U.S. patent application number 14/896727 was filed with the patent office on 2016-06-16 for system and method for diagnosing the selective catalytic reduction system of a motor vehicle.
This patent application is currently assigned to RENAULT S.A.S. The applicant listed for this patent is RENAULT S.A.S. Invention is credited to Romain CHANZY, Damiano DI-PENTA.
Application Number | 20160169073 14/896727 |
Document ID | / |
Family ID | 49474568 |
Filed Date | 2016-06-16 |
United States Patent
Application |
20160169073 |
Kind Code |
A1 |
CHANZY; Romain ; et
al. |
June 16, 2016 |
SYSTEM AND METHOD FOR DIAGNOSING THE SELECTIVE CATALYTIC REDUCTION
SYSTEM OF A MOTOR VEHICLE
Abstract
A system and method for diagnosing selective catalytic reduction
system of a motor vehicle, the system including an internal
combustion engine connected by an exhaust manifold to,
successively, an assembly including a nitrogen oxide catalyst and a
particle filter and a selective catalytic reduction system, a
mechanism draining mass of ammonia stored in the selective
catalytic reduction system, a mechanism controlling draining, and a
mechanism injecting urea positioned upstream of the selective
catalytic reduction system, a mechanism measuring quantity of
ammonia at an outlet of the selective catalytic reduction system, a
system determining maximum mass of ammonia stored in the selective
catalytic reduction system, and a comparison mechanism configured
to transmit a fault signal based on a result of a comparison
between the maximum mass of ammonia stored in the selective
catalytic reduction system and a threshold.
Inventors: |
CHANZY; Romain; (Paris,
FR) ; DI-PENTA; Damiano; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RENAULT S.A.S |
Boulogne Billancourt |
|
FR |
|
|
Assignee: |
RENAULT S.A.S
Boulogne Billancourt
FR
|
Family ID: |
49474568 |
Appl. No.: |
14/896727 |
Filed: |
June 13, 2014 |
PCT Filed: |
June 13, 2014 |
PCT NO: |
PCT/FR2014/051452 |
371 Date: |
December 8, 2015 |
Current U.S.
Class: |
60/274 ;
60/286 |
Current CPC
Class: |
Y02A 50/2325 20180101;
F01N 11/002 20130101; F01N 2900/1616 20130101; Y02T 10/12 20130101;
F01N 2560/026 20130101; Y02T 10/40 20130101; F01N 3/2066 20130101;
F01N 2560/02 20130101; F01N 3/206 20130101; F01N 3/208 20130101;
F01N 2570/18 20130101; Y02A 50/20 20180101; Y02T 10/47 20130101;
Y02T 10/24 20130101; F01N 3/021 20130101; F01N 2610/02
20130101 |
International
Class: |
F01N 3/20 20060101
F01N003/20; F01N 3/021 20060101 F01N003/021 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2013 |
FR |
1356261 |
Claims
1-10. (canceled)
11: A system for diagnosing selective catalytic reduction system of
a motor vehicle including an internal combustion engine connected
via an exhaust manifold successively to an assembly including a
nitrous oxide catalyst and a particulate filter, and a selective
catalytic reduction system, the system comprising: a means for
evacuation of ammonia mass stored in the selective catalytic
reduction system; a urea injection means arranged upstream of the
selective catalytic reduction system; a means for control of the
evacuation and injection; a means for measuring quantity of ammonia
at an outlet from the selective catalytic reduction system; a
system for determining maximum mass of ammonia stored in the
selective catalytic reduction system; a means for comparing a value
determined for the maximum mass of ammonia stored in the selective
catalytic reduction system with a threshold, and to emit a fault
signal as a function of the comparison result.
12: The system as claimed in claim 11, wherein the means for
determining the maximum mass of ammonia stored in the selective
catalytic reduction system comprises: a means for modeling the
selective catalytic reduction system, and to estimate levels of
ammonia and nitrous oxides downstream of the selective catalytic
reduction system via a model; a means for determining a level of
ammonia at the outlet from the selective catalytic reduction system
as a function of the signal received from the measurement means; a
calculation means configured to determine a difference between the
level of ammonia measured at the outlet from the selective
catalytic reduction system and modeled values for levels of ammonia
and nitrous oxides downstream of the selective catalytic reduction
system, to determine a new value for the maximum mass of ammonia
stored in the selective catalytic reduction system if the
difference is positive, and to transmit the new value for the
maximum mass of ammonia stored in the selective catalytic reduction
system to the means for modeling the selective catalytic reduction
system to determine new values until the difference is zero; the
calculation means configured to emit the maximum mass of ammonia
stored in the selective catalytic reduction system when the
difference is zero.
13: The system as claimed in claim 11, wherein the fault signal for
the selective catalytic reduction system assumes a first value if
the value determined for the maximum mass of ammonia stored in the
selective catalytic reduction system is less than a threshold,
while it assumes a second value if that is not the case.
