FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“DPF PM ACCUMULATION QUANTITY ESTIMATION DEVICE”
MITSUBISHI HEAVY INDUSTRIES, LTD., a Japanese
company, of 16-5, Konan 2-chome, Minato-ku, Tokyo
1088215, Japan
The following specification particularly describes the invention and the
manner in which it is to be performed.
2
TITLE
PM ACCUMULATION AMOUNT ESTIMATION DEVICE FOR DPF
[Technical Field]
5 [0001]
The present invention relates to a PM accumulation amount estimation device
for estimating an accumulation amount of PM (Particulate Matter, hereinafter simply
referred to as PM) accumulated in a diesel particulate filter (hereinafter, simply
referred to as DPF) for collecting the PM in the exhaust gas emitted from a diesel
10 engine.
BACKGROUND ART
[0002]
DPFs have been known as an effective technology for removing PM in exhaust
15 gas from a diesel engine.
The DPF is a PM collecting device using a filter and is arranged in an exhaust
path. The DPF is configured to collect PM such as soot exhausted from the engine by
a filter and then remove PM from the exhaust gas. A part of the PM collected by the
DPF is combusted by exhaust gas of high temperature exhausted from the engine
20 (natural regeneration), and the rest of the collected PM accumulates in the DPF.
When the accumulation of PM progresses excessively, PM collection performance
declines and the engine output declines. Therefore, in DPFs, it is necessary to
perform an active regeneration at an appropriate timing to actively burn the PM
accumulated in the filter and regenerate the filter.
25 [0003]
To determine an appropriate timing for performing the active regeneration, it
is necessary to accurately estimate a PM accumulation amount of the filter. If the
PM accumulation amount is underestimated, the active regeneration timing is
delayed. This causes decline of the PM collection performance, decline of the engine
30 output, and so on, and possibly causes damage to the DPF due to excessive
temperature rise during the active regeneration. In contrast, if the PM
accumulation amount is overestimated, the active regeneration is performed
frequently and issues such as deterioration of fuel economy and oil dilution.
[0004]
35 The formula for estimating the accumulation amount of PM accumulated in
the filter of the DPF is typically represented by the following formula (1).
3
PM accumulation amount = PM emission amount – PM regeneration amount•••(1)
The PM emission amount here is an amount of PM contained in the exhaust
gas exhausted from the engine. Further, the PM regeneration amount particularly is
a passive regeneration amount, which is an amount of PM burned by the exhaust gas
of high temperature exhausted from the engine during normal 5 operation and not
during the active regeneration.
[0005]
The above PM emission amount is computed using a map having an engine
rotation speed and a fuel injection amount as input data. On the other hand, the PM
10 regeneration amount is computed based on measured values from a variety of sensors
such as a temperature sensor, a pressure sensor, an airflow meter, in addition to the
engine rotation speed and the fuel injection amount. Thus, if a sensor such as the
airflow meter fails, it is difficult to estimate the PM regeneration amount.
[0006]
15 Patent Reference 1 discloses a technology for avoiding excessive accumulation
of PM in a filter when sensors necessary for estimating the PM regeneration amount,
such as the airflow meter fails. According to Patent Reference 1, in such case, the
PM accumulation amount is computed as PM accumulation amount ≒ PM emission
amount without computing the PM regeneration amount according to the above
20 formula (1) so as to prevent underestimation of the PM accumulation amount.
[Citation List]
[Patent Reference]
[0007]
25 [Patent Reference 1]
JP 2006-316746 A
SUMMARY
[Technical Problem]
30 [0008]
However, when computing the PM accumulation amount as described in Patent
Reference 1, the PM regeneration amount is completely disregarded and thus, the PM
accumulation amount is overestimated. Therefore, the active regeneration of the
DPF is performed more frequently, resulting in the issues such as deterioration of the
35 fuel economy and the oil dilution. Further, the airflow meter (especially, a hot wire
airflow meter) tends to fail from being dirty, and is likely to have an abnormality
4
compared to other sensors.
