SE1650214A1 - A method and a system for predicting a service need of an exhaust gas aftertreatment system - Google Patents

Abstract

18 ABSTRACT A method for predicting a service need of a unit (2, 3, 4) within anexhaust gas aftertreatment system of an internal combustion5 engine (1), comprising the steps:- continuously measuring a lubricating engine oil level withinan oil sump of the engine,- based on the measured oil level, determining an oilconsumption of the engine, 10 - based on at least the determined oil consumption and on aknown oil quality factor, estimating an amount of phosphorusstored in the exhaust gas aftertreatment system, - based on said estimated amount of phosphorus, predicting aservice need of said at least one unit. (Pig. 1)

Description

A method and a svstem for predictinq a service need of an exhaust aas aftertreatment svstem TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for predicting a serviceneed of at least one unit within an exhaust gas aftertreatmentsystem of an internal combustion engine according to thepreamble of claim 1. The invention further relates to an evaluationsystem according to the preamble of claim 8, an exhaust gasaftertreatment system, and a motor vehicle. The invention alsorelates to a computer program, a computer program product, and an electronic control unit.

By oil is herein intended lubricating engine oil.

The internal combustion engine can be a diesel engine, a biofuelengine, or any other type of engine having an exhaust gas aftertreatment system, such as Otto engines.

BACKGROUND AND PRIOR ART Exhaust gas aftertreatment systems comprising units such asoxidation catalysts, particulate filters and selective catalyticreduction (SCR) units are used for reducing pollutants present inexhaust gases of internal combustion engines, in particular fromdiesel engines. The primary purpose of the oxidation catalyst is tooxidise nitrogen oxide (NO) present in the exhaust gases to N02.N02 is needed to increase the reaction rate over the SCR unit, mounted downstream of the oxidation catalyst, as well as to enhance soot oxidation in the particulate filter. The oxidationcatalyst is also used to oxidise carbon monoxide (CO) andhydrocarbon (HC) present in the exhaust gases. A secondarypurpose of the oxidation catalyst is to oxide hydrocarbons underexothermal conditions to create heat for soot regeneration of theparticulate filter, i.e. removal of soot particles clogging the filter at an elevated temperature.

The particulate filter is located downstream of the oxidationcatalyst. lt relies on passive regeneration supported by NOz-basedoxidation of trapped carbon particulates and is particularlyimportant to reduce emissions of particulate matter from dieselengines. Downstream of the particulate filter, a reductant such asAdBlue is dosed before the exhaust gases enter into the SCR unitor units. One or more ammonia slip catalysts (ASC) may be addeddownstream of the SCR unit with the purpose of handling any excess ammonia.

Since exhaust gas aftertreatment systems to a large extent rely onreactions occurring on the surfaces within the units of the systems,it is important that the surfaces of the system remain active anddo not become blocked by pollutants from the fuel or engine oil,such as sulfur, phosphorus, potassium, sodium, calcium, etc.Sulfur and phosphorus are well-known catalyst poisons derivedfrom e.g. bio diesel fuel and additives used in lubricating engineoil. However, sulfur poisoning is to a large extent more controllablethan phosphorus poisoning. ln order to remove sulfur from theexhaust gas aftertreatment system, the system is regularlysubjected to a regeneration process at high temperature, during which sulfur desorbs. Such a regeneration is carried out in situ by simply raising the temperature locally to a temperature of at least300°C. The regeneration process also removes soot particlesclogging the particulate filter. However, ash particles, initiallybeing smaller than the soot particles but agglomerating andgrowing over time, are generally left behind in the particulate filter also upon regeneration.

WO2009106946 discloses a method for predicting a service needdue to sulfur poisoning of a NOX trapping catalytic converter withinan exhaust gas aftertreatment system. According to this method,a fuel consumption and an oil consumption of the engine aremeasured or estimated, and an estimated amount of sulfurpoisoning of the catalytic converter is calculated based on theseconsumptions and on factors relating to the amount of sulfur withinthe fuel and oil, respectively. As the amount of estimated sulfurpoisoning exceeds a predetermined threshold, a regeneration iscarried out. Regeneration is carried out by raising the temperaturewithin the catalytic converter so that sulfur desorbs from surfaces of the catalytic converter.

