with reference to the accompanying drawings.
[0045] Referring to FIG. 1, there is schematically shown a
combustion control system of a diesel engine 1 as an internal
combustion engine, which is an embodiment of the present
invention.
[0046] As shown, an intake passage 2 of engine 1 has at its
upstream part a compressor 3a of a turbo-charger 3. Air led into
intake passage 2 is super-compressed by compressor 3a, cooled by an
intercooler 4, flow-controlled by an intake throttle valve 5 and
fed to respective combustion chambers through a collector 6. Fuel
fed into a fuel pipe is compressed by a fuel injection pump 7 and
led to a common rail 8 and directly injected to the respective
combustion chambers from corresponding fuel injection valves 9. The
air and the fuel thus fed to each combustion chamber are subjected
to a combustion caused by a compression ignition. Exhaust gas
produced as a result of the combustion is led to an exhaust passage
10.
[0047] Fuel injection pump 7, common rail 8 and fuel injection
valves 9 thus constitute a common rail type fuel injection
device.
[0048] Part of the exhaust gas led to exhaust passage 10 is
returned back to the intake system as EGR gas through an EGR
passage 11 and an EGR valve 12. The most part of the exhaust gas
drives an exhaust turbine 3b of turbocharger 3.
[0049] At a part of exhaust passage 10 downstream of exhaust
turbine 3b, there is disposed a NOx trap catalyst 13 for purifying
the exhaust gas. That is, NOx trap catalyst 13 functions to trap
NOx in the exhaust gas when the exhaust air/fuel ratio is lean and
to release the trapped NOx (viz., desorption of the trapped NOx)
therefrom when the exhaust air/fuel ratio is rich. To NOx trap
catalyst 13, there is attached an oxidation catalyst (viz.,
precious metal catalyst) for oxidizing HC and CO in the exhaust
gas.
[0050] At a part of exhaust passage 10 downstream of NOx trap
catalyst 13, there is disposed a diesel particulate filter (or DPF)
14 for cleaning the exhaust gas. That is, DPF 14 functions to
collect particulate matter (or PM) in the exhaust gas. Also to DPF
14, there is attached an oxidation catalyst (viz., precious metal
catalyst) for oxidizing HC and CO in the exhaust gas.
[0051] If desired, NOx trap catalyst 13 and DPF 14 may be arranged
at mutually reversed positions. Furthermore, if desired, to DPF 14,
there may be attached NOx trap catalyst 13 to constitute an
integrated exhaust gas purifying unit.
[0052] Denoted by numeral 20 is a control unit constructed by a
microcomputer, that comprises CPU, RAM, ROM and input and output
interfaces. To control unit 20, there are fed information signals
from an engine speed sensor 21 that senses an engine speed "Ne", an
accelerator position sensor 22 that senses an accelerator position
"APO", an air flow meter 23 that senses an intake air quantity
"Qac" and a water temperature sensor 24 that senses the temperature
"Tw" of an engine cooling water.
[0053] To control unit 20, there are further fed information
signals from a catalyst temperature sensor 25 that senses the
temperature of NOx trap catalyst 13, an exhaust pressure sensor 26
that senses a pressure of the exhaust gas at an inlet side of DPF
14, a DPF temperature sensor 27 that senses the temperature of DPF
14, and an exhaust air/fuel ratio sensor 28 that senses an exhaust
air/fuel ratio of the exhaust gas at an outlet side of DPF 14.
[0054] The exhaust air/fuel ratio will be referred to as
"exhaust-.lambda." and the numeral value of the ratio represents an
excess rate of air.
[0055] If desired, the temperature of NOx trap catalyst 13 and that
of DPF 14 may be indirectly derived from the temperature of the
exhaust gas that flows downstream of such device 13 and/or 14.
[0056] By processing the information signals fed thereto, control
unit 20 issues instruction signals to fuel injection valves 9 for
controlling the fuel injection quantity and fuel injection timing,
to intake throttle valve 5 for controlling an open degree of the
same and to EGR valve 12 for controlling an open degree of the
same.
[0057] As will be described in detail hereinafter, in addition to
the above-mentioned control, control unit 20 carries out an exhaust
gas purifying control that includes a control for regeneration of
DPF 14 by burning collected PM on DPF 14, a control for desorption
or release of trapped NOx from NOx trap catalyst 13 and a control
for recovery of sulfur poisoning of NOx trap catalyst 13.
[0058] For carrying out the exhaust gas purifying control,
programmed operation steps are executed by control unit 20, which
are shown in flowcharts in FIGS. 2 to 12.
[0059] The flowchart shown in FIG. 2 is a general flowchart that
shows the entire of operation steps executed by control unit
20.
[0060] At step S1, the information signals from the various sensors
are read. That is, the engine speed "Ne", the accelerator position
"APO", the intake air quantity "Qac", the temperature of NOx trap
catalyst 13, the pressure of the exhaust gas at an inlet side of
DPF 14, the temperature of DPF 14 and the exhaust-.lambda. at the
outlet side of DPF 14 are read.
[0061] At step S2, judgment is carried out as to whether NOx trap
catalyst 13 is under activation (or hot) condition or inactivation
(or cool) condition. If the temperature of the catalyst 13 is lower
than "T5" that is the lowest activation temperature of the catalyst
13, the operation flow goes to an after-mentioned "catalyst
activation promotion mode" of FIG. 12 judging that the catalyst 13
is still under the inactivation condition. While, if the
temperature of the catalyst 13 is equal to or higher than "T5", the
operation flow goes to step S3 judging that the catalyst 13 is
under the activation condition (viz., the activation condition
achieved after completion of an after-mentioned catalyst activation
promotion mode).
