U.S. patent application number 11/660509 was filed with the patent office on 2007-11-08 for particulate matter remaining amount estimating method for particulate filter and particulate filter regenerating method.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Takeshi Hashizume, Tomoyuki Kogo.
Application Number | 20070256408 11/660509 |
Document ID | / |
Family ID | 35355773 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256408 |
Kind Code |
A1 |
Kogo; Tomoyuki ; et
al. |
November 8, 2007 |
Particulate Matter Remaining Amount Estimating Method for
Particulate Filter and Particulate Filter Regenerating Method
Abstract
Every time a specified period of time is counted during
execution of filter regeneration control, a PM remaining amount
every time that the specified period of time passes is estimated by
subtracting the product of the specified period of time, a PM
removal rate per unit time, and a PM remaining amount at the point
when the specified period of time started to be counted from the PM
remaining amount at the point when the specified period of time
started to be counted. As a result, the PM remaining amount during
execution of filter regeneration control which oxidizes and removes
particulate matter that has accumulated on a particulate filter is
estimated with greater accuracy.
Inventors: |
Kogo; Tomoyuki; (Susono-shi,
JP) ; Hashizume; Takeshi; (Mishima-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
1, TOYOTA-CHO
TOYOTA-SHI
JP
471-8571
|
Family ID: |
35355773 |
Appl. No.: |
11/660509 |
Filed: |
August 25, 2005 |
PCT Filed: |
August 25, 2005 |
PCT NO: |
PCT/IB05/02521 |
371 Date: |
February 20, 2007 |
Current U.S.
Class: |
60/286 ;
60/295 |
Current CPC
Class: |
F01N 9/002 20130101;
F01N 3/0253 20130101; Y02T 10/47 20130101; F01N 3/023 20130101;
Y02T 10/40 20130101 |
Class at
Publication: |
060/286 ;
060/295 |
International
Class: |
F01N 3/023 20060101
F01N003/023; F01N 9/00 20060101 F01N009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2004 |
JP |
2004-248564 |
Claims
1. A method for estimating an amount of particulate matter
remaining on a particulate filter, which is provided in an exhaust
passage of an internal combustion engine and traps particulate
matter in exhaust gas, comprising: executing a filter regeneration
control which oxidizes and removes the particulate matter that has
accumulated on the particulate filter by raising the temperature of
the particulate filter; and estimating the remaining amount of the
particulate matter accumulated on the particulate filter is
estimated based on a particulate matter removal rate per unit time
during execution of the filter regeneration control, a particulate
matter accumulation amount on the particulate filter at the start
of execution of the filter regeneration control, and the time
elapsed from the start of execution of the filter regeneration
control.
2. The method for estimating an amount of particulate matter
remaining on a particulate filter according to claim 1, further
comprising: starting to count the elapsed time at the start of
execution of the filter regeneration control; every time a
specified period of time is counted in the elapsed time,
subtracting the product of the specified period of time, the
particulate matter removal rate per unit time, and a remaining
amount of the particulate matter at the point when the specified
period of time started to be counted, from the remaining amount of
particulate matter at the point when the specified period of time
started to be counted; and estimating the remaining amount of
particulate matter every time the specified period of time passes
according to the subtraction calculation.
3. The method for estimating an amount of particulate matter
remaining on a particulate filter according to claim 1, wherein the
particulate matter removal rate per unit time is set to be a higher
value the greater the flow rate of exhaust gas flowing into the
particulate filter.
4. The method for estimating an amount of particulate matter
remaining on a particulate filter according to claim 1, wherein the
particulate matter removal rate per unit time is set to be a higher
value the higher an oxygen concentration of exhaust gas flowing
into the particulate filter.
5. The method for estimating an amount of particulate matter
remaining on a particulate filter according to claim 1, wherein the
particulate matter removal rate per unit time is set to be a higher
value the higher the temperature of the particulate filter.
6. A method for regenerating a particulate filter, comprising:
calculating, according to the method for estimating an amount of
particulate matter remaining on a particulate filter according to
claim 3, a remaining amount of particulate matter at the point an
operating state of the internal combustion engine changes, when the
operating state of the internal combustion engine changes during
execution of the filter regeneration control; calculating a
duration of the filter regeneration control necessary to oxidize
and remove remaining particulate matter based on the calculated
remaining amount of particulate matter and the particulate matter
removal rate per unit time set in accordance with the operating
state of the internal combustion engine after the operating state
of the internal combustion engine changed; and stopping the filter
regeneration control when the duration is equal to, or greater
than, a predetermined duration.
