U.S. patent application number 12/293321 was filed with the patent office on 2009-05-28 for exhaust purification device of internal combustion engine, and control method thereof.
Invention is credited to Tomoyuki Ono.
Application Number | 20090133385 12/293321 |
Document ID | / |
Family ID | 38353574 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133385 |
Kind Code |
A1 |
Ono; Tomoyuki |
May 28, 2009 |
EXHAUST PURIFICATION DEVICE OF INTERNAL COMBUSTION ENGINE, AND
CONTROL METHOD THEREOF
Abstract
An exhaust purification device includes a particulate filter
(10), an air flow meter (7) that detects the amount of fresh air
flowing in an intake passageway (3), and an EGR device (30) that
supplies gas to a site in the intake passageway (3) between the air
flow meter (7) and the particulate filter (10). The exhaust
purification device detects the amount of flow of exhaust passing
through the particulate filter on the basis of the amount of gas
supplied by the EGR device (30), and the intake air amount detected
by the air flow meter (S108), and detects the differential pressure
between the upstream side and the downstream side of the
particulate filter, and determines whether the particulate filter
is clogged on the basis of the amount of flow and the differential
pressure of exhaust (S110).
Inventors: |
Ono; Tomoyuki;
(Shizuoka-ken, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Family ID: |
38353574 |
Appl. No.: |
12/293321 |
Filed: |
March 15, 2007 |
PCT Filed: |
March 15, 2007 |
PCT NO: |
PCT/IB2007/000747 |
371 Date: |
September 17, 2008 |
Current U.S.
Class: |
60/277 ; 60/287;
60/311; 60/605.2 |
Current CPC
Class: |
F02M 26/06 20160201;
F02D 41/0055 20130101; Y02T 10/40 20130101; F02D 2200/0812
20130101; Y02T 10/47 20130101; F02D 41/0052 20130101; F01N 9/002
20130101; F02M 26/15 20160201; F02M 26/05 20160201 |
Class at
Publication: |
60/277 ; 60/287;
60/311; 60/605.2 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2006 |
JP |
2006-074400 |
Claims
1.-9. (canceled)
10. An exhaust purification device of an internal combustion
engine, comprising: a particulate filter that is provided in an
exhaust passageway and that traps a particulate matter in exhaust;
an intake air amount detection portion that detects an amount of
fresh air flowing in an intake passageway; a gas supply portion
that supplies a gas to the intake passageway that is on a
downstream side of the intake air amount detection portion and on
an upstream side of the particulate filter; an exhaust flow
calculation portion that calculates an amount of flow of exhaust
passing through the particulate filter based on the amount of the
gas supplied and the amount of fresh air detected; a differential
pressure detection portion that detects a differential pressure
between the upstream side and the downstream side of the
particulate filter in the exhaust passageway; and a clogging
determination portion that determines whether the particulate
filter is clogged based on the amount of flow of exhaust calculated
and the differential pressure detected; a turbocharger that has a
turbine in the exhaust passageway, and a compressor in the intake
passageway, a high-pressure EGR passageway that connects the
exhaust passageway upstream of the particulate filter and the
intake passageway downstream of the intake air amount detection
portion; and a high-pressure EGR valve that changes the passageway
cross-sectional area of the high-pressure EGR passageway; wherein
the gas supply portion is an EGR device that has an EGR passageway
that connects the exhaust passageway downstream of the particulate
filter and the intake passageway downstream of the intake air
amount detection portion, and an EGR valve that is provided in the
EGR passageway and that changes a passageway cross-sectional area
of the EGR passageway; wherein the amount of the gas supplied by
the gas supply portion is the amount of an EGR gas detected by EGR
gas amount detection portion for detecting the amount of the EGR
gas flowing in the EGR passageway; wherein the EGR passageway is a
low-pressure EGR passageway that connects the exhaust passageway
downstream of the turbine and the intake passageway upstream of the
compressor; wherein when it is determined by the clogging
determination portion whether the particulate filter is clogged,
the degree of opening of the EGR valve is made smaller than when it
is not determined whether the particulate filter is clogged, and
the EGR gas amount flowing in the high-pressure EGR passageway is
changed by the high-pressure EGR valve so that the EGR gas amount
supplied into a cylinder of the internal combustion engine is
constant.
11. The exhaust purification device of the internal combustion
engine according to claim 10, wherein the clogging determination
portion estimates an amount of the particulate matter trapped on
the particulate filter.
12. The exhaust purification device of the internal combustion
engine according to claim 10, wherein the EGR gas amount detection
portion detects the amount of flow of gas in the low-pressure EGR
passageway from at least the differential pressure between the
passageway on the upstream side of the EGR valve and the passageway
on the downstream side of the EGR valve, and a degree of opening of
the EGR valve.
13. The exhaust purification device of the internal combustion
engine according to claim 10, wherein when the clogging
determination portion determines whether the particulate filter is
clogged, the degree of opening of the EGR valve is fixed.
14. The exhaust purification device of the internal combustion
engine according to claim 13, wherein the degree of opening of the
EGR valve is fixed to a fully closed state when it is determined by
the clogging determination portion whether the particulate filter
is clogged.
15. The exhaust purification device of the internal combustion
engine according to claim 10, wherein when it is determined by the
clogging determination portion whether the particulate filter is
clogged, the degree of opening of the EGR valve is set to a degree
of opening that is not the fully closed state, and the exhaust flow
calculation portion estimates the amount of flow of exhaust passing
through the particulate filter based on the amount of fresh air
detected by the intake air amount detection portion and the amount
of the EGR gas detected by the EGR gas amount detection portion,
and the clogging determination portion determines whether the
particulate filter is clogged based on the amount of flow of
exhaust estimated by the exhaust flow calculation portion and the
differential pressure detected by the differential pressure
detection portion.
