U.S. patent application number 11/802943 was filed with the patent office on 2007-12-06 for exhaust gas purification system and method of purifying exhaust gas.
This patent application is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Jun Tahara, Tadashi Toyota, Masaru Yamada.
Application Number | 20070277509 11/802943 |
Document ID | / |
Family ID | 38650739 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070277509 |
Kind Code |
A1 |
Tahara; Jun ; et
al. |
December 6, 2007 |
Exhaust gas purification system and method of purifying exhaust
gas
Abstract
Decreases in the volume of intake air to an engine in response
to environmental changes results in an increase in amount of PM
emissions. In view of this situation, a correction coefficient of
fuel supply interval is calculated based on the variation in amount
of PM emissions to adjust a reference fuel supply interval in order
to determine an target fuel supply interval. By adjusting the fuel
supply interval, a fuel supply amount appropriate to the variation
in amount of PM emissions, thereby preventing clogging of the
injection hole of a supplemental fuel valve, while maintaining fuel
economy.
Inventors: |
Tahara; Jun; (Toyota-shi,
JP) ; Yamada; Masaru; (Kariya-shi, JP) ;
Toyota; Tadashi; (Kariya-shi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
Toyota Jidosha Kabushiki
Kaisha
Kabushiki Kaisha Toyota Jidoshokki
|
Family ID: |
38650739 |
Appl. No.: |
11/802943 |
Filed: |
May 29, 2007 |
Current U.S.
Class: |
60/286 |
Current CPC
Class: |
F02D 41/402 20130101;
F02D 41/1467 20130101; F02M 2200/06 20130101; F01N 2900/1602
20130101; F01N 2570/04 20130101; Y02T 10/40 20130101; F01N 3/0253
20130101; F01N 3/0842 20130101; F01N 9/005 20130101; Y02T 10/47
20130101; F02D 41/029 20130101; F01N 3/0885 20130101; F01N
2900/1811 20130101; F01N 2610/03 20130101; F01N 9/002 20130101;
F02D 41/1446 20130101; F01N 2610/1493 20130101; F02D 2200/0812
20130101; F01N 13/0097 20140603; F02D 2200/0802 20130101 |
Class at
Publication: |
60/286 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2006 |
JP |
2006-149654 |
Claims
1. An exhaust gas purification system comprising: a catalyst
disposed in an exhaust passage of an internal combustion engine; a
supplemental fuel valve that supplies fuel to the exhaust passage;
and an adjusting portion that adjusts a supplemental amount of fuel
that is supplied from the supplemental fuel valve based on a
variation in an amount of particulate matter emitted from a
combustion chamber of the internal combustion engine.
2. The exhaust gas purification system according to claim 1,
wherein the adjusting portion adjusts the supplemental amount of
fuel that is supplied from the supplemental fuel valve to the
exhaust passage per unit time.
3. The exhaust gas purification system according to claim 2,
wherein the adjusting portion multiplies a reference fuel supply
interval by a correction coefficient that depends on the variation
in amount of particulate matter emitted to determine a target fuel
supply interval.
4. The exhaust gas purification system according to claim 3,
wherein the adjusting portion multiplies the reference fuel supply
interval by a correction coefficient to change the fuel supply
interval to determine the target fuel supply interval, when an
actual intake air volume to the internal combustion engine is
smaller than a reference intake air volume.
5. The exhaust gas purification system according to claim 1,
wherein: the adjusting portion adjusts a fuel supply interval of
fuel that is supplied from the supplemental fuel valve to the
exhaust passage per unit time.
6. The exhaust gas purification system according to claim 5,
further comprising: a supplemental fuel valve temperature
estimating portion for estimating a temperature of the supplemental
fuel valve, wherein the adjusting portion compares a first
correction coefficient with a second correction coefficient each
other, the first correction coefficient is used to change the fuel
supply interval when the actual intake air volume to the internal
combustion engine is smaller than the reference intake air volume,
the second correction coefficient is used to change the fuel supply
interval when the estimated temperature of the supplemental fuel
valve rises, and multiplies the reference fuel supply interval by
the correction coefficient of the first and second correction
coefficients that yields a shorter fuel supply interval to
determine the target fuel supply interval.
7. The exhaust gas purification system according to claim 1,
further comprising: a catalyst temperature detecting portion for
detecting a temperature of the catalyst, wherein the adjusting
portion reduces the supplemental amount of fuel per unit time
according to the detected catalyst temperature when the detected
catalyst temperature is equal to or higher than a preset value.
8. The exhaust gas purification system according to claim 1,
further comprising: a catalyst temperature detecting portion for
detecting a temperature of the catalyst, wherein the adjusting
portion reduces the supplemental amount of fuel per unit time
according to the detected catalyst temperature when the variation
in the detected catalyst temperature is equal to or greater than a
preset value.
9. The exhaust gas purification system according to claim 1,
further comprising: a coolant temperature detecting portion for
detecting a coolant temperature in the internal combustion engine,
wherein the adjusting portion reduces the supplemental amount of
fuel per unit time according to the detected catalyst temperature
when the variation in the detected coolant temperature is equal to
or greater than a preset value.
10. The exhaust gas purification system according to claim 7,
wherein a fuel injection amount per unit time is reduced by
shortening the fuel supply interval, while the fuel supply duration
per interval is reduced.
11. The exhaust gas purification system according to claim 1,
wherein the internal combustion engine is a diesel engine.
12. The exhaust gas purification system according to claim 1,
wherein the internal combustion engine is mounted on a vehicle.
13. The exhaust gas purification method comprising: supplying fuel
to an exhaust passage of an internal combustion engine, the exhaust
passage having a catalyst disposed therein; and adjusting an
supplemental amount of fuel that is supplied from the supplemental
fuel valve based on a variation in an amount of particulate matter
emitted from a combustion chamber of the internal combustion
engine.
14. The exhaust gas purification method according to claim 13,
wherein the supplemental amount of fuel that is supplied from the
supplemental fuel valve to the exhaust passage per unit time is
adjusted in order to adjust the supplemental amount of the
fuel.
