DESCRIPTION
EXHAUST EMISSION CONTROL DEVICE OF DIESEL ENGINE
TECHNICAL FIELD
[0001]
The present invention relates to an exhaust emission
control device of a diesel engine, and particularly relates to
regeneration control of a diesel particulate_^filter
(hereinafter abbreviated as DPF) which collects particulate
matter (hereinafter abbreviated as PM) contained in exhaust
gas.
BACKGROUND ART
[0002] I
In emission control of a diesel engine, a reduction in

PM is as important as a reduction in NOx. As a technique
effective for the reduction, DPF is well known.
The DPF is a PM collection device which uses a filter.
In an engine operation state where an exhaust gas temperature
isvlow, the PM is continuously accumulated in the DPF so that
forced regeneration in which a temperature is forcibly
increased and the PM is thereby burnt is performed.
[0003]
In the forced regeneration of the DPF, late post injection
(an injection timing is retarded and combustion is not caused

in a cylinder) in which the PM is injected into a cylinder is
performed, oxidation reaction is caused in a diesel oxidation
catalyst (hereinafter abbreviated as DOC) disposed at a stage
prior to the DPF, the temperature in the part of the DPF is
increased to a high temperature by heat of reaction, and the
PM accumulated in the DPF is thereby burnt.
Consequently, the temperature needs to be increased to
the high temperature and, in terms of reducing a forced
regeneration time period of the DPF, the temperature of gas
passing through the DPF needs to be maintained as high as
possible. However, when the temperature of the exhaust gas
passing through the DPF is increased to the high temperature
in a state where a large amount of the PM is accumulated in the
DPF, there is danger that a large amount of the PM is burnt at

once and the temperature is excessively increased.
On the other hand, when the gas temperature is set to a
low value, the regeneration time period is prolonged and danger
that late post injection fuel is dropped into an oil pan from
the wall surface in the cylinder and an oil dilution quantity
is^.increased is enhanced.
[00Q4]
Accordingly, various improvements and proposals such as
control in which an inlettemperature of the DPF is constantly
maintained at. a target inlet temperature and control in which
the target inlet temperature is changed in accordance with the
2

regeneration state of the DPF have been made.
For example, Japanese Patent Application Laid-open No.
2007-239470 (Patent Document 1) discloses that an inlet
temperature target value of the DPF is determined based on any
of a soot accumulation quantity, a soot accumulation quantity
change rate, a DPF temperature, and a DPF temperature change
rate.
[0005] ..,.^*
In addition, Japanese Patent No. 3951619 (Patent Document
2) discloses a technique in which a target DPF inlet temperature
is stepwise changed such that the target temperature is
increased to the target temperature at the next step when the
target DPF inlet temperature is maintained for a predetermined
period of time or longer. I
[0006]
Further, Japanese Patent Application Laid-open No.
2009-138702 (Patent Document 3) discloses that a period of time ,
elapsed since start of the forced regeneration of the DPF is
measured, a DPF inlet temperature target value is set to a lower
value as the measured period of time is shorter, and a forced
regeneration unit sets the injection quantity of sub fuel
injection in accordance with the target temperature to perform
the sub fuel injection.
[0007]
Patent Document 1: Japanese Patent Application Laid-open
3
11-445PCT
^ No. 2007-239740
Patent Document 2: Japanese Patent No. 3951619
Patent Document 3: Japanese Patent Application Laid-open
No. 2009-138702
[0008]
However, when the target temperature is set in accordance
with the regeneration elapsed time period, there are cases where
the actual DPF temperature is completely diXSerent from the
target temperature due to a difference in operation condition,
and hence it is difficult to perform stable control. In
addition, in the method using the PM accumulation quantity, it
is necessary to estimate the PM accumulation quantity so that
the method greatly depends on accuracy in estimation, and hence
there is a problem that control logic becomes coit|plicated.
t •
DISCLOSURE OF THE INVENTION
__- _ — ^ . b
[0009]
The present invention has been achieved in view of the
problems, .and an object thereof is to provide an exhaust
emission control device of a diesel engine capable of increasing
the DPF temperature to reduce the regeneration time period in
order to reduce the oil dilution quantity, and reducing the
danger of an excessive temperature increase of the DPF in the
forced regeneration of the DPF.
