U.S. patent application number 12/273897 was filed with the patent office on 2009-05-28 for particulate matter trap filter regeneration temperature control for internal combustion engine.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Hiroaki KANEKO, Toru NISHIZAWA, Hitoshi ONODERA.
Application Number | 20090133387 12/273897 |
Document ID | / |
Family ID | 40239688 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133387 |
Kind Code |
A1 |
NISHIZAWA; Toru ; et
al. |
May 28, 2009 |
PARTICULATE MATTER TRAP FILTER REGENERATION TEMPERATURE CONTROL FOR
INTERNAL COMBUSTION ENGINE
Abstract
An internal combustion engine (1) comprises a fuel injector (9),
a filter (13) which traps particulate matter in exhaust gas, and a
catalyst (14) which oxidizes unburnt fuel or carbon monoxide in the
exhaust gas on the upstream side of the filter (13). When
regeneration of the filter (13) is required, a controller (21)
determines a post-injection fuel injection timing and a
post-injection fuel injection amount of the fuel injector (9) on
the basis of an upstream exhaust gas temperature (Texh) and a
catalyst temperature (Tcat) (S16, S17, S19, S20, S22, S23, S25,
S26, S28), thereby optimizing the regeneration temperature
condition of the filter (13).
Inventors: |
NISHIZAWA; Toru;
(Fujisawa-shi, JP) ; KANEKO; Hiroaki;
(Yokohama-shi, JP) ; ONODERA; Hitoshi;
(Yokosuka-shi, JP) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
40239688 |
Appl. No.: |
12/273897 |
Filed: |
November 19, 2008 |
Current U.S.
Class: |
60/286 ; 60/274;
60/295 |
Current CPC
Class: |
Y02T 10/22 20130101;
F02D 41/029 20130101; Y02T 10/12 20130101 |
Class at
Publication: |
60/286 ; 60/295;
60/274 |
International
Class: |
F01N 3/025 20060101
F01N003/025 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2007 |
JP |
2007-302828 |
Oct 10, 2008 |
JP |
2008-264214 |
Claims
1. A filter regeneration temperature control device for an internal
combustion engine, the engine comprising a fuel injector, an
exhaust passage, a filter which traps particulate matter in exhaust
gas in the exhaust passage, and a catalyst which promotes oxidation
of unburnt fuel or carbon monoxide in the exhaust gas in the
exhaust passage on an upstream side of the filter, the device
comprising: a sensor which detects an upstream exhaust gas
temperature in the exhaust passage upstream of the catalyst; a
sensor which detects any one of a downstream exhaust gas
temperature in the exhaust passage downstream of the catalyst and a
temperature of the filter, as a catalyst temperature of the
catalyst; and a programmable controller programmed to: determine if
regeneration of the filter is required; determine a post-injection
fuel injection timing and a post-injection fuel injection amount on
the basis of the upstream exhaust gas temperature and the catalyst
temperature when regeneration of the filter is required; and
control the fuel injector to perform a post-injection fuel
injection corresponding to the post-injection fuel injection timing
and the post-injection fuel injection amount.
2. The filter regeneration temperature control device as defined in
claim 1, wherein the controller is further programmed to: control
the fuel injector, when regeneration of the filter is required, to
perform a post-injection fuel injection on the basis of a basic
post-injection fuel injection timing and a basic post-injection
fuel injection amount; and determine the fuel injection timing and
the fuel injection amount by applying correction to the basic
post-injection fuel injection timing and the basic post-injection
fuel injection amount on the basis of the upstream exhaust gas
temperature and the catalyst temperature detected after an
immediately preceding post-injection fuel injection.
3. The filter regeneration temperature control device as defined in
claim 2, further comprising a sensor which detects an engine
rotation speed of the internal combustion engine and a sensor which
detects an engine load of the internal combustion engine, wherein
the controller is further programmed to set the basic
post-injection fuel injection timing to a more advanced value and
the basic post-injection fuel injection amount to a larger value as
the engine load decreases and the engine rotation speed
decreases.
4. The filter regeneration temperature control device as defined in
claim 2, wherein the controller is further programmed to: compare
the upstream exhaust gas temperature with a predetermined target
upstream exhaust gas temperature; apply retard-correction to the
basic post-injection fuel injection timing or decrease-correction
to the basic post-injection fuel injection amount to determine the
post-injection fuel injection timing and the post-injection fuel
injection amount, when the upstream exhaust gas temperature is
higher than the target upstream exhaust gas temperature; and apply
advance-correction to the basic post-injection fuel injection
timing or increase-correction to the basic post-injection fuel
injection amount to determine the post-injection fuel injection
timing and the post-injection fuel injection amount, when the
upstream exhaust gas temperature is lower than the target upstream
exhaust gas temperature.
5. The filter regeneration temperature control device as defined in
claim 2, wherein the controller is further programmed to: compare
the catalyst temperature with a predetermined target catalyst
temperature; apply advance-correction to the basic post-injection
fuel injection timing or decrease-correction to the basic
post-injection fuel injection amount to determine the
post-injection fuel injection timing and the post-injection fuel
injection amount, when the catalyst temperature is higher than the
target catalyst temperature; and apply retard-correction to the
basic post-injection fuel injection timing or increase-correction
to the basic post-injection fuel injection amount to determine the
post-injection fuel injection timing and the post-injection fuel
injection amount, when the catalyst temperature is lower than the
target catalyst temperature.
6. The filter regeneration temperature control device as defined in
claim 2, wherein the controller is further programmed to: apply
retard-correction to the basic post-injection fuel injection timing
while not applying correction to the basic post-injection fuel
injection amount to determine the post-injection fuel injection
timing and the post-injection fuel injection amount in a first
region in which the upstream exhaust gas temperature is higher than
a predetermined target upstream exhaust gas temperature and the
catalyst temperature is lower than a predetermined target catalyst
temperature; apply increase-correction to the basic post-injection
fuel injection amount while not applying correction to the basic
post-injection fuel injection timing to determine the
post-injection fuel injection timing and the post-injection fuel
injection amount in a second region in which the upstream exhaust
gas temperature is lower than the target upstream exhaust gas
temperature and the catalyst temperature is lower than a
predetermined target catalyst temperature; apply advance-correction
to the basic post-injection fuel injection timing while not
applying correction to the basic post-injection fuel injection
amount to determine the post-injection fuel injection timing and
the post-injection fuel injection amount in a third region in which
the upstream exhaust gas temperature is lower than the target
upstream exhaust gas temperature and the catalyst temperature is
higher than the target catalyst temperature; and apply
decrease-correction to the basic post-injection fuel injection
amount while not applying correction to the basic post-injection
fuel injection timing to determine the post-injection fuel
injection timing and the post-injection fuel injection amount in a
fourth region in which the upstream exhaust gas temperature is
higher than the target upstream exhaust gas temperature and the
catalyst temperature is higher than the target catalyst
temperature.
7. The filter regeneration temperature control device as defined in
claim 1, wherein the controller is further programmed to: determine
if regeneration of the filter is complete; and control the fuel
injector to stop the post-injection fuel injection, when
regeneration of the filter is complete.
8. The filter regeneration temperature control device as defined in
claim 1, wherein the catalyst comprises an oxidation catalyst or a
three-way catalyst.
9. A filter regeneration temperature control device for an internal
combustion engine, the engine comprising a fuel injector, an
exhaust passage, a filter which traps particulate matter in exhaust
gas in the exhaust passage, and a catalyst which promotes oxidation
of unburnt fuel or carbon monoxide in the exhaust gas in the
exhaust passage on an upstream side of the filter, the device
comprising: means for detecting an upstream exhaust gas temperature
in the exhaust passage upstream of the catalyst; means for
detecting any one of a downstream exhaust gas temperature in the
exhaust passage downstream of the catalyst and a temperature of the
filter, as a catalyst temperature of the catalyst; means) for
determining if regeneration of the filter is required; means for
determining a post-injection fuel injection timing and a
post-injection fuel injection amount on the basis of the upstream
exhaust gas temperature and the catalyst temperature when
regeneration of the filter is required; and means for controlling
the fuel injector to perform a post-injection fuel injection
corresponding to the post-injection fuel injection timing and the
post-injection fuel injection amount.
