U.S. patent application number 14/357826 was filed with the patent office on 2014-10-02 for method and system pertaining to monitoring particle emissions in combustion engine exhausts.
This patent application is currently assigned to SCANIA CV AB. The applicant listed for this patent is SCANIA CV AB. Invention is credited to Ola Stenlaa.
Application Number | 20140290217 14/357826 |
Document ID | / |
Family ID | 48429956 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140290217 |
Kind Code |
A1 |
Stenlaa; Ola |
October 2, 2014 |
METHOD AND SYSTEM PERTAINING TO MONITORING PARTICLE EMISSIONS IN
COMBUSTION ENGINE EXHAUSTS
Abstract
A method for determining particle emissions from a combustion
engine: a post-treatment system including at least one particle
filter post-treats an exhaust flow from combustion in the engine. A
PM (particulate matter) sensor situated upstream of the particle
filter determines, at a location upstream of the particle filter, a
first particle content of the exhaust flow arising from the engine
and uses the determined first particle content as a basis for
determining whether the particle content of the exhaust flow
downstream of the particle filter fulfils a first condition. Also,
a system and a vehicle for performing the method are disclosed.
Inventors: |
Stenlaa; Ola; (Sodertalje,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCANIA CV AB |
Sodertalje |
|
SE |
|
|
Assignee: |
SCANIA CV AB
Sodertalje
SE
|
Family ID: |
48429956 |
Appl. No.: |
14/357826 |
Filed: |
November 13, 2012 |
PCT Filed: |
November 13, 2012 |
PCT NO: |
PCT/SE2012/051240 |
371 Date: |
May 13, 2014 |
Current U.S.
Class: |
60/274 ;
60/286 |
Current CPC
Class: |
Y02T 10/47 20130101;
F01N 3/10 20130101; F01N 2550/04 20130101; F01N 2560/05 20130101;
F01N 2550/02 20130101; Y02T 10/40 20130101; F01N 11/00
20130101 |
Class at
Publication: |
60/274 ;
60/286 |
International
Class: |
F01N 3/10 20060101
F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2011 |
SE |
1151073-2 |
Claims
1. A method for determination of particle emissions in exhaust flow
from a combustion engine, comprising: post-treating an exhaust flow
arising from combustion in said combustion engine by passing said
exhaust flow through at least one particle filter; using a PM
sensor situated upstream of said filter in said exhaust flow to
determine, at a location upstream of said particle filter in said
exhaust flow, a first particle content of said exhaust flow arising
from said engine; and using said determined first particle content
as a basis for determining whether a particle content of said
exhaust flow downstream of said particle filter fulfils a first
condition.
2. A method according to claim 1, wherein said particle content
released downstream of said particle filter fulfils said first
condition when said first particle content is less than a second
particle content.
3. A method according to claim 2, wherein said second particle
content is a maximum permissible particle emission for said
engine.
4. A method according to claim 2, wherein said second particle
content is a maximum permissible particle emission for said engine
multiplied by a first factor.
5. A method according to claim 2, wherein each of said first and
second particle contents is determined as any of the following: a
number of particles or a particle mass per unit volume; a number of
particles or a particle mass per unit time; and a number of
particles or a particle mass per work performed by said engine.
6. A method according to claim 1, wherein said first condition
depends on the engine's work.
7. A method according to claim 2, wherein said first condition
depends on how full the particle filter is.
8. A method according to claim 7, wherein said particle content of
said exhaust flow downstream of said particle filter fulfils said
first condition when said first particle content is less than a
second particle content which changes with increasing fullness of
said filter.
9. A method according to claim 1, wherein said first condition
depends on a differential pressure across the particle filter.
10. A method according to claim 1, further comprising determining a
first particle content of said exhaust flow arising from said
engine at a location upstream in said exhaust flow of said particle
filter over a plurality of times; and wherein said particle content
of said exhaust flow downstream in said exhaust flow of said
particle filter fulfils said first condition when a combined value
of said particle content determinations pertaining to said
plurality of times fulfils said first condition.
11. A method according to claim 1, further comprising determining a
function of said PM sensor on the basis of a signal delivered by
said PM sensor wherein said signal represents a particle content of
said exhaust flow.
12. A method according to claim 11, wherein said function of said
PM sensor is determined on the basis of variations in said sensor
signal.
13. A method according to claim 11, further comprising: controlling
said particle content delivered by said engine by controlling said
engine; and determining whether said signal delivered by said PM
sensor corresponds to an expected sensor signal.
14. A method according to claim 11, further comprising generating a
further signal which indicates malfunction of said PM sensor when
said signal delivered by said PM sensor does not correspond to
expected sensor signals.
