U.S. patent application number 14/266298 was filed with the patent office on 2014-10-30 for method of controlling a diesel particulate filter.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Markus HEMM, Giacomo LATROFA, Christian SCHAEFER, Giuseppe SCHIAVONE.
Application Number | 20140318103 14/266298 |
Document ID | / |
Family ID | 48627039 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140318103 |
Kind Code |
A1 |
LATROFA; Giacomo ; et
al. |
October 30, 2014 |
METHOD OF CONTROLLING A DIESEL PARTICULATE FILTER
Abstract
A method and apparatus for controlling a diesel particulate
filter is disclosed. The control is carried out with the aid of a
soot loading model selected from a plurality of available soot
loading models including at least one soot loading physical model
which makes use of signals from an exhaust gas pressure sensor. A
reliability score is allocated to each soot loading model such that
the soot loading model with the best reliability score is used for
the diesel particulate filter control. If a DPF parking effect is
identified based on an engine shut-off time a DPF inlet temperature
either the reliability score of the soot loading physical model or
the reliability scores of all remaining (non-physical) soot loading
models are changed, and use of the soot loading physical model is
avoided or disabled to help the control of the diesel particulate
filter.
Inventors: |
LATROFA; Giacomo; (Torino,
DE) ; SCHIAVONE; Giuseppe; (Bitonto, DE) ;
HEMM; Markus; (Buettelborn, DE) ; SCHAEFER;
Christian; (Bad Nauheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
Detroit |
MI |
US |
|
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
48627039 |
Appl. No.: |
14/266298 |
Filed: |
April 30, 2014 |
Current U.S.
Class: |
60/274 ;
60/297 |
Current CPC
Class: |
F01N 2900/1606 20130101;
F02D 2041/1433 20130101; Y02T 10/47 20130101; F01N 3/0238 20130101;
F01N 2900/0422 20130101; F01N 2900/1602 20130101; F02D 2200/0812
20130101; Y02T 10/40 20130101; F01N 9/005 20130101; F01N 9/002
20130101; F02D 41/029 20130101 |
Class at
Publication: |
60/274 ;
60/297 |
International
Class: |
F01N 3/021 20060101
F01N003/021 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2013 |
GB |
1307754.0 |
Claims
1-9. (canceled)
10. A method for controlling a diesel particulate filter (DPF)
comprising: defining a plurality of soot loading models including a
soot loading physical model and at least one soot loading
non-physical model which makes use of signals from an exhaust gas
pressure sensor; allocating a reliability score to each of the
plurality of soot loading models; identifying a DPF parking effect
when an engine shut-off time is longer than a first time threshold
and an inlet temperature of the diesel particulate filter is less
than a first temperature threshold; and changing the reliability
score for either the soot loading physical model or all of the soot
loading non-physical models from a previous value for disabling the
soot loading physical model in the control of the diesel
particulate filter; wherein the soot loading model with the highest
reliability score is enabled for controlling the diesel particulate
filter.
11. The method according to claim 10, further comprising restoring
the reliability scores for either the soot loading physical model
or of all of the soot loading non-physical models to the previous
values when the inlet temperature is higher than a second
temperature threshold and an elapsed time is longer than a second
time threshold.
12. The method according to claim 10 wherein changing a reliability
score is carried out by lowering the reliability score of the soot
loading physical model.
13. The method according to claim 10 wherein changing the
reliability score is carried out by increasing the reliability
score for all of the soot loading non-physical models.
14. The method according to claim 10 wherein the at least one soot
loading non-physical models comprises a soot loading statistical
model.
15. A control apparatus for an exhaust system of an internal
combustion of the type having a diesel particulate filter and an
exhaust gas pressure sensor, the control apparatus comprising an
electronic control unit having: a memory storing an instruction set
and a plurality of soot loading models including a soot loading
physical model and at least one soot loading non-physical model,
wherein the soot loading physical model makes use of signals from
the exhaust gas pressure sensor; and a microcontroller executing
the instruction set and configured to: allocate a reliability score
to each of the plurality of soot loading models; identify a DPF
parking effect when an engine shut-off time is longer than a first
time threshold and an inlet temperature of the diesel particulate
filter is less than a first temperature threshold; and change the
reliability score for either the soot loading physical model or all
of the soot loading non-physical models from a previous value for
disabling the soot loading physical model in the control of the
diesel particulate filter; wherein the soot loading model with the
highest reliability score is enabled for controlling the diesel
particulate filter.
