U.S. patent application number 11/816505 was filed with the patent office on 2009-01-29 for exhaust gas purification device for internal combustion engine.
This patent application is currently assigned to MITSUBISHI FUSO TRUCK AND BUS CORPORATION. Invention is credited to Toru Kawatani, Nobuhiro Kondo, Minehiro Murata, Yoshinaka Takeda, Hitoshi Yokomura.
Application Number | 20090025370 11/816505 |
Document ID | / |
Family ID | 36941066 |
Filed Date | 2009-01-29 |
United States Patent
Application |
20090025370 |
Kind Code |
A1 |
Kondo; Nobuhiro ; et
al. |
January 29, 2009 |
EXHAUST GAS PURIFICATION DEVICE FOR INTERNAL COMBUSTION ENGINE
Abstract
An auxiliary agent supply means (32, 58) is provided to supply,
upstream of an exhaust gas purification means (24, 56, 78), an
auxiliary agent for maintaining the exhaust gas purifying function
of the exhaust gas purification means (24, 56, 78). A control means
(38) for controlling the auxiliary agent supply means (32, 58),
thereby regulating the amount of the auxiliary agent supplied
includes a standard supply quantity determination section (40, 50,
68, 86) for determining standard supply quantity of the auxiliary
agent required to maintain the exhaust gas purifying function, a
target supply quantity determination section (42, 52, 70, 88) for
determining target supply quantity of the auxiliary agent, by
correcting the standard supply quantity on the basis of exhaust
pressure, and a supply control section (44, 54, 72, 90) for
controlling the auxiliary agent supply means to supply the
auxiliary agent in the target supply quantity.
Inventors: |
Kondo; Nobuhiro; (Kanagawa,
JP) ; Kawatani; Toru; (Kanagawa, JP) ; Takeda;
Yoshinaka; (Kanagawa, JP) ; Yokomura; Hitoshi;
(Kanagawa, JP) ; Murata; Minehiro; (Kanagawa,
JP) |
Correspondence
Address: |
ROSSI, KIMMS & McDOWELL LLP.
20609 Gordon Park Square, Suite 150
Ashburn
VA
20147
US
|
Assignee: |
MITSUBISHI FUSO TRUCK AND BUS
CORPORATION
Kawasaki-shi, Kanagawa
JP
|
Family ID: |
36941066 |
Appl. No.: |
11/816505 |
Filed: |
February 24, 2006 |
PCT Filed: |
February 24, 2006 |
PCT NO: |
PCT/JP2006/303379 |
371 Date: |
September 11, 2007 |
Current U.S.
Class: |
60/286 |
Current CPC
Class: |
F01N 13/0097 20140603;
F02B 29/0425 20130101; B01D 53/94 20130101; F01N 2610/146 20130101;
F01N 3/0871 20130101; Y02T 10/12 20130101; F01N 3/0814 20130101;
F01N 2900/14 20130101; F01N 9/002 20130101; F01N 2610/02 20130101;
F01N 3/0885 20130101; F01N 3/208 20130101; F02B 37/00 20130101;
F01N 3/0235 20130101; F01N 2570/14 20130101; F02M 26/05 20160201;
F01N 3/2066 20130101; F01N 2570/04 20130101; F01N 2240/36 20130101;
B01D 53/9495 20130101; F01N 2260/14 20130101; Y02T 10/40 20130101;
B01D 53/90 20130101; F01N 3/0842 20130101; F01N 2560/08 20130101;
F01N 3/0253 20130101 |
Class at
Publication: |
60/286 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2005 |
JP |
2005-053461 |
Claims
1. An exhaust gas purification device for an internal combustion
engine, comprising: an exhaust gas purification means provided in
an exhaust passage of the internal combustion engine for purifying
exhaust gas exhausted from the internal combustion engine, an
auxiliary agent supply means for supplying an auxiliary agent for
maintaining the exhaust gas purifying function of the exhaust gas
purification means, into the exhaust passage, upstream of the
exhaust gas purification means, a variation factor parameter
detection means for detecting the value of a variation factor
parameter which causes variations in the amount of the auxiliary
agent supplied, and a control means for controlling the auxiliary
agent supply means, thereby regulating the amount of the auxiliary
agent supplied into the exhaust passage, wherein the control means
includes a standard supply quantity determination section for
determining standard supply quantity of the auxiliary agent
required to maintain the exhaust gas purifying function of the
exhaust gas purification means; a target supply quantity
determination section for determining target supply quantity of the
auxiliary agent, by correcting the standard supply quantity
determined by the standard supply quantity determination section,
on the basis of the value of the parameter detected by the
variation factor parameter detection means; and a supply control
section for controlling the auxiliary agent supply means to supply
the auxiliary agent in the target supply quantity determined by the
target supply quantity determination section.
2. The exhaust gas purification device for the internal combustion
engine according to claim 1, wherein the variation factor parameter
detection means includes an exhaust pressure detection means for
detecting exhaust pressure in the exhaust passage, upstream of the
exhaust gas purification means, and the variation factor parameter
is the exhaust pressure.
3. The exhaust gas purification device for the internal combustion
engine according to claim 2, wherein the auxiliary agent supply
means is designed to supply and stop supplying the auxiliary agent
by opening and closing a solenoid valve, and the supply control
section performs duty cycle control of opening and closing of the
solenoid valve so as to supply the auxiliary agent into the exhaust
passage in the target supply quantity.
4. The exhaust gas purification device for the internal combustion
engine according to claim 3, wherein the supply control section
performs the duty cycle control of opening and closing of the
solenoid valve such that the duty cycle becomes greater as the
exhaust pressure increases.
5. The exhaust gas purification device for the internal combustion
engine according to claim 1, wherein the variation factor parameter
detection means includes an auxiliary agent temperature detection
means for detecting the temperature of the auxiliary agent, and the
variation factor parameter is the auxiliary agent temperature.
6. The exhaust gas purification device for the internal combustion
engine according to claim 5, wherein the variation factor parameter
detection means further includes an exhaust pressure detection
means for detecting exhaust pressure in the exhaust passage,
upstream of the exhaust gas purification means, and the target
supply quantity determination section determines the target supply
quantity by correcting the standard supply quantity on the basis of
the exhaust pressure detected by the exhaust pressure detection
means and the auxiliary agent temperature detected by the auxiliary
agent temperature detection means.
7. The exhaust gas purification device for the internal combustion
engine according to claim 6, wherein the auxiliary agent supply
means is designed to supply and stop supplying the auxiliary agent
by opening and closing a solenoid valve, and the supply control
section performs duty cycle control of opening and closing of the
solenoid valve so as to supply the auxiliary agent into the exhaust
passage in the target supply quantity.
8. The exhaust gas purification device for the internal combustion
engine according to claim 7, wherein the supply control section
performs the duty cycle control of opening and closing of the
solenoid valve such that a duty cycle for the duty cycle control
becomes smaller as the auxiliary agent temperature increases.
9. The exhaust gas purification device for the internal combustion
engine according to claim 1, wherein the exhaust gas purification
means is an NOx adsorption catalyst designed to adsorb NOx in
exhaust gas that enters into the NOx adsorption catalyst when the
air-fuel ratio of the exhaust gas is lean, and release and reduce
the adsorbed NOx when the air-fuel ratio of the exhaust gas is
rich, the auxiliary agent supply means supplies fuel as the
auxiliary agent into the exhaust passage, upstream of the NOx
adsorption catalyst, and the standard supply quantity determination
means determines standard supply quantity of the fuel required to
cause the NOx adsorption catalyst to release and reduce the NOx
adsorbed by the NOx adsorption catalyst.
10. The exhaust gas purification device for the internal combustion
engine according to claim 1, wherein the exhaust gas purification
means is an NOx adsorption catalyst designed to adsorb NOx in
exhaust gas that enters into the NOx adsorption catalyst when the
air-fuel ratio of the exhaust gas is lean, and release and reduce
the adsorbed NOx when the air-fuel ratio of the exhaust gas is
rich, the auxiliary agent supply means supplies fuel as the
auxiliary agent into the exhaust passage, upstream of the NOx
adsorption catalyst, and the standard supply quantity determination
means determines standard supply quantity of the fuel required to
restore the NOx adsorption capacity of the NOx adsorption catalyst
that has lowered due to sulfur component adsorbed from the exhaust
gas by the NOx adsorption catalyst, by causing the NOx adsorption
catalyst to release the adsorbed sulfur component.
11. The exhaust gas purification device for the internal combustion
engine according to claim 1, wherein the exhaust gas purification
means is a NOx catalyst designed to selectively reduce NOx in the
exhaust gas, the auxiliary agent supply means supplies urea water
as the auxiliary agent into the exhaust passage, upstream of the
NOx catalyst, and the standard supply quantity determination means
determines standard supply quantity of the urea water required for
the NOx catalyst to selectively reduce the NOx in the exhaust
gas.
12. The exhaust gas purification device for the internal combustion
engine according to claim 1, wherein the exhaust gas purification
means is a particulate filter designed to trap particulate matter
in the exhaust gas, the auxiliary agent supply means supplies fuel
as the auxiliary agent into the exhaust passage, upstream of the
particulate filter, and the standard supply quantity determination
means determines standard supply quantity of the fuel required to
regenerate the particulate filter by burning off particulate matter
trapped by the particulate filter.
13. The exhaust gas purification device for the internal combustion
engine according to claim 2, further comprising an exhaust throttle
disposed in the exhaust passage to regulate exhaust gas flow rate
in the exhaust passage, wherein the exhaust pressure detection
means detects the exhaust pressure in the exhaust passage, upstream
of the exhaust throttle, and the auxiliary agent supply means is
disposed upstream of the exhaust throttle.
