SE538762C2 - An apparatus with a particulate filter and a related method - Google Patents

Abstract

l7 Abstract lnvention regards an apparatus (5) at least in part to be arranged in a channel(12) for exhaust gas discharged from a combustion engine (4). The apparatus (5)comprises a particulate filter (15) arranged to collect particulate matter present inthe exhaust gas, a first pressure sensor (14A) positioned upstream of theparticulate filter (15) and a second pressure sensor (14B) positioned downstreamof the particulate filter (15). The pressure sensors (14A, 14B) are configured toprovide information on the exhaust gas pressure so that a differential pressureacross the particulate filter (15) is determined. The apparatus further comprises aparticulate matter sensor (17) positioned downstream of the particulate filter (15)and comprising ionizing means (17A) configured to ionize the particulate matterso that an ion current is created in said channel (12) when the exhaust gascarrying the particulate matter is ionized, and detecting means (17B) locateddownstream of the ionizing means (17A) in said channel (12). The detectingmeans (17B) are configured to detect the ion current and, in response to thedetected ion current, generate a signal comprising information on the particulatematter carried by the exhaust gas. The invention also regards a thereto relatedmethod. (Pig. s)

Description

An apparatus with a particulate filter and a thereto related method Technical fieldThe present invention relates to an apparatus with a particulate filter and amethod for managing a particulate filter. lt also relates to a vehicle and a computer program.

BackgroundParticulate matter (PM) or soot is one of the major harmful emissions generated by diesel engines. ln consequence, levels of soot emission are subject tolegislative regulation worldwide. ln order to reduce these emissions,aftertreatment systems, targeting removal of soot from the exhausts, are typicallyarranged in connection with modern diesel engines. One of the main componentsof such a system is a diesel particulate filter (DPF), normally positioned in anexhaust passage of the combustion engine, downstream of the catalyst. Theaftertreatment systems could also include other types of catalysts such asoxidation catalysts and selective reduction catalysts for nitrogen oxide removal. ln the related context, research has shown that adverse health effects fromexposure to PM are increasing with decreasing particle size. Hence, theconventional, i.e. mass-based PM-emission limits are in several marketscomplemented with emission limits as regards number of the emitted particles.Above-mentioned DPFs are particularly suitable to adequately treat the exhaustgas with respect to the number of emitted particles.

A DPF is typically made up of a so-called wall-flow monolith, comprising anextruded, often ceramic, structure with a large number of parallel, axiallyextending channels. The adjacent channels in the DPF are alternately plugged ateach end, allowing the exhaust gas to flow through the porous filter walls while capturing the PM. 2 The amount of soot in the DPF is typically detected indirectly, by means ofdifferential pressure measurement or by soot loading models based on engineoperating parameters, such as volume flow rate of the exhaust gas. Here,correlation between the measured differential pressure and the actual soot loadmay not be sufficiently accurate in order to achieve optimal regeneration timing.This is, at least in part, due to the fact that a change in differential pressure acrossthe filter may be induced by other parameters of the combustion process thansoot build-up in the filter. ln this context, a certain soot load of the filter isbeneficial for its operation - improves filtering properties of the DPF itself by making it more fine-meshed. ln order to, due to excessive PM build-up, avoid large pressure drop over the DPFand the negative effect this has on the fuel economy, the soot is oxidized intocarbon dioxide and nitrogen, using oxygen or nitrogen dioxide. This process iscalled regeneration and can be performed either passively, i.e. without additionalenergy input using only the exhaust gas stream, or actively, where the exhausttemperature is raised using active engine measures or using fuel injection.

The regeneration process in general, and the continuous process in particular,seek to arrive at a so called soot balance point, where equilibrium between theamount of soot accumulated by the filter and the amount of soot oxidized isachieved. lf the oxidation of soot is insufficient, PM build-up will increase, and sowill the pressure drop. This pressure drop could trigger active regenerationmeasures where the accumulated soot load is burnt off the filter by running theengine in a manner that elevates exhaust gas temperature to soot combustiontemperatures. Active regeneration, however, consumes fuel and needs to be kept at a minimum.

WO 2011/110920 discloses a system for estimating soot load of a particulatefilter. The system comprises two pressure sensors, one on each side of aparticulate filter, and, in addition, a device for detecting deposited amount of theparticulate matter provided downstream of the filter. The detection device weighs 3 the deposited particles in order to identify the amount of the deposited particulate.The obtained results, combined with the measured pressure drop, are used tofurther improve the soot load estimate. Such a device could typicallyunderestimate the number of the emitted particles. ln the presented context, the objective of the present invention is to provide anapparatus and a method permitting more precise estimates and a faster responseto changes in the soot load of a particulate filter.