15. The exhaust gas purification method according to claim 14,
wherein a reference fuel supply interval is multiplied by a
correction coefficient that depends on the variation in amount of
particulate matter emitted to determine a target fuel supply
interval in order to adjust the supplemental amount of the
fuel.
16. The exhaust gas purification method according to claim 15,
wherein the reference fuel supply interval is multiplied by a
correction coefficient that adjusts the fuel supply interval to
determine the target fuel supply interval when an actual intake air
volume to the internal combustion engine is smaller than a
reference intake air volume in order to adjust the amount of the
fuel.
17. The exhaust gas purification method according to claim 13,
wherein the degree of fuel is an interval of fuel that is supplied
from the supplemental fuel valve to the exhaust passage.
18. The exhaust gas purification method according to claim 17,
further comprising: estimating a temperature of the supplemental
fuel valve, wherein a first correction coefficient and a second
correction coefficient are compared with each other, the first
correction coefficient is used to change the fuel supply interval
when the actual intake air volume to the internal combustion engine
is smaller than the reference intake air volume, and the second
correction coefficient is used to change the fuel supply interval
when the estimated temperature of the supplemental fuel valve
rises; and wherein the reference fuel supply interval is multiplied
by the correction coefficient of the first and second correction
coefficients that yields a shorter fuel supply interval, whereby
the target fuel supply interval is determined.
19. The exhaust gas purification method according to claim 13,
further comprising: detecting the catalyst temperature, wherein the
supplemental amount of the fuel per unit time is reduced when the
detected catalyst temperature is equal to or higher than a preset
value in order to adjust the supplemental amount of the fuel.
20. The exhaust gas purification method according to claim 19,
wherein a fuel injection amount per unit time is reduced by
shortening the fuel supply interval, while the fuel supply duration
per interval is reduced.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2006-149654 filed on May 30, 2006 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a system and a method for
purifying exhaust gas from an internal combustion engine using a
catalyst. More particularly, the invention relates to an exhaust
gas purification system having a supplemental fuel valve that
supplies fuel to an exhaust passage as well as to an exhaust gas
purification method for supplying fuel to the exhaust passage.
[0004] 2. Description of the Related Art
[0005] Generally, lean burn internal combustion engines, such as
diesel engines, operate predominantly in lean burn mode with a high
air-fuel ratio (lean mixture). Thus, such engines generally are
equipped with a NO.sub.X storage catalyst in the exhaust passage to
purify the exhaust gas by absorbing nitrogen oxides (hereinafter
"NO.sub.X") contained in exhaust gas.
[0006] When the amount of NOx absorbed by in the NO.sub.X storage
catalyst reaches saturation, an NOx reduction reaction is necessary
to revive the NOx storing capacity of the catalyst. One approach to
reducing NOx is to add an NOx reductant (light oil or other fuel)
upstream of the NOx storage catalyst in the exhaust passage in
order to decrease the oxygen concentration in the catalytic
converter, and then, to use reductants, such as excess hydrocarbon
and carbon monoxide, to promote NOx reduction.
[0007] Exhaust gas from diesel engines contains particulate matter
whose principal component is carbon (hereinafter "PM"), soot,
soluble organic fraction (SOF) and so forth. These emissions cause
air pollution. A conventional exhaust gas purification system for
diesel engines, which is designed to purify such PM and other
emissions, has a particulate filter disposed in the exhaust
passage. The particulate filter traps PM contained in the exhaust
gas passing through the exhaust passage, thereby reducing the
amount of PM emissions released to the atmosphere. For example, a
diesel particulate filter (DPF) or a diesel particulate-NO.sub.X
reduction system (DPNR) catalyst may be used as a particulate
filter.
[0008] PM deposits accumulate on the particulate filter as the
amount of PM trapped in the filter increases, causing the
particulate filter to become clogged with the PM deposits. Thus,
pressure loss of the exhaust gas passing through the particulate
filter increases, and accordingly, engine exhaust backpressure
increases. This reduces engine power output and fuel economy. In
order to solve the aforementioned problems, a conventional art
supplies fuel to the exhaust passage (upstream of the particulate
filter) to increase the exhaust gas temperature, thereby promoting
oxidization (combustion) of the PM deposits on the particulate
filter (PM catalyst regeneration process.)
[0009] As described above, in the NOx reduction process and the PM
catalyst regeneration process, both intended to maintain the
exhaust gas purification performance of the catalyst, fuel is
supplied to the exhaust passage using a supplemental fuel valve
disposed in the exhaust passage. However, because the injection
hole of the supplemental fuel valve is exposed to the interior of
the exhaust passage, some substances contained in the exhaust gas,
such as soot and SOF, may adhere to and form deposits on the hole
of the valve. This creates a concern that exposing the deposits to
high-temperature exhaust gas may alter the properties of the
substances and solidify them, and clog the hole of the valve. One
example approach for preventing the supplemental fuel valve from
becoming clogged is described in JP-A-2003-222019, in which fuel is
supplied at all times, except during NOx reduction and PM catalyst
regeneration, to decrease the temperature of the distal end of the
supplemental fuel valve.
[0010] If the volume of intake air to the engine is decreased, due,
for example, to environmental changes, such as changes in
atmospheric pressure when driving from a lower altitude to higher
altitude, or upon a shift from normal to transient driving. This
results in an increase in amount of PM emissions. As the amount of
PM emissions increases, the amount of PM adhering and entering the
injection hole of the supplemental fuel valve increases, which
helps PM deposits build up. The PM deposits may clog the injection
hole of the supplemental fuel valve.
[0011] In order to solve such a problem as injection hole clogging,
the supplemental amount of fuel (the supplemental amount of fuel
per unit time) may be adjusted when the amount of PM emissions
reaches the maximum in the allowable fluctuation. However,
adjustment of the supplemental amount of fuel in such a manner may
create another concern about a tendency of reduced fuel
economy.
SUMMARY OF THE INVENTION
[0012] The invention provides an exhaust gas purification system
that maintains fuel economy, while preventing clogging of the
injection hole of the supplemental fuel valve.
[0013] A first aspect of the invention is directed to an exhaust
gas purification system having a catalyst disposed in an exhaust
passage in an internal combustion engine and a supplemental fuel
valve for supplying fuel to the exhaust passage. The exhaust gas
purification system includes an adjusting means for adjusting the
amount of fuel that is supplied from the supplemental fuel valve to
the exhaust passage based on the variation in the amount of
particulate matter emissions from a combustion chamber in the
internal combustion engine.