7. A method for regenerating a particulate filter, comprising:
calculating, according to the method for estimating an amount of
particulate matter remaining on a particulate filter according to
claim 4, a remaining amount of particulate matter at the point an
operating state of the internal combustion engine changes, when the
operating state of the internal combustion engine changes during
execution of the filter regeneration control; calculating a
duration of the filter regeneration control necessary to oxidize
and remove remaining particulate matter based on the calculated
remaining amount of particulate matter and the particulate matter
removal rate per unit time set in accordance with the operating
state of the internal combustion engine after the operating state
of the internal combustion engine changed; and stopping the filter
regeneration control when the duration is equal to, or greater
than, a predetermined duration.
8. A method for regenerating a particulate filter, comprising:
calculating, according to the method for estimating an amount of
particulate matter remaining on a particulate filter according to
claim 5, a remaining amount of particulate matter at the point an
operating state of the internal combustion engine changes, when the
operating state of the internal combustion engine changes during
execution of the filter regeneration control; calculating a
duration of the filter regeneration control necessary to oxidize
and remove remaining particulate matter based on the calculated
remaining amount of particulate matter and the particulate matter
removal rate per unit time set in accordance with the operating
state of the internal combustion engine after the operating state
of the internal combustion engine changed; and stopping the filter
regeneration control when the duration is equal to, or greater
than, a predetermined duration.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a method for estimating the amount
of particulate matter remaining on a particulate filter, which is
provided in an exhaust passage of an internal combustion engine and
traps particulate matter contained in exhaust gas, during filter
regeneration control which oxidizes and removes particulate matter
that has accumulated on the particulate filter. The invention also
relates to a method for regenerating a particulate filter.
[0003] 2. Description of the Related Art
[0004] In an internal combustion engine provided with a particulate
filter (hereinafter simply referred to as "filter") that traps
particulate matter (hereinafter simply referred to as "PM") in
exhaust gas in an exhaust passage, filter regeneration control is
performed which oxidizes and removes PM that has accumulated on the
filter by raising the temperature of the filter.
[0005] Further, JP(A) 2003-293733 discloses technology which
estimates the amount of PM remaining on the filter during execution
of filter regeneration control (hereinafter also referred to as "PM
remaining amount") based on the amount of PM accumulated on the
filter at the start of execution of the filter regeneration control
(hereinafter also referred to as "PM accumulation amount"). Here,
the amount of PM removed per unit time during the execution of
filter regeneration control (hereinafter simply referred to as "PM
removal amount") is determined according to the PM accumulation
amount at the start of filter regeneration control. The amount of
change from the amount of PM accumulated on the filter at the start
of filter regeneration control is calculated by adding up the
amount of PM removed per unit time. The PM remaining amount
accumulated on the filter during filter regeneration control is
estimated from the calculated amount of change and the PM
accumulation amount at the start of filter regeneration control.
Also, the PM removal amount per unit time during the execution of
filter regeneration control is set to be larger the greater the PM
accumulation amount at the start of execution of the filter
regeneration control.
[0006] Also, U.S. Pat. No. 2,616,074 and JP(A) 2000-170521 are
examples of documents relating to this invention.
[0007] In filter regeneration control, in order to make the end
timing of that control more appropriate, it is necessary to know
the PM remaining amount while the filter regeneration control is
being executed. Further, when the filter regeneration control is
stopped prematurely, i.e., when the filter regeneration control is
stopped while there is still PM on the filter, and the PM remaining
amount at the time that the filter regeneration control was stopped
is not known, it also becomes difficult to know the PM accumulation
amount after that point. As a result, the next cycle of filter
regeneration control might not be able to be started at the
appropriate timing.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing problems, this invention thus
provides technology that enables the amount of PM remaining on the
filter during execution of filter regeneration control to be
estimated with greater accuracy.
[0009] Thus, one exemplary embodiment of the invention relates to a
method for estimating the amount of PM remaining on a filter, which
is provided in an exhaust passage of an internal combustion engine
and traps PM in exhaust gas, during execution of filter
regeneration control which oxidizes and removes PM that has
accumulated on the filter, by raising the temperature of the
filter. This filter PM remaining amount estimating method estimates
the PM remaining amount based on a PM removal rate per unit time
during execution of the filter regeneration control, a PM
accumulation amount at the start of execution of the filter
regeneration control, and the time elapsed from the start of
execution of the filter regeneration control.