10. A filter regeneration temperature control method for an
internal combustion engine, the engine comprising a fuel injector,
an exhaust passage, a filter which traps particulate matter in
exhaust gas in the exhaust passage, and a catalyst which promotes
oxidation of unburnt fuel or carbon monoxide in the exhaust gas in
the exhaust passage on an upstream side of the filter, the method
comprising: detecting an upstream exhaust gas temperature in the
exhaust passage upstream of the catalyst; detecting any one of a
downstream exhaust gas temperature in the exhaust passage
downstream of the catalyst and a temperature of the filter, as a
catalyst temperature of the catalyst; determining if regeneration
of the filter is required; determining a post-injection fuel
injection timing and a post-injection fuel injection amount on the
basis of the upstream exhaust gas temperature and the catalyst
temperature when regeneration of the filter is required; and
controlling the fuel injector to perform a post-injection fuel
injection corresponding to the post-injection fuel injection timing
and the post-injection fuel injection amount.
Description
FIELD OF THE INVENTION
[0001] This invention relates to regeneration temperature control
of a particulate matter trap filter that traps particulate matter
in the exhaust gas of a diesel engine.
BACKGROUND OF THE INVENTION
[0002] JP2003-336520A, published by the Japan Patent Office in
2003, discloses a regeneration method for a particulate matter trap
filter that traps particulate matter discharged from a diesel
engine.
[0003] The prior art increases unburnt fuel, which is mainly
constituted by hydrocarbon (HC), and carbon monoxide (CO) in the
exhaust gas when filter regeneration is required, by causing fuel
injectors to perform a post-injection fuel injection in an
expansion stroke or an exhaust stroke after a main injection. An
oxidation catalyst or a three-way catalyst is installed in an
exhaust passage of the diesel engine on the upstream side of the
particulate matter trap filter so as to promote oxidation of the
unburnt fuel and carbon monoxide.
[0004] Oxidation heat that is generated accompanying oxidation of
the unburnt fuel or carbon monoxide causes the exhaust gas
temperature to rise, and resultantly causes the temperature of the
particulate matter trap filter located downstream to rise. As the
filter temperature rises, the particulate matter deposited on the
filter burns. By burning the particulate matter deposited on the
filter, the filter is regenerated so that it can trap particulate
matter again.
SUMMARY OF THE INVENTION
[0005] Since a diesel engine operates by burning a fuel with excess
air, the exhaust gas temperature tends to be lower than that of a
spark ignition internal combustion engine, which operates by
burning a fuel with a stoichiometric amount of air in most cases.
On the other hand, it is necessary to raise the temperature of the
particulate matter trap filter to a temperature at which
particulate matter burns in order to burn the particulate matter
deposited on the filter. The catalyst is disposed on the upstream
side of the filter so as to generate oxidation heat by oxidizing
unburnt fuel and carbon monoxide.
[0006] According to experiments performed by the inventors, the
post-injection fuel injection must be controlled such that a
temperature of exhaust gas on the upstream side of the particulate
matter trap filter and a temperature of the catalyst itself are
kept in preferable temperature regions, respectively, so as to
regenerate the filter appropriately.
[0007] When there is a change in the fuel injection characteristics
of a fuel injector due to temporal degradation thereof, or when an
error occurs during crank angle detection due to temporal
degradation of a crank angle sensor, an actual post-injection fuel
injection timing may deviate from an optimum post-injection fuel
injection timing or an actual post-injection fuel injection amount
may deviate from an optimum fuel injection amount. Temporal
degradation of the fuel injector or the crank angle sensor may make
filter regeneration difficult or adversely affect the fuel
consumption of the engine due to an excessive post-injection fuel
injection amount.
[0008] Is it therefore an object of this invention to control the
exhaust gas temperature upstream of the catalyst and the catalyst
temperature to optimum temperatures for filter regeneration even
when an error occurs in the post-injection fuel injection timing or
the post-injection fuel injection amount due to temporal
degradation of a fuel injector or a crank angle sensor.
[0009] To achieve the above object, this invention provides a
filter regeneration temperature control device for such an internal
combustion engine that comprises a fuel injector, an exhaust
passage, a filter which traps particulate matter in exhaust gas in
the exhaust passage, and a catalyst which promotes oxidation of
unburnt fuel or carbon monoxide in the exhaust gas in the exhaust
passage upstream of the filter. The device comprises a sensor which
detects an upstream exhaust gas temperature in the exhaust passage
upstream of the catalyst, a sensor which detects any one of a
downstream exhaust gas temperature in the exhaust passage
downstream of the catalyst and a temperature of the filter, as a
catalyst temperature of the catalyst, and a programmable controller
programmed to control the fuel injector. The controller is
programmed to determine if regeneration of the filter is required,
determine a post-injection fuel injection timing and a
post-injection fuel injection amount on the basis of the upstream
exhaust gas temperature and the catalyst temperature when
regeneration of the filter is required, and control the fuel
injector to perform a post-injection fuel injection corresponding
to the post-injection fuel injection timing and the post-injection
fuel injection amount.
[0010] This invention also provides a filter regeneration
temperature control method for the above-described internal
combustion engine. The method comprises detecting an upstream
exhaust gas temperature in the exhaust passage upstream of the
catalyst, detecting a catalyst temperature of the catalyst,
determining if regeneration of the filter is required, determining
a post-injection fuel injection timing and a post-injection fuel
injection amount on the basis of the upstream exhaust gas
temperature and the catalyst temperature when regeneration of the
filter is required, and controlling the fuel injector to perform a
post-injection fuel injection corresponding to the post-injection
fuel injection timing and the post-injection fuel injection
amount.
[0011] 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
[0012] FIG. 1 is a schematic diagram of a diesel engine to which
this invention is applied.
[0013] FIGS. 2A-2C are diagrams showing variations in an upstream
exhaust gas temperature on an upstream side of a catalyst, a
catalyst temperature, and an oil dilution ratio with respect to a
post-injection fuel injection timing, according to this
invention.
[0014] FIG. 3 is a diagram describing a control algorithm of a
filter regeneration temperature control device according to this
invention.
[0015] FIGS. 4A and 4B are a flowchart describing a filter
regeneration routine performed by a controller according to this
invention.
[0016] FIG. 5 is a controller diagram showing the characteristics
of a basic post-injection fuel injection amount map stored by the
controller.
[0017] FIG. 6 is a diagram showing the characteristics of a basic
post-injection fuel injection timing map stored by the
controller.
[0018] FIG. 7 is a diagram showing the characteristics of a target
intake air amount map stored by the controller.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Referring to FIG. 1 of the drawings, a multi-cylinder diesel
engine 1 for a vehicle comprises an intake passage 2 in which a
compressor of a variable nozzle turbocharger 3, an inter-cooler 4,
and an intake throttle 5 are installed. Intake air of the diesel
engine 1 is turbocharged by the compressor of the turbocharger 3,
cooled by the inter-cooler 4, and, after being subjected to flow
rate regulation by the intake throttle 5, supplied to a combustion
chamber formed in each cylinder of the diesel engine 1 via an
intake collector 6.
[0020] The diesel engine 1 comprises a common-rail type fuel
injection device. The common-rail type fuel injection device
comprises a high-pressure fuel pump 7, a common-rail 8, and a fuel
injector 9 disposed in each cylinder. The high-pressure fuel pump 7
pressurizes fuel and supplies it to the common-rail 8, and the fuel
injector 9 injects the fuel stored in the common-rail 8 directly
into the combustion chamber in each cylinder.
[0021] An air-fuel mixture, being a mixture of the air aspirated
into the combustion chamber and the fuel injected by the fuel
injector 9, is ignited by compression ignition in a compression
stroke of a piston which reciprocates in the cylinder, and burns in
the combustion chamber. Exhaust gas generated by combustion of the
air-fuel mixture is discharged into an exhaust passage 10.
[0022] A part of the exhaust gas thus discharged into the exhaust
passage 10 flows into an exhaust gas recirculation (EGR) passage
11, and is recirculated into the intake collector 6 via an EGR
valve 12 disposed in the EGR passage 11. The other part of the
exhaust gas is discharged into the atmosphere through a catalyst 14
and a diesel particulate filter (DPF) 13 after driving a turbine of
the turbocharger 3.
[0023] The DPF 13 is a known particulate matter trap filter which
traps particulate matter contained in the exhaust gas of a diesel
engine. The DPF 13 cannot trap particulate matter beyond a
predetermined amount. It is necessary to remove the particulate
matter deposited on the DPF 13 by causing it to burn when a deposit
amount of the particulate matter reaches the predetermined amount.