SummaryThe above stated objective is achieved by means of the apparatus, the method, the vehicle and the computer program according to the independent claims.

Accordingly, a first aspect relates to an apparatus at least in part to be arranged ina channel for exhaust gas discharged from a combustion engine, said apparatuscomprising: a particulate filter arranged to collect particulate matter present in theexhaust gas, a first pressure sensor positioned upstream of the particulate filterand a second pressure sensor positioned downstream of the particulate filter, saidpressure sensors being configured to provide information on the exhaust gaspressure so that a differential pressure across the particulate filter is determined,and a particulate matter sensor positioned downstream of the particulate filter,said sensor comprising: ionizing means configured to ionize the particulate matterso that an ion current is created in said channel when the exhaust gas carryingthe particulate matter is ionized, and detecting means located downstream of theionizing means in said channel, said detecting means being configured to detectthe ion current and, in response to the detected ion current, generate a signalcomprising information on the particulate matter carried by the exhaust gas.

Positive effects and advantages of the invention at hand are presented below withreference to the first aspect of the invention. 4 Once the particulate matter traverses the particulate filter, the ionizing effect,applied through the ionizing means, will liberate electrons from atoms ormolecules of the particulate matter, thereby creating ions. The exhaust gascomprising ionized particulate matter, i.e. an ion current, subsequently reachesdetecting means located in the exhaust gas channel, downstream of the ionizingmeans. The detecting means will detect the ion current and, in response to thedetected ion current, generate a signal comprising information on the particulatematter carried by the exhaust gas. Combining thus obtained information on thefiltered, i.e. non-collected, particles with the differential pressure informationobtained by means of the pressure sensors gives a more complete understandingof the condition of the particulate filter. This may subsequently be used for variouspurposes. Ultimately, condition and performance of the particle filter may herebybe calculated with greater accuracy. Also, the present invention allows to morerapidly identify changes to condition and performance of the particle filter. ln a related context, more accurate information on the condition of the particulatefilter means that the possible need to regenerate the filter may unambiguously bedetermined sooner and with greater precision. This prolongs useful life of theparticle filter and positively impacts on fuel economy.

A second aspect relates to a method for managing a particulate filter arranged tocollect particulate matter present in exhaust gas discharged from a combustionengine. The method comprises: - collecting, by means of a particulate filter, particulate matterpresent in exhaust gas discharged from a combustion engine, - determining a differential pressure across the particulate filter, - emitting an ionizing radiation so that an ion current is createdwhen the exhaust gas carrying the particulate matter iscontacted by the ionizing radiation, - ionizing the exhaust gas carrying the particulate matter so that ion current is created in said channel, and 5 - detecting the ion current, - generating, in response to the detected the ion current, asignal comprising information on the particulate matter carriedby the exhaust gas.

A third aspect relates to a vehicle comprising the claimed apparatus.

Different embodiments of the invention are disclosed in the dependent claims and in the detailed description.

Brief description of the drawinqsFig. 1 is a schematical view from above of a vehicle.

Fig. 2 is a contextual, schematical view of an apparatus according to oneembodiment of the present invention, said apparatus comprising a particulatefilter, two pressure sensors and a particulate matter sensor.

Fig. 3 schematically illustrates the operation of a particulate matter sensor of the present invention.

Fig. 4 is a flow chart comprising method steps according to one embodiment ofthe present invention.

Further advantages and features of embodiments will become apparent whenreading the following detailed description in conjunction with the drawings.

Detailed descriptionThe present invention will now be described more fully, hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown. Thisinvention may, however, be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, 6 and will fully convey the scope of the invention to those skilled in the art. ln thedrawings, like reference signs refer to like elements.

Fig. 1 is a schematical view from above of a vehicle 1. The shown vehicle 1 is atruck or a trailer-hauling tractor having a chassis 9 and a front pair of wheels 10Aand a rear pair of wheels 1OB. The shown vehicle 1 is only an example, why thevehicle of the present invention may also be realized as a bus or a thereto similarvehicle. A driver's cab 7 is positioned far forward on the vehicle 1. A control unit19, located below the driver's cab 7, controls the operation state of an internalcombustion engine 4 in accordance with the operating condition of the combustionengine 4 and/or driver inputs. Exhaust gases generated during the combustionprocess are channeled into an exhaust system 11 for further treatment.Accordingly and as schematically shown in Fig. 1, the combustion engine 4 is influid communication with the exhaust system 11. This further treatment of theexhaust gases could also be controlled by the control unit 19. Certain constituentsof the exhaust system 11 will be discussed in greater detail in connection withFigs. 2 and 3.