[0062] If desired, the activation condition judgment of NOx trap
catalyst 13 may be carried out based on the concentration of at
least one of HC and CO detected at an outlet side of the catalyst
13. That is, if the concentration of HC or CO is higher than a
threshold value, judgment is so made that the catalyst 13 is under
the inactivation condition. The concentration judgment of HC or CO
may be carried out based on an output level of the air/fuel ratio
sensor 28. The estimation is so made that the concentration of HC
or CO increases as the rich degree of the exhaust air/fuel ratio
increases.
[0063] At step S3, the quantity of NOx trapped by and accumulated
on NOx trap catalyst 13 (viz., NOx accumulation quantity) is
calculated. As is described in column 8 of U.S. Pat. No. 5,473,887,
the NOx accumulation quantity may be estimated from an integrated
value of engine speed, or a travel distance of the vehicle. In case
of using the integrated value of engine speed for the estimation,
the integrated value should be reset to zero at the time when the
desorption of trapped NOx from NOx trap catalyst 13 is completed
and/or when the sulfur poisoning recovery is completed together
with the desorption of trapped NOx.
[0064] At step S4, the quantity of sulfur (viz., sulfur
accumulation quantity) accumulated on NOx trap catalyst 13 due to
the sulfur poisoning is calculated. Like in the above-mentioned NOx
accumulation quantity, the sulfur accumulation quantity may be
estimated from the integrated value of engine speed or the travel
distance of the vehicle. In case of using the integrated value of
engine speed for the estimation, the integrated value should be
reset to zero at the time when the sulfur poisoning recovery is
completed.
[0065] At step S5, the quantity of PM (viz., PM accumulation
quantity) trapped by and accumulated on DPF 14 is calculated. The
method of this calculation is as follows.
[0066] In view of the fact that the exhaust pressure at the inlet
side of DPF 14 increases with increase of the PM accumulation
quantity, the PM accumulation quantity is estimated by comparing
the current exhaust pressure at the inlet side of DPF 14 that is
detected by exhaust pressure sensor 26 with a reference exhaust
pressure that has been previously derived in a corresponding
operation condition of the engine. The current operation condition
is derived from the engine speed and engine load. If desired, the
PM accumulation quantity may be derived from a combination of the
integrated value of engine speed (or the travel distance of the
vehicle) and the exhaust pressure.
[0067] At step S6, judgment is carried out as to whether "reg-flag"
set for indicating the state of "DPF regeneration mode" has been
raised or not. If "reg-flag=1" has been established, the operation
flow goes to an after-mentioned control for the "DPF regeneration
mode" of FIG. 3.
[0068] At step S7, judgment is carried out as to whether
"desul-flag" set for indicating the state of "sulfur poisoning
recovery mode" of NOx trap catalyst 13 has been raised or not. If
"desul-flag=1" has been established, the operation flow goes to an
after-mentioned control for the "sulfur poisoning recovery mode" of
FIG. 4.
[0069] At step S8, judgment is carried out as to whether "sp-flag"
set for indicating the state of "rich spike mode" for NOx
desorption of NOx trap catalyst 13 has been raised or not. If
"sp-flag=1" has been established, the operation flow goes to an
after-mentioned control for the "rich spike mode" of FIG. 5.
[0070] At step S9, judgment is carried out as to whether "rec-flag"
set for indicating the state of "melt down suppression mode" after
the DPF regeneration and sulfur poisoning recovery has been raised
or not. If "rec-flag=1" has been established, the operation flow
goes to an after-mentioned control for the "melt down suppression
mode" of FIG. 6.
[0071] At step S10, judgment is carried out as to whether
"rq-DPF-flag" set for indicating presence/absence of request for
DPF regeneration has been raised or not. If "rq-DPF-flag=1" has
been established due to presence of such request, the operation
flow goes to the flowchart of FIG. 7 to determine the order of
priority of regeneration in case of presence of request for DPF
regeneration.
[0072] At step S11, judgment is carried out as to
whether"req-desul" set for indicating presence/absence of request
for "sulfur poisoning recovery" has been raised or not. If
"req-desul=1" has been established due to presence of such request,
the operation flow goes to the flowchart of FIG. 8 to determine the
order of priority of regeneration in case of presence of request
for sulfur poisoning recovery.
[0073] At step S12, judgment is carried out as to whether the PM
accumulation quantity calculated at step S5 has reached a
predetermined quantity PM1 or not, that is, whether it is the time
for DPF regeneration or not.
[0074] If "PM accumulation quantity>PM1" is established judging
that it is the time for DPF regeneration, the operation flow goes
to the flowchart of FIG. 9. As is seen from the flowchart of this
drawing, at step S701, the "rq-DPF-flag" is turned to 1 to issue
the request for DPF regeneration.
[0075] At step S13, judgment is carried out as to whether the
sulfur accumulation quantity calculated at step S4 has reached a
predetermined quantity S1 or not, that is, whether it is the time
for the sulfur poisoning recovery or not.
[0076] If "sulfur accumulation quantity>S1" is established
judging that it is the time for the sulfur poisoning recovery, the
operation flow goes to the flowchart of FIG. 10. As is seen from
the flowchart of this drawing, at step S801, the "rq-desul-flag" is
turned to 1 to issue the request for the sulfur poisoning
recovery.
[0077] At step S14, judgment is carried out as to whether the NOx
accumulation quantity on NOx trap catalyst 13 calculated at step S3
has reached a predetermined quantity NOx1 or not, that is, whether
it is the time for the NOx desorption from the catalyst 13 or
not.
[0078] If "NOx accumulation quantity>NOx1" is established
judging that it is the time for the NOx desorption, the operation
flow goes to the flowchart of FIG. 11. As is seen from the
flowchart of this drawing, at step S901, the "rq-sp-flag" is turned
to 1 to issue the request for NOx desorption, viz., the request for
rich spike operation.
[0079] In the following, the "DPF regeneration mode" will be
described in detail with reference to the flowchart of FIG. 3.