[0010] When PM that has accumulated on the filter is removed by
filter regeneration control, the PM removal amount per unit time
changes according to the PM accumulation amount. That is, during
execution of the filter regeneration control, the PM accumulation
amount gradually reduces over time. As a result, the PM removal
amount per unit time also gradually decreases.
[0011] Therefore, when the PM removal amount during execution of
the filter regeneration control is calculated by determining the PM
removal amount per unit time according to the PM accumulation
amount at the start of regeneration and then adding up the PM
removal amounts per unit time, that calculated PM removal amount
may be a larger value than the actual PM removal amount. Therefore,
when the PM remaining amount during execution of the filter
regeneration control is calculated by subtracting the thus
calculated PM removal amount from the PM accumulation amount at the
start of execution of the filter regeneration control, that
calculated PM remaining amount may be off from the actual PM
remaining amount.
[0012] Therefore, this invention uses the PM removal rate per unit
time during execution of the filter regeneration control to
estimate the PM remaining amount during execution of the filter
regeneration control. The PM removal rate in this case is the PM
removal amount per unit PM accumulation amount. That is, the PM
removal rate per unit time is the PM removal amount per unit PM
accumulation amount in a unit of time, i.e., (PM removal amount per
unit PM accumulation amount) per unit time. This PM removal rate
per unit time can be determined beforehand through experimentation
or the like.
[0013] The PM removal rate per unit time does not change even if
the PM accumulation amount gradually decreases over time during
execution of the filter regeneration control. Therefore, the
invention makes it possible to more accurately estimate the PM
remaining amount during execution of the filter regeneration
control.
[0014] In this invention, the PM remaining amount may be estimated
every time a specified period of time passes, by starting to count
the elapsed time at the start of execution of the filter
regeneration control, and, every time a specified period of time in
this elapsed time is counted, subtracting the product of the
specified period of time, the PM removal rate per unit time, and
the PM remaining amount at the point when counting of the specified
period of time started from the PM remaining amount at the point
when counting of the specified time started.
[0015] In this case, the specified period of time is preferably a
preset value and as short as possible. For example, the specified
period of time may be a unit of time which determines the PM
removal rate per unit time.
[0016] According to the method described above, the PM accumulation
amount at the point when the specified period of time has been
counted from the start of execution of the filter regeneration
control, i.e., the PM accumulation amount at the point when the
specified period of time has passed from the start of execution of
the filter regeneration control, is calculated by subtracting the
product of the specified period of time, the PM removal rate per
unit time, and the PM accumulation amount at the start of the
filter regeneration control from the PM accumulation amount at the
start of filter regeneration control.
[0017] Then, the PM accumulation amount (PM remaining amount)
gradually decreases as time passes after the start of execution of
the filter regeneration control. However, after the specified
period of time has passed from the start of execution of the filter
regeneration control, and every time the specified period of time
is counted, i.e., every time the specified period of time passes,
that specified period of time, the PM removal rate per unit time,
and the PM remaining amount at the point at which the specified
period of time at that time started to be counted are multiplied
together to calculate the PM removal amount to be removed from the
filter during the specified period of time at that time. This PM
removal amount is then subtracted from the PM remaining amount at
the point at which the specified period of time at that time
started to be counted to calculate the PM remaining amount at the
point at which the specified period of time at that time was
counted.
[0018] This kind of method enables the PM removal amount to be
removed every time the specified period of time passes to be
calculated more accurately during execution of the filter
regeneration control. As a result, the PM remaining amount every
time the specified period of time passes can be estimated with
greater accuracy.
[0019] In the foregoing method for estimating the amount of
particulate matter remaining on a filter, the PM removal rate per
unit time may be set to a higher value the greater the flow rate of
exhaust gas flowing into the filter.
[0020] This is because the heat quantity and oxygen amount supplied
to the PM accumulated on the filter increases the greater the flow
rate of the exhaust gas flowing into the filter, which tends to
promote oxidation and removal of PM by the filter regeneration
control.
[0021] As a result, the PM removal rate per unit time can be set to
a more accurate value, thus enabling the PM remaining amount during
execution of filter regeneration control to be estimated more
accurately.
[0022] In the foregoing method for estimating the amount of
particulate matter remaining on a filter, the PM removal rate per
unit time may be set to a higher value the greater the oxygen
concentration in the exhaust gas flowing into the filter.
