TITLE
EXHAUST GAS PURIFICATION SYSTEM FOR ENGINE
[Technical Field]
[00015 ]
The present invention relates to an exhaust gas purification system for an
engine provided with a DPF, particularly to a technique of controlling a timing of
combustion removal of PM accumulated in the DPF.
10 BACKGROUND ART
[0002]
As a technique effective for removing particulate matter (exhaust particulate,
hereinafter referred to as PM) contained in an exhaust gas of a diesel engine, a diesel
particulate filter (hereinafter referred to as DPF) is known. DPF is a device for
15 collecting PM employing a filter. DPF is provided on an exhaust passage of an
engine, and is a device for collecting PM including soot exhausted from the engine
with a filter and removing PM from the exhaust gas. A part of PM collected by the
DPF will be combusted by a high-temperature exhaust gas exhausted from the engine
during operation, but the remainder of the PM will be accumulated in the filter of the
20 DPF. However, as DPF has a limited capacity for collecting PM, excessive progress
of accumulation of PM may result in decline in the performance of collecting PM or
reduction in the engine output. Thus, it is necessary for the DPF that a regeneration
treatment for the filter where PM accumulated in the filter is combusted to
regenerate the filter, is performed at an appropriate timing.
25 [0003]
In order to get the appropriate timing to perform the regeneration treatment,
it is necessary to accurately estimate the PM accumulation state in the DPF. If the
PM accumulation state is underestimated, the time to perform the regeneration
treatment may be delayed, and thus the engine output may be reduced due to
30 excessive accumulation of PM, or the DPF may be damaged due to excessive heat
during the regeneration treatment. On the other hand, if the PM accumulation state
is overestimated, the frequency of performing the regeneration treatment may become
high, and thus problems such as worsening of fuel consumption and oil dilution may
occur.
35 [0004]
A technique for accurately estimating the PM accumulation state in a DPF and
3
performing the regeneration treatment at an appropriate timing is disclosed by the
present applicant (Patent Document 1). According to the technique of Patent
Document 1, the PM accumulation state of DPF is evaluated with a concept of
“collection stages”, and the PM accumulation state is classified into six collection
stages divided according to the PM accumulation state. In addition, as shown in Fig5 .
15, operation to be performed in the regeneration treatment is preliminarily
determined depending upon the collection stage.
[0005]
In the technique of Patent Document 1, the collection stage is determined
10 based on the flowchart illustrated in Fig. 16. That is, according to the flowchart of
Fig. 16, the current collection stage is determined in step S51, then the procedure
move ahead to step S52. The “current collection stage” in step S51 is the collection
stage which has been determined in the preceding cycle in the flow of Fig. 16 and
which is stored in an ECU.
15 [0006]
When the current collection stage X is determined as one of 1 to 6 (S52), four
evaluation indices of (1) PM accumulation amount estimate, (2) cumulative operation
time, (3) cumulative fuel consumption and (4) DPF corrected pressure difference are
compared with the thresholds Qx, Tx, Qfx and dPx, respectively, in step S53. If a
20 state where any one of the four indices exceeds the threshold is continued for a
predetermined period of time, 1 is added to the collection stage number in step S55.
If DPF is determined to be undergoing regeneration in step S54, the addition to the
collection stage number is not performed.
[0007]
25 According to Patent Document 1, the PM accumulation state is
comprehensively evaluated by the four evaluation indices of (1) to (4), whereby it is
possible to more accurately estimate the PM accumulation state compared with the
case where the PM accumulation state is evaluated with a single index. Further,
operation to be performed in the regeneration treatment is preliminarily determined
30 depending upon the collection stage, whereby an appropriate regeneration treatment
can be performed at an appropriate timing depending upon the PM accumulate state.
[Citation List]
[Patent Literature]
35 [0008]
[PTL 1]
4
JP 2011-163199 A
[PTL 2]
JP 2002-295234 A
[PTL 3]
JP 3985098 5 B
[PTL 4]
JP 4606939 B
SUMMARY
10 [Technical Problem]
[0009]
The above four evaluation indices (1) to (4) in the Patent Document 1 are
calculated based on output values from different types of sensors such as a
temperature sensor, a DPF differential pressure sensor and an air flow meter. Thus,
15 in a case of a failure of the sensors, the four evaluation indices (1) to (4) may be
erroneously calculated, and thus the collection stage may be erroneously evaluated.
[0010]
Each of Patent Documents 2 to 4 discloses a technique of determining the PM
accumulation state of a DPF without using a sensor with a failure in the case of a
20 failure of the sensor. However, the technique disclosed in each of Patent Documents
2 to 4 is, in the first place, a technique of evaluating the PM accumulation state with
a single index and is a technique different from Patent Document 1. Thus, the
technique disclosed in each of Patent Documents 2 to 4 cannot be directly applied to
the technique of Patent Document 1.
25 [0011]
The present invention has been made in view of the above problems and is to
provide an exhaust gas purification system for an engine capable of accurately
estimating the PM accumulation state and performing an appropriate regeneration
treatment at an appropriate timing even when a defect of a sensor used for
30 calculation of an evaluation index for the PM accumulation state of the filter is
detected.