[0080] That is, as is seen from the flowchart of FIG. 2, when the
PM accumulation quantity has reached the predetermined amount PM1
and thus, the "reg-flag" is turned to 1, the flowchart of FIG. 3 is
started.
[0081] At step S101, for actually carrying out the DPF
regeneration, the engine combustion is switched from a normal lean
combustion mode to a split retard combustion mode (SRCM) according
to the present invention.
[0082] In the following, the split retard combustion mode (SRCM)
will be described. It is to be noted that in addition to the DPF
regeneration, the split retard combustion mode (SRCM) is used for
the sulfur poisoning recovery, NOx desorption (or rich spike) and
catalyst activation promotion.
[0083] For carrying out the DPF regeneration, it is necessary to
control the "exhaust .lambda." within a range from 1.0 to 1.4 and
control the temperature of DPF 14 over 600.degree. C. For carrying
out the sulfur poisoning recovery of NOx trap catalyst 13, it is
necessary to control the "exhaust .lambda." smaller than 1.0 and
control the exhaust temperature over 600.degree. C.
[0084] In a normal operation of the internal combustion engine at a
lean air/fuel ratio, a pilot fuel injection is usually carried out.
The pilot fuel injection timing is set at 40.degree. to 10.degree.
BTDC (before top dead center), the pilot fuel injection quantity is
set at 1 to 3 mm.sup.3/stroke, the main fuel injection timing is
set at 10.degree. to -20.degree. BTDC, and the interval between the
pilot fuel injection and the main fuel injection is within a range
from 10.degree. to 30.degree. in CA (crank angle).
[0085] For actualizing the lower .lambda. and the higher
temperature exhaust for the DPF regeneration and sulfur poisoning
recovery from a normal operation of the engine, it is necessary to
reduce the intake air quantity. However, when the quantity of
intake air is reduced, the compression end temperature in each
cylinder is inevitably lowered, which affects the combustion
characteristic of the air/fuel mixture. Thus, as will be understood
from the time chart of FIG. 13, that shows a combustion
characteristic of a first reference, if the pilot fuel injection is
set like in the fuel injection of the normal lean combustion, it is
necessary to advance the injection timing of the main fuel
injection. In such setting of fuel injection quantity and fuel
injection timing, retarding the fuel injection timing for the
purpose of increasing the exhaust temperature brings about an
unstable combustion, and thus, the retarding has a limit of its own
and thus actualization of the lower .lambda. and higher temperature
exhaust is considerably difficult.
[0086] In view of the above, the above-mentioned Laid-open Japanese
Patent Application (Tokkai) 2000-320386 employs a measure to split
the main fuel injection. With this splitting, a retarding limit of
the fuel injection timing is expanded to actualize the lower
.lambda. and higher temperature exhaust. This is depicted by the
time chart of FIG. 14 that shows the combustion characteristic of a
second reference.
[0087] However, in case of the '386 publication, during a brisk
combustion of previously injected fuel, a subsequent fuel injection
is carried out. Thus, as is seen from the time chart of FIG. 14, a
continuous combustion is inevitably carried out. That is, since a
split fuel for the main combustion is injected to a flame of the
combustion of fuel that has been previously injected, the split
fuel is forced to start its combustion as soon as it is injected.
Thus, percentage of diffusive combustion is increased, so that a
partial equivalent ratio becomes very rich causing a severe
deterioration of emission characteristic (viz., smoke).
[0088] Accordingly, in the present invention, as is seen from the
time chart of FIG. 15, the fuel injections ((a) and (b)) are so
controlled that the main combustion for producing a torque and a
preliminary combustion effected before the main combustion are both
carried out, and the preliminary combustion is carried out at a
timing in the vicinity of TDC (viz., top dead center) of
compression stroke and the main combustion is started after
completion of the preliminary combustion.
[0089] That is, under the compression stroke, fuel is injected to
effect the preliminary combustion to increase the incylinder
temperature (viz., compression end temperature) in the vicinity of
TDC, as is indicated by reference "a". As is known, the fuel
injection quantity bringing about a heat release of the preliminary
combustion depends on the operation condition of the engine.
[0090] However, in the invention, the quantity of fuel injected for
the preliminary combustion is so determined as to realize a certain
heat release from the preliminary combustion and the incylinder
temperature obtained at the time just before the fuel injection for
the main combustion shows a level that is higher than a self
ignition temperature that enables a self ignition of the fuel in
the combustion chamber. Furthermore, in the invention, the fuel
injection quantity and fuel injection timing for the preliminary
combustion are varied in accordance with the compression end
temperature that is estimated in each operation condition of the
engine. With this, stability of the preliminary combustion is
improved.
[0091] After completion of the preliminary combustion, the fuel for
the main combustion is injected at a timing after TDC (viz., top
dead center) as is indicated by reference "b".
[0092] That is, by increasing the incylinder temperature by
effecting the preliminary combustion, the retarding limit of the
main combustion is expanded to improve a controllability for
obtaining a target or desired temperature. Furthermore, by
injecting fuel for the main combustion after the preliminary
combustion is completed, an ignition retarding period for the main
combustion is obtained, so that the rate of premixed combustion for
the main combustion is increased for suppressing or at least
minimizing emission of the smoke.
[0093] Although depending on the engine speed, the period (viz.,
interval period) from start timing of the preliminary combustion to
that of the main combustion should be controlled larger than
20.degree. in CA (crank angle). If not, the completion of the
preliminary combustion is not obtained, that is, the heat release
by the preliminary combustion is not sufficiently carried out. With
such interval period, deterioration of the main combustion
characteristic is suppressed and thus deterioration of the smoke
characteristic is suppressed. Furthermore, since the main
combustion is forced to start in the expansion stroke, the burning
speed of the fuel is very late, and thus, the main combustion is
completed at a timing of over 50.degree. ATDC (after top dead
center) of compression stroke. Because the completion of the main
combustion is delayed, the main combustion becomes slow and thus
combustion noise is minimized.