14. The exhaust gas purification device for the internal combustion
engine according to claim 6, further comprising an exhaust throttle
disposed in the exhaust passage to regulate exhaust gas flow rate
in the exhaust passage, wherein the exhaust pressure detection
means detects the exhaust pressure in the exhaust passage, upstream
of the exhaust throttle, and the auxiliary agent supply means is
disposed upstream of the exhaust throttle.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust gas purification
device for an internal combustion engine, and more specifically, an
exhaust gas purification device using an auxiliary agent to
maintain an exhaust gas purifying function.
BACKGROUND ART
[0002] In order to convert pollutants contained in the exhaust gas
of an internal combustion engine, such as HC (carbon hydrate), CO
(carbon monoxide) and NOx (nitrogen oxides), to purify the exhaust
gas, an exhaust gas purification catalyst is conventionally used.
In the case of a diesel engine, a particulate filter for trapping
particulate matter contained in exhaust is used, in addition to
such exhaust gas purification catalyst. In some of exhaust gas
purification devices such as exhaust gas purification catalysts and
particulate filters, an auxiliary agent is used to maintain their
exhaust gas purifying function.
[0003] In some particulate filters, when the particulate matter
trapped and accumulated in the particulate filter reaches a
predetermined amount, fuel is supplied as an auxiliary agent into
an exhaust passage, upstream of the particulate filter, to burn off
the particulate matter trapped by the particulate filter, thereby
regenerating the particulate filter and maintaining the particulate
trap function. There are also known exhaust gas purification
catalysts in which an auxiliary agent is supplied into the exhaust
passage in like manner to maintain the exhaust gas purifying
function.
[0004] For example, as a catalyst for converting NOx contained in
exhaust gas into unharmful substances, there is known a NOx
adsorption catalyst designed to adsorb NOx contained in exhaust gas
when the air-fuel ratio of the exhaust gas is lean, and release and
reduce the adsorbed NOx when the air-fuel ratio of the exhaust gas
is rich. Since the capacity of the NOx adsorption catalyst to
adsorb NOx has a limit, it is necessary to cause the adsorbed NOx
to be released and reduced. Thus, from Japanese Unexamined Patent
Publication No. 2000-205005 (hereinafter referred to as Patent
Document 1), for example, there is known an exhaust gas
purification device in which, in order to maintain the exhaust gas
purifying function of the NOx adsorption catalyst by causing it to
release and reduce the adsorbed NOx, a fuel addition valve is
provided to the exhaust passage, upstream of the NOx adsorption
catalyst, so that fuel required to cause the release and reduction
of NOx is injected from the fuel addition valve into the exhaust
passage and supplied to the NOx adsorption catalyst.
[0005] In the exhaust gas purification device shown in Patent
Document 1, fuel in the amount required to cause the NOx adsorption
catalyst to release and reduce the adsorbed NOx is injected into
the exhaust passage, upstream of the NOx adsorption catalyst, by
means of the fuel addition valve, so that exhaust gas with a rich
air-fuel ratio enters the NOx adsorption catalyst and causes the
NOx adsorption catalyst to release and reduce the adsorbed NOx. In
this process, the amount of fuel supplied is regulated by varying
the valve open time of the fuel addition valve, where the amount of
fuel injected into the exhaust pipe increases as the valve open
time becomes longer.
[0006] The amount of fuel required to cause the NOx adsorption
catalyst to release and reduce the adsorbed NOx, or the valve open
time of the fuel addition valve needs to be determined on the basis
of NOx accumulation quantity, namely the amount of NOx adsorbed by
the NOx adsorption catalyst, etc. It is however difficult to
directly detect the NOx accumulation quantity. Thus, actually, the
valve open time corresponding to the required fuel quantity is
determined from a map set in advance to give the valve open time as
a function of intake air quantity and engine revolution speed.
[0007] The amount of fuel injected from the fuel addition valve
into the exhaust passage, however, varies depending on exhaust
pressure in the exhaust passage and the temperature of fuel
supplied. Thus, even when the valve open time corresponding to the
required fuel quantity is accurately obtained on the basis of the
intake air quantity and the engine revolution speed, the amount of
fuel actually injected from the fuel addition valve into the
exhaust passage can be different from the fuel quantity obtained
from the map.
[0008] Specifically, if the supply pressure of fuel to be injected
is fixed, pressure difference between the fuel supply pressure and
the exhaust pressure is smaller when the exhaust pressure is
higher, compared with when the exhaust pressure is lower. Thus, the
amount of fuel actually supplied into the exhaust passage in the
same valve open time becomes smaller as the exhaust pressure
increases. Particularly when an exhaust throttle valve is provided
in the exhaust passage for using it as an exhaust brake, or for
such purpose as controlling the temperature of the exhaust gas
purification catalyst or the particulate filter, the exhaust
pressure varies to a great degree, depending on the opening and
closing of the exhaust throttle valve, and therefore has a greater
influence on the amount of fuel supplied.
[0009] Further, fuel has lower viscosity in the case where the
temperature of fuel is higher, compared with that in the case where
the temperature of fuel is lower. Thus, the amount of fuel actually
supplied into the exhaust passage in the same valve open time
becomes greater as the fuel temperature increases.
[0010] As stated above, the amount of fuel supplied from the fuel
addition valve into the exhaust passage varies depending on the
exhaust pressure and the fuel temperature. Thus, fuel in the amount
required is not always supplied to the NOx adsorption catalyst,
which leads to problems such that NOx is not sufficiently converted
into unharmful substances by the NOx adsorption catalyst, that the
adsorbed NOx is not sufficiently released so that the purifying
capacity of the NOx adsorption catalyst lowers, and that fuel is
added excessively so that excess fuel is emitted into the
atmosphere.
DISCLOSURE OF THE INVENTION
[0011] The present invention has been made to solve the problems as
mentioned above, and the primary object of the present invention is
to provide an exhaust gas purification device for an internal
combustion engine which can stably maintain an exhaust gas
purifying function by accurately supplying an auxiliary agent
required for maintaining the exhaust gas purifying function.
[0012] An exhaust gas purification device for an internal
combustion engine according to the present invention comprises: an
exhaust gas purification means provided in an exhaust passage of
the internal combustion engine for purifying exhaust gas exhausted
from the internal combustion engine; an auxiliary agent supply
means for supplying an auxiliary agent for maintaining the exhaust
gas purifying function of the exhaust gas purification means, into
the exhaust passage, upstream of the exhaust gas purification
means; a variation factor parameter detection means for detecting
the value of a variation factor parameter which causes variations
in the amount of the auxiliary agent supplied; and a control means
for controlling the auxiliary agent supply means, thereby
regulating the amount of the auxiliary agent supplied into the
exhaust passage, wherein the control means includes a standard
supply quantity determination section for determining standard
supply quantity of the auxiliary agent required to maintain the
exhaust gas purifying function of the exhaust gas purification
means; a target supply quantity determination section for
determining target supply quantity of the auxiliary agent, by
correcting the standard supply quantity determined by the standard
supply quantity determination section, on the basis of the value of
the parameter detected by the variation factor parameter detection
means; and a supply control section for controlling the auxiliary
agent supply means to supply the auxiliary agent in the target
supply quantity determined by the target supply quantity
determination section.
[0013] In the exhaust gas purification device for the internal
combustion engine according to the present invention, the standard
supply quantity of the auxiliary agent required to maintain the
exhaust gas purifying function of the exhaust gas purification
means is corrected on the basis of the value of the variation
factor parameter, and the auxiliary agent is supplied into the
exhaust passage in the quantity corrected this way. Thus, the
auxiliary agent can be supplied into the exhaust passage accurately
in the amount required to maintain the exhaust gas purifying
function of the exhaust gas purification means, obviating the
influence of the variation factor on the amount of the auxiliary
agent supplied.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a diagram showing the overall structure of an
exhaust gas purification device for an internal combustion engine
according to a first embodiment of the present invention;
[0015] FIG. 2 is a block diagram for light oil supply control by an
ECU of FIG. 1;
[0016] FIG. 3 is a flow chart showing the light oil supply control
by the ECU of FIG. 1;
[0017] FIG. 4 is a diagram showing a characteristic of an exhaust
pressure Pex-correction factor Rp map used by the ECU of FIG.
1;
[0018] FIG. 5 is a diagram showing a characteristic of a light oil
temperature Tf-correction factor Rt map used by the ECU of FIG.
1;
[0019] FIG. 6 is a diagram showing a characteristic of a target
supply quantity Mt-duty cycle Dt map used by the ECU of FIG. 1;
[0020] FIG. 7 is a block diagram for light oil supply control in an
exhaust gas purification device for an internal combustion engine
according to a second embodiment of the present invention;
[0021] FIG. 8 is a diagram showing the schematic structure of an
exhaust gas purification device for an internal combustion engine
according to a third embodiment of the present invention;
[0022] FIG. 9 is a block diagram for urea water supply control in
the exhaust gas purification device of FIG. 8;
[0023] FIG. 10 is a flow chart showing the urea water supply
control in the exhaust gas purification device of FIG. 8;
[0024] FIG. 11 is a diagram showing a characteristic of an exhaust
pressure Pex-correction factor Rp map used in the urea water supply
control in the exhaust gas purification device of FIG. 8;
[0025] FIG. 12 is a diagram showing a characteristic of a urea
water temperature Tu-correction factor Rp map used in the urea
water supply control in the exhaust gas purification device of FIG.
8;
[0026] FIG. 13 is a diagram showing the schematic structure of an
exhaust gas purification device for an internal combustion engine
according to a fourth embodiment of the present invention; and
[0027] FIG. 14 is a block diagram showing light oil supply control
in the exhaust gas purification device of FIG. 13.