The present inventive apparatus (not shown in Fig. 1) is suitable forimplementation in the vehicles of the above-discussed kind. Moreover, theapparatus may be implemented in other fields where particle filters are arrangedin connection with combustion engines, e.g. marine engines, locomotives and/or stationary power plants.

Fig. 2 is a contextual, schematical view of an inventive apparatus 5 according toone embodiment of the present invention. The apparatus 5 is arrangeddownstream of a catalyst 13 in a channel 12 for exhaust gas discharged from acombustion engine 4. The apparatus 5 comprises a particulate filter 15 arrangedto collect particulate matter present in the exhaust gas. A first pressure sensor14A is positioned upstream of the particulate filter 15 and a second pressuresensor 14B is positioned downstream of the particulate filter 15. The pressuresensors 14A, 14B measure the exhaust gas pressure. These pressure sensors 7 14A, 14B are configured to provide information on the exhaust gas pressure sothat a differential pressure across the particulate filter 15 is determined.

A particulate matter sensor 17 is positioned downstream of the particulate filter15. The particulate matter sensor 17 will be more thoroughly discussed inconnection with Fig. 3. The apparatus 5 further comprises a control unit 19.Various sensors, such as pressure sensors 14A, 14B, exhaust gas temperaturesensors (not shown) and the like, are connected to the control unit 19. Outputsignals from these sensors are input to the control unit 19. The control unit 19 willalso be discussed in more detail in connection with Fig. 3.

Fig. 3 schematically illustrates the operation of a particulate matter sensor 17 ofthe present invention. The sensor 17 comprises ionizing means 17A and detectingmeans 17B, both arranged in a channel 12 for exhaust gas discharged from acombustion engine (not shown). Flow direction of the exhaust gas is denoted byarrows. The ionizing means 17A are configured to ionize the particulate matter sothat an ion current is created in said channel 12 when the exhaust gas carryingthe particulate matter is ionized. The ionizing effect, applied through the ionizingmeans, will liberate electrons from atoms or molecules of the particulate matter,thereby creating ions. ln an embodiment (not shown), the ionizing means 17Acomprises a device generating an electric field. By way of example, this devicecould comprise a pair of oppositely charged elements facing each other such thatan electric field is created between these elements. The particulate matter passesbetween the elements and is exposed to this electric field. ln a furtherembodiment (not shown), the ionizing means 17A comprises a robust and suitablyarranged radiation source, such as a UV-light source or an X-ray-source.

The exhaust gas comprising ionized particulate matter, i.e. carrying an ion current,subsequently reaches detecting means located in the exhaust gas channel,downstream of the ionizing means. The detecting means 17B are configured todetect the ion current and, in response to the detected ion current, generate asignal comprising information on the particulate matter carried by the exhaust gas. 8 Combining thus obtained information on the filtered, i.e. non-collected, particleswith the differential pressure information obtained by means of the pressuresensors gives a more complete understanding of the condition of the particulatefilter. ln an embodiment (not shown), the detecting means 17B comprises a net-shapedstructure made in conductive material, said net-shaped structure being arrangedradially in said channel 12 for exhaust gas. The travelling ionized particles willeventually contact the net-shaped structure whereupon a current signal isgenerated in the structure. The current signal is harvested and treated using usualmethods known to the person skilled in the art. ln a further embodiment (not shown), the detecting means 17B comprises a coilarranged axially in said channel 12 for exhaust gas. The coil delimits an axiallyextending core section. Some of the travelling ionized particles will longitudinallytraverse the core section, thus inducing a voltage signal in the coil. Analogously tothe above, the voltage signal is harvested and treated using usual methods knownto the person skilled in the art.

A control unit 19 typically has a processing unit 29 and a memory unit 39connected to the processing unit 29. The processing unit 29 may comprise one orseveral CPUs (CPU - Central Processing Unit). The memory unit 39 could be ofthe non-volatile kind, e.g. a flash memory, or a RAM-memory (RAM - RandomAccess l\/lemory). The processing unit 29 is configured to carry out the instructionsof the computer program P with computer instructions. The computer program Pcould be recorded on a carrier, typically a computer readable medium, prior tobeing loaded onto the memory unit 39. Alternatively, it could be preinstalled in said memory unit 39.