This operation is referred to as regeneration of the DPF 13.
[0024] When performing regeneration of the DPF 13, therefore, it is
necessary to raise the temperature of the DPF 13 to a combustion
temperature of the particulate matter.
[0025] The catalyst 14 is constituted by an oxidation catalyst made
from a noble metal such as platinum. The catalyst 14 functions to
generate oxidation heat by promoting oxidation of unburnt fuel,
which is mainly constituted by hydrocarbon (HC), and carbon
monoxide (CO) in the exhaust gas. The oxidation heat thus generated
increases the temperature of exhaust gas, and hence, a
high-temperature exhaust gas is supplied to the DPF 13 so as to
raise the temperature of DPF 13 to the combustion temperature of
the particulate matter, thereby burning the particulate matter
deposited in the DPF 13. Instead of providing the catalyst 14 on
the upstream side of the DPF 13, it is possible to coat the DPF 13
with a catalytic material. It is also possible to constitute the
catalyst 14 by a three-way catalyst, which is known to have an
oxidizing function.
[0026] To regenerate the DPF 13, therefore, it is necessary to
increase the amount of unburnt fuel and carbon monoxide in the
exhaust gas. This requirement is fulfilled by causing the fuel
injectors 9 to perform a post-injection fuel injection in an
expansion stroke or an exhaust stroke of the piston after
performing a main fuel injection for combustion.
[0027] Further, for successful regeneration of the DPF 13, it is
necessary to control the post-injection fuel injection such that
the exhaust gas temperature on the upstream side of the catalyst 14
(hereinafter referred to as an upstream exhaust gas temperature)
and the temperature of the catalyst 14 itself (hereinafter referred
to as a catalyst temperature) are raised to predetermined
temperatures, respectively.
[0028] The filter regeneration temperature control device according
to this invention comprises a programmable controller 21 for
controlling a post-injection fuel injection timing and a
post-injection fuel injection amount of the fuel injectors 9. The
controller 21 is constituted by a microcomputer comprising a
central processing unit (CPU), a read-only memory (ROM), a random
access memory (RAM), and an input/output interface (I/O interface).
The controller may be constituted by a plurality of
microcomputers.
[0029] The filter regeneration temperature control device further
comprises a crank angle sensor 23 which detects an engine rotation
speed of the diesel engine 1 and an accelerator pedal depression
sensor 22 which detects an engine load of the diesel engine 1.
Detection data from these sensors 22, 23 are input into the
controller 21 via a signal circuit.
[0030] The controller 21 also functions as an engine controller for
controlling the main fuel injection of the fuel injectors 9, as
well as an intake air amount and an EGR rate of the diesel engine
1. For these purposes, the controller 21 calculates a main fuel
injection amount and a main fuel injection timing on the basis of
the engine load and the engine rotation speed, and outputs a
corresponding pulse width signal to the fuel injectors 9 at a
calculated main fuel injection timing. The controller 21 controls
the intake air amount by regulating the opening of the intake
throttle 5. The controller controls the EGR rate by regulating the
opening of the EGR valve 12.
[0031] Next, control of the post-injection fuel injection performed
by the controller 21 for regeneration of the DPF 13 will be
described.
[0032] When the particulate matter deposit amount in the DPF 13 has
reached a predetermined threshold value, the controller 21
increases a proportion of unburnt fuel and carbon monoxide in the
exhaust gas by performing a post-injection fuel injection in the
expansion stroke or the exhaust stroke of each piston immediately
after the main injection. The unburnt fuel and carbon monoxide in
the exhaust gas are oxidized in the catalyst 14 and oxidation heat
generated thereby raises the exhaust gas temperature. A resultant
high-temperature exhaust gas flows into the DPF 13, thereby raising
the filter temperature. An increase in the filter temperature
causes the particulate matter deposited in the DPF 13 to burn,
thereby regenerating the DPF 13.
[0033] A determination as to whether or not the deposit amount of
particulate matter in the DPF 13 has reached the predetermined
threshold amount is made on the basis of a differential pressure
.DELTA.P between the upstream and downstream sides of the DPF 13.
For this purpose, the filter regeneration temperature control
device further comprises a differential pressure sensor 26 which
detects the differential pressure .DELTA.P between the upstream and
downstream sides of the DPF 13. The differential pressure .DELTA.P
detected by the differential pressure sensor 26 is input into the
controller 21 via a signal circuit.
[0034] In the ROM of the controller 21, maps which define a basic
post-injection fuel injection amount QPbase and a basic
post-injection fuel injection timing ITPbase according to the
engine load and the engine rotation speed are stored in advance.
The maps have characteristics as shown in FIGS. 5 and 6. When
regeneration of the DPF 13 is required, the controller 21
determines the basic post-injection fuel injection amount QPbase
and the basic post-injection fuel injection timing ITPbase from the
engine load and the engine rotation speed by referring to these
maps. The controller 21 causes the fuel injectors 9 to perform a
post-injection fuel injection according to the basic post-injection
fuel injection amount QPbase and the basic post-injection fuel
injection timing ITPbase thus determined.
[0035] The filter regeneration temperature control device has
target values with respect to the upstream exhaust gas temperature
and the catalyst temperature when regeneration the DPF 13 is
underway. Specifically, the upstream exhaust gas temperature is set
at 650 degrees centigrade (650.degree. C.) and the target catalyst
temperature is set at 680.degree. C.
[0036] It should be noted, however, that the target upstream
exhaust gas temperature and the target catalyst temperature are not
limited to these values. When the specifications of the diesel
engine 1 or the DPF 13 differ, the target upstream exhaust gas
temperature and the target catalyst temperature take different
values. For example, in certain cases, the target upstream exhaust
gas temperature may be set at 550.degree. C. and the target
catalyst temperature may be set at 600.degree. C. In other cases,
the target upstream exhaust gas temperature may be set at
600.degree. C. and the target catalyst temperature may be set at
650.degree. C. In all cases, the target catalyst temperature should
be higher than the target upstream exhaust gas temperature.
[0037] The controller 21 performs feedback control of the
post-injection fuel injection timing and the post-injection fuel
injection amount of the fuel injectors 9 such that the upstream
exhaust gas temperature and the catalyst temperature coincide with
the target upstream exhaust gas temperature and the target catalyst
temperature, respectively.
[0038] For this purpose, the filter regeneration temperature
control device further comprises a first temperature sensor 24
disposed in an inlet of the catalyst 14 to detect the upstream
exhaust gas temperature, and a second temperature sensor 25
disposed in an outlet of the catalyst 14 to detect the catalyst
temperature.
[0039] The location of the first temperature sensor 24 should not
be limited to the inlet of the catalyst 14. It may be disposed in
any location in the exhaust passage 10 between an exhaust port of
the diesel engine 1 and the catalyst 14. Likewise, the location of
the second temperature sensor 25 should not be limited to the
outlet of the catalyst 14. For example, it is possible to detect
the temperature of the DPF 13 and regards it as a temperature of
the catalyst 14. Detection data from the first temperature sensor
24 and the second temperature sensor 25 are respectively input into
the controller 21 via signal circuits.
[0040] When there is a change in the fuel injection characteristics
of the fuel injectors 9 due to temporal degradation thereof or when
an error occurs during crank angle detection due to temporal
degradation of the crank angle sensor 22, the actual post-injection
fuel injection timing may deviate from the basic post-injection
fuel injection timing ITPbase or the actual post-injection fuel
injection amount may deviate from the basic post-injection fuel
injection amount QPbase.
[0041] When such temporal degradation occurs, the exhaust gas
temperature in the exhaust passage 10 upstream of the catalyst 14,
or in other words the upstream exhaust gas temperature, may deviate
greatly from the target upstream exhaust gas temperature, or the
catalyst temperature may deviate greatly from the target catalyst
temperature. As a result, regeneration of the DPF 13 may fail.
Further, when the actual post-injection fuel injection amount
exceeds the basic post-injection fuel injection amount QPbase, the
air-fuel ratio of the air-fuel mixture in the combustion chamber of
the diesel engine 1 may become excessively rich, which adversely
affects the fuel consumption of the diesel engine 1. Further, when
the actual post-injection fuel injection timing is retarded from
the basic post-injection fuel injection timing ITPbase, an oil
dilution ratio may also be affected due to adhered fuel adhered to
cylinder walls.