US2013/O239553 discloses an exhaust gas aftertreatment systemconfigured to determine a total amount of sulfur stored on anoxidation catalyst unit or a selective catalytic reduction unit. Thisis achieved by first calculating an oil consumption and a fuelconsumption of the engine. Based thereon and on an estimatedamount of sulfur in the fuel and oil respectively, the total amountof sulfur stored in the unit is estimated. The oil consumption iscalculated using an engine speed/load map. Adsorbed sulfur can be desorbed by means of a regeneration at high temperature.

However, even though regeneration at high temperature can remove sulfur from the surfaces within the exhaust gasaftertreatment system, the units of the exhaust gas aftertreatmentsystem nevertheless age and become deteriorated over time. Onereason for this is the accumulation of other additives than sulfur,which additives are impossible to remove by regeneration at hightemperature and which reduce the function of the units. Ashparticles agglomerating over time in the particulate filter clog thefilter and give rise to a back pressure, thus increasing the fuelconsumption of the engine. Even though regeneration at hightemperature removes soot clogging the particulate filter, the filtertherefore has to be removed and cleaned more thoroughly, orexchanged, at some point, due to the accumulated ash particles.Thus, the entire exhaust gas aftertreatment system or individualdevices therein will at some point need to be replaced or otherwiseserviced, such as temporarily removed and cleaned. lt is desirableto be able to predict when such a service is needed and tocontinuously be able to assess the health of the exhaust gas aftertreatment system.

SUMMARY OF THE INVENTION lt is an objective of the present invention to provide a method anda system for predicting a service need of one or several unitswithin an exhaust gas aftertreatment system, which service need cannot be met by a regeneration at elevated temperature.

This objective is, according to a first aspect of the invention,achieved by the initially defined method, characterised in that it further comprises the steps: - based on at least the determined oil consumption and on aknown oil quality factor, estimating an amount of phosphorusstored in the exhaust gas aftertreatment system, - based on said estimated amount of phosphorus, predicting a service need of said at least one unit.

The method according to the invention enables prediction of aservice need based on the amount of phosphorus accumulated inthe exhaust gas aftertreatment system, in particular in an oxidationcatalyst unit or in the form of ash in a particulate filter providedtherein. Phosphorus is not possible to desorb by means of aregeneration at high temperature and stored phosphorus thereforebecomes a problem over time, reducing the efficiency of theexhaust gas aftertreatment system. Since phosphorus does notdesorb as sulfur does, it is easier to estimate the total amount ofstored phosphorus in the units within the exhaust gasaftertreatment system, also after several regeneration cycles.Estimating the amount of phosphorus instead of sulfur thereforefacilitates prediction of a service need that cannot be fulfilled byin situ regeneration at high temperature. l\/leasuring the oil level continuously, such as at a certainfrequency, to determine the oil consumption instead of estimatingit based on e.g. engine operation conditions gives a more accuratedetermination of the oil consumption. The relevant oil consumptionis here the accumulated oil consumption of the engine with thepresent exhaust gas aftertreatment system connected thereto.This may be the accumulated oil consumption since the exhaustgas aftertreatment system was new, or since a relevant unit of the system was replaced. An oil level sensor is preferably used, which on one hand senses the slow decrease in oil level caused by oilconsumption during use of the engine, and on the other hand sudden increases caused by refilling of oil.

The oil phosphorus content of the oil. The product of the phosphorus quality factor comprises information relating to acontent of the oil and the accumulated oil consumption thusprovides an estimate as to the amount of phosphorus accumulatedwithin the exhaust gas aftertreatment system. The oil quality factormay also comprise information relating to other additives, such assulfur, potassium, sodium, calcium, etc., and the amount of thoseelements in the units within the exhaust gas aftertreatment system can thereby also be estimated using suitable algorithms.

A model may be used in the step of predicting the service need ofthe at least one unit, which model is based on previous testing andanalyses of used exhaust gas aftertreatment systems. The modelis used to predict the relative amount of phosphorus accumulated in the different units of the exhaust gas aftertreatment system.