[0009]
In view of the above issues, it is an object of the present invention to provide a
PM accumulation amount estimation device for estimating a PM accumulation
amount with higher accuracy than a conventional device, even when 5 an abnormality
is found in an airflow meter.
[Solution to Problem]
[0010]
10 The present invention has been made to solve the above issues of the related
art and to achieve the above object.
A PM accumulation amount estimation device according to an aspect of the
present invention comprises:
a diesel particulate filter (DPF) configured to collect exhaust gas particulate
15 matter (PM) in exhaust gas exhausted to an exhaust path from an internal
combustion engine;
a PM accumulation amount estimation unit configured to estimate a PM
accumulation amount of PM accumulating in the DPF;
an emission amount computation unit configured to compute a PM emission
20 amount of the PM exhausted to the exhaust path; and
a passive regeneration amount computation unit configured to compute a PM
regeneration amount of the PM passively regenerated in the DPF, and
the PM accumulation amount estimation unit is configured to estimate the PM
accumulation amount in the DPF based on a difference between the PM emission
25 amount computed by the emission amount computation unit and the PM regeneration
amount computed by the passive regeneration amount computation unit,
the passive regeneration amount computation unit is configured to compute a
passive regeneration amount of PM regenerated passively by adding a PM
regeneration amount of PM regenerated by oxygen in the exhaust gas and a PM
30 regeneration amount of PM regenerated by nitrogen dioxide in the exhaust gas, the
PM regeneration amount by the nitrogen dioxide being computed based on data which
is at least in part computed based on an airflow volume measured by an airflow meter
provided in an air supply path for supplying air to the internal combustion engine,
and
35 when an abnormality is found in the airflow meter, the PM accumulation
amount in the DPF is estimated by computing the PM regeneration amount by the
5
nitrogen dioxide without using the airflow measured by the airflow meter.
[0011]
In this aspect of the present invention, the passive regeneration amount is
estimated separately as to the PM regeneration amount of PM regenerated by oxygen
and the PM regeneration amount of PM regenerated by nitrogen 5 dioxide. In this
process, flow volume data of the exhaust gas which is used for computation of the PM
regeneration amount by nitrogen dioxide is computed from the airflow volume
measured by the airflow meter. In contrast, for computation of the PM regeneration
amount by oxygen, the airflow volume measured by the airflow meter is not used.
10 When an abnormality is found in the airflow volume measured by the airflow meter,
the PM regeneration amount by nitrogen dioxide is computed without using the
airflow measured by the airflow meter. Then, this PM regeneration amount by
nitrogen dioxide which is calculated in the above manner is added to the PM
regeneration amount by oxygen so as to compute (estimate) the PM accumulation
15 amount in the DPF.
[0012]
Therefore, in this PM accumulation amount estimation device for the DPF
according to the present invention, computation of at least the PM regeneration
amount of PM by oxygen continues even when an abnormality is found in the airflow
20 meter. Thus, compared to the conventional case, the PM accumulation amount can
be estimated accurately.
[0013]
It is preferable in the present invention that, when an abnormality is found in
the airflow meter, the PM accumulation amount in the DPF is estimated by
25 computing an airflow volume using an alternative means to the airflow meter to
compute the PM regeneration amount by the nitrogen dioxide.
[0014]
In the above invention, the alternative means may be constituted by a
pressure/temperature measuring unit and an airflow volume computation unit, the
30 pressure/temperature measuring unit being configured to measure a pressure and a
temperature at an air supply manifold part which is connected to an upstream side of
the internal combustion engine, the airflow volume computation unit being configured
to compute the airflow volume from the pressure and temperature measured by the
pressure/temperature measuring unit. With this configuration, even when an
35 abnormality is found in the airflow meter, the PM accumulation amount can be
estimated even more accurately than the conventional case. Further, a temperature
6
sensor, a pressure sensor, and the like for EGR control which are installed in the
airflow manifold part can be used as the pressure/temperature measuring unit.
