GB2544762A - Improvements in or relating to exhaust gas treatment - Google Patents

Improvements in or relating to exhaust gas treatment Download PDF

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Publication number
GB2544762A
GB2544762A GB1520810.1A GB201520810A GB2544762A GB 2544762 A GB2544762 A GB 2544762A GB 201520810 A GB201520810 A GB 201520810A GB 2544762 A GB2544762 A GB 2544762A
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United Kingdom
Prior art keywords
lnt
diagnostic tool
engine
control system
exhaust gas
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GB1520810.1A
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GB201520810D0 (en
Inventor
Norton Jeremy
Smith Paul
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Ford Global Technologies LLC
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Ford Global Technologies LLC
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Priority to GB1520810.1A priority Critical patent/GB2544762A/en
Publication of GB201520810D0 publication Critical patent/GB201520810D0/en
Publication of GB2544762A publication Critical patent/GB2544762A/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/005—Controlling exhaust gas recirculation [EGR] according to engine operating conditions
    • F02D41/0055—Special engine operating conditions, e.g. for regeneration of exhaust gas treatment apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/07—Mixed pressure loops, i.e. wherein recirculated exhaust gas is either taken out upstream of the turbine and reintroduced upstream of the compressor, or is taken out downstream of the turbine and reintroduced downstream of the compressor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/18—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an adsorber or absorber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2270/00—Mixing air with exhaust gases
    • F01N2270/10—Mixing air with exhaust gases for rendering exhaust innocuous, e.g. by dilution
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2430/00—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
    • F01N2430/06—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics by varying fuel-air ratio, e.g. by enriching fuel-air mixture
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
    • F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/08—Parameters used for exhaust control or diagnosing said parameters being related to the engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
    • F01N2900/1614—NOx amount trapped in catalyst
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D21/00—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas
    • F02D21/06—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air
    • F02D21/08—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/70—Input parameters for engine control said parameters being related to the vehicle exterior
    • F02D2200/701—Information about vehicle position, e.g. from navigation system or GPS signal
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D35/00—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for
    • F02D35/0015—Controlling engines, dependent on conditions exterior or interior to engines, not otherwise provided for using exhaust gas sensors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
    • F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M2026/001—Arrangements; Control features; Details
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/05—High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream of the compressor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/06—Low pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust downstream of the turbocharger turbine and reintroduced into the intake system upstream of the compressor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Testing Of Engines (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Abstract

A control system is provided for a diesel engine including an exhaust gas recirculation (EGR) system configured to be operable in either one of a high pressure mode and a low pressure mode and a Lean NOx Trap (LNT); the control system comprises at least one engine diagnostic tool configured to model or monitor at least one characteristic of the engine indicative of the suitability of running a rich purge, a hydrocarbon flow controller configured to control the rate at which hydrocarbons are introduced to the engine, and an LNT diagnostic tool configured to model or monitor available capacity of the LNT. The control system is configured such that when the LNT diagnostic tool identifies that the available capacity of the LNT has reached a predetermined threshold and the engine diagnostic tool indicates that a rich purge is not possible, the EGR is operated in high pressure mode. The engine diagnostic tool may be implemented through a link with a telematics module provided within the engine, and may record and process data relating to journeys taken and the vehicles location.