BEST MODE OF CARRYING OUT THE INVENTION
[0028] With reference to the accompanying drawings, embodiments of
the present invention will be described below.
[0029] FIG. 1 shows the system structure of a four-cylinder diesel
engine (hereinafter referred to as an engine) to which an exhaust
gas purification device according to a first embodiment of the
present invention is applied. Referring to FIG. 1, the structure of
the exhaust gas purification device according to the present
invention will be described.
[0030] As shown in FIG. 1, the engine 1 is an inline four-cylinder
diesel engine, in which fuel is directly supplied into each
cylinder by means of a fuel injection valve (not shown) provided
for each cylinder.
[0031] A turbocharger 4 is provided to an intake passage 2. Intake
air sucked in through an air cleaner (not shown) flows from the
intake passage 2 to a compressor 4a of the turbocharger 4. After
compressed by the compressor 4a, the intake air is passed through
an intercooler 10, and then introduced into an intake manifold
8.
[0032] An air flow sensor 10 for detecting the amount of intake air
flow to the engine 1 is provided to the intake passage 2, upstream
of the compressor 4a. Further, an intake throttle valve 12 for
regulating the amount of intake air taken into the engine 1 is
provided in the intake passage 2, downstream of the intercooler
6.
[0033] Exhaust ports (not shown) through which exhaust gas is
exhausted from the respective cylinders of the engine 1 are
connected to an exhaust pipe (exhaust passage) 16 by means of an
exhaust manifold 14. An EGR passage 20 is provided to connect the
exhaust manifold 14 and the intake manifold 8, with an EGR valve 18
disposed between the exhaust manifold 14 and the intake manifold
8.
[0034] The exhaust pipe 16 is connected to an exhaust
after-treatment device 22 through a turbine 4b of the turbocharger
4. The turbine 4b is coupled with the compressor 4a, and receives
exhaust gas flowing in the exhaust pipe 16, thereby driving the
compressor 4a.
[0035] The exhaust after-treatment device 22 has a casing, within
which an NOx adsorption catalyst 24 as an exhaust gas purification
means is disposed on the upstream side and a DPF (diesel
particulate filter) 26 is disposed downstream of the NOx adsorption
catalyst 24. The NOx adsorption catalyst 24 has a function of
adsorbing NOx contained in exhaust gas when the exhaust air-fuel
ratio is lean, and releasing and reducing the adsorbed NOx when the
exhaust air-fuel ratio is rich. The NOx adsorption catalyst 24
having such function is in itself publicly known. The DPF 26 has a
function of trapping particulate matter contained in exhaust gas.
Also the DPF 26 is in itself publicly known. The exhaust gas
purified by these NOx adsorption catalyst 24 and DPF 26 is emitted
into the atmosphere.
[0036] Upstream of the exhaust after-treatment device 22, an
exhaust throttle valve 28 functioning as an exhaust brake is
provided, and upstream of the exhaust throttle valve 28, an exhaust
pressure sensor (exhaust pressure detection means) 30 for detecting
exhaust pressure in the exhaust pipe 16 is provided.
[0037] Further, in order to make the exhaust air-fuel ratio rich to
cause the NOx adsorption catalyst 24 to release and reduce the
adsorbed NOx, there is provided, upstream of the exhaust throttle
valve 28, a light oil addition valve (auxiliary agent supply means)
32 for injecting light oil, which is the same fuel as that supplied
to the engine 1, into the exhaust pipe 16, as an auxiliary agent.
The light oil addition valve 32 is a solenoid valve designed to be
opened to inject light oil by energizing a solenoid, and closed to
stop supplying the light oil by stopping energizing the solenoid.
Thus, when light oil supply pressure is fixed, light oil is
supplied into the exhaust pipe 16 in the amount proportional to the
time of energizing the light oil addition valve 32.
[0038] Light oil is supplied to the light oil addition valve 32
through a light oil supply passage 34. A light oil temperature
sensor (auxiliary agent temperature detection means) 36 for
detecting the temperature of the light oil supplied to the light
oil addition valve 32 is provided to the light oil supply passage
34.
[0039] An ECU (control means) 38 is a control device for performing
general control on the exhaust gas purification device according to
the present invention, including control on the engine 1. The ECU
comprises a CPU, memory devices, timer counters, etc. and
determines the values of a variety of control variables, including
fuel supply quantity for each cylinder, and controls a variety of
devices on the basis of the control variable values determined.
[0040] To the input of the ECU 38, there are connected a variety of
sensors including the air flow sensor 10, the exhaust pressure
sensor 30 and the light oil temperature sensor 36 to collect
information required for a variety of controls. To the output of
the ECU 38, there are connected a variety of devices including the
fuel injection valve (not shown) for each cylinder and the light
oil addition valve 32, which devices are controlled on the basis of
control variable values determined.
[0041] In the exhaust gas purification device for the internal
combustion engine having the configuration described above, exhaust
gas exhausted from the engine 1 during the operation of the engine
1 is introduced through the exhaust pipe 16 into the exhaust
after-treatment device 22, where NOx contained in the exhaust gas
is adsorbed by the NOx adsorption catalyst 24 and particulate
matter contained in the exhaust gas is trapped by the DPF 26.
[0042] The removal of particulate matter is carried out as follows:
Light oil is injected from the light oil addition valve 32 into the
exhaust pipe 16 and oxidized on the NOx adsorption catalyst 24. The
resulting high-temperature gas is forced to flow into the DPF 26,
so that the particulate matter trapped by the DPF 26 is removed
from the DPF 26 by oxidation.
[0043] The NOx which is not adsorbed but remains in the exhaust gas
because the amount of NOx adsorbed by the NOx adsorption catalyst
24 has reached the limit enters the DPF 26 downstream of the NOx
catalyst 24 and acts as an oxidizer to oxidize the particulate
matter trapped by the DPF 26. Consequently, the particulate matter
is removed from the DPF 26 by oxidation while the NOx flown into
the DPF 26 turns into N.sub.2, which is emitted into the
atmosphere.
[0044] The conversion of NOx is carried out as follows: By carrying
out lean operation, the NOx adsorption catalyst is caused to adsorb
the NOx contained in the exhaust gas. After the amount of NOx
adsorbed by the NOx adsorption catalyst 24 reaches a certain level,
light oil is injected from the light oil addition valve 32 into the
exhaust pipe 16 to make the exhaust air-fuel ratio rich. Supplied
with exhaust gas with a rich air-fuel ratio obtained in this
manner, the NOx adsorption catalyst 24 releases and reduces the
adsorbed NOx, thereby restoring the adsorption capacity of the NOx
adsorption catalyst 24. After the regeneration of the NOx
adsorption catalyst 24 by release and reduction of the adsorbed NOx
is completed, the injection of the light oil from the light oil
addition valve 32 is terminated.
[0045] By appropriately repeating the regeneration of the NOx
adsorption catalyst 24 and of the DPF 26, the exhaust gas purifying
function of the NOx adsorption catalyst 24 and of the DPF 26 is
maintained.
[0046] Next, referring to FIGS. 2 to 6, control of light oil supply
from the light oil addition valve 32 will be described.
[0047] FIG. 2 shows the configuration of control blocks for
carrying out the light oil supply control in the ECU 38, and FIG. 3
is a flow chart showing the light oil supply control performed by
those control blocks.
[0048] As shown in FIG. 2, the ECU 38 includes a standard supply
quantity determination section 40 for determining standard supply
quantity Mb of the light oil required to cause the NOx adsorption
catalyst 24 to release and reduce the NOx adsorbed by the NOx
adsorption catalyst 24, thereby maintaining the NOx adsorption
capacity of the NOx adsorption catalyst 24; a target supply
quantity determination section 42 for determining target supply
quantity Mt by correcting the standard supply quantity Mb
determined by the standard supply quantity determination section
40, on the basis of exhaust pressure Pex detected by the exhaust
pressure sensor 30 and light oil temperature Tf detected by the
light oil temperature sensor 36; and a supply control section 44
for controlling the light oil addition valve 32 so that light oil
is supplied into the exhaust passage in the target supply quantity
Mt determined by the target supply quantity determination section
42.
[0049] More specifically, intake air flow rate Qa detected by the
air flow sensor 10 and engine revolution speed Ne detected by the
revolution speed sensor 46 are fed to the standard supply quantity
determination section 40, and from a map stored in advance,
standard supply quantity Mb of the light oil required to cause the
NOx adsorption catalyst 24 to release and reduce the adsorbed NOx
is determined on the basis of these intake air flow rate Qa and
engine revolution speed Ne (Step S10 in FIG. 3).
[0050] The standard supply quantity Mb determined by the standard
supply quantity determination section 40 is sent to the target
supply quantity determination section 42. Exhaust pressure Pex
detected by the exhaust pressure sensor 30 and light oil
temperature Tf detected by the light oil temperature sensor 36 are
fed to the target supply quantity determination section 42, and the
target supply quantity determination section 42 corrects the
standard supply quantity Mb on the basis of these exhaust pressure
Pex and light oil temperature Tf.
[0051] The amount of light oil supplied from the light oil addition
valve 32 is regulated by varying the valve open time thereof, where
the amount of fuel injected into the exhaust pipe 16 increases as
the valve open time becomes longer. Accordingly, if the light oil
supply pressure is fixed, the amount of light oil actually supplied
into the exhaust pipe 16 in the same valve open time becomes
smaller as the exhaust pressure increases. Further, light oil has
lower viscosity in the case where the temperature of the light oil
is higher, compared with the case where the temperature of the
light oil is lower. Thus, the amount of light oil actually supplied
into the exhaust pipe 16 in the same valve open time becomes
greater as the light oil temperature increases.