14: The system as claimed in claim 12, wherein the means for
modeling the selective catalytic reduction system is configured to
estimate the ammonia level downstream of the selective catalytic
reduction system via a model, as a function of the ratio between
the nitrogen dioxide and the nitrous oxides downstream of the
exhaust manifold, temperature upstream of the selective catalytic
reduction system, the mass of urea injected upstream of the
selective catalytic reduction system, the maximum mass of ammonia
stored in the selective catalytic reduction system, exhaust gas
flow, the level of ammonia upstream of the selective catalytic
reduction system, and the level of nitrous oxides upstream of the
selective catalytic reduction system.
15: The system as claimed in claim 14, wherein the means for
modeling the selective catalytic reduction system is configured to
determine the ratio between nitrogen dioxide and nitrogen monoxide
downstream of the exhaust manifold, as a function of temperature
upstream of the assembly of the particulate filter and the
catalyst, exhaust gas flow of the internal combustion engine, and
level of nitrous oxides downstream of the exhaust manifold.
16: A method for diagnosing a selective catalytic reduction system
of a motor vehicle including an internal combustion engine
connected via an exhaust manifold successively to an assembly
including a nitrous oxide catalyst and a particulate filter, and a
selective catalytic reduction system, the method comprising:
evacuation of ammonia mass stored in the selective catalytic
reduction system; injection, upstream of the selective catalytic
reduction system, of a mass of urea greater than a maximum mass
which can be stored by the selective catalytic reduction system;
determination of the maximum mass of ammonia stored in the
selective catalytic reduction system; and emission of a fault
signal as a function of a result of comparison of a value
determined for the maximum mass of ammonia stored in the selective
catalytic reduction system with a threshold.
17: The method as claimed in claim 16, wherein the maximum mass of
ammonia stored in the selective catalytic reduction system is
determined by performing: initialization of a model with a saved
value for the maximum mass which can be stored in the selective
catalytic reduction system; estimation of levels of ammonia and
nitrous oxides downstream of the selective catalytic reduction
system via a model; measurement of an ammonia level at the outlet
from the selective catalytic reduction system; determination of a
difference between the ammonia level at the outlet from the
selective catalytic reduction system and the modeled values for the
levels of ammonia and nitrous oxides downstream of the selective
catalytic reduction system; and if the difference is positive,
determination of a new value for the maximum mass of ammonia stored
in the selective catalytic reduction system, and determination of
new values for the levels of ammonia and nitrous oxides downstream
of the selective catalytic reduction system via the model until the
difference is zero; when the difference is zero, a value of the
maximum mass stored in the selective catalytic reduction system is
emitted.
18: The method as claimed in claim 16, wherein if the value
determined for the maximum mass of ammonia stored in the selective
catalytic reduction system is less than a threshold, a fault signal
assuming a first value is emitted for the selective catalytic
reduction system, while it assumes a second value if this is not
the case.
19: The method as claimed in claim 17, wherein the levels of
ammonia and nitrous oxides downstream of the selective catalytic
reduction system are estimated via a model, as a function of the
ratio between the quantity of nitrogen monoxide and nitrogen
dioxide downstream of the exhaust manifold, the temperature
upstream of the selective catalytic reduction system, the mass of
urea injected upstream of the selective catalytic reduction system,
the maximum mass of ammonia stored in the selective catalytic
reduction system, exhaust gas flow, the level of ammonia upstream
of the selective catalytic reduction system, and the level of
nitrous oxides upstream of the selective catalytic reduction
system.
20: The method as claimed in claim 19, wherein the ratio between
the nitrogen monoxide and the nitrogen dioxide downstream of the
exhaust manifold is determined as a function of the temperature
upstream of the assembly of the particulate filter and the
catalyst, exhaust gas flow from the internal combustion engine, and
the level of nitrous oxides downstream of the exhaust manifold.
Description
[0001] The area of the invention is the on-board diagnosis of
functions of a motor vehicle, more particularly the diagnosis of
the catalytic reduction of polluting emissions of a diesel-type
motor vehicle.
[0002] In order to respond to the lower limits for the permitted
emission of pollutants from motor vehicles, increasingly complex
exhaust gas after-treatment systems are provided in the exhaust
tract of lean-burn engines. These allow reduction in particular of
the emissions of particulates and nitrous oxides, as well as carbon
monoxide and unburnt hydrocarbons.
[0003] The selective catalytic reduction system (SCR) is known as
an effective means for treatment for nitrous oxides (NO.sub.X). The
system comprises continuous treatment of nitrous oxide emissions
(nitrates and nitrites). It requires the use of a catalyst and a
reducing agent injector arranged in the exhaust system.