[0014] A second aspect of the invention is similar to the first
aspect, except that the exhaust gas purification system further
includes an adjusting means that adjusts the amount of fuel that is
supplied from the supplemental fuel valve to the exhaust passage
per unit time based on the variation in the amount of particulate
matter (PM) emissions from the combustion chamber in the internal
combustion engine.
[0015] The volume of intake air to the engine decreases upon
environmental changes, such as atmospheric pressure change due to
driving from a lower altitude to a higher altitude, or upon a shift
from normal to transient driving. This results in an increase in
amount of PM emissions. In view of such situation, the fuel supply
amount per unit time is adjusted based on the variation in amount
of PM emissions (e.g. variation in actual intake air volume). This
provides a fuel supply amount appropriate to the variation in
amount of PM emissions, thereby preventing excessive fuel supply.
Therefore, clogging of the injection hole of the supplemental fuel
valve is prevented, while fuel economy is maintained.
[0016] According to the second aspect, one approach to adjusting
the fuel supply amount per unit time, in which a reference fuel
supply interval is multiplied by a correction coefficient to
determine an target fuel supply interval; where the reference fuel
supply interval depends on the operating condition of the internal
combustion engine, and the correction coefficient depends on the
variation in amount of PM emissions. More specifically, in this
approach, if the actual intake air volume to the internal
combustion engine is smaller than the reference intake air volume
(if the air volume ratio (actual intake air volume divided by
reference intake air volume) is low), the reference fuel supply
interval is multiplied by a correction coefficient to determine the
target fuel supply interval, where the correction coefficient
changes or shortens the fuel supply interval, that is, increasing
the fuel supply amount per unit time.
[0017] In the exhaust gas purification system having the
supplemental fuel valve for supplying fuel to the exhaust passage,
as the atmospheric temperature (exhaust gas temperature) at the
distal end of the supplemental fuel valve increases from a
reference preset value, the temperature of the distal end of the
supplemental fuel valve also increases, producing PM deposits. The
PM deposits may clog the injection hole of the fuel supply valve.
Therefore, there arises a need to increase the fuel supply amount.
In view of this situation, according to a third aspect of the
invention, the target fuel supply interval is determined in
consideration of the temperature of the distal end of the
supplemental fuel valve.
[0018] The third aspect of the invention is similar to the first
aspect of the invention, except that exhaust gas purification
system further includes: an adjusting means for adjusting the fuel
supply interval for supplying fuel from the supplemental fuel valve
to the exhaust passage based on the variation in amount of
particulate matter emission from the combustion chamber in the
internal combustion engine (variation in amount of PM emissions);
and a supplemental fuel valve temperature estimating means for
estimating a temperature of the supplemental fuel valve. The
adjusting means compares first and second correction coefficients
with each other, where the first correction coefficient changes or
shortens the fuel supply interval if the actual intake air volume
in the internal combustion engine is smaller than the reference
intake air volume, and the second correction coefficient changes or
shortens the fuel supply interval if the temperature of the
supplemental fuel valve, estimated by the supplemental fuel valve
temperature estimating means, increases. The reference fuel supply
interval is multiplied the one of the first and second correction
coefficients that results in a shorter fuel supply interval, to
determine the target fuel supply interval.
[0019] As described above, the correction coefficient that results
in a shorter fuel supply interval (a larger fuel supply amount per
unit time) is selected to adjust the reference fuel supply
interval, one correction coefficient depending on the variation in
amount of PM emissions, the other correction coefficient depending
on the temperature of the distal end of the supplemental fuel
valve. This allows the fuel supply interval to be adjusted for
either one of the condition changes that is more likely to cause
clogging of the injection hole of the supplemental fuel valve;
where the condition changes are a rise in temperature of the distal
end of the supplemental fuel valve and an increase in amount of PM
emissions due to environmental changes or during transient driving
conditions. Thereby, clogging of the injection hole of the
supplemental fuel valve can be effectively prevented. Moreover, a
fuel supply amount appropriate to the foregoing specific condition
change is provided. This prevents excessive fuel supply. Therefore,
while fuel economy is maintained, and clogging of the injection
hole of the supplemental fuel valve is prevented.
[0020] Although increasing the fuel supply amount per unit time
prevents clogging of the injection hole of the supplemental fuel
valve, the fuel will also react with oxygen in the catalyst, which
may cause the catalyst temperature to exceed a certain range of
values (e.g. 750.degree. C.). One approach is offered to avoid this
situation, in which when a catalyst temperature is equal to or
higher than a prescribed value, the fuel supply amount per unit
time is reduced depending on the catalyst temperature (i.e.
variation in catalyst temperature relative to the preset value).
This approach helps avoid a problem of thermal degradation of the
catalyst due to excessively high catalyst temperatures caused by
the increased amount of fuel supply.
[0021] One example approach is offered to reduce the fuel supply
amount per unit time, in which the target fuel supply interval,
shorter than the reference fuel supply interval, (e.g. the
corrected target fuel supply interval) is used to shorten the fuel
supply duration per interval shown in FIG. 8. This approach not
only ensures a shorter fuel supply interval, which can prevent
clogging of the injection hole of the supplemental fuel valve, but
also ensures a smaller total amount of fuel supply. Thus, while an
excessive increase in catalyst temperature is prevented, clogging
of the injection hole of the supplemental fuel valve is also
prevented.
[0022] Another approach is offered to prevent an excessive rise in
catalyst temperature, in which a restrictive correction or increase
of the fuel supply amount per unit time is performed such that the
catalyst temperature, estimated based on the exhaust gas
temperature, does not exceed a prescribed value.
[0023] The inventions according to the second and third aspects may
further include a catalyst temperature detecting means that detects
a temperature of the catalyst. If the variation in catalyst
temperature, detected by the temperature detecting means, is equal
to or higher than a preset value, the adjusting means may reduce
the fuel supply amount per unit time depending on the variation in
catalyst temperature.
[0024] The inventions according to the second and third aspects may
further include a coolant temperature detecting means for detecting
the temperature of the coolant in the internal combustion engine.