[Solution to Problem]
[0012]
35 To solve the above problems, the present invention provides an exhaust gas
purification system for an engine comprising a DPF for collecting PM in an exhaust
5
gas exhausted from an engine to an exhaust passage and a PM accumulation
evaluation part for classifying a PM accumulation state of the DPF into multiple
evaluation stages based on a plurality of evaluation indices,
said PM accumulation evaluation part including:
a current stage determination part for determining a current evaluation stage5 ;
and
an evaluation stage determination part for moving up the current evaluation
stage to an evaluation stage of a next rank when a value of each of a prescribed
number of the evaluation indices is greater than each threshold value;
10 and being configured to repeatedly perform determination of the current
evaluation stage by the current stage determination part and determination of
whether to move up the current evaluation stage to the evaluation stage of the next
rank by the evaluation stage determination part; and
said PM accumulation evaluation part further including:
15 a defect detection part for detecting a defect of different types of sensors used
for calculating each of the plurality of evaluation indices; and
a current stage redetermination part for redetermining the current evaluation
stage without using, among the different types of sensors, a sensor of which a defect
is detected by the defect detection part;
20 and being configured to newly redetermine the current evaluation stage by the
current stage redetermination part as substituted for the current evaluation stage
determined by the current stage determination part upon a defect of the sensor being
detected by the defect detection part.
[0013]
25 In the exhaust gas purification system of an engine of the above invention,
which is configured to classify a PM accumulation state of the DPF into multiple
evaluation stages based on a plurality of evaluation indices and to repeatedly perform
determination of the current evaluation stage by the current stage determination part
and determination of whether to move up the current evaluation stage to the
30 evaluation stage of the next rank by the evaluation stage determination part, the
current evaluation stage is newly redetermined by the current stage redetermination
part as substituted for the current evaluation stage determined by the current stage
determination part upon a defect of the sensor being detected by the defect detection
part.
35 Thus, even in a case of a failure of a sensor, the current evaluation stage is
newly redetermined by the current stage redetermination part, whereby it is possible
6
to improve the accuracy of estimating the PM accumulation state during a failure of a
sensor.
[0014]
It is preferred that upon a defect of the sensor being detected by the defect
detection part, the current evaluation stage is newly redetermined by the curren5 t
stage redetermination part by using an evaluation index other than an evaluation
index based on an output value of the sensor of which a defect is detected.
According to this configuration, the current evaluation stage is newly
redetermined by using an evaluation index other than an evaluation index based on
10 an output value of the sensor of which a defect is detected, whereby it is possible to
improve the accuracy of estimating the PM accumulation state during a failure of a
sensor.
[0015]
In this case, it is preferred that upon a defect of the sensor being detected by
15 the defect detection part, determination of whether to move up the current evaluation
stage to the evaluation stage of the next rank is performed by the evaluation stage
determination part by using the evaluation index other than the evaluation index
based on the output value of the sensor of which a defect is detected.
According to this configuration, determination of whether to move up the
20 current evaluation stage to the evaluation stage of the next rank is performed by
using the evaluation index other than the evaluation index based on the output value
of the sensor of which a defect is detected, whereby it is possible to further improve
the accuracy of estimating the PM accumulation state during a failure of a sensor.
[0016]
25 It is preferred that upon a defect of a supply air flow meter as one of the
sensors being detected by the defect detection part, an evaluation index is calculated
based on a supply air flow rate calculated by an alternative unit as substituted for a
supply air flow rate measured by the supply air flow meter of which a defect is
detected, and the current evaluation stage is newly redetermined by the current stage
30 redetermination part by using the evaluation index calculated by the alternative unit
and at least one of the other evaluation indices.
According to this configuration, in a case where a defect of the supply air flow
meter is detected, an evaluation index is calculated based on a supply air flow rate
calculated by an alternative unit as substituted for a supply air flow rate measured
35 by the supply air flow meter, and the current evaluation stage is newly redetermined
by using the evaluation index calculated by the alternative unit and at least one of
7
the other evaluation indices, whereby it is possible to improve the accuracy of
estimating the PM accumulation state during a failure of the supply air flow meter.
[0017]
In this case, it is preferred that upon a defect of the supply air flow meter as
one of the sensors being detected by the defect detection part, the evaluation index i5 s
calculated based on the supply air flow rate calculated by the alternative unit as
substituted for the supply air flow rate measured by the supply air flow meter of
which a defect is detected, and determination of whether to move up the current
evaluation stage to the evaluation stage of the next rank is performed by the
10 evaluation stage determination part by using the evaluation index calculated by the
alternative unit and at least one of the other evaluation indices.
[0018]
According to this configuration, in a case where a defect of the supply air flow
meter is detected, the evaluation index is calculated based on the supply air flow rate
15 calculated by the alternative unit as substituted for the supply air flow rate measured
by the supply air flow meter, and determination of whether to move up the current
evaluation stage to the evaluation stage of the next rank is performed by the
evaluation stage determination part by using the evaluation index calculated by the
alternative unit and at least one of the other evaluation indices, whereby it is possible
20 to further improve the accuracy of estimating the PM accumulation state during a
failure of the supply air flow meter.
[0019]
The alternative unit may include a pressure/temperature measuring device for
measuring a pressure and a temperature at an intake manifold part connected to the
25 engine on the upstream side, and a supply air flow rate calculation part for
calculating the supply air flow rate from the measured pressure and temperature.
Alternatively, the alternative unit may include a rotational speed/injection
amount calculation unit for calculating an engine rotational speed and a fuel injection
amount of the engine, and a supply air flow rate calculation part for calculating the
30 supply air flow rate from a map of a relationship between the engine rotational speed
and the fuel injection amount, and the supply flow rate, of the engine.
