U.S. patent application number 12/910083 was filed with the patent office on 2011-05-05 for exhaust gas purification apparatus for internal combustion engine.
This patent application is currently assigned to KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Junichi TAKAHASHI.
Application Number | 20110099977 12/910083 |
Document ID | / |
Family ID | 43536380 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110099977 |
Kind Code |
A1 |
TAKAHASHI; Junichi |
May 5, 2011 |
EXHAUST GAS PURIFICATION APPARATUS FOR INTERNAL COMBUSTION
ENGINE
Abstract
An exhaust gas purification apparatus includes an exhaust
passage through which exhaust gas discharged from an engine flows,
a selective catalytic reduction catalyst provided in the exhaust
passage, a urea water supply device for supplying urea water into
the exhaust passage upstream of the selective catalytic reduction
catalyst, a sensor responding to respective quantities of NOx and
ammonia downstream of the selective catalytic reduction catalyst
and detecting a value based on the response by the sensor, an
exhaust gas recirculation passage through which a part of exhaust
gas is refluxed to an intake system of the engine, an exhaust gas
recirculation control valve for controlling amount of exhaust gas
that is refluxed through the exhaust gas recirculation passage and
a control device for controlling quantity of urea water supplied
from the urea water supply device to the exhaust passage and also
opening and closing of the exhaust gas recirculation control valve.
The control device controls opening and closing of the exhaust gas
recirculation control valve so as to increase or decrease the
amount of exhaust gas refluxed through the exhaust gas
recirculation passage for a predetermined period of time and also
determines quantity of urea water based on change between the
values detected by the sensor before and after changing opening and
closing of the exhaust gas recirculation control valve.
Inventors: |
TAKAHASHI; Junichi;
(Aichi-ken, JP) |
Assignee: |
KABUSHIKI KAISHA TOYOTA
JIDOSHOKKI
Kariya-shi
JP
|
Family ID: |
43536380 |
Appl. No.: |
12/910083 |
Filed: |
October 22, 2010 |
Current U.S.
Class: |
60/274 ; 60/276;
60/287; 60/301 |
Current CPC
Class: |
F01N 2560/026 20130101;
Y02T 10/24 20130101; F02M 26/05 20160201; Y02T 10/12 20130101; F01N
2900/1622 20130101; F01N 3/208 20130101; Y02T 10/40 20130101; F01N
2610/02 20130101; F01N 9/00 20130101; Y02T 10/47 20130101; F02D
41/005 20130101 |
Class at
Publication: |
60/274 ; 60/287;
60/276; 60/301 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 9/00 20060101 F01N009/00; F01N 11/00 20060101
F01N011/00; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2009 |
JP |
P2009-249592 |
Claims
1. An exhaust gas purification apparatus comprising: an exhaust
passage through which exhaust gas discharged from an engine flows;
a selective catalytic reduction catalyst provided in the exhaust
passage; a urea water supply device for supplying urea water into
the exhaust passage upstream of the selective catalytic reduction
catalyst; a sensor responding to respective quantities of NOx and
ammonia downstream of the selective catalytic reduction catalyst
and detecting a value based on the response by the sensor; an
exhaust gas recirculation passage through which a part of exhaust
gas is refluxed to an intake system of the engine; an exhaust gas
recirculation control valve for controlling amount of exhaust gas
that is refluxed through the exhaust gas recirculation passage; and
a control device for controlling quantity of urea water supplied
from the urea water supply device to the exhaust passage and also
opening and closing of the exhaust gas recirculation control valve,
wherein the control device controls opening and closing of the
exhaust gas recirculation control valve so as to increase or
decrease the amount of exhaust gas refluxed through the exhaust gas
recirculation passage for a predetermined period of time and also
determines quantity of urea water based on change between the
values detected by the sensor before and after changing opening and
closing of the exhaust gas recirculation control valve.
2. The exhaust gas purification apparatus according to claim 1,
wherein the sensor detects quantity of NOx and has
cross-sensitivity between ammonia and NOx.
3. The exhaust gas purification apparatus according to claim 1,
wherein when the amount of exhaust gas refluxed is decreased and
the change between the values of the sensor tends to increase, the
control device determines that the quantity of ammonia in the
selective catalytic reduction catalyst is inadequate, thereby
controlling so as to increase the quantity of urea water to be
supplied, wherein when the amount of exhaust gas refluxed is
decreased and the change between the values of the sensor tends to
decrease, the control device determines that the quantity of
ammonia in the selective catalytic reduction catalyst is excessive,
thereby controlling so as to decrease the quantity of urea water to
be supplied.
4. The exhaust gas purification apparatus according to claim 1,
wherein when the amount of exhaust gas refluxed is increased and
the change between the values of the sensor tends to: increase, the
control device determines that the quantity of ammonia in the
selective catalytic reduction catalyst is excessive, thereby
controlling so as to decrease the quantity of urea water to be
supplied, wherein when the amount of exhaust gas refluxed is
increased and the change between the values of the sensor tends to
decrease, the control device determines that the quantity of
ammonia in the selective catalytic reduction catalyst is
inadequate, thereby controlling so as to increase the quantity of
urea water to be supplied.
5. The exhaust gas purification apparatus according to claim 1,
wherein the control device controls the quantity of urea water to
be supplied based on calculated amount of ammonia adsorbed on the
selective catalytic reduction catalyst.
6. The exhaust gas purification apparatus according to claim 1,
wherein the control device controls opening and closing of the
exhaust gas recirculation control valve after the control device
determines that the engine is in a steady state when engine speed
and amount of fuel injection keeps substantially constant values,
respectively.
7. The exhaust gas purification apparatus according to claim 1,
wherein the control device stores the detected values of the sensor
as history data and corrects the value of the sensor that includes
a variation caused by manufacturing error or secular change, based
on the history data.