If the variation in coolant temperature, detected by the coolant
temperature detecting means, is equal to or greater than a preset
value, the adjusting means reduces the fuel supply amount per unit
time depending on the variation in coolant temperature.
[0025] The internal combustion engine may be a diesel engine. The
internal combustion engine may be mounted on a vehicle.
[0026] Further, a fourth aspect of the invention is directed to an
exhaust gas purification method that supplies fuel to an exhaust
passage in an internal combustion engine, the exhaust passage
having a catalyst disposed therein. The exhaust gas purification
method includes adjusting the amount of fuel that is supplied from
the supplemental fuel valve to the exhaust passage based on the
variation in amount of particulate matter emission from a
combustion chamber in the internal combustion engine.
[0027] According to the fourth aspect, the amount of fuel may be a
amount of fuel that is supplied from the supplemental fuel valve to
the exhaust passage per unit time.
[0028] According to the fourth aspect, in order to adjust the
degree of fuel, the reference fuel supply interval may be
multiplied by the correction coefficient that depends on the
variation in amount of particulate matter emission to determine the
target fuel supply interval.
[0029] According to the fourth aspect, in order to adjust the
degree of fuel, if the actual intake air volume to the internal
combustion engine is smaller than the reference intake air volume,
the reference fuel supply interval may be multiplied by a
correction coefficient for adjusting or shortening the fuel supply
interval to determine the target fuel supply interval.
[0030] According to the fourth aspect, the degree of fuel may be an
interval of fuel that is supplied from the supplemental fuel valve
to the exhaust passage.
[0031] The invention according to the fourth aspect further may
include estimating the temperature of the supplemental fuel valve.
In order to adjust the degree of fuel, the first and second
correction coefficients are compared with each other, where the
first correction coefficient is for changing or shortening the fuel
supply interval if the actual intake air volume to the internal
combustion engine is smaller than the reference intake air volume,
and the second correction coefficient is for changing or shortening
the fuel supply interval if the temperature of the supplemental
fuel valve, which is estimated by the supplemental fuel valve
temperature estimating means, rises. Then, the reference fuel
supply interval is multiplied by either one of the first and second
correction coefficients, which results in a shorter fuel supply
interval, and the target fuel supply interval is determined.
[0032] The invention according to the fourth aspect may further
include detecting the temperature of the catalyst temperature. In
order to adjust the degree of fuel, when the catalyst temperature
detected by the catalyst temperature detecting means is equal to
higher than a preset value, the fuel supply amount per unit time is
reduced depending on the catalyst temperature.
[0033] According to the fourth aspect, a fuel injection amount per
unit time may be reduced by adjusting or shortening the fuel supply
interval, while the fuel supply duration per interval is
reduced.
[0034] A fifth aspect of the invention is directed to an exhaust
gas purification system having: a catalyst disposed in an exhaust
passage in an internal combustion engine; a supplemental fuel valve
for supplying fuel to the exhaust passage; and an adjusting portion
for adjusting a degree of fuel that is supplied from the
supplemental fuel valve to the exhaust passage based on the
variation in amount of particulate matter emission from a
combustion chamber in the internal combustion engine.
[0035] A sixth aspect of the invention the exhaust gas purification
method may further include adjusting the degree of fuel that is
supplied from the supplemental fuel valve to the exhaust passage
based on the variation in amount of particulate matter emission
from the combustion chamber in the internal combustion engine.
[0036] According to the aforementioned aspects of the invention, in
view of the amount of PM emissions that can increase from the
amount under the flat and normal driving conditions, the fuel
supply amount per unit time (fuel supply interval) is adjusted
based on the variation in amount of PM emissions. This provides a
fuel supply amount appropriate to the variation in amount of PM
emissions, thereby preventing clogging of the injection hole of the
supplemental fuel valve, while maintaining fuel economy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The foregoing and further objects, features and advantages
of the invention will become apparent from the following
description of example embodiments with reference to the
accompanying drawings, wherein like numerals are used to represent
like elements and wherein:
[0038] FIG. 1 is a schematic diagram showing an example of a diesel
engine equipped with an exhaust gas purification system according
to the invention.
[0039] FIG. 2 is a block diagram of the configuration of a control
system, including an ECU.
[0040] FIG. 3 is a flowchart showing an example of a correction
process of fuel supply interval executed by the ECU.
[0041] FIG. 4 is a map for calculating a reference fuel supply
interval, which is used in the correction process of fuel supply
interval of FIG. 3.
[0042] FIG. 5 is a map illustrating a correction coefficient of
fuel supply interval, which is used in the correction process of
fuel supply interval of FIG. 3.
[0043] FIG. 6 is a map illustrating .lamda. correction coefficient
for amount of PM emissions, which is used in the correction process
of fuel supply interval of FIG. 3.
[0044] FIG. 7 is a map illustrating a correction coefficient of
fuel supply interval, which is used in the correction process of
fuel supply interval of FIG. 3.
[0045] FIG. 8 illustrates a fuel supply interval and supply
duration.
[0046] FIG. 9 is another example illustrating the map of correction
coefficient of fuel supply interval, which varies depending on the
temperature of the distal end of the supplemental fuel valve.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0047] One embodiment of the invention will be described below with
reference to the drawings. A general configuration of a diesel
engine using a fuel supply apparatus of the invention is described
with reference to FIG. 1.
[0048] In this embodiment, the diesel engine 1 (hereinafter
referred to as "engine 1") may be a common rail in-cylinder
direct-injection four-cylinder engine. The engine 1 includes, as
main components, a fuel supply system 2, combustion chambers 3, an
intake system 6 and an exhaust system 7.
[0049] The fuel supply system 2 includes a fuel supply pump 21, a
common rail 22, injectors (fuel injection valves) 23, a
supplemental fuel valve 25, an engine fuel passage 26 and a fuel
passage 27.