[0052] Thus, in connection with the exhaust pressure Pex, a
correction factor Rp corresponding to the detected exhaust pressure
Pex is determined from a map stored in advance (Step S12 in FIG.
3), where the map is prepared such that the correction factor Rp
becomes smaller as the exhaust pressure Pex increases, as shown in
FIG. 4. By dividing the standard supply quantity Mb by the
correction factor Rp, the target supply quantity determination
section 42 corrects the standard supply quantity Mb to obtain
pressure-corrected supply quantity Mp (Step S14 in FIG. 3).
[0053] It is to be noted that the correction factor Rp is set to
1.0 in a standard state in which the exhaust pressure is equal to
the exhaust pressure value based on which the map used to determine
the standard supply quantity Mb is set.
[0054] By correcting the standard supply quantity Mb using the
correction factor Rp in this manner, the pressure-corrected supply
quantity Mp is greater than the standard supply quantity Mb when
the exhaust pressure Pex is higher than the exhaust pressure value
in the standard state. Thus, the shortage of supply quantity due to
an increase in exhaust pressure Pex is compensated for. Conversely,
the pressure-corrected supply quantity Mp is smaller than the
standard supply quantity Mb when the exhaust pressure Pex is lower
than the exhaust pressure value in the standard state. Thus, the
excess of supply quantity due to a decrease in exhaust pressure Pex
is obviated.
[0055] Next, in connection with the light oil temperature Tf, a
correction factor Rt corresponding to the detected light oil
temperature Tf is determined from a map stored in advance (Step S16
in FIG. 3), where the map is prepared such that the correction
factor Rt becomes greater as the light oil temperature Tf
increases, as shown in FIG. 5. By dividing the pressure-corrected
supply quantity Mp by the correction factor Rt, the target supply
quantity determination section 42 corrects the pressure-corrected
supply quantity Mp to obtain target supply quantity Mt (Step S18 in
FIG. 3).
[0056] It is to be noted that the correction factor Rt is set to
1.0 in a standard state in which the light oil temperature is equal
to the light oil temperature value based on which the map used to
determine the standard supply quantity Mb is set.
[0057] Here, the correction using the correction factor Rt is made
to the pressure-corrected supply quantity Mp. However, since the
pressure-corrected supply quantity Mp results from correcting the
standard supply quantity Mb on the basis of the exhaust pressure
Pex as mentioned above, the correction using the correction factor
Rt is essentially made to the standard supply quantity Mb.
Accordingly, by correcting the pressure-corrected supply quantity
Mp, or essentially, the standard supply quantity Mb using the
correction factor Rt in this manner, the target supply quantity Mt
becomes smaller as the light oil temperature Tf increases, and
thereby the excess of supply quantity due to a rise in light oil
temperature Tf is obviated. Conversely, the target supply quantity
Mt becomes greater as the light oil temperature Tf decreases, and
thereby the shortage of supply quantity due to a drop in light oil
temperature Tf is compensated for.
[0058] In the flow chart of FIG. 3, first at Steps S12 and S14, the
pressure-corrected supply quantity Mp is obtained by correcting the
standard supply quantity Mb on the basis of the exhaust pressure
Pex, and then at Steps S16 and S18, the target supply quantity Mt
is determined by correcting the pressure-corrected supply quantity
Mp on the basis of the light oil temperature Tf. It is to be noted,
however, that the order of the steps is not limited to this.
[0059] For example, Steps 12 and S14 can be interchanged with Steps
S16 and S18. Specifically, it can be arranged such that first,
temperature-corrected supply quantity is obtained by correcting the
standard supply quantity Mb using the correction factor Rt
corresponding to the light oil temperature Tf, and then the target
supply quantity Mt is obtained by correcting the
temperature-corrected supply quantity using the correction factor
Rp corresponding to the exhaust pressure Pex.
[0060] Alternatively, it can be arranged such that first, the
correction factor Rp corresponding to the exhaust pressure Pex and
the correction factor Rt corresponding to the light oil temperature
Tf are determined from the respective maps, and then, the target
supply quantity Mt is obtained by dividing the standard supply
quantity Mb by the correction factors Rp and Rt, successively.
[0061] Further, although in the above-described case, correction is
made by dividing the standard supply quantity Mb, the
pressure-corrected supply quantity Mp or the temperature-corrected
supply quantity by the correction factor Rp or the correction
factor Rt, it can be arranged such that the reciprocal of each
correction factor is obtained from a map stored in advance so that
correction is made by multiplying the supply quantity by the
reciprocal.
[0062] After the target supply quantity Mt of the light oil
required to cause the NOx adsorption catalyst 24 to release and
reduce the adsorbed NOx is determined in this manner, the supply
control section 44 determines, from a map stored in advance, valve
open time of the light oil addition valve 32 required for the light
oil addition valve 32 to inject light oil in the target supply
quantity Mt (Step S20 in FIG. 3). Since the control on the light
oil addition valve 32 is performed in control cycles of a
predetermined period, the map is prepared to give the valve open
time of the light oil addition valve 32 corresponding to the target
supply quantity Mt, in the form of duty cycle Dt relative to the
maximum valve open time in one control cycle, as shown in FIG.
6.
[0063] After determining the duty cycle Dt corresponding to the
target supply quantity Mt from the map, the supply control section
44 drives the light oil addition valve 32 to open according to the
duty cycle Dt (Step S22 in FIG. 3), so that light oil in a quantity
equivalent to the target supply quantity Mt is injected from the
light oil addition valve 32 into the exhaust pipe 16. This makes
the exhaust air-fuel ratio rich, so that the NOx adsorbed by the
NOx adsorption catalyst 24 is properly released and reduced.
[0064] It is to be noted that the exhaust pressure sensor 30 is
disposed upstream of the exhaust throttle 28. Thus, even when the
pressure in the exhaust pipe 16 varies due to the opening and
closing of the exhaust throttle 28, light oil is always supplied
properly in the amount required to cause the NOx adsorption
catalyst 24 to release and reduce the adsorbed NOx, in spite of
variations in pressure in the exhaust pipe 16, since, as mentioned
above, the standard supply quantity Mb is corrected on the basis of
the exhaust pressure detected by this exhaust pressure sensor
30.
[0065] As described above, in the exhaust gas purification device
according to the first embodiment of the present invention, the
amount of supply of light oil required to cause the NOx adsorption
catalyst 24 to release and reduce the adsorbed NOx, thereby
maintaining the NOx adsorption capacity of the NOx adsorption
catalyst 24 is controlled properly, without being affected by
variations in exhaust pressure and in light oil temperature. Thus,
the exhaust gas purifying function can be stably maintained, and
the emission of excess light oil into the atmosphere can be
prevented.
[0066] It is to be noted that although in the exhaust gas
purification device according to the above-described first
embodiment, the target supply quantity Mt is determined by
correcting the standard supply quantity Mb of the light oil
required to maintain the NOx adsorption capacity of the NOx
adsorption catalyst 24, on the basis of both the exhaust pressure
Pex and the light oil temperature Tf, the correction may be made on
the basis of either of them. The control accuracy in this case is
lower, compared with when the correction is made on the basis of
both the exhaust pressure Pex and the light oil temperature Tf, but
higher, compared with the conventional exhaust gas purification
device which takes account of neither of the exhaust pressure and
the light oil temperature.
[0067] Further, although in the above-described first embodiment,
the standard supply quantity Mb of the light oil required to cause
the NOx adsorption catalyst 24 to release and reduce the adsorbed
NOx is determined from a map stored in advance, on the basis of the
intake air flow rate Qa and the engine revolution speed Ne, the way
to determine the standard supply quantity Mb is not limited to
this. For example, the standard supply quantity Mb may be
determined on the basis of a decrease in NOx adsorption capacity
which can be detected by a NOx sensor provided downstream of the
NOx adsorption catalyst 24. There are a variety of known techniques
that can be used.
[0068] Further, although the above-described first embodiment of
the present invention is an exhaust gas purification device applied
to the diesel engine, it is not limited to the diesel engine but
applicable to any types of engines using a NOx adsorption catalyst.
In the case of a gasoline engine, gasoline is used as an auxiliary
agent, in place of light oil.
[0069] The NOx adsorption catalyst 24 used in the above-described
exhaust gas purification device according to the first embodiment
adsorbs SOx (sulfur oxides) produced by combustion of sulfur in
fuel, which results in a deterioration in NOx adsorption function.
Thus, it is necessary to restore the deteriorated NOx adsorption
function by causing the NOx adsorption catalyst 24 to release the
SOx adsorbed by the NOx adsorption catalyst 24. The SOx adsorbed by
the NOx adsorption catalyst 24 can be released from the NOx
adsorption catalyst 24 by raising the temperature of the NOx
adsorption catalyst 24, and the temperature of the NOx adsorption
catalyst 24 can be raised by supplying light oil to the NOx
adsorption catalyst 24 by means of the light oil addition valve 32
used in the first embodiment and burning it.
[0070] Next, as a second embodiment of the present invention, an
exhaust gas purification device designed to release the SOx
adsorbed by the NOx adsorption catalyst 24 in this manner will be
described.
[0071] Since the overall system structure is as shown in FIG. 1,
namely the same as the first embodiment, the same reference signs
will be used for the same elements as those of the first
embodiment, for which a detailed description will be omitted, and
essential elements different from the first embodiment will be
mainly described bellow.
[0072] FIG. 7 shows the configuration of control blocks arranged in
an ECU 38 (control means), which carries out oil supply control for
releasing SOx.