16. The exhaust purification device of the internal combustion
engine according to claim 10, wherein determination by the clogging
determination portion as to whether the particulate filter is
clogged is performed when at least one of (i) a condition that the
internal combustion engine is in a steady state, (ii) a condition
that temperature of the particulate filter is within a
predetermined range, and (iii) a condition that the vehicle has
traveled a predetermined distance, is met.
17. A control method of an exhaust purification device of an
internal combustion engine which includes: a particulate filter
that is provided in an exhaust passageway and that traps a
particulate matter in exhaust; an intake air amount detection
portion that detects an amount of fresh air flowing in an intake
passageway; a gas supply portion that supplies a gas to the intake
passageway that is on a downstream side of the intake air amount
detection portion and on an upstream side of the particulate
filter; a differential pressure detection portion that detects a
differential pressure between the upstream side and the downstream
side of the particulate filter in the exhaust passageway; a
turbocharger that has a turbine in the exhaust passageway, and a
compressor in the intake passageway; a high-pressure EGR passageway
that connects the exhaust passageway upstream of the particulate
filter and the intake passageway downstream of the intake air
amount detection portion; and a high-pressure EGR valve that
changes the passageway cross-sectional area of the high-pressure
EGR passageway; wherein the EGR passageway is a low-pressure EGR
passageway that connects the exhaust passageway downstream of the
turbine and the intake passageway upstream of the compressor; the
control method comprising: calculating an amount of flow of exhaust
passing through the particulate filter based on the amount of the
gas supplied and the amount of fresh air detected; and determining
whether the particulate filter is clogged based on the amount of
flow of exhaust calculated and the differential pressure detected;
wherein: the gas supply portion is an EGR device that has an EGR
passageway that connects the exhaust passageway downstream of the
particulate filter and the intake passageway downstream of the
intake air amount detection portion, an EGR valve that is provided
in the EGR passageway and that changes a passageway cross-sectional
area of the EGR passageway; the amount of the gas supplied by the
gas supply portion is the amount of an EGR gas detected by EGR gas
amount detection portion that detects the amount of the EGR gas
flowing in the EGR passageway; and when it is determined by the
clogging determination portion whether the particulate filter is
clogged, the degree of opening of the EGR valve is made smaller
than when it is not determined whether the particulate filter is
clogged, and the EGR gas amount flowing in the high-pressure EGR
passageway is changed by the high-pressure EGR valve so that the
EGR gas amount supplied into a cylinder of the internal combustion
engine is constant.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to an exhaust purification device of
an internal combustion engine and a control method thereof.
[0003] 2. Description of the Related Art
[0004] In an exhaust purification device of an internal combustion
engine equipped with an EGR (exhaust gas recirculation) passageway
that connects an exhaust passageway downstream of a particulate
filter and an intake passageway downstream of an air flow meter, a
technology that determines the presence/absence of the clogging of
the particulate filter on the basis of the differential pressure
between the upstream side and the downstream side of the
particulate filter is disclosed in Japanese Patent Application
Publication No. JP-A-2005-69207.
[0005] However, if the degree of opening of an EGR valve provided
in an EGR passageway is changed, the amount of exhaust that passes
through the particulate filter changes. Therefore, the differential
pressure between the upstream side and the downstream side of the
particulate filter changes, so that there is a possibility of error
in the determination regarding the clogging of the particulate
filter.
SUMMARY OF THE INVENTION
[0006] It is an object of the invention to provide a technology
capable of more accurately determining the presence/absence of the
clogging of a particulate filter in an exhaust purification device
of the internal combustion engine.
[0007] An exhaust purification device of an internal combustion
engine according to a first aspect of the invention includes: a
particulate filter that is provided in an exhaust passageway and
that traps a particulate matter in exhaust; intake air amount
detection means for detecting an amount of fresh air flowing in an
intake passageway; gas supply means for supplying a gas to the
intake passageway that is on a downstream side of the intake air
amount detection means and on an upstream side of the particulate
filter; exhaust flow calculation means for calculating an amount of
flow of exhaust passing through the particulate filter based on the
amount of the gas supplied and the amount of fresh air detected;
differential pressure detection means for detecting a differential
pressure between the upstream side and the downstream side of the
particulate filter in the exhaust passageway; and clogging
determination means for determining whether the particulate filter
is clogged based on the amount of flow of exhaust calculated and
the differential pressure detected.
[0008] In the first aspect, there is a correlation between the
amount of flow of exhaust passing through the particulate filter,
the amount of fresh air detected by the intake air amount detection
means, and the amount of gas supplied by the gas supply means. For
example, as the amount of fresh air decreases, the amount of flow
of exhaust also decreases. Besides, for example, as the amount of
gas supplied by the gas supply means decreases, the amount of flow
of exhaust decreases. From the foregoing relationship, the exhaust
flow calculation means calculates the amount of flow of exhaust
passing through the particulate filter on the basis of the amount
of gas supplied by the gas supply means and the intake air amount
detected by the intake air amount detection means.
[0009] In the first aspect, when the particulate filter traps
particulate matter, the passage resistance against exhaust passing
through the particulate filter becomes greater. Therefore, there is
a correlation between the differential pressure between the
upstream side and the downstream side of the particulate filter
detected by the differential pressure detection means, and the
amount of particulate matter trapped on the particulate filter.
Besides, when the passage resistance against exhaust passing
through the particulate filter becomes greater, the amount of flow
of exhaust passing through the particulate filter decreases, and
therefore the differential pressure detected by the differential
pressure detection means becomes smaller. From these relationship,
the clogging determination means determines whether the particulate
filter is clogged on the basis of the amount of flow of exhaust
calculated by the exhaust flow calculation means, and the
differential pressure detected by the differential pressure
detection means.