[0023] This is because the oxygen amount supplied to the PM
accumulated on the filter increases the greater the oxygen
concentration in the exhaust gas flowing into the filter, which
tends to promote oxidation and removal of PM by the filter
regeneration control.
[0024] As a result, the PM removal rate per unit time can be set to
a more accurate value, thus enabling the PM remaining amount during
execution of filter regeneration control to be estimated more
accurately.
[0025] In the foregoing method for estimating the amount of
particulate matter remaining on a filter, the PM removal rate per
unit time may be set to a higher value the higher the temperature
of the filter.
[0026] This is because higher filter temperatures tend to promote
the oxidation and removal of PM by the filter regeneration
control.
[0027] As a result, the PM removal rate per unit time can be set to
a more accurate value, thus enabling the PM remaining amount during
execution of filter regeneration control to be estimated more
accurately.
[0028] Another exemplary embodiment of the invention relates to a
method for regenerating a filter. When the operating state of the
internal combustion engine changes during execution of the filter
regeneration control, the regenerating method calculates the PM
remaining amount at the time of that change according to the method
for estimating the amount of PM remaining on a filter described
above which changes the PM removal rate per unit time according to
any one of at least a flow rate of exhaust gas flowing into the
filter, an oxygen concentration in the exhaust gas flowing into the
filter, and the temperature of the filter. A duration of the filter
regeneration control necessary to oxidize and remove the remaining
PM is then calculated based on the PM remaining amount at that time
and the PM removal rate per unit time which is set according to the
new (i.e., changed) operating state of the internal combustion
engine. The filter regeneration control stops when that duration is
equal to, or greater than, a specified duration.
[0029] When the operating state of the internal combustion engine
changes, the flow rate, oxygen concentration, and temperature of
the exhaust gas flowing into the filter may also change. When those
change, the temperature of the filter may also change. Therefore,
when the operating state of the internal combustion engine changes
during execution of the filter regeneration control, the PM removal
rate per unit time may be different after the change than it was
before the change.
[0030] If the PM removal rate per unit time drops due to a change
in operating state of the internal combustion engine, the duration
of the filter regeneration control necessary to oxidize and remove
the remaining PM becomes longer. If the filter regeneration control
is executed for too long, however, it may lead to deterioration in
exhaust gas emissions.
[0031] Thus, the invention calculates the duration of the filter
regeneration control necessary for oxidizing and removing the
remaining PM based on the PM remaining amount at the point when the
operating state of the internal combustion engine changed and the
PM removal rate per unit time that is set according to the
operating state of the internal combustion engine after the
operating state has changed. The filter regeneration control is
then stopped when the calculated duration is equal to, or greater
than, a specified duration.
[0032] The specified duration in this case is a period of time that
is equal to, or less than, a threshold value at which it can be
determined that there is a risk of leading to a deterioration in
fuel efficiency or exhaust gas emissions due to the filter
regeneration control being executed for too long.
[0033] The invention makes it possible to inhibit the filter
regeneration control from being executed for too long. As a result,
it is possible to suppress deterioration in fuel efficiency and
exhaust gas emissions.
[0034] The method for estimating the amount of particulate matter
remaining on a particulate filter according to the invention makes
it possible to more accurately estimate the PM remaining amount
during execution of filter regeneration control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The above mentioned and other features, advantages,
technical and industrial significance of this invention will be
better understood by reading the following detailed description of
preferred embodiments of the invention, when considered in
connection with the accompanying drawings, in which:
[0036] FIG. 1 is a schematic diagram of an internal combustion
engine and intake and exhaust systems thereof according to first
and second exemplary embodiments of the invention;
[0037] FIG. 2 is a graph showing the shift in PM remaining amount
during execution of filter regeneration control;
[0038] FIG. 3 is a flowchart illustrating a PM remaining amount
estimating routine for estimating the PM remaining amount during
execution of filter regeneration control, according to the first
and second exemplary embodiments of the invention; and
[0039] FIG. 4 is a flowchart illustrating a routine for controlling
the stopping or continuation of the filter regeneration control,
according to the second exemplary embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] In the following description and the accompanying drawings,
the present invention will be described in more detail in terms of
exemplary embodiments.