8. The exhaust gas purification apparatus according to claim 7,
wherein the history data includes a plurality of mean values of the
values of the sensor detected multiple times, wherein the value of
the sensor is corrected by detecting a difference between the
latest mean value and the previous mean value.
9. The exhaust gas purification apparatus according to claim 7,
wherein the history data includes standard sensor value, wherein
the control device corrects the value of the sensor including the
variation caused by the manufacturing error by comparing the value
of the sensor detected under a predetermined operating condition of
the exhaust gas recirculation with the standard sensor value stored
previously.
10. A method for purifying exhaust gas, wherein an exhaust gas
purification apparatus comprising: an exhaust passage through which
exhaust gas discharged from an engine flows; a selective catalytic
reduction catalyst provided in the exhaust passage; a urea water
supply device for supplying urea water into the exhaust passage
upstream of the selective catalytic reduction catalyst; a sensor
reacting to respective quantities of NOx and ammonia downstream of
the selective catalytic reduction catalyst and detecting a value
based on the reaction; an exhaust gas recirculation passage through
which a part of exhaust gas refluxes to an intake system of the
engine; an exhaust gas recirculation control valve for controlling
amount of exhaust gas that is refluxed through the exhaust gas
recirculation passage, wherein the method for the exhaust gas
purification apparatus comprising the steps of: controlling opening
and closing of the exhaust gas recirculation control valve so as to
increase or decrease the amount of exhaust gas refluxed through the
exhaust gas recirculation passage for a predetermined period of
time, departing from normal exhaust gas recirculation control,
detecting change between the values detected by the sensor before
and after changing opening and closing of the exhaust gas
recirculation control valve, and controlling quantity of urea water
supplied from the urea water supply device to the exhaust passage
based on the change.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an exhaust gas purification
apparatus for an internal combustion engine.
[0002] NOx (nitrogen oxides) contained in exhaust gas discharged
from an internal combustion engine is reduced by an exhaust gas
purification apparatus. Specifically, the exhaust gas purification
apparatus for a diesel engine uses a selective catalytic reduction
catalyst (hereinafter referred to as SCR catalyst) in the exhaust
system of the diesel engine. The SCR catalyst is supplied with a
reducing agent such as urea and ammonia generated from the urea is
adsorbed on the SCR catalyst for selectively reducing NOx contained
in exhaust gas.
[0003] Published Japanese translation 2009-507175 of PCT
International Publication (pages 5-9, FIG. 1) discloses an exhaust
gas purification apparatus including a urea SCR catalyst provided
in the exhaust system of an internal combustion engine, a reactant
supply device for supplying ammonia as a reactant (reducing agent)
to the SCR catalyst and NOx sensors provided upstream and
downstream of the SCR catalyst. Concentration of NOx contained in
exhaust gas discharged from the engine is detected by the upstream
NOx sensor and the quantity of ammonia to be supplied to the SCR
catalyst is determined based on the detected NOx concentration. Sum
of the concentration of NOx that is discharged without being
removed in the SCR catalyst and the quantity of ammonia that slips
(overflows) due to excessive supply of ammonia is detected by the
downstream NOx sensor. The quantity of ammonia to be supplied to
the SCR catalyst is corrected based on the sum, thus making
possible suppression of the quantity of ammonia that slips.
[0004] However, a NOx sensor normally has a cross-sensitivity for
NOx and ammonia and, therefore, it is very difficult to estimate
the concentrations of NOx and ammonia in exhaust gas based on the
detection signal (sum) from the downstream NOx sensor according to
the apparatus of the above Publication (pages 5-9, FIG. 1). Since
it can not be instantly determined that the signal from the
downstream NOx sensor is due to ammonia slip, especially when
ammonia slips a lot, it takes a long time before ammonia slipping
is stopped. Therefore, there is a fear of odor caused by ammonia
slipping to the outside.
[0005] The present invention is directed to providing an exhaust
gas purification apparatus for an internal combustion engine that
determines the state of quantity of ammonia in SCR catalyst easily
and suppresses the quantity of ammonia slipping from the SCR
catalyst.
SUMMARY OF THE INVENTION
[0006] An exhaust gas purification apparatus includes an exhaust
passage through which exhaust gas discharged from an engine flows,
a selective catalytic reduction catalyst provided in the exhaust
passage, a urea water supply device for supplying urea water into
the exhaust passage upstream of the selective catalytic reduction
catalyst, a sensor responding to respective quantities of NOx and
ammonia downstream of the selective catalytic reduction catalyst
and detecting a value based on the response by the sensor, an
exhaust gas recirculation passage through which a part of exhaust
gas is refluxed to an intake system of the engine, an exhaust gas
recirculation control valve for controlling amount of exhaust gas
that is refluxed through the exhaust gas recirculation passage and
a control device for controlling quantity of urea water supplied
from the urea water supply device to the exhaust passage and also
opening and closing of the exhaust gas recirculation control valve.
The control device controls opening and closing of the exhaust gas
recirculation control valve so as to increase or decrease the
amount of exhaust gas refluxed through the exhaust gas
recirculation passage for a predetermined period of time and also
determines quantity of urea water based on change between the
values detected by the sensor before and after changing opening and
closing of the exhaust gas recirculation control valve.