[Advantageous Effects]
[0020]
35 According to the present invention, it is possible to provide an exhaust gas
purification system for an engine capable of accurately estimating the PM
8
accumulation state and performing an appropriate regeneration treatment at an
appropriate timing even when a defect of a sensor used for calculation of an
evaluation index for the PM accumulation state of the filter is detected.
BRIEF DESCRIPTION OF DRAWING5 S
[0021]
[FIG.1] Fig. 1 is a schematic diagram illustrating an entire construction of a
diesel engine to which an exhaust gas purification system for an engine according to
the present invention is applied.
10 [FIG.2] Fig. 2 is a block diagram illustrating a construction of a PM
accumulation state estimation part according to the present invention.
[FIG.3] Fig. 3 is a chart showing six collection stages divided according to PM
accumulation amount as one of the evaluation indices.
[FIG.4] Fig. 4 is a flowchart illustrating a behavior of a PM accumulation state
15 estimation part in a first embodiment.
[FIG.5] Fig. 5 is a flowchart illustrating a behavior of a current stage
redetermination part in the first embodiment.
[FIG.6] Fig. 6 is a flowchart illustrating a behavior of a defect detection part in
the first embodiment.
20 [FIG.7] Fig. 7 is a block diagram illustrating relationship between evaluation
indices and output values of sensors in the first embodiment.
[FIG.8] Fig. 8 is a flowchart illustrating a behavior of a PM accumulation state
estimation part in a second embodiment.
[FIG.9] Fig. 9 is a flowchart illustrating a behavior of a current stage
25 redetermination part in the second embodiment.
[FIG.10] Fig. 10 is a block diagram illustrating relationship between evaluation
indices and output values of sensors in the second embodiment.
[FIG.11] Fig. 11 is a flowchart illustrating a behavior of a PM accumulation state
estimation part in a third embodiment.
30 [FIG.12] Fig. 12 is a flowchart illustrating a behavior of a current stage
redetermination part in the third embodiment.
[FIG.13] Fig. 13 is a block diagram illustrating relationship between evaluation
indices and output values of sensors in the third embodiment.
[FIG.14] Fig. 14 is a block diagram illustrating a behavior of an alternative unit
35 in the third embodiment.
[FIG.15] Fig. 15 is a chart showing a relationship between collection stages and
9
operation performed in a regeneration treatment.
[FIG.16] Fig. 16 is a flowchart illustrating the flow of determining collection
stages in Patent Document 1.
DETAILED DESCRIPTIO5 N
[0022]
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,
10 materials, shapes, relative positions and the like of components described in the
embodiments shall be interpreted as illustrative only and not limitative of the scope
of the present invention.
[0023]
Fig. 1 is a schematic diagram illustrating an entire construction of a diesel
15 engine to which an exhaust gas purification system for an engine according to the
present invention is applied. First, an entire construction in a case where the
exhaust gas purification system according to the present invention is applied to a
diesel engine will be described with reference to Fig. 1.
[0024]
20 As illustrated in Fig. 1, the diesel engine to which the exhaust gas purification
system according to the present invention is applied comprises an engine 2, an intake
passage 6 and an intake manifold 4 which a supply air to be supplied to the engine 2
is passed through, an exhaust passage 10 and an exhaust manifold 8 which an
exhaust gas exhausted from the engine 2 is passed through, different types of sensors
25 provided on the intake passage 6 and the exhaust passage 10, and an ECU 50.
[0025]
On the exhaust passage 10, provided is an exhaust gas purification apparatus
30 including a DOC (oxidation catalyst) 32 and a DPF 34 on the downstream side of
the DOC 32. DOC 32 has a function of oxidizing hydrocarbons (HC) and carbon oxide
30 (CO) in the exhaust gas for removal as well as oxidizing nitrogen oxide (NO) in the
exhaust gas to generate nitrogen dioxide (NO2). As described above, the DPF 34 is a
device for colleting PM including soot contained in the exhaust gas with a filter and
removing them from the exhaust gas.
[0026]
35 Between the exhaust passage 10 and the intake passage 6, a turbocharger 12
is provided. The turbocharger 12 has an exhaust gas turbine 12b disposed on the
10
exhaust passage 10 and a compressor 12a disposed on the intake passage 6, which is
configured to be coaxially driven by the exhaust gas turbine 12b. On the intake
passage 6, an intercooler 14 and a throttle valve 16 are provided, and the diesel
engine is configured so that the supply air discharged from the compressor 12a is
cooled by the intercooler 14 by heat exchange with atmospheric air and then is flow5 n
into a combustion chamber of the engine 2 through the intake manifold 4.
[0027]
Further, the diesel engine is provided with a common rail fuel injection
apparatus (not shown) for controlling the injection timing and the injection amount of
10 fuel and injecting the fuel into the combustion chamber of the engine 2. The ECU 50
is configured to send an input control signal to the common rail fuel injection
apparatus so that a predetermined amount of the fuel is supplied at a predetermined
injection timing from a common rail of the common rail fuel injection apparatus to a
fuel injection valve. The numerical symbol 22 in the figure indicates the input
15 position of the control signal from the ECU 50 to the common rail fuel injection
apparatus.