15. (canceled)
16. A computer program product comprising a non-transitory
computer-readable medium which stores a computer program, wherein
said program, when executed in a computer, causes said computer to
apply the method according to claim 2.
17. A system for determining particle emissions pertaining to a
combustion engine, comprising: a post-treatment system comprising
at least one particle filter configured and located in an exhaust
flow from said combustion engine to post-treat said exhaust flow
arising from combustion in said combustion engine; a PM sensor
situated upstream of said filter in said exchange flow and
configured and operable to determine, at a location upstream of
said particle filter, a first particle content of said exhaust flow
arising from said engine; and a determining device configured and
operable for using said determined first particle content as a
basis for determining whether a particle content of said exhaust
flow downstream of said particle filter fulfils a first
condition.
18. A vehicle with a combustion engine and an exhaust flow and
provided with a system according to claim 17.
19. A method according to claim 11, wherein said controlling said
engine comprises controlling at least one from among fuel supply,
EGR supply and air supply for said combustion.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to exhaust cleaning and in
particular to a method for determining a particle content in an
exhaust flow according to the preamble of claim 1. The invention
relates also to a system and a vehicle, and to a computer programme
and a computer programme product, which implement the method
according to the invention.
BACKGROUND TO THE INVENTION
[0002] Growing official concern about pollution and air quality,
especially in major urban areas, has led to the adoption of
emission standards and requirements in many jurisdictions.
[0003] Such emission standards often set requirements which define
acceptable limits for exhaust emissions from vehicles equipped with
combustion engines. These standards often regulate, for example,
levels for emissions of nitrogen oxides (NO.sub.x), hydrocarbons
(HC) and carbon monoxide (CO). These emission requirements also
usually cover, for at least certain kinds of vehicle, the presence
of particles in exhaust emissions.
[0004] These regulations are often organised in such a way that
increasingly stringent emission level requirements are introduced
at intervals of one or a few years. The endeavour to meet these
requirements has therefore led to the development of systems for
post-treatment (cleaning) of the exhaust gases which are formed
during combustion in combustion engines.
[0005] These post-treatment systems often comprise some form of
catalytic cleaning process whereby one or more catalysts are used
to clean the exhaust gases. Such post-treatment systems often
comprise other components as alternatives to, or in combination
with, the one or more catalysts, e.g. post-treatment systems on
vehicles with diesel engines often comprise particle filters.
[0006] Soot particles are formed during combustion of fuel in the
combustion chambers (e.g. cylinders) of a combustion engine. As
above, these soot particles are likewise subject to emission
requirements and standards, which may entail using particle filters
to intercept the soot particles. In such cases the exhaust flow is
for example led through a filter structure whereby soot particles
are captured from the passing exhaust flow in order to be stored in
the particle filter.
[0007] There are various methods for reducing emissions from a
combustion engine. As well as requirements concerning emission
levels, it is also becoming increasingly common for there to be
statutory requirements for vehicles to have internal diagnostic
systems, so-called OBD (on-board diagnostics) systems to ensure
that not only at for example the time of visits to workshops but
also in day-to-day operation vehicles actually meet established
requirements concerning emissions. In the case of particle
emissions this may for example be achieved by means of a particle
sensor, referred to in the description and claims set out below as
a PM (particulate matter, particulate mass) sensor, situated in the
tailpipe of the exhaust system to measure the particle content of
the exhaust flow before it is released into the vehicle's
surroundings.
[0008] Post-treatment systems with particle filters can be very
effective and the resulting particle content after the exhaust flow
has passed through the vehicle's post-treatment system is often low
when the system is fully functional. This also means that the
signals which the sensor delivers will indicate low or no particle
emission.
SUMMARY OF THE INVENTION
[0009] An object of the invention is to propose a method for
diagnosis of a combustion engine pertaining to a vehicle. This
object is achieved with a method according to claim 1.
[0010] The present invention proposes a method for diagnosis of a
combustion engine whereby a post-treatment system comprising at
least one particle filter is provided to post-treat an exhaust flow
arising from combustion in said engine. The method comprises [0011]
using a PM sensor situated upstream of said particle filter to
determine, at a location upstream of said particle filter, a first
particle content in said exhaust flow arising from said engine, and
[0012] using said first particle content determined to determine
whether the particle content of said exhaust flow downstream of
said particle filter fulfils a first condition.
[0013] By determining a particle content at a location upstream of
said particle filter and then using this particle content as a
basis for determining whether the particle content downstream of
the filter fulfils a first condition, e.g. being less than a second
particle content, it is for example possible to determine whether
the particle content in the exhaust flow released after said the
filter into the engine's surroundings, e.g. the surroundings of a
vehicle, is within prescribed requirements. These requirements may
for example take the form of a maximum permissible particle content
defined for example as particle mass per unit engine power output,
e.g. a certain particle mass per kW of developed or deliverable
power output, and said condition may also take the form of the
particle content released having to meet the requirements. Said
second particle content may for example be set at a level which
just meets the requirements or meets them with a desired margin. As
explained below, the condition, e.g. the second particle content,
may also be set at a higher level than the requirements.