Description

IMPROVEMENTS IN OR RELATING TO EXHAUST GAS TREATMENT
This invention relates to improvements in or relating to exhaust gas treatment systems for use on diesel vehicles and, in particular, to improving the performance of the Lean NOx Trap.
It is known to provide a Lean NOx Trap (LNT) as part of the exhaust treatment for a diesel vehicle. The LNT comprises a NOx adsorber that is designed to reduce oxides of nitrogen emitted in the exhaust gas. The adsorbent may be barium oxide (BaO) or barium carbonate (BaC03) and it is configured to catch the NO and N02 molecules present in the exhaust gas, by converting to form barium nitrate (Ba(N03)2). Once substantially all of the barium oxide or barium carbonate has been converted to form barium nitrate, the trap is effectively full and cannot trap further NOx compounds.
In order to regenerate the trap, it is necessary to clear the trap of all of the absorbed NOx. This is typically achieved through a “rich purge” during which the engine is run with an excess of hydrocarbons for a short time so that the level of hydrocarbons in the exhaust is increased. The hydrocarbons in the exhaust, or carbon monoxide or hydrogen cause the nitrate to disintegrate thus restoring the adsorber to be able to trap further NOx compounds.
However, a “rich purge” can only be carried out under certain engine conditions. If these conditions are not met, the LNT trap can become full and cannot trap further NOx compounds. The resulting NOx in the exhaust gas stream may exceed the stringent limits set by the Euro 6.2 and US Federal Tier 2 Bin 5 regulations governing acceptable levels of pollutants in vehicle exhaust gas streams.
It is against this background that the present invention has arisen.
According to the present invention there is provided a control system for a diesel engine including an exhaust gas recirculation (EGR) system configured to be operable in either one of a high pressure mode and a low pressure mode and a Lean NOx Trap (LNT); the control system comprising: at least one engine diagnostic tool configured to model or monitor at least one characteristic of the engine indicative of the suitability of running a rich purge; a hydrocarbon flow controller configured to control the rate at which hydrocarbons are introduced to the engine; and an LNT diagnostic tool configured to model or monitor available capacity of the LNT; wherein the control system is configured such that when the LNT diagnostic tool identifies that the available capacity of the LNT has reached a predetermined threshold and the engine diagnostic tool indicates that a rich purge is not possible, the EGR is operated in high pressure mode.
The invention proposes to switch from low pressure EGR (LPEGR) to high pressure EGR (HPEGR) during conditions where the LNT is approaching full capacity and the engine is unable to undertaken a rich purge to convert the stored NOx. There are various reasons why a vehicle may be unable to perform a rich purge and these include, but are not limited to: exhaust temperatures that are too low to provide sufficient conversion; insufficient torque due to low speed driving; prolonged idling and/or extremely transient driving.
By switching from LPEGR to HPEGR mode the LNT capacity will increase and result in reduced NOx slippage from the LNT. Switching from LPEGR to HPEGR will also result in higher exhaust temperatures which may contribute to more optimal NOx conversion. Increasing the NOx storage capacity by switching to HPEGR also allows the vehicle more time to be driven in more optimal conditions for a rich purge.
The LNT diagnostic tool may comprise a sensor configured to measure the NOx incident on the LNT. The NOx sensor may be located within the LNT to measure the NOx as it becomes incident on the trap. Alternatively or additionally, the NOx can be measured upstream of the LNT, either in conjunction with other exhaust gas treatment modules or at the exit of the diesel engine itself.
The LNT diagnostic tool may comprise a sensor configured to measure the NOx downstream of the LNT. When the LNT approaches capacity NOx slip may occur and this can be measured by a NOx sensor downstream of the LNT.
The LNT diagnostic tool may comprise a tool to model the available capacity of the LNT on the basis of at least one of the following: exhaust composition based on measure engine data conducted during calibration phase and measured parameters during the vehicle operation such as air flow, boost pressure and fuel flow; run time of the LNT; temperature of the LNT; and fuel composition used. In some embodiments, the diagnostic tool models the available capacity of the LNT. This modelling may be purely theoretical or it may be based on measurements other than NOx. The modelling may be very simple and relate only to the run time of the LNT since its last rich purge. In some embodiments, additional layers of measured data from other parts of the engine may be included in the modelling. The composition of the fuel used will influence the rate at which the LNT becomes full. For example, the rate of exhaustion of the adsorber will differ if the vehicle is running on an ethanol based biofuel rather than a standard hydrocarbon diesel and therefore this information can be combined with the run time to give a modified schedule for purging the LNT.
The engine diagnostic tool may comprise an exhaust gas temperature sensor. The temperature of the exhaust gas must exceed a predetermined threshold before a rich purge can be undertaken. Therefore one of the simplest implementations of the engine diagnostic tool may be the data obtained from an exhaust gas temperature sensor.
The engine diagnostic tool may comprise a device for recording and processing the data obtained from the exhaust gas temperature sensor. Exceeding the predetermined threshold for a short time, at the end of a journey would not be suitable for a rich purge and therefore the data from the temperature sensor may be stored and integrated over time to confirm that a rich purge should be possible as the exhaust gas temperature has remained over the predetermined threshold for a predetermined time.