[0010] As for the aforementioned clogging determination, it may
also be determined whether or not the clogging has occurred in the
particulate filter, and the amount of particulate matter trapped on
the particulate filter may be estimated.
[0011] In the exhaust purification device of the internal
combustion engine in accordance with the foregoing first aspect,
the gas supply means may be an EGR device that has an EGR
passageway that connects the exhaust passageway downstream of the
particulate filter and the intake passageway downstream of the
intake air amount detection means, and an EGR valve that is
provided in the EGR passageway and that changes a passageway
cross-sectional area of the EGR passageway. The amount of the gas
supplied by the gas supply means may be the amount of an EGR gas
detected by EGR gas amount detection means for detecting the amount
of the EGR gas flowing in the EGR passageway.
[0012] In the foregoing aspect, when the amount of the EGR gas
flowing in the EGR passageway is changed by operating the EGR
valve, the amount of flow of exhaust passing through the
particulate filter correspondingly changes. The value obtained by
summing the EGR gas amount flowing in the EGR passageway and the
amount of fresh air is the amount of flow of exhaust passing
through the particulate filter. Specifically, the exhaust flow
calculation means calculates the amount of flow of exhaust passing
through the particulate filter on the basis of the amount of the
EGR gas detected by the EGR gas amount detection means, and the
amount of fresh air detected by the intake air amount detection
means.
[0013] Besides, since the amount of flow of exhaust passing through
the particulate filter and the differential pressure between
upstream side and the downstream side of the particulate filter
have a correlation with the amount of particulate matter trapped on
the particulate filter, the knowledge of the amount of flow of
exhaust and the differential pressure allows the detection of the
clogging of the particulate filter.
[0014] In the foregoing aspect, the exhaust purification device may
further include a turbocharger that has a turbine in the exhaust
passageway, and a compressor in the intake passageway. The EGR
passageway may be a low-pressure EGR passageway that connects the
exhaust passageway downstream of the turbine and the intake
passageway upstream of the compressor.
[0015] The pressure in the exhaust passageway downstream of the
turbine is close to the atmospheric pressure although it is higher
than the atmospheric pressure. Besides, the pressure in the intake
passageway upstream of the compressor is lower than the atmospheric
pressure. Therefore, the pressure of the EGR gas flowing in the
low-pressure EGR passageway is low in comparison with the case
where the exhaust passageway upstream of the turbine and the intake
passageway downstream of the compressor are connected.
[0016] In the case where the EGR gas flows in the low-pressure EGR
passageway, the amount of exhaust combining the amount of the EGR
gas and the amount fresh air passes through the particulate filter.
In this case, too, the clogging of the particulate filter can be
detected according to the foregoing aspect.
[0017] In the foregoing aspect, the EGR gas amount detection means
may detect the amount of flow of gas in the low-pressure EGR
passageway from at least the differential pressure between the
passageway on the upstream side of the EGR valve and the passageway
on the downstream side of the EGR valve, and a degree of opening of
the EGR valve.
[0018] In the foregoing aspect, when it is determined by the
clogging determination means whether the particulate filter is
clogged, the degree of opening of the EGR valve may be made smaller
than when it is not determined whether the particulate filter is
clogged.
[0019] If the degree of opening of the EGR valve is made smaller,
the EGR gas amount decreases. Therefore, the amount of flow of
exhaust passing through the particulate filter approaches the
amount of fresh air. This makes it possible to decrease the effect
that the EGR gas has on the amount of flow of exhaust passing
through the particulate filter, so that the accuracy of the
clogging determination can be improved. Furthermore, by fully
closing the EGR valve, the amount of fresh air and the amount of
flow of exhaust become equal, so that the accuracy of the clogging
determination can be further improved.
[0020] In the foregoing aspect, when the clogging determination
means determines whether the particulate filter is clogged, the
degree of opening of the EGR valve may be fixed.
[0021] If the degree of opening of the EGR valve changes, the
amount of flow of exhaust passing through the particulate filter
changes. Due to this, there is possibility of making an error in
the determination regarding the clogging by the clogging
determination means. According to the foregoing aspect, by fixing
the degree of opening of the EGR valve, the fluctuation in the EGR
gas amount flowing in the EGR passageway can be restrained, and
therefore the accuracy of the clogging determination can be
improved. Incidentally, when the degree of opening of the EGR valve
is fixed, it may be fixed in the fully closed state.
[0022] In the foregoing aspect, the exhaust purification device may
further include a high-pressure EGR passageway that connects the
exhaust passageway upstream of the particulate filter and the
intake passageway downstream of the intake air amount detection
means, and a high-pressure EGR valve that changes the passageway
cross-sectional area of the high-pressure EGR passageway. If the
amount of the EGR gas flowing in the EGR passageway is changed when
the clogging determination means determines whether the particulate
filter is clogged, the EGR gas amount flowing in the high-pressure
EGR passageway may be changed by the high-pressure EGR valve so
that the EGR gas amount supplied into a cylinder of the internal
combustion engine is constant.
[0023] If the amount of EGR gas flowing in the EGR passageway is
decreased, the accuracy of the clogging determination can be
improved, but the EGR gas amount supplied into the cylinder
decreases. However, if the EGR gas is caused to flow into the
high-pressure EGR passageway so as to compensate for the decrease
in the amount of EGR gas flowing in the EGR passageway, the EGR gas
amount supplied into the cylinder can be kept constant. This makes
it possible to restrain, for example, the generation of NOx.