[0010]
4
, 11-445PCT
In order to solve the problems described above, the :
present invention is an exhaust emission control device of a
diesel engine including a diesel oxidation catalyst (DOC) and
a diesel particulate filter (DPP) which collects particulate
matter (PM) in an exhaust passage and performing regeneration
on the PM collected in the DPF, the exhaust emission control
device including a regeneration control unit which increases,
when an accumulation quantity of the PM exceeds^ predetermined
value, a temperature of the DPF to a temperature in a vicinity
of a predetermined target set temperature to burn and remove
the accumulated PM by controlling a temperature increase unit,
the regeneration control unit including a late post fuel
injection control unit which injects fuel into a combustion
chamber at a timing when no contribution is made to c|pmbustion,
the late post fuel injection control unit including a DPF target
temperature setting unit which sets a target value of a DPF
temperature including an inlet temperature, an exit temperature, ^
or an internal temperature of the DPF, and a calculation portion
which calculates a late post injection quantity command value
based on a deviation between the target value of the DPF
temperature set by the DPF target temperature setting unit and
an actual DPF temperature, the DPF target temperature setting
unit including a temperature increase rate setting portion
which sets a temperature increase change rate such that, until
-
the target set temperature at which the PM is burnt is reached
5
11-445PCT
^ after start of late post injection, the temperature increase •
change rate is',reduced in accordance with an increase in
temperature or a period of time elapsed since the start of the
late post injection, and a targ'et temperature of the DPF
temperature being calculated based on the temperature increase
rate from the temperature increase rate setting portion.
[0011]
According to the invention described ab&5?«, since the DPF
target temperature setting unit includes the temperature
increase rate calculation portion which sets the temperature
increase change rate such that, until the target set temperature
at which the PM is burnt is reached after the start of the late
post injection, the temperature increase change rate is reduced
in accordance with the period of time elapsed sinc$ the start
of the late post injection or the increase in DPF temperature,
Iand
the target temperature of the DPF temperature is calculated ^
based on the temperature increase rate from the temperature ;
increase rate calculation portion, when the DPF temperature,^
e.g., the DPF inlet temperature is low (e.g., about 300°C) , the
target temperature is quickly increased and, when the DPF inlet ',
temperature is high (e.g., about 570°C) , the target temperature
is slowly increased.
With this arrangement, it is possible to quickly attain
the target set temperature (610 to 650°C) as the combustion
6 j
, 11-445PCT
temperature of the DPF, prevent an excessive temperature j
increase, and reduce an oil dilution quantity while reducing
the danger of the excessive temperature increase of the DPF.
A - " •
In addition, even when an operation condition is changed
and temperature increase characteristics are changed
accordingly, the change rate of the target temperature
determined by the temperature increase rate setting portion is
determined and the target temperature is deiajsained by using
the change rate, and hence it is possible to stably attain the
target set temperature and stably perform temperature increase
control.
[0012]
In addition, in the invention described above, the
temperature increase rate setting portion of the |DPF target
temperature set'ting unit may preferably include a first
temperature increase rate setting portion which sets the
temperature increase change rate of the target temperature such ,
that the temperature increase change rate of the target
temperature is stepwise or continuously reduced in accordance
with the increase in temperature.
Specifically, the stepwise temperature increase change
rate in the first temperature increase rate setting portion may
preferably include two stages of a first-stage change rate and
a second-stage change rate lower than the first-stage change
rate, the target set temperature may preferably correspond to
7
, 11-445PCT
•- I*
#
the DPF inlet temperature of 610 to 650°C, and a switching
temperature at iwhich the change rate is switched between the
first-stage and second-stage change rates may preferably
correspond to the DPF inlet temperature of 500 to 600°C.
[0013]
In this manner, the switching temperature of the, changerate
is set to the DPF inlet temperature of 500 to 600°C, the
target temperature is quickly increased at the first-stage
change rate until the DPF inlet temperature reaches the
switching temperature, and the target temperature is slowly
increased at the second-stage change rate lower than the
first-stage change rate when the DPF inlet temperature exceeds
the switching temperature. Consequently, it is possible to
I
quickly attain the target set temperature and prevent the
excessive temperature increase, i
[0014]
Further, in the invention described above, the
temperature increase rate'setting portion of the DPF target'
temperature setting unit may preferably include a second
temperature increase rate setting portion which sets the
temperature increase change rate of the target temperature such
that the temperature increase change rate of the target
temperature- is stepwise or continuously reduced until the
target set temperature is reached in accordance with the period
8
, 11-445PCT
of time elapsed since the start of the late post injection. •
[0015]
Specifically, the stepwise temperature increase change
rate in the second temperature increase rate setting portion
may preferably include two stages of a first-stage change rate
and a second-stage change rate lower than the first-stage change
rate, the target set temperature may preferably correspond to
the DPF inlet temperature of 610 to 650^C, a^d^witching time
when the change rate is switched between the first-stage and
second-stage change rates may preferably be set after a lapse
of a predetermined period of time after the start of the late
post injection.
[0016]
As described above, since the switching between the
first-stage and feecond-stage change rates is set after the lapse
( ••
of the predetermined period of time after the start of the late ^
post injection, it becomes possible to manage a regeneration ;
behavior of the DPF by using time so that the regeneration
behavior can be made constant and the management thereof is
thereby facilitated. ,
[0017]
Furthermore, in the invention described above, the
exhaust emission control device of a diesel engine may
preferably further include a feed forward control portion which
calculates a basic command value of the late post injection
9
, 11-445PCT
• .
quantity command value in accordance with an operation state -
of the engine, aipd a feed forward correction unit which corrects
the command value from the feed forward control portion in
. w
accordance with the calculated target temperature of the DPF
temperature.