[0014] As below, the invention affords the further advantage that
problems in ensuring the reliability of the sensor in sensor
solutions of the kind described above can be reduced and that an
improved method for determining particle emissions from combustion
in a combustion engine can be achieved.
[0015] In one embodiment the engine may itself meet prevailing
requirements in that the particle content in said exhaust flow
downstream of said particle filter may be arranged to fulfil said
first condition if said first particle content determined fulfils
said first condition. In another embodiment the particle filter of
said exhaust flow downstream of said particle filter may be such as
to fulfil said first condition if said first particle content
determined conforms to a specific ratio to said maximum permissible
particle emission, e.g. by being not more than said maximum
permissible particle emission multiplied by some appropriate
factor.
[0016] In one embodiment, said first condition depends on a
differential pressure across the particle filter, e.g. in that a
condition in the form of a particle content may depend on the
differential pressure so that the maximum level which said first
particle content may reach can be arranged to decrease in step with
increasing differential pressure.
[0017] The present invention affords also the advantage that the PM
sensor, owing to the higher particle content of the exhaust flow
upstream of the particle filter, will more frequently or more or
less regularly deliver a signal which indicates that there is soot
in the exhaust flow. The signal will thus also be significantly
more reliable and therefore also easier to diagnose. Unlike sensor
location downstream of the particle filter as above, it is for
example possible for a suddenly omitted signal to be analysed
immediately and serve for example as an indication that the sensor
is malfunctioning. Locating the PM sensor upstream affords the
further advantage that it can with greater certainty be so located
as to have passing it a well-mixed and homogeneous exhaust flow
without substantial distribution problems, potentially also
providing assurance of measured values which are more correct.
[0018] Thus the present invention makes it possible to monitor that
requirements with regard to particle emission after the particle
filter are met without having to conduct actual measurement of the
particle content after the particle filter, even in the case of
engines whose particle content in the exhaust flow upstream of the
filter does not meet prevailing requirements.
[0019] Further characteristics of the present invention and
advantages thereof are indicated by the detailed description of
embodiment examples set out below and the attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1a depicts schematically a vehicle on which the present
invention may be employed.
[0021] FIG. 1b depicts a control unit in the control system for the
vehicle depicted in FIG. 1.
[0022] FIG. 2 depicts the post-treatment system in more detail for
the vehicle depicted in FIG. 1.
[0023] FIG. 3 depicts an example of a method according to the
present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0024] The expression "particle content" in the description and
claims set out below comprises both content in the form of unit
weight and content/concentration, i.e. the unit number of
particles. Moreover, the unit may be any suitable unit and the
content may be expressed as, for example, weight or number of
particles per unit volume, per unit time, per work performed or per
distance travelled by the vehicle.
[0025] FIG. 1a depicts a power train of a vehicle 100 according to
an embodiment of the present invention. The vehicle schematically
depicted in FIG. 1 has only one axle provided with tractive wheels
113, 114 but the invention is also applicable on vehicles in which
more than one axle is provided with tractive wheels. The power
train comprises a combustion engine 101 which is connected in a
conventional way, via an output shaft of the engine, usually via a
flywheel 102, to a gearbox 103 via a clutch 106. The engine is
controlled by the vehicle's control system via a control unit 115.
The clutch 106, which may for example take the form of an
automatically controlled clutch, and the gearbox 103 are also
controlled by the vehicle's control system by means of one or more
suitable control units (not depicted). The vehicle's power train
may of course also be of some other kind, e.g. a type with
conventional automatic gearbox etc.
[0026] An output shaft 107 from the gearbox 103 then drives the
tractive wheels 113, 114 via a final gear 108, e.g. a conventional
differential, and driveshafts 104, 105 which are connected to said
final gear 108.
[0027] The vehicle 100 further comprises a post-treatment system
(exhaust cleaning system) 200 for treatment (cleaning) of exhaust
emissions arising from combustion in the engine's combustion
chambers (e.g. cylinders).
[0028] The post-treatment system is depicted in more detail in FIG.
2, showing the vehicle's engine 101 from which the exhaust gases
(the exhaust flow) generated by the combustion are led through a
turbo unit 220. In turbo engines the exhaust flow arising from the
combustion often drives a turbo unit which itself compresses the
incoming air for the combustion in the cylinders. Alternatively,
the turbo unit may for example be of compound type. The function of
various kinds of turbo unit is well-known and is therefore not
described in more detail here. The exhaust flow is then led via a
pipe 204 (indicated by arrows) to a particle filter (diesel
particulate filter, DPF) 202 via an oxidation catalyst (diesel
oxidation catalyst, DOC) 205.