[0028]
Further, an EGR tube 23 is branched from the exhaust passage 10 at a position
on the downstream side of the exhaust manifold 8, which is connected to the intake
20 manifold 4. On the EGR tube 23, an EGR valve 24 is provided, and by controlling
opening and closing of the EGR valve 24, a part of the exhaust gas exhausted from
the engine 2 is recirculated into the engine 2 through the EGR tube 23.
[0029]
The exhaust gas discharged from the engine 2 is passed through the exhaust
25 manifold 8 and the exhaust passage 10 and then drives the exhaust gas turbine 12b to
coaxially drive the compressor 12a. After being passed through the exhaust passage
10, the exhaust gas is flown into the DOC 32 and the DPF 34 of the exhaust gas
purification apparatus 30.
[0030]
30 Further, the exhaust purification apparatus 30 is provided with a DOC inlet
temperature sensor 36 for sensing an inlet temperature of the DOC 32, and a DPF
inlet temperature sensor 38 and a DPF outlet temperature sensor 42 for sensing an
inlet temperature and an outlet temperature of the DPF, respectively. The
temperature data measured by the DOC inlet temperature sensor 36, the DPF inlet
35 temperature sensor 38, and the DPF outlet temperature sensor 42 are input into the
ECU 50 as voltage signals, for example. The exhaust purification apparatus 30 is
11
provided also with a DPF differential pressure sensor 40 for sensing a pressure
difference between the inlet and outlet of the DPF 34, and the pressure difference
measured by the DPF differential pressure sensor 40 is also input into the ECU 50 as
a voltage signal, for example.
[00315 ]
On the intake passage 6, an air flow meter 26 (a supply air flow meter) for
sensing a flow rate of the supply air and an intake temperature sensor 28 for sensing
a temperature of the supply air are provided on the upstream side of the compressor
12a. The measured values by the air flow meter 26 and the intake temperature
10 sensor 28 are also input into the ECU 50 as voltage signals, for example. Further, on
the intake passage 6, a supply air absolute pressure sensor 18 for sensing a supply air
absolute pressure and a supply air temperature sensor 20 for sensing a supply air
temperature on the downstream side of the throttle valve 16, and the measured
values by the supply air absolute pressure sensor 18 and the supply air temperature
15 sensor 20 are also input into the ECU 50 as voltage signals, for example.
[0032]
Further, the ECU 50 is configured to calculate target opening degrees of the
EGR valve 24 and the throttle valve 16 based on the input values from the above
different types of sensors and to control the opening degrees of the EGR valve 24 and
20 the throttle valve 16. Further, the ECU 50 is configured to receive input signals via
a cable 44 from different types of sensors such as a crank sensor, a cam sensor, an
accelerator sensor and a throttle sensor and to calculate an engine rotational speed
and a fuel injection amount. Further, the ECU 50 is connected to a body ECU (not
shown) and the like via a cable 46. Further, the ECU 50 is configured to receive a
25 signal related to a flow rate of the supply air from an alternative unit, which will be
described below.
[0033]
The ECU 50 comprises a central processing unit (CPU), a random access
memory (RAM), a read only memory (ROM) and a microcomputer including e.g. an I/O
30 interface. The above various signals from the sensors are input into the CPU via the
I/O interface. The CPU is configured to perform various controls according to control
programs stored in the ROM. Further, as illustrated in Fig. 1, a PM accumulation
state estimation part 52 according to the present invention is configured by the ECU
50.
35 [0034]
The PM accumulation state estimation part 52 according to the present
12
invention 52 is a part for classifying a PM accumulation state of the DPF 34 into
multiple evaluation stages based on a plurality of evaluation indices. As shown in
Fig. 3, according to the present invention, the PM accumulation state of the DPF is
evaluated by, for example, classifying it into six collection stages (evaluation stages)
divided according to e.g. a PM accumulation amount. The chart shown in Fig. 3 i5 s
preliminarily stored in the ECU 50. The chart of Fig. 3 is a chart in which the PM
accumulation state is classified into six collection stages divided according to the PM
accumulation amount which is one of the evaluation indices; and similar charts in
terms of the other respective evaluation indices (a cumulative operation time, a
10 cumulative fuel injection amount and DPF corrected pressure difference) are also
generated, which will be described below, and are preliminarily stored in the ECU 50.
[0035]
The DPF corrected pressure difference, which is a value converted as a
pressure difference between the inlet and outlet of the DPF in a standard state based
15 on the ratio of a volume flow rate of the exhaust gas to a standard gas amount, is
employed in view of the fact that the pressure difference between the inlet and outlet
of the DPF is varied with the volume flow rate of the exhaust gas even when the PM
accumulation amount in the DPF is the same.
[0036]
20 Fig. 2 is a block diagram illustrating a construction of the PM accumulation
state estimation part 52 according to the present invention. As illustrated in Fig. 2,
the PM accumulation state estimation part 52 includes a current stage determination
part 52a for determining a current collection stage and an evaluation stage
determination part 52b for moving up the current collection stage to an evaluation
25 stage of a next rank when a value of each of a prescribed number of the evaluation
indices is greater than each threshold value, and is configured to repeatedly perform
determination of the current collection stage by the current stage determination part
52a and determination of whether to move up the current collection stage to the
evaluation stage of the next rank by the evaluation stage determination part52b.