[0004] The system therefore requires the addition of an additional
tank containing the reducing agent (AdBlue for example), the
specific injection system, a system for mixing the reducing agent
with the exhaust gases, and a catalyst system accelerating the
reduction of nitrous oxides by the reducing agent injected and/or
stored on the catalyst. It is noted that, in order to optimize the
efficiency of nitrous oxide treatment, the mixture entering the
catalyst of the selective catalytic reduction system SCR must be as
homogenous as possible, which requires the use of the
abovementioned mixing system.
[0005] In this system, the quantity of reducing agent injected and
the quantity of reducing agent stored on the catalyst must be
finely adapted: in fact, an overdose of reducing agent (stored or
injected) would only pointlessly increase the consumption of
reducing agent and perhaps generate emissions of ammonia at the
exhaust (a highly odorous and highly toxic compound). Under-dosing
however limits the efficiency obtained and hence increases the
emissions of nitrous oxides at the exhaust.
[0006] Chemically, the selective catalytic reduction system stores
the ammonia (NH.sub.3) contained in the reducing agent, such as
urea. The ammonia thus stored in the selective catalytic reduction
system then reduces the nitrous oxides (NO.sub.x). For optimum
efficiency of the selective catalytic reduction system, it is
necessary to control the stored mass of ammonia (NH.sub.3), also
called the ammonia buffer (NH.sub.3). However, as the selective
catalytic reduction system ages, its ammonia storage capacity
(NH.sub.3) degrades, leading to a loss of efficiency.
[0007] Euro 5 and Euro 6 standards impose an on-board diagnosis
(OBD) system for the entire selective catalytic reduction system.
This therefore requires recurrent verification that the selective
catalytic reduction system remains sufficiently effective at
treating nitrous oxides (NO.sub.x) to meet the on-board diagnosis
thresholds. Until now, diagnosis of the selective catalytic
reduction system SCR has been based on the degradation of
efficiency of the treatment of nitrous oxides (NO.sub.x).
[0008] However, it is not possible at present to diagnose the loss
of storage capacity for the ammonia (NH.sub.3) which is a more
direct consequence of ageing. The main difficulty of the new
diagnostic method is that it must be able to discriminate between a
reversible efficiency loss, which is compensated for example by
adapting the control of the urea injection, from a definitive loss
when the SCR no longer has any storage sites for ammonia NH.sub.3
for treating the nitrous oxides NO.sub.x. This requires diagnosis
of the ammonia storage capacity (ASC), a value characterized by a
maximum mass of ammonia (NH.sub.3) which can be stored, which is a
direct reflection of the ageing state of the SCR.
[0009] From the prior art, the following documents are known.
[0010] Document WO 2008/103113 discloses an on-board diagnosis
(OBD) of the SCR system based on the efficiency of the treatment of
nitrous oxides NO.sub.x under specific conditions. The efficiency
of treatment of the nitrous oxides NO.sub.x by the selective
catalytic reduction system SCR greatly depends on the
NO.sub.2/NO.sub.x ratio between the nitrogen dioxide and the
nitrous oxides at the inlet to the selective catalytic reduction
system SCR. This ratio cannot be measured and is affected by the
sulphurization level of the catalyst DOC, and by the soot level of
the particulate filter FAP upstream of the selective catalytic
reduction system SCR. The efficiency determined by the model of the
on-board selective catalytic reduction system SCR is compared with
that determined via a sensor for nitrous oxides NO.sub.x arranged
downstream of the selective catalytic reduction system SCR, under
conditions where the NO.sub.2/NO.sub.x ratio is a priori nominal,
i.e. after desulphurization of the catalyst DOC and/or regeneration
of the particulate filter FAP. If, under nominal conditions, the
efficiency measured is less than the efficiency calculated by the
model, a failure of the selective catalytic reduction system SCR is
detected.
[0011] Document WO 2007/037730 discloses a diagnosis system for the
selective catalytic reduction system SCR based on comparison of the
efficiency of the treatment of the nitrous oxides NO.sub.x by a
nitrous oxides NO.sub.x sensor arranged downstream of the selective
catalytic reduction system SCR, with a nominal efficiency at a
given engine operating point (load, speed). If the efficiency of
the SCR is lower than the reference, a failure is detected.
[0012] There is therefore a need for a system and a method for
diagnosis of the selective catalytic reduction system taking into
account the loss of ammonia storage capacity, a direct consequence
of ageing.
[0013] An object of the invention is a system for diagnosing the
selective catalytic reduction system of a motor vehicle equipped
with an internal combustion engine connected via an exhaust
manifold successively to an assembly comprising a nitrous oxide
catalyst and a particulate filter, and a selective catalytic
reduction system. The system comprises: [0014] a means for
evacuation of the ammonia mass stored in the selective catalytic
reduction system, [0015] a urea injection means arranged upstream
of the selective catalytic reduction system, [0016] a means for
control of the evacuation and injection, [0017] a means for
measuring the quantity of ammonia at the outlet from the selective
catalytic reduction system, [0018] a system for determining the
maximum mass of ammonia stored in the selective catalytic reduction
system, [0019] a means for comparing the value determined for the
maximum mass of ammonia stored in the selective catalytic reduction
system with a threshold, and able to emit a fault signal as a
function of the comparison result.