[0029] The oxidation catalyst DOC 205 has various functions and is
normally used primarily to oxidise remaining hydrocarbons and
carbon monoxide in the exhaust flow to carbon dioxide and water.
The oxidation of hydrocarbons (i.e. oxidation of fuel) results also
in the formation of heat which may be utilised to raise the
temperature of the particle filter at the time of its emptying, its
so-called regeneration. The oxidation catalyst may also be used to
oxidise nitrogen monoxide (NO) to nitrogen dioxide (NO.sub.2) which
may be utilised in so-called passive regeneration.
[0030] Post-treatment systems of the type referred to may also
comprise other components, e.g. a (single, in the present example)
SCR (selective catalytic reduction) catalyst 201 situated
downstream of the particle filter 202. SCR catalysts use ammonia
(NH.sub.3), or a compound from which ammonia can be
generated/formed, as additive to reduce the amount of nitrogen
oxides NO.sub.x.
[0031] Moreover, the post-treatment system 200 may also comprise
more components than as exemplified above or, conversely, fewer
components. It may for example comprise an ASC (ammonia slip
catalyst) (not depicted) in addition to, or instead of, said DOC
205 and/or SCR 201. In the embodiment depicted, DOC 205, DPF 202
and also the SCR catalyst 201 are integrated in a combined exhaust
cleaning unit 203, but it should be noted that DOC 205 and DPF 202
need not be integrated in a single exhaust cleaning unit, as they
may be arranged in some other way deemed appropriate.
[0032] According to the present invention, the post-treatment
system 200 comprises a PM sensor 222 situated upstream of DPF 202.
This PM sensor, like other sensors associated with the
post-treatment system, e.g. a pressure sensor 209, may deliver
signals to a control unit 208, or some other suitable control unit,
which controls or monitors the function of the post-treatment
system. For example, the determination of appropriate times for
regeneration of the particle filter may be done by the control unit
208 at least partly on the basis of signals from the pressure
sensor 209 which measures the differential pressure across the
filter. The fuller the filter becomes, the greater will be the
pressure difference across it. The pressure sensor may for example
also be used for diagnosis of DPF 202 but also when determining
whether a particle content after the particle filter fulfils a
condition according to the present invention, as described
below.
[0033] Control systems in modern vehicles generally comprise a
communication bus system consisting of one or more communication
buses for connecting together a number of electronic control units
(ECUs), e.g. the control units or controllers 115, 208, and various
components located on the vehicle. Such a control system may
comprise a large number of control units and the responsibility for
a specific function may be shared by two or more of them.
[0034] For the sake of simplicity, only the control units 115, 208
appear in FIG. 1a.
[0035] In the embodiment depicted, the present invention is
implemented in the control unit 208, which as above is responsible
in the embodiment depicted for other functions in the
post-treatment system, e.g. regeneration (emptying) of the particle
filter 202, although the invention may equally well be implemented
in a control unit dedicated to it, or wholly or partly in one or
more other control units with which the vehicle is already
provided, e.g. the engine control unit 115.
[0036] The function according to the present invention of the
control unit 208 (or the control unit or units in which the present
invention is implemented) will depend not only on signals from the
PM sensor 222 but probably also on, for example, information
received from, for example, the control unit or units which control
engine functions, i.e. in the present example the control unit
115.
[0037] Control units of the type depicted are normally adapted to
receiving sensor signals from various parts of the vehicle. The
control unit 208 may for example receive sensor signals as above
and also from the engine control unit 115 and other control units.
Such control units are also usually adapted to delivering control
signals to various parts and components of the vehicle, e.g. the
control unit 208 may for example deliver signals to the engine
control unit 115.
[0038] The control is often governed by programmed instructions,
typically in the form of a computer programme which, when executed
in a computer or control unit, causes the computer/control unit to
effect desired forms of control action, e.g. method steps according
to the present invention.
[0039] The computer programme usually forms part of a computer
programme product which comprises a digital storage medium 121 (see
FIG. 1b) with the computer programme 109 stored on it. Said digital
storage medium 121 may for example take the form of any from among
ROM (read-only memory), PROM (programmable read-only memory), EPROM
(erasable PROM), flash memory, EEPROM (electrically erasable PROM),
a hard disc unit etc., and be situated in or in communication with
the control unit, in which case the computer programme is executed
by the control unit. The vehicle's behaviour in a specific
situation may thus be modified by altering the computer programme's
instructions.