[0050] The fuel supply pump 21 draws fuel from the fuel tank and
pressurizes the fuel to supply the pressurized fuel to the common
rail 22 through the engine fuel passage 26. The common rail 22
functions as an accumulator for maintaining the pressure of fuel
supplied from the fuel supply pump 21 at a prescribed level
(accumulating the high-pressure fuel supplied from the fuel supply
pump 21). The common rail 22 distributes the accumulated fuel to
the injectors 23. Each injector 23 is an electromagnetically driven
valve designed to open when a specified voltage is applied and
spray fuel into the associated combustion chamber 3.
[0051] The fuel supply pump 21 is designed to supply part of the
fuel drawn from the fuel tank to the supplemental fuel valve 25
through the fuel passage 27. The supplemental fuel valve 25 is an
electromagnetically driven valve designed to open when a specified
voltage is applied and supply fuel to the exhaust system 7 (from
exhaust ports 71 to an exhaust manifold 72). An injection hole of
the supplemental fuel valve 25 is exposed to the interior of the
exhaust system 7.
[0052] The intake system 6 has an intake manifold 63 connected to
intake ports formed in the cylinder head. An intake pipe 64,
included in the intake passage, is connected to the intake manifold
63. An air cleaner 65, an airflow meter 32 and a throttle valve 62
are disposed in the intake passage in order from the upstream side.
The airflow meter 32 is designed to output an electric signal that
indicates the volume of airflow into the intake passage through the
air cleaner 65.
[0053] The exhaust system 7 has an exhaust manifold 72 connected to
the exhaust ports 71 formed on the cylinder head. Exhaust pipes 73
and 74, included in the exhaust passage, are connected to the
exhaust manifold 72. A catalytic converter 4 is also disposed in
the exhaust passage.
[0054] The catalytic converter 4 includes a NO.sub.X storage
reduction catalyst 4a and a DPNR catalyst 4b. The NO.sub.X storage
reduction catalyst 4a is designed to absorb NO.sub.X in the
presence of a high oxygen concentration in exhaust gas when the
oxygen concentration in the exhaust gas is high and to reduce
NO.sub.X to NO.sub.2 or NO as emissions in the presence of a low
oxygen concentration and a large amount of reduction component
(unburnt component of fuel, such as HC) in exhaust gas when the
oxygen concentration is low and an excess of reductant (e.g.,
unburned fuel, such as HC) in exhaust gas. The NO.sub.X emissions
in the form of NO.sub.2 or NO react immediately with HC or CO
contained in exhaust gas, so that the NO.sub.2 or NO is reduced to
N.sub.2. The reduction of NO.sub.2 or NO to N.sub.2 causes HC or CO
to be oxidized to H.sub.2O or CO.sub.2.
[0055] In one example, the DPNR catalyst 4b employs a porous
ceramic structure that contains the NO.sub.X storage reduction
catalyst. The PM in exhaust gas is trapped when passing through the
porous wall. When the air-fuel ratio of the exhaust gas is lean,
the NO.sub.X storage reduction catalyst absorbs NO.sub.X contained
in exhaust gas. When the air fuel ratio is rich, the stored
NO.sub.X is reduced. The DPNR catalyst 4b also oxidizes and burns
the trapped PM.
[0056] The exhaust gas purification system includes the catalytic
converter 4, the supplemental fuel valve 25, and the fuel passage
27 as well as an electronic control unit (ECU) 100. The ECU 100
controls the operation of the supplemental fuel valve 25.
[0057] The engine 1 has a turbocharger (compressor) 5. The
turbocharger 5 includes a turbine shaft 5a, a turbine wheel 5b and
a compressor impeller 5c, the turbine wheel 5b and the compressor
impeller 5c are connected to each other via the turbine shaft 5a.
The compressor impeller 5c faces the interior of the intake pipe
64, while the turbine wheel 5b exposes the interior of the exhaust
pipe 73. The turbocharger 5 thus configured utilizes an exhaust
flow (exhaust pressure) received by the turbine wheel 5b to rotate
the compressor impeller 5c in order to forcibly induct air into the
engine. In this embodiment, the turbocharger 5 is a variable nozzle
turbocharger having a variable nozzle vane mechanism 5d on the side
of the turbine wheel 5b. The boost pressure of the engine 1 may be
regulated by controlling the opening degree of the variable nozzle
vane mechanism 5d.
[0058] The intake system 6 has an intercooler 61 provided on the
intake pipe 64. The intercooler 61 is designed to cool intake air
whose temperature has increased due to the forced induction by the
turbocharger 5. The throttle valve 62 is also provided in the
intake pipe 64 downstream of the intercooler 61. The throttle valve
62 is an electronically controlled valve whose opening varies
continuously. The throttle valve 62 reduces the cross-section of
the intake air passage under certain conditions to control
(decrease) the volume of intake air.
[0059] The engine 1 has an exhaust gas recirculation (EGR) passage
8 that connects the intake system 6 and the exhaust system 7. The
EGR passage 8 recirculates some exhaust gas to the intake system 6
as required and supply such exhaust gas back to the combustion
chambers 3 to lower the combustion temperature. This decreases the
amount of NO.sub.X emissions. The EGR passage 8 has an EGR valve 81
and an EGR cooler 82 that cools exhaust gas passing (recirculating)
through the EGR passage 8. The volume of EGR to be introduced from
the exhaust system 7 to the intake system 6 (volume of exhaust gas
to be recirculated) may be adjusted by controlling the opening
degree of the EGR valve 81.
[0060] The sensors will now be described. The engine 1 has several
types of sensors installed at specific locations thereof. The
sensors output signals that indicate the environmental conditions
of the specific locations as well as signals indicating the
operating conditions of the engine 1.
[0061] For instance, the airflow meter 32, upstream of the throttle
valve 62 in the intake system 6, outputs a signal that indicates
the detected flow rate of the intake air (intake air volume). The
intake temperature sensor 33, provided on the intake manifold 63,
outputs a signal that indicates the detected temperature of the
intake air. The intake pressure sensor 34, provided on the intake
manifold 63, outputs a signal that indicates the detected pressure
of the intake air. An A/F (air-fuel ratio) sensor 35, downstream of
the catalytic converter 4 in the exhaust system 7, outputs a
detection signal, which continuously varies depending on the oxygen
concentration in exhaust gas. An exhaust gas temperature sensor 36,
downstream of the catalytic converter 4 in the exhaust system 7,
outputs a that indicates the detected exhaust gas temperature. A
rail pressure sensor 37 outputs a signal that indicates the
detected pressure of the fuel stored in the common rail 22. A fuel
pressure sensor 38 outputs a signal that indicates the detected
pressure of fuel flowing through the fuel passage 27 (fuel
pressure).