[0020] The means for determining the maximum mass of ammonia stored
in the selective catalytic reduction system may comprise a means
for determining the ammonia level at the outlet from the selective
catalytic reduction system as a function of the signal received
from the measuring means, and a means for modeling the selective
catalytic reduction system, and able to estimate the levels of
ammonia and nitrous oxides downstream of the selective catalytic
reduction system via a model. The means for determining the maximum
mass may also comprise a calculation means able to determine the
difference between the level of ammonia measured at the outlet from
the selective catalytic reduction system and the modeled values for
the levels of ammonia and nitrous oxides downstream of the
selective catalytic reduction system, and to determine a new value
for the maximum mass of ammonia stored in the selective catalytic
reduction system if the difference is positive, and to transmit the
new value for the maximum mass of ammonia stored in the selective
catalytic reduction system to the means for modeling the selective
catalytic reduction system in order to determine new values until
the difference is zero. The calculation means may be able to
transmit the maximum mass of ammonia stored in the selective
catalytic reduction system when the difference is zero.
[0021] The fault signal for the selective catalytic reduction
system may assume a first value if the value determined for the
maximum mass of ammonia stored in the selective catalytic reduction
system is less than a threshold, while it assumes a second value if
this is not the case.
[0022] The means for modeling the selective catalytic reduction
system may be able to estimate the ammonia level downstream of the
selective catalytic reduction via a model, as a function of the
ratio between the nitrogen dioxide and the nitrous oxides
downstream of the exhaust manifold, the temperature upstream of the
selective catalytic reduction system, the mass of urea injected
upstream of the selective catalytic reduction system, the maximum
mass of ammonia stored in the selective catalytic reduction system,
the exhaust gas flow, the level of ammonia upstream of the
selective catalytic reduction system, and the level of nitrous
oxides upstream of the selective catalytic reduction system.
[0023] The means for modeling the selective catalytic reduction
system may also be able to determine the ratio between nitrogen
dioxide and nitrogen monoxide downstream of the exhaust manifold,
as a function of the temperature upstream of the assembly of the
particulate filter and the catalyst, the exhaust gas flow from the
internal combustion engine, and the level of nitrous oxides
downstream of the exhaust manifold.
[0024] Another object of the invention is a method for diagnosing
the selective catalytic reduction system of a motor vehicle
equipped with an internal combustion engine connected via an
exhaust manifold successively to an assembly comprising a nitrous
oxide catalyst and a particulate filter, and a selective catalytic
reduction system. The method comprises the following steps: [0025]
evacuation of the ammonia mass stored in the selective catalytic
reduction system, [0026] injection, upstream of the selective
catalytic reduction system, of a mass of urea greater than the
maximum mass which can be stored by the selective catalytic
reduction system, [0027] determination of the maximum mass of
ammonia stored in the selective catalytic reduction system, [0028]
emission of a fault signal as a function of the result of
comparison of the value determined for the maximum mass of ammonia
stored in the selective catalytic reduction system with a
threshold.
[0029] The maximum mass of ammonia stored in the selective
catalytic reduction system may be determined by performing the
following steps: [0030] initialization of a model with a saved
value for the maximum mass which can be stored in the selective
catalytic reduction system, [0031] estimation of the levels of
ammonia and nitrous oxides downstream of the selective catalytic
reduction system via a model, [0032] measurement of the ammonia
level at the outlet from the selective catalytic reduction system,
[0033] determination of the difference between the ammonia level at
the outlet from the selective catalytic reduction system and the
modeled values for the levels of ammonia and nitrous oxides
downstream of the selective catalytic reduction system, [0034] if
the difference is positive, determination of a new value for the
maximum mass of ammonia stored in the selective catalytic reduction
system, and determination of new values for the levels of ammonia
and nitrous oxides downstream of the selective catalytic reduction
system via the model until the difference is zero, [0035] when the
difference is zero, the value of the maximum mass stored in the
selective catalytic reduction system is emitted.
[0036] If the value determined for the maximum mass of ammonia
stored in the selective catalytic reduction system is less than a
threshold, a fault signal assuming a first value may be emitted for
the selective catalytic reduction system, while it assumes a second
value if this is not the case.