[0040] An example of a control unit (the control unit 208) depicted
schematically in FIG. 1b may itself comprise a calculation unit 120
which may for example take the form of any suitable kind of
processor or microcomputer, e.g. a circuit for digital signal
processing (Digital Signal Processor, DSP), or a circuit with a
predetermined specific function (Application Specific Integrated
Circuit, ASIC). The calculation unit 120 is connected to a memory
unit 121 which provides it with, for example, the stored programme
code 109 and/or the stored data which the calculation unit needs
for it to be able to perform calculations. The calculation unit is
also arranged to store partial or final results of calculations in
the memory unit 121.
[0041] The control unit is further provided with respective devices
122, 123, 124, 125 for receiving and sending input and output
signals. These signals may comprise waveforms, pulses or other
attributes which the input signal receiving devices 122, 125 can
detect as information for processing by the calculation unit 120.
The output signal sending devices 123, 124 are arranged to convert
calculation results from the calculation unit 120 to output signals
for conveying to other parts of the vehicle's control system and/or
the component/components for which the signals are intended. Each
of the connections to the respective devices for receiving and
sending input and output signals may take the form of one or more
from among a cable, a data bus, e.g. a CAN (Controller Area
Network) bus, an MOST (Media Oriented Systems Transport) bus or
some other bus configuration, or a wireless connection.
[0042] As mentioned above, the combustion in the combustion
chambers of the engine 101 results in the formation of particles
which should not and in many cases are not permitted to be released
into the vehicle's surroundings. The particles formed during
combustion in, for example, a diesel engine consist largely of
hydrocarbons, carbon (soot) and inorganic substances such as
sulphur and ash. Soot particles may for example be formed when the
fuel/air ratio during combustion in the engine's combustion
chambers becomes too great, i.e. when there is a so-called "rich"
fuel mixture with too high a proportion of fuel relative to that of
air.
[0043] Although the fuel/air ratio for a specific combustion, i.e.
the amounts of air and fuel injected during a specific piston
stroke, may be such that the requirement for non-sooting combustion
is met, the fuel/air ratio may still occur locally in parts of the
combustion chamber where the proportion of fuel is higher and the
mixture is thus richer, potentially giving rise to soot during
combustion.
[0044] Soot may for example also be formed by oil splash from the
engine's lubrication reaching the combustion chamber, e.g. via the
movements of the piston. Metal fragments from wear and/or
manufacture of the engine may for example give rise to particle
formation. The vehicle's fuel may be more or less "clean" and thus
itself give rise to sundry particle formation during
combustion.
[0045] These soot particles are thus gathered up by the particle
filter 202 by the exhaust flow being led through the filter
structure, in which they are captured from the passing exhaust flow
in order to be stored in the filter. A particle filter can usually
separate a very large proportion of the particles present in the
exhaust flow.
[0046] Statutory requirements have already been adopted in certain
jurisdictions, and are expected in others, for vehicles to have
their own systems, so-called OBD (on-board diagnostics) systems,
making it possible to ensure that not only on the occasion for
example of workshop visit checks but also in commercial operation
the vehicle's particle emissions stay below prescribed levels.
[0047] This may be achieved in a relatively straightforward way by
having a particle sensor (PM sensor) associated with the tailpipe
of the post-treatment system, i.e. substantially at the location
where the exhaust flow is released into the vehicle's surroundings.
This location is indicated by ref. 221 in FIG. 2. By monitoring
signals from the sensor 221, e.g. by means of a control unit
corresponding to the control unit 208, it is possible to ensure
that the particle content of the exhaust flow leaving the vehicle
will also be below prescribed levels.
[0048] This sensor location does however have disadvantages.
Particle capture from the exhaust flow by means of particle filters
is usually so effective that the amount of particles actually
leaving the vehicle is in general very small when the filter is
fully functional.
[0049] This means that so long as the particle filter is working as
intended it will be difficult to know whether the sensor is
actually working, since the signals delivered by it will indicate
very low or no particle contents. Experiments have shown that the
particle contents of an exhaust flow after passing through a
particle filter may be so low that in the case of many sensors it
may take a long time (e.g. of the order of 5-15 minutes) before a
signal indicating any particle presence at all is delivered.
[0050] This applies not only during normal running of the vehicle
but also in cases of provocation, i.e. in situations where the
engine is deliberately tested by being controlled in such a way
that high particle contents should be delivered.
[0051] Thus it may be difficult to know whether the PM sensor 221
is actually healthy and working as expected, since signals from it
which indicate low or no particle contents will at best be due to
the post-treatment system being fully functional but might also be
due to the sensor malfunctioning.
[0052] The location 221 indicated in FIG. 2 has the further
disadvantage that at times when the filter malfunctions, e.g.
because a mechanical fault suddenly occurs, causing a marked
increase in particle emission, it is very difficult to predict how
the exhaust flow path will change in such situations since,
depending on the flow path, there will be no certainty that the
sensor is so located that the raised particle contents will
actually be detected.