[0024] In the foregoing aspect, when it is determined by the
clogging determination means whether the particulate filter is
clogged, the EGR valve may be set at a degree of opening that is
not the fully closed state. The exhaust flow calculation means may
estimate the amount of flow of exhaust passing through the
particulate filter based on the amount of fresh air detected by the
intake air amount detection means and the amount of the EGR gas
detected by the EGR gas amount detection means, and the clogging
determination means may determine whether the particulate filter is
clogged based on the amount of flow of exhaust estimated by the
exhaust flow calculation means and the differential pressure
detected by the differential pressure detection means.
[0025] If the degree of opening of the EGR valve changes, the EGR
gas amount flowing in the EGR passageway also changes. However,
even in the case where the degree of opening of the EGR valve is
changing with the elapse of time, the current amount of flow of
exhaust can be determined as the current amount of fresh air and an
estimated EGR gas amount provided that the EGR gas amount can be
estimated from one moment to another. Due to this, even when the
amount of EGR gas fluctuates because the degree of opening of the
EGR valve is not fixed, the clogging determination on the
particulate filter can be performed with good accuracy.
[0026] In the foregoing aspect, determination by the clogging
determination means as to whether the particulate filter is clogged
may be performed when at least one of (i) a condition that the
internal combustion engine is in a steady state, (ii) a condition
that temperature of the particulate filter is within a
predetermined range, and (iii) a condition that the vehicle has
traveled a predetermined distance, is met.
[0027] The exhaust purification device of the internal combustion
engine in accordance with the foregoing aspect is able to more
accurately perform the clogging determination on the particulate
filter.
[0028] A control method of an exhaust purification device of an
internal combustion engine according to a second aspect of the
invention is for an exhaust purification device of an internal
combustion engine that includes: a particulate filter that is
provided in an exhaust passageway and that traps a particulate
matter in exhaust; intake air amount detection means for detecting
an amount of fresh air flowing in an intake passageway; gas supply
means for supplying a gas to the intake passageway that is on a
downstream side of the intake air amount detection means and on an
upstream side of the particulate filter; and differential pressure
detection means for detecting a differential pressure between the
upstream side and the downstream side of the particulate filter in
the exhaust passageway. In the control method of the exhaust
purification device of the internal combustion engine, an amount of
flow of exhaust passing through the particulate filter is
calculated based on the amount of the gas supplied and the amount
of fresh air detected, and it is determined whether the particulate
filter is clogged based on the amount of flow of exhaust calculated
and the differential pressure detected.
[0029] In the control method according to the second aspect, the
gas supply means may be an EGR device that has an EGR passageway
that connects the exhaust passageway downstream of the particulate
filter and the intake passageway downstream of the intake air
amount detection means, an EGR valve that is provided in the EGR
passageway and that changes a passageway cross-sectional area of
the EGR passageway, and EGR gas amount detection means for
detecting an amount of an EGR gas flowing in the EGR passageway.
The amount of the gas supplied by the gas supply means may be the
amount of the EGR gas detected by the EGR gas amount detection
means. The present invention also concerns an exhaust purification
device of an internal combustion engine which comprises a
particulate filter provided in an exhaust passageway and that traps
a particulate matter in exhaust; an intake air amount detection
portion that detects an amount of fresh air flowing in an intake
passageway; a gas supply portion that supplies a gas to the intake
passageway that is on a downstream side of the intake air amount
detection portion and on an upstream side of the particulate
filter; an exhaust flow calculation portion that calculates an
amount of flow of exhaust passing through the particulate filter
based on the amount of the gas supplied and the amount of fresh air
detected; a differential pressure detection portion that detects a
differential pressure between the upstream side and the downstream
side of the particulate filter in the exhaust passageway; and a
clogging determination portion that determines whether the
particulate filter is clogged based on the amount of flow of
exhaust calculated and the differential pressure detected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The foregoing and/or further objects, features and
advantages of the invention will become more apparent from the
following description of example embodiments with reference to the
accompanying drawings, in which the same or corresponding portions
are denoted by the same reference numerals and wherein:
[0031] FIG. 1 is a diagram schematically showing an overall
construction of an internal combustion engine and its
intake-exhaust system to which an exhaust gas purification device
of an internal combustion engine in accordance with an embodiment
of the invention is applied;
[0032] FIG. 2 is a flowchart showing the flow of determination
regarding particulate filter clogging according to a first
embodiment of the invention;
[0033] FIG. 3 is a flowchart showing the flow of determination
regarding particulate filter clogging according to a second
embodiment of the invention;
[0034] FIG. 4 is a flowchart showing the flow of determination
regarding particulate filter clogging according to a third
embodiment of the invention; and
[0035] FIG. 5 is another flowchart showing the flow of
determination regarding particulate filter clogging according to a
third embodiment of the invention.
DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS
[0036] Example embodiments of the exhaust purification device of an
internal combustion engine in accordance with the invention will be
described hereinafter with reference to the drawings.
i. First Embodiment
[0037] An internal combustion engine 1 shown in FIG. 1 is a
water-cooled four-stroke diesel engine that has four cylinders
2.
[0038] An intake pipe 3 and an exhaust pipe 4 are connected to the
internal combustion engine 1. An intermediate portion of the intake
pipe 3 is provided with a compressor housing 5a of a turbocharger 5
that acts using energy of exhaust as a drive source. The intake
pipe 3 upstream of the compressor housing 5a is provided with a
first throttle 6 that adjusts the amount of flow of intake flowing
in the intake pipe 3. The first throttle 6 is opened and closed by
an electric actuator. The intake pipe 3 upstream of the first
throttle 6 is provided with an air flow meter 7 that outputs a
signal that is in accordance with the amount of flow of intake
flowing in the intake pipe 3. The intake air amount of the internal
combustion engine 1 is measured by the air flow meter 7. In this
embodiment, the air flow meter 7 corresponds to intake air amount
detection means in the invention.