[0018]
That is, since the DPF taifqet temperature is changed, the
required feed forward quantity, i.e., the hars4^ command value
is changed. Accordingly, by correcting the basic command value,
it is possible to perform the stable late post fuel injection.
In particular, it becomes possible to control the late post fuel
injection quantity when the target set temperature is
approached with high accuracy, and hence it is possible to
reduce the danger of the excessive temperature incrfease of the
DPF.
[0019]
According to the present invention, since the temperature ,
increase change rate of the target temperature is set by the
temperature increase rate setting portion of the DPF target
temperature setting unit such that, until the target set ,
temperature at which the PM is burnt is reached after the start
of the late post injection, the temperature increase change rate
of the target temperature is reduced in accordance with the
increase in temperature or the period of time elapsed since the
start of the late post injection, it is possible to quickly
10 i
, 11-445PCT
attain the target set temperature (610 to 650°C) as the' :;
combustion temperature of the DPF, prevent the excessive
temperature increa_se, and reduce the oil dilution quantity
i •'
! while reducing the danger of the excessive temperature increase
of the DPF.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] •-*—^
FIG. 1 is a schematic structural view of an exhaust
emission control device of a diesel engine according to
embodiments of the present invention;
FIG. 2 is a structural block diagram showing a first
embodiment of a DPF target temperature setting unit;
FIG. 3 is an explanatory view showing a change i!n DPF inlet
temperature tar'get value in the first embodiment;
IFIG.
4 is a structural block diagram showing a second ,
embodiment; ,
FIG. 5 is an explanatory view showing a change in DPF inlet
temperature target value in the second embodiment;
> , •
FIG. 6 is a structural block diagram showing a third,
embodiment;
FIG. 7 is an explanatory view showing a change in DFP inlet
temperature target value in the third embodiment;
FIG. 8 is a structural block diagram showing a fourth
embodiment;
11

FIG. 9 is an explanatory view showing a change in DPF i'nlet
temperature target value in the fourth embodiment;
FIG. 10 is a structural block diagram showing a fifth
embodiment;
FIG. 11 is an explanatory view showing a change in DPF
inlet temperature target value in the fifth embodiment; and
FIG. 12 is a structural,block diagram showing a sixth
embodiment. '-m.^^
BEST MODE FOR CARRYING OUT THE INVENTION
[0021]
A detailed description is given hereinbelow of the
present invention by using embodiments shown in the drawings.
Note that the scope of the present invention is not limited only
to dimensions, materials, shapes, and relative arrangements of
constituent parts described in the embodiments unless ^
specifically described. ;
[0022] ^ • .
With-reference to FIG. 1, a description is given of the
overall structure of an exhaust emission control device of ^
diesel engine according to the present invention.
As shown in FIG. 1, in an exhaust passage 3 of a diesel
engine (hereinafter referred to as an engine) 1, there is
provided an exhaust emission af tertreatment device 11 including
DOC 7 and DPF 9 for collecting PM which is disposed on the i
12
, 11-445PCT
downstream side of the DOC 7.
In addition, in the exhaust passage 3, there is provided
an exhaust turbocharger 17 having an exhaust turbine 13 and a
compressor 15 which is driven coakially by the exhaust turbine
13. Air discharged from the compressor 15 of the exhaust
turbocharger 17 enters into an intercooler 21 through an air
supply passage 19 to be cooled,, and the flow rate of the air
is controlled by an intake throttle valve 23v«—5rhereafter, the
. air flows into a combustion chamber from an intake manifold 25
through an intake port via an intake valve of the engine 1.
[0023]'
Further, in the engine 1, a fuel injection device (not
shown) which controls the injection timing, injection quantity,
and injection pressure of fuel to inject the fueli into the
combustion chamber is connected to a regeneration control unit
(ECU) 29 via a connection terminal 27.
Furthermore, an EGR (Exhaust Gas Recirculation) passage ;
33 is branched from some m^idpoint in the exhaust passage 3 or
an exhaust manifold 31, and a part of exhaust gas is sent to
thfe part on the downstream side of the intake throttle valve
23 via an EGR valve 35.
[0024]
Combustion gas resulting from combustion in the
combustion chamber of the engine 1, i.e., exhaust gas 37 passes
through the exhaust manifold 31 and the exhaust passage 3,
13
, 11-445PCT «.
drives ,the exhaust turbine 13 of the exhaust turbocharger 17
to serve as the power source of the compressor 15, and then flows
into the exhaust emission aftertreatment device 11 through the
exhaust passage 3.
•
Moreover, to the regeneration control unit 29 of the DPF
9, signals from a DPF inlet temperature sensor 39 and a DPF exit
temperature sensor 41 are inputted. In addition, a fuel
injection quantity signal 44 from an engiri'§"*'^tation speed
sensor 43 and the fuel injection device is also inputted to the
regeneration control unit (ECU) 29. Further, in the
regeneration control unit 29, there are provided a storage
portion which stores various map data items and a timer which
measures a period of time elapsed since the start of late post
fuel injection. *
[0025]
IWhen
the accumulation quantity of the PM accumulated in v
the DPF 9 exceeds a predetermined value, the regeneration >'
control unit 2 9 increases > the inlet temperature of the DPF 9.
to a temperature in the vicinity of a target set temperature
> , •
('610 to 650°C) to burn and remove the accumulated PM by ' controlling a temperature increase unit.