[0094] As is understood from the graph of FIG. 16, in the split
retard combustion mode (SRCM) according to the present invention,
such a combustion as to feature a high exhaust temperature and low
smoke exhaust is actualized even under richer condition in the
air/fuel mixture. In the graph of FIG. 16, the emission
characteristic exhibited by the present invention is shown by bars
indicated by numeral (3), and the emission characteristic exhibited
by the first and second references are shown by bars indicated by
numerals (1) and (2) respectively. As is seen from this graph, in
the present invention, also the concentration of HC in the exhaust
gas is very small.
[0095] Due to employment of the preliminary combustion, the
retarding limit of the main combustion is expanded. Thus, even when
the fuel injection timing for the main combustion is retarded, the
combustion at lower .lambda. is stable, which enables the high
exhaust temperature.
[0096] As is understood from the graph of FIG. 17, when the timing
of the main combustion is retarded, the premixed rate for the main
combustion is increased. Thus, even when the value of .lambda. is
small, undesired smoke emission is suppressed by retarding the main
combustion. Furthermore, when the timing of the main combustion is
retarded, higher exhaust temperature is realized. Thus, by varying
the fuel injection timing for the main combustion, the exhaust
temperature can be controlled.
[0097] FIG. 18 is a map showing a target fuel injection timing for
the preliminary combustion using the engine speed Ne and the engine
load Q as parameters.
[0098] FIG. 19 is a map showing a target fuel injection quantity
for the preliminary combustion using the engine speed Ne and the
engine load Q as parameters.
[0099] FIG. 20 is a map showing a target fuel injection timing for
the main combustion to achieve a target exhaust temperature, using
the engine speed Ne and the engine load Q as parameters.
[0100] When, under a low load condition of the engine, a target
exhaust temperature is required, the combustion timing of the main
combustion is largely retarded. Thus, in such condition, it tends
to occur that even when the preliminary combustion is effected, the
incylinder temperature is not kept sufficiently high to the time
when the fuel injection for the main combustion is started. That
is, there may be such a case that only one preliminary combustion
fails to keep the incylinder temperature sufficiently high to the
timing for the fuel injection for the main combustion.
[0101] In view of such anxiety, as is seen from FIG. 21, in the
present invention, a plurality of preliminary combustions are
effected before the main combustion in such a manner that the heat
releases by the respective preliminary combustions are not
overlapped. With this measure, both lower smoke emission and high
exhaust temperature are achieved even under the low load condition
of the engine.
[0102] Thus, when the lower .lambda. and high exhaust temperature
are needed for effecting the DPF regeneration and sulfur poisoning
recovery, switching to the split retard combustion mode (SRCM) is
carried out in the present invention.
[0103] Two types (viz., type-1 and type-2) of such switching will
be described in detail with reference to the flowcharts of FIGS.
22A and 22B.
[0104] In one type (viz., type-1) of the switching shown in FIG.
22A, at step S1101, switching to a fuel injection control for the
preliminary combustion is effected. That is, the fuel injection is
carried out at a fuel injection timing for a preliminary combustion
(see FIG. 18) with a fuel injection quantity for the preliminary
combustion (see FIG. 19).
[0105] At step S1102, the fuel injection for the main combustion is
carried out at a retarded fuel injection timing. That is, although
the fuel injection timing for the preliminary combustion is
instantly switched, switching of the fuel injection timing for the
main combustion is carried out with a retard. More specifically,
switching is gradually made by repeating several cycles for
obtaining a target main fuel injection timing as shown in FIG. 20.
Since the torque produced is reduced as the fuel injection timing
is retarded, the fuel injection quantity for the main injection is
gradually increased to compensate for the torque reduction by the
retarded fuel injection timing, for keeping the torque
produced.
[0106] That is, when the switching from a normal combustion mode to
the split retard combustion mode (SRCM) is carried out for
effecting the regeneration of DPF 14 and NOx trap catalyst 13,
fresh air quantity needed by the engine and the EGR quantity are
varied due to change of the target .lambda., which induces a
fluctuation of the intake system of the engine. As has been
mentioned hereinabove, since the preliminary combustion effected at
the timing in the vicinity of the top dead center of compression
stroke is hardly affected by the fluctuation of the intake system,
switching to the target value can be instantly made. However, the
main combustion after the compression stroke is easily affected by
the fluctuation of the intake system, and thus, if the switching to
the target value for the main combustion is instantly made,
unstable ignition is induced causing a misfiring of the main
combustion.
[0107] The above description will be easily understood from the
following.
[0108] That is, the fresh air quantity and the behavior of the EGR
gas, that change in accordance with the change of the target
.lambda. induced by the combustion mode switching, affect the main
combustion. That is, although the throttle opening can instantly
take a target throttle opening, it takes a certain time lag that a
differential pressure between upstream and downstream portions of
throttle valve 5 is developed to a degree corresponding to the
target throttle opening, which tends to induce a severe lack of
fresh air. In such case, the compression end temperature becomes
excessively reduced and thus in a worst case, the main combustion
is subjected to a misfiring. Like the above, since the differential
pressure between upstream and downstream portions of the EGR valve
12 is unstable at the transient time, there is such a case that the
EGR gas is excessively increased. In this case, an ignition retard
becomes marked and thus in a worst case the main combustion is
subjected to a misfiring. Furthermore, due to occurrence of such
lack of fresh air and the excessive increase of the EGR gas, the
misfiring tendency of the main combustion tends to be much
increased.
[0109] Accordingly, in the present invention, as has been mentioned
hereinabove, switching to the preliminary combustion is effected at
first for the purpose of obtaining a compression end temperature
that enables the main combustion, and then, switching to the main
combustion is gradually carried out, and when the fluctuation of
the intake system becomes sufficiently small, the switching to the
main combustion is actually carried out.