[0015]
Further, in the above invention, the alternative means may be constituted by a
rotation speed/injection amount measuring unit and an airflow 5 volume computation
unit, the rotation speed/injection amount measuring unit being configured to measure
an engine rotation speed and a fuel injection amount of the internal combustion
engine, the airflow volume computation unit being configured to compute the airflow
volume from a map including a relationship between the engine rotation speed and
10 the fuel injection amount. With this configuration, even when an abnormality is
found in the airflow meter, the PM accumulation amount can be estimated even more
accurately than the conventional case. Further, a variety of sensor installed for
controlling the internal combustion engine can be used as the rotation speed/injection
amount measuring unit.
15 [0016]
Furthermore, in the above invention, when an abnormality is found in the
airflow meter, the PM accumulation amount in the DPF is estimated by computing
the PM regeneration amount by nitrogen oxide as zero.
Even when the PM regeneration amount by NO2 is computed as zero, the
20 passive regeneration amount computation unit of the present invention is configured
to compute a PM passive regeneration amount by adding the PM regeneration amount
by oxygen and the PM regeneration amount by nitrogen dioxide. Therefore, as the
PM regeneration amount by oxygen is computed, it is possible to compute the PM
passive regeneration amount even more accurately than the conventional case.
25
[Advantageous Effects]
[0017]
According to the present invention, it is possible to provide a PM accumulation
amount estimation device which is capable of, even when an abnormality is found in
30 the airflow meter, estimating a PM accumulation amount in the DPF with higher
accuracy than a conventional device and avoiding issues such as deterioration of fuel
economy and oil dilution resulting from frequent active regeneration,.
BRIEF DESCRIPTION OF DRAWINGS
35 [0018]
[FIG.1] FIG.1 is an illustration of an overall configuration of a diesel engine
7
equipped with a DPF.
[FIG.2] FIG.2 is a block diagram illustrating an emission amount computation
unit according an embodiment of the present invention.
[FIG.3] FIG.3 is a block diagram illustrating a passive regeneration amount
computation unit according to an embodiment of the 5 present invention.
[FIG.4] FIG.4 is a flow chart illustrating a control flow of the passive
regeneration amount computation unit according to a first embodiment.
[FIG.5] FIG.5 is a flow chart illustrating an abnormality determination process
of the airflow meter according to an embodiment of the present invention.
10 [FIG.6] FIG.6 is a flow chart illustrating a recovery determination process of
the airflow meter according to an embodiment of the present invention.
[FIG.7A] FIG.7A is a flow chart illustrating a control flow according to a second
embodiment.
[FIG.7B] FIG.7B is a block diagram illustrating an airflow volume map 61
15 according an embodiment of the present invention.
[FIG.8] FIG.8 is a flow chart illustrating a control flow according to a third
embodiment.
DETAILED DESCRIPTION
20 [0019]
Embodiments of the present invention will now be described in detail with
reference to the accompanying drawings. It is intended, however, that unless
particularly specified, dimensions, materials, shapes, relative positions and the like of
components described in the embodiments shall be interpreted as illustrative only
25 and not limitative of the scope of the present invention.
[0020]
FIG.1 is an illustration of an overall configuration of a diesel engine equipped
with a DPF. In reference to FIG.1, the overall configuration of the case where the
PM accumulation amount estimation device of the present invention is applied to a
30 diesel engine.
[0021]
As illustrated in FIG.1, an exhaust path 3 is connected to a downstream side of
an internal combustion engine 1 of a diesel engine via an exhaust manifold 29. In
the exhaust path 3, an exhaust gas after-treatment device 9 is provided. The
35 exhaust gas after-treatment device 9 comprises a DOC (Diesel Oxidation Catalyst) 5
and a DPF arranged on a downstream side of the DOC 5. The DOC 5 has a function
8
to oxidize and remove hydrocarbon (HC) and carbon monoxide (CO) in the exhaust gas
and also to oxidize nitrogen monoxide (NO) in the exhaust gas so as to generate
nitrogen dioxide (NO2). The DPF 7, as described above, is configured to collect PM
contained in the exhaust gas, such as soot, using a filter so as to remove PM from the
5 exhaust gas.