[0007] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
The invention together with objects and advantages thereof, may
best be understood by reference to the following description of the
presently preferred embodiments together with the accompanying
drawings in which:
[0009] FIG. 1 is a schematic view showing an exhaust gas
purification apparatus and its associated components according to a
first embodiment of the present invention;
[0010] FIG. 2A is a configuration map 1 showing the relation
between the state of quantity of ammonia and the OUT-NOx sensor
value (or the value detected by OUT-NOx sensor as will be described
later) during the EGR decrease control in the exhaust gas
purification apparatus according to the first embodiment;
[0011] FIG. 2B is a schematic configuration figure showing the
relation among the quantity of NOx emission, the quantity of
ammonia and the OUT-NOx sensor value and explaining what the map 1
means;
[0012] FIG. 3 is a flow chart showing a processing routine for the
exhaust gas purification apparatus according to the first
embodiment;
[0013] FIG. 4A is a configuration map 2 showing the relation
between the state of quantity of ammonia and the OUT-NOx sensor
value during the EGR increase control in an exhaust gas
purification apparatus according to a second embodiment;
[0014] FIG. 4B is a schematic configuration figure showing the
relation among the quantity of NOx emission, the quantity of
ammonia and the OUT-NOx sensor value and explaining what the map 2
means;
[0015] FIG. 5 is a flow chart showing a processing routine for the
exhaust gas purification apparatus according to the second
embodiment;
[0016] FIG. 6A is a flow chart showing a processing routine for
correcting the OUT-NOx sensor value based on history data stored
due to secular change in an exhaust gas purification apparatus
according to a third embodiment; and
[0017] FIG. 6B is a flow chart showing a processing routine for
correcting the error of the OUT-NOx sensor value due to the
manufacturing error, based on history data in the exhaust gas
purification apparatus according to the third-embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The following will describe the exhaust gas purification
apparatus for a diesel engine as an internal combustion engine
according to the first embodiment with reference to FIGS. 1 through
3. Referring to FIG. 1, the exhaust gas purification apparatus is
designated generally by 10 and the diesel engine by 11. As shown in
FIG. 1, the diesel engine (hereinafter referred to as engine)
includes an intake manifold 12 and an exhaust manifold 13. The
intake manifold 12 is connected at the inlet thereof through an
intake duct 14 to the outlet of a compressor 16 of a turbocharger
15 and the inlet of the compressor 16 is connected to an air
cleaner (not shown). On the other hand, the exhaust manifold 13 is
connected at the outlet thereof through an exhaust duct 17 to the
inlet of an exhaust gas turbine 18 of the turbocharger 15 and the
outlet of the exhaust gas turbine 18 is connected to an exhaust
passage 19. Exhaust gas discharged from the engine 11 flows through
the exhaust gas turbine 18 and the exhaust passage 19.
[0019] The engine 11 has an exhaust gas recirculation passage
(hereinafter referred to as EGR passage) 20 through which the
exhaust duct 17 and the intake duct 14 are connected to each other
and a part of exhaust gas is refluxed to the intake system of the
engine 11. An EGR control valve 21 is provided in the EGR passage
20 for controlling the amount of exhaust gas that is refluxed
through the EGR passage 20.
[0020] A diesel oxidation catalyst (hereinafter referred to as DOC)
22 is provided in the exhaust passage 19 for oxidizing hydrocarbons
and carbon monoxide contained in exhaust gas. Noble metal catalyst
such as platinum is used for the DOC 22. A diesel particulate
filter (hereinafter referred to as DPF) 23 is provided downstream
of the DOC 22 for capturing and collecting particulate matter
contained in exhaust gas.
[0021] A selective catalytic reduction catalyst (hereinafter
referred to as SCR catalyst) 24 is provided downstream of the DPF
23 for selectively reducing NOx contained in exhaust gas. Ammonia
adsorption type Fe zeolite having a high NOx purification rate
under a low temperature is used for the SCR catalyst 24. An IN-NOx
sensor 26 is provided in an exhaust gas pipe 25 upstream of the SCR
catalyst 24 for detecting the quantity of NOx contained in exhaust
gas. The quantity of NOx detected by the IN-NOx sensor 26 will be
hereinafter referred to as quantity of IN-NOx. The exhaust gas pipe
25 forms a part of the exhaust passage 19.
[0022] A urea water supply valve 27 is provided in the exhaust gas
pipe 25 between the IN-NOx sensor 26 and the SCR catalyst 24 and
connected to a urea water tank 30 through a supply pipe 28 and a
supply pump 29. The urea water supply valve 27 corresponds to the
urea water supply device of the invention. Urea water reserved in
the urea water tank 30 is pumped by a supply pump 29 and injected
through the urea water supply valve 27 to exhaust gas flowing
through the exhaust gas pipe 25. Ammonia (NH3) generated by
hydrolysis of urea water is adsorbed on the SCR catalyst 24 and NOx
contained in exhaust gas is selectively reduced by the ammonia
adsorbed on the SCR catalyst 24.
[0023] A temperature sensor 31 is provided in the exhaust gas pipe
25 between the urea water supply valve 27 and the SCR catalyst 24
for detecting the temperature of the SCR catalyst 24. A diesel
oxidation catalyst 32 (hereinafter referred to as DOC) is provided
downstream of the SCR catalyst 24 for oxidizing ammonia slipped
from the SCR catalyst 24. An OUT-NOx sensor 33 is provided in the
exhaust gas pipe 25 between the SCR catalyst 24 and the DOC 32 for
detecting the quantity of NOx contained in exhaust gas flowing
through the SCR catalyst 24. The OUT-NOx sensor 33 that corresponds
to a sensor responding to respective quantities of NOx and ammonia
has cross-sensitivity between ammonia and NOx and can detect the
quantities of discharged NOx and slipped ammonia.
[0024] A control device 34 for controlling the operation of the
exhaust gas purification apparatus 10 is connected to the IN-NOx
sensor 26, the temperature sensor 31, the OUT-NOx sensor 33, the
urea water supply valve 27, the supply pump 29 and the EGR control
valve 21. The control device 34 is operable to control the quantity
of urea water supplied from the urea water supply valve 27 to the
exhaust passage 19, but also to change forcibly the amount of
exhaust gas refluxed through the EGR passage 20 by controlling
opening and closing of the EGR control valve 21.