[0062] The ECU will now be described. As shown in FIG. 2, the ECU
100 includes a CPU 101, a ROM 102, a RAM 103 and a backup RAM 104.
The ROM 102 stores several control programs, maps to be used for
executing these control programs, and other data. The CPU 101
executes various operations in accordance with the respective
control programs and maps stored in the ROM 102. The results of the
operations in the CPU 101 and data inputted from the respective
sensors are temporarily stored in RAM 103. The backup RAM 104 is a
nonvolatile memory for saving stored data upon power-off, such as
the engine 1 stop.
[0063] The ROM 102, the CPU 101, the RAM 103 and the backup RAM 104
are connected to each other via a bus 107, while being connected to
an input interface 105 and an output interface 106.
[0064] The input interface 105 connects to the airflow meter 32,
the intake temperature sensor 33, the intake pressure sensor 34,
the A/F sensor 35, the exhaust gas temperature sensor 36, the rail
pressure sensor 37, and the fuel pressure sensor 38. In addition,
the input interface 105 connects to a water temperature sensor 31,
an atmospheric pressure sensor 39, an accelerator depression sensor
40 and a crankshaft position sensor 41. The water temperature 31
outputs a signal that indicates the detected coolant temperature in
the engine 1. The atmospheric pressure sensor 39 detects the
atmospheric pressure variable due to environmental conditions,
including altitude. The accelerator depression sensor 40 outputs a
signal that indicates the detected displacement of the accelerator
pedal. The crankshaft position sensor 41 outputs a pulse when the
output shaft (crankshaft) of the engine 1 rotates by a given angle.
In turn, the output interface 106 connects to the injector 23, the
supplemental fuel valve 25, the variable nozzle vane mechanism 5d,
the throttle valve 62, the EGR valve 81 and others.
[0065] The ECU 100 executes the respective controls in the engine 1
based on the outputs from the aforementioned sensors. The ECU 100
also executes PM catalyst regeneration control and a correction
process of fuel supply interval, which will be described later.
[0066] Next, the PM catalyst regeneration control will be
described. The ECU 100 first estimates the amount of PM deposits in
the DPNR catalyst 4b. One approach to estimating the amount of PM
deposits is to use a map plotted with experimental data on the
amount of PM adhesion that varies depending on the operating
conditions of the engine 1 (e.g. exhaust gas temperature, fuel
injection amount and engine speed). The amounts of PM adhesion read
from the map are summed to obtain the amount of PM deposits.
Another approach would be to estimate the amount of PM deposits
based on the vehicle driving distance or driving duration. Still
another alternative is to use a pressure differential sensor,
disposed in the catalytic converter 4, to detect the pressure
differential between upstream and downstream of the DPNR catalyst
4b. The amount of PM deposits trapped by the DPNR catalyst 4b is
calculated based on the output from the differential pressure
sensor.
[0067] If the estimate amount of PM deposits is equal to or larger
than a specified reference value, the ECU 100 determines to start
regeneration of the DPNR catalyst 4b and executes the PM catalyst
regeneration control. More specifically, the ECU 100 calculates a
required fuel supply amount and supply interval based on the engine
speed output from the crankshaft position sensor 41 with reference
to the map previously plotted with the experimental results.
According to the calculation result, the ECU 100 controls the
operation of the supplemental fuel valve 25, through which fuel is
supplied to the exhaust system 7 continuously. The fuel supply
results in a rise in temperature of the DPNR catalyst 4b, which
promotes oxidization of the PM deposits in the DPNR catalyst 4b to
H.sub.2O and CO.sub.2 emissions.
[0068] Other than the PM catalyst regeneration control, the ECU 100
may execute sulfur poisoning recovery control or NO.sub.X reduction
control. The sulfur poisoning recovery control releases sulfur from
the NO.sub.X storage reduction catalyst 4a and the DPNR catalyst
4b. This is achieved by increasing the catalyst temperature by
continuously supplying fuel from the supplemental fuel valve 25,
while controlling the air-fuel ratio of exhaust gas to the
stoichiometric or richer ratio. The NO.sub.X reduction control is
intended to reduce the NO.sub.X stored in the NO.sub.X storage
reduction catalyst 4a and the DPNR catalyst 4b to N.sub.2, CO.sub.2
and H.sub.2O by intermittently supplying fuel from the supplemental
fuel valve 25.
[0069] The PM catalyst regeneration control, the sulfur poisoning
recovery control and the NO.sub.X reduction control are performed
individually as appropriate. When it is necessary to perform all
three control simulataneously, these controls may be performed in
the sequence described above.
[0070] Next, the correction process of fuel supply interval will be
described. As stated previously, the volume of intake air to the
engine 1 mounted on the vehicle decreases following certain
environmental changes, such as atmospheric pressure change, or upon
a shift from normal to transient driving. This increases the amount
of PM emissions. As the amount of PM emissions increases, the
amount of PM adhering and entering the injection hole of the
supplemental fuel valve 25 increases, which helps PM deposits build
up. The PM deposits may clog the injection hole of the supplemental
fuel valve 25. As the exhaust gas temperature at the distal end of
the supplemental fuel valve 25 increases from the reference preset
temperature, the temperature of the distal end itself of the
supplemental fuel valve 25 also increases, producing PM deposits.
The PM deposits may clog the injection hole of the supplemental
fuel valve 25.
[0071] In order to solve this problem, in this embodiment, a
correction coefficient of the fuel supply interval, eminttemp,
which is used for correcting the fuel supply interval, is
calculated based on the temperature of the distal end of the
supplemental fuel valve 25. In addition, a correction coefficient
of the fuel supply interval, emintpm, which is used for correcting
the fuel supply interval, is calculated based on the variation in
amount of PM emissions due to environmental changes or during
transient driving conditions. Between eminttemp and emintpm, the
correction coefficient of the fuel supply interval that results in
a larger amount of fuel supply per unit time, is selected as an
target fuel supply interval. This provides the feature of
maintaining fuel economy, while preventing clogging of the
injection hole of the supplemental fuel valve 25.