[0022]
An air supply path 13 is connected to an upstream side of the internal
combustion engine 1 via an air supply manifold 18. An exhaust turbocharger 11 is
provided between the air supply path 13 and the exhaust path 3. This exhaust
10 turbocharger 11 comprises an exhaust turbine 11b arranged in the exhaust path 3 and
a compressor 11a arranged in the air supply path 13. The compressor 11a is
configured to be coaxially driven by the exhaust turbine 11b. In the air supply path
13, an intercooler 15 and an air supply throttle valve 17 are provided. The air 26
discharged from the compressor 11a is cooled by the intercooler 15 and then, an
15 airflow volume of the air 26 is controlled by the air supply throttle valve 17. Then,
the controlled air 26 enters a combustion chamber inside each cylinder of the internal
combustion engine via the air supply manifold 18.
[0023]
In the internal combustion engine 1, a common rail fuel injection unit (not
20 shown) is provided. The common rail fuel injection unit is configured to inject fuel
into the combustion chamber in the cylinder by controlling an injection volume and an
injection timing of the fuel. An ECU 19 is configured to input a control signal to the
common rail fuel injection unit so that a prescribed amount of fuel is supplied at a
prescribed timing to a fuel injection valve from a common rail of the common rail fuel
25 injection unit. A symbol 21 in the drawing indicates an input position of the control
signal which is inputted to the common rail fuel injection unit from the ECU 19.
[0024]
An EGR pipe 23 branches off from the exhaust path 3 at a position disposed
immediately downstream from the exhaust manifold 29. The EGR pipe 23 is
30 connected to the air supply manifold 18 disposed on a downstream side of the air
supply throttle valve 17. Further, an EGR valve 25 is arranged in the EGR pipe 23.
By controlling opening and closing of the EGR valve 25, a part of the exhaust gas 27
exhausted from the internal combustion engine 1 passes through the EGR pipe 23 to
recirculate in the internal combustion engine 1.
35 [0025]
The exhaust gas 27 exhausted from the internal combustion engine 1 passes
9
through the exhaust manifold 29 and the exhaust path 3 and then drives the exhaust
turbine 11b to coaxially drive the compressor 11a as described above. After passing
through the exhaust path 3, the exhaust gas 27 flows to the DOC 5 and the DPF 7 of
the exhaust gas after-treatment device 9.
5 [0026]
An airflow meter 31 and an intake air temperature sensor 33 are arranged in
the air supply path 13. The airflow meter 31 is configured to measure an airflow
volume of the air flowing toward the compressor 11a. Then, signals as to the airflow
volume measured by the airflow meter and the intake air temperature measured by
10 the intake air temperature sensor 33 are inputted to the ECU 19.
[0027]
A DOC inlet temperature sensor 35, a DPF inlet temperature sensor 37, a DPF
differential pressure sensor 38 and a DPF outlet temperature sensor 39 are arranged
in the exhaust path 3. Signals as to a DOC inlet temperature, a DPF inlet
15 temperature, a DPF outlet temperature, etc. are inputted to the ECU 19.
[0028]
An engine rotation speed and a fuel injection amount are computed in the ECU
19 based on the input signals from a variety of sensors such as a crank sensor, a cam
sensor, an accelerator sensor and a throttle sensor.
20 [0029]
Further, an air supply temperature sensor 41 and an air supply pressure
sensor 43 are arranged on a downstream side of the air supply throttle valve 17. The
air supply temperature sensor 41 and the air supply pressure sensor 43 are
configured to measure a temperature and a pressure in the air supply manifold 18,
25 respectively. Signals as to the air supply temperature measured by the air supply
temperature sensor 31 and the air supply pressure measured by the air supply
pressure sensor 43 are inputted to the ECU 19. An optimum EGR amount is
computed in the ECU 19 based on these air supply temperature and air supply
pressure, so as to control opening and closing of the EGR valve 25.