[0039] The intake pipe 3 downstream of the compressor housing 5a is
provided with an intercooler 8 that performs heat exchange between
the intake and external air. The intake pipe 3 downstream of the
intercooler 8 is provided with a second throttle 9 that adjust the
amount of flow of intake flowing in the intake pipe 3. The second
throttle 9 is opened and closed by an electric actuator.
[0040] On the other hand, an intermediate portion of the exhaust
pipe 4 is provided with a turbine housing 5b of the turbocharger 5.
The exhaust pipe 4 downstream of the turbine housing 5b is provided
with a particulate filter (hereinafter, simply referred to as
"filter") 10. A storage reduction type NOx catalyst (hereinafter,
simply referred to as "NOx catalyst") is supported on the filter
10. This filter traps particulate matter in exhaust. The NOx
catalyst stores oxides of nitrogen (NOx) from exhaust when the
oxygen concentration in the exhaust flowing into the NOx catalyst
is high, and releases stored NOx when the oxygen concentration in
the exhaust flowing into the NOx catalyst has dropped. On the
occasion, if a reducing component, such as hydrocarbon (HC), carbon
monoxide (CO), etc., is present in the exhaust, the NOx released
from the NOx catalyst is reduced. In this description, the term
"storage (or store)" is used in the meaning of holding a substance
(solid, liquid, gas molecules) in at least one of the manners that
include adsorption, adhesion, absorption, trapping, occlusion,
etc.
[0041] A differential pressure sensor 11 that measures the pressure
difference between the upstream side and the downstream side of the
filter 10 is attached to the filter 10. The amount of particulate
matter (hereinafter, referred to also as "PM") deposited on the
filter 10 can be detected by the differential pressure sensor 11.
In this embodiment, the differential pressure sensor 11 corresponds
to differential pressure detection means in the invention. In the
exhaust pipe 4 downstream of the filter 10, an exhaust temperature
sensor 12 that detects the temperature of the exhaust flowing in
the exhaust pipe 4 is attached. The temperature of the filter 10 is
detected by the exhaust temperature sensor 12.
[0042] The internal combustion engine 1 is equipped with a
low-pressure EGR device 30 that recirculates a portion of the
exhaust that flows in the exhaust pipe 4, to the intake pipe 3 at
low pressure. The low-pressure EGR device 30 has a low-pressure EGR
passageway 31, a low-pressure EGR valve 32, and an EGR cooler 33.
The low-pressure EGR passageway 31 connects the exhaust pipe 4 on
the downstream side of the filter 10 and the intake pipe 3 that
extends upstream of the compressor housing 5a and downstream of the
first throttle 6. Via the low-pressure EGR passageway 31, exhaust
is recirculated at low pressure. In this embodiment, the exhaust
recirculated via the low-pressure EGR passageway 31 is termed
low-pressure EGR gas. Besides, the amount of low-pressure EGR gas
that flows through the low-pressure EGR passageway 31 is adjusted
by adjusting the passageway cross-sectional area of the
low-pressure EGR passageway 31 with changes in the degree of
opening of the low-pressure EGR valve 32. The EGR cooler 33 drops
the temperature of low-pressure EGR gas by causing heat exchange
between the low-pressure EGR gas passing through the EGR cooler 33
and cooling water of the internal combustion engine 1. In this
embodiment, the low-pressure EGR device 30 corresponds to gas
supply means in the invention.
[0043] The internal combustion engine 1 is also equipped with a
high-pressure EGR device 40 that recirculates a portion of the
exhaust that flows in the exhaust pipe 4, to the intake pipe 3 at
high pressure. This high-pressure EGR device 40 has a high-pressure
EGR passageway 41, and a high-pressure EGR valve 42. The
high-pressure EGR passageway 41 connects the exhaust pipe 4 on the
upstream side of the turbine housing 5b and the intake pipe 3
downstream of the second throttle 9. Via the high-pressure EGR
passageway 41, exhaust is recirculated at high pressure. In this
embodiment, the exhaust recirculated via the high-pressure EGR
passageway 41 is termed high-pressure EGR gas. As the passageway
cross-sectional area of the high-pressure EGR passageway 41 changes
with changes in the degree of opening of the high-pressure EGR
valve 42, the amount of high-pressure EGR gas that flows through
the high-pressure EGR passageway 41 is adjusted.
[0044] An exhaust pressure sensor 13 that detects the pressure of
exhaust is attached to the exhaust pipe 4 between the turbine
housing 5b and the filter 10.
[0045] The internal combustion engine 1 constructed as described
above is provided with an ECU 20 that is an electronic control unit
for controlling the internal combustion engine 1. This ECU 20
controls the state of operation of the internal combustion engine 1
in accordance with the operation condition of the internal
combustion engine 1 and a driver's request. Besides the
aforementioned sensors, an accelerator operation amount sensor 15
that outputs an electric signal in accordance with the amount of
the driver's depression of an accelerator pedal 14 to detect the
engine load, a crank position sensor 16 that detects the engine
rotation speed, and a cooling water temperature sensor 17 that
detects the temperature of cooling water of the internal combustion
engine 1 are connected to the ECU 20 via electric wiring, so that
the output signals of these various sensors are input to the ECU
20. Furthermore, the first throttle 6, the second throttle 9, the
low-pressure EGR valve 32 and the high-pressure EGR valve 42 are
connected to the ECU 20 via electric wiring. The ECU 20 controls
these appliances and the like.