[0041] A first exemplary embodiment of the invention will first be
described. FIG. 1 is a schematic diagram of an internal combustion
engine and intake and exhaust systems thereof according to this
exemplary embodiment. The internal combustion engine 1 is a diesel
engine for driving a vehicle. A piston 3 is slidably provided in a
cylinder 2 of the internal combustion engine 1. An intake port 4
and an exhaust port 5 are connected to a combustion chamber in an
upper portion in the cylinder 2. The portion of the intake port 4
which is open to the combustion chamber is opened and closed by an
intake valve 6, and the portion of the exhaust port 5 which is open
to the combustion chamber is opened and closed by an exhaust valve
7. The intake port 4 is connected to an intake passage 8 and the
exhaust port 5 is connected to an exhaust passage 9. Also, a fuel
injection valve 10 which injects fuel directly into the cylinder 2
is provided in the cylinder 2.
[0042] The intake passage 8 is provided with a throttle valve 15
which controls the intake air amount and an airflow meter 16 which
outputs an electric signal indicative of the intake air amount.
[0043] The exhaust passage 9 is provided with a filter 11 that
traps PM in the exhaust gas. This filter 11 carries an oxidation
catalyst. The catalyst carried on the filter 11 need only have an
oxidizing function, so a NOx storage-reduction catalyst, for
example, may be used. Also, the catalyst does not have to be
carried on the filter 11 itself, i.e., the catalyst may be disposed
in the exhaust passage 9 upstream of the filter 11.
[0044] A fuel adding valve 12 which adds fuel to the exhaust gas is
provided in the exhaust passage 9 upstream of the filter 11. An
oxygen concentration sensor 14 that outputs an electric signal
indicative of the oxygen concentration in the exhaust gas is
provided in the exhaust passage 9 upstream of the filter 11 and
downstream of the fuel adding valve 12. Also, an exhaust gas
temperature sensor 13 which outputs an electric signal indicative
of the temperature of the exhaust is provided in the exhaust
passage 9 downstream of the filter 11.
[0045] An ECU 20 for controlling the internal combustion engine 1
is disposed adjacent to the internal combustion engine 1 which is
structured as described above. Various sensors are connected to the
ECU 20 via electrical wiring, through which they send output
signals to the ECU 20. Some of these sensors include the exhaust
gas temperature sensor 13, the oxygen concentration sensor 14, the
airflow meter 16, a crank position sensor 17 which outputs an
electric signal indicative of the crank angle, and an accelerator
opening amount sensor 18 which outputs an electric signal
indicative of the accelerator opening amount. The ECU 20 is also
electrically connected to the fuel injection valve 10, the fuel
adding valve 12, and the throttle valve 15, which are controlled by
the ECU 20.
[0046] Next, the filter regeneration control will be described. In
this exemplary embodiment, the filter regeneration control for
oxidizing and removing accumulated PM starts when the PM
accumulation amount at the filter 11, which is estimated based on
the accumulated fuel injection quantity from the fuel injection
valve 10 and the like, becomes a preset PM accumulation amount Qst
for starting regeneration. In the filter regeneration control
according to this exemplary embodiment, the temperature of the
filter 11 rises by oxidation heat generated when fuel is added from
the fuel adding valve 12 and that added fuel is oxidized at the
oxidation catalyst carried on the filter 11. As a result, the PM
accumulated on the filter 11 is oxidized and removed. In the filter
regeneration control, instead of fuel being added from the fuel
adding valve 12, fuel may be supplied to the oxidation catalyst
carried on the filter 11 by a secondary fuel injection after a main
fuel injection has been performed by the fuel injection valve
10.
[0047] Next, the method for estimating the amount of PM remaining
during execution of filter regeneration control will be described.
When filter regeneration control is performed, it is extremely
important to know the PM remaining amount during execution of the
filter regeneration control in order to make the end timing of the
filter regeneration control, as well as the start timing of the
next cycle of filter regeneration control when the filter
regeneration control has been stopped while PM still remains on the
filter, more appropriate.
[0048] Regarding this, the shift in the PM remaining amount during
execution of filter regeneration control will be described based on
the graph shown in FIG. 2. In FIG. 2, the vertical axis represents
the PM remaining amount (i.e., PM accumulation amount) and the
horizontal axis represents the time passed since the start of
execution of the filter regeneration control.
[0049] When the PM accumulated on the filter 11 is oxidized by
filter regeneration control, the heat quantity generated by
oxidation of the PM increases the greater the PM accumulation
amount. Therefore, oxidation of the PM that exists around the
oxidized PM is further promoted. During execution of the filter
regeneration control, however, oxidation and removal of the PM
progresses over time so the PM accumulation amount decreases. As
the PM accumulation amount decreases, so does the heat quantity
generated by oxidation of the PM, which makes it more difficult for
oxidation of the PM existing around the oxidized PM to progress.