30 [0030]
The ECU 19 is configured by a microcomputer which comprises a CPU, a RAM,
a ROM and an I/O interface. The signals from these sensors are inputted to the CPU
from via an I/O interface. The CPU is configured to execute various types of control
according to control programs stored in the ROM. Further, as illustrated in FIG.1,
35 an accumulation amount estimation unit 50, an emission amount computation unit 51
and a passive regeneration amount computation unit 52 of the present invention are
10
constituted by the ECU 19.
[0031]
The emission amount computation unit 51 is configured to compute a PM
amount (a PM emission amount) of the PM contained in the exhaust gas exhausted
from the internal combustion engine 1. The PM emission amount 5 is computed by the
emission amount computation unit 51, as illustrated in FIG.2, using a PM emission
amount map 55 having an engine rotation speed and a fuel injection amount as input
data. This PM emission amount map 55 is produced by performing experiments and
the like, and is stored in the ROM of the ECU 19 in advance.
10 [0032]
The passive regeneration amount computation unit 52 is configured to compute
a passive regeneration amount, i.e. a PM amount (a PM regeneration amount) of the
PM burnt by the high temperature exhaust gas exhausted from the internal
combustion engine 1 during the normal operation instead of during active
15 regeneration. This PM regeneration amount is, as illustrated in FIG.3, computed by
computing each of a PM regeneration amount of PM regenerated by oxygen (O2) and a
PM regeneration amount of PM regenerated by nitrogen dioxide (NO2) and adding
them together.
[0033]
20 The PM regeneration amount of PM regenerated by oxygen is computed using
an O2 regeneration amount having the DPF inlet and outlet temperatures and oxygen
concentration as input data. Meanwhile, the oxygen concentration may be measured
by O2 sensor or the like. In the present embodiment, however, the oxygen
concentration is computed in the ECU 19 based on a pressure and a temperature of
25 the exhaust gas, the fuel injection amount, an EGR circulation rate, and the like.
[0034]
The PM regeneration amount of PM regenerated by nitrogen dioxide is
computed using a NO2 regeneration amount map having the DPF inlet and outlet
average temperatures, an airflow volume (a volume of the exhaust gas), a DOC
30 temperature, the engine rotation speed, the fuel injection amount, and DPF inlet and
outlet temperatures as input data. Meanwhile, the volume of the exhaust gas is
computed from the airflow volume measured by the above described airflow meter 31.
Further, as described later, when an abnormality is found in the airflow meter 31, the
airflow volume is computed using an alternative means 60 to the airflow meter 31.
35 [0035]
The above O2 regeneration amount map and NO2 regeneration amount map are
11
produced by performing experiments, etc. and are stored in the ROM of the ECU 19 in
advance.
[0036]
The PM accumulation amount estimation unit 51 is configured to compute (to
estimate) the PM accumulation amount in the DPF based on the following 5 formula (2)
from a difference between the PM emission amount computed by the emission amount
computation unit 51 and the PM regeneration amount computed by the passive
regeneration amount computation unit 52.
10 PM accumulation amount = PM emission amount – PM regeneration amount
= PM emission amount – (PM regeneration amount by O2 +
PM regeneration amount by NO2) •••(2)
[0037]

15 A first embodiment of the PM accumulation amount estimation device with the
above configuration equipped with the DPF 7 and PM accumulation amount
estimation unit 50 is described below. FIG.4 is a flow chart illustrating a control
flow of the passive regeneration amount computation unit according to a first
embodiment.