[0072] A specific example of the correction process of fuel supply
interval is described below with reference to the flowchart in FIG.
3. The ECU 100 executes the correction process of fuel supply
interval. A routine of this correction process is repeated at a
predetermined time interval.
[0073] In step ST1, the engine speed Ne is read from the output of
the crankshaft position sensor 41 to calculate a required fuel
supply amount Q based on the engine speed Ne with reference to a
map, such as that shown in FIG. 4. The relationship between the
engine speed Ne and the required fuel supply amount Q is obtained
in advance by experiments, calculation, etc. Then, the map used to
calculate the required fuel supply amount Q is prepared by plotting
the relationship between the engine speed Ne and the required fuel
supply amount Q, and stored in the ROM 102 of the ECU 100.
[0074] In step ST2, a reference fuel supply interval Tb (see FIG.
8) is calculated based on the required fuel supply amount Q and the
engine speed Ne with reference to the map shown in FIG. 4. The map
for calculating the reference fuel supply interval is also plotted
with experimental and calculation data on the relationship between
the required fuel supply amount Q and engine speed Ne, and the
reference fuel supply interval Tb. The ROM 102 in the ECU 100
stores this map in advance. In step ST2, a reference exhaust gas
temperature (ambient temperature of the supplemental fuel valve 25)
is also obtained when the reference fuel supply interval Tb is
calculated.
[0075] In step ST3, the correction coefficient of the fuel supply
interval, eminttemp, which is used to correct the fuel supply
interval, is calculated based on the temperature of the distal end
of the supplemental fuel valve 25.
[0076] More specifically, based on the difference between the
reference exhaust gas temperature obtained in step ST2 and the
current exhaust gas temperature (change in exhaust gas temperature
.DELTA.Th), the correction coefficient of fuel supply interval,
eminttemp, is calculated with reference to the map shown in FIG. 5.
The map for calculating the correction coefficient of fuel supply
interval shown in FIG. 5 is plotted with experiments and
calculation data on the relationship between the variation in
exhaust gas temperature .DELTA.Th and the correction coefficient of
fuel supply interval, eminttemp. The ROM 102 in the ECU 100 stores
this map in advance. The correction coefficient of fuel supply
interval, eminttemp, is preset smaller as the variation in exhaust
gas temperature .DELTA.Th increases. As the correction coefficient
of fuel supply interval, eminttemp, which is calculated based on
the temperature of the distal end of the supplemental fuel valve,
is reduced, the fuel supply interval becomes shorter.
[0077] It should be understood that the exhaust gas temperature
(ambient temperature of the supplemental fuel valve 25) may be
calculated using a specific map for calculating the exhaust gas
temperature. The map may use experimental and calculation data on
engine speed Ne, intake temperature, atmospheric pressure and so
forth as parameters. The ROM 102 in the ECU 100 may store this map
in advance. Alternatively, an exhaust gas temperature sensor may be
provided to detect and output the exhaust gas temperature upstream
of the turbocharger 5.
[0078] In step ST4, the correction coefficient of fuel supply
interval, emintpm, used to correct the fuel supply interval is
calculated based the variation in amount of PM emissions due to
environmental changes or during transient driving conditions.
[0079] More specifically, first an air volume ratio and a .lamda.
(excess air ratio) correction coefficient for amount of PM
emissions are calculated.
[0080] The air volume ratio will now be described. The air volume
ratio, gnr, is calculated by dividing the actual intake air volume
to the engine 1, which is obtained from the output signal of the
airflow meter 32, by the reference intake air volume on a flat
driving condition (air volume ratio gnr=intake air volume divided
by reference intake air volume).
[0081] Next the calculation of the .lamda. correction coefficient
for amount of PM emissions will be described. Based on the air
volume ratio gnr calculated in the aforementioned process, and the
atmospheric pressure (detected value), obtained from the output
signal of the atmospheric pressure sensor 39, the .lamda.
correction coefficient, emgpmlmd, for amount of PM emissions is
calculated with reference to a map of FIG. 6. The .lamda.
correction coefficient map of FIG. 6 is plotted with experimental
and calculation data on the .lamda. correction coefficient, using
air volume ratio gnr and atmospheric as parameters. The ROM 102 in
the ECU 100 stores this map in advance. The .lamda. correction
coefficient, emgpmlmd, is increased as the air volume ratio gnr and
the atmospheric pressure decrease.
[0082] Based on the .lamda. correction coefficient, emgpmlmd, thus
calculated, the correction coefficient of fuel supply interval,
emintpm, is calculated with reference to a map of FIG. 7. The map
for calculating the correction coefficient of fuel supply interval
shown in FIG. 7 is plotted with experiments and calculation data on
the relationship between the k correction coefficient, emgpmlmd,
and the correction coefficient of fuel supply interval, emintpm.
The ROM 102 in the ECU 100 stores this map in advance. The
correction coefficient of fuel supply interval, emintpm, is preset
smaller as the variation in amount of PM emissions (.lamda.
correction coefficient, emgpmlmd) increases. As the correction
coefficient of fuel supply interval, emintpm, decreases, the fuel
supply interval becomes shorter.
[0083] In steps ST5 to ST7, the correction coefficient of fuel
supply interval, eminttemp, calculated in step ST3, is compared
with the correction coefficient of fuel supply interval, emintpm,
calculated in step ST4. The smaller value of the two is selected,
that is the one which results in a larger amount of fuel supply per
unit time. More specifically, if the correction coefficient of fuel
supply interval, eminttemp, which depends on the temperature of the
distal end of the supplemental fuel valve, is smaller than the
correction coefficient of fuel supply interval, emintpm, which
depends on the variation in amount of PM emissions (if the result
of the determination in step ST5 is true), the correction
coefficient, eminttemp, is selected as a correction coefficient of
the target fuel supply interval, emintad (step ST6). In contrast,
if the correction coefficient of fuel supply interval, emintpm, is
smaller than the correction coefficient of fuel supply interval,
eminttemp (if the result of the determination in step ST5 is
false), the correction coefficient, emintpm, is selected as a
correction coefficient of the target fuel supply interval, emintad
(step ST7).