The engine diagnostic tool may comprise a device for recording and processing data relating to journeys undertaken. This device can be used to predict suitability of a given journey for a rich purge. For example, if the daily commute is always a short journey in sub optimal driving conditions, then a journey commencing at this time and including prolonged idling is clearly not an appropriate journey on which to attempt a rich purge. Conversely, a regular journey that is just long enough for a rich purge and has just sufficient high torque and steady high speed driving to facilitate a rich purge can be identified on the basis of past behaviour. This identification on the basis of past behaviour enables a proactive initiation of the rich purge which can take place earlier in the journey than would potentially be the case for a diagnostic tool based purely on measured real time conditions.
The engine diagnostic tool may be implemented through a link with a telematics module provided within the vehicle. The telematics module may include relevant data such as the vehicle’s location, the identity of the driver and the intended journey planned through the satellite navigation system. Much of this information, already collected for other purposes, may be helpful in determining the suitability of undertaking a rich purge of the LNT. LNTs have NOx conversion characteristics defined mainly by temperature, although the physical configuration of the LNT will also have some impact. Driving conditions that cause the temperature of the gases entering the LNT to fall outside of the LNT’s operating window, risk compromising the vehicle’s emissions profile. For example, at low speed driving cycles, the LNT is colder than required to provide sufficient NOx conversion.
Diesel vehicles equipped with low pressure EGR (LPEGR) will increase the space velocity of the exhaust gases passing through the LNT. This reduces the NOx storage capacity meaning that, when operated in LPEGR mode the LNT will reach capacity more quickly than if the EGR is operating in high pressure mode.
The NOx storage capacity is reduced because the exhaust gas temperatures will be higher when the LNT is operated in HPEGR mode and this means that the temperature of the exhaust gases will be closer to the optimum temperature for NOx absorption. Furthermore, if the LNT is situated before the lower pressure EGR take off point, the exhaust flow is increased as it will include the gas that has been recirculated through the EGR. In contrast, the LNT is often situated after the EGR take off point in HPEGR systems. This increased exhaust gas flow will increase the velocity of the gas within the LNT and thereby reduce the effectiveness of storage.
The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which:
Figure 1 is a schematic illustrating the steps used by the control system of the present invention.
Firstly, at step 100, the available capacity of the LNT is monitored or modelled. This step asks the question: has a predetermined threshold been reached?
This threshold indicates the point at which a rich purge would be preferable in order to ensure optimum operation of the LNT. The threshold may be 75% of full capacity, 80%, 85%, 95% or even 99% of full capacity. The threshold may be altered depending on the vehicle’s history. For example, if a very high percentage of a vehicle’s driving takes place on motorways, autobahn or freeways, then the threshold can be set high, for example 95%, on the basis that conditions would be right for a rich purge most of the time and therefore the threshold can safely be set high.
Conversely, if the majority of a vehicle’s driving takes place in the city and is characterised by prolonged idling and extensive low torque driving, then the threshold will be set low, for example 75%, in order to allow time for a journey in which a rich purge may be carried out before the LNT is completely full.
In order for this system to fail safe, the threshold will initially be set low and will only be raised once a plurality of successful cycles have been executed.
Determining whether the LNT has reached the predetermined threshold can be achieved through sensing the NOx upstream of the LNT and then calculating, based on the predicted efficiency of the adsorber in the LNT, the remaining available capacity within the LNT. Alternatively or additionally, this can be achieved through sensing the NOx downstream of the LNT to identify NOx slip, i.e. NOx that has passed through the LNT unconverted. Alternatively or additionally, this can be achieved by modelling the expected state of the LNT based on the time since the last rich purge, the temperature of the exhaust gas or modelled composition of the exhaust gas.
The diagnostic tool that models or monitors the available capacity of the LNT may combine more than one of the above mentioned inputs in order that, if one sensor or data set were to be corrupted or absent, then the available capacity of the LNT could continue to be monitored.
Until the predetermined threshold is reached, the “NO” loop illustrated in Figure 1 returns the system to continue to model or monitor the state of the LNT.
When the predetermined threshold is reached, the “YES” route takes the system forward to the next question, namely, can a rich purge be safely undertaken? A rich purge can only be undertaken when the exhaust temperature exceeds a certain threshold value. The threshold value will depend on the LNT technology used, both in terms of the catalyst selected and the flow configuration of the LNT design, but it is typically within the range of 250°C to 500°C. This can be achieved under continuous driving conditions, i.e. no prolonged idling and additionally preferably at relatively high torque.
The suitability of a rich purge can be identified through a combination of different data inputs, either real time physical inputs from one or more sensors situated in different parts of the engine or using historical data recorded from various sources. All combinations and permutations of data and analysis may be referred to generally as a diagnostic tool. The diagnostic tool may be implemented through the vehicle’s existing telematics module which may include GPS data, driver data, fuel data (biofuel or standard hydrocarbon diesel) amongst many others.
If a rich purge can be undertaken then the control system proceeds through the “YES” loop to step 400 which is a rich purge.
If a rich purge cannot be undertaken then the control system proceeds through the “NO” loop to step 300 which is changing the EGR to operate in high pressure mode.
Whilst the EGR is operated in high pressure mode, the diagnostic tools monitoring or modelling the engine behaviour continue to review the status of the engine to identify when a rich purge can take place.
It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.