30 [0037]
Further, as illustrated in Fig. 2, the PM accumulate state estimation part 52
further includes a defect detection part 52d for detecting a defect of different types of
sensors used for calculating each of the plurality of evaluation indices and a current
stage redetermination part 52c for redetermining the current collection stage without
35 using, among the different types of sensors, a sensor of which a defect is detected by
the defect detection part 52d, and is configured to newly redetermine the current
13
collection stage by the current stage redetermination part 52c as substituted for the
current collection stage determined by the current stage determination part 52a upon
a defect of the sensor being detected by the defect detection part 52d.
[0038]
Further, the PM accumulate state estimation part 52 is configured so tha5 t
upon a defect of the sensor being detected by the defect detection part 52d, the
current collection stage is newly redetermined by the current stage redetermination
part 52c by using an evaluation index other than an evaluation index based on an
output value of the sensor of which a defect is detected. Further, the PM accumulate
10 state estimation part 52 is configured so that upon a defect of the sensor being
detected by the defect detection part 52d, determination of whether to move up the
current collection stage to the collection stage of the next rank is performed by the
evaluation stage determination part 52c by using the evaluation index other than the
evaluation index based on the output value of the sensor of which a defect is detected.
15 [0039]
(First Embodiment)
A behavior of the PM accumulation state estimation part 52 configured as
above will be described with reference to the flowcharts shown in Fig. 4 to Fig. 6.
First, as illustrated in Fig. 4, in step S11, a current collection stage is
20 determined by the above-described current stage determination part 52a. The
current collection stage in step S11 is a collection stage which has been determined in
the preceding cycle in the flowchart illustrated in Fig. 2 and is stored in the ECU 50.
[0040]
Then, in step S12, detection determination is performed for the sensors by the
25 above-described defect detection part 52d. That is, as illustrated in Fig. 6, whether a
defect determination condition is satisfied is judged in step S31. Such judgment is
made according to whether, in a case where the signal output from the sensor is a
voltage signal, for example, the magnitude of the voltage falls within a prescribed
range. Similarly, in a case where the signal output from the sensor is an electric
30 current or a resistance, the judgment is made by the magnitude of the electric current
or the resistance. Then, if the value of the signal output from the sensor is within
the prescribed range (the case of “NO” in S31), the sensor is determined to be normal.
On the other hand, if the value of the signal output from the sensor is out of the
prescribed range (the case of “YES” in S31), duration of time is measured in step S32,
35 and whether the measured duration exceeds a defect determination deciding period is
judged in step S33. Then, if the measured duration exceeds the defect determination
14
deciding period, the sensor is determined to have a defect. On the other hand, if the
measured duration does not exceed the defect determination deciding period, the
procedure returns to step 31, and the following steps are repeated.
[0041]
Then, if the sensor is determined to have a defect in step S12 (the case o5 f
“YES” in S12), a warning is given to e.g. an operator in step S13, and then the current
collection stage determined in step S11 is once cleared in S14. Then, the evaluation
index based on the output value of the sensor of which a defect is detected is
invalidated in step S15. An example of such an invalidation processing will be
10 described with reference to Fig. 7. This example is of a case where defects of two
sensors including the DPF inlet temperature sensor 38 and the DPF outlet
temperature sensor 42 have been detected.
[0042]
As illustrate in Fig. 7, a plurality of evaluation indices are calculated based on
15 output values of different types of sensors which have been input into the ECU 50.
For example, a PM emission amount is calculated from the engine rotational speed
and the fuel injection amount, and a PM regeneration amount is calculated from the
engine rotational speed, the DPF inlet temperature, the DPF outlet temperature, the
O2 concentration, the supply air flow rate and the fuel injection amount. The
20 difference between the PM emission amount and the PM regeneration amount is
temporally cumulated to obtain a PM accumulation amount estimate. Further, for
example, as illustrated in Fig. 7, a DPF corrected pressure difference is calculated
from the DPF inlet temperature, the DPF outlet temperature, the DPF pressure
difference, the supply air flow rate and the fuel injection amount. In this
25 embodiment, four evaluation indices including a cumulative operation time and a
cumulative fuel consumption of the engine 2 in addition to the PM accumulation
amount estimate and the DPF corrected pressure difference are used. In step 20, the
current evaluation stage is newly redetermined by the above-described current stage
redetermination part 52c, by using two evaluation indices including the cumulative
30 operation time and the cumulative fuel consumption without using, among the above
four evaluation indices, the PM accumulation amount evaluated value and the DPF
corrected pressure difference which are calculated based on the DPF inlet
temperature and the DPF outlet temperature as output values of the sensors of which
defects have been detected.
35 [0043]
That is, the above-described invalidation processing means not to use an
15
evaluation value based on an output of a sensor of which a defect is detected in the
following estimation of the PM accumulation state.
[0044]
The O2 concentration can be measured by e.g. an O2 sensor; however, in this
embodiment, it is calculated by the ECU 50 based on the pressure and temperature o5 f
the exhaust gas, the fuel injection amount, the EGR recirculation ratio and the like.
[0045]
Fig. 5 is a flowchart related to the current stage redetermination in step S20.
As illustrated in Fig. 5, in the redetermination of the current collection stage, first,
10 the collection stage 1 representing the lowest stage is set as an initial value in step
S21, and in step S22, determination of whether to move up the current collection
stage to the collection stage of the next rank is performed by using two evaluation
indices including the cumulative operation time and the cumulative fuel consumption.