16. The control apparatus according to claim 15, wherein the
microcontroller is configured to restore the reliability scores for
either the soot loading physical model or of all of the soot
loading non-physical models to the previous values when the inlet
temperature is higher than a second temperature threshold and an
elapsed time is longer than a second time threshold.
17. The control apparatus according to claim 15, wherein the
microcontroller is configured to change a reliability score by
lowering the reliability score of the soot loading physical
model.
18. The control apparatus according to claim 15, wherein the
microcontroller is configured to change the reliability score by
increasing the reliability score for all of the soot loading
non-physical models.
19. The control apparatus according to claim 15, wherein the at
least one soot loading non-physical models comprises a soot loading
statistical model.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to British Patent
Application No. 1307754.0 filed Apr. 30, 2013, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The technical field relates to a method of controlling a
diesel particulate filter (DPF), and more particularly a method to
the identify the DPF parking effect in order not to worsening the
soot loading evaluation.
BACKGROUND
[0003] It is known that modern engines are provided with one or
more exhaust aftertreatment devices. The aftertreatment devices may
be any device configured to change the composition of the exhaust
gases, such as a diesel oxidation catalyst (DOC) located in the
exhaust line for degrading residual hydrocarbons (HC) and carbon
oxides (CO) contained in the exhaust gas, and a diesel particulate
filter (DPF) located in the exhaust line downstream the DOC, for
capturing and removing diesel particulate matter (soot) from the
exhaust gas. The diesel particulate filter collects liquid and
solid particles in a porous substrate structure, while allowing
exhaust gases to flow through. As it reaches its nominal storage
capacity, the DPF needs to be cleaned by a process called
regeneration. A DPF physical model returns a soot loading
evaluation starting from the differential pressure signal read
across the DPF by an exhaust gas pressure (EGP) sensor. This is
applied to the overall soot estimation strategy in order to
optimize the DPF regeneration frequency.
[0004] A particular condition related to the estimation of the soot
loading appears during a prolonged vehicle disuse, if the soot in
the DPF reaches very low temperatures. This condition is well known
as parking effect. As a result, when the vehicle is started again,
even if the soot quantity is not changed in the trap, there is a
significant pressure drop reduction across the filter, thus leading
to a soot loading under-estimation by the DPF physical model,
taking into account the information of the EGP sensor.
[0005] In DE 10 2006 062515, a method of controlling a DPF is
shown, which attempts to consider the parking effect. The method
involves measuring concentration of one of exhaust gas components
such as nitric oxide and nitrogen dioxide in an exhaust gas mass
flow downstream of a DPF. A functional condition and/or a loading
condition of the particle filter with soot are determined from the
measured concentration. A diagnostic signal is assigned to the
functional condition and/or loading condition. However, there is a
need in the art to provide a method of controlling the DPF, which
is more reliable in identifying the parking condition and avoiding
soot loading under-prediction.
SUMMARY
[0006] An embodiment of the present disclosure provides a method of
controlling a diesel particulate filter, wherein the control is
carried out with the aid of a soot loading model selected from a
plurality of available soot loading models. The soot loading models
include at least one soot loading physical model which makes use of
signals from an exhaust gas pressure sensor, wherein a reliability
score is allocated to each soot loading model and wherein the soot
loading model with the best reliability score is used for the
diesel particulate filter control.
[0007] The method includes identifying a DPF parking effect if an
engine shut-off time is longer than a first time threshold and a
DPF inlet temperature is less than a first temperature threshold.
This step can be carried out before or shortly after cranking. If a
parking effect is identified because the above conditions are met,
either the reliability score of the soot loading physical model or
the reliability scores of all remaining (non-physical) soot loading
models are changed, and use of the soot loading physical model is
avoided or disabled to help the control of the diesel particulate
filter.
[0008] In the first alternative the reliability score of the soot
loading physical model is changed, such that its new reliability
score indicates that it is less reliable. The score may be lowered,
such that a lower score indicates a reduced reliability. In the
second alternative the reliability scores of all remaining soot
loading models, i.e. of all non-physical soot loading models, are
changed. This is done such that the new scores render all remaining
soot loading models to be more reliable than before and in
particular to be more reliable than the soot loading physical
model. In both alternatives, which as a matter of fact can be
combined, the likelihood that the soot loading physical model is
used for DPF control is reduced.