According to one embodiment, said at least one unit is selectedfrom an oxidation catalyst unit, a particulate filter and a three-waycatalytic converter. Thus, in case of a diesel or a biofuel engine,the units may be one or both of a particulate filter and an oxidationcatalyst unit, and in case of an Otto engine, the unit may be oneof a three-way catalytic converter and, if present, a particulate filter.

According to one embodiment, said at least one unit is an oxidation catalyst unit. The oxidation catalyst is commonly provided directly downstream of the internal combustion engine in an exhaust gasaftertreatment system for diesel engines and is therefore oftensubjected to conditions that may lead to phosphorus poisoning anddeactivation of the oxidation catalyst. Also ash containingphosphorus may accumulate in the oxidation catalyst and give rise to a back pressure.

According to another embodiment, said at least one unit is aparticulate filter. The particulate filter is sensitive to accumulationof ash, which contains phosphorus and which cannot be removedusing a regeneration at high temperature. The amount ofphosphorus that the particulate filter has been exposed to is hereused to determine when and if the particulate filter needs to be removed and cleaned, or exchanged.

An SCR unit provided downstream of a particulate filter is normallynot as exposed to phosphorus poisoning, since most of thephosphorus accumulate in the oxidation catalyst and in the particulate filter.

According to one embodiment, the step of predicting a serviceneed of said at least one unit comprises comparing said estimatedamount of phosphorus to a predetermined threshold level. This isan efficient way of predicting a service need, since the amount ofphosphorus that the different units within the exhaust gasaftertreatment system can store with acceptable function is oftenknown from previous testing and analyses of used exhaust gasaftertreatment systems. lf the predetermined threshold level isexceeded, an error code may be generated and an error message or signal communicated.

According to one embodiment, the method further comprisesdetermining a fuel consumption of the engine, wherein theestimation of the amount of phosphorus stored in said at least oneunit is based also on the determined fuel consumption and on aknown fuel quality factor. This is particularly relevant for exhaustgas aftertreatment systems of biofuel engines, using e.g. biodieselas a fuel, since biofuel often contains relatively high levels ofphosphorus originating from fertilisers used in the production offeedstock for biofuel. The fuel quality factor comprises informationrelating to a phosphorus content of the fuel. The fuel quality factor may also comprise information relating to other additives.

According to one embodiment, the predicted service need is aneed to replace said at least one unit. The poisoned unit can bereplaced by a corresponding new unit, or by a previously used and externally cleaned unit.

According to another aspect of the invention, the above mentionedobjective is achieved by the initially defined evaluation system,which is characterised in that it comprises means configured toestimate an amount of phosphorus stored in the exhaust gasaftertreatment system based on at least the determined oilconsumption and on a known oil quality factor, and based thereonpredict a service need of said at least one unit. Advantages andadvantageous features of such an evaluation system appears from the above description of the proposed method.

The invention also relates to an exhaust gas aftertreatment systemcomprising the proposed evaluation system and to a motor vehicle comprising such an exhaust gas aftertreatment system.

The invention further relates to a computer programme comprisingcomputer programme code for causing a computer to implementthe proposed method when the computer programme is executed in the computer.

Furthermore, the invention relates to a computer program productcomprising a non-transitory data storage medium which can beread by a computer and on which the program code of theproposed computer program is stored.