Then, for example, if any one of the two evaluation indices is greater than the
15 threshold and such a state is maintained for a prescribed period of time (the case of
“YES” in S22), after checking that the DPF is not undergoing regeneration in step S23,
the current collection stage is moved up to the next rank in step S24. Then, the
procedure returns to step S22, and again, determination of whether to move up the
current collection stage to the next rank is repeated. By repeating the above
20 procedure until both of the two evaluation indices i.e. the cumulative operation time
and the cumulative fuel consumption fall below the thresholds, the current collection
stage is redetermined, and it will be the collection stage in step S16.
[0046]
On the other hand, if no defect of the sensors is detected in step S12, the
25 current collection stage determined in step S11 will directly be the collection stage in
step S15.
[0047]
Then, in step S17 and the following steps, determination of whether to move
up the current collection stage in step S16 to the next rank is performed by the above30
described evaluation stage determination part 52b. That is, in step S17,
determination of whether to move up the current collection stage in step S16 to the
next rank is performed by using the above four evaluation indices. Such a
determination is made according to, for example, whether at least one of the four
evaluation indices is greater than the threshold value and such a state is maintained
35 for a prescribed period of time. Further, in this case, as shown in Fig. 4, by
performing determination of whether to move up the current collection stage by using
16
the two evaluation indices including the cumulative operation time and the
cumulative fuel consumption without using the PM accumulation amount evaluated
value and the DPF corrected pressure difference which are calculated based on the
DPF inlet temperature and the DPF outlet temperature as output values of the
sensors of which defects have been detected, it is possible to improve the estimatio5 n
accuracy of the PM accumulation state during a failure of a sensor..
[0048]
As illustrated in Fig. 4, if any one of the two evaluation indices i.e. the
cumulative operation time and the cumulative fuel consumption is greater than the
10 threshold value and such a state is maintained for a prescribed period of time (the
case of “YES” in S17), after checking that the DPF is not undergoing regeneration in
step S18, the current collection stage is moved up to the next rank in step S19, and
then the procedure ends. On the other hand, if both of the two evaluation indices i.e.
the cumulative operation time and the cumulative fuel consumption are below the
15 threshold values, or if the duration where any one of the two evaluation indices is
greater than the threshold value is less than a prescribed period of time in step S17
(the case of “NO” in S17), the procedure directly ends. The procedures illustrated in
the flowcharts of Fig. 4 to Fig. 6 are configured to be repeatedly performed every
prescribed length of time and/or at a prescribed timing (e.g. when the driving distance
20 reaches a prescribed value) during operation of the engine 2.
[0049]
The exhaust gas purification system of an engine according to this embodiment,
as described above, is configured to classify the PM accumulation state of the DPF 34
into six collection stages (evaluation stages), for example, based on four evaluation
25 indices (the PM accumulation amount evaluated value, the DPF corrected pressure
difference, the cumulative operation time and the cumulative fuel consumption) and
to repeatedly perform determination of the current collection stage by the current
stage determination part 52a and determination of whether to move up the current
evaluation stage to the evaluation stage of the next rank by the evaluation stage
30 determination part 52b. Also, the exhaust gas purification system of an engine
according to this embodiment is configured so that when a defect of a sensor is
detected by the defect detection part 52d, the current evaluation stage is newly
redetermined by the current stage redetermination part 52c as substituted for the
current collection stage determined by the current stage determination part 52a by
35 using an evaluation index other than an evaluation index based on an output value of
the sensor of which a defect is detected.
17
Thus, in a case of a failure of a sensor, the current collection stage is newly
redetermined by using an evaluation index other than an evaluation index based on
an output value of the sensor of which a defect is detected, whereby it is possible to
improve the accuracy of estimating the PM accumulation stateduring a failure of a
sensor5 .
[0050]
Further, as described above, the exhaust gas purification system of an engine
according to this embodiment is configured so that when a defect of a sensor is
detected by the defect detection part 52d, determination of whether to move up the
10 current evaluation stage to the evaluation stage of the next rank is performed by the
evaluation stage determination part 52b by using the evaluation index other than the
evaluation index based on the output value of the sensor of which a defect is detected,
whereby it is possible to further improve the accuracy of estimating the PM
accumulation state during a failure of a sensor.
15 [0051]
In the above description of the embodiment, an example where the PM
accumulation state of the DPF 34 is classified into six collection stages (evaluation
stages) based on four evaluation indices is described; however, the present invention
is by no means limited to this example. The number of the evaluation indices is not
20 limited as long as the PM accumulation state of the DPF 34 is classified based on at
least two evaluation indices, and it does not have to be four. Further, the number of
the collection stages (evaluation stages) for classification is not limited, and it does
not have to be six.
[0052]
25 (Second embodiment)
In the above embodiment, an example of a case where defects of two sensors i.e.
the DPF inlet temperature sensor 38 and the DPF outlet temperature sensor 42 are
detected is described. In this second embodiment, an example of a case where a
defect of the DPF differential pressure sensor 40 is detected will be described with
30 reference to Fig. 8 to Fig. 10. In this embodiment, the essential constitution is the
same as in the above embodiment, and the same elements as those of the above
embodiment are assigned with the same reference numerals as those of the above
embodiment, and the same description thereof will be omitted.