[0046] In this embodiment, the ECU 20 performs a clogging
determination on the filter 10. If the ECU 20 determines that the
filter 10 is clogged, the ECU 20 performs a restoration process of
the filter 10. When performing the clogging determination on the
filter 10, the ECU 20 fixes the low-pressure EGR valve 32 to a
fully closed state. When the degree of opening of the low-pressure
EGR valve 32 is fixed to the fully closed state, the amount of flow
of exhaust passing through the filter 10 can easily be estimated on
the basis of the intake air amount detected by the air flow meter
7. Therefore, the accuracy of the clogging determination can be
improved.
[0047] In this embodiment, the clogging determination on the filter
10 is performed as follows. Herein, the cross-sectional area of the
exhaust pipe 4 immediately upstream of the filter 10 is represented
by A0, and the flow speed of exhaust therein is represented by U0.
Besides, the clogging of the filter 10 with PM is considered as
throttling, and the cross-sectional area of the filter 10 is
represented by A1, and the flow speed of exhaust in the filter 10
is represented by Ucat.
[0048] If the foregoing relationship is applied to the Bernoulli
theorem, Equation 1 can be obtained.
.rho.U.sub.0.sup.2/2+P.sub.0=.rho.U.sub.cat.sup.2/2+P.sub.1
Equation 1
[0049] In the equation, P0 is the pressure of exhaust immediately
upstream of the filter 10, and P1 is the pressure of exhaust
immediately downstream of the filter 10. It is assumed that the
liquid density .rho. is constant. Since the relationship of
Equation 2 holds between the flow speed of exhaust and the
cross-sectional area, the differential pressure .DELTA.P between
the upstream side and the downstream side of the filter 10
(hereinafter, referred to as "across-filter differential pressure")
can be expressed as in Equation 3.
U 0 A 0 = U cat A 1 Equation 2 .DELTA. P = ( P 0 - P 1 ) = .rho. U
cat 2 / 2 - .rho. U 0 2 / 2 = p U cat 2 / 2 - .rho. U cat 2 ( A 1 /
A 0 ) 2 / 2 Equation 3 ##EQU00001##
[0050] Then, Equation 3 can be re-written as Equation 4.
.DELTA.P/U.sub.cat.sup.2=.rho.(1-(A.sub.1/A.sub.0).sup.2)/2
Equation 4
[0051] In this equation, .DELTA.P/Ucat.sup.2 is a value that
correlates with the degree of clogging of the filter 10.
[0052] In this embodiment, if the .DELTA.P/Ucat.sup.2 is greater
than a predetermined value R1, the ECU 20 determines that the
filter 10 is clogged, and then carries out the restoration process
of the filter 10.
[0053] The flow of the clogging determination on the filter 10 in
this embodiment will next be described. FIG. 2 is a flowchart
showing the flow of the clogging determination on the filter 10
according to this embodiment. The routine of this flowchart is
repeatedly executed at every predetermined time.
[0054] In step S101, it is determined whether or not a condition
for determining the presence of the clogging of a filter 10 is met.
In this step, it is determined whether or not a state suitable to
perform the clogging determination on the filter 10 has been
assumed. For example, it is determined whether or not the internal
combustion engine 1 is in a steady state, or whether or not the
temperature of the filter 10 is in a predetermined range. It is
also allowable to determine whether or not the vehicle has traveled
such a predetermined distance that PM can deposit to a large
amount. If an affirmative determination is made in step S101, the
process proceeds to step S102. On the other hand, if a negative
determination is made, the routine is ended.
[0055] In step S102, the ECU 20 controls the low-pressure EGR valve
32 to the fully closed state. That is, the ECU 20 controls the
valve 32 so that the exhaust passing through the filter 10 will not
contain the low-pressure EGR gas. This facilitates the calculation
of the amount of flow of exhaust passing through the filter 10.
[0056] In step S103, the air flow meter 7 detects a fresh air
amount Ga.
[0057] In step S104, the differential pressure sensor 11 detects
the across-filter differential pressure .DELTA.P.
[0058] In step S105, the exhaust temperature sensor 12 detects the
temperature of the exhaust passing through the filter 10
(hereinafter, referred to as "filter-passing exhaust temperature")
Tcat. The filter-passing exhaust temperature is used to convert the
mass flow of exhaust passing through the filter 10 into a volume
flow.
[0059] In step S106, the ECU 20 calculates the fuel injection
amount Gf. The fuel injection amount Gf is the amount of fuel
injected into the cylinders 2, and is calculated on the basis of
the engine rotation speed, the engine load, etc.
[0060] In step S107, the exhaust pressure sensor 13 detects the
pressure P6 in the exhaust pipe 4 upstream of the filter 10
(hereinafter, referred to as "filter upstream-side pressure").
[0061] In step S108, the ECU 20 calculates the volume flow Vcat of
exhaust passing through the filter 10. The volume flow Vcat can be
obtained through the following equation (equation of state of gas).
In the equation, R is the gas constant.
V.sub.cat=(G.sub.a+G.sub.f)RT.sub.cat/P.sub.6 Equation 5
[0062] In this embodiment the ECU 20 that finds the volume flow
Vcat corresponds to exhaust flow calculation means.
[0063] In step S109, the ECU 20 calculates a mean flow speed Ucat
of exhaust passing through the filter 10 (hereinafter, referred to
as "mean exhaust flow speed"). The mean exhaust flow speed Ucat is
calculated by dividing the volume flow Vcat calculated in step S108
by the cross-sectional area A of the filter 10. The cross-sectional
area A of the filter 10 is found beforehand.
[0064] In step S110, the ECU 20 determines whether or not
.DELTA.P/Ucat.sup.2 is greater than the predetermined value R1. As
mentioned above, .DELTA.P/Ucat.sup.2 has a correlation with the
degree of clogging of the filter 10. The predetermined value R1 is
found beforehand through experiments or the like, as a lower limit
value of the value at the time of occurrence of the clogging of the
filter 10. If an affirmative determination is made in step S110,
the process proceeds to step S111. On the other hand, if a negative
determination is made, the process proceeds to step S112.