[0073] As shown in FIG. 7, the ECU 38 includes a standard supply
quantity determination section 50 for determining standard supply
quantity Mb of the fuel required to cause the NOx adsorption
catalyst 24 to release sulfur compound adsorbed by the NOx
adsorption catalyst 24, thereby restoring the deteriorating NOx
adsorption capacity; a target supply quantity determination section
52 for determining target supply quantity Mt by correcting the
standard supply quantity Mb determined by the standard supply
quantity determination section 50, on the basis of exhaust pressure
Pex detected by the exhaust pressure sensor 30 and light oil
temperature Tf detected by the light oil temperature sensor 36; and
a supply control section 54 for controlling the light oil addition
valve 32 so that light oil is supplied into the exhaust passage in
the target supply quantity Mt determined by the target supply
quantity determination section 52.
[0074] An exhaust temperature sensor 48 for detecting the
temperature of exhaust gas entering the NOx adsorption catalyst 24
is connected to the standard supply quantity determination section
50. The standard supply quantity determination section 50 estimates
SOx accumulation quantity, i.e., the amount of SOx adsorbed by the
NOx adsorption catalyst 24, from cumulative fuel supply quantity
for each cylinder which is calculated within the ECU 38, and
determines standard supply quantity Mb of the light oil required to
raise the temperature of the NOx adsorption catalyst 24 to an
optimal temperature (600.degree. C., for example) for releasing
SOx, from a map stored in advance, on the basis of this estimated
SOx accumulation quantity and the exhaust temperature Tex detected
by the exhaust temperature sensor 48.
[0075] Like the above-described first embodiment, correction of the
standard supply quantity Mb determined by the standard supply
quantity determination section 50 and control of light oil
injection from the light oil addition valve 32 are carried out
according to a flow chart including the same steps as Steps S12 to
S22 of the flow chart of FIG. 3.
[0076] Specifically, the target supply quantity determination
section 52 receives the standard supply quantity Mb from the
standard supply quantity determination section 50 and corrects the
standard supply quantity Mb on the basis of the exhaust pressure
Pex detected by the exhaust pressure sensor 30 and the light oil
temperature Tf detected by the light oil temperature sensor 36.
[0077] The correction of the standard supply quantity Mb is
performed in the same manner as in the first embodiment. In
connection with the exhaust pressure Pex, a correction factor Rp
corresponding to the detected exhaust pressure Pex is determined
from a map stored in advance (Step S12 in FIG. 3), where the map is
prepared such that the correction factor Rp becomes smaller as the
exhaust pressure Pex increases, as shown in FIG. 4. By dividing the
standard supply quantity Mb by the correction factor Rp, the target
supply quantity determination section 52 corrects the standard
supply quantity Mb to obtain pressure-corrected supply quantity Mp
(Step S14 in FIG. 3).
[0078] By correcting the standard supply quantity Mb using the
correction factor Rp in this manner, the pressure-corrected supply
quantity Mp is greater than the standard supply quantity Mb when
the exhaust pressure Pex is higher than the exhaust pressure value
of the standard state. Thus, the shortage of supply quantity due to
an increase in exhaust pressure Pex is compensated for. Conversely,
the pressure-corrected supply quantity Mp is smaller than the
standard supply quantity Mb when the exhaust pressure Pex is lower
than the exhaust pressure value of the standard state. Thus, the
excess of supply quantity due to a decrease in exhaust pressure Pex
is obviated.
[0079] In connection with the light oil temperature Tf, a
correction factor Rt corresponding to the detected light oil
temperature Tf is determined from a map stored in advance (Step S16
in FIG. 3), where the map is prepared such that the correction
factor Rt becomes greater as the light oil temperature Tf
increases, as shown in FIG. 5. By dividing the pressure-corrected
supply quantity Mp by the correction factor Rt, the target supply
quantity determination section 52 corrects the pressure-corrected
supply quantity Mp to obtain target supply quantity Mt (Step S18 in
FIG. 3).
[0080] Here, the correction using the correction factor Rt is made
to the pressure-corrected supply quantity Mp. However, as mentioned
in respect of the first embodiment, since the pressure-corrected
supply quantity Mp results from correcting the standard supply
quantity Mb on the basis of the exhaust pressure Pex, the
correction using the correction factor Rt is essentially made to
the standard supply quantity Mb. Accordingly, by correcting the
pressure-corrected supply quantity Mp, or essentially, the standard
supply quantity Mb using the correction factor Rt in this manner,
the target supply quantity Mp becomes smaller as the light oil
temperature Tf increases. Thus, the excess of supply quantity due
to a rise in light oil temperature Tf is obviated. Conversely, the
target supply quantity Mt becomes greater as the light oil
temperature Tf decreases. Thus, the shortage of supply quantity due
to a drop in light oil temperature is compensated for.
[0081] It is to be noted that in the flow chart of FIG. 3, the
order of Steps S12, S14 and Steps S16, S18 is not limited to this,
as in the first embodiment.
[0082] Further, although in the above-described case, correction is
made by dividing the standard supply quantity Mb, the
pressure-corrected supply quantity Mp or the temperature-corrected
supply quantity by the correction factor Rp or the correction
factor Rt, it can be arranged such that the reciprocal of each
correction factor is obtained from a map stored so that correction
is made by multiplying the supply quantity by the reciprocal.
[0083] After the target supply quantity Mt of the light oil
required to cause the NOx adsorption catalyst 24 to release the
adsorbed SOx is determined in this manner, the supply control
section 54 determines, from a map stored in advance, valve open
time of the light oil addition valve 32 required for the light oil
addition valve 32 to inject light oil in the target supply quantity
Mt, in the form of duty cycle Dt (Step S20 in FIG. 3), as in the
first embodiment.
[0084] After determining the duty cycle Dt corresponding to the
target supply quantity Mt from the map, the supply control section
54 drives the light oil addition valve 32 to open according to the
duty cycle Dt thus determined (Step S22 in FIG. 3), so that light
oil in a quantity equivalent to the target supply quantity Mt is
injected from the light oil addition valve 32 into the exhaust pipe
16. Due to the exhaust heat, the light oil in the exhaust gas
decomposes into HC, which reaches the NOx adsorption catalyst and
burns. This causes a rise in temperature of the NOx adsorption
catalyst 24, so that SOx adsorbed by the NOx adsorption catalyst 24
is released properly and the NOx adsorption capacity of the NOx
adsorption catalyst 24 is restored.
[0085] As described above, in the exhaust gas purification device
according to the second embodiment of the present invention, the
amount of supply of light oil required to cause the NOx adsorption
catalyst 24 to release the adsorbed SOx, thereby maintaining the
NOx adsorption capacity of the NOx adsorption catalyst 24 is
controlled properly, without being affected by variations in
exhaust pressure and in light oil temperature. Thus, the exhaust
gas purifying function of the NOx adsorption catalyst 24 can be
stably maintained, and the emission of excess light oil into the
atmosphere can be prevented.
[0086] It is to be noted that although in the exhaust gas
purification device according to the second embodiment, the target
supply quantity Mt is determined by correcting the standard supply
quantity Mb of the light oil required to maintain the NOx
adsorption capacity of the NOx adsorption catalyst 24, on the basis
of both the exhaust pressure Pex and the light oil temperature Tf,
the correction may be made on the basis of either of them. The
control accuracy in this case is lower, compared with when the
correction is made on the basis of both the exhaust pressure Pex
and the light oil temperature Tf, but higher, compared with the
conventional exhaust gas purification device which takes account of
neither of the exhaust pressure and the light oil temperature.
[0087] Further, although in the above-described case, the standard
supply quantity Mb of the light oil required to cause the NOx
adsorption catalyst 24 to release SOx is determined from a map
stored in advance, on the basis of the cumulative fuel supply
quantity for each cylinder and the exhaust temperature Tex, the way
to determine the standard supply quantity Mb is not limited to
this. There are a variety of known techniques that can be used.
[0088] It is also possible to arrange the first embodiment of the
exhaust gas purification device to also carry out the SOx release
control in the second embodiment, in a manner such that the supply
of the light oil for release and reduction of NOx and the supply of
the light oil for release of SOx are both carried out by means of
the same light oil addition valve 32.
[0089] Further, although the above-described second embodiment of
the present invention is an exhaust gas purification device applied
to the diesel engine, it is not limited to the diesel engine but
applicable to any types of engines using an NOx adsorption
catalyst. In the case of a gasoline engine, gasoline is used as an
auxiliary agent, in place of light oil.
[0090] Next, referring to FIGS. 8 to 11, a third embodiment of the
present invention will be described.
[0091] FIG. 8 shows the structure of an exhaust gas purification
device according to the third embodiment of the present invention.
The structure of an engine, which forms a base for the exhaust gas
purification device, and an intake system of the engine is the same
as that for the first embodiment. In FIG. 8, the same reference
signs are used for the same elements as those of the first
embodiment.
[0092] In an exhaust pipe 16 connected to an exhaust manifold (not
shown) of an engine, a turbine (not shown) of a turbocharger is
incorporated, and downstream of the turbine, a selective reduction
type NOx catalyst (hereinafter referred to as an SCR catalyst) 56
as an exhaust gas purification means is connected to the exhaust
pipe 16. The SCR catalyst 56 promotes denitration reaction between
ammonia and NOx contained in exhaust gas to selectively reduce NOx,
namely convert NOx to unharmful substances.
[0093] An exhaust throttle valve 28 functioning as an exhaust brake
is provided upstream of the SCR catalyst 56, and an exhaust
pressure sensor (exhaust pressure detection means) 30 for detecting
exhaust pressure in the exhaust pipe 16 is provide upstream of the
exhaust throttle valve 28.