[0053]
35 As illustrated in Fig. 10, the DPF pressure difference, which is an output value
of the DPF differential pressure sensor 40, is a base for calculation of the DPF
18
corrected pressure difference, which is one of the four evaluation indices. Thus, in
this embodiment, as illustrated in Fig. 8 and Fig. 9, in step S20, the current
evaluation stage is newly redetermined by the above-described current stage
redetermination part 52c by using three evaluation indices i.e. the PM accumulation
amount estimate the cumulative operation time and the cumulative fuel consumptio5 n
without using, among the above four evaluation indices, the DPF corrected pressure
difference which is an output value of the sensor of which defects have been detected.
[0054]
Further, in this embodiment, as illustrated in Fig. 8, in step S17 and the
10 following steps, determination of whether to move up the current collection stage in
step S16 to the next rank is performed by the above-described evaluation stage
determination part 52b by using three evaluation indices i.e. the PM accumulation
amount estimate, the cumulative operation time and the cumulative fuel consumption
without using the DPF corrected pressure difference which is an output value of the
15 sensor of which defects have been detected.
[0055]
Thus, the exhaust gas purification system of an engine of the present invention
is a system which is applicable to a case where a defect of at least one sensor among
different types of sensors used for calculation of a plurality of evaluation indices is
20 detected.
[0056]
(Third embodiment)
The third embodiment of the present invention will be described with reference
to Fig. 11 to Fig. 13. In this embodiment, the essential constitution is the same as in
25 the above embodiment, and the same elements as those of the above embodiment are
assigned with the same reference numerals as those of the above embodiment, and
the same description thereof will be omitted.
[0057]
In the above-described embodiments, when a defect of a sensor is detected by
30 the defect detection part 52d, the current evaluation stage is newly redetermined by
the current stage redetermination part 52c, and whether to move up the current
evaluation stage to the next rank is determined by the evaluation stage
determination part 52b, by using an evaluation index other than an evaluation index
based on an output value of the sensor of which a defect is detected.
35 [0058]
However, the present invention is not limited thereto, and as illustrated in Fig.
19
11 to Fig. 13, it may be configured so that when a defect of the air flow meter 26 (a
supply air flow meter), which is one of the sensors, is detected by the defect detection
part 52d, the evaluation indices (the PM accumulation amount estimate and the DPF
corrected pressure difference) are calculated based on a supply air flow rate
calculated by an alternative unit 60 as illustrated in Fig. 13, as substituted for 5 a
supply air flow rate measured by the air flow meter 26 of which a defect is detected,
and by using the calculated PM accumulation amount estimate and DPF corrected
pressure difference in addition to the cumulative operation time and the cumulative
fuel injection amount, the current evaluation stage is newly redetermined, and
10 whether to move up the current evaluation stage to the next rank is determined by
the evaluation stage determination part 52b.
[0059]
The is, as illustrated in Fig. 11, in step S15’, an alternative value of the supply
air flow rate is calculated by the alternative unit 60 as substituted for the supply air
15 flow rate measured by the air flow meter 26, and as illustrated in Fig. 11 and Fig. 12,
in step S20, the current evaluation stage is newly redetermined by the abovedescribed
current stage redetermination part 52c by using four evaluation indices
including the PM accumulation amount estimate and DPF corrected pressure
difference calculated based on the alternative value of the supply air flow. Further,
20 as illustrated in Fig. 11, in step S17’ and the following steps, whether to move up the
current collection stage in step S16 to the next rank is determined by the abovedescribed
evaluation stage determination part 52b by using four evaluation indices
including the PM accumulation amount estimate and DPF corrected pressure
difference calculated based on the alternative value of the supply air flow.
25 [0060]
According to the exhaust gas purification system of an engine in this
embodiment, in a case where a defect of the air flow meter 26 (a supply air flow
meter) is detected, the PM accumulation estimate and the DPF corrected pressure
difference are calculated based on the supply air flow rate calculated by the
30 alternative unit 60 as substituted for the supply air flow rate measured by the air
flow meter 26, and the current evaluation stage is redetermined by using the above
PM accumulation estimate and DPF corrected pressure difference in addition to the
cumulative operation time and the cumulative fuel injection amount, whereby it is
possible to improve the accuracy of estimating the PM accumulation state during a
35 failure of the supply air flow meter.
[0061]
20
Further, according to the exhaust gas purification system of an engine in this
embodiment, in a case where a defect of the air flow meter 26 (a supply air flow
meter) is detected, the PM accumulation estimate and the DPF corrected pressure
difference are calculated based on the supply air flow rate calculated by the
alternative unit 60 as substituted for the supply air flow rate measured by the ai5 r
flow meter 26,
whether to move up the current evaluation stage to the next rank is determined by
using the above PM accumulation amount estimate and DPF corrected pressure
difference in addition to the cumulative operation time and the cumulative fuel
10 injection amount, whereby it is possible to further improve the accuracy of estimating
the PM accumulation state during a failure of the supply air flow meter.
[0062]
The alternative unit 60 of the exhaust gas purification system of an engine in
this embodiment may include the above-described supply air absolute pressure sensor
15 18 and supply temperature sensor 20 (a pressure/temperature measuring device), and
the ECU 50 (a supply air flow rate calculation part) for calculating an alternative
value of the supply air flow rate from the measured pressure and temperature.