First, the burning and removing of the PM by the
regeneration control unit 29 is described.
When a condition for starting forced regeneration is
judged on the basis of, e.g., the running distance, the I
14
•
, 11-445PCT
operation time of an engine, or the total fuel consumption ;
quantity in the'pase of a vehicle, and the forced regeneration
is started, DOC temperature increase control for activating the
DOC 7 is executed. In the DOC temperature increase control,
the quantity of air flowing into the combustion chamber is
reduced by reducing the opening of the intake throttle valve
23, and unburned fuel in the ex]p.aust gas is thereby increased.
In addition, in early post injection, the fiset^ost injection
which injects fuel in a quantity smaller than that in main
injection is performed immediately after the main injection in
a state where the pressure in the cylinder is still high. By
the early post injection, an exhaust gas temperature is
increased without influencing the output of the engine, and the
exhaust gas having the increased temperature flows i|ito the DOC
7 to thereby activate the DOC 7. Subsequently, the unburned
fuel in the exhaust gas is oxidized with the activation of the
DOC 7, and the exhaust gas temperature is increased by heat of <
oxidation generated during the oxidation.
[0026]
Then, it is determined whether a DOC inlet temperature
reaches a predetermined temperature or the DPF inlet
temperature reaches a predetermined temperature and, when the
DOC inlet temperature or the DPF inlet temperature exceeds the
predetermined temperature, the inlet temperature of the DPF 9
is further increased by late post injection. The late post
15
, 11-445PCT _^ ^
injection mentioned herein denotes the second post injection
which injects the fuel in a state where the crank angle is near
the bottom dead center after the early post injection. By the
late post injection, the fuel is flown from the combustion
chamber to the exhaust passage 3 when the exhaust valve is open,
the discharged fuel is caused to react in the already activated
DOC 7, the exhaust gas temperat,ure is further increased by the
generated heat of oxidation to a temperature-required for the
regeneration of the DPF 9 such as, e.g., 610 to 650°C, and the
burning of the PM is thereby facilitated.
[0027]
Next, a description is given of the above-mentioned late
post injection with reference to FG. 12 which is explained later
in a fifth embodiment in which the outline of late posr injection
quantity contro'l in the regeneration control unit 29 is
described. "•
The regeneration control unit 29 includes a late post fuel '
injection control unit 50>which injects the fuel at a timing
when no contribution is made to combustion in the combustion
chamber, and the late post fuel injection control unit 50 '
includes a feed forward control unit 53 which specifies a basic
injection quantity (basic operation quantity) of the late post
inj ection quantity based on a feed forward quantity map (FF map)
51 in which the basic injection quantity is set based on the
engine rotation speed and the fuel injection quantity (engine
16
, 11-445PCT
m
load), and a feed back control unit 55 which specifies a late ;
, post correction .injection quantity (correction operation
quantity) based on a deviation between the target inlet
temperature of the DPF 9 and the actual DPF inlet temperature.
[0028]
The feed back control unit 55 includes a DPF target
temperature setting unit 52 whi^ch sets the target value of the
inlet temperature of the DPF, inputs the acitu^l DPF inlet
temperature and the target inlet temperature to an
adder-subtracter 57 to calculate a deviation therebetween as
a control quantity, and performs a feed back calculation on the
deviation in a PID calculation portion (calculation portion)
59 to calculate a correction injection quantity as a feed back
control command value. I
Subsequently, the basic injection quantity from the feed
forward control unit 53 and the correction injection quantity
from the feed back control unit 55 are added together in an adder
61, and outputted as a late post fuel injection quantity command
signal.
[0029]
The present invention increases the target temperature
set by the DPF target temperature setting unit 52 of the feed
back control unit 55 to reduce the regeneration time period,
allow the regeneration process to be completed in a short time
period, and reduce the oil dilution quantity, and sets the
17 . :
, 11-445PCT
target temperature which allows a reduction in the danger of -
the excessive temperature increase of the DPF.
[0030]
(First Embodiment)
With reference to FIGS. 2 and 3, a first embodiment of
the DPF target temperature setting unit 52 is described.
In FIG. 2, the actually ijieasured value of the DPF inlet
temperature is inputted from the DPF inlet t-«H^rature sensor
39. Based on the temperature, the target change rate (increase
rate) of the DPF inlet temperature is calculated by using a first
target change rate map (first temperature increase rate setting
portion) 101. In the first target change rate map 101, the
increase rate is constantly 5°C/sec when the temperature is not
mare than 600°C, while the increase rate is 0.5°C/slc when the
temperature exceeds 600°C. <
Note that, as the temperature inputted to the first target
change rate map 101, the target temperature calculated at the
previous calculation cycle may also be used instead of the
actually measured value inputted from the DPF inlet temperature ,
sensor 39. This is because the actually measured value can be *
considered as a value substantially equal to the value of the
-
target temperature.