The invention also relates to an electronic control unit of a motorvehicle comprising an execution means, a memory connected tothe execution means and a data storage medium which isconnected to the execution means and on which the computer program code of the proposed computer program is stored Other advantageous features as well as advantages of the present invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will in the following be describedwith reference to the appended drawings, in which:Fig. 1 schematically shows an evaluation system according to an embodiment of the invention, Fig. 2 is a flow chart illustrating a method according to theinvenüon,andFig. 3 schematically shows an electronic control unit according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THEINVENTION An exhaust gas aftertreatment system of an internal combustionengine 1 in a motor vehicle according to an embodiment of theinvention is schematically shown in fig. 1. The exhaust gasaftertreatment system comprises an oxidation catalyst unit 2, aparticulate filter 3 located downstream of the oxidation catalystunit 2, and further a selective catalytic reduction (SCR) unit 4located downstream of the particulate filter 3. An oil level sensor5 is provided in the engine 1, configured to continuously measurea lubricating engine oil level in an oil sump (not shown) of theengine 1. A control unit 6 comprising a processor is connected tothe oil level sensor 5. The control unit 6 is configured to determinean oil consumption of the engine 1 based on the measuredlubricating engine oil level. lt is further configured to estimate anamount of phosphorus stored in the exhaust gas aftertreatmentsystem based on, at least, the determined oil consumption and ona known oil quality factor. Based on the estimated amount ofphosphorus, the control unit 6 is further configured to predict aservice need of the oxidation catalyst unit 2, which service needcan be in the form of replacement or removal and cleaning. The oillevel sensor 5 and the control unit 6 forms an evaluation system for predicting a service need of the exhaust gas aftertreatment 11 system. The control unit 6 may in one embodiment be in the form of an electronic control unit 30 such as shown in fig. 3.

The oil level sensor 5 may be any kind of oil level sensor that issuitable for measuring the amount of lubricating oil within the oilsump and send a signal relating thereto to e.g. the control unit 6.Such an oil level sensor 5 can be in the form of a float switch, suchas a mechanical or a magnetic float switch, but also other kinds ofoil level sensors are possible. The signal from the oil level sensor may be subjected to filtering in order to reduce noise.

During operation of the internal combustion engine 1, exhaustgases are generated and follow the direction of the arrows throughthe exhaust gas aftertreatment system before being emittedthrough an exhaust pipe 7.

A method according to an embodiment of the invention isillustrated in fig. 2. ln a first step S1, the lubricating engine oil levelwithin the oil sump of the engine 1 is measured continuously overtime, e.g. at a certain frequency. Data relating to the oil level aresent from the oil level sensor 5 to the control unit 6 and are storedin a database, which may be located in a storage means within thecontrol unit 6. The data are in a step S2 used to determine an oilconsumption of the engine 1. ln a step S3, the determined oilconsumption is used to estimate an amount of phosphorus storedin the exhaust gas aftertreatment system. Therefrom, the amountof phosphorus stored in the oxidation catalyst unit 2 can beestimated. For estimation of the amount of phosphorus stored inthe exhaust gas aftertreatment system, an oil quality factor is used, containing information about the amount of phosphorus 12 within the oil. The oil quality factor is specific for the used oil andis assumed to be known such that the amount of phosphorus in theoil does not need to be measured using a sensor. Based on theestimated amount of phosphorus stored in the exhaust gasaftertreatment system, it is in a step S4 predicted when a serviceof the exhaust gas aftertreatment system will be needed. Thisservice can be in the form of an exchange of one or more units within the exhaust gas aftertreatment system.

Also the fuel consumption and a corresponding fuel quality valuemay be used in step S3 when estimating the amount of phosphorusstored in the exhaust gas aftertreatment system, in particular for biofuel engines.

The step S4 of predicting a service need may comprise comparingthe estimated amount of phosphorus to a predetermined thresholdlevel of phosphorus. lf the threshold level is exceeded, an errorcode may be generated and an error message can becommunicated, for example to a driver of a vehicle comprising theexhaust gas aftertreatment system, or to a central service station, a haulage company, etc.

The method according to the invention is not only applicable toexhaust gas aftertreatment systems such as the one describedabove, but may also be used to predict a service need of unitswithin other types of exhaust gas aftertreatment systems, such asa three-way catalytic converter (TWC) within an exhaust gasaftertreatment system of an Otto engine running on e.g. gaseousfuel such as natural gas or bio gas. Such a TWC unit is subjected to higher temperatures than the units of an exhaust gas 13 aftertreatment system of e.g. a diesel engine, since the Ottoengine operates at a higher temperature. Problems with sulfuraccumulation are thereby avoided in TWC units, but phosphorussuch exhaustto the is known to cause problems also inWith invention, a service need of a TWC unit can be predicted. gas aftertreatment systems. the method according All of the method steps, as well as any sub-sequence of steps,described above with reference to fig. 2, may be controlled bymeans of a programmed computer apparatus. Computer programcode for implementing a method according to the invention issuitably included in a computer program which is readable into aninternal memory of a computer, such as the internal memory of anelectronic control unit of a motor vehicle. Such a computerprogram is suitably provided through a computer program productcomprising a data storing medium readable by an electroniccontrol unit, which data storing medium has the computer programstored thereon. Said data storing medium is for example an opticaldata storing medium in the form of a CD-ROM-disc, a DVD-disc,etc., a magnetic data storing medium in the form of a hard disc, adiskette, a tape etc., or a Flash memory or a memory of the typeROM, PROM, EPROM or EEPROM.