[0025] Departing from the normal EGR control, the control device 34
is operable to force the opening of the EGR control valve 21 in the
direction to close the valve for a predetermined period of time,
thereby decreasing the amount of exhaust gas refluxed through the
EGR passage 20 (This control will be hereinafter referred to EGR
decrease control). Accordingly, the quantity of NOx in exhaust gas
discharged to the exhaust passage 19 is increased. The state of
quantity of ammonia in the SCR catalyst 24 (i.e. excessive,
inadequate, appropriate) can be determined by detecting the change
of values of the OUT-NOx sensor 33 before and after the EGR
decrease control.
[0026] FIG. 2A is a configuration map 1 showing the relation
between the state of quantity of ammonia and the OUT-NOx sensor
value (a value detected by the OUT-NOx sensor 33) during the EGR
decrease control. If the quantity of ammonia is excessive and
ammonia slip occurs, the OUT-NOx sensor value shows a decreasing
tendency when the quantity of IN-NOx increases. If the quantity of
ammonia is inadequate and NOx reduction is not performed, the
OUT-NOx sensor value shows an increasing tendency when the quantity
of IN-NOx increases. If the quantity of ammonia is appropriate and
NOx reduction is performed, the OUT-NOx sensor value shows a
slightly increasing or a slightly decreasing tendency (or no
change) when the quantity of IN-NOx increases.
[0027] FIG. 2B is a schematic configuration figure showing the
relation among the quantity of NOx emission, the quantity of
ammonia and the OUT-NOx sensor value for explaining what the map 1
means. The characteristic curve of the figure shows a
characteristic of the relation when the quantity of urea water
supplied by the urea water supply valve 27 is set at a certain
constant value. As shown in FIG. 2B, with the quantities of NOx
emission and the ammonia on the axis of abscissas and the OUT-NOx
sensor value on the axis of ordinate, the characteristic curve is
convex downward by the cross-sensitivity of the OUT-NOx sensor 33.
This characteristic curve shows that the quantity of ammonia is the
most appropriate for the quantity of NOx emission when the OUT-NOx
sensor value is minimum. The characteristic curve is divided into
three regions depending on the value of NOx emission. The region
which includes the minimum OUT-NOx sensor value represents the
ammonia appropriate region. The region in which the quantities of
NOx emission and ammonia are less than those of the ammonia
appropriate region represents the ammonia excessive region and the
region in which the quantities of NOx emission and ammonia are more
than those of the ammonia appropriate region represents the ammonia
inadequate region.
[0028] When the quantity of IN-NOx increases in the ammonia
excessive region, the point P1 on the characteristic curve moves in
arrow direction shown in FIG. 2B and, therefore, the OUT-NOx sensor
value shows a decreasing tendency. When the quantity of IN-NOx
increases in the ammonia inadequate region, the point Q1 on the
characteristic curve moves in arrow direction shown in FIG. 2B and,
therefore, the OUT-NOx sensor value shows an increasing tendency.
When the quantity of IN-NOx increases in the ammonia appropriate
region, points R1, S1 on the characteristic curve move in arrow
directions shown in FIG. 2B and, therefore, the OUT-NOx sensor
values show a slightly decreasing tendency and a slightly
increasing tendency, respectively.
[0029] As appreciated from the above, by monitoring the change of
the OUT-NOx sensor values during the EGR decrease control, it can
be determined easily which region of the OUT-NOx sensor value
having cross-sensitivity is being detected. Therefore, the quantity
of urea water to be supplied from the urea water supply valve 27
can be controlled based on the above determination. In other words,
when the OUT-NOx sensor value tends to decrease, the control device
34 determines that the quantity of ammonia contained in the exhaust
gas is excessively large, thereby controlling so as to decrease the
quantity of urea water to be supplied from the urea water supply
valve 27. When the OUT-NOx sensor value tends to increase, the
control device 34 determines that the quantity of ammonia contained
in the exhaust gas is inadequate, thereby controlling so as to
increase the quantity of urea water to be supplied from the urea
water supply valve 27. Further, when the OUT-NOx sensor value shows
a slightly increasing or decreasing tendency, the control device 34
determines that the quantity of ammonia contained in the exhaust
gas is appropriate, thereby controlling so as to keep the quantity
of urea water being supplied from the urea water supply valve 27
unchanged.
[0030] The following will describe a process for controlling the
exhaust gas purification apparatus 10 with reference to the flow
chart shown in FIG. 3. When the processing routine starts, the time
counter, the engine speed and the amount of fuel injection are read
at S101. Then, at S102, the control device 34 determines whether
the engine 11 is in a steady state or not based on the data of the
time counter, the engine speed and the amount of fuel injection
read at S101. The engine speed and the amount of fuel injection
change rapidly just after the engine 11 is started and will be
stabilized when the engine speed reaches a constant speed in a
certain period of time after the engine-start. When the vehicle is
accelerated for overtaking and the like, the engine speed and the
amount of fuel injection change rapidly. The steady state means
that the engine speed and the amount of fuel injection keep
substantially constant values, respectively. Such state occurs
e.g., when the vehicle is running at a constant speed. A state of a
vehicle when the engine speed or the amount of fuel injection
change rapidly just after the engine 11 is started or when the
vehicle is accelerated rapidly is not a steady state. When it is
determined at S102 that the engine 11 is not in the steady state,
the control returns to S101 and the data is read again.
[0031] When it is determined at S102 that the engine 11 is in the
steady state, the control proceeds to S103 where the value detected
by the OUT-NOx sensor 33 is detected. Then at S104, the EGR
decrease control is executed forcibly, so that the operation of the
EGR control valve 21 is controlled so that the opening of the EGR
control valve 21 is decreased for a certain period of time.
Accordingly, amount of exhaust gas refluxed through the EGR passage
20 decreases, thereby increasing the quantity of IN-NOx in exhaust
gas discharged into the exhaust passage 19. The above certain
period of time is previously set to an appropriate time in
accordance with the temperature of the SCR catalyst 24.