[00311
Next, in a target value calculation portion 103, the
18
, 11-445PCT
target temperature is calculated based on the actually meastired 2
value of the DF^ inlet temperature and the calculated target
change rate. The target temperature is inputted to a selection
portion 105, and a signal from a target temperature upper limit
value setting portion 107 which sets the upper limit value of
the target temperature is also inputted to the selection portion
105 . The target temperature upper limit value mentioned herein
denotes the upper limit value of the target-^efl^erature which
is set on the basis of the temperature at which catalyst
degradation of the DPF 9 occurs. The target temperature upper
limit value is set to, e.g., 630°C.
Then, in the selection portion 105, the smaller one of
the calculated value of the target value calculation portion
103 and the target temperature upper limit value is selected
and outputted a's the target temperature of the DPF inlet
temperature. »
[0032]
FIG. 3 shows the state of a change in DPF inlet target
temperature. For example, when the late post fuel injection
• > , •
is started at the DPF inlet temperature of 280°C, a first-stage ',
temperature increase is performed at a constant rate of a
first-stage change rate (first-stage temperature increase
rate) of 5°C/sec. That is, the temperature increase
corresponds to the part of a constant gradient A.
19
i
, 11-445PCT ,,
[0033] , -
Next, wheri the switching temperature of the change rate
of 600°C (500 to,6aO°C) is reached, thereafter, a second-stage
temperature increase is performed at a constant rate of a
second-stage change rate (second-stage temperature increase
rate) of 0.5°C/sec. That is, the temperature increase
corresponds to the part of a Constant gradient B.
[0034] '''^"
Subsequently, when the inlet target set temperature of
the DPF 9, e.g., 630°C (610 to 650°C) is reached, the constant
gradient temperature increase control is ended and the DPF
target temperature setting unit 52 is controlled such that 630°C
(610 to 650°C) is maintained. Note that a dotted line C
I
indicates, as a conventional art, a case where the DPF inlet
Itarget
set temperature is constantly 600°C.
[0035]
1
Thus, the temperature increase rate of the inlet target
temperature of the DPF is changed in two stages. The switching
teitiperature of the temperature increase rate of the target
temperature is set to 500 to 600°C in the DPF inlet temperature,
the target temperature is quickly increased at the first-stage
change rate of 5°C/sec until the DPF inlet temperature reaches
the switching temperature and, when the DPF temperature exceeds
the switching temperature, the target temperature is slowly
20
, H-445PCT
increased by changing the temperature at the second-stage •
change rate of Q.5°C/sec which is lower than the first-stage
change rate. Consequently, it is possible to quickly attain
the target set temperature and prevent the excessive
temperature increase.
Accordingly, it is possible to quickly attain a DPF inlet
target set temperature T (610»to 650°C) as the combustion
temperature of the DPF 9 and prevent the excessive temperature
increase, and reduce the oil dilution quantity while reducing
the danger of an excessive temperature increase of the DPF.
[0036]
In addition, by inputting the target temperature upper
limit value to the selection portion 105 such that the target
temperature upper limit value set based on the degradation
temperature of the DPF catalyst is not exceeded, it is possible
to prevent the problem caused by the excessive temperature *
increase of the DPF.
Further, for example', the target set temperature (610 to
650°C) is set to a value closest to the upper limit value by
• t . •
setting the target temperature upper limit value such that the *
target temperature upper limit,value corresponds to the inlet
temperature target set value T and the target set value is
increased, whereby it is possible to allow the regeneration at
a high temperature, improve regeneration efficiency, and reduce
21
, 11-445PCT _ ^
t h e o i l d i l u t i o n q u a n t i t y.
[0037]
(Second Embodiment)
With reference to FIGS. 4 and 5, a second embodiment of
the DPF target temperature setting unit 52 is described.
The temperature increase rate is changed in two stages
in the first embodiment, while the second embodiment is
characterized in that the temperature incf'Sa^ rate is
continuously changed until the target set temperature T is
reached. The structure of the second embodiment is otherwise
the same as that of the first embodiment.
[0038]
Instead of the first target change rate map 101 of the
first embodiment, a second target change rate map? (first '
temperature inctease rate setting portion) 201 shown in FIG.
4 is used in the second embodiment. The second target change <•
rate map 201 has a feature in which the change rate (increase »
rate) of the DPF inlet temperature is continuously reduced as.
the DPF inlet temperature is increased.
Consequently, the DPF inlet temperature target value is calculated on the basis of the continuously changing change rate
of the target temperature, and hence the inlet temperature
target value can be minutely calculated so that it is possible
to enhance accuracy in the calculation of the inlet temperature
target value. Consequently, even when the target set |
22
i'
, 11-445PCT
temperature T is set to a value closest or equal to the target
upper limit value, the control of the target temperature is
stabilized, and hence it is possible to reliably prevent the
excessive temperature increase.-
FIG. 5 shows the state of a change in DPF inlet target
temperature. From the start of the late post injection to the
target set temperature T, the DPF inlet target temperature is
changed such that the increase rate is contiraiously reduced as
the DPF inlet target temperature is increased.