[0110] Thus, in the present invention, the main combustion is
stably established, and thus smoothed switching of the combustion
control is achieved.
[0111] The switching speed for the main combustion is set in
accordance with retard factors of the intake system (which are the
collector capacitor, 2 to 3 repetition cycles and the like), and a
real .lambda. (which is determined based on the fresh air quantity,
the fluctuation of the EGR system and the like). For example, the
switching to the main combustion may be so made that 1/3 of an
entire retard is effected for one cycle and the entire retard is
established by repeating 3 cycles.
[0112] In the other type (viz., type-2) of the switching shown in
FIG. 22B, at step S1111, a retardation timing needed for subsidence
of the transient fluctuation (viz., fresh air quantity and EGR gas
quantity) of the intake system is determined in accordance with a
target .lambda. for the combustion after the combustion switching.
This may be achieved by looking up a suitable map.
[0113] At step S1112, like the above-mentioned step S1101,
switching to the fuel injection control for a preliminary
combustion is effected. That is, the fuel injection is carried out
at a timing for the preliminary combustion (see FIG. 18) with a
fuel injection quantity for the preliminary combustion (see FIG.
19).
[0114] At step S1113, judgment is carried out as to whether a time
when a transient fluctuation of the fresh intake air and EGR gas
induced by operation of the intake system subsides has passed or
not. The time may be previously derived through experiments. If
YES, that is, when it is judged that the time has passed, the
operation flow goes to step S1114.
[0115] At step S1114, switching to the fuel injection for the main
combustion is carried out.
[0116] As is seen from the above, in the other type of switching,
when the transient fluctuation of the fresh air intake air and EGR
gas subsides and thus when the differential pressure between the
upstream and downstream portions of the throttle valve 5 becomes
stable, switching to the main combustion is actually effected.
Thus, stable main combustion is achieved, and thus, smoothed
switching of the combustion control is effected.
[0117] Referring back to FIG. 3, at step S101, for carrying out the
DPF regeneration, the engine combustion is switched from the normal
lean combustion mode to the split retard combustion mode (SRCM)
according to the present invention.
[0118] Then, at step S102, the exhaust .lambda. is controlled to a
target value. In the regeneration of DPF 14, the target value of
the exhaust .lambda. depends on the PM accumulation quantity.
Accordingly, by comparing the exhaust pressure at the inlet side of
DPF 14 with a reference exhaust pressure that has been previously
derived in a corresponding operation condition of the engine, the
PM accumulation quantity is estimated, and then by using the map of
FIG. 23, the target .lambda. corresponding to the estimated PM
accumulation quantity is looked up.
[0119] After the switching to the split retard combustion mode
(SRCM) is effected at step S101, the fresh air quantity is
controlled by intake throttle valve 5 and EGR valve 12 for
achieving the target air/fuel ratio. More specifically, at first,
the intake throttle valve 5 is so controlled as to achieve a target
intake air quantity (viz., target intake air quantity for an
operation on .lambda.=1) that is provided by multiplying the target
.lambda. by a value looked up from the map of FIG. 24, and if the
air/fuel ratio differs from the target value, intake throttle valve
5 and/or EGR valve 12 is controlled to bring the air/fuel ratio to
the target value.
[0120] When the switching to the split retard combustion mode
(SRCM) is actually made, the fuel injection timing is greatly
retarded. Thus, in the invention, in addition to the
above-mentioned control for the intake air quantity, the following
control for suppressing a torque fluctuation, that would be induced
at the switching, is carried out. That is, the target intake air
quantity and fuel injection quantity provided based on the map of
FIG. 24 are corrected by means of a torque correction factor K1
looked up from the map of FIG. 25 that shows a relation between the
target fuel injection timing for the main fuel injection and the
correction factor K1.
[0121] When the target air/fuel ratio is reduced to or near a
stoichiometric value, undesirable pumping loss tends to occur.
Thus, in the invention, the target intake air quantity and the fuel
injection quantity for the main combustion are corrected by means
of a correction factor K2 that is looked up from the map of FIG. 26
that shows a relation between the target .lambda. and the
correction factor K2.
[0122] Referring back to FIG. 3, at step S103, judgment is carried
out as to whether the temperature of DPF 14 has exceeded a target
upper limit T22 under regeneration of DPF 14 or not.
[0123] If "DPF temperature>T22" is made, the operation flow goes
to step S111 judging that the temperature of DPF 14 has exceeded
the upper limit during the regeneration of DPF 14. At step S111,
the fuel injection timing for the main combustion is advanced to
lower the exhaust temperature, and then, at step S112, a torque
correction (viz., reduction of the fuel injection quantity for the
main combustion) is carried out for compensating a torque change
(viz., increase) caused by the advancing of the fuel injection
timing.
[0124] If, at step S103, "DPF temperature<T22" is made, the
operation flow goes to step S104 to judge whether the temperature
of DPF 14 has become below a target lower limit T21 under
regeneration of DPF 14 or not.
[0125] If "DPF temperature<T21" is made, the operation flow goes
to step S109 judging that the temperature of DPF 14 has become
below the lower limit T21 during the regeneration of DPF 14. At
step S109, the fuel injection timing for the main combustion is
retarded to increase the exhaust temperature, and then at step
S110, a torque correction (viz., increase of the fuel injection
quantity for the main combustion) is carried out for compensating a
torque drop caused by the retardation of the fuel injection
timing.
[0126] If, at step S104, "DPF temperature.gtoreq.T21" is made, the
operation flow goes to step S105. At this step S105, judgment is
carried out as to whether a predetermined time "tDPFreg" has passed
from the start of the DPF regeneration or not. If YES, the
operation flow goes to step S106 judging that the PM accumulated on
DPF 14 has completely burnt.
[0127] At step S106, switching from the split retard combustion
mode to the normal combustion mode is made because the regeneration
of DPF 14 has been completed. With this switching, heating of DPF
14 is stopped.