[0053] This disadvantage may be mitigated by having after the
particle filter, but still upstream of the PM sensor, a remixer to
homogenise the exhaust flow and thereby increase the probability
that raised particle contents will also be detected by the sensor.
However, such remixers do by their very nature give rise to
pressure drops resulting in undesirable increases in fuel
consumption in addition to the actual cost of the remixer.
Alternatively, the flow path between particle filter and PM sensor
may be lengthened by a solution involving longer pipes, but
likewise at increased cost.
[0054] However, these solutions to the above problems likewise
suffer from uncertainty of sensor function. Although this
uncertainty may be mitigated by using more than one sensor, this
still involves not only increased cost but also problems in that
the sensors will deliver signals so rarely that correct function is
difficult to verify, and it will also be difficult to ensure that
the vehicle's emissions do not exceed prescribed levels.
[0055] As above, the PM sensor is located according to the present
invention upstream of the particle filter instead of downstream, as
illustrated by the sensor 222 in FIG. 2. Such problems can be
reduced or completely eliminated by the method according to the
invention of using the sensor situated upstream of the filter to
determine whether the vehicle's emissions are below prescribed
levels.
[0056] A method 300 according to the present invention for
determining a particle emission is illustrated in FIG. 3. In the
embodiment depicted the method is implemented in the control unit
208 and begins at step 301 by determining whether the vehicle's
engine 101 has been started. If it has, the method moves on the
step 302, otherwise it stays at step 301 or ends.
[0057] Step 302 determines whether signals are being received from
the PM sensor 202. The method stays at step 202 until sensor
signals are received but not beyond the time when a timer t.sub.1
reaches a time T.sub.1. If no sensor signals are received before
the counter reaches T.sub.1, which may for example be part of a
second or a suitable number of seconds, the method can move on to a
step 303 for diagnosis of the sensor, see below. If, on the
contrary, sensor signals are received within time T.sub.1, the
method moves on to step 304 for determination of a particle content
of the exhaust flow.
[0058] Step 304 determines a first particle content on the basis of
the signals delivered by the PM sensor 222. As the determination is
by means of a PM sensor situated upstream of the particle filter
202, a continuous flow of particles will be continually passing the
sensor when the engine is in operation.
[0059] This also means that the particle content at the PM sensor
222 will be substantially greater than downstream of the filter,
and the sensor's measurements according to the present invention
will result in the delivery of a continuous signal. This signal
will be delivered more quickly, since the higher particle content
means that the smallest amount of particles required for the sensor
to indicate their presence will be reached more quickly. The signal
will also indicate a higher amount of particles, making both size
determination and diagnosis easier.
[0060] As well as the PM sensor 222 being situated in an
environment where the exhaust flow has a higher particle content,
its location upstream of the particle filter affords the further
advantage of allowing it to be in a well-mixed and homogenous
exhaust flow and thus be able to take measurements in a
representative part of the exhaust flow. In the embodiment
depicted, the PM sensor is situated upstream of both DPF 202 and
DOC 205, but as exemplified below it might be at a number of
different locations (but always upstream of the particle filter
202).
[0061] When a first particle content has been determined at step
304 on the basis of the signals delivered by the PM sensor, the
method moves on to step 305, in which the first particle content
determined is compared with a second particle content.
[0062] If it is determined at step 305 that the particle content
determined at step 304 is greater than said second particle
content, the method moves on to step 307 for further investigation.
It is for example possible for steps 301-305 to be repeated one or
more times until they have been run through y times, and the
respective number of times x is incremented each time the method
moves to step 307. The method may for example go back to step 301
from step 307 when a timer t.sub.2 has calculated a time T.sub.2,
e.g. a suitable number of seconds. By this procedure it is possible
to determine whether the raised particle content is only temporary
before dropping back below a prescribed level. If raised levels
persist after said plurality of determinations, i.e. x.gtoreq.y,
the method may move on to a step 308 in order if possible to
establish by diagnosis the reason for the raised contents. This
diagnosis may for example be conducted by means of the diagnostic
method described in the parallel Swedish patent application
entitled "METHOD AND SYSTEM FOR DIAGNOSIS OF A COMBUSTION ENGINE"
("FORFARANDE OCH SYSTEM FOR DIAGNOSTISERING AV EN
FORBRANNINGSMOTOR", application number 1151074-0) with the same
inventor and filing date as the present application. Said
application proposes a method for diagnosis of a combustion engine
pertaining to a vehicle whereby a particle content of an exhaust
flow from said engine is determined at a location upstream of a
particle filter by means of a PM sensor situated upstream of the
filter. Whether the engine is malfunctioning is determined on the
basis of the particle content determined. The method referred to
makes it possible for malfunctions to be detected at a very early
stage and for suitable remedial action to be taken. Faults which
would perhaps otherwise not be detected until a substantially later
time, e.g. on the occasion of a workshop visit, may by means of the
method described in said patent application be detected
substantially earlier.