Claims (8)

1. A control system for a diesel engine including an exhaust gas recirculation (EGR) system configured to be operable in either one of a high pressure mode and a low pressure mode and a Lean NOx Trap (LNT); the control system comprising: at least one engine diagnostic tool configured to model or monitor at least one characteristic of the engine indicative of the suitability of running a rich purge; a hydrocarbon flow controller configured to control the rate at which hydrocarbons are introduced to the engine; and an LNT diagnostic tool configured to model or monitor available capacity of the LNT; wherein the control system is configured such that when the LNT diagnostic tool identifies that the available capacity of the LNT has reached a predetermined threshold and the engine diagnostic tool indicates that a rich purge is not possible, the EGR is operated in high pressure mode.
2. The control system according to claim 1, wherein the LNT diagnostic tool comprises a sensor configured to measure the NOx incident on the LNT.
3. The control system according to claim 1 or claim 2, wherein the LNT diagnostic tool comprises a sensor configured to measure the NOx downstream of the LNT.
4. The control system according to claim 1, wherein the LNT diagnostic tool comprises a tool to model the available capacity of the LNT on the basis of at least one of the following: run time of the LNT, temperature of the LNT, fuel composition used.
5. The control system according to any one of claims 1 to 4, wherein the engine diagnostic tool comprises an exhaust gas temperature sensor.
6. The control system according to claim 5, wherein the engine diagnostic tool further comprises a device for recording and processing the data obtained from the exhaust gas temperature sensor.
7. The control system according to any one of claims 1 to 6, wherein the engine diagnostic tool comprises a device for recording and processing data relating to journeys undertaken.
8. The control system according to any one of claims 1 to 7, wherein the engine diagnostic tool is implemented through a link with a telematics module provided within the vehicle. The telematics module may include relevant data such as the vehicle’s location, the identity of the driver and the intended journey planned through the satellite navigation system. Much of this information, already collected for other purposes, may be helpful in determining the suitability of undertaking a rich purge of the LNT.
GB1520810.1A 2015-11-25 2015-11-25 Improvements in or relating to exhaust gas treatment Withdrawn GB2544762A (en)

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US20040182068A1 (en) * 2003-03-18 2004-09-23 Jing Sun Method and apparatus for estimating oxygen storage capacity and stored NOx in a lean NOx trap (LNT)
JP2008175100A (en) * 2007-01-17 2008-07-31 Toyota Motor Corp Exhaust gas recirculation device for internal combustion engine
US20100070153A1 (en) * 2008-09-16 2010-03-18 International Truck Intellectual Property Company, Llc Engine Idle Control Using GPS Telematics

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Publication number Priority date Publication date Assignee Title
US20040182068A1 (en) * 2003-03-18 2004-09-23 Jing Sun Method and apparatus for estimating oxygen storage capacity and stored NOx in a lean NOx trap (LNT)
JP2008175100A (en) * 2007-01-17 2008-07-31 Toyota Motor Corp Exhaust gas recirculation device for internal combustion engine
US20100070153A1 (en) * 2008-09-16 2010-03-18 International Truck Intellectual Property Company, Llc Engine Idle Control Using GPS Telematics

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111042956A (en) * 2019-12-26 2020-04-21 潍柴动力股份有限公司 EGR flow fault judgment method, device and equipment
CN111042956B (en) * 2019-12-26 2021-02-23 潍柴动力股份有限公司 EGR flow fault judgment method, device and equipment

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