[0128] At step S107, the reg-flag is turned to 0 due to completion
of the DPF regeneration.
[0129] Then, at step S108, the rec-flag is turned to 1 for
preparation of an after-mentioned "melt-down suppression mode".
That is, if there is cinder (viz., burnable rest) of particulate
matter (PM) on DPF 14 even when the DPF regeneration has been
finished, a rapid increase of the exhaust .lambda. causes a sudden
burning of the cinder, which has a possibility of inducing melting
of DPF 14. Thus, it is necessary to prepare such melt-down
suppression mode.
[0130] In the following, control for the sulfur poisoning recovery
mode will be described in detail with reference to the flowchart of
FIG. 4.
[0131] As is seen from the flowchart of FIG. 2, when the sulfur
accumulation quantity of NOx trap catalyst 13 reaches the
predetermined quantity S1 to induce "rq-desul-flag=1" inducing
"desul-flag=1" in an after-mentioned flowchart of FIG. 8, the
control for the sulfur poisoning recovery starts like the manner as
shown in the flowchart of FIG. 4.
[0132] At step S201, for carrying out the sulfur poisoning recovery
of NOx trap catalyst 13, the engine combustion is switched from the
normal combustion mode to the split retard combustion mode (SRCM)
according to the present invention.
[0133] At step S202, the exhaust .lambda. is controlled to a
stoichiometric value. This control is carried out by setting the
target .lambda. to a stoichiometric ratio.
[0134] At step S203, judgment is carried out as to whether the
temperature of NOx trap catalyst 13 is higher than a predetermined
temperature T4 or not. If the catalyst 13 is produced basically by
Ba (viz., barium), it is necessary to keep the temperature of the
catalyst 13 over 600.degree. C. in rich-stoichiometric atmosphere
for normal activation of the same. Thus, in such catalyst 13, the
predetermined temperature T4 is set at 600.degree. C.
[0135] If the catalyst temperature is lower than the predetermined
value T4, the operation flow goes to step S210 to retard the fuel
injection timing for the main combustion thereby to increase the
exhaust temperature, and then at step S211, a torque correction is
carried out for compensating a torque change caused by the
retardation of the fuel injection timing.
[0136] At step S204, judgment is carried out as to whether a
predetermined time "tdesul" has passed from the start of the sulfur
poisoning recovery mode or not. If YES, the operation flow goes to
step S205 judging that the sulfur poisoning has been recovered or
removed.
[0137] At step S205, because of completion of the sulfur poisoning
recovery, the engine combustion is switched from the split retard
combustion mode (SRCM) to the normal combustion mode stopping
heating of NOx trap catalyst 13. At the same time, the
stoichiometric air/fuel ratio operation is cancelled.
[0138] At step S206, because of completion of the sulfur poisoning
recovery, the "desul-flag" is turned to 0.
[0139] At step S207, the rec-flag is turned to 1 for preparation of
after-mentioned "melt-down suppression mode". That is, if a certain
amount of particulate matter (PM) is left on DPF 14 after
completion of the sulfur poisoning recovery, a rapid increase of
the exhaust .lambda. causes a sudden burning of the particulate
matter (PM), which has a possibility of inducing melting of DPF 14.
Thus, it is necessary to prepare such melt-down suppression
mode.
[0140] At step S208, the rq-sp-flag is turned to 0 to disable the
request for rich spike operation. That is, under the sulfur
poisoning recovery mode, NOx trap catalyst 13 is kept exposed to a
stoichiometric exhaust atmosphere for a certain time, and thus, the
NOx desorption is carried out at the same time. Thus, if a request
for the NOx desorption (viz., request for rich spike operation) has
been issued, it is necessary to cancel such request.
[0141] In the following, control for the rich spike mode (viz., NOx
desorption mode) will be described in detail with reference to the
flowchart of FIG. 5.
[0142] As is seen from the flowchart of FIG. 2, when the NOx
accumulation quantity on NOx trap catalyst 13 reaches the
predetermined quantity NOx1 to induce "rq-sp-flag=1 inducing
"sp-flag=1" in an after-mentioned flowchart of FIG. 7 or 8, the
control for the rich spike mode starts like the manner shown in the
flowchart of FIG. 5.
[0143] At step S301, for carrying out the NOx desorption, the
engine combustion is switched from a normal combustion mode to the
split retard combustion mode (SRCM) according to the present
invention.
[0144] At step S302, the exhaust .lambda. is controlled to a rich
value. That is, the control is carried out by controlling intake
throttle valve 5 for achieving a target intake air quantity for the
rich spike operation, and then, like in the above-mentioned case of
DPF regeneration, by controlling the fresh intake air by intake
throttle valve 5 and/or EGR valve 12.
[0145] At step S303, judgment is carried out as to whether a
predetermined time "tspike" has passed from the start of the rich
spike mode or not. If YES, the operation flow goes to step S304
judging that the NOx desorption has completely effected.
[0146] At step S304, because of completion of the NOx desorption,
the engine combustion is switched from the split retard combustion
mode (SRCM) to the normal combustion mode. At the same time, the
rich air/fuel ratio operation is cancelled.
[0147] At step S305, because of completion of the NOx desorption,
the sp-flag is turned to 0.
[0148] In the following, control for the melt-down suppression mode
will be described in detail with reference to the flowchart of FIG.
6.
[0149] As is seen from the flowchart of FIG. 2, when the DPF
regeneration or sulfur poisoning recovery is finished to induce
"rec-flag=1" in the flowchart of FIG. 3 or 4, the control for the
metal-down suppression mode starts in such a manner as shown in the
flowchart of FIG. 6.
[0150] At step S401, the exhaust .lambda. is controlled to a target
value, for example, ".lambda..ltoreq.1.4". That is, just after the
DPF regeneration for example, the DPF 14 is still highly heated.