[0063] Alternatively, a service indicator may for example be set in
the vehicle's control system, e.g. together with a fault code for
the too high particle emissions, with a view to the vehicle being
taken in for servicing as soon as possible.
[0064] If said first particle content is less than said second
particle content, the method moves on to step 306 at which it is
determined that the vehicle's emission levels are below the
prescribed levels applicable to the vehicle. On the basis of said
first particle content determined it is thus possible to determine
whether the particle content of the exhaust flow downstream of said
particle filter fulfils a defined condition, e.g. that it is less
than said second particle content. The method then ends at step
309.
[0065] Said second particle content may for example be the highest
particle content which the vehicle is permitted to release by
prevailing regulations, and may therefore be different for
different vehicles, but also different for similar vehicles running
in different jurisdictions which have different particle emission
requirements. Emissions are usually standardised with respect to a
specific running cycle, and said second particle content may for
example be determined by the permissible amount of particles per
kWh of work performed by the engine, i.e. the more work the engine
performs, the greater the emissions allowed in the exhaust flow.
Emission requirements are often expressed in particle mass per unit
of engine work, e.g. kg/kWh, g/kWh or mg/kWh, and this engine work
may for example take the form of power output developed or
deliverable.
[0066] This second particle content may however also be a content
higher than prevailing requirements.
[0067] Said second particle content may thus depend on various
parameters and may for example be determined at step 305 as a
function of one or more from among pressure before and after the
particle filter, differential pressure across the filter, time,
exhaust temperature and exhaust flow, such data possibly being for
example used to determine a second particle content which meets
prevailing emission requirements.
[0068] Many engines from various manufacturers currently release
too high a particle content from their combustion to enable them
able to meet requirements about the presence of particles without
post-treatment by means of particle filters. However, there are
engines, e.g. at least certain engines made for example by Scania,
which have such good combustion that the resulting emissions of
particles meet requirements with regard to PM emissions even before
the exhaust flow reaches the particle filter. In such engines the
filter is thus used to render the exhaust flow still cleaner.
[0069] In one embodiment it is therefore possible as above for said
second particle content at step 305 to represent a statutory
emission level, so the present invention is very suitable for
engines in which prescribed emission levels can be maintained even
before particle filtration. Determining that the particle mass even
before the particle filter is below statutory level means that the
particle content after DPF will automatically also be kept below
statutory level even if DPF malfunctions.
[0070] The invention thus makes it possible to monitor that
requirements about particle emissions after the particle filter are
complied with without any need for actual measurement of particle
content after the filter.
[0071] In the case of engines which cannot meet particle emission
requirements without downstream filter treatment, said second
particle content may be a value higher than prevailing
requirements.
[0072] The second particle content may for example be set with
respect to the filter's cleaning capacity, which may for example be
determined theoretically or be measured. Said second particle
content may thus be set to a level which, despite being higher than
prescribed requirements, still provides assurance that the particle
content actually leaving the vehicle will still be below prescribed
levels.
[0073] Particles separated from the exhaust flow by means of the
particle filter accumulate in the filter, which will thus fill with
soot over time. Depending for example on current running
conditions, the driver's mode of driving and the vehicle's load, a
larger or smaller amount of soot particles will be generated and
the filter will fill with soot/particles more or less quickly. When
it reaches a certain level, the filter has to be "emptied", which
is done by so-called regeneration, which will be familiar to one
skilled in the art. However, the filter's cleaning capacity may
vary with how full it is, so said second particle content in one
embodiment may also be arranged to vary with the filter's fullness,
which may for example be determined on the basis of signals from a
pressure sensor 209 which measures the differential pressure across
the filter. The fuller the filter becomes, the greater will be the
pressure difference across it. In one embodiment said second
particle content may therefore be arranged to depend on the
differential pressure across the filter in that it may be arranged
to decrease in step with increasing differential pressure.
[0074] In the method described above, particle emissions are
approved on the basis of a single value. In one embodiment, a
plurality of values are instead determined for said first particle
content and may then be combined to arrive at an average value
which is compared with said second particle content. In this
embodiment, individual values may be allowed to exceed said second
particle content so long as their combined value is less than said
second particle content. The method illustrated in FIG. 3 may also
be repeated at certain intervals, e.g. once per second, once per
minute or at some other shorter or longer suitable interval.