[0039]
(Third Embodiment)
With reference to FIGS. 6 and 7, a third embodiment of
the DPF target temperature setting unit 52 is described.
The temperature increase rate of the DPF temfjerature,or
the DPF target temperature is changed in each of the first and
. second embodiments, while in the third embodiment, the target

change rate is changed in accordance with a period of time
elapsed since the start of the late post fuel injection.
Consequently, the third embodiment is characterized in that a
third target change rate map (second temperature increase rate
setting portion) 301 is further provided.
[0040] I
In the third target change rate map 301 of FIG. 6, in
accordance with a regeneration elapsed time period, e.g., a
period of time elapsed since the start of the late post fuel
23
i
I 11-445PCT ^ ,,
#
injection, the target change rate is constantly ml when the
regeneration elapsed time period is not longer than tl and, when
• the regeneration elapsed time period is longer than tl, the
increase rate is constantly m2. The output from the second
target change rate map 201 and the output from the third target
change rate map 301 are inputted to a selection portion 303>.
and the smaller one of them is selected and inputted to the target
value calculation portion 103. •-»—'-
[0041]
FIG. 7 shows the state of a change in DPF inlet target
temperature. For example, assuming that tl = 1 minute is
satisfied, when the late post fuel injection is started at the
DPF inlet temperature of 280°C, a first-stage temperature
increase is performed at a constant rate of a first-stage change
rate ml. That is, the temperature increase corresponds to the
part of a constant gradient Al. '
[0042] ;'
Next, when the elapsed time period reaches one minute,'
thereafter, a second-stage temperature increase is performed
at a constant rate of a second-stage change rate m2. That is,' *
the temperature increase corresponds to the part of a constant
gradient Bl.
[0043]
Subsequently, when the inlet target set temperature of
the DPF 9, i.e., 630°C (610 to 650°C) is reached, the constant
24
, 11-445PCT
gradient temperature increase control is ended and the DPF j
1
!
target temperature setting unit 52 is controlled such that 630°C
(610 to 650°C) i? maintained. Note that the time tl is
calculated by a timer incorporated in the regeneration control
device 29.
[0044]
Thus, the temperature increase rate of the inlet target
temperature of the DPF 9 is changed in two st"§ges. The target
temperature is quickly increased at the first-stage change rate
ml and, when the elapsed time period exceeds one minute, the
target temperature is slowly increased at the second-stage
change rate m2 which is lower than the first-stage change rate.
Consequently, it is possible to quickly attain the target set
temperature and prevent the excessive temperature*increase.
Further, the switching between the first-stage change
rate and the second-stage change rate is set after a lapse of t
a predetermined period of time after the start of the late post ''
injection, and hence it becomes possible to manage the
regeneration behavior of the DPF by using time so that the
regeneration behavior can be made constant and stabilized.>
[0045]
(Fourth Embodiment)
With reference to FIGS. 8 and 9, a fourth embodiment of
the DPF target temperature setting unit 52 is described.
25
, 11-445PCT
In contrast to the change in two stages of the third target
change rate map 301 of the third embodiment, the fourth
embodiment is characterized in that a fourth target change rate
map (second temperature increase rate setting portion) 401
having a feature in which the change rate is continuously
changed is provided.
[0046] ,
The fourth target change rate map 4 0i*-h^s a feature in
which the change rate (increase rate) of the DPF inlet
temperature is continuously reduced with an increase in
regeneration elapsed time period.
Consequently, the DPF inlet temperature target value is
calculated on the basis of the change rate of the target
temperature which changes with the increase in regeneration
elapsed time pe^riod, and hence it is possible to minutely
calculate the inlet temperature target value. >,
As a result, it is possible to enhance accuracy in the ;
calculation of the inlet temperature target value. • .
Consequently, even when the target set temperature T is set to
> . • a.value closest or equal to the target upper limit value, the ^
control of the target temperature is stabilized, and hence it
is possible to reliably prevent the excessive temperature
increase.
FIG. 9 shows the state of a change in DPF inlet target
temperature. From the start of the late post injection to the
2 6
, 11-445PCT
target set temperature T, the DPF inlet target temperature is -
changed such that the increase rate is continuously reduced as
the DPF inlet target temperature is increased.
[0047]
(Fifth Embodiment)
With reference to FIGS, 10 and 11, a fifth embodiment of
the DPF target temperature setting unit 52 is described.
In contrast to the third and fourth emboGLuHents, the fifth
embodiment is characterized in that a target temperature map
501 in which the target temperature is set based on the period
of time elapsed since the start of the late post fuel injection
is further provided.