[0009] An apparatus is also disclosed for controlling a diesel
particulate filter. The apparatus includes a DPF controller
configured to control the DPF using a soot loading model selected
from a plurality of available soot loading models. Again, the soot
loading models include at least one soot loading physical model
which makes use of signals from an exhaust gas pressure sensor. The
controller is configured to allocate a reliability score for each
soot loading model and to identify the soot loading model with the
best reliability score for controlling the diesel particulate
filter control. The controller is configured to identify a DPF
parking effect if an engine shut-off time is longer than a first
time threshold and a DPF inlet temperature is less than a first
temperature threshold. The controller is configured to change the
reliability score of the soot loading physical model or the
reliability scores of all remaining (non-physical) soot loading
models are changed, and use of the soot loading physical model is
avoided or disabled to help the control of the diesel particulate
filter.
[0010] An advantage of this strategy is that all needed parameters
for identifying the parking effect are defined and the related
countermeasure, i.e. not to use a physical soot loading model
during the parking effect, is established.
[0011] According to another embodiment, the method further includes
the step of restoring the reliability score of the physical model
or the reliability scores of all remaining soot loading models to
their previous values if the DPF inlet temperature is higher than a
second temperature threshold and an elapsed time is longer than a
second time threshold. This serves to allow that the soot loading
physical model is used or enabled to help control the diesel
particulate filter. The previous values are the reliability scores
before the detection of the parking effect, so this step
neutralizes the prior change of the reliability score or
scores.
[0012] Similarly, the controller is configured to restore the
reliability score of the physical model or the reliability scores
of all remaining soot loading to their previous value(s) if the DPF
inlet temperature is higher than a second temperature threshold and
an elapsed time is longer than a second time threshold, which
serves to to allow that the soot loading physical model is used or
enabled to help the control the diesel particulate filter.
[0013] An advantage of this strategy is an ability to define all
parameters, establishing until when said parking effect strategy
should be maintained.
[0014] According to a further embodiment, changing a reliability
score is carried out by lowering the reliability score of the at
least one soot loading physical model. Assuming again that a
lowered score indicates a less reliable model, this helps to avoid
that a soot loading physical model has the best reliability score
out of the multitude of available soot loading models. Similarly,
the controller is configured to lower the reliability score of the
at least one soot loading physical model, to avoid that a soot
loading physical model has the best reliability score out of the
multitude of available soot loading models. This improves the
likelihood that soot estimation is correct if a parking effect is
identified.
[0015] According to a still further embodiment, a change of
reliability scores is carried out by increasing the reliability
scores of all remaining soot loading models, that is the
non-physical models, such that a non-physical soot loading model
has a better or the best reliability score out of the multitude of
available soot loading models. Similarly, the controller is
configured to increase the reliability scores of all available soot
loading models, to allow that a non-physical soot loading model has
the best reliability score out of the multitude of available soot
loading models. This embodiment, in an alternative way, brings the
advantage that the soot loading physical models not having anymore
the best reliability score among the other soot loading models will
not be chosen as the soot loading model helping the control of the
DPF.
[0016] According to another embodiment, the multitude of available
soot loading models includes a soot loading statistical model, and
the soot loading statistical model is chosen for helping the
control of the diesel particulate filter if it shows a reliability
score better than the reliability score of said soot loading
physical model. Similarly, the controller is configured to choose a
soot loading model wherein the multitude of available soot loading
models includes a soot loading statistical model, and the soot
loading statistical model is chosen for helping the control of the
diesel particulate filter, if it shows a reliability score better
than the reliability score of said soot loading physical model. In
this way, the soot loading estimation will be performed by a model,
which will not suffer the problem of the soot loading
under-estimation, since it is not related to the exhaust gas
pressure sensor signals, but it is an available soot loading
statistical model.