[0075] The present invention thus makes it possible to monitor that
requirements concerning particle emissions after the particle
filter are met without having to actually measure the particle
content after the filter, even on engines where the particle
content of the exhaust flow upstream of the filter does not meet
prevailing requirements.
[0076] Locating the PM sensor upstream of the particle filter to
monitor emission requirements has further advantages. Since the
sensor is so situated that measurement signals will be continually
delivered, its function may be verified by observing the signal
delivered by it over time. So long as it delivers substantially
continuous signals, or delivers for similar operating situations
substantially the same signal, the sensor may be regarded as
working properly. If on the contrary it suddenly indicates
substantially lower emissions than normal for a given running
situation, it may be assumed that the sensor is malfunctioning, and
a service flag may for example be activated in the vehicle's
control system to indicate a need for servicing.
[0077] The sensor may for example be of a type which delivers for
example a voltage or current or presents a capacitance, inductance
or resistance which varies with the presence of particles, in which
case the control unit 208 may then use appropriate mathematical
relationships or a table to convert measured values received to
corresponding particle contents. The sensor may however also be of
a type with its own control logic, in which case this internal
control logic will calculate a content which is then conveyed to
the control unit, e.g. via the vehicle network or a dedicated
cable.
[0078] The sensor may also be used to detect situations where the
particle content of the exhaust flow suddenly exceeds a normal
level or a regulation level. Even if the particle filter itself
often provides assurance that requirements concerning actual
emissions in the vehicle's surroundings are still complied with,
the higher particle content nevertheless indicates that the engine
is not fully functional, which is another situation where it is
desirable that the vehicle come in for servicing as soon as
possible to rectify the cause or causes of the increased particle
content in the exhaust gases. This is described in more detail in
the aforesaid parallel patent application entitled "METHOD AND
SYSTEM FOR DIAGNOSIS OF A COMBUSTION ENGINE" ("FORFARANDE OCH
SYSTEM FOR DIAGNOSTISERING AV EN FORBRANNINGSMOTOR").
[0079] The present invention affords the further advantage that
active testing of sensor function can be performed. The engine may
for example be deliberately set to operating points which may be
expected to result in substantially higher particle emissions. By
observing at the same time the signals delivered by the sensor, it
can be determined whether they actually reflect the expected
increase in the particle content of the exhaust flow. So long as
expected changes in its signal occur, the sensor may also be
assumed to be working properly. If the signals do not increase
despite the increased particle emissions due to the running
situation, the sensor may be assumed to be malfunctioning.
[0080] As previously mentioned, locating the PM sensor 222 upstream
of the particle filter affords also the advantage that it can with
greater certainty be so situated as to cause its signals to be
representative of the exhaust flow produced by the engine. The
sensor may for example be situated, as in FIG. 2, after a turbo
unit 220 from which the exhaust flow is usually delivered in a
predictable way. It may for example also be situated downstream of
DOC 205 but upstream of the particle filter 202. In the embodiment
depicted, the SCR catalyst 203 is downstream of the particle
filter, but in one embodiment it is instead upstream of DPF 202, in
which case the sensor may be downstream or upstream of the
catalyst.
[0081] The vehicle may also be equipped with a so-called exhaust
brake which the sensor 222 may for example be upstream of. It may
also be situated in the EGR feedback of part of the exhaust flow as
is commonly the case in vehicles of the above kind, since this part
of the exhaust flow is representative of the composition of the
total exhaust flow. The sensor 222 may for example also be situated
upstream of the turbo unit 220. The turbo unit may be of the type
with fixed geometry (FGT) or of the type with variable geometry
(VGT) and be provided with turbines to feed power back to
crankshafts (turbo compound) or some other part of the power train.
The vehicle may also be provided with a so-called ammonia slip
catalyst (ASC) which the PM sensor may be situated upstream or
downstream of. There are thus a large number of possible locations
for the PM sensor upstream of the particle filter.
[0082] Moreover, said second particle content has hitherto been
referred to in relation to various requirements, but it may also be
set, e.g. in jurisdictions where there are no regulatory
requirements, to a value determined by the vehicle's manufacturer.
It may for example be based on a value which provides assurance of
good engine function.
[0083] Moreover, the present invention is exemplified above in
relation to vehicles. The invention is nevertheless also applicable
to any other means of transport/processes in which particle filter
systems as above are applicable, e.g. watercraft or aircraft with
combustion processes as above.
[0084] Further embodiments of the method and system according to
the invention are referred to in the attached claims.
[0085] It should also be noted that the system may be modified
according to different embodiments of the method according to the
invention (and vice versa) and that the present invention is in no
way restricted to the embodiments described above of the method
according to the invention, but relates to and comprises all
embodiments within the protective scope of the attached independent
claims.
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