That is, during execution of the filter regeneration control, the
PM accumulation amount gradually decreases over time thus making it
more difficult for the oxidation of the PM to progress. As a
result, the decrease amount per unit time of the PM remaining
amount also decreases over time. Therefore, during execution of the
filter regeneration control, the PM remaining amount decreases
exponentially over time, as shown in FIG. 2.
[0050] Thus, in this exemplary embodiment, the PM remaining amount
during execution of filter regeneration control is estimated using
a PM removal rate per unit time Rt during the execution of filter
regeneration control. The PM removal rate per unit time Rt is the
PM removed amount per unit time in units of PM accumulation amount.
Unless the operating state of the internal combustion engine
changes, this PM removal rate per unit time Rt remains a constant
value regardless of the passing of time during the execution of
filter regeneration control.
[0051] Hereinafter, a specific filter PM remaining amount
estimation method during execution of filter regeneration control
according to this exemplary embodiment will be described. In this
exemplary embodiment, the time elapsing from the start of execution
of filter regeneration control starts to be counted upon the start
of execution of the filter regeneration control. A PM remaining
amount Q1 at the point when a specified period of time .DELTA.t has
been counted from the start of execution of the filter regeneration
control is calculated by subtracting the product of the specified
period of time .DELTA.t, the PM removal rate per unit time Rt, and
the PM accumulation amount Qst at the start of regeneration from
the PM accumulation amount at the starting point of execution of
the filter regeneration control, i.e., from the PM accumulation
amount Qst at the start of regeneration.
[0052] Then, after the specified period of time .DELTA.t has passed
from the start of execution of filter regeneration control, and
every time that specified period of time .DELTA.t is counted, the
PM remaining amount at that time is calculated. That is, every time
the specified period of time .DELTA.t is counted, that specified
period of time .DELTA.t, the PM removal rate per unit time, Rt and
the PM remaining amount at the time the specified period of time
.DELTA.t that time started to be counted, i.e., a PM remaining
amount Q.sub.n-1 at the point when counting of the last specified
period of time .DELTA.t ends, are multiplied together to calculate
the PM removal amount to be removed from the filter 11 during the
specified period of time .DELTA.t that time. This calculated PM
removal amount is then subtracted from the PM remaining amount
Q.sub.n-1 at the point when the specified period of time .DELTA.t
starts to be counted at that time to calculate a PM remaining
amount Q.sub.n-1 at the point when the specified period of time
.DELTA.t that time has been counted.
[0053] Here, a PM remaining amount estimation routine for
estimating the PM remaining amount during execution of filter
regeneration control according to this exemplary embodiment will be
described with reference to the flowchart shown in FIG. 3. This
routine is stored beforehand in the ECU 20 and is executed every
time the crankshaft rotates a specified crank angle while the
internal combustion engine 1 is running.
[0054] In this routine, first at step S101, the ECU 20 determines
whether the filter regeneration control is being executed. If this
determination is YES, the ECU 20 proceeds on to step S102. If the
determination is NO, the ECU 20 ends execution of this cycle of the
routine.
[0055] In step S102, the ECU 20 determines whether a specified
period of time .DELTA.t has been counted since the start of
execution of filter regeneration control, i.e., whether a specified
period of time .DELTA.t has passed since the start of execution of
filter regeneration control. As described above, counting of the
time that passes from the start of execution of the filter
regeneration control is started at the start of execution of filter
regeneration control. If the determination in step S102 is YES, the
ECU 20 proceeds on to step S103. If, on the other hand, that
determination is NO, the ECU 20 proceeds on to step S105.
[0056] In step S103, the ECU 20 calculates a PM remaining amount Q1
at the current point, i.e., at the point when the specified period
of time .DELTA.t has been counted since the start of execution of
the filter regeneration control. This calculation is performed by
subtracting the product of the specified period of time .DELTA.t,
the PM removal rate per unit time Rt, and the PM accumulation
amount Qst at the start of regeneration from the PM accumulation
amount Qst at the start of regeneration.