[0017] The above-described embodiments may be readily implemented
in an automotive system including an internal combustion engine,
for example a Diesel engine having a diesel particulate filter, an
exhaust gas pressure sensor, and an electronic control unit
configured to control the diesel particulate in the above-described
manner. In particular, the electronic control unit may include
program code for carrying out all the steps of the method described
above when it is executed by a computer, microprocessor or
controller. The computer program may be part of a transitory
computer program product such as an electromagnetic or optical
signal which carries, by means of modulation such as QPSK, binary
data representing the computer program. In the alternative the
computer program may be part of a non-transitory computer program
product which is embodied in a conventional data carrier such as a
flash memory, an Asic, a CD or the like. The computer program
product can be a component of a control apparatus for an internal
combustion engine, including an Electronic Control Unit (ECU), a
data carrier associated to the ECU, and the computer program stored
in a data carrier. In this case, when the control apparatus
executes the computer program control of the DPF described above is
carried out.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The present disclosure will hereinafter be described in
conjunction with the following drawing figures, wherein like
numerals denote like elements, and:
[0019] FIG. 1 shows an automotive system;
[0020] FIG. 2 is a section of an internal combustion engine shown
in FIG. 1;
[0021] FIG. 3 is a schematic view of an after-treatment system
according to the present disclosure;
[0022] FIGS. 4a-4c are a schematic representation of the parking
effect;
[0023] FIG. 5 is a graph depicting the soot level under-estimation
due to the parking effect; and
[0024] FIG. 6 shows the flowchart of the method according to the
present disclosure.
DETAILED DESCRIPTION OF THE DRAWINGS
[0025] The following detailed description is merely exemplary in
nature and is not intended to limit the present disclosure, the
application or uses of the present disclosure. Furthermore, there
is no intention to be bound by any theory presented in the
preceding background or the following detailed description.
[0026] Some embodiments may include an automotive system 100, as
shown in FIGS. 1 and 2, that includes an internal combustion engine
(ICE) 110 having an engine block 120 defining at least one cylinder
125 having a piston 140 coupled to rotate a crankshaft 145. A
cylinder head 130 cooperates with the piston 140 to define a
combustion chamber 150.
[0027] A fuel and air mixture (not shown) is disposed in the
combustion chamber 150 and ignited, resulting in hot expanding
exhaust gasses causing reciprocal movement of the piston 140. The
fuel is provided by at least one fuel injector 160 and the air
through at least one intake port 210. The fuel is provided at high
pressure to the fuel injector 160 from a fuel rail 170 in fluid
communication with a high pressure fuel pump 180 that increase the
pressure of the fuel received from a fuel source 190.
[0028] Each of the cylinders 125 has at least two valves 215,
actuated by a camshaft 135 rotating in time with the crankshaft
145. The valves 215 selectively allow air or an air-fuel mixture
into the combustion chamber 150 from the port 210 and alternately
allow exhaust gases to exit through a port 220. In some examples, a
cam phaser 155 may selectively vary the timing between the camshaft
135 and the crankshaft 145.
[0029] Air may be distributed to the air intake port(s) 210 through
an intake manifold 200. An air intake duct 205 may provide air from
the ambient environment to the intake manifold 200. In other
embodiments, a throttle body 330 may be provided to regulate the
flow of air into the manifold 200. In still other embodiments, a
forced air system such as a turbocharger 230, having a compressor
240 rotationally coupled to a turbine 250, may be provided.
Rotation of the compressor 240 increases the pressure and
temperature of the air in the duct 205 and manifold 200. An
intercooler 260 disposed in the duct 205 may reduce the temperature
of the air. The turbine 250 rotates by receiving exhaust gases from
an exhaust manifold 225 that directs exhaust gases from the exhaust
ports 220 and through a series of vanes prior to expansion through
the turbine 250. The exhaust gases exit the turbine 250 and are
directed into an exhaust system 270. This example shows a variable
geometry turbine (VGT) with a VGT actuator 290 arranged to move the
vanes to alter the flow of the exhaust gases through the turbine
250. In other embodiments, the turbocharger 230 may be fixed
geometry and/or include a waste gate.