[0065] In this embodiment, the ECU 20 performing the process of
step S110 corresponds to clogging determination means in the
invention.
[0066] In step S111, the ECU 20 requests a control for performing
the restoration process of the filter 10. For example, the ECU 20
sets a restoration process control request flag to 1. This
restoration process control request flag is set to 1 when there is
a need to perform the restoration process of the filter 10, and is
set to 0 when there is no need to perform the restoration process
of the filter 10.
[0067] In step S112, the ECU 20 resets the request for the control
for performing the restoration process of the filter 10. For
example, the restoration process control request flag is set to
0.
[0068] Thus, since the ECU 20 controls the low-pressure EGR valve
32 to the fully closed state at the time of determining whether the
filter 10 is clogged, the clogging determination on the filter 10
can be more accurately performed. Although in this embodiment the
ECU 20 controls the low-pressure EGR valve 32 to the fully closed
state at the time of determining whether the filter 10 is clogged,
the degree of opening of the low-pressure EGR valve 32 may instead
be controlled to a fixed degree of opening that is other than the
fully closed state. In this case, the amount of low-pressure EGR
gas flowing through the low-pressure EGR passageway 31 is directly
measured or is estimated. Then, the amount of low-pressure EGR gas
and the fresh air amount detected by the air flow meter 7 are
combined to calculate the amount of flow of exhaust passing through
the filter 10.
[0069] Furthermore, in the case where the low-pressure EGR device
30 is not provided but, for example, a system for supplying
secondary air to the filter 10 is provided, the supply of secondary
air may be stopped when the clogging determination on the filter 10
is performed. Besides, the amount of supply of secondary air may be
constant.
ii. Second Embodiment
[0070] In this embodiment, the EGR gas amount supplied into the
cylinders 2 is kept constant by supplying an amount of
high-pressure EGR gas that corresponds to the amount of decrease of
the low-pressure EGR gas.
[0071] It is to be noted herein that when the degree of opening of
the low-pressure EGR valve 32 is changed, the ER gas amount
supplied into the cylinders 2 changes. For example, when the
low-pressure EGR valve 32 is controlled to the fully closed state
in first embodiment, the supply of the low-pressure EGR gas into
the cylinders 2 discontinues. Therefore, there is possibility of
lack of the EGR gas in the cylinders.
[0072] In second embodiment, on the other hand, the degree of
opening of the high-pressure EGR valve 42 is controlled so that the
EGR gas amount supplied into the cylinders 2 is constant. In
reality, the degree of opening of the high-pressure EGR valve 42 is
controlled so that the intake air amount is constant. What is taken
into the cylinders 2 includes fresh air and EGR gas. If the state
of operation of the internal combustion engine 1 does not change,
the amount of fresh air and EGR gas combined does not change.
Therefore, the EGR gas amount and the fresh air amount have a
relationship in which, for example, if the EGR gas amount
decreases, the fresh air amount increases. That is, the EGR gas
amount can be kept constant by controlling the degree of opening of
the high-pressure EGR valve 42 so that the amount of fresh air,
that is, the intake air amount measured by the air flow meter 7, is
constant.
[0073] FIG. 3 is a flowchart showing the flow of the clogging
determination on the filter 10 in accordance with this embodiment.
The routine of this flowchart is repeatedly executed at every
predetermined time. The steps of executing the same processes as
those executed in the routine shown in the flowchart of FIG. 2 are
affixed with the same reference characters, and the description
thereof will be omitted.
[0074] In step S201, the ECU 20 calculates a target fresh air
amount Gat. The target fresh air amount Gat is calculated on the
basis of the rotation speed and the load of the internal combustion
engine 1. The relationship between the target fresh air amount Gat
and the engine rotation speed and the engine load is found and
presented in the form of a map beforehand through experiments or
the like, and is stored in the ECU 20.
[0075] In step S202, the ECU 20 controls the degree of opening of
the high-pressure EGR valve 42. The degree of opening of the
high-pressure EGR valve 42 is feedback-controlled so that the fresh
air amount Ga detected in step S103 equals the target fresh air
amount Gat calculated in step S201. It is to be noted herein that
the ECU 20 controls the degree of opening of the high-pressure EGR
valve 42 in the increasing direction if the ECU 20 controls the
degree of opening of the low-pressure EGR valve 32 in the
decreasing direction.
[0076] Since the high-pressure EGR gas through the high-pressure
EGR passageway 41 flows from the exhaust pipe 4 upstream of the
filter 10 to the intake pipe 3 downstream of the air flow meter 7,
the high-pressure EGR gas has substantially no influence on the
relationship between the fresh air amount and the amount of flow of
exhaust passing through the filter 10. Therefore, at the time of
the clogging determination on the filter 10, it is not necessary to
take the high-pressure EGR gas amount into account.
[0077] In this manner, if the degree of opening of the low-pressure
EGR valve 32 is changed while the ECU 20 performing the clogging
determination on the filter 10, the degree of opening of the
high-pressure EGR valve 42 is correspondingly changed, so that the
EGR gas amount supplied into the cylinders 2 can be kept constant.