20 [0038]
As illustrated in FIG.4, after start, an abnormality of the airflow meter (AFM)
is first determined (S1). Next, if the AFM is operating normally (YES in S1), the
airflow volume is measured by the AFM (S2) and then the PM regeneration amount
by NO2 is computed (S3). Then, the PM regeneration amount by O2 separately
25 computed is added to the PM regeneration amount by NO2 to compute the PM
regeneration amount (S4).
[0039]
In contrast, if the abnormality of the airflow meter (AFM) is determined (NO
in S1), a warning is given to an operator, etc. (S5) and then the EGR valve 25 is fully
30 closed (S6). Next, the airflow volume is computed in the ECU 19 (S7) using the
following formulas (3), (4) which are stored in advance in the ROM, based on the
temperature and pressure inside the air supply manifold 18 measured by the air
supply temperature sensor 41 and the air supply pressure sensor 43. Then, flow
volume data of the exhaust gas is computed from this airflow volume so as to compute
35 the PM regeneration amount by NO2 (S3).
Gcyl = (ρ • Vstrk • Ne / 60) • (2 / Icyc) • Ncyl • Ev •••(3)
12
Ρ = P / RT •••(4)
Here, Gcyl is an airflow volume, ρ is a supply air density, P is an absolute
pressure of the airflow manifold part, T is a temperature of the airflow manifold part,
R is a gas state constant, Vstrk is a stroke volume per cylinder, Ne is the engine
rotation speed, Icyc is a stroke, Ncyl is the number of cylinders, 5 and Ev is volume
efficiency, and these are separately computed from maps.
[0040]
Specifically, in the first embodiment, the alternative means 60 replaces the
airflow meter to compute the airflow volume. The alternative means 60 is configured
10 by the ECU 19 (the airflow volume computation unit) for computing the airflow
volume from the pressure and temperature measured by the air supply temperature
sensor 41 and the air supply pressure sensor 43 (pressure temperature measuring
means) for measuring the pressure and temperature of the air supply manifold 18.
[0041]
15 Next, the process of determining the abnormality of the AFM (S1) illustrated
in FIG.4 is described in details in reference to FIG.5 and FIG.6. FIG.5 is a flow
chart illustrating an abnormality determination process of the airflow meter
according to an embodiment of the present invention. FIG.6 is a flow chart
illustrating a recovery determination process of the airflow meter according to an
20 embodiment of the present invention.
[0042]
To determine abnormality of the AFM, as illustrated in FIG.5, it is first
determined whether an ignition switch is on or off (S8). If the ignition switch is ON,
counting of an abnormality elapsed time starts (S9) and then, it is determined
25 whether or not the airflow volume measured by the AFM is within a prescribed
threshold range (S10). This threshold range can be set, for instance, by computing a
range of the airflow volume during normal operation in correspondence to a
prescribed engine rotation speed. If the airflow volume measured by the AFM is not
within the prescribed threshold range (YES in S10), it is then determined whether or
30 not the abnormality elapsed time exceeds a preset abnormality determination time
(S11) and if YES, it is determined that the AFM has abnormality and an abnormality
flag is set ON (S12) and then, the abnormality elapsed time is reset (S13). In
contrast, if the airflow volume measured by the AFM is within the prescribed
threshold range (NO in S10), the abnormality elapsed time is reset (S13). Further, if
35 the abnormality elapsed time has not exceeded the preset abnormality determination
time in S11, the abnormality elapsed time is counted (S14) and then the process
13
repeats the step of determining the abnormality of the airflow volume measured by
the AFM in S10 again.
[0043]
To determine recovery of the AFM, as illustrated in FIG.6, an ON/OFF state of
the abnormality flag is determined (S14). If the abnormality flag 5 is ON, counting of
a recovery elapsed time starts (S15) and then, in the same manner as S10, it is
determined whether or not the airflow volume measured by the AFM is within the
prescribed threshold range (S16). Then, if the airflow volume measured by the AFM
is within the prescribed threshold range (NO in S16), it is then determined whether
10 or not the recovery elapsed time exceeds a preset recovery determination time (S17)
and if YES, it is determined that the AFM has recovered from the abnormal state and
an abnormality flag is set OFF (S18) and then the abnormality elapsed time is reset
(S19). In contrast, if the recovery elapsed time has not exceeded the preset recovery
determination time in S17, the recovery elapsed time is counted (S20) and then the
15 process repeats the step of determining the abnormality of the airflow volume
measured by the AFM in S16 again.