[0030] The exhaust system 270 may include an exhaust pipe 275
having one or more exhaust aftertreatment devices 280. The
aftertreatment devices may be any device configured to change the
composition of the exhaust gases. Some examples of aftertreatment
devices 280 include, but are not limited to, catalytic converters
(two and three way), oxidation catalysts, lean NOx traps,
hydrocarbon adsorbers, selective catalytic reduction (SCR) systems,
and particulate filters 282. In particular, a diesel particulate
filter (or DPF) is a device designed to remove diesel particulate
matter or soot from the exhaust gas of a diesel engine. Wall-flow
diesel particulate filters usually remove 85% or more of the soot,
and under certain conditions can attain soot removal efficiencies
of close to 100%. Some filters are single-use, intended for
disposal and replacement once full of accumulated ash. Others are
designed to burn off the accumulated particulate either passively
through the use of a catalyst or by active means such as a fuel
burner which heats the filter to soot combustion temperatures;
engine programming to run when the filter is full in a manner that
elevates exhaust temperature or produces high amounts of NOx to
oxidize the accumulated ash, or through other methods. The process
of particulate burn off is known as "filter regeneration."
[0031] Other embodiments may include an exhaust gas recirculation
(EGR) system 300 coupled between the exhaust manifold 225 and the
intake manifold 200. The EGR system 300 may include an EGR cooler
310 to reduce the temperature of the exhaust gases in the EGR
system 300. An EGR valve 320 regulates a flow of exhaust gases in
the EGR system 300.
[0032] The automotive system 100 may further include an electronic
control unit (ECU) 450 in communication with one or more sensors
and/or devices associated with the engine 110 and equipped with a
data carrier 40. The ECU 450 may receive input signals from various
sensors configured to generate the signals in proportion to various
physical parameters associated with the engine 110. The sensors
include, but are not limited to, a mass airflow and temperature
sensor 340, a manifold pressure and temperature sensor 350, a
combustion pressure sensor 360, coolant and oil temperature and
level sensors 380, a fuel rail pressure sensor 400, a cam position
sensor 410, a crank position sensor 420, exhaust pressure and
temperature sensors 430, an EGR temperature sensor 440, and an
accelerator pedal position sensor 445. Furthermore, the ECU 450 may
generate output signals to various control devices that are
arranged to control the operation of the engine 110 and its various
sensors and devices, including, but not limited to, the fuel
injectors 160, the throttle body 330, the EGR Valve 320, the VGT
actuator 290, and the cam phaser 155. Note, dashed lines are used
to indicate communication between the ECU 450 and the various
sensors and devices, but some are omitted for clarity.
[0033] Turning now to the ECU 450, this apparatus may include a
micro controller or digital central processing unit (CPU) in
communication with a memory system and an interface bus. The CPU is
configured to execute instructions stored as a program in the
memory system, and send and receive signals to and from the
interface bus. The memory system may include various storage types
including optical storage, magnetic storage, solid state storage,
and other non-volatile memory. The interface bus may be configured
to send, receive, and modulate analog and/or digital signals
to/from the various sensors and control devices. The program may
embody the methods disclosed herein, allowing the CPU to carryout
out the steps of such methods and control the ICE 110.
[0034] The diesel particulate filter (DPF) 282 collects liquid and
solid particles in a porous substrate structure, while allowing
exhaust gases to flow through. As it reaches its nominal storage
capacity, needs to be cleaned by a process called regeneration,
during which the exhaust gas temperature is increased substantially
to create a condition, whereby the soot contained in the DPF is
burned, that is to say oxidized. A DPF physical model returns a
soot loading evaluation starting from the differential pressure
signal read across the DPF by an exhaust gas pressure (EGP) sensor
283, as shown in FIG. 3. This basic information is corrected,
considering the pressure drop on the DPF filter in clean conditions
and divided by the volumetric flow rate of the exhaust gas, in
order to obtain the so called "flow resistance". The physical model
soot estimation is directly correlated to the flow resistance
information, that is returned to give an accurate indication of the
soot storage level at different exhaust conditions (especially in
terms of temperature), wherein the only EGP information could not
be accurate. This physical model is applied to the overall soot
estimation strategy in order to optimize the DPF regeneration
frequency.
[0035] As mentioned, a particular condition related to the
estimation of the soot loading is the so called DPF parking effect.