[0032] Then at S105, the value detected by the OUT-NOx sensor 33
after the execution of the EGR decrease control is detected. Let a1
and a2 as the values (values detected by the OUT-NOx sensor 33
detected at S103, S105, respectively) before and after the EGR
decrease control, respectively. At S106, a difference value for the
above values, i.e., .DELTA.a=a1-a2 is calculated. At S107, if
.DELTA.a<-d (d is positive number), it is determined that the
value detected by the OUT-NOx sensor 33 shows a decreasing
tendency. If .DELTA.a>d, it is determined that the value
detected by the OUT-NOx sensor 33 shows an increasing tendency. If
-d.ltoreq..DELTA.a.ltoreq.d, it is determined that the value
detected by the OUT-NOx sensor 33 shows a slightly increasing or
decreasing tendency.
[0033] At S107, based on the map 1 showing the relation between the
state of quantity of ammonia and the OUT-NOx sensor value during
the EGR decrease control, determination of the state of quantity of
ammonia (i.e. excessive, inadequate or appropriate state) is made
on the calculated OUT-NOx sensor value. For example, if the OUT-NOx
sensor value shows a decreasing tendency (.DELTA.a<-d), it is
determined that the quantity of ammonia is in the excessive state.
If the OUT-NOx sensor value shows an increasing tendency
(.DELTA.a>d), it is determined that the quantity of ammonia is
in the inadequate state. If the OUT-NOx sensor value shows a
slightly increasing or decreasing tendency
(-.ltoreq..DELTA.a.ltoreq.d), it is determined that the quantity of
ammonia is in the appropriate state.
[0034] At S108, based on the quantity of ammonia determined at
S107, a correction coefficient is assigned. For example, correction
coefficients 0.7, 1.3 and 1.0 are assigned for the excessive,
inadequate and appropriate states, respectively. At S109, the
quantity of urea water to be supplied is calculated. This
calculation is made based on the following calculation formula.
Quantity of urea water to be supplied=base supply
quantity.times.correction coefficient. For example, the quantity of
urea water to be supplied in case of the excessive state is the
base supply quantity.times.0.7. The quantity of urea water to be
supplied in the case of the inadequate state is the base supply
quantity.times.1.3. The quantity of urea water to be supplied in
the case of the appropriate state is the base supply
quantity.times.1.0.
[0035] At S110, a calculated amount of urea water is injected by
the urea water supply valve 27. Then, at S111, it is determined
whether time t0 has elapsed or not. When the time t0 has elapsed,
the control procedure returns to the start and the sequence of
procedures from S101 through S110 are executed again. When the time
t0 has not yet elapsed, the procedure returns to S111. The above
procedure is executed at a predetermined timing automatically based
on a program stored in a memory of the control device 34.
[0036] The exhaust gas purification apparatus 10 according to the
first embodiment offers the following advantageous effects. [0037]
(1) Departing from the normal EGR control, the control device 34 is
operable to force the opening of the EGR control valve 21 in the
direction to close the valve for a predetermined period of time,
thereby decreasing the amount of exhaust gas refluxed through the
EGR passage 20. Accordingly, the quantity of NOx in exhaust gas
discharged to the exhaust passage 19 is increased. By detecting the
change of values of the OUT-NOx sensor 33 before and after the EGR
decrease control, the state of quantity of ammonia in the SCR
catalyst 24 (i.e. excessive, inadequate or appropriate) can be
determined. [0038] (2) The map 1 shows the relation between the
state of quantity of ammonia and the OUT-NOx sensor value during
the EGR decrease control. If the quantity of ammonia is excessive
and ammonia is slipping, the OUT-NOx sensor value shows a
decreasing tendency when the quantity of IN-NOx increases. If the
quantity of ammonia is inadequate and NOx reduction is not
performed, the OUT-NOx sensor value shows an increasing tendency
when the quantity of IN-NOx increases. If the quantity of ammonia
is appropriate and NOx reduction is performed, the OUT-NOx sensor
value shows a slightly increasing or decreasing tendency (or no
change) when the quantity of IN-NOx increases. The state of
quantity of ammonia in the SCR catalyst 24 can be determined from
the OUT-NOx sensor value based on the map 1. [0039] (3) When the
OUT-NOx sensor value shows a decreasing tendency after the EGR
decrease control, the control device 34 determines that ammonia
contained in the exhaust gas is excessive, thereby controlling to
decrease the quantity of urea water to be supplied from the urea
water supply valve 27. When the OUT-NOx sensor value shows an
increasing tendency, the control device 34 determines that ammonia
contained in the exhaust gas is inadequate, thereby controlling to
increase the quantity of urea water to be supplied from the urea
water supply valve 27. Further, when the OUT-NOx sensor value shows
a slightly increasing or decreasing tendency, the control device 34
determines that ammonia contained in the exhaust gas is
appropriate, thereby controlling to keep the quantity of urea water
to be supplied from the urea water supply valve 27 unchanged. Since
the quantity of urea water to be supplied can be controlled
appropriately in accordance with the quantity of ammonia, the
ammonia slip from the SCR catalyst 24 can be suppressed. Also, by
shortening the predetermined time of the EGR decrease control, the
increase in the quantity of NOx can be suppressed to a level that
causes no tangible ill effects. [0040] (4) Since the state of the
quantity of ammonia can be determined in a short time by the EGR
decrease control, the control is robust and the quantity of ammonia
slip can be suppressed in a short time. [0041] (5) Since the system
according to the first embodiment is accomplished only by adding
software (program) of the EGR decrease control and the control of
increase and decrease of the quantity of urea to be supplied
(quantity of urea supply) without adding any hardware, cost
increase for changing the system can be kept low.