[0037] The levels of ammonia and nitrous oxides downstream of the
selective catalytic reduction system may be estimated via a model,
as a function of the ratio between the quantity of nitrogen
monoxide and nitrogen dioxide downstream of the exhaust manifold,
the temperature upstream of the selective catalytic reduction
system, the mass of urea injected upstream of the selective
catalytic reduction system, the maximum mass of ammonia stored in
the selective catalytic reduction system, the exhaust gas flow, the
level of ammonia upstream of the selective catalytic reduction
system, and the level of nitrous oxides upstream of the selective
catalytic reduction system.
[0038] The ratio between the nitrogen monoxide and the nitrogen
dioxide downstream of the exhaust manifold may be determined as a
function of the temperature upstream of the assembly of the
particulate filter and the catalyst, the exhaust gas flow from the
internal combustion engine, and the level of nitrous oxides
downstream of the exhaust manifold.
[0039] Further aims, characteristics and advantages will appear
from reading the description below, given solely as a
non-limitative example, and with reference to the attached drawings
on which:
[0040] FIG. 1 shows the principal elements of an internal
combustion engine equipped with a selective catalytic reduction
system and an on-board diagnostic system,
[0041] FIG. 2 illustrates the main elements of a system for
determining the maximum ammonia storage capacity, and
[0042] FIG. 3 illustrates the main steps of the method for
diagnosing the selective catalytic reduction system.
[0043] FIG. 1 illustrates an internal combustion engine 1 of a
motor vehicle connected by its exhaust manifold to an exhaust pipe.
Mounted on the exhaust pipe downstream of the exhaust manifold, we
see successively a first temperature sensor 2, an assembly 3
comprising an oxidation catalyst and a particulate filter, a urea
injector 4, a second temperature sensor 5, a selective catalytic
reduction system 6 and a nitrous oxide sensor 7.
[0044] Preferably, the oxidation catalyst is housed in the assembly
3 upstream of the particulate filter, i.e. closer to the engine 1,
so as to reach its ignition temperature more quickly.
[0045] Also preferably, the second temperature sensor 5 is
installed upstream of the injector 4, such that the temperature
measurement is not disrupted by the urea injection.
[0046] The internal combustion engine 1 is connected directly or
via a control means to an on-board diagnostic system 8 via a
connection providing the exhaust gas flow and the flow of nitrous
oxides NO.sub.x. These flows result from a map or from an
estimation means, depending in particular on the operating point of
the internal combustion engine 1.
[0047] The first temperature sensor 2 is connected to the on-board
diagnostic system 8 via a connection 2a providing the temperature
upstream of the assembly 3.
[0048] The second temperature sensor 5 is connected to the on-board
diagnostic system 8 via a connection 5a providing the temperature
upstream of the selective catalytic reduction system 6.
[0049] The nitrous oxides sensor 7 is connected to the on-board
diagnostic system 8 via a connection 7a providing the quantity of
nitrous oxides and ammonia downstream of the selective catalytic
reduction system 6.
[0050] To diagnose the selective catalytic reduction system (SCR),
the maximum mass of ammonia stored is estimated under conditions of
leakage of this ammonia. The nitrous oxides (NO.sub.x) sensor,
reference 7, arranged downstream of the selective catalytic
reduction system 6, cannot distinguish nitrous oxides (NO.sub.x)
from ammonia (NH.sub.3). This property can then be exploited to
detect leaks of ammonia (NH.sub.3), deduce from this the maximum
mass of ammonia stored, and diagnose a failure as a function of
this value.
[0051] However, to estimate the maximum mass of ammonia stored, it
is necessary to estimate the mass of ammonia stored at a given
instant as a function of a model of the selective catalytic
reduction system 6. The model described below is included in the
system 9 for determining the maximum ammonia storage capacity. To
be able to estimate the maximum mass of ammonia stored, the model
is linked to the nitrous oxides NO.sub.x sensor, reference 7.
[0052] Also, to determine the maximum mass of ammonia stored, the
selective catalytic reduction system is evacuated via a control
means 8a for the evacuation and injection of urea, linked to an
actuator via connection 6a. Alternatively, the control means 8a may
interrupt the urea injection by the injector 4 in order to obtain
an effect equivalent to evacuation by consumption of all the
ammonia present in the selective catalytic reduction system. Since
evacuation allows an absolute reference value to be set, the mass
determined does not comprise any relativity and can therefore be
compared with a threshold by a comparison means 8b in order to
determine a failure of the selective catalytic reduction
system.
[0053] The description presented below firstly comprises
presentation of the modeling of the selective catalytic reduction
system 6, then the method and system of diagnosing the selective
catalytic reduction system.
[0054] FIG. 2 illustrates a system 9 for determining the maximum
ammonia storage capacity. This has a means 9a for determining the
ammonia level at the outlet from the selective catalytic reduction
system 6, as a function of the measurement by the nitrous oxides
sensor 7.