[0094] Further, in order to supply ammonia required for conversion
of NOx to the SCR catalyst 56, a urea water addition valve
(auxiliary agent supply means) 58 for injecting urea water as an
auxiliary agent into the exhaust pipe 16 is provided upstream of
the exhaust throttle valve 28. The urea water addition valve 58 is
a solenoid valve designed to be opened to inject urea water by
energizing a solenoid, and closed to stop injecting the urea water
by stopping energizing the solenoid. Thus, when urea water supply
pressure is fixed, urea water is supplied into the exhaust pipe 16
in the amount corresponding to the time of energizing the urea
water addition valve 58.
[0095] Due to the heat of the exhaust gas, the urea water injected
from the urea water addition valve 58 into the exhaust pipe 68
hydrolyzes into ammonia, which is supplied to the SCR catalyst 56
and used for conversion of NOx.
[0096] Urea water is supplied to the urea water addition valve 58
from a urea water storage tank (not shown), through a urea water
supply passage 60. A urea water temperature sensor (auxiliary agent
temperature detection means) 62 for detecting the temperature of
the urea water supplied to the urea water addition valve 58 is
provided to the urea water supply passage 60.
[0097] An upstream exhaust temperature sensor 64 for detecting the
temperature of exhaust gas entering the SCR catalyst 56 is provided
to the exhaust pipe 16, upstream of the SCR catalyst 56. Further, a
downstream exhaust temperature sensor 66 for detecting the
temperature of exhaust gas exiting the SCR catalyst 56 is provided
to the exhaust pipe 16, downstream of the SCR catalyst 56.
[0098] As in the above-described first embodiment, to the input of
an ECU (control means) 38, which is a control device for performing
general control on the exhaust gas purification device according to
the present invention, including control on the engine, there are
connected a variety of sensors including the exhaust pressure
sensor 30, the urea water temperature sensor 62, the upstream
exhaust temperature sensor 64 and the downstream exhaust
temperature sensor 66 to collect information required for a variety
of controls. To the output of the ECU 38, there are connected a
variety of devices including the fuel injection valve (not shown)
for each cylinder and the urea water addition valve 58, which
devices are controlled on the basis of control variable values
determined in the ECU 38.
[0099] In the exhaust gas purification device having the
configuration described above, exhaust gas exhausted from the
engine is introduced through the exhaust pipe 16 into the SCR
catalyst 56, while the urea water injected from the urea water
addition valve 58 into the exhaust pipe 68 hydrolyzes into ammonia
due to the heat of the exhaust gas, and the ammonia is supplied to
the SCR catalyst 56. On the SCR catalyst 56, denitration reaction
between ammonia and NOx in exhaust gas is promoted, so that NOx is
converted to unharmful substances.
[0100] By supplying urea water into the exhaust pipe 16 as an
auxiliary agent in this manner, the exhaust gas purifying function
of the SCR catalyst 56 is maintained.
[0101] Next, referring to FIGS. 9 to 12, control of urea water
supply from the urea water addition valve 58 will be described.
[0102] FIG. 9 shows the configuration of control blocks arranged in
the ECU 38 for carrying out the urea water supply control, and FIG.
10 is a flow chart showing the urea water supply control.
[0103] As shown in FIG. 9, the ECU 38 includes a standard supply
quantity determination section 68 for determining standard supply
quantity Mb of the urea water required for the SCR catalyst 56 to
selectively reduce NOx contained in exhaust gas; a target supply
quantity determination section 70 for determining target supply
quantity Mt by correcting the standard supply quantity Mb
determined by the standard supply quantity determination section
68, on the basis of exhaust pressure Pex detected by the exhaust
pressure sensor 30 and urea water temperature Tu detected by the
urea water temperature sensor 62; and a supply control section 72
for controlling the urea water addition valve 58 so that urea water
is supplied into the exhaust pipe 16 in the target supply quantity
Mt determined by the target supply quantity determination section
70.
[0104] More specifically, exhaust temperature Texu upstream of the
SCR catalyst 56 detected by the upstream exhaust temperature sensor
64, exhaust temperature Texd downstream of the SCR catalyst 56
detected by the downstream exhaust temperature sensor 66, and
engine revolution speed Ne detected by the revolution speed sensor
46 are fed to the standard supply quantity determination section
68. From a map stored in advance, standard supply quantity Mb of
the urea water required for the SCR catalyst 56 to selectively
reduce NOx contained in exhaust gas is determined on the basis of
fuel supply quantity for each cylinder which is calculated within
the ECU 38, estimated NOx emission quantity and NOx conversion
ratio which are determined from maps stored in advance, exhaust
temperature Texu, exhaust temperature Texd and engine revolution
speed Ne which are fed from the above-mentioned sensors, etc. (Step
S110 in FIG. 10).
[0105] The above-mentioned technique for the standard supply
quantity determination section 68 to determine the standard supply
quantity Mb is in itself publicly known, and the manner of
determining the standard supply quantity Mb of the urea water
required for the SCR catalyst 56 to selectively reduce NOx
contained in exhaust gas is not limited to this.
[0106] The standard supply quantity Mb determined by the standard
supply quantity determination section 68 is sent to the target
supply quantity determination section 70. To the target supply
quantity determination section 70, exhaust pressure Pex detected by
the exhaust pressure sensor 30 and urea water temperature Tu
detected by the urea water temperature sensor 62 are fed, and the
target supply quantity determination section 70 corrects the
standard supply quantity Mb on the basis of these exhaust pressure
Pex and urea water temperature Tu.
[0107] As in the first embodiment, the amount of urea water
injected from the urea water addition valve 58 is regulated by
varying the valve open time of the urea water addition valve 58,
where the amount of urea water injected into the exhaust pipe 16
increases as the valve open time becomes longer. Accordingly, when
the urea water supply pressure is fixed, the amount of urea water
actually supplied into the exhaust pipe 16 in the same valve open
time becomes smaller as the exhaust pressure increases. Further,
urea water has lower viscosity in the case where the temperature of
urea water is higher, compared with the case where the temperature
of urea water is lower. Accordingly, the amount of urea water
actually supplied into the exhaust pipe 16 in the same valve open
time becomes greater as the urea water temperature increases.
[0108] Thus, in connection with the exhaust pressure Pex, a
correction factor Rp corresponding to the detected exhaust pressure
Pex is determined from a map stored in advance (Step S112 in FIG.
10), where the map is prepared such that the correction factor Rp
becomes smaller as the exhaust pressure Pex increases, as shown in
FIG. 11. By dividing the standard supply quantity Mb by the
correction factor Rp, the target supply quantity determination
section 70 corrects the standard supply quantity Mb to obtain
pressure-corrected supply quantity Mp (Step S114 in FIG. 10).
[0109] It is to be noted that the correction factor Rp is set to
1.0 in a standard state in which the exhaust pressure is equal to
the exhaust pressure value based on which the map used to determine
the standard supply quantity Mb is set.
[0110] By correcting the standard supply quantity Mb using the
correction factor Rp in this manner, the pressure-corrected supply
quantity Mp is greater than the standard supply quantity Mb when
the exhaust pressure Pex is higher than the exhaust pressure value
of the standard state. Thus, the shortage of supply quantity due to
an increase in exhaust pressure Pex is compensated for. Conversely,
the pressure-corrected supply quantity Mp is smaller than the
standard supply quantity Mb when the exhaust pressure Pex is lower
than the exhaust pressure value of the standard state. Thus, the
excess of supply quantity due to a decrease in exhaust pressure Pex
is obviated.
[0111] Next, in connection with the urea water temperature Tu, a
correction factor Rt corresponding to the detected urea water
temperature Tu is determined from a map stored in advance (Step
S116 in FIG. 10), where the map is prepared such that the
correction factor Rt becomes greater as the urea water temperature
Tu increases, as shown in FIG. 12. By dividing the
pressure-corrected supply quantity Mp by the correction factor Rt,
the target supply quantity determination section 70 corrects the
pressure-corrected supply quantity Mp to obtain target supply
quantity Mt (Step S118 in FIG. 10).
[0112] It is to be noted that the correction factor Rt is set to
1.0 in a standard state in which the urea water temperature is
equal to the urea water temperature value based on which the map
used to determine the standard supply quantity Mb is set.
[0113] Here, the correction using the correction factor Rt is made
to the pressure-corrected supply quantity Mp. However, since the
pressure-corrected supply quantity Mp results from correcting the
standard supply quantity Mb on the basis of the exhaust pressure
Pex as mentioned above, the correction using the correction factor
Rt is essentially made to the standard supply quantity Mb.
Accordingly, by correcting the pressure-corrected supply quantity
Mp, or essentially, the standard supply quantity Mb using the
correction factor Rt in this manner, the target supply quantity Mt
becomes smaller as the urea water temperature Tu increases. Thus,
the excess of supply quantity due to a rise in urea water
temperature Tf is obviated. Conversely, the target supply quantity
Mp becomes greater as the urea water temperature Tu decreases.
Thus, the shortage of supply quantity due to a drop in urea water
temperature Tu is compensated for.
[0114] In the flow chart of FIG. 10, as stated above, first at
Steps S112 and S114, the pressure-corrected supply quantity Mp is
obtained by correcting the standard supply quantity Mb on the basis
of the exhaust pressure Pex, and then at Steps S116 and S118, the
target supply quantity Mt is determined by correcting the
pressure-corrected supply quantity Mp on the basis of the urea
water temperature Tu. It is to be noted, however, that the order of
the steps is not limited to this, like the first embodiment.
[0115] For example, Steps S112 and S114 can be interchanged with
Steps S116 and S118. Specifically, it can be arranged such that
first, temperature-corrected supply quantity is obtained by
correcting the standard supply quantity Mb using the correction
factor Rt corresponding to the urea water temperature Tu, and then
the target supply quantity Mt is obtained by correcting the
temperature-corrected supply quantity using the correction factor
Rp corresponding to the exhaust pressure Pex.