[0048]
The target temperature calculated from the J:arget >
temperature map'501 in which the target temperature is set in
I -
accordance with the period of time elapsed since the start of
the late post fuel injection is directly inputted to the
selection portion 105 and^ the minimum value is thereby
calculated-, and hence, even when there is an error in the
variations of the elapsed time period or the DPF temperature
(data on the measurement of the DPF inlet temperature) m a case
where the target temperature is calculated by using the second
target change rate map 20l or the fourth target change rate map
401, the target temperature is reliably set by the target
f
temperature map 501 so that the control of the late post fuel I
27 ,
, 11-445PCT
# . . .
injection quantity is stabilized. -
FIG. 11 shows the state of a change in DPF inlet target
temperature. From the start of the late post injection to the
target set temperature T, the DPF inlet target temperature is
changed such that the increase rate is continuously reduced as
the DPF inlet target temperature is increased.
[0049] ,
(Sixth Embodiment) -,»_—'-
With reference to FIG. 12, a sixth embodiment is
described.
As described above, the regeneration control unit 29
includes the feed forward control portion 53 which calculates
the basic command value of the late post injection quantity
command value in accordance with the operation stiate of the
engine, and the'feed back control unit 55 which specifies the
Ilate
post correction injection quantity (correction operation ,
quantity) based on the deviation between the target inlet ;
temperature of the DPF 9 and the actual DPF inlet temperature.,
In the sixth embodiment, the target inlet temperature of
the feed back control unit 55 is changed, and hence it is ,
necessary to change a feed forward quantity correspondingly to
the change. Consequently, the sixth embodiment is
-
characterized in that an FF factor map (feed forward correction
unit) 503 which corrects the feed forward quantity is provided.
[0050]
28
, 11-445PCT
The setting of the target temperature in the DPF target
temperature setting unit 52 in FIG. 12 is as described in each
I of the first to fifth embodiments, and the setting of the first
embodiment is shown as an example in FIG. 12.
The DPF inlet target temperature set value T (°C) , the
switching temperature {°C), the first-stage increase rate
(°C/sec) , and the second-stage* increase rate (°C/sec) are
inputted, and the DPF inlet target temperature is calculated,
i [0051]
The actually measured DPF inlet temperature and the
above-described DPF inlet target temperature are inputted to
• the adder-subtracter 57, the deviation therebetween is
calculated as the control quantity, the deviation is subjected
t
to the feed back calculation in the PID calculation portion 59,
and the feed back control command value is calculated and ,
outputted to the adder 61. "•
[0052]
On the other hand, ih the feed forward control unit 53,-
the late post injection quantity for maintaining the switching
> . •
temperature (e.g., 600°C) is set in the FF (feed forward)
quantity map 51.
In addition, in an FF quantity correction base map 505,
a difference between the late post injection quantity for
maintaining the DPF inlet temperature target set value T (e.g. ,
29
11-445PCT
630°C) and the late post injection quantity for maintaining the -
switching temperature is set.
Further, in the FF quantity factor map 503, there is set
a control factor corresponding to the ratio between (the inlet
temperature target set value T - the switching temperature) and
the inlet target temperature after the switching temperature
is reached, i.e., the temperature position of the inlet target
temperature between the inlet temperature target set value T
and the switching temperature after the switching temperature
is reached.
[0053]
With the configuration described above, the target
temperature set by the DPF target temperature setting unit 52
is inputted to the adder-subtracter 57, and the conrrol factor
corresponding to the target temperature is calculated by using
the FF quantity factor map 503. ••
Then, the late post injection quantity to be corrected ''
calculated by the FF quantity correction base map 505 is
multiplied by the control factor in a multiplier 507. The
>, •
correction quantity of the late post injection quantity • ^
-
suitable for the target temperature is calculated in the
multiplier 507, the correction quantity is inputted to an adder
509 to be added to the control quantity from the FF quantity
map 51, and outputted as a feed forward command value.
30
, 11-445PCT
Subsequently, the feed forward coitimand value is added to- the .
coinmand value from the feed back control unit 55 in the adder
61.
[0054]
Note that the correction control in which the control
factor corresponding to the target temperature is calculated
by using the FF quantity factor map 503 and the multiplication
using the control factor is performed in the.-jaiii-tiplier 507 is
a control operation which is performed only during the
second-stage change (the second-stage temperature increase
rate).
Consequently, the correction is not performed during the
first-stage change (the first-stage temperature increase rate) ,
That is, the switching temperature 600°C is alreadyireached'in
a region during'the second-stage change, and hence there is a
possibility that an overshoot occurs and the excessive ^
temperature increase is caused depending on the subsequent ;
temperature increase contrpl. Accordingly, it is necessary to^
determine the late post fuel injection quantity with high
accuracy. Therefore, as in the present embodiment, the lat^
post fuel injection quantity is corrected in accordance with
the target temperature and the late post fuel injection quantity
is stably and reliably controlled. On the other hand, during
the first-stage change, it is an objective to quickly attain
the temperature of about 600°C which allows combustion, and
31
11-445PCT
^ hence the feed forward quantity of the feed forward control'unit --
53 is not corrected based on the target temperature set by the
DPF target temperature setting unit 52.