Still with reference to the control unit 19, it may be configured to determine, on thebasis of the detected ion current, the number of particles that make up theparticulate matter carried by the exhaust gas. As an alternative, this functionality, 9 realized through dedicated means for determining the number of particles thatmake up the particulate matter, may be integrated in the apparatus 5. ln a related embodiment, the control unit 19 may be configured to establish sizedistribution of the particles that make up the particulate matter carried by theexhaust gas. This is typically achieved using previously obtained data regardingthe number of particles that make up the particulate matter. Information regardingsize distribution of the particles may inter alia be used in order to fine-tuneregeneration cycles. As an alternative, the apparatus 5 may comprise said meansfor establishing size distribution of the particles that make up the particulatematter. ln yet another embodiment, the control unit 19 may be configured to estimate sootload of the particle filter. This is typically achieved using previously obtained dataregarding the size distribution of the particles. Furthermore, the control unit 19may be configured to compare the estimated soot load value of the particulatefilter 15 to a referential soot load value. Here, regeneration of the particulate filter15 is initiated if the estimated soot load value of the particulate filter 15 differsfrom the referential soot load value. The referential soot load value may be asingle value or it may be expressed as an interval. Alternatively, means forestimating soot load of the particulate filter may be employed in order to calculatethe soot load estimate, said means being part of the apparatus 5. ln this context, regeneration of the particulate filter can occur by soot oxidation ofthe trapped particles either with oxygen (active regeneration) or nitrogen dioxide(passive regeneration) - both briefly discussed in the Background-section. Foractive regeneration, exhaust gas temperatures need to be temporarily increasedby suitable manipulation of the combustion engine or by injection of additional fueldirectly into the exhaust channel upstream a catalyst. Passive regenerationoccurs at temperatures as low as 250 °C and can thus regenerate the particulatefilter continuously. lO The control unit 19 may initiate either active or passive regeneration of the particlefilter. Moreover, it may combine time periods of active regeneration and timeperiods of passive regeneration in order to ensure a proper regeneration of theparticulate filter. When it comes to active regeneration, initiation is synonymouswith suppiying extra fuel into the exhaust channel 12. The extra fuel may besupplied by adding, via a fuel addition valve (not shown), the fuel into the exhaustgas or by performing a supplemental fuel injection, which differs from the ordinary,scheduled fuel injection of the combustion engine.

Alternatively, the control unit 19 may be configured to generate an indicativesignal if above criterion is fulfilled. The indicative signal signifies that theparticulate filter requires regeneration. ln this context, filter regeneration shouldgenerally occur without involving the driver, including without informing him/herthat a regeneration process is ongoing.

The above-described control unit 19 controls various actuators, such as fuelinjection valves and the fuel addition valve. This may be implemented in variousmanners that are known to those of skill in the art and, for that reason, are notdescribed in detail herein.

Fig. 4 is a flow chart comprising method steps according to one embodiment ofthe present invention. The flow chart shows a method for an apparatus with aparticulate filter previously described in connection with Figs. 1-3.

The method comprises collecting 40, by means of a particulate filter 15,particulate matter present in exhaust gas discharged from a combustion engine 4.A differential pressure across the particulate filter 15 is subsequently determined50. An ionizing radiation is thereafter emitted 60 so that an ion current is createdwhen the exhaust gas carrying the particulate matter is contacted by the ionizingradiation. The exhaust gas carrying the particulate matter is thereafter ionized 70so that an ion current is created in said channel 12. Finally, the ion current is ll detected 80, and a signal is generated 90, in response to the detected ion current,said comprising information on the particulate matter carried by the exhaust gas. ln addition, the number of particles that make up the particulate matter carried bythe exhaust gas may be determined on the basis of the detected ion current.

The previously obtained data regarding the number of particles may be used toestablish size distribution of the particles that make up the particulate mattercarried by the exhaust gas. ln the related context and in order to establish thecondition of the particulate filter, soot load of the particulate filter may thereafterbe estimated using data regarding size distribution of the particles.

Hereby estimated soot load value of the particulate filter 15 may be compared to areferential soot load value. This referential value could be based on the historicaldata as regards condition of the particulate filter. ln consequence, an indicativesignal could be generated if the estimated soot load value of the particulate filterdiffers from the referential soot load value, said indicative signal signifying that theparticulate filter requires regeneration. Various regenerative processes availableare thoroughly described in connection with Fig. 3.

The present invention also relates to a computer program P that comprises acomputer program code to cause the previously discussed control unit, or acomputer connected to the control unit, to perform the method described above. ln addition, a computer program product is provided comprising a computerprogram code stored on a computer-readable medium to perform the methoddescribed above, when the computer program code is executed by the control unitor by a computer connected to the control unit. ln the drawings and specification, there have been disclosed typical preferredembodiments of the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes of limitation,the scope of the invention being set forth in the following claims.