[0044]
In this PM accumulation amount estimation device for the DPF according to
the present invention, computation of the PM regeneration amount continues even
20 when an abnormality is found in the airflow meter 31. Thus, compared to the
conventional case, the PM accumulation amount can be estimated accurately.
Further, the air supply temperature sensor 41 and the air supply pressure sensor 43
for EGR control can be used as the pressure/temperature measuring means of the
alternative means 60. Thus, the alternative means 60 can be configured without
25 additionally providing sensors
[0045]

A second embodiment of the PM accumulation amount estimation device of
the present invention for the DPF is described below. FIG.7 is a flow chart
30 illustrating a control flow of a passive regeneration amount computation unit
according to the second embodiment. This control flow of the second embodiment
illustrated in FIG.7 has basically the same configuration as the control flow of the
first embodiment, and the same reference numerals are given without adding
explanations for the steps that are the same as the first embodiment.
35 [0046]
As illustrated in FIG.7A, the second embodiment is different from the first
14
embodiment in that when the abnormality is found in the AFM (NO in S1), the airflow
volume is computed by an airflow volume map 61 (S7’) instead of computing the
airflow volume from the pressure and temperature of the airflow manifold (S7). The
airflow volume map 61 is a map having the engine rotation speed and the fuel
injection amount as input data as illustrated 5 in FIG.7B.
The engine rotation speed and the fuel injection amount are, as described
above, computed in the ECU 19 based on input signals from a variety of sensors such
as a crank sensor, a cam sensor, an accelerator sensor and a throttle sensor. Further,
this airflow volume map 61 is produced by performing experiments, etc. and is stored
10 in the ROM of the ECU 19 in advance.
[0047]
Specifically, in the second embodiment, the alternative means 60 replaces the
airflow meter to compute the airflow volume. The alternative means 60 is configured
by an ECU 19 (a rotation speed/injection amount measuring unit) and a variety of
15 sensors for computing the engine rotation speed and the fuel injection amount, and
the ECU 19 (the airflow volume computation unit) for computing the airflow volume
from the airflow volume map 61 and these engine rotation speed and fuel injection
amount.
[0048]
20 In this PM accumulation amount estimation device for the DPF according to
the present invention is configured to continue computing the PM regeneration
amount even when an abnormality is found in the airflow meter 31. Thus, compared
to the conventional case, the PM accumulation amount can be estimated accurately.
Further, the sensors and the like for controlling the internal combustion engine 1 can
25 be used as the rotation speed/injection amount measuring unit of the alternative
means 60. Thus, the alternative means 60 can be configured without additionally
providing sensors
[0049]

30 A third embodiment of the PM accumulation amount estimation device of the
present invention for the DPF is described below. FIG.8 is a flow chart illustrating a
control flow of a passive regeneration amount computation unit according to the third
embodiment. This control flow of the third embodiment illustrated in FIG.8 has
basically the same configuration as the control flow of the first embodiment, and the
35 same reference numerals are given without adding explanations for the steps that are
the same as the first embodiment.
15
[0050]
As illustrated in FIG.8, the third embodiment is different from the first
embodiment in that when the abnormality is found in the AFM (NO in S1), the PM
regeneration amount by NO2 is set as zero (S3’), instead of computing the airflow
volume from the pressure and temperature of the airflow manifold 5 (S7) to compute
the PM regeneration amount by NO2 (S3).
[0051]
Specifically, the PM accumulation amount is estimated based on the following
formula (2’) stating that the PM regeneration amount by NO2 is zero and the PM
10 regeneration amount≒ the PM regeneration amount by O2 in the above-described
formula (2).