[0042] The inventors investigated experimentally variation in the
upstream exhaust gas temperature, the catalyst temperature, and the
oil dilution ratio when the post-injection fuel injection timing
deviates from the basic post-injection fuel injection timing
ITPbase and the post-injection fuel injection amount deviates from
the basic post-injection fuel injection amount QPbase, while the
engine load and the engine rotation speed are constant. The results
are shown in FIGS. 2A-2C.
[0043] Lines in FIGS. 2A-2C show how the exhaust gas temperature,
the catalyst temperature, and the oil dilution ratio vary when the
post-injection fuel injection timing deviates from the basic
post-injection fuel injection timing ITPbase. A solid line denotes
a case where the post-injection fuel injection amount coincides
with the basic post-injection fuel injection amount QPbase. A
broken line denotes a case where the post-injection fuel injection
amount is greater than the basic post-injection fuel injection
amount QPbase. A dotted line denotes a case where the
post-injection fuel injection amount is smaller than the basic
post-injection fuel injection amount QPbase.
[0044] Referring to FIGS. 2A and 2B, the solid line, which
represents the case where the post-injection fuel injection
coincides with the basic post-injection fuel injection amount
QPbase, shows that the upstream exhaust gas temperature Texh
coincides with the target upstream exhaust gas temperature
650.degree. C. and the catalyst temperature Tcat coincides with the
target catalyst temperature 680.degree. C. when the post-injection
fuel injection timing coincides with the basic post-injection fuel
injection timing ITPbase.
[0045] At a point Al on the solid line where the post-injection
fuel injection timing is advanced with respect to the basic
post-injection fuel injection timing ITPbase, for example, the
upstream exhaust gas temperature Texh is higher than the target
upstream exhaust gas temperature 650.degree. C. and the catalyst
temperature Tcat is lower than the target catalyst temperature
680.degree. C. At the point A1, since the post-injection fuel
injection timing is more advanced than the basic post-injection
fuel injection timing ITPbase, the proportion of the post-injection
fuel injection amount that burns in the combustion chamber
increases, and therefore, the upstream exhaust gas temperature Texh
becomes higher than the target upstream exhaust gas temperature
650.degree. C. In contrast, the proportion of the post-injection
fuel injection amount that does not burn in the combustion chamber
but after-burns in the exhaust passage 10 decreases, and therefore,
the catalyst temperature Tcat becomes lower than the target
catalyst temperature 680.degree. C.
[0046] Conversely, at a point C1 on the solid line where the
post-injection fuel injection timing is retarded with respect to
the basic post-injection fuel injection timing ITPbase, for
example, the upstream exhaust gas temperature Texh is lower than
the target upstream exhaust gas temperature 650.degree. C. and the
catalyst temperature Tcat is higher than the target catalyst
temperature 680.degree. C. At the point C1, since the
post-injection fuel injection timing is more retarded than the
basic post-injection fuel injection timing ITPbase, the proportion
of the post-injection fuel injection amount that burns in the
combustion chamber decreases, and therefore, the upstream exhaust
gas temperature Texh becomes lower than the target upstream exhaust
gas temperature 650.degree. C. In contrast, the proportion of the
post-injection fuel injection amount that does not burn in the
combustion chamber but after-burns in the exhaust passage 10
increases, and therefore, the catalyst temperature Tcat becomes
higher than the target catalyst temperature 680.degree. C.
[0047] The broken line, which represents a case where the
post-injection fuel injection amount is greater than the basic
post-injection fuel injection amount QPbase, shows that the
difference from the solid line depends on the post-injection fuel
injection timing. Specifically, in a region where the
post-injection fuel injection timing is advanced from the basic
post-injection fuel injection timing ITPbase, the upstream exhaust
gas temperature Texh is greatly affected by the post-injection fuel
injection amount, as shown in FIG. 2A. In a region where the
post-injection fuel injection timing is retarded from the basic
post-injection fuel injection timing ITPbase, the catalyst
temperature Tcat is greatly affected by the post-injection fuel
injection amount, as shown in FIG. 2B.
[0048] In other words, with respect to the upstream exhaust gas
temperature Texh, there is no significant difference between the
solid line and the broken line in the region where the
post-injection fuel injection timing is retarded from the basic
post-injection fuel injection timing ITPbase, but in the region
where the post-injection fuel injection timing is advanced from the
basic post-injection fuel injection timing ITPbase, there is a
significant difference between the broken line and the solid line.
With respect to the catalyst temperature Tcat, there is no
significant difference between the solid line and the broken line
in the region where the post-injection fuel injection timing is
advanced from the basic post-injection fuel injection timing
ITPbase, but in the region where the post-injection fuel injection
timing is retarded from the basic post-injection fuel injection
timing ITPbase, there is a significant difference between the
broken line and the solid line.
[0049] Accordingly, at a point D1A where the post-injection fuel
injection timing is slightly advanced from the basic post-injection
fuel injection timing ITPbase, the upstream exhaust gas temperature
is apparently higher than the target upstream exhaust gas
temperature 650.degree. C. while the catalyst temperature Tcat
stays at the target catalyst temperature 680.degree. C.
[0050] The dotted line, which represents a case where the
post-injection fuel injection amount is smaller than the basic
post-injection fuel injection amount QPbase, also shows that the
difference from the solid line depends on the post-injection fuel
injection timing. Specifically, in the region where the
post-injection fuel injection timing is advanced from the basic
post-injection fuel injection timing ITPbase, the upstream exhaust
gas temperature Texh is greatly affected by the post-injection fuel
injection amount, as shown in FIG. 2A. In the region where the
post-injection fuel injection timing is retarded from the basic
post-injection fuel injection timing ITPbase, the catalyst
temperature Tcat is greatly affected by the post-injection fuel
injection amount, as shown in FIG. 2B.
[0051] Accordingly, at a point B1 where the post-injection fuel
injection timing is advanced from the basic post-injection fuel
injection timing ITPbase, the upstream exhaust gas temperature Texh
becomes lower than the target upstream exhaust gas temperature
650.degree. C. At a point B1A where the post-injection fuel
injection timing is retarded from the basic post-injection fuel
injection timing ITPbase, the catalyst temperature Tcat becomes
lower than the target upstream exhaust gas temperature 680.degree.
C.
[0052] As described above, in the region where the post-injection
fuel injection timing is retarded from the basic post-injection
fuel injection timing ITPbase, the difference between the
post-injection fuel injection amount and the basic post-injection
fuel injection amount QPbase scarcely affects the upstream exhaust
gas temperature Texh while it greatly affects the catalyst
temperature Tcat. In a region where the post-injection fuel
injection timing is advanced from the basic post-injection fuel
injection timing ITPbase, the difference between the post-injection
fuel injection amount and the basic post-injection fuel injection
amount QPbase greatly affects the upstream exhaust gas temperature
Texh but scarcely affects the catalyst temperature Tcat.
[0053] Referring to FIG. 2C, the oil dilution ratio increases as
the post-injection fuel injection timing is retarded irrespective
of the difference between the post-injection fuel injection amount
and the basic post-injection fuel injection amount QPbase. In other
words, when the post-injection fuel injection timing is advanced
from the basic post-injection fuel injection timing ITPbase, the
oil dilution ratio is smaller than the predetermined value shown in
the figure, and when the post-injection fuel injection timing is
retarded from the basic post-injection fuel injection timing
ITPbase, the oil dilution ratio is greater than the predetermined
value.
[0054] Herein, oil dilution means a phenomenon whereby the fuel
injected by the fuel injector 9 in the post-injection fuel
injection collides with a cylinder wall to form a wall flow, and
the wall flow invades a crank chamber through a gap between a
piston ring and the cylinder wall and mixes with engine oil in the
crank chamber.
[0055] As can be understood from FIG. 2C, the oil dilution ratio
becomes smaller as the post-injection fuel injection timing
advances. The reason is that the surface area of the cylinder wall
facing the combustion chamber decreases as the piston approaches
top dead center. When the post-injection fuel injection timing
advances, it means that the post-injection fuel injection is
performed at a crank angle nearer to top dead center of the piston
where the surface area of the cylinder facing the combustion
chamber is smallest. Accordingly, the amount of injected fuel
forming a wall flow decreases as the post-injection fuel injection
timing is advanced. On the contrary, as the post-injection fuel
injection timing is retarded, the corresponding piston position
becomes distant from top dead center and the surface area of the
cylinder wall facing the combustion chamber increases. As a result,
the oil dilution ratio increases as the post-injection fuel
injection timing is retarded. An increase in the oil dilution ratio
adversely affects the fuel consumption of the vehicle.