The DPF parking effect takes place during a prolonged engine
shut-off (an engine shut-off time threshold can be established by
calibration) and if the soot in DPF reaches very low temperatures
(such temperature can be evaluated at the DPF inlet and a DPF inlet
temperature threshold can be established by calibration). During
this period, the particulate properties change leading to a
remarkable decrease of pressure signal evaluated across the DPF. It
means that, when the vehicle is started again, even if the soot
quantity is not changed in the trap, there is a significant
pressure drop reduction across the filter, thus leading to a soot
loading under-estimation by the DPF physical model, which takes
into account the information of the EGP sensor 283.
[0036] In FIG. 4 is schematically shown the so called parking
effect. In the upper part, (FIG. 4a) the soot layer 500 is
deposited on the DPF substrate 510. This is a normal situation
before the vehicle parking, for example in a case when there is a
high pressure drop, due to the fact that the last regeneration
process was performed a long time ago. In FIG. 4b, supposing a long
parking time and low DPF inlet temperature, the increasing of the
soot permeability leads to a lower pressure drop sensed across the
filter, notwithstanding the soot layer 501 remains unchanged.
Finally, as shown in FIG. 4c, after the parking the following soot
500 has the same properties of the soot before the vehicle parking.
Therefore, the pressure drop will increase accordingly to the soot
loading, but starting from a lower level and without any
possibility to consider this offset until a regeneration process
will take place.
[0037] As already mentioned, during the vehicle parking the soot
quantity stored inside the DPF does not change. But, in terms of
physical model behavior, this results in a lower drop of the
differential pressure measured across the filter. This is due to
the fact that the particulate permeability increases during this
period, so that the particulate offers a lower resistance and
consequently there is a lower pressure drop across the DPF. The
pressure drop reduction leads to an under-estimation of the
physical soot model based on it. In FIG. 5, the DPF loading and the
coolant temperature behavior vs. time are shown. As can be seen,
after the cold start, the apparent DPF loading is lowered by about
28%. As soon as new soot is stored inside the DPF, the physical
model of the DPF loading will show an increase of the loading
itself, but without taking into account the lost amount prediction.
This potentially drastic under-evaluation by the soot physical
model might lead to a not properly working DPF regeneration, due to
a real amount of soot too high at the beginning of the regeneration
process.
[0038] The present method starts from the following consideration:
the current model, which estimates soot loading models, also known
as ranked model, is a software that evaluates the reliability of
different available soot loading models (e.g. the physical model)
in every driving condition, for example, checking the actual value
of signals, like ambient air temperature, exhaust temperature,
exhaust mass flow rate, exhaust NOx concentration. In this way,
knowing the strength and the drawbacks of each soot model, the
software recognizes if the current engine condition allows each
soot loading model to return a reliable evaluation of the soot
trapped. Consequently, the reliability score, which is associated
with a soot loading model that does not return the proper
estimation is modified by means of calibration factors. In
particular, a change of the reliability score can be more or less
severe, depending on how bad is the soot model evaluation in every
specific case. Then, case by case, the soot loading information,
which comes from the best ranked model is chosen and contributes to
build a new soot loading information that always takes the best
estimation available.
[0039] Some relevant parameters have to be taken into account.
First of all, the elapsed time with the engine not running (vehicle
disuse); the reduction of the pressure drop signal is dependent on
the length of the engine shut-off. For example, at a DPF inlet
temperature of -10.degree. C., after 2 h the reduction in pressure
drop is negligible, while after 6 h, such reduction is about 16%.
Therefore, a first time threshold t.sub.1 for the engine shut-off
time (condition 1) is requested to enable the strategy. Also
relevant is the DPF inlet temperature, since the parking effect
takes place only below a certain temperature. For example in a
specific engine application, for an engine shut-off time of about
12 h, at 0.degree. C. the reduction in pressure drop is negligible,
while at -25.degree. C., such reduction is about 22%. Therefore, a
first temperature threshold T.sub.1 for DPF inlet temperature
(condition 2) at engine start is also requested to enable the
strategy.
[0040] Once parking effect is recognized according to the previous
conditions (shut-off time, DPF inlet temperature), the strategy
must be kept active even if the DPF temperature condition is no
longer satisfied, since the pressure drop takes place even if the
DPF inlet temperature is above the previous threshold (condition 2)
and until the same temperature has not overcome a different
threshold for a certain time. In fact, by performing two different
cold starts in the same conditions (shut-off time: 12 h,
pre-conditioning temperature: -25.degree. C.), it results that: the
time after cranking corresponding to the end of parking effect is
different (e.g. 330 s vs 290 s); the DPF inlet temperature
corresponding to the end of parking effect is different (e.g.