[0042] The following will describe the exhaust gas purification
apparatus according to the second embodiment with reference to
FIGS. 4 and 5. The exhaust gas purification apparatus according to
the second embodiment is made by replacing the EGR decrease control
by the EGR increase control in the exhaust gas purification
apparatus according to the first embodiment. The rest of the
structure and the operation of the exhaust gas purification
apparatus according to the second embodiment are the same as those
of the exhaust gas purification apparatus according to the first
embodiment. The following description will use the same reference
numerals for the common elements or components in the first and the
second embodiments, and the description of such elements or
components will be omitted.
[0043] Departing from the normal EGR control, the control device 34
is operable to force the opening of the EGR control valve 21 in the
direction to open the valve for a predetermined period of time,
thereby increasing the amount of exhaust gas refluxed through the
EGR passage 20 (This control is hereinafter referred to EGR
increase control). Accordingly, the quantity of NOx in exhaust gas
discharged to the exhaust passage 19 is decreased. The state of
quantity of ammonia in the SCR catalyst 24 (i.e. excessive,
inadequate, appropriate) can be determined by detecting the change
of values of the OUT-NOx sensor 33 before and after the EGR
increase control.
[0044] FIG. 4A is a configuration map 2 showing the relation
between the state of quantity of ammonia and the OUT-NOx sensor
value (a value detected by the OUT-NOx sensor 33) during EGR
increase control. If the quantity of ammonia is excessive and
ammonia slip occurs, the OUT-NOx sensor value shows an increasing
tendency when the quantity of IN-NOx decreases. If the quantity of
ammonia is inadequate and NOx reduction is not performed, the
OUT-NOx sensor value shows a decreasing tendency when the quantity
of IN-NOx decreases. If the quantity of ammonia is appropriate and
NOx reduction is performed, the OUT-NOx sensor value shows a
slightly increasing or a slightly decreasing tendency (or a no
change) when the quantity of IN-NOx decreases.
[0045] FIG. 4B is a schematic configuration figure showing the
relation among the quantity of NOx emission, the quantity of
ammonia and the OUT-NOx sensor value for explaining what the map 2
means. Like the characteristic curve shown in FIG. 2B, this
characteristic curve is convex downward with the quantities of NOx
emission and the ammonia on the axis of abscissas and the OUT-NOx
sensor value on the axis of ordinate.
[0046] This characteristic curve shows that the quantity of ammonia
is the most appropriate for the quantity of NOx emission when the
OUT-NOx sensor value is minimum. The characteristic curve is
divided into three regions depending on the value of NOx emission.
The region which includes the minimum OUT-NOx sensor value
represents the ammonia appropriate region. The region in which the
quantities of NOx emission and ammonia are less than those of the
ammonia appropriate region represents the ammonia excessive region
and the region in which the quantities of NOx emission and ammonia
are more than those of the ammonia appropriate region represents
the ammonia inadequate region.
[0047] When the quantity of IN-NOx decreases in the ammonia
excessive region, the point P2 on the characteristic curve moves in
arrow direction shown in FIG. 4B and, therefore, the OUT-NOx sensor
value shows an increasing tendency. When the quantity of IN-NOx
decreases in the ammonia inadequate region, the point Q2 on the
characteristic curve moves in arrow direction shown in FIG. 4B and,
therefore, the OUT-NOx sensor value shows a decreasing tendency.
When the quantity of IN-NOx decreases in the ammonia appropriate
region, points R2, S2 on the characteristic curve move in arrow
direction shown in FIG. 4B and, therefore, the OUT-NOx sensor
values show a slightly increasing tendency and a slightly
decreasing tendency, respectively.
[0048] As appreciated from the above, by monitoring the change of
the OUT-NOx sensor values during the EGR increase control, it can
be determined easily which region of the OUT-NOx sensor value
having cross-sensitivity is being detected. Therefore, the quantity
of urea water to be supplied from the urea water supply valve 27
can be controlled based on the above determination. In other words,
when the OUT-NOx sensor value tends to increase, the control device
34 determines that the quantity of ammonia contained in the exhaust
gas is excessively large, thereby controlling so as to decrease the
quantity of urea water to be supplied from the urea water supply
valve 27. When the OUT-NOx sensor value tends to decrease, the
control device 34 determines that the quantity of ammonia contained
in the exhaust gas is inadequate, thereby controlling so as to
increase the quantity of urea water to be supplied from the urea
water supply valve 27. Further, when the OUT-NOx sensor value shows
a slightly decreasing or increasing tendency, the control device 34
determines that the quantity of ammonia contained in the exhaust
gas is appropriate, thereby controlling so as to keep the quantity
of urea water being supplied from the urea water supply valve 27
unchanged.
[0049] The following will describe a process for controlling the
exhaust gas purification apparatus 10 with reference to the flow
chart shown in FIG. 5. When the processing routine starts, the time
counter, the engine speed and the amount of fuel injection are read
at S201. Then, at S202, the control device 34 determines whether
the engine 11 is in a steady state or not based on the data of the
time counter, the engine speed and the amount of fuel injection
read at S201. The definition of the steady state in the second
embodiment is the same as that of the steady state described in the
first embodiment.
[0050] When it is determined at S202 that the engine 11 is not in
the steady state, the control returns to S201 and the data is read
again.
[0051] When it is determined at S202 that the engine 11 is in the
steady state, the control proceeds to S203 where the value detected
by the OUT-NOx sensor 33 is detected. Then at S204, the EGR
increase control is executed forcibly, so that the operation of the
EGR control valve 21 is controlled so that the opening degree of
the EGR control valve 21 is increased for a certain period of time.
Accordingly, amount of exhaust gas refluxed through the EGR passage
20 increases, thereby decreasing the quantity of IN-NOx in exhaust
gas discharged into the exhaust passage 19. The above certain
period of time is previously set to an appropriate time in
accordance with the temperature of the SCR catalyst 24.