[0055]
According to the sixth embodiment, since the DPF target
temperature is changed, by correcting the required feed forward
quantity, i.e., the basic command value, it is possible to
perform the stable late post fuel injection^.-vEn particular,
even when the regeneration time period is reduced, the
regeneration efficiency is enhanced, and the oil dilution
quantity is reduced by setting the DPF inlet temperature target
set value T (e.g., 63Q°C) to a temperature higher than about
600°C as the conventional temperature to increase the DPF
temperature to a high temperature, it is possible to'reduce the
danger of the excessive temperature increase of the DPF.
[0056]
In the description of each of the first to sixth '
embodiments, although the-description has been made with theinlet
temperature of the DPF used as the object of the control,
V
the exit temperature or the internal temperature may also be
controlled as the object.
INDUSTRIAL APPLICABILITY
[0057]
32
11-445PCT
I- it •
^ According to the present invention, m forced • .
regeneration of DPF, it is possible to increase a DPF
i,
temperature to a high temperature to reduce a recognition time
period in order to reduce an oil dilution quantity and also
reduce the danger of an excessive temperature increase of the
DPF, and hence the present invention is suitably used in an
exhaust emission control device of a diesel engine.

CLAIMS
1. An exhaust emission control device of a diesel engine comprising a diesel oxidation catalyst (DOC) and a diesel
particulate filter (DPF) which collects particulate matter (PM)
in an exhaust passage and performing regeneration on the PM
collected in the DPF,
the exhaust emission control device comprising:
a regeneration control unit which in.crg^ses, when an
accumulation quantity of the PM exceeds a predetermined value,
a temperature of the DPF to a temperature in a vicinity of a
predetermined target set temperature to burn and remove the
accumulated PM by controlling a temperature increase unit,
the regeneration control unit comprising a late post fuel
injection control unit which injects fuel into a .combustion
chamber at a timp.ng when no contribution is made to combustion,
the late post fuel injection control unit comprising a DPF
target temperature setting unit which sets a target value of
a DPF temperature including an inlet temperature, an exit
temperature, or an internal temperature of the DPF, and a
calculation portion which calculates a late post injection
quantity command value based on a deviation between the target
value of the DPF temperature set by the DPF target temperature
setting unit and an actual DPF temperature,
the DPF target temperature setting unit comprising a
temperature increase rate setting portion which sets a
34
11-445PCT
temperature increase change rate such that, until the ta'rget .^
set temperature at which the PM is burnt is reached after start
of late post injection, the temperature increase change rate
is reduced in accordance with an*increase in temperature or a
period of time elapsed since the start of the late post injection,
and
a target temperature of the DPF temperature being
calculated based on the temperature increa.aa-5^ate from the
temperature increase rate setting portion.
2. The exhaust emission control device of a diesel engine
according to claim 1, wherein the temperature increase rate
setting portion of the DPF target temperature setting unit
comprises a first temperature increase rate settifig portion
which sets the temperature increase change rate of the target
temperature such that the temperature increase change rate of
the target temperature is stepwise or continuously reduced in i
accordance with the increase in temperature.
. \ 3. The exhaust emission control device of a diesel engine
according to claim 2, wherein the stepwise temperature increase
change rate in the first temperature increase rate setting
portion comprises two stages of a first-stage change rate and
a second-stage change rate lower than the first-stage change
rate, the target set temperature corresponds to the DPF inlet
35
11-445PCT
temperature of 610 to 650°C, and a switching temperature at which j
the change rate is switched between the first-stage and
second-stage change rates corresponds to the DPF inlet
temperature of 500 to 600°C.
4. The exhaust emission control device of a diesel engine
according to claim 1, wherein, the temperature increase rate
setting portion of the DPF target temperat-ftr^ setting unit
comprises a second temperature increase rate setting portion
which sets the temperature increase change rate of the target
temperature such that the temperature increase change rate of
the target temperature is stepwise or continuously reduced
until the target set temperature is reached in accordance with
the period of time elapsed since the start of th4 late post
injection. '
5. The exhaust emission control device of a diesel engine ^
according to claim 4, wherein the stepwise temperature increase
change rate in the second temperature increase rate setting
pottion comprises two stages of a first-stage change rate and
a second-stage change rate lower than the first-stage change
rate, the target set temperature corresponds to the DPF inlet
temperature of 610 to 650°C, and switching time when the change
rate is switched between the first-stage and second-stage
36

change rates is set after a lapse of a predetermined period of
time after the. start of the late post injection.

6. The exhaust emission control device of a diesel engine
according to claim 1, further comprising:
a feed forward control portion which calculates a basic
command value of the late post injection quantity command value
in accordance with an operation state of tj^^^^nqine; and
a feed forward correction unit which corrects the command
value from the feed forward control portion in accordance with
the calculated target temperature of the DPF temperature.
7. The exhaust emission control device of a diesel'engine
according to any one of claims 1 to 6, wherein an ijpper limit
value of the target set temperature is an upper limit value that
Iis
set based on A temperature at which catalyst degradation of
the DPF occurs.