[0055] Also there is a means 9b for modeling the selective
catalytic reduction system. The modeling of the selective catalytic
reduction system begins by estimating the ammonia mass. This is
given by a reduced model based on the physico-chemical phenomena
taking place in the exhaust tract.
[0056] The ratio .alpha. between the nitrogen dioxide (NO.sub.2)
and the nitrous oxides (NO.sub.x), imposed by the combination of
the oxidation catalyst (DOC) and the particulate filter (FAP) at
the inlet to the selective catalytic reduction system 6, has a
great influence on the efficiency of the selective catalytic
reduction system 6.
[0057] However, this ratio .alpha. between the nitrogen dioxide
(NO.sub.2) and the nitrous oxides (NO.sub.x) cannot be measured. It
must therefore be estimated via a model or map as a function of the
exhaust gas flow q.sub.ech and the temperature at the inlet to the
oxidation catalyst (DOC), called T.sub.doc. The exhaust flow
q.sub.ech is measured or modeled as a function of the different
engine gas flows.
[0058] We can then determine the level of nitrogen monoxide
X.sup.in.sub.no and nitrogen dioxide X.sup.in.sub.no2 at the inlet
to the selective catalytic reduction system as a function of the
level of nitrous oxides (NO.sub.x) at the outlet from the engine
X.sup.in.sub.nox and the ratio between the nitrogen dioxide
(NO.sub.2) and the nitrous oxides (NO.sub.x), called .alpha.. The
following equation explains this determination.
X.sub.no2.sup.in=.alpha.(T.sub.doc,q.sub.ech)X.sub.nox.sup.in
X.sub.no.sup.in=(1-.alpha.(T.sub.doc,q.sub.ech))X.sub.nox.sup.in
(Eq. 1)
[0059] It is noted that the level of nitrous oxides (NO.sub.x) at
the outlet from the engine X.sup.in.sub.nox can be measured via a
sensor or estimated via a model.
[0060] The simplified reactional mechanism below reflects the
function of the selective catalytic reduction system:
NH.sub.3+*.fwdarw.NH.sub.3*+ . . .
NH.sub.3*.fwdarw.NH.sub.3+*
NO+NH.sub.3*.fwdarw.N.sub.2+ . . .
NO+NO.sub.2+2NH.sub.3*.fwdarw.2N.sub.2+ . . .
NO.sub.2+NH.sub.3*.fwdarw.N.sub.2+ . . .
NH.sub.3+O.sub.2.fwdarw.N.sub.2+ . . . (Eq. 2)
wherein: *: is a site which can receive a molecule of ammonia
NH.sub.3 NH.sub.3*: represents a stored molecule of ammonia
NH.sub.3 O.sub.2: a molecule of dioxygen N.sub.2: a molecule of
dinitrogen NO: a molecule of nitrogen monoxide NO.sub.2: a molecule
of nitrogen dioxide.
[0061] It is possible to model the reactional mechanism described
below in order to obtain dynamically the level X.sup.out.sub.nox of
nitrous oxides (NO.sub.x) and the level X.sup.out.sub.nh3 of
ammonia (NH.sub.3) downstream of the selective catalytic reduction
system, and the stored mass m.sub.nh3 (also called the buffer) of
ammonia (NH.sub.3) as a function of the level X.sup.in.sub.nox of
nitrous oxides (NO.sub.x) and the level X.sup.in.sub.nh3 of ammonia
(NH.sub.3) upstream of the selective catalytic reduction system,
the exhaust gas flow q.sub.ech, the temperature T.sub.scr of these
gases at the inlet to the selective catalytic reduction system, and
finally the maximum mass of ammonia stored in the selective
catalytic reduction system, called m.sup.max.sub.nh3.
[0062] The equation system illustrates such a model.
m nh 3 t = f ( X nox in , X nh 3 in , m nh 3 , T scr , q ech ,
.alpha. , m nh 3 max ) X nox out = h nox ( X nox in , X nh 3 in , m
nh 3 , T scr , q ech , .alpha. , m nh 3 max ) X nh 3 out = h nh 3 (
X nox in , X nh 3 in , m nh 3 , T scr , q ech , .alpha. , m nh 3
max ) ( Eq . 3 ) ##EQU00001##
[0063] The level X.sup.in.sub.nh3 of ammonia (NH.sub.3) upstream of
the selective catalytic reduction system can be estimated as a
function of the injected urea quantity.