[0052] Then at S205, the value detected by the OUT-NOx sensor 33
after the execution of the EGR increase control is detected. Let m1
and m2 as the values (values detected by the OUT-NOx sensor 33 at
S203, S205, respectively) before and after the EGR increase
control, respectively. At S206, a difference value for the above
values, i.e., .DELTA.m=m1-m2 is calculated. At S207, if
.DELTA.m<-n (n is positive number), it is determined that the
value detected by the OUT-NOx sensor 33 shows an increasing
tendency, if .DELTA.m>n, it is determined that the value
detected by the OUT-NOx sensor 33 shows a decreasing tendency and
if -n.ltoreq..DELTA.m.ltoreq.n, it is determined that the value
detected by the OUT-NOx sensor 33 shows a slightly increasing or
decreasing tendency.
[0053] At S207, based on the map 2 showing the relation between the
state of quantity of ammonia and the OUT-NOx sensor value during
the EGR increase control, determination of the state of quantity of
ammonia (i.e. excessive, inadequate or appropriate state) is made
on the calculated OUT-NOx sensor value. For example, if the OUT-NOx
sensor value shows an increasing tendency (.DELTA.m<-n), it is
determined that the quantity of ammonia is in the excessive state.
If the OUT-NOx sensor value shows a decreasing tendency
(.DELTA.m>n), it is determined that the quantity of ammonia is
in the inadequate state. If the OUT-NOx sensor value shows a
slightly increasing or decreasing tendency
(-n.ltoreq..DELTA.m.ltoreq.n), it is determined that the quantity
of ammonia is in the appropriate state.
[0054] At S208, based on the quantity of ammonia determined at
S207, a correction coefficient is assigned. For example, correction
coefficients 0.7, 1.3 and 1.0 are assigned for the excessive,
inadequate and appropriate states, respectively. At S209, the
quantity of urea water to be supplied is calculated. This
calculation is executed based on the following calculation formula.
Quantity of urea water to be supplied=base supply
quantity.times.correction coefficient. For example, the quantity of
urea water to be supplied in case of the excessive state is the
base supply quantity.times.0.7. The quantity of urea water to be
supplied in case of the inadequate state is the base supply
quantity.times.1.3. The quantity of urea water to be supplied in
the case of the appropriate state is the base supply
quantity.times.1.0.
[0055] At S210, a calculated amount of urea water is injected by
the urea water supply valve 27. Then, at S211, it is determined
whether time t0 has elapsed or not. When the time t0 has elapsed,
the control procedure returns to the start and the sequence of
procedures from S201 through S210 are executed again. When the time
t0 has not yet elapsed, the procedure returns to S211. The above
procedure is executed at a predetermined timing automatically based
on a program stored in a memory of the control device 34.
[0056] The exhaust gas purification apparatus according to the
second embodiment offers the following advantageous effects. [0057]
(6) Departing from the normal EGR control, the control device 34 is
operable to force the opening of the EGR control valve 21 in the
direction to open the valve for a predetermined period of time,
thereby increasing the amount of exhaust gas refluxed through the
EGR passage 20. Accordingly, the quantity of NOx in exhaust gas
discharged to the exhaust passage 19 is decreased. By detecting the
change of values of the OUT-NOx sensor 33 before and after the EGR
increase control, the state of quantity of ammonia in the SCR
catalyst 24 (i.e. excessive, inadequate or appropriate) can be
determined. [0058] (7) The map 2 shows a relation between a state
of quantity of ammonia and an OUT-NOx sensor value during the EGR
increase control. If the quantity of ammonia is excessive and
ammonia is slipping, the OUT-NOx sensor value represents an
increasing tendency when the quantity of IN-NOx decreases. If the
quantity of ammonia is inadequate and NOx reduction is not
performed, the OUT-NOx sensor value represents a decreasing
tendency when the quantity of IN-NOx decreases. If the quantity of
ammonia is appropriate and NOx reduction is performed, the OUT-NOx
sensor value represents a slightly increasing or decreasing
tendency (or no change) when the quantity of IN-NOx decreases. The
state of quantity of ammonia in the SCR catalyst 24 can be
determined from the OUT-NOx sensor value based on the map 2. [0059]
(8) When the OUT-NOx sensor value shows an increasing tendency
after the EGR increase control, the control device 34 determines
that ammonia contained in the exhaust gas is excessive, thereby
controlling to decrease the quantity of urea water to be supplied
from the urea water supply valve 27. When the OUT-NOx sensor value
shows a decreasing tendency, the control device 34 determines that
ammonia contained in the exhaust gas is inadequate, thereby
controlling to increase the quantity of urea water to be supplied
from the urea water supply valve 27. Further, when the OUT-NOx
sensor value shows a slightly increasing or decreasing tendency,
the control device 34 determines that ammonia contained in the
exhaust gas is appropriate, thereby controlling to keep the
quantity of urea water to be supplied from the urea water supply
valve 27 unchanged. Since the quantity of urea water to be supplied
can be controlled appropriately in accordance with the quantity of
ammonia, the ammonia slip from SCR catalyst 24 can be suppressed.
Also, by shortening the predetermined time of the EGR increase
control, the increase in the quantity of NOx can be suppressed to a
level that causes no tangible ill effects. [0060] (9) Since the
state of the quantity of ammonia can be determined in a short time
by the EGR increase control, the control is robust and the quantity
of ammonia slip can be suppressed in a short time. [0061] (10)
Since the system according to the second embodiment is accomplished
only by adding software (program) of the EGR increase control and
the control of increase and decrease of the quantity of urea to be
supplied without adding any hardware, cost increase for changing
the system can be kept low.
[0062] The following will describe the exhaust gas purification
apparatus according to the third embodiment with reference to FIG.
3. The third embodiment differs from the first embodiment in that
the OUT-NOx sensor values before and after EGR decrease control are
stored as history data that is used for correcting the OUT-NOx
sensor values. The following description will use the same
reference numerals for the common elements or components in the
first and the third embodiments and the description of such
elements or components will be omitted.