Fig. 3 illustrates very schematically an electronic control unit 30comprising an execution means 31, such as a central processor(CPU), for implementing a method, or a subsequence of method steps, unit executing a computer program code foraccording to the invention. The execution means 31 communicateswith a memory 32, for example of the type RAM, through a data bus 33. The electronic control unit 30 comprises also a non- 14 transitory data storage medium 34, for example in the form of aFlash memory or a memory of the type ROM, PROM, EPROM orEEPROl\/I. The execution means 31 communicates with the datastorage medium 34 through the data bus 33. A computer programcomprising computer program code for implementing a methodaccording to the invention is stored on the data storage medium34.

The invention is of course not in any way restricted to the em-bodiments described above, but many possibilities to modifica-tions thereof would be apparent to a person with skill in the artwithout departing from the scope of the invention as defined in the appended claims.

Claims (13)

1. A method for predicting a service need of at least one unit(2, 3, 4) within an exhaust gas aftertreatment system of an internalcombustion engine (1), comprising the steps:- continuously measuring a lubricating engine oil level withinan oil sump of the engine (1),- based on the measured lubricating engine oil level, determining an oil consumption of the engine (1),characterised inthat it further comprises the steps: - based on at least the determined oil consumption and on aknown oil quality factor, estimating an amount of phosphorusstored in the exhaust gas aftertreatment system, - based on said estimated amount of phosphorus, predicting a service need of said at least one unit (2, 3, 4).

2. The method according to claim 1, wherein said at least oneunit is selected from an oxidation catalyst unit (2), a particulate filter (3) and a three-way catalytic converter.

3. The method according to claim 1, wherein said at least one unit is an oxidation catalyst unit (2).

4. The method according to claim 1, wherein said at least one unit is a particulate filter (3).

5. The method according to any one of the preceding claims, wherein the step of predicting a service need of said at least one 16 unit (2, 3, 4) comprises comparing said estimated amount of phosphorus to a predetermined threshold level.

6. The method according to any one of the preceding claims,further comprising determining a fuel consumption of the engine(1), wherein the estimation of the amount of phosphorus stored insaid at least one unit (2, 3, 4) is based also on the determined fuel consumption and on a known fuel quality factor.

7. The method according to any one of the preceding claims,wherein the predicted service need is a need to replace said at least one unit (2, 3, 4).

8. An evaluation system configured to predict a service need ofat least one unit (2, 3, 4) within an exhaust gas aftertreatmentsystem of an internal combustion engine (1), comprising: - an oil level sensor (5) configured to continuously measure alubricating engine oil level within an oil sump of the engine(1), - means (6, 30) configured to determine an oil consumption ofthe engine (1) based on the measured lubricating engine oillevel, characterised in that it comprises means (6, 30) configured to estimate an amountof phosphorus stored in the exhaust gas aftertreatment systembased on at least the determined oil consumption and on a knownoil quality factor, and based thereon predict a service need of said at least one unit (2, 3, 4).

9. An exhaust gas aftertreatment system comprising an evaluation system according to claim 8. 17

10. A motor vehicle comprising an exhaust gas aftertreatment system according to claim 9.

11. A computer program comprising computer program code forcausing a computer to implement a method according to any of thein the claims 1-7 when the computer program is executed computer.

12. A computer program product comprising a non-transitorydata storage medium which can be read by a computer and onwhich the program code of a computer program according to claim 11 is stored.

13. An electronic control unit (30) of a motor vehicle comprisingan execution means (31), a memory (32) connected to theexecution means (31) and a data storage medium (34) which isconnected to the execution means (31) and on which the computerprogram code of a computer program according to claim 11 is stored.