If, under such condition, the exhaust .lambda. is instantly
controlled to a lean level, the cinder (viz., burnable rest) of
particulate matter (PM) on DPF 14 is suddenly burnt, which has a
possibility of inducing melting of DPF 14. Thus, it is necessary to
provide the exhaust .lambda. with such upper limit target value.
Since, in the melt-down suppression mode, a lower exhaust
temperature is preferable, the split retard combustion mode is not
used. That is, the exhaust .lambda. is controlled to the target
value under the normal combustion mode.
[0151] At step S402, judgment is carried out as to whether or not
the DPF temperature has become lower than a predetermined
temperature T3 (for example 500.degree. C.) that is the lowest
level for enabling a rapid oxidation of particulate matter (PM). If
NO, that is, when the DPF temperature is higher than T3, the
control for the exhaust .lambda. is continued. If YES, that is,
when the DPF temperature is lower than T3, the operation flow goes
to step S403 judging that the undesired melting of DPF 14 may be
avoided even if the oxygen concentration in the exhaust gas becomes
to the level of the atmospheric air.
[0152] At step S403, the control for the exhaust .lambda. is
stopped because of disappearance of fear of the melt-down.
[0153] At step S404, because of completion of the melt-down
suppression mode, the rec-flag is turned to 0.
[0154] In the following, control-1 for determining the order of
priority of regeneration will be described with reference to the
flowchart of FIG. 7.
[0155] This control-1 is carried out when request for the DPF
regeneration and one of request for the sulfur poisoning recovery
and request for the NOx desorption are issued at the same time.
[0156] As is seen from the flowchart of FIG. 2, when the request
for DPF regeneration is issued to induce "rq-DPF-flag=1", the
control-1 for determining the order starts in such a manner as
shown in the flowchart of FIG. 7.
[0157] At step S501, judgment is carried out as to whether, after
issuance of request for the DPF regeneration, the sulfur
accumulation quantity has reached the predetermined quantity S1 or
not, that is, whether the timing for the sulfur poisoning recovery
has come or not, like the case of the above-mentioned step S13.
[0158] If YES, the operation flow goes to step S801 of the
flowchart of FIG. 10 judging that the timing for the sulfur
poisoning recovery has come. At the step S801, the rq-desul-flag is
turned to 1 to issue a request for the sulfur-poisoning recovery.
In this case, the order of priority is decided by the flowchart of
FIG. 8, as will be described hereinafter.
[0159] If NO at step S501, that is, when it is judged that the
timing for the sulfur poisoning recovery has not come yet, the
operation flow goes to step S502.
[0160] At step S502, judgment is carried out as to whether
"rq-sp-flag=1" has been established or not, that is, whether the
request for the NOx desorption has been issued or not. If NO, the
operation flow goes to step S503.
[0161] At step S503, judgment is carried out as to whether, after
issuance of request for the DPF regeneration, the NOx accumulation
quantity has reached the predetermined quantity NOx1 or not, that
is, whether the timing for the NOx desorption has come or not, like
the case of the above-mentioned step S14.
[0162] If YES, that is, when the NOx accumulation quantity is
judged greater than the predetermined quantity NOx1, the operation
flow goes to step S901 of the flowchart of FIG. 11. At the step
S901, the rq-sp-flag is turned to 1 to issue a request for the NOx
desorption (viz., request for rich spike operation).
[0163] If NO at step S503, that is, when the NOx accumulation
quantity is judged smaller than the predetermined quantity NOx1,
the operation flow goes to step S504. That is, in such case, only
the request for DPF regeneration is issued.
[0164] At step S504, judgment is carried out as to whether or not
the current engine operation is under a possible condition enabling
the DPF regeneration and sulfur poisoning recovery with reference
to the map of FIG. 28. As is seen from this map, the possible
condition is the condition wherein the engine speed and engine load
are not low, irregularity of temperature increase is relatively
small and deterioration degree of the exhaust performance does not
exceed an allowable value.
[0165] If YES, that is, when the current engine operation condition
is judged to be under the possible condition, the operation flow
goes to step S505 where the reg-flag is turned to 1 for preparation
of the DPF regeneration.
[0166] If YES at step S502, that is, when "rq-sp-flag=1" has been
established, the operation flow goes to step S506 judging that the
request for the DPF regeneration and the request for NOx desorption
have been issued at the same time.
[0167] At step S506, judgment is carried out as to whether or not
the current engine operation is under a low NOx condition that
enables reduction in NOx in the exhaust gas (for example, under a
stationary condition). If YES, that is, when it is judged that the
current engine operation is under the low NOx condition, the
operation flow goes to step S507 inferring that under such low NOx
condition, deterioration of the exhaust property at the tail pipe
is hardly seen even when the regeneration of the NOx trap catalyst
13 is delayed, and thus it is preferable to give priority to the
DPF regeneration that would affect the operation of the engine.
[0168] If NO at step S506, that is, when it is judged that the
current engine operation is not under the low NOx condition (that
is, under high NOx condition, such as under vehicle acceleration
condition), the operation flow goes to step S508 inferring that
under such high NOx condition, it is preferable to give priority to
the regeneration of NOx trap catalyst 13 for suppressing the
deterioration of the exhaust property at the tail pipe. At step
S508, the sp-flag is turned to 1 for preparation of the NOx
desorption (viz., rich spike operation).
[0169] At step S507, judgment is carried out as to whether or not
the temperature of DPF 14 is higher than an activation temperature
T6 of the oxidation catalyst carried on DPF 14. If, before starting
operation for increasing the exhaust temperature, the temperature
of the oxidation catalyst of DPF 14 is lower than the activation
temperature T6, it takes a longer time to reach the temperature
that enables the regeneration of DPF 14, and thus, there is a fear
of deterioration of NOx characteristic in the tail pipe of the
exhaust system during the temperature increase. Thus, in such case,
it is preferable to give priority to the regeneration of NOx trap
catalyst 13. Accordingly, also in this case, the operation flow
goes to step S508 inducing "sp-flag=1" for preparation of NOx
desorption (viz., rich spike operation).