Claims (16)

l2 Claims

1. An apparatus (5) at least in part to be arranged in a channel (12) forexhaust gas discharged from a combustion engine (4), said apparatus (5) comprising: a particulate filter (15) arranged to collect particulate matter present in theexhaust gas, a first pressure sensor (14A) positioned upstream of the particulate filter (15)and a second pressure sensor (14B) positioned downstream of the particulatefilter (15), said pressure sensors (14A, 14B) being configured to provideinformation on the exhaust gas pressure so that a differential pressure acrossthe particulate filter (15) is determined, and a particulate matter sensor (17) positioned downstream of the particulate filter(15), wherein said sensor (17) comprises: ionizing means (17A) configured to ionize the particulate matter so that an ioncurrent is created in said channel (12) when the exhaust gas carrying theparticulate matter is ionized, and detecting means (17B) located downstream of the ionizing means (17A) insaid channel (12), said detecting means (17B) being configured to detect theion current and, in response to the detected ion current, generate a signalcomprising information on the particulate matter carried by the exhaust gas, wherein the apparatus (5) further comprises: means for determining, on the basis of the detected ion current, the number ofparticles that make up the particulate matter carried by the exhaust gas and 13 means for establishing size distribution of the particles that make up theparticulate matter carried by the exhaust gas.

2. An apparatus (5) according to claim 1, wherein the ionizing means (17A)comprises a device generating an electric field.

3. An apparatus (5) according to claim 1, wherein the ionizing means (17A)comprises a radiation source, such as a UV-light source or an X-ray-source.

4. An apparatus (5) according to any of preceding claims, wherein thedetecting means (17B) comprises a net-shaped structure made in conductivematerial, said net-shaped structure being arranged radially in said channel (12)for exhaust gas.

5. An apparatus (5) according to any of claims 1-3, wherein the detectingmeans (17B) comprises a coil arranged axially in said channel (12) for exhaustgas.

6. An apparatus (5) according to any of the preceding claims, wherein theapparatus (5) further comprises means for estimating soot load of theparticulate filter.

7. An apparatus (5) according to claim 1, the apparatus (5) further comprisinga control unit (19) being configured to: - determine, on the basis of the detected ion current, the number ofparticles that make up the particulate matter carried by the exhaustgas.

8. An apparatus (5) according to claim 7, the control unit (19) further beingconfigured to: 14 - establish size distribution of the particles that make up the particulatematter carried by the exhaust gas.

9. An apparatus (5) according to claim 8, the control unit (19) further beingconfigured to: - estimate soot load of the particulate filter.

10. An apparatus (5) according to claim 9, the control unit (19) further beingconfigured to: - compare the estimated soot load value of the particulate filter (15) to areferential soot load value, and - initiate regeneration of the particulate filter (15), if the estimated sootload value of the particulate filter (15) differs from the referential sootload value.

11. A vehicle (1) comprising an apparatus (5) according to any of preceding claims.

12. A method comprising the steps of: - collecting (40), by means of a particulate filter (15), particulate matterpresent in exhaust gas discharged from a combustion engine (4), - determining (50) a differential pressure across the particulate filter (15), - emitting (60) an ionizing radiation so that an ion current is createdwhen the exhaust gas carrying the particulate matter is contacted bythe ionizing radiation, - ionizing (70) the exhaust gas carrying the particulate matter so that anion current is created in said channel (12), - detecting (80) the ion current, - generating (90), in response to the detected ion current, a signalcomprising information on the particulate matter carried by the exhaust gaS, the method further comprising the steps of: - determining, on the basis of the detected ion current, the number ofparticles that make up the particulate matter carried by the exhaustgas,and - establishing size distribution of the particles that make up theparticulate matter carried by the exhaust gas.

13. A method according to ciaim 12, further comprising the step of: - estimating soot load of the particulate filter.

14. A method according to claim 13, further comprising the step of: - comparing the estimated soot load value of the particulate filter (15) toa referential soot load value, and - generating an indicative signal, if the estimated soot load value of theparticulate filter (15) differs from the referential soot load value, saidindicative signal signifying that the particulate filter (15) requiresregeneration.

15. A computer program P, wherein said computer program P comprises acomputer program code to cause a control unit (19), or a computerconnected to the control unit (19), to perform the method according to anyof claims 12-14. 16

16. A computer program product comprising a computer program code storedon a computer-readable medium to perform the method according to any ofthe claims 12-14, when the computer program code is executed by a controlunit (19) or by a computer connected to the control unit (19).