[0064] With reference still to FIG. 2, we see that the means 9b for
modeling the selective catalytic reduction system determines the
variation in mass dm.sub.nh3/dt of ammonia (NH.sub.3) as a function
of time, the level X.sup.out.sub.nox of nitrous oxides (NO.sub.x)
and the level X.sup.out.sub.nh3 of ammonia (NH.sub.3) downstream of
the selective catalytic reduction system, as a function of the
level X.sup.in.sub.nox of nitrous oxides (NO.sub.x) upstream of the
selective catalytic reduction system and the flow q.sub.ech of
exhaust gas from the internal combustion engine 1, the temperature
T.sub.scr of these gases at the inlet to the selective catalytic
reduction system from the second temperature sensor 5, the ratio
.alpha. between the nitrogen dioxide (NO.sub.2) and the nitrous
oxides (NO.sub.x), the maximum mass m.sup.max.sub.nh3 of ammonia
stored in the selective catalytic reduction system, the level
X.sup.in.sub.nh3 of ammonia (NH.sub.3) upstream of the selective
catalytic reduction system, and the current mass m.sub.nh3 of
ammonia stored in the selective catalytic reduction system. It is
noted that the maximum mass m.sup.max.sub.nh3 of ammonia stored in
the selective catalytic reduction system is a datum for design of
the selective catalytic reduction system 6.
[0065] By knowing the variation in mass of ammonia over time
dm.sub.nh3/dt, the level X.sup.out.sub.nox of nitrous oxides
(NO.sub.x) and the level X.sup.out.sub.nh3 of ammonia (NH.sub.3)
downstream of the selective catalytic reduction system, it is
possible to determine the maximum mass of ammonia stored via an
observer. Prior to definition of the observer, the measurement from
the nitrous oxides sensor (NO.sub.x) downstream of the selective
catalytic reduction system is broken down to take account of its
capacity to measure both nitrous oxides and ammonia. The following
equation takes into account this breakdown.
X.sub.nox.sup.out,capt=X.sub.nox.sup.out+X.sub.nh3.sup.out (Eq.
4)
wherein: X.sup.out,capt.sub.nox: value of the measurement of the
nitrous oxides sensor X.sup.out.sub.nox: level of nitrous oxides
X.sup.out.sub.nh3: level of ammonia (NH.sub.3) downstream of the
selective catalytic reduction system.
[0066] This distribution between two contributions, as has been
described above, reflects the fact that it is not possible to
distinguish between nitrous oxides (NO.sub.x) and ammonia
(NH.sub.3) at the selective catalytic reduction system.
[0067] By combining equations 3 and 4, we propose the following
observer:
m nh 3 t = f ( X nox in , X nh 3 in , m nh 3 , T scr , q ech ,
.alpha. , m nh 3 max ) X nox out = h nox ( X nox in , X nh 3 in , m
nh 3 , T scr , q ech , .alpha. , m nh 3 max ) X nh 3 out = h nh 3 (
X nox in , X nh 3 in , m nh 3 , T scr , q ech , .alpha. , m nh 3
max ) m nh 3 max t = K .DELTA. ( Eq . 5 ) ##EQU00002##
wherein:
.DELTA.=X.sub.nox.sup.out,capt-X.sub.nox.sup.out-X.sub.nh3.sup.out
(Eq. 6)
K: strictly positive gain
[0068] On FIG. 2, we can see that the system 9 for determining the
maximum ammonia storage capacity also comprises a subtractor 9c
connected at the inlet to the means 9a for determining the ammonia
level at the outlet from the selective catalytic reduction system
6, and to the means 9b for modeling the selective catalytic
reduction system, and connected at the outlet to a calculation
means 9d able to determine the maximum mass m.sup.max.sub.nh3 of
ammonia stored in the selective catalytic reduction system as a
function of the signal received from the subtractor 9c and from a
memory 9e.
[0069] The subtractor 9c allows determination of the parameter
.DELTA. by application of equation 6, by subtracting the values
received from the means 9b for modeling the selective catalytic
reduction system from the value received from the determination
means 9a.
[0070] The calculation means 9d determines the maximum mass
m.sup.max.sub.nh3 of ammonia stored in the selective catalytic
reduction system as a function of the signal received from the
memory 9e when the system 9 for determining the maximum ammonia
storage capacity is initialized. In other situations, the
calculation means 9d determines the maximum mass m.sup.max.sub.nh3
of ammonia stored in the selective catalytic reduction system by
integrating, relative to time, the product of parameter .DELTA. by
the saved constant K. In doing this, the calculation means 9d
applies the third equation of the equation system (Eq 5).
[0071] The calculation means 9d also estimates whether the
parameter .DELTA. is zero. If so, the calculation means 9d emits
the determined value for the maximum mass m.sup.max.sub.nh3 of
ammonia stored in the selective catalytic reduction system.
[0072] The comparison means 8b receives from the calculation means
9d a signal carrying the maximum mass m.sup.max.sub.nh3 of ammonia
stored in the selective catalytic reduction system 6. The
comparison means 8b performs the comparison of the maximum mass
with a memorized threshold, allowing a distinction between a
selective catalytic reduction system in good condition and a faulty
selective catalytic reduction system. If the maximum mass is
greater than the threshold, a signal for absence of failure is
transmitted, otherwise a failure signal is transmitted.