[0063]
That is, when a defect of the air flow meter 26 is detected, by totally closing
20 the EGR valve and by means of an absolute pressure and a temperature of the intake
manifold 4 measured by the supply air absolute pressure sensor 18 and the supply air
temperature sensor 20, the supply air flow rate may be calculated by the ECU 50
based on the following formulae (1) and (2):
Gcyl=(ρ∙Vstrk∙Ne/60)∙(2/Icyc) ∙Ncyl∙Ev (1)
25 ρ=P/RT (2)
wherein Gcyl is supply air flow rate, ρ is density of supply air, P is absolute pressure
at the intake manifold part, T is temperature at the intake manifold part, R is the gas
state constant, Vstrk is a stroke volume per a cylinder, Ne is engine rotational speed,
Icyc is number of strokes, Ncyl is number of cylinders, and Ev is volumetric efficiency
30 which may be separately calculated from a map.
[0064]
Alternatively, the alternative unit 60 of the exhaust gas purification system of
an engine in this embodiment may include different types of sensors and the ECU 50
(a rotational speed/injection amount calculation unit) which are necessary for
35 calculating the engine rotational speed and the fuel injection amount of the engine 2,
and the ECU 50 (a supply air flow rate calculation part) for calculating the supply air
21
flow rate from a relationship between the engine rotational speed and the fuel
injection amount, and the supply flow rate, of the engine 2.
[0065]
That is, when a defect of the air flow meter 26 is detected, as illustrated in Fig.
14, an alternative value of the supply air flow rate is calculated by means of a suupl5 y
air flow rate map 62 based on input data including the engine rotational speed and
the fuel injection amount which are calculated by the ECU 50 based on the input
signals from the above-described different types of sensors such as a crank sensor, a
cam sensor, an accelerator sensor and a throttle sensor, which are not shown. The
10 supply air flow rate map 62 may be generated from experimental data and may be
preliminarily stored in the ROM of the ECU 50.
[0066]
Some preferred embodiments of the present invention are described above;
however, the present invention is by no means limited thereto and further
15 modifications and variations may be made without departing from the scope of the
invention.
[Industrial Applicability]
[0067]
20 The present invention is useful as an exhaust gas purification system of an
engine provided with a DPF, particularly as an exhaust gas purification system of an
engine capable of appropriately controlling the timing of combustion removal of PM
accumulated in the DPF.
25

We claim:-
1. An exhaust gas purification system for an engine comprising a DPF for
collecting PM in an exhaust gas exhausted from an engine to an exhaust passage an5 d
a PM accumulation state evaluation part for classifying a PM accumulation state of
the DPF into multiple evaluation stages based on a plurality of evaluation indices,
said PM accumulation state evaluation part including:
a current stage determination part for determining a current evaluation stage;
10 and
an evaluation stage determination part for moving up the current evaluation
stage to an evaluation stage of a next rank when a value of each of a prescribed
number of the evaluation indices is greater than each threshold value;
and being configured to repeatedly perform determination of the current
15 evaluation stage by the current stage determination part and determination of
whether to move up the current evaluation stage to the evaluation stage of the next
rank by the evaluation stage determination part; and
said PM accumulation evaluation part further including:
a defect detection part for detecting a defect of different types of sensors used
20 for calculating each of the plurality of evaluation indices; and
a current stage redetermination part for redetermining the current evaluation
stage without using, among the different types of sensors, a sensor of which a defect
is detected by the defect detection part;
and being configured to newly redetermine the current evaluation stage by the
25 current stage redetermination part as substituted for the current evaluation stage
determined by the current stage determination part upon a defect of the sensor being
detected by the defect detection part, by using an evaluation index other than an
evaluation index based on an output value of the sensor of which a defect is detected.
30 2. The exhaust gas purification system for an engine according to claim 1,
wherein upon a defect of a supply air flow meter as one of the sensors being detected
by the defect detection part, an evaluation index is calculated based on a supply air
flow rate calculated by an alternative unit as substituted for a supply air flow rate
measured by the supply air flow meter of which a defect is detected, and the current
35 evaluation stage is newly redetermined by the current stage redetermination part by
using the evaluation index calculated by the alternative unit and at least one of the
other evaluation indices.
3. The exhaust gas purification system for an engine according to claim 1,
wherein upon a defect of the sensor being detected by the defect detection part,
determination of whether to move up the current evaluation stage to the evaluatio5 n
stage of the next rank is performed by the evaluation stage determination part by
using the evaluation index other than the evaluation index based on the output value
of the sensor of which a defect is detected.
10 4. The exhaust gas purification system for an engine according to claim 2,
wherein upon a defect of the supply air flow meter as one of the sensors being
detected by the defect detection part, the evaluation index is calculated based on the
supply air flow rate calculated by the alternative unit as substituted for the supply
air flow rate measured by the supply air flow meter of which a defect is detected, and
15 determination of whether to move up the current evaluation stage to the evaluation
stage of the next rank is performed by the evaluation stage determination part by
using the evaluation index calculated by the alternative unit and at least one of the
other evaluation indices.
20 5. The exhaust gas purification system for an engine according to claim 2 or 4,
wherein the alternative unit includes a pressure/temperature measuring device for
measuring a pressure and a temperature at an intake manifold part connected to the
engine on the upstream side, and a supply air flow rate calculation part for
calculating the supply air flow rate from the measured pressure and temperature.
25
6. The exhaust gas purification system for an engine according to claim 2 or 4,
wherein the alternative unit includes a rotational speed/injection amount calculation
unit for calculating an engine rotational speed and a fuel injection amount of the
engine, and a supply air flow rate calculation part for calculating the supply air flow
30 rate from a map of a relationship between the engine rotational speed and the fuel
injection amount, and the supply flow rate, of the engine.