[0056] The filter regeneration temperature control device according
to this invention takes advantage of the characteristics shown in
FIGS. 2A-2C and performs feedback correction of the basic
post-injection fuel injection timing ITPbase and/or the basic
post-injection fuel injection amount QPbase on the basis of the
upstream exhaust gas temperature Texh and the catalyst temperature
Tcat. Even when there is a change in fuel injection characteristics
of the fuel injectors 9 due to temporal degradation thereof or an
error occurs during crank angle detection due to temporal
degradation of a crank angle sensor 22, regeneration of the DPF 13
is performed under a favorable temperature condition by applying
feedback correction to the basic post-injection fuel injection
timing ITPbase and/or the basic post-injection fuel injection
amount QPbase on the basis of the upstream exhaust gas temperature
Texh and the catalyst temperature Tcat.
[0057] Next, referring to FIG. 3, DPF regeneration temperature
control performed by the filter regeneration temperature control
device will be described in detail.
[0058] FIG. 3 shows four temperature regions A-D divided according
to the upstream exhaust gas temperature Texh and the catalyst
temperature Tcat. FIG. 3 further shows the contents of correction
of the post-injection fuel injection timing/amount in each
temperature region performed by the filter regeneration temperature
control device together with the results thereof. Arrows R1-R7
denote variation in the temperature condition. Arrows R1, R4, and
R6 shows that feedback correction of the post-injection fuel
injection timing/amount performed in the temperature regions A, C,
and D causes the temperature condition to converge in a center
target zone. Arrows R2, R3, R5, and R7 shows that feedback
correction of the post-injection fuel injection timing/amount in
the temperature regions B, C, and D causes the temperature
condition to shift to an adjacent temperature region. Herein, the
temperature condition is defined by the exhaust gas temperature
Texh represented by the ordinate in the diagram shown in FIG. 3 and
the catalyst temperature Tcat represented by the abscissa in the
diagram.
[0059] The center target zone is defined by an upstream exhaust gas
temperature of 650.degree. C. and a catalyst temperature of
680.degree. C.
[0060] In FIG. 3, the four temperature regions A-D are divided as
follows:
[0061] Region A: temperature region in which the upstream exhaust
gas temperature Texh is higher than the target upstream exhaust gas
temperature 650.degree. C. and the catalyst temperature Tcat is
lower that the target catalyst temperature 680.degree. C.
[0062] Region B: temperature region in which the upstream exhaust
gas temperature Texh is lower than the target upstream exhaust gas
temperature 650.degree. C. and the catalyst temperature Tcat is
lower than the target catalyst temperature 680.degree. C.
[0063] Region C: temperature region in which the upstream exhaust
gas temperature Texh is lower than the target upstream exhaust gas
temperature 650.degree. C. and the catalyst temperature Tcat is
higher than the target catalyst temperature 680.degree. C.
[0064] Region D: temperature region in which the upstream exhaust
gas temperature Texh is higher than the target upstream exhaust gas
temperature 650.degree. C. and the catalyst temperature Tcat is
higher than the target catalyst temperature 680.degree. C.
[0065] In FIGS. 2A and 2B, the point A1 belongs to the region A.
The point B1 and the point B1A belong to the region B. The point C1
and the point C1A belong to the region C. The point D1 and the
point D1A belong to the region D.
[0066] When a post-injection fuel injection is performed to
regenerate the DPF 13, the controller 21 determines the region A-D
to which the current temperature condition belongs on the basis of
the upstream exhaust gas temperature Texh detected by the first
temperature sensor 24 and the catalyst temperature Tcat detected by
the second temperature sensor 25. Further, the basic post-injection
fuel injection amount QPbase and the basic post-injection fuel
injection timing ITPbase are corrected according to the determined
region. Correction of the post-injection fuel injection
timing/amount performed in the respective regions A-D will now be
described.
(1) Region A
[0067] In the region A, as the point A in FIGS. 2A and 2B shows,
the post-injection fuel injection amount coincides with the basic
post-injection fuel injection amount QPbase, but the post-injection
fuel injection timing is advanced with respect to the basic
post-injection fuel injection timing ITPbase. In the region A, the
basic post-injection fuel injection timing ITPbase is
retard-corrected. By repeatedly performing this retard-correction,
the temperature condition shifts towards the center target zone as
shown by the arrow R1 in FIG. 3. Another case where the
post-injection fuel injection amount is greater than the basic
post-injection fuel injection amount QPbase and the post-injection
fuel injection timing is advanced with respect to the basic
post-injection fuel injection timing ITPbase also belongs to the
region A. In this case also, the the basic post-injection fuel
injection timing ITPbase is retard-corrected. By repeatedly
performing this retard-correction, the temperature condition shifts
towards the region D. In the region D, the basic post-injection
fuel injection amount QPbase is decrease-corrected as described
later.
[0068] Referring again to FIGS. 2A and 2B, when the basic
post-injection fuel injection timing ITPbase is retard-corrected at
the point A1, the upstream exhaust gas temperature Texh and the
catalyst temperature Tcat shift respectively in the right hand
direction of the figures along the solid line curve such that the
upstream exhaust gas temperature Texh descends to the target
upstream exhaust gas temperature 650.degree. C. and the catalyst
temperature Tcat ascends to the target catalyst temperature
680.degree. C. Thus, the temperature condition converges in the
hatched region in FIGS. 2A and 2B.
(2) Region B
[0069] In the region B, the following two situations can exist.
Specifically, as the point B1 in FIGS. 2A and 2B shows, the
post-injection fuel injection amount is smaller than the basic
post-injection fuel injection amount QPbase and the post-injection
fuel injection timing is advanced with respect to the basic
post-injection fuel injection timing ITPbase. Alternatively, as the
point B1A in FIGS. 2A and 2B shows, the post-injection fuel
injection amount is smaller than the basic post-injection fuel
injection amount QPbase and the post-injection fuel injection
timing is retarded with respect to the basic post-injection fuel
injection timing ITPbase. In the region B, the basic post-injection
fuel injection amount QPbase is increase-corrected. By repeatedly
performing this increase-correction, the temperature condition
shifts to the region A or the region B as shown by the arrow R2 or
R3 in FIG. 3.
[0070] Referring again to FIGS. 2A and 2B, when the basic
post-injection fuel injection amount QPbase is increase-corrected
at the point B1, the upstream exhaust gas temperature Texh ascends
beyond the target upstream exhaust gas temperature 650.degree. C.
towards the point A1. When the basic post-injection fuel injection
amount QPbase is increase-corrected at the point B1A, the catalyst
temperature Tcat ascends beyond the target catalyst temperature
680.degree. C. towards the point C1.
(3) Region C
[0071] In the region C, the following two situations can exist.
Specifically, as the point C1 in FIGS. 2A and 2B shows, the
post-injection fuel injection amount coincides with the basic
post-injection fuel injection amount QPbase and the post-injection
fuel injection timing is retarded with respect to the basic
post-injection fuel injection timing ITPbase. Alternatively, as the
point C1A in FIGS. 2A and 2B shows, the post-injection fuel
injection amount is greater than the basic post-injection fuel
injection amount QPbase and the post-injection fuel injection
timing is retarded with respect to the basic post-injection fuel
injection timing ITPbase. In the region C, the basic post-injection
fuel injection timing ITPbase is advance-corrected. By repeatedly
performing this advance-correction, the temperature condition
shifts towards the center target zone as shown by the arrow R4 in
FIG. 3.
[0072] Referring again to FIGS. 2A and 2B, when the basic
post-injection fuel injection timing ITPbase is advance-corrected
at the point C1, the upstream exhaust gas temperature Texh and the
catalyst temperature Tcat shift respectively in the left hand
direction of the figures along the solid line curve such that the
temperature condition reaches the hatched region. On the other
hand, when the same process is applied to the temperature condition
represented by the point C1A in FIGS. 2A and 2B, the temperature
condition shifts to the region D as shown by the arrow R5 in FIG.
3.
[0073] Referring again to FIGS. 2A and 2B, when the basic
post-injection fuel injection timing ITPbase is advance-corrected
at the point C1A, the upstream exhaust gas temperature Texh ascends
along the broken line curve. By repeatedly performing this
advance-correction, the temperature condition shifts to the region
D, in which the upstream exhaust gas temperature Texh exceeds the
target upstream exhaust gas temperature 650.degree. C. and the
catalyst temperature Tcat reaches the vicinity of the point D1,
which is higher than the target catalyst temperature 680.degree.