[0057] Next, the ECU 20 proceeds on to step S104, where it stores
the PM remaining amount Q1 calculated in step S103, after which the
routine ends. Here, the stored PM remaining amount Q1 is the PM
remaining amount at the time the next specified period of time
.DELTA.t starts to be counted (i.e., at the time the second
specified period of time .DELTA.t starts to be counted).
[0058] Meanwhile, at step S105, the ECU 20 determines whether the
time that has passed since the start of execution of the filter
regeneration control is longer than the specified period of time
.DELTA.t. If this determination is YES, then the ECU 20 proceeds on
to step S106. If, on the other hand, the determination is NO, the
ECU 20 determines that the time that has passed since the start of
execution of the filter regeneration control has not reached the
specified period of time .DELTA.t and ends execution of this cycle
of the routine.
[0059] In step S106, the ECU 20 determines whether the specified
period of time .DELTA.t since the end of the counting of the last
specified period of time .DELTA.t has been counted, i.e., whether
the specified period of time .DELTA.t since the counting of the
last specified period of time .DELTA.t ended has passed. If this
determination is YES, the ECU 20 proceeds on to step S107. If the
determination is NO, the ECU determines that the time that has
passed since the time the counting of the last specified period of
time .DELTA.t ended has not reached the specified period of time
.DELTA.t, and ends execution of this cycle of the routine.
[0060] In step S107, the ECU calculates a PM remaining amount
Q.sub.n at the current point, i.e., at the point when the counting
of the present specified period of time .DELTA.t ends. This
calculation is performed by subtracting the product of the
specified period of time .DELTA.t, the PM removal rate per unit
time Rt, and the PM remaining amount at the point when counting of
the present specified period of time .DELTA.t started, i.e., the PM
accumulation amount Q.sub.n-1 at the point when counting of the
last specified period of time .DELTA.t ended, from the PM
accumulation amount Q.sub.n-1 at the point when counting of the
last specified period of time .DELTA.t ended.
[0061] Next, the ECU 20 proceeds to step S108, where it stores the
PM remaining amount Q.sub.n calculated in step S107, after which
the routine ends. Here, the stored PM remaining amount Q.sub.n is
the PM remaining amount at the point when the count of the next
specified period of time .DELTA.t starts (i.e., at the point when
the counting of a n+1 specified period of time .DELTA.t starts,
where n is the count of the present specified period of time).
[0062] By executing the routine described above, the PM remaining
amount every time the specified period of time .DELTA.t passes can
be more accurately estimated during execution of filter
regeneration control.
[0063] The specified period of time .DELTA.t according to this
exemplary embodiment is preferably made as short as possible. Also,
when the PM removal rate per unit time Rt is set as the PM removal
rate per 1 min, for example, the specified period of time .DELTA.t
may also be set to 1 min.
[0064] Next, the method of setting the PM removal rate per unit
time Rt during execution of filter regeneration control according
to this exemplary embodiment will be described. The state of PM
oxidation and removal during execution of filter regeneration
control changes depending on the flow rate and oxygen concentration
of the exhaust gas flowing into the filter 11, as well as on the
temperature of the filter 11. Therefore, in this exemplary
embodiment, the PM removal rate per unit time Rt is changed
according to these values. That is, the PM removal rate per unit
time Rt is set to a higher value the greater the tendency for PM
oxidation and removal to be promoted during execution of filter
regeneration control.
[0065] More specifically, the heat quantity and oxygen from the
exhaust gas supplied for PM oxidation increase the greater the flow
rate of exhaust gas flowing into the filter 11. Also, the oxygen
from the exhaust gas supplied to the PM increases the higher the
oxygen concentration in the exhaust gas. Accordingly, PM oxidation
and removal tend to be promoted the greater the flow rate of
exhaust gas flowing into the filter 11 and the higher the oxygen
concentration in the exhaust gas. For this reason, the PM removal
rate per unit time Rt is set to a high value. Similarly, the heat
quantity supplied for PM oxidation increases the higher the
temperature of the filter 11, which tends to promote PM oxidation
and removal, so the PM removal rate per unit time Rt is set to a
high value.
[0066] By setting the PM removal rate per unit time in this way, it
is possible to set the PM removal rate per unit time to a more
accurate value, and therefore possible to more accurately estimate
the PM remaining amount during execution of filter regeneration
control.
[0067] The flow rate of exhaust gas flowing into the filter 11 is
estimated based on a detection value from the airflow meter 16.