148.degree. C. vs 167.degree. C.); the time interval between a DPF
inlet temperature of 125.degree. C. and the end of parking effect
is the same (e.g. 150 s). Therefore, a second temperature threshold
T.sub.2 for DPF inlet temperature and a second time threshold
t.sub.2 (condition 3) are requested. When these thresholds are
overcome, it is possible to disable the strategy, since the
physical model can be again considered reliable.
[0041] In FIG. 6 a schematic flowchart of the new method is shown.
After the engine disuse due to the vehicle parking, with the engine
in the purely optional condition S20 "wait for cranking", the
present method identifies S21 the DPF parking effect, if the engine
shut-off time is higher than a first calibratable time threshold
t.sub.1 (condition 1, for example, 6 h) and the DPF inlet
temperature is lower than a first calibratable temperature
threshold T.sub.1 (condition 2, e.g. -20.degree. C.).
[0042] After having identified the DPF parking effect, the method
will change S22 the reliability score RS of either the soot loading
physical model and/or of all remaining soot loading models. For
example, the reliability score RS of all available physical models
for soot loading estimation, based on the exhaust gas pressure
sensor 283 can be lowered. As an alternative, the reliability score
RS of all available non-physical model (for example, soot loading
statistical models) can be increased. In any case, for helping the
control of the DPF (i.e. performing the soot loading estimation)
the best ranked model will not be any more a physical model but a
different available one, for example a statistical model or however
any non-physical model, which is not based on the EGP sensor
signal. As known, a statistical model is a model that links a
driving style to an average soot production. As for driving style
can be intended a driving profile (for example, "urban",
"extra-urban" or "highway" that is caught by the model, checking
the current values of some key vehicle parameters (for example,
gear ratio, engine and vehicle speed, load). For each of these
driving conditions an average soot emitted can be identified by
means of experimental activities: this information, is then used to
build the soot level evaluation of the model. When the method
recognizes the DPF parking effect, therefore, a statistical model
will have a better rank than a DPF physical model and will be used
instead, thus avoiding the problem of the soot loading
under-estimation.
[0043] The method considers the parking effect still valid until
when the condition 3, related to the DPF temperature, will not be
satisfied and the condition 3 about the related elapsed time will
not be satisfied as well. In other words, the method will restore
S25 the previous reliability score RS values (i.e. the soot loading
physical model will be again the best ranked model), if the DPF
inlet temperature is higher than S23 the second temperature
threshold T.sub.2 and, after this temperature condition has been
satisfied, the elapsed time is higher than S24 the second time
threshold t.sub.2. When applying the method in the real world, the
engine cranking can finally be performed S26, which however is out
of scope of the present disclosure which concerns the DPF control
only.
[0044] The benefit of this new method is easy to be understood.
While, without any correction, in case of cold start at -25.degree.
C. after a shut-off time of 12 h, a large drop (about -28%) is
observed in the ranked model evaluation, due to the error that
affects the physical model, in case of detected parking effect,
with the engine still off, the ranked model is frozen with the last
available value of the soot loading. As soon as the engine is
started, the method here proposed modifies the soot loading models
reliability score RS and the ranked model considers the soot flow
coming from other available models, for example statistical models.
After the DPF inlet temperature is higher than a calibratable
threshold and the debouncing time is elapsed, parking detection is
switched off. Therefore, the physical model reliability score RS
comes back to the previous value and the ranked model again
considers the soot loading physical model as the most reliable: the
under-estimation prevented is about of 40%.
[0045] Summarizing, the present strategy allows an improved
accuracy in soot loading evaluation, that means an optimization of
the regeneration frequency, so avoiding thermal stress for the
components, due to soot loading under-estimation.
[0046] While at least one exemplary embodiment has been presented
in the foregoing summary and detailed description, it should be
appreciated that a vast number of variations exist. It should also
be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration in any way. Rather, the
foregoing summary and detailed description will provide those
skilled in the art with a convenient road map for implementing at
least one exemplary embodiment, it being understood that various
changes may be made in the function and arrangement of elements
described in an exemplary embodiment without departing from the
scope as set forth in the appended claims and their legal
equivalents.
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