C.
(4) Region D
[0074] In the region D, as the point D1 and the point D1A in FIGS.
2A and 2B show, the post-injection fuel injection amount is greater
than the basic post-injection fuel injection amount QPbase and the
post-injection fuel injection timing is slightly advanced with
respect to the basic post-injection fuel injection timing ITPbase.
However, at the point D1, the upstream exhaust gas temperature Tcat
is higher than the target upstream exhaust gas temperature
650.degree. C. and the catalyst temperature Texh is higher than the
target catalyst temperature. At the point D1A, the upstream exhaust
gas temperature Tcat is higher than the target upstream exhaust gas
temperature 650.degree. C. and the catalyst temperature Texh
approximately coincides with the target catalyst temperature
680.degree. C. In the region D, the basic post-injection fuel
injection amount QPbase is decrease-corrected. By repeatedly
performing this decrease-correction, the temperature condition
represented by the point D1 shifts towards the center target zone
as shown by the arrow R6 in FIG. 3.
[0075] Referring again to FIGS. 2A and 2B, when the basic
post-injection fuel injection amount QPbase is decrease-corrected
at the point D1, the upstream exhaust gas temperature Texh descends
towards the target upstream exhaust gas temperature 650.degree. C.
and the catalyst temperature Tcat descends towards the target
catalyst temperature 680.degree. C. Thus, the temperature condition
converges in the hatched region in FIGS. 2A and 2B.
[0076] On the other hand, by repeatedly performing the above
process, the temperature condition represented by the point D1A in
FIGS. 2A and 2B shifts to the region A as shown by the arrow R7 in
FIG. 3.
[0077] Referring again to FIGS. 2A and 2B, when the basic
post-injection fuel injection amount QPbase is decrease-corrected
at the point D1A, the upstream exhaust gas temperature Texh
descends towards the target upstream exhaust gas temperature
650.degree. C. On the other hand, the catalyst temperature Tcat,
which coincides with the target catalyst temperature 680.degree. C.
prior to correction, falls below the target catalyst temperature
680.degree. C. when the basic post-injection fuel injection amount
QPbase is decrease-corrected. As a result, the temperature
condition represented by the point D1A shifts to the region A.
[0078] As described above, the temperature condition shifts as
indicated by the arrows R1-R7 in FIG. 3 when the post-injection
fuel injection timing/amount are corrected according to the
temperature regions A-D during regeneration of the DPF 13. A shift
represented by the arrows R1, R4, and R6 denotes that the
temperature condition converges in the center target zone in FIG.
3. By maintaining the post-injection fuel injection amount and the
post-injection fuel injection timing after correction, the
temperature condition is thereafter kept in the center target zone
in FIG. 3.
[0079] On the other hand, a shift shown by the arrows R2, R3, R5,
and R7 denotes a shift to another temperature region such that the
temperature condition does not converge in the center target zone
in FIG. 3. In this case, the filter regeneration temperature
control device further performs the following processing.
[0080] 1) When the temperature condition has shifted to the region
A following the arrow R2, the correction for the region A is
applied to cause the temperature condition to converge in the
center target zone as shown by the arrow R1 in FIG. 3.
[0081] 2) When the temperature condition has shifted to the region
C following the arrow R3, the correction for the region C is
applied to cause the temperature condition to converge in the
center target zone as shown by the arrow R4 in FIG. 3. However, as
a result of the correction for the region C, the temperature
condition may shift to the region D as shown by the arrow R5 in
FIG. 3. In this case, the following processing 3) is performed.
[0082] 3) When the temperature condition has shifted to the region
D following the arrow R5, the correction for the region D is
applied to cause the temperature condition to converge in the
center target zone as shown by the arrow R6 in FIG. 3. However, as
a result of the correction for the region D, the temperature
condition may shift to the region A as shown by the arrow R7 in
FIG. 3. In this case, the following processing 4) is performed.
[0083] 4) When the temperature condition has shifted to the region
A following the arrow R7, the correction for the region A is
applied to cause the temperature condition to converge in the
center target zone as shown by the arrow R1 in FIG. 3.
[0084] As described above, even when errors occur in the
post-injection fuel injection timing or the post-injection amount
due to temporal degradation of the fuel injectors 9 or the crank
angle sensor 23 when the DPF 13 is regenerated, the controller 21
first determines the temperature region A-D, and repeatedly
performs correction of the post-injection fuel injection timing or
the post-injection fuel injection amount according to the
determined region A-D, thereby controlling the upstream exhaust gas
temperature Texh to the target upstream exhaust gas temperature
650.degree. C. and the catalyst temperature Tcat to the target
catalyst temperature 680.degree. C., respectively.
[0085] To realize this control, the controller 21 is programmed to
perform a filter regeneration routine shown in FIGS. 4A and 4B.
This routine is performed repeatedly in synchronization with the
rotation of the diesel engine 1. Since the fuel injector 9 is
installed in every cylinder, the routine is performed at a timing
corresponding to top dead center of the piston in each cylinder and
correction of the post-injection fuel injection timing/amount is
performed for each fuel injector 9.
[0086] Since the timing of the post-injection fuel injection is
different from the timing of the routine execution, corrected
values are stored in the RAM and the controller 21 controls the
fuel injector 9 to perform a post-injection fuel injection of a
corrected post-injection fuel injection amount by executing a
different routine. Since the timing of the post-injection fuel
injection is different from the timing of the routine execution,
the execution timing of the filter regeneration routine is not
limited to the above.
[0087] It is possible to perform the routine at fixed time
intervals. It is also possible to perform the routine only once in
every rotation of the diesel engine 1 and apply the corrected
values for all the fuel injectors 9 instead of performing the
routine individually for each fuel injector 9.
[0088] Referring to FIGS. 4A and 4B, in a step SI, the controller
21 reads the engine load detected by the accelerator pedal
depression sensor 22, the engine rotation speed detected by the
crank angle sensor 23, the upstream exhaust gas temperature Texh
detected by the first temperature sensor 24, the catalyst
temperature Tcat detected by the second temperature sensor 25, and
the differential pressure .DELTA.P between the upstream and
downstream sides of the DPF 13 detected by the differential
pressure sensor 26.
[0089] In a step S2, the controller 21 calculates a particulate
matter deposit amount of the DPF 13. The particulate matter deposit
amount can be calculated from the differential pressure .DELTA.P
and an exhaust gas flow rate in the DPF 13. Alternatively, it can
be calculated by accumulating a particulate matter deposit amount
per unit time according to operation conditions of the diesel
engine 1. These methods of calculating the particulate matter
deposit amount are known by JP 2004-197722A, published from the
Japan Patent Office in 2004, the contents of which are herein
incorporated by reference.
[0090] In a step S3, the controller 21 determines if a
post-injection fuel injection correction flag is at unity. The
post-injection fuel injection correction flag takes a value of zero
or unity and its initial value is zero. When the post-injection
fuel injection correction flag is not at unity, the controller 21
proceeds to the processing of a step S4. When the post-injection
fuel injection correction flag is at unity, the controller 21
proceeds to the processing of a step S11.
[0091] In the step S4, the controller 21 determines if a DPF
regeneration flag is at unity. The DPF regeneration flag takes a
value of zero or unity and its initial value is zero. When the DPF
regeneration flag is not at unity, the controller 21 proceeds to
the processing of a step S5. When the DPF regeneration flag is at
unity, the controller 21 proceeds to the processing of a step
S7.
[0092] In the step S5, the controller 21 determines if the
particulate matter deposit amount has exceeded a predetermined
value PM1. When the particulate matter deposit amount has not
exceeded the predetermined value PM1, the controller 21 terminates
the filter regeneration routine. When the particulate matter
deposit amount has exceeded the predetermined value PM1, the
controller 21 sets the DPF regeneration flag at unity in a step S6
and terminates the filter regeneration routine.
[0093] In this way, when the particulate matter deposit amount is
in excess of the predetermined value PM1 during an operation of the
diesel engine 1, the DPF regeneration flag is first set at unity in
the step S6. On the next occasion of routine execution, the
determination in the step S4 shifts to be affirmative and the
controller 21 proceeds to the processing of the step S7 onward.