PM accumulation amount = PM emission amount – PM regeneration amount
= PM emission amount –PM regeneration amount by O2
•••(2’)
15 [0052]
Even when the PM regeneration amount by NO2 is computed as zero, the
passive regeneration amount computation unit of the present invention is configured
to compute a PM passive regeneration amount of the PM regenerated passively by
adding the PM regeneration amount by O2 and the PM regeneration amount by NO2.
20 Therefore, the PM regeneration amount by O2 is taken into account as the PM
regeneration amount. As a result, compared to the conventional case, it is possible
to compute the PM passive regeneration amount accurately in this situation.
[0053]
While the embodiments of the present invention have been described, it is
25 obvious to those skilled in the art that various changes may be made without
departing from the scope of the invention.
[0054]
According to the present invention, the PM accumulation amount estimation
device of the present invention is preferably usable as a PM accumulation amount
30 estimation device which is capable of accurately estimating the PM accumulation
amount of the PM accumulated in the DPF.
35
16
We claim:-
1. A PM accumulation amount estimation device comprising:
a diesel particulate filter (DPF) configured to collect exhaust gas particulate
matter (PM) in exhaust gas exhausted to an exhaust path 5 from an internal
combustion engine;
a PM accumulation amount estimation unit configured to estimate a PM
accumulation amount of PM accumulating in the DPF;
10
an emission amount computation unit configured to compute a PM emission
amount of the PM exhausted to the exhaust path; and
a passive regeneration amount computation unit configured to compute a PM
15 regeneration amount of the PM passively regenerated in the DPF,
wherein the PM accumulation amount estimation unit is configured to estimate
the PM accumulation amount in the DPF based on a difference between the PM
emission amount computed by the emission amount computation unit and the
20 PM regeneration amount computed by the passive regeneration amount
computation unit,
wherein the passive regeneration amount computation unit is configured to
compute a passive regeneration amount of PM regenerated passively by adding
25 a PM regeneration amount of PM regenerated by oxygen in the exhaust gas and
a PM regeneration amount of PM regenerated by nitrogen dioxide in the
exhaust gas, the PM regeneration amount by the nitrogen dioxide being
computed based on data which is at least in part computed based on an airflow
volume measured by an airflow meter provided in an air supply path for
30 supplying air to the internal combustion engine, and
wherein when an abnormality is found in the airflow meter, the PM accumulation
amount in the DPF is estimated by computing the PM regeneration amount by
the nitrogen dioxide without using the airflow measured by the airflow meter.
35
17
2. The PM accumulation amount estimation device according to claim 1,
wherein when an abnormality is found in the airflow meter, the PM accumulation
amount in the DPF is estimated by computing an airflow volume using an
alternative means to the airflow meter to compute the PM regeneration 5 amount
by the nitrogen dioxide.
3. The PM accumulation amount estimation device according to claim 2,
10
wherein the alternative means is constituted by a pressure/temperature
measuring unit and an airflow volume computation unit, the
pressure/temperature measuring unit being configured to measure a pressure
and a temperature at an air supply manifold part which is connected to an
15 upstream side of the internal combustion engine, the airflow volume
computation unit being configured to compute the airflow volume from the
pressure and temperature measured by the pressure/temperature measuring
unit.
20
4. The PM accumulation amount estimation device according to claim 2,
wherein the alternative means is constituted by a rotation speed/injection
amount measuring unit and an airflow volume computation unit, the rotation
25 speed/injection amount measuring unit being configured to measure an engine
rotation speed and a fuel injection amount of the internal combustion engine,
the airflow volume computation unit being configured to compute the airflow
volume from a map including a relationship between the engine rotation speed
and the fuel injection amount.
5. The PM accumulation amount estimation device according to claim 1,
wherein when an abnormality is found in the airflow meter, the PM accumulation
35 amount in the DPF is estimated by computing the PM regeneration amount by
the nitrogen oxide as zero.