[0116] Alternatively, it can be arranged such that first, the
correction factor Rp corresponding to the exhaust pressure Pex and
the correction factor Rt corresponding to the urea water
temperature Tu are determined from the respective maps, and then,
the target supply quantity Mt is obtained by dividing the standard
supply quantity Mb by the correction factors Rp and Rt,
successively.
[0117] Further, although in the above-described case, correction is
made by dividing the standard supply quantity Mb, the
pressure-corrected supply quantity Mp or the temperature-corrected
supply quantity by the correction factor Rp or the correction
factor Rt, it can be arranged such that the reciprocal of each
correction factor is obtained from a map stored in advance so that
correction is made by multiplying the supply quantity by the
reciprocal.
[0118] After the target supply quantity Mt of the urea water
required for the SCR catalyst 56 to selectively reduce NOx is
determined in this manner, the supply control section 72
determines, from a map stored in advance, valve open time of the
urea water addition valve 58 required for the urea water addition
valve 58 to inject urea water in the target supply quantity Mt
(Step S120 in FIG. 10). As in the first embodiment, since the
control on the urea water addition valve 58 is performed in control
cycles of a predetermined period, the map is prepared to give the
valve open time of the urea water addition valve 58 corresponding
to the target supply quantity Mt, in the form of duty cycle Dt
relative to the maximum valve open time in one control cycle.
Although graphical representation is omitted, the relation between
the target supply quantity Mt and the duty cycle Dt is a
proportional one similar to that shown in FIG. 6 in respect of the
first embodiment.
[0119] After determining the duty cycle Dt corresponding to the
target supply quantity Mt from the map, the supply control section
72 drives the urea water addition valve 58 to open according to the
determined duty cycle Dt (Step S122 in FIG. 10), so that urea water
in a quantity equivalent to the target supply quantity Mt is
injected from the urea water addition valve 58 into the exhaust
pipe 16. Due to the heat of the exhaust gas, the urea water
injected into the exhaust pipe 16 in this manner hydrolyzes into
ammonia, which acts as a reducing agent to selectively reduce NOx
contained in exhaust gas on the SCR catalyst 56.
[0120] It is to be noted that the exhaust pressure sensor 30 is
disposed upstream of the exhaust throttle valve 28. Thus, even when
the pressure in the exhaust pipe 16 varies due to the opening and
closing of the exhaust throttle valve 28, urea water is always
supplied properly in the amount required for the SCR catalyst 56 to
selectively reduce NOx, in spite of variations in pressure in the
exhaust pipe 16, since, as mentioned above, the standard supply
quantity Mb is corrected on the basis of the exhaust pressure Pex
detected by this exhaust pressure sensor 30.
[0121] As described above, in the exhaust gas purification device
according to the third embodiment of the present invention, the
amount of supply of urea water required for the SCR catalyst 56 to
selectively reduce NOx contained in exhaust gas, thereby
maintaining its NOx conversion capacity is controlled properly,
without being affected by variations in exhaust pressure and in
urea water temperature. Thus, the exhaust gas purifying function
can be stably maintained, and the emission of excess urea water or
ammonia into the atmosphere can be prevented.
[0122] It is to be noted that although in the above-described
exhaust gas purification device according to the third embodiment,
the target supply quantity Mt is determined by correcting the
standard supply quantity Mb of the urea water required to maintain
the NOx conversion capacity of the SCR catalyst 56, on the basis of
both the exhaust pressure Pex and the urea water temperature Tu,
the correction can be made on the basis of either of them. The
control accuracy in this case is lower, compared with when the
correction is made on the basis of both the exhaust pressure Pex
and the urea water temperature Tu, but higher, compared with the
conventional exhaust gas purification device which takes account of
neither of the exhaust pressure and the urea water temperature.
[0123] Further, although the above-described third embodiment of
the present invention is an exhaust gas purification device applied
to the diesel engine, it is not limited to the diesel engine but
applicable to any types of engines using an SCR catalyst to
selectively reduce NOx contained in exhaust gas by supplying urea
water.
[0124] Next, referring to FIGS. 13 to 14, an exhaust gas
purification device according to a fourth embodiment of the present
invention will be described.
[0125] FIG. 13 shows the structure of an exhaust gas purification
device according to the fourth embodiment of the present invention.
The structure of an engine, which forms a base for the exhaust gas
purification device, and an intake system is the same as that for
the first embodiment. In FIG. 13, the same reference signs are used
for the same elements as those of the first embodiment.
[0126] In an exhaust pipe 16 connected to an exhaust manifold (not
shown) of an engine, a turbine (not shown) of a turbocharger is
incorporated, and downstream of the turbine, an exhaust
after-treatment device 74 is connected to the exhaust pipe 16.
[0127] The exhaust after-treatment device 74 has a casing, within
which an oxidation catalyst 76 is disposed on the upstream side and
a DPF (diesel particulate filter) 78 as an exhaust gas purification
means is disposed downstream of the oxidation catalyst 76. The DPF
78 has a porous honeycomb structure made of ceramic, and has a
function of trapping particulate matter contained in exhaust gas
when the exhaust gas flows through it.
[0128] The particulate matter trapped by the DPF 78 accumulates on
the DPF 78, which causes a gradual decrease in the trap capacity of
the DPF 78 and an increase in resistance exerted on the flowing
exhaust gas. Thus, it is necessary to burn off the particulate
matter when the accumulation of the particulate matter reaches a
certain level, thereby maintaining the trap capacity of the DPF 78.
In order to raise the exhaust temperature to a level at which the
particulate matter can be burned off, the oxidation catalyst 76 is
used. Specifically, light oil is supplied as an auxiliary agent to
the oxidation catalyst 76 in a manner described later and burned,
and this combustion of light oil raises the exhaust temperature, so
that the particulate matter accumulated in the DPF 78 is removed by
burning.
[0129] To the after-treatment device 74, an inlet temperature
sensor 80 for detecting exhaust temperature Tin at the inlet side
of the DPF 78 and an inlet pressure sensor 82 for detecting exhaust
pressure Pin at the inlet side of the DPF 78 are provided between
the oxidation catalyst 76 and the DPF 78, and an outlet pressure
sensor 84 for detecting exhaust pressure Pout at the outlet side of
the DPF 78 is provided downstream of the DPF 78.
[0130] Upstream of the exhaust after-treatment device 74, an
exhaust throttle valve 28 functioning as an exhaust brake is
provided, and upstream of the exhaust throttle valve 28, an exhaust
pressure sensor (exhaust pressure detection means) 30 for detecting
exhaust pressure in the exhaust pipe 16 is provided.
[0131] Further, in order to supply the light oil required to burn
off the particulate matter accumulated in the DPF 78, to the
oxidation catalyst 76, a light oil addition valve (auxiliary agent
supply means) 32 for injecting light oil as an auxiliary agent into
the exhaust pipe 16 is provided upstream of the exhaust throttle
valve 28. This light oil addition valve 32 is of the same type as
that used in the first embodiment, and designed to be opened to
inject light oil by energizing a solenoid, and closed to stop
injecting the light oil by stopping energizing the solenoid. Thus,
when light oil supply pressure is fixed, light oil is supplied into
the exhaust pipe 16 in the amount according to the time of
energizing the light oil addition valve 32.
[0132] The same light oil as that supplied to each cylinder of the
engine is supplied to the light oil addition valve 32 through a
light oil supply passage 34. A light oil temperature sensor
(auxiliary agent temperature detection means) 36 for detecting the
temperature of the light oil supplied to the light oil addition
valve 32 is provided to the light oil supply passage 34.
[0133] As in the first embodiment, to the input of an ECU (control
means) 38, which is a control device for performing general control
on the exhaust gas purification device according to the present
invention, including control on the engine, there are connected a
variety of sensors including the exhaust pressure sensor 30, the
inlet temperature sensor 80, the inlet pressure sensor 82 and the
outlet temperature sensor 84 to collect information required for a
variety of controls. To the output of the ECU 38, there are
connected a variety of devices including the fuel injection valve
(not shown) for each cylinder and the light oil addition valve 32,
which devices are controlled on the basis of control variable
values determined in the ECU 38.
[0134] In the exhaust gas purification device having the
configuration described above, exhaust gas exhausted from the
engine is introduced through the exhaust pipe 16 into the exhaust
after-treatment device 74, and when the exhaust gas flows through
the DPF 78, particulate matter contained in the exhaust gas is
trapped and accumulated in the DPF 78. When, from a difference
between a value detected by the inlet pressure sensor 82 and a
value detected by the outlet pressure sensor 84, etc., it is
determined that the amount of particulate matter accumulated in the
DPF 78 has reached a predetermined level, light oil is injected
from the light oil addition valve 32 into the exhaust pipe 16, as
an auxiliary agent. Due to the heat of the exhaust gas, the light
oil injected decomposes into HC, which is supplied to the oxidation
catalyst 76, and oxidation reaction of the HC is promoted by the
oxidation catalyst so that the HC burns. This combustion of HC
raises the exhaust gas entering the DPF 78 to a temperature suited
for burning-off of the particulate matter accumulated in the DPF 78
(500.degree. C., for example). Consequently, the particulate matter
accumulated in the DPF 78 is removed, so that the particulate trap
function that has lowered is restored and the exhaust gas purifying
function of the DPF 78 is maintained.
[0135] Next, referring to FIG. 14, control of light oil supply from
the light oil addition valve 32 will be described. FIG. 14 shows
the configuration of control blocks arranged in the ECU 38 for
carrying out the light oil supply control.