[0094] In the step S7, the controller 21 determines the basic
post-injection fuel injection amount QPbase and the basic
post-injection fuel injection timing ITPbase from the engine
rotation speed and the engine load by referring to maps which are
stored in the ROM in advance and have characteristics shown in
FIGS. 5 and 6.
[0095] Referring to FIG. 5, the basic post-injection fuel injection
amount QPbase is a variable corresponding to the engine load and
the engine rotation speed. The reason for this is to maintain the
upstream exhaust gas temperature Texh at the target upstream
exhaust gas temperature 650.degree. C. and the catalyst temperature
Tcat at the target catalyst temperature 680.degree. C. irrespective
of variations in the engine load and the engine rotation speed. In
this map, when the engine rotation speed is constant, the basic
post-injection fuel injection amount QPbase increases as the engine
load decreases. The reason for this is that a larger post-injection
fuel injection amount is required to raise the upstream exhaust gas
temperature Texh or the catalyst temperature Tcat under a small
engine load.
[0096] Referring to FIG. 6, when the engine rotation speed is
constant, the basic post-injection fuel injection timing ITPbase is
set to advance as the engine load decreases. The reason for this is
to maintain a high temperature in the combustion chamber under a
small engine load, at which the temperature in the combustion
chamber tends to decrease, by advancing the basic post-injection
fuel injection timing ITPbase to increase the ignition quality of
the air-fuel mixture in the combustion chamber.
[0097] In a following step S8, the controller 21 sets a
post-injection fuel injection signal to be output to the fuel
injector 9 such that the fuel injector 9 injects fuel corresponding
to the basic post-injection fuel injection amount QPbase at a
timing corresponding to the basic post-injection fuel injection
timing ITPbase. The post-injection fuel injection signal is set as
a pulse width modulation signal. As described above, the execution
timing of the filter regeneration routine and the post-injection
fuel injection timing by the fuel injector 9 are different, and
therefore the post-injection fuel injection signal is output to the
fuel injector 9 at a timing corresponding to the basic
post-injection fuel injection timing ITPbase by executing the
different routine by the controller 21 or another controller.
[0098] In a step S9, the controller 21 controls an oxygen
concentration in the exhaust gas not to exceed a predetermined
concentration. When the particulate matter deposited in the DPF 13
burns rapidly, the catalyst temperature Tcat rises rapidly and may
cause heat damage to the DPF 13. To avoid such rapid burning of the
particulate matter, it is necessary to control the oxygen
concentration in the exhaust gas not to exceed the predetermined
concentration. Specifically, the controller 21 throttles the intake
throttle 5 to decrease the intake air flow rate so as to maintain
the excess air factor A at approximately 1.3.
[0099] Referring to FIG. 7, the intake air flow rate is defined in
advance as shown by the solid line according to the engine load and
the engine rotation speed such that a predetermined engine output
torque is obtained when regeneration of the DPF 13 is not
performed. The two solid lines in the figure denote a target intake
air flow rate. The right solid line gives a greater value than the
left solid line. Although only two solid lines are presented in the
figure, numerous lines are defined between the two solid lines when
these characteristics are stored in a form of a map. When
regeneration of the DPF 13 is performed, the solid lines shift to
the positions depicted by the broken lines in the figure. As a
result, the target intake air flow rate is decrease corrected with
respect to an identical engine load and an identical engine
rotation speed during regeneration of the DPF 13. A map having the
contents described above is stored in the ROM of the controller 21
in advance.
[0100] When regeneration of the DPF 13 is performed, the controller
21 refers to this map to throttle the intake throttle 5 so as to
maintain the excess air factor A of the exhaust gas at
approximately 1.3.
[0101] In a following step S10, the controller 21 sets the
post-injection fuel injection correction flag at unity and
terminates the filter regeneration routine.
[0102] On the next occasion of routine execution, therefore, the
determination in the step S3 shifts to be affirmative and the
controller 21 performs the processing of the step S11 onward.
[0103] In the step S11, the controller 21 determines if the
differential pressure .DELTA.P between the upstream and downstream
sides of the DPF 13 is equal to or smaller than a regeneration
termination determination value Pre-DPF. The regeneration
termination determination value Pre-DPF is a value which increases
as the exhaust gas flow rate increases, and is defined in a map
stored in the ROM in advance. The exhaust gas flow rate can be
calculated using the engine load and the engine rotation speed as
parameters. By referring to the map from the exhaust gas flow rate
thus calculated, the regeneration termination determination value
Pre-DPF can be determined. Since setting of the regeneration
termination determination value Pre-DPF is not a subject matter of
this invention, detail description thereof is herein omitted.
[0104] When the differential pressure .DELTA.P is equal to or
smaller than the regeneration termination determination value
Pre-DPF in the step S11, it means that regeneration of the DPF 13
is complete. In this case, the controller 21 determines in a step
S30 to stop correction of the post-injection fuel injection timing
and the post-injection fuel injection amount and stop the
post-injection fuel injection itself. In a following step S31, the
controller 21 resets both the post-injection fuel injection
correction flag and the DPF regeneration flag to zero and then
terminates the routine.
[0105] The determination as to whether or not regeneration of the
DPF 13 is complete can be made in a different way. For example, it
is possible to accumulate an elapsed time from the start of
regeneration of the DPF 13 and determine that regeneration is
complete when the accumulated time reaches a predetermined
time.
[0106] At the beginning of regeneration of the DPF 13, the
differential pressure .DELTA.P between the upstream and downstream
sides of the DPF 13 is greater than the regeneration termination
determination value Pre-DPF. In this case, the controller 21
determines in a step S12 if the upstream exhaust gas temperature
Texh coincides with the target upstream exhaust gas temperature
650.degree. C. and the catalyst temperature Tcat coincides with the
target catalyst temperature 680.degree. C.
[0107] If there is no temporal degradation in the fuel injectors 9
or the crank angle sensor 23, the target upstream exhaust gas
temperature 650.degree. C. and the target catalyst temperature
680.degree. C. should be achieved by controlling the fuel injectors
9 to inject fuel corresponding to the basic post-injection fuel
injection amount QPbase at the basic post-injection fuel injection
timing ITPbase. When on the other hand, the post-injection fuel
injection timing deviates from the basic post-injection fuel
injection timing ITPbase or the post-injection fuel injection
amount deviates from the basic post-injection fuel injection amount
QPbase due to temporal degradation of the fuel injector 9 or the
crank angle sensor 23, the exhaust gas temperature Texh deviates
from the target upstream exhaust gas temperature 650.degree. C. or
the catalyst temperature Tcat deviates from the target catalyst
temperature 680.degree. C.
[0108] In other words, if the upstream exhaust gas temperature Texh
deviates from the target upstream exhaust gas temperature
650.degree. C. or the catalyst temperature Tcat deviates from the
target catalyst temperature 680.degree. C. while the fuel injectors
9 inject fuel corresponding to the basic post-injection fuel
injection amount QPbase at a timing corresponding to the basic
post-injection fuel injection timing ITPbase, it can be concluded
that the fuel injectors 9 or the crank angle sensor 23 has suffered
temporal degradation.
[0109] When the determination in the step S12 is affirmative, the
upstream exhaust gas temperature Texh and the catalyst temperature
Tcat are maintained at their respective target values, and hence,
correction of the post-injection fuel injection timing or the
post-injection fuel injection amount is not necessary. In this
case, the controller 21 determines in a step S28 to maintain the
current values of the post-injection fuel injection timing and the
post-injection fuel injection amount, and sets the post-injection
fuel injection signal accordingly in the step S29. The
post-injection fuel injection signal set in this way is output to
the corresponding fuel injector 9 at a set timing by executing the
different routine.
[0110] When the determination in the step S12 is negative, the
controller 21 determines in a step S13 if the upstream exhaust gas
temperature Texh is higher than the target upstream exhaust gas
temperature 650.degree. C. When the upstream exhaust gas
temperature Texh is higher than the target upstream exhaust gas
temperature 650.degree. C., the controller 21 determines in a step
S14 if the catalyst temperature Tcat is higher than the target
catalyst temperature 680.degree. C. When the upstream exhaust gas
temperature Texh is not higher than the target upstream exhaust gas
temperature 650.degree. C., the controller 21 determines in a step
S15 if the catalyst temperature Tcat is higher than the target
catalyst temperature 680.degree. C.