Alternatively, only the failure signal is emitted, and only when
the emission conditions are combined.
[0073] Use of the observer described above will be better
understood from reading the numerical example below.
[0074] Let us assume that the maximum mass of ammonia which can be
stored in a selective catalytic reduction system in good condition
is equal to 4 g.
[0075] Also, as we are in leakage conditions for ammonia
(NH.sub.3), we can ignore the nitrous oxides (NO.sub.x) at the
outlet from the selective catalytic reduction system. In fact the
nitrous oxides will be reduced by the excess of ammonia
(NH.sub.3).
[0076] The model is initialized with a maximum m.sup.max.sub.nh3 of
ammonia stored in the catalyst equal to the value of the maximum
mass of ammonia which can be stored in a selective catalytic
reduction system in good condition, or 4 g in the present example,
then the values for the level of nitrous oxides and ammonia
(NH.sub.3) downstream of the selective catalytic reduction system
are determined.
[0077] Then we determine the value of parameter .DELTA. as a
function of the modeled values for the levels of nitrous oxides and
ammonia (NH.sub.3) downstream of the selective catalytic reduction
system, and of the measurement from the nitrous oxides sensor.
[0078] If parameter .DELTA. is positive, the maximum mass
m.sup.max.sub.nh3 of ammonia stored in the catalyst is less than
the maximum mass with which the selective catalytic reduction
system was modeled.
[0079] We then determine a new maximum mass as a function of the
parameter .DELTA. determined. The new maximum mass is re-injected
at the inlet to the model, such that we determine new values for
the levels of nitrous oxides and ammonia (NH.sub.3) downstream of
the selective catalytic reduction system.
[0080] These new values are then compared with the measurement of
the nitrous oxides level at the outlet from the selective catalytic
reduction system, in order to determine a new value for parameter
.DELTA.. If parameter .DELTA. is positive, the method continues by
determining new values for the maximum mass m.sup.max.sub.nh3 of
ammonia stored in the catalyst, and the levels of nitrous oxides
and ammonia (NH.sub.3) downstream of the selective catalytic
reduction system, until we obtain a value of zero for parameter
.DELTA..
[0081] As soon as parameter .DELTA. is zero, the current value of
the maximum mass m.sup.max.sub.nh3 of ammonia stored in the
catalyst is saved and compared with a threshold. If the value is
greater than the threshold, the selective catalytic reduction
system is in good condition, otherwise a fault is detected and a
warning signal emitted.
[0082] The method for diagnosing the selective catalytic reduction
system illustrated by FIG. 3 uses the models and equations
explained above.
[0083] The method comprises a first step 10 during which the
ammonia mass is evacuated. In fact, in order to perform the
diagnosis under the best conditions, an evacuation is performed so
that the estimate of the maximum mass m.sup.max.sub.nh3 of ammonia
stored in the selective catalytic reduction system can begin from
an absolute reference substantially equal to zero. This evacuation
takes place by cutting the urea injection for a few minutes.
[0084] During the second step 11, a specific mass of urea is
injected which is sufficiently high for the selective catalytic
reduction system to either reach or exceed the limit for leakage of
ammonia (NH.sub.3). In other words, more ammonia (NH.sub.3) is
injected than the system can theoretically contain. The mass to be
injected may be determined as a function of the maximum mass of
ammonia stored in a catalytic reduction system having no fault.
[0085] During a third step 12, we estimate the ammonia level
x.sup.out.sub.nh3 and the nitrous oxides level x.sup.out.sub.nh3
downstream of the selective catalytic reduction system via the
model by applying equation 5. We also measure the level
x.sup.out,capt.sub.nox of ammonia downstream of the selective
catalytic reduction system via the nitrous oxides sensor 7. We then
determine parameter .DELTA. by applying equation 6. If parameter
.DELTA. is positive, a new value is determined for the maximum mass
m.sup.max.sub.nh3 of ammonia stored in the selective catalytic
reduction system as a function of the value of the parameter
.DELTA.. New values are then determined for the level of ammonia
x.sup.out.sub.nh3 and nitrous oxides x.sup.out.sub.nh3 downstream
of the selective catalytic reduction system via the model before
determining a new value for parameter .DELTA..
[0086] The third step is repeated until the value of parameter
.DELTA. is zero. The last value of the maximum mass
m.sup.max.sub.nh3 of ammonia stored in the selective catalytic
reduction system is then saved.
[0087] During a fourth step 13, we compare the maximum mass
m.sup.max.sub.nh3 of ammonia stored in the selective catalytic
reduction with a threshold. If the maximum mass is greater than the
threshold, the selective catalytic reduction system has no fault.
If this is not the case, the selective catalytic reduction system
has a fault.
[0088] A signal corresponding to the state of the selective
catalytic reduction system is then transmitted at the outlet.
* * * * *