Also, the oxygen concentration in the exhaust gas flowing into the
filter 11 may either be detected by the oxygen concentration sensor
14, or estimated based on the intake air amount and the fuel
injection amount from the fuel injection valve 10. Further, the
temperature of the filter 11 is estimated based on a detection
value from the exhaust gas temperature sensor 13.
[0068] Next, a second exemplary embodiment of the invention will be
described. The general structure of an internal combustion engine
and the intake and exhaust systems thereof according to the second
exemplary embodiment is similar to that described in the first
exemplary embodiment above, so a description thereof will be
omitted.
[0069] Here, a method for regenerating a filter when the operating
state of the internal combustion engine 1 has changed during filter
regeneration control according to the second exemplary embodiment
will be described.
[0070] When the operating state of the internal combustion engine 1
changes, that change may produce changes in the flow rate and
oxygen concentration of the exhaust gas flowing into the filter 11,
as well as in the temperature of the filter 11. Therefore, if the
operating state of the internal combustion engine 1 changes during
execution of the filter regeneration control, so too might the PM
removal rate per unit time Rt.
[0071] If the PM removal rate per unit time Rt drops as a result of
a change in the operating state of the internal combustion engine 1
during execution of filter regeneration control, the duration of
the filter regeneration control necessary to oxidize and remove the
remaining PM increases. If the filter regeneration control is
executed for too long, however, it may lead to a deterioration in
fuel efficiency and exhaust gas emissions.
[0072] Therefore, in this exemplary embodiment, by executing the
control routine shown in FIG. 4, the filter regeneration control is
stopped when the operating state of the internal combustion engine
1 changes during execution of the filter regeneration control and
it has been determined that the duration of the filter regeneration
control is too long.
[0073] FIG. 4 is a flowchart illustrating a routine for controlling
the stopping or continuation of the filter regeneration control
according to this exemplary embodiment. This routine is stored in
advance in the ECU 20 and is executed every time the crankshaft
rotates a specified crank angle while the internal combustion
engine 1 is running.
[0074] In this routine, first in step S201, the ECU 20 determines
whether the filter regeneration control is being executed. If this
determination is YES, the ECU 20 proceeds on to step S202. If, on
the other hand, that determination is NO, the ECU 20 ends execution
of this cycle of the routine.
[0075] In step S202, the ECU 20 determines whether the operating
state of the internal combustion engine 1 has changed. If this
determination is YES, the ECU 20 proceeds on to step S203. If that
determination is NO, the ECU 20 proceeds on to step S207, where the
filter regeneration control is continued.
[0076] In step S203, the ECU 20 changes the value of the PM removal
rate per unit time Rt based on the temperature of the filter 11 and
the flow rate and oxygen concentration of the exhaust gas after the
change in operating state of the internal combustion engine 1.
Because the temperature of the filter 11 and the flow rate and
oxygen concentration of the exhaust gas become values in accordance
with the operating state of the internal combustion engine 1, the
relationship between the operating state of the internal combustion
engine 1 and the PM removal rate per unit time Rt may be obtained
through experimentation or the like and mapped beforehand, and the
value of the PM removal rate per unit time Rt may be derived from
this map.
[0077] Next, the ECU 20 proceeds on to step S204, where it
calculates the duration of the filter regeneration control
necessary to oxidize and remove the remaining PM based on the PM
removal rate per unit time Rt that was changed in step S203 and a
PM remaining amount Qch at the present time, i.e., at the time when
the operating state of the internal combustion engine 1 changed.
The PM remaining amount Qch at the present time is estimated by the
method for estimating the remaining amount of PM in the filter
during execution of the filter regeneration control according to
the first exemplary embodiment.
[0078] Next, the ECU 20 proceeds on to step S205, where it is
determined whether the duration of the filter regeneration control
calculated in step S204 is equal to, or greater than, a specified
duration .DELTA.tc. Here, the specified duration .DELTA.tc is the
time of a threshold value at which it is possible to determine that
there is a possibility of fuel efficiency and exhaust gas emissions
deteriorating due to the filter regeneration control being executed
for too long. If the determination in step S205 is YES, the ECU 20
proceeds on to step S206. If the determination in step S205 is NO,
on the other hand, the ECU 20 proceeds on to step S207.
[0079] In step S206, the ECU 20 stops the fuel regeneration control
and ends execution of this cycle of the routine.
[0080] By executing the routine described above, the filter
regeneration control can be inhibited from being executed for too
long. As a result, it is possible to suppress deterioration in fuel
efficiency and exhaust gas emissions.
* * * * *