[0111] When the determination in the step S14 is affirmative, it
means that the temperature condition defined by the upstream
exhaust gas temperature Texh and the catalyst temperature Tcat
corresponds to the region D. When the determination in the step S14
is negative, the temperature condition corresponds to the region A.
When the determination in the step S15 is affirmative, the
temperature condition corresponds to the region C. When the
determination in the step S15 is negative, the temperature
condition corresponds to the region B.
[0112] When the determination in the step S14 is affirmative, or in
other words when the temperature condition corresponds to the
region D, the controller 21 performs the processing of steps
S16-S18.
[0113] First, in the step S16, the controller 21 applies
decrease-correction to the post-injection fuel injection amount.
The object to be corrected is the post-injection fuel injection
amount calculated on the immediately preceding occasion when the
routine was performed. The initial value of the post-injection fuel
injection amount is the basic post-injection fuel injection amount
QPbase. When the processing of the step S16 is performed repeatedly
during regeneration of the DPF 13, the post-injection fuel
injection amount that was decrease corrected in the step S16 on the
last occasion when the routine was performed is further decrease
corrected on the present occasion. Thus, the post-injection fuel
injection amount is decreased by a predetermined amount every time
the processing of the step S16 is performed.
[0114] In the step S17, the controller 21 sets the post-injection
fuel injection timing equal to the post-injection fuel injection
timing that was set on the last occasion when the routine was
performed. In other words, the controller 21 maintains the value of
the post-injection fuel injection timing without correcting it.
[0115] In the step S18, the controller 21 sets a post-injection
fuel injection signal corresponding to the post-injection fuel
injection amount calculated in the step S16. The post-injection
fuel injection signal set in this way is output to the fuel
injector 9 at a timing corresponding to the post-injection fuel
injection timing set in the step S17 by executing the different
routine. After performing the processing of the step S18, the
controller 21 terminates the routine.
[0116] When the determination in the step S14 is negative, or in
other words when the temperature condition corresponds to the
region A, the controller 21 performs the processing of steps
S19-S21.
[0117] In the step S19, the controller 21 applies retard-correction
to the post-injection fuel injection timing. The object to be
corrected is the post-injection fuel injection timing calculated on
the immediately preceding occasion when the routine was performed.
The initial value of the post-injection fuel injection timing is
the basic post-injection fuel injection timing ITPbase. When the
processing of the step S19 is performed repeatedly during
regeneration of the DPF 13, the post-injection fuel injection
timing that was retard corrected in the step S19 on the last
occasion when the routine was performed is further retard corrected
on the present occasion. Thus, the post-injection fuel injection
timing is retarded by a predetermined crank angle every time the
processing of the step S19 is performed.
[0118] In the step S20, the controller 21 sets the post-injection
fuel injection amount equal to the post-injection fuel injection
amount that was set on the last occasion when the routine was
performed. In other words, the controller 21 maintains the value of
the post-injection fuel injection amount without correcting it.
[0119] In the step S21, the controller 21 sets a post-injection
fuel injection signal corresponding to the post-injection fuel
injection amount calculated in the step S20. The post-injection
fuel injection signal set in this way is output at a timing
corresponding to the post-injection fuel injection timing
calculated in the step S19 to the fuel injector 9 by executing the
different routine. After performing the processing of the step S21,
the controller 21 terminates the routine.
[0120] When the determination in the step S15 is affirmative, or in
other words when the temperature condition corresponds to the
region C, the controller 21 performs the processing of steps
S22-S24.
[0121] In the step S22, the controller 21 applies
advance-correction to the post-injection fuel injection timing. The
object to be corrected is the post-injection fuel injection timing
calculated on the immediately preceding occasion when the routine
was performed. The initial value of the post-injection fuel
injection timing is the basic post-injection fuel injection timing
ITPbase. When the processing of the step S22 is performed
repeatedly during regeneration of the DPF 13, the post-injection
fuel injection timing that was advance-corrected in the step S22 on
the last occasion when the routine was performed is further
advance-corrected on the present occasion. Thus, the post-injection
fuel injection timing is advanced by a predetermined crank angle
every time the processing of the step S22 is performed.
[0122] In the step S23, the controller 21 sets the post-injection
fuel injection amount equal to the post-injection fuel injection
amount that was set on the last occasion when the routine was
performed. In other words, the controller 21 maintains the value of
the post-injection fuel injection amount without correcting it.
[0123] In the step S24, the controller 21 sets a post-injection
fuel injection signal corresponding to the post-injection fuel
injection amount set in the step S23. The post-injection fuel
injection signal set in this way is output at a timing
corresponding to the post-injection fuel injection timing
calculated in the step S22 to the fuel injector 9 by executing the
different routine. After performing the processing of the step S24,
the controller 21 terminates the routine.
[0124] When the determination in the step S15 is negative, or in
other words the temperature condition corresponds to the region B,
the controller 21 performs the processing of steps S25-S27.
[0125] In the step S25, the controller 21 applies
increase-correction to the post-injection fuel injection amount.
The object to be corrected is the post-injection fuel injection
amount calculated on the immediately preceding occasion when the
routine was performed. The initial value of the post-injection fuel
injection amount is the basic post-injection fuel injection amount
QPbase. When the processing of the step S25 is performed repeatedly
during regeneration of the DPF 13, the post-injection fuel
injection amount that was increase corrected in the step S25 on the
last occasion when the routine was performed is further
increase-corrected on the present occasion. Thus, the
post-injection fuel injection amount is increased by a
predetermined amount every time the processing of the step S25 is
performed.
[0126] In the step S26, the controller 21 sets the post-injection
fuel injection timing to the post-injection fuel injection timing
that was set on the last occasion when the routine was performed.
In other words, the controller 21 maintains the value of the
post-injection fuel injection timing without correcting it.
[0127] In the step S27, the controller 21 sets a post-injection
fuel injection signal corresponding to the post-injection fuel
injection amount set in the step S25. The post-injection fuel
injection signal set in this way is output at a timing
corresponding to the post-injection fuel injection timing set in
the step S26 to the fuel injector 9 by executing the different
routine. After performing the processing of the step S27, the
controller 21 terminates the routine.
[0128] An increment used in increase-correction of the
post-injection fuel injection amount in the step S16, a decrement
used in decrease-correction of the post-injection fuel injection
amount in the step S25, a retard-correction amount used in
retard-correction of the post-injection fuel injection timing in
the step S19, and an advance-correction amount used in
advance-correction of the post-injection fuel injection timing in
the step S22 can be set variedly. For example, they can be set at
large values which require only one single post-injection fuel
injection to cause the temperature condition to coincide with the
target temperature condition or shift to another temperature
region, or at small values which requires several post-injection
fuel injections until the temperature condition converges with the
target temperature condition or shifts to another temperature
region. What is important here is to realize the target temperature
condition in an early period after the start of regeneration of the
DPF 13.
[0129] The increment, the decrement, the retard-correction amount,
and the advance-correction amount described above may be set at
fixed values or as variables determined on the basis of the
difference between the upstream exhaust gas temperature Texh and
the target upstream exhaust gas temperature and the difference
between the catalyst temperature Tcat and the target catalyst
temperature as parameters.
[0130] As described above, the filter regeneration temperature
control device according to this invention corrects the
post-injection fuel injection amount or the post-injection fuel
injection timing for regeneration of the DPF 13 on the basis of the
upstream exhaust gas temperature Texh and the catalyst temperature
Tcat. Accordingly, the temperature of the catalyst 14 and the
upstream exhaust gas temperature upstream of the catalyst 14 can be
controlled to optimum temperatures for regeneration of the DPF 13
even when the fuel injectors 9 or the crank angle sensor 23 suffer
temporal degradation.
[0131] The contents of Tokugan 2007-302828 with a filing date of
Nov. 22, 2007 in Japan and Tokugan 2008-264214 with a filing date
of October 10 in Japan, are hereby incorporated by reference.
[0132] Although the invention has been described above with
reference to certain embodiments, 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.
[0133] For example, application of the filter regeneration
temperature control device according to this invention is not
limited to a multi-cylinder diesel engine for a vehicle. It can be
applied to any internal combustion engine comprising a filter which
traps particulate matter in exhaust gas, and a catalyst which
promotes oxidation of unburnt fuel or carbon monoxide contained in
exhaust gas on the upstream side of the filter.
[0134] The embodiments of this invention in which an exclusive
property or privilege is claimed are defined as follows:
* * * * *