[0084] In step ST8, the correction coefficient of the target fuel
supply interval, emintad, selected in step ST6 or ST7, is
multiplied by the reference fuel supply interval, calculated in
step ST2, to obtain an target fuel supply interval (target fuel
supply interval=[reference fuel supply interval prior to
correction].times.emintad). Then, the routine ends.
[0085] In accordance with the correction process of fuel supply
interval, either the correction coefficient of fuel supply
interval, eminttemp or emintpm, is selected to correct the target
fuel supply interval. In particular, the correction coefficient
that results in a shorter fuel supply interval (a larger amount of
fuel supply per unit time) is selected. This allows the fuel supply
interval to be appropriately corrected for either one of condition
changes that is more likely to cause clogging of the injection hole
of the supplemental fuel valve 25; where the temperature of the
distal end of the supplemental fuel valve 25 rises or the amount of
PM emissions increases due to environmental changes or during
transient driving conditions. Thereby, clogging of the injection
hole of the supplemental fuel valve 25 is effectively prevented.
Also, in accordance with the correction process of fuel supply
interval, a fuel supply amount (fuel supply amount per unit time)
appropriate to the foregoing specific condition change is provided.
This maintains fuel economy in contrast to the case where the fuel
supply amount is adjusted when the amount of PM emissions reaches
the maximum in the allowable fluctuation.
[0086] Although increasing the fuel supply amount per unit time
prevents clogging of the injection hole of the supplemental fuel
valve 25, the fuel also reacts with oxygen in the catalyst, which
can cause the catalyst temperature to exceed a certain range of
values (e.g. 750.degree. C.). One approach to avoid such situation
is offered as follows. The temperature of the DPNR catalyst 4b is
estimated based on the exhaust gas temperature detected by the
exhaust gas temperature sensor 35. If the estimated catalyst
temperature is equal to or higher than a prescribed temperature,
the fuel supply amount per unit time is reduced according to the
estimated catalyst temperature (more specifically, variation in
catalyst temperature relative to a preset value). Therefore, an
excessive rise in catalyst temperature is prevented. It should be
understood that the prescribed temperature for the catalyst
temperature may be obtained empirically by taking the certain range
of the catalyst temperature (e.g. 750.degree. C.) into
consideration.
[0087] One approach to reducing the fuel supply amount per unit
time, the fuel supply duration per interval shown in FIG. 8 may be
shortened, while the target fuel supply interval remains unchanged
after the fuel supply interval has been corrected. This approach
not only ensures a shorter fuel supply interval, which prevents
clogging of the injection hole of the supplemental fuel valve 25,
also ensures a smaller total amount of fuel supply. Thus, while an
excessive rise in catalyst temperature is prevented, clogging of
the injection hole of the supplemental fuel valve 25 is also
prevented.
[0088] To prevent an excessive increase in catalyst temperature,
the following approach may also be taken. The temperature of the
DPNR catalyst 4b may be estimated based on the exhaust gas
temperature detected by the exhaust gas temperature sensor 35.
Then, based on the estimated current catalyst temperature and the
target fuel supply interval the increase in catalyst temperature,
resulting from the fuel supplies at the target fuel supply
interval, is estimated. A restrictive correction or increase of the
fuel supply amount per unit time is performed so that the estimated
catalyst temperature does not exceed a prescribed value (a value
determined based on the maximum allowable catalyst
temperature).
[0089] Another embodiment of the invention is further described. In
the embodiment described above, one of either the correction
coefficient of fuel supply interval, eminttemp or emintpm, is used
to determine the target fuel supply interval. However, the
invention is not limited to the aforementioned embodiment. Instead,
the target fuel supply interval may be calculated using only the
correction coefficient of fuel supply interval, emintpm.
[0090] Also in the embodiment described above, the reference fuel
supply interval Tb is multiplied by the correction coefficient of
fuel supply interval, eminttemp or emintpm, to correct the fuel
supply amount. Alternatively, the reference fuel supply duration
per interval (see FIG. 8) may be multiplied by the correction
coefficient of fuel supply interval, eminttemp or emintpm, to
correct the fuel supply amount per unit time. To correct the
reference fuel supply duration per interval, the correction
coefficient of fuel supply interval, eminttemp, is preset larger as
the variation in exhaust gas temperature .DELTA.Th increases. In
addition, the correction coefficient of fuel supply interval,
emintpm, is preset larger as the variation in amount of PM
emissions (.lamda. correction coefficient, emgpmlmd) increases.
[0091] In the above-described embodiment, the correction
coefficient of fuel supply interval, eminttemp, which depends on
the temperature of the distal end of the supplemental fuel valve
25, is calculated based on the variation in exhaust gas temperature
.DELTA.Th. Alternatively, the correction coefficient of fuel supply
interval, eminttemp, may be calculated based on the coolant
temperature in the engine 1, obtained from a signal output by the
water temperature sensor 31, with reference to a map of FIG. 9.
[0092] In the above-described embodiment, a direct-injection
four-cylinder diesel engine is equipped with the exhaust gas
purification system of the invention. However, the invention is not
limited to this embodiment. Alternatively, other diesel engines
having any number of cylinders, such as a direct-injection
six-cylinder diesel engine, may be equipped with the exhaust gas
purification system of the invention as well. In addition, the
invention is limited to use with direct-injection diesel engines,
but may also be applied to other types of diesel engines. Further,
the invention may be used not only with vehicle engines, but also
for engines designed for other purposes.
[0093] In the embodiment previously described, the catalytic
converter 4 includes the NO.sub.X storage reduction catalyst 4a and
the DPNR catalyst 4b. Alternatively, the catalytic converter 4 may
include a DPF in addition to the NO.sub.X storage reduction
catalyst 4a or an oxidation catalyst.
[0094] While the invention has been described with reference to
example embodiments thereof, it is to be understood that the
invention is not limited to the described embodiments or
constructions. To the contrary, the invention is intended to cover
various modifications and equivalent arrangements. In addition,
while the various elements of the embodiments are shown in various
combinations and configurations, other combinations and
configurations, including more, less or only a single element, are
also within the scope of the invention.
* * * * *