This makes it possible to restrain the generation of NOx or the
like while the ECU 20 is performing the clogging determination on
the filter 10.
iii. Third Embodiment
[0078] In this embodiment, while the degree of opening of the
low-pressure EGR valve 32 is changing with the elapse of time, the
low-pressure EGR gas amount at the current degree of opening is
estimated. By adding the current intake air amount measured by the
air flow meter 7 to the estimated value, the amount of flow of
exhaust passing through the filter 10 with the current degree of
opening is calculated. Specifically, the sum of the low-pressure
EGR gas amount and the fresh air amount is equal to the amount of
flow of exhaust passing through the filter 10. Therefore, even
while the degree of opening of the low-pressure EGR valve 32 is
changing with the elapse of time, the amount of flow of exhaust
passing through the filter 10 with the current degree of opening
can be calculated by estimating the low-pressure EGR gas amount
that corresponds to the degree of opening and detecting the fresh
air amount provided at the time of that degree of opening.
Incidentally, the amount of flow of the low-pressure EGR gas is
estimated from the differential pressure between the upstream side
and the downstream side of the low-pressure EGR valve 32, the
degree of opening of the low-pressure EGR valve 32, etc.
[0079] FIGS. 4 and 5 are a flowchart showing the flow of the
clogging determination on the filter 10 in accordance with this
embodiment. The routine of this flowchart is repeatedly executed at
every predetermined time. The steps of executing the same processes
as those executed in the routine shown in the flowchart of FIG. 2
are affixed with the same reference characters, and the description
thereof will be omitted.
[0080] In step S301, the cooling water temperature sensor 17
detects the temperature of the cooling water of the internal
combustion engine 1.
[0081] In step S302, the ECU 20 calculates the cooling efficiency
of the EGR cooler 33. The cooling efficiency of the EGR cooler 33
has a correlation with the cooling water temperature. Therefore,
for example, a relationship between the cooling water temperature
and the cooling efficiency of the EGR cooler 33 is found and
presented in a map beforehand through experiments or the like, and
is stored in the ECU 20. By substituting the cooling water
temperature found in step S301 in this map, the cooling efficiency
of the EGR cooler 33 can be obtained.
[0082] In step S303, the density of the low-pressure EGR gas is
calculated. If the pressure and the temperature of the low-pressure
EGR gas are known, the density of the low-pressure EGR gas is
obtained by substituting the pressure and temperature values in the
equation of state (equation of state of gas).
[0083] The temperature of the low-pressure EGR gas can be
calculated, for example, on the basis of the exhaust temperature T7
detected by the exhaust temperature sensor 12, the cooling
efficiency of the EGR cooler 33 and the amount of temperature drop
that occurs when the low-pressure EGR gas flows through the
low-pressure EGR passageway 31. These relationships may be found
beforehand through experiments or the like. Furthermore, the
temperature of the low-pressure EGR gas may also be found, for
example, by using a sensor.
[0084] Furthermore, the pressure of the low-pressure EGR gas is
detected, for example, by a pressure sensor attached to the
low-pressure EGR passageway 31. Besides, the pressure in the intake
pipe 3 connected to the low-pressure EGR passageway 31 and the
pressure of the low-pressure EGR gas may be equal. The temperature
and the pressure may be estimated from other sensors, or the state
of operation of the internal combustion engine 1.
[0085] In step S304, the differential pressure between the upstream
side and the downstream side of the low-pressure EGR valve 32
(hereinafter, referred to as "across-low-pressure EGR valve
differential pressure") is detected. The across-low-pressure EGR
valve differential pressure can be obtained by, for example, using
a differential pressure sensor that is attached to the low-pressure
EGR passageway 31 so as to detect the differential pressure between
the upstream side and the downstream side of the low-pressure EGR
valve 32.
[0086] In step S305, the ECU 20 calculates the opening area of the
low-pressure EGR valve 32. For example, the relationship between
the opening area and the command value when the ECU 20 controls the
degree of opening of the low-pressure EGR valve 32 is found and
presented in a map beforehand. Then, by substituting a command
value, the opening area can be obtained.
[0087] In step S306, the ECU 20 calculates the amount of
low-pressure EGR gas Vegr passing through the low-pressure EGR
valve 32.
[0088] Equation 4 is converted as in the following equation.
Ucat= {square root over
(2.DELTA.P/(.rho.(1-(A.sub.1/A.sub.0).sup.2)))} Equation 6
Then, by replacing Ucat with the flow speed Uegr of the
low-pressure EGR gas, and replacing the A1 with the opening area
Aegr of the low-pressure EGR valve 32, the following equation can
be obtained.
Uegr= {square root over (2.DELTA.P.sub.egr/.rho..sub.egr)}.times.
{square root over (1/(1-(A.sub.egr/A.sub.0).sup.2))} Equation 7
[0089] The amount Vegr of low-pressure EGR gas passing through the
low-pressure EGR valve 32 can be obtained as in Equation 8.
V egr = U egr A egr = A 0 A egr 2 .DELTA. P egr / ( .rho. egr ( A 0
2 - A egr 2 ) ) Equation 8 ##EQU00002##
[0090] In this embodiment, the ECU 20 calculating the amount Vegr
of low-pressure EGR gas corresponds to EGR gas amount detection
means.
[0091] In step S307, the ECU 20 calculates the amount Vcat of flow
of exhaust passing through the filter 10. The amount Vcat of flow
of exhaust is calculated through Equation 9 as a value obtained by
summing the amount of flow of low-pressure EGR gas passing through
the low-pressure EGR valve 32, and the amount of flow of fresh
air.
V.sub.cat=V.sub.egr+(G.sub.a+G.sub.f)RT.sub.cat/P.sub.6 Equation
9
[0092] Thus, even in the case where the low-pressure EGR valve 32
is at a degree of opening other than the fully closed state and is
changing with the elapse of time, the amount of flow of exhaust
passing through the filter 10 can be found in accordance with the
degree of opening of the low-pressure EGR valve 32, so that the
clogging determination on the filter 10 can be performed in a wider
range of the state of operation.
* * * * *