[0063] The OUT-NOx sensor value detected by the OUT-NOx sensor 33
shows a variation caused by manufacturing error of devices such as
the SCR catalyst 24 and the OUT-NOx sensor 33. The OUT-NOx sensor
value also changes from its standard value due to the secular
change (deterioration) of the SCR catalyst 24, the OUT-NOx sensor
33 and the like. In the present third embodiment, the OUT-NOx
sensor values are stored in the control device 34 as history data.
By analyzing the history data at a predetermined interval, the
variation due to the manufacturing error and the change of the
OUT-NOx sensor values due to the secular change can be checked and
determined.
[0064] FIG. 6A is the flow chart showing the processing routine for
correcting the error of the OUT-NOx sensor value due to the secular
change. At S301, the OUT-NOx sensor value is stored in the control
device 34 as history data. At S302, the mean value of the history
data is calculated at a predetermined interval. For example, the
mean value (mean value of ten times) of the OUT-NOx sensor values
(a1 or a2) is calculated for each ten times of operation according
to the processing routine shown in FIG. 3 and such mean value is
stored in the control device 34. At S303, it is determined from the
stored data of the mean values whether or not there is any
influence due to the secular change. If the mean value of the
OUT-NOx sensor values is significantly higher than that of the
OUT-NOx sensor values stored previously or if the mean values of
the OUT-NOx sensor values are found increasing continuously, the
control device 34 determines that the secular change affects the
OUT-NOx sensor value. Thus, the OUT-NOx sensor value is corrected
by detecting a difference between the latest mean value and the
previous mean value.
[0065] At S304, the OUT-NOx sensor value is corrected based on the
determination at S303. For example, when it is determined that the
mean value of the OUT-NOx sensor values is higher than that of the
OUT-NOx sensor values detected previously and the OUT-NOx sensor
value is affected by the secular change, the OUT-NOx sensor value
detected is corrected so as to approximate its standard sensor
value as much as possible. That is, the sensor values detected
after the correction are regarded to be larger than their standard
sensor values and the EGR control is performed based on the value
that is obtained by subtracting the correction value from the
OUT-NOx sensor value detected. The correction of errors due to the
secular change is performed at a predetermined timing automatically
according to the program stored in the memory of the control device
34.
[0066] FIG. 6B is the flow chart showing the processing routine for
correcting OUT-NOx sensor value affected by the manufacturing
error. OUT-NOx sensor value detected under a predetermined
condition is regarded as the standard sensor value and stored in
the memory in advance.
[0067] At S401, the EGR control is performed under the same
condition as that in which the standard sensor value was detected
and the OUT-NOx sensor values detected are stored in the control
device 34 as the detected value. Specifically, the operation of the
exhaust gas purification apparatus may be controlled so that the
same condition where the standard sensor value was detected is
reproduced and the OUT-NOx sensor values then detected may be
stored as the detected value. Alternatively, among the history data
of OUT-NOx sensor values stored in the control device 34, the
OUT-NOx sensor values detected under the same condition where the
standard sensor value was detected may be chosen and regarded as
the value detected.
[0068] At S402, the OUT-NOx sensor value detected at S401 are
compared with the standard sensor value and then corrected,
accordingly. When the OUT-NOx sensor value is larger than the
standard sensor value, the OUT-NOx sensor value is corrected so as
to approximate its standard OUT-NOx sensor value as much as
possible. In other words, the OUT-NOx sensor values detected after
the correction are regarded to be larger than their standard
OUT-NOx sensor values and then the EGR control is performed based
on the value that is obtained by subtracting the correction value
from the OUT-NOx sensor value.
[0069] The correction of the manufacturing error may be performed
initially for each device or when the SCR catalyst 24, the OUT-NOx
sensor 33 and the like are replaced with new ones for maintenance.
The correction is performed automatically at a predetermined timing
based on the program stored in the memory of the control device
34.
[0070] Since the correction of the manufacturing error and error
due to the secular change is performed based on the stored OUT-NOx
sensor values, it is possible to suppress the influence due to the
manufacturing error and the error due to secular change. Other
advantageous effects are the same as those described in the first
embodiment and the description thereof will be omitted.
[0071] The present invention is not limited to the above
embodiments and the invention may be practiced in various manners
as exemplified below.
[0072] In the first and the second embodiments, the state of the
quantity of ammonia is determined by the change of the OUT-NOx
sensor values before and after the EGR increase or decrease
control. Subsequently, a correction coefficient for urea supply is
assigned based on the state of the quantity of ammonia and the
quantity of urea to be supplied is calculated according to the
correction coefficient. However, the amount of urea to be supplied
may be calculated without using the correction coefficient. That
is, the amount of ammonia (NH3) adsorbed on the SCR catalyst 24 is
calculated from the quantity of IN-NOx (detected by the IN-NOx
sensor 26), the value of the OUT-NOx sensor or the temperature of
the SCR catalyst 24 (detected by the temperature sensor 31) and the
amount of urea corresponding to the ammonia adsorption is
calculated.
[0073] In the first and the second embodiments, the single control
device is used for controlling the quantity of urea water to be
supplied from the urea water supply valve 27 and the operation of
the EGR control valve 21. The quantity of urea water supplied
through the urea water supply valve 27 and the operation of the EGR
control valve 21 may be controlled by separate control devices that
communicate with each other.
[0074] In the third embodiment, the mean value of the OUT-NOx
sensor values is used as history data. However, the cumulative
value of the OUT-NOx sensor values, the number of times of
significant corrections of the quantity of injection, and the mean
value or the cumulative value of the corrected quantities of
injection (corrected injection quantities) may be used as history
data. When the amount of adsorption of ammonia (NH3) is calculated,
the amount of adsorption of ammonia (NH3) may be also dealt with as
history data.
* * * * *