[0170] If YES at step S507, that is, when it is judged that the
temperature of DPF 14 is higher than T6, the operation flow goes to
the above-mentioned step 5504 intending to give priority to the
regeneration of DPF 14.
[0171] In the following, control-2 for determining the order of
priority of regeneration will be described with reference to the
flowchart of FIG. 8.
[0172] This control-2 is carried out when request for the sulfur
poisoning recovery and request for the NOx desorption are issued at
the same time.
[0173] As is seen from the flowchart of FIG. 2, when the request
for sulfur poisoning recovery is issued to induce
"rq-desul-flag=1", the control-2 for determining the order starts
in such a manner as shown in the flowchart of FIG. 8.
[0174] At step S601, judgment is carried out as to whether, after
issuance of request for the sulfur poisoning recovery, the PM
accumulation quantity has reached the predetermined quantity PM1 or
not, that is, whether the timing for the regeneration of DPF 14 has
come or not, like the case of the above-mentioned step S12.
[0175] If YES, the operation flow goes to step S701 of the
flowchart of FIG. 9 judging that the timing for the regeneration of
DPF 14 has come. At step S701, the rq-DPF-flag is turned to 1 to
issue a request for the regeneration of DPF 14. In this case, the
order of priority is decided by the flowchart of FIG. 7.
[0176] If NO at step S601, that is, when it is judged that the
timing for the regeneration of DPF 14 has not come yet, the
operation flow goes to step S602.
[0177] At step S602, judgment is carried out as to whether the
temperature of the catalyst 13 is higher than a predetermined
temperature T1 or not. If YES, the operation flow goes to step
S603.
[0178] At step S603, judgment is carried out as to whether or not
the current engine operation is under a possible condition that
enables the DPF regeneration and sulfur poisoning recovery with
reference to the map of FIG. 28.
[0179] If the current engine operation condition is judged to be
the condition (viz., possible condition) that enables the sulfur
poisoning recovery, the operation flow goes to step S604 to induce
"desul-flag=1" for preparation of sulfur poisoning recovery.
[0180] If, at step S602, it is judged that the temperature of the
catalyst 13 is lower than T1, the operation flow goes to step S605.
That is, even if, under such lower temperature of the catalyst, the
operation for increasing the exhaust temperature is started, it
takes a longer time to reach the temperature that enables the
sulfur poisoning recovery, and thus, there is a fear of
deterioration of NOx characteristic in the tail pipe of the exhaust
system during the temperature increase. Thus, in such case, it is
preferable to give priority to the NOx desorption. Accordingly, the
operation flow goes to step S605.
[0181] At step S605, judgment is carried out as to whether
"rq-sp-flag=1" has been established or not, that is, whether the
request for the NOx desorption has been issued or not. If YES, the
operation flow goes to step S607 to induce "sp-flag=1" for
preparation of the NOx desorption (viz., rich spike operation).
[0182] If NO at step S605, that is, when it is judged that
"rq-sp-flag=1" has not been established, the operation flow goes to
step S606.
[0183] At step S606, judgment is carried out as to whether after
issuance of the request for the sulfur poisoning recovery, the NOx
accumulation quantity has reached the predetermined quantity NOx1
or not, that is, whether the timing for the NOx adsorption has come
or not, like the case of the above-mentioned step S14.
[0184] If YES, that is, when it is judged that the NOx accumulation
quantity is larger than the predetermined quantity NOx1, the
operation flow goes to step S901 of the flowchart of FIG. 11 to
induce "rq-sp-flag=1".
[0185] In the following, control for carrying out the "catalyst
activation promotion mode" will be described with reference to the
flowchart of FIG. 12.
[0186] As is seen from the flowchart of FIG. 2, when the
temperature of NOx trap catalyst 13 is lower than a predetermined
temperature T5 that is the lowest activation temperature of the
catalyst 13, the operation flow goes to step S1001 of the flowchart
of FIG. 12.
[0187] At step S1001, judgment is carried out as to whether or not
the current engine operation is under a possible condition that
enables the catalyst activation promotion. Since the catalyst
activation promotion is carried out by the split retard combustion
mode (SRCM) according to the invention, such judgment means a
judgment as to whether the current engine operation enables the
split retard combustion or not. Specifically, such judgment is
carried out with reference to the map of FIG. 28 with the possible
zone of the DPF regeneration and sulfur poisoning recovery replaced
with a possible zone of the catalyst activation promotion. If YES,
that is, when it is judged that the current engine operation
enables the catalyst activation promotion, the operation flow goes
to step S1002.
[0188] At step S1002, for achieving the catalyst activation
promotion, the engine combustion is switched from the normal lean
combustion mode to the split retard combustion mode (SRCM)
according to the present invention. With this switching, the
exhaust temperature is increased and thus, heating of the catalyst
is promoted. Also in this case, the control is effected by setting
the target .lambda.. That is, for the control to the target
.lambda., a torque correction is made in view of a torque reduction
caused by the retard combustion.
[0189] At step S1003, judgment is carried out as to whether the
temperature of NOx trap catalyst 13 has become higher than T5 or
not. If YES, that is, when it is judged that the temperature has
exceeded T5, the operation flow goes to step S1004 to switch the
engine combustion from the split retard combustion mode to the
normal lean combustion mode.
[0190] The entire contents of Japanese Patent Application
2003-284311 filed Jul. 31, 2003 are incorporated herein by
reference.
[0191] Although the invention has been described above with
reference to the embodiment of the invention, the invention is not
limited to such embodiment as described above. Various
modifications and variations of such embodiment may be carried out
by those skilled in the art, in light of the above description.
* * * * *