[0136] As shown in FIG. 14, the ECU 38 includes a standard supply
quantity determination section 86 for determining standard supply
quantity of the light oil required to burn off particulate matter
trapped by the DPF 78, thereby regenerating the DPF 78; a target
supply quantity determination section 88 for determining target
supply quantity Mt by correcting the standard supply quantity Mb
determined by the standard supply quantity determination section
86, on the basis of exhaust pressure Pex detected by the exhaust
pressure sensor 30 and light oil temperature Tf detected by the
light oil temperature sensor 62; and a supply control section 90
for controlling the light oil addition valve 32 so that light oil
is supplied into the exhaust pipe 16 in the target supply quantity
Mt determined by the target supply quantity determination section
88.
[0137] More specifically, exhaust pressure Pin at the inlet side of
the DPF 78, which is detected by the inlet pressure sensor 82,
exhaust pressure Pout at the outlet side of the DPF 78, which is
detected by the outlet pressure sensor 84, and exhaust temperature
Tin at the inlet side of the DPF 78, which is detected by the inlet
temperature sensor 80, are fed to the standard supply quantity
determination section 86. From a map stored in advance, the
standard supply quantity determination section 86 determines
standard supply quantity Mb of the light oil required to raise the
temperature of exhaust gas entering the DPF 78 to burn off
particulate matter on the basis of the amount of accumulated
particulate matter, which is estimated from a difference between
the exhaust pressure Pin and the exhaust pressure Pout, and the
exhaust temperature Tin.
[0138] The manner of determining the standard supply quantity Mb is
not limited to this. There are a variety of known techniques that
can be used.
[0139] As in the first embodiment, correction of the standard
supply quantity Mb determined by the standard supply quantity
determination section 86 and control of light oil injection from
the light oil addition valve 32 are carried out according a flow
chart including the same steps as Steps S12 to S22 of the flow
chart of FIG. 3.
[0140] Specifically, the standard supply quantity Mb determined by
the standard supply quantity determination section 86 is sent to
the target supply quantity determination section 88. To the target
supply quantity determination section 88, exhaust pressure Pex
detected by the exhaust pressure sensor 30 and light oil
temperature Tf detected by the light oil temperature sensor 36 are
fed, and the target supply quantity determination section 88
corrects the standard supply quantity Mb on the basis of these
exhaust pressure Pex and light oil temperature Tf.
[0141] The correction of the standard supply quantity Mb is
performed in the same manner as in the first embodiment. In
connection with the exhaust pressure Pex, a correction factor Rp
corresponding to the detected exhaust pressure Pex is determined
from a map stored in advance (Step S12 in FIG. 3), where the map is
prepared such that the correction factor Rp becomes smaller as the
exhaust pressure Pex increases, as shown in FIG. 4. By dividing the
standard supply quantity Mb by the correction factor Rp, the target
supply quantity determination section 88 corrects the standard
supply quantity Mb to obtain pressure-corrected supply quantity Mp
(Step S14 in FIG. 3).
[0142] By correcting the standard supply quantity Mb using the
correction factor Rp in this manner, the pressure-corrected supply
quantity Mp is greater than the standard supply quantity Mb when
the exhaust pressure Pex is higher than the exhaust pressure value
in the standard state. Thus, the shortage of supply quantity due to
an increase in exhaust pressure Pex is compensated for. Conversely,
the pressure-corrected supply quantity Mp is smaller than the
standard supply quantity Mb when the exhaust pressure Pex is lower
than the exhaust pressure value in the standard state. Thus, the
excess of supply quantity due to a decrease in exhaust pressure Pex
is obviated.
[0143] In connection with the light oil temperature Tf, a
correction factor Rt corresponding to the detected light oil
temperature Tf is determined from a map stored in advance (Step S16
in FIG. 3), where the map is prepared such that the correction
factor Rt becomes greater as the light oil temperature Tf
increases, as shown in FIG. 5. By dividing the pressure-corrected
supply quantity Mp by the correction factor Rt, the target supply
quantity determination section 88 corrects the pressure-corrected
supply quantity Mp to obtain target supply quantity Mt (Step S18 in
FIG. 3).
[0144] Here, the correction using the correction factor Rt is made
to the pressure-corrected supply quantity Mp. However, as mentioned
in respect of the first embodiment, since the pressure-corrected
supply quantity Mp results from correcting the standard supply
quantity Mb on the basis of the exhaust pressure Pex, the
correction using the correction factor Rt is essentially made to
the standard supply quantity Mb. Accordingly, by correcting the
pressure-corrected supply quantity Mp, or essentially, the standard
supply quantity Mb using the correction factor Rt in this manner,
the target supply quantity Mp becomes smaller as the light oil
temperature Tf increases. Thus, the excess of supply quantity due
to a rise in light oil temperature Tf is obviated. Conversely, the
target supply quantity Mt becomes greater as the light oil
temperature Tf decreases. Thus, the shortage of supply quantity due
to a drop in light oil temperature is compensated for.
[0145] In the flow chart of FIG. 3, as stated above, first at Steps
S12 and S14, the pressure-corrected supply quantity Mp is obtained
by correcting the standard supply quantity Mb on the basis of the
exhaust pressure Pex, and then at Steps S16 and S18, the target
supply quantity Mt is determined by correcting the
pressure-corrected supply quantity Mp on the basis of the light oil
temperature Tf. It is to be noted, however, that the order of the
steps is not limited to this, like the first embodiment.
[0146] Alternatively, it can be arranged such that first, the
correction factor Rp corresponding to the exhaust pressure Pex and
the correction factor Rt corresponding to the light oil temperature
Tf are determined from the respective maps, and then, the target
supply quantity Mt is obtained by dividing the standard supply
quantity Mb by the correction factors Rp and Rt, successively.
[0147] Further, although in the above-described case, correction is
made by dividing the standard supply quantity Mb, the
pressure-corrected supply quantity Mp or the temperature-corrected
supply quantity by the correction factor Rp or the correction
factor Rt, it can be arranged such that the reciprocal of each
correction factor is obtained from a map stored in advance so that
correction is made by multiplying the supply quantity by the
reciprocal.
[0148] After the target supply quantity Mt of the light oil
required to remove the particulate matter accumulated in the DPF 78
by burning is determined in this manner, the supply control section
90 determines, from a map stored in advance, valve open time of the
light oil addition valve 32 required for the light oil addition
valve 32 to inject light oil in the target supply quantity Mt (Step
S20 in FIG. 3). As in the first embodiment, since the control on
the light oil addition valve 32 is performed in control cycles of a
predetermined period, the map is prepared to give the valve open
time of the light oil addition valve 32 corresponding to the target
supply quantity Mt, in the form of duty cycle Dt relative to the
maximum valve open time in one control cycle, as shown in FIG.
6.
[0149] After determining the duty cycle Dt corresponding to the
target supply quantity Mt from the map, the supply control section
90 drives the light oil addition valve 32 to open according to the
determined duty cycle Dt (Step S22 in FIG. 3), so that light oil in
a quantity equivalent to the target supply quantity Mt is injected
from the light oil addition valve 32 into the exhaust pipe 16. Due
to the heat of the exhaust gas, the light oil injected into the
exhaust pipe 16 in this manner decomposes into HC, and oxidation
reaction of the HC is promoted on the oxidation catalyst 76 so that
the HC burns to raise the exhaust temperature. The exhaust gas
raised in temperature by the combustion of HC flows through the DPF
78, and thereby the particulate matter accumulated in the DPF 78 is
burned off so that the particulate trap capacity of the DPF 78 is
restored.
[0150] It is to be noted that the exhaust pressure sensor 30 is
disposed upstream of the exhaust throttle valve 28. Thus, even when
the pressure in the exhaust pipe 16 varies due to the opening and
closing of the exhaust throttle valve 28, light oil is always
supplied properly in the amount required for burning-off of the
particulate matter accumulated in the DPF 78, in spite of
variations in pressure in the exhaust pipe 16, since, as mentioned
above, the standard supply quantity Mb is corrected on the basis of
the exhaust pressure Pex detected by this exhaust pressure sensor
30.
[0151] As described above, in the exhaust gas purification device
according to the fourth embodiment of the present invention, the
amount of supply of light oil required to raise the exhaust
temperature to remove the particulate matter accumulated in the DPF
78 by burning to thereby maintain the particulate trap capacity of
the DPF 78 is controlled properly, without being affected by
variations in exhaust pressure and in light oil temperature. Thus,
the exhaust gas purifying function can be stably maintained, and
the emission of excess light oil into the atmosphere can be
prevented.
[0152] It is to be noted that although in the above-described
exhaust gas purification device according to the fourth embodiment,
the target supply quantity Mt is determined by correcting the
standard supply quantity Mb of the light oil required to maintain
the particulate trap capacity of the DPF 78, on the basis of both
the exhaust pressure Pex and the light oil temperature Tf, the
correction may be made on the basis of either of them. The control
accuracy in this case is lower, compared with when the correction
is made on the basis of both the exhaust pressure Pex and the light
oil temperature Tf, but higher, compared with the conventional
exhaust gas purification device which takes account of neither of
the exhaust pressure and the light oil temperature.
[0153] Further, although the above-described fourth embodiment of
the present invention is an exhaust gas purification device applied
to the diesel engine, it is not limited to the diesel engine but
applicable to any types of engines designed to remove particulate
matter from exhaust gas by means of a DPF.
[0154] In the above, embodiments of the present invention has been
described. The present invention is, however, not limited to the
above-described embodiments. When applied to any exhaust gas
purification device designed to supply an auxiliary agent for
maintaining the exhaust gas purifying function of an exhaust gas
purification means, into an exhaust passage, upstream of the
exhaust gas purification means, the present invention can produce
similar positive effects.
* * * * *