GB2513614A - Method of operating a lean NOx trap in an internal combustion engine - Google Patents

Abstract

Disclosed is a method of operating a Lean NO Trap (LNT) 285 in an exhaust pipe 275 of an internal combustion engine 110. The method comprises the steps of calculating a NOx quantity stored in the lean NOx trap 285, calculating a NOx mass flow downstream of the lean NOx trap 285, calculating a NOx storage ratio between the NOx quantity stored and a NOx limit capacity of the lean NOx trap 285 and calculating a tail pipe NOx emission ratio between the NOx mass flow downstream of the lean NOx trap 285 and a tail pipe NOx emission limit. The calculated ratios are used to determine a parameter representative of the lean NOx trap 285 status. A threshold of the parameter representative of the lean NOx trap 285 status ratio is calculated as a function of an age of the lean NOx trap 285 and of an engine 110 operating point. A DeN0x request to purge the NOx trap is generated if the parameter is greater than the threshold. An associated apparatus, computer program and engine controller or also disclosed.

Description

MBTHOD OF OPERATING A LEAN NO TRAP IN AN INTERNAL

COMBUSTION ENGINE

TEcHNIcAL FIELD

The present disclosure relates to a method of operating a Lean NQ Trap in an Internal Corrbustion Engine.

It is known that exhaust gas after-treatment of an Internal Cortustion Engine, for example a Diesel engine, may be provided, among other devices, with a Lean NQ< Trap (LNT) which represents a cost efficient alternative to SCR (Selective Catalytic Reduction).

A Lean NO Trap (LNT) traps nitrogen oxides (NOv) contained in the exhaust gas and is located in the exhaust pipe upstream of a Diesel Particulate Filter (DPF) In fact, a LNT is a catalytic device containing catalysts, such as Rhodium, Pt and Pd, and adsorbents, such as barium based elements, which provide active sites suitable for binding the nitrogen oxides (NO) contained in the exhaust gas, in order to trap them within the device itself.

Lean NO Traps (LNT) are subjected to periodic regeneration processes or events, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NO) from the LNT.

For this reason, Lean NO Traps (LNT) are operated cyclically, for example by switching the engine from a lean burn operating mode to a rich operating mode, in order to perform a regeneration event also referenced as a INOX regeneration.

Generally speaking, internal combustion engines are currently operated with multi-injection patterns, namely for each engine cycle, a train of injection pulses is performed typically, starting from a S pilot injection pulse and following a main injection pulse, eventually terminating with after and post injections.

The number of impulses of the train of impulses and their timing is dependent on the combustion mode. After injections may be used, for example but not exclusively, to achieve the needed temperature for LNT regeneration events. Fuel after-injections are fuel injections in a cylinder of the engine that occur after the Top Dead Center (Tm) of the piston.

It is also known that DeNQ regeneration efficiency and cost depend on the engine operating point. The benefit corning from a DeN depends on the status of the Lean NO,< Trap itself and on the driving conditions.

Physical parameters related to the LNT status are only partially representative of the appropriateness of a DeNO regeneration from the point of view of the global NO efficiency: external factors such as driving conditions and engine-out emissions play an important role and have to be considered when the possibility of a DeNOX has to be evaluated. With current regulations approaching more random driving cycle for emission homologation, DeNOX request logics using only physical parameters or only driving conditions are not suited to ensure that the NQ (and other pollutants) emission limits are respected by the LNT applications in every situation.

A known logic for a DeNOX Request uses the information coming from a known Physical Model of the LNT with a variable representing NO,1 absolute storage which is modified in order to obtain a marginal DeNO,1 frequency reduction according to the driving conditions. This logic compares the absolute NO storage quantity (corrected with the factors mentioned before) with a variable representing a NO storage capacity of the LNT and requires a DeNO regeneration if the ratio between these two variables, namely the relative NO storage, is above a calibratable threshold. In any case, a DeNO.X request is not generated if the NO,, storage capacity is below a minimum value.

This known approach has the following limits.

The NO,{ storage efficiency of a LNT can be very different at the same relative storage and at the same U1T temperature, since it depends also on exhaust mass flow, sulphur load and ageing level of the catalyst.

A NO,, Storage/NQ< Capacity logic such as the one described above doesn't take these factors into account.

In fact, depending on the amount of NO that enters the LNT, the optinal condition in which a DeNO,< can be executed might vary, even at the same ratio between NO,, storage and NO capacity.

The driving conditions and their variation can lead to a low DeNQ< efficiency or to a previous natural NO,, desorption before the NQ< storage/NOX capacity criterion generates a DeNO,, request, making this method unable to maintain an acceptable system efficiency.

An object of an errbodiment of the invention is to provide a logic that is able to contine physical information representing the status of the LNT and the external conditions that define the potential benefit of a DeNQ.

A further object of an embodiment of the invention is to prcvide a strategy that takes into account conditions in which NO,< Relative Storage has not reached the limit value but the NO efficiency is very low, for exaniple due to very high space velocity.

Still another object of an embodiment of the invention is to improve the performance of the LNT with a view to the respect of emission regulations even with non-predictable driving cycles.

Mother object is to provide an enhanced strateg9 for LNT management improving the N performance of the catalyst without using complex devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle.

Another object of the present disclosure is to meet these goals by means of a simple, rational and inexpensive solution.

These objects are achieved by a method, by an engine, by an apparatus, by an automotive system, by a computer program and a computer program product, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SURY

An embodiment of the invention provides a method of operating a Lean NO,, Trap in an exhaust pipe of an Internal Coritustion Engine, the method comprising the steps of: -calculating a NO,, quantity stored in the Lean NO,, Trap, -calculating a NO,, mass flow downstream of the Lean NO,, Trap, -calculating a NO,, storage ratio between the NO,, quantity stored and a NO,, liinit capacity of the Lean NO,, Trap, -calculating a tail pipe NO,, emission ratio between the NO,, mass flow downstream of the Lean NO,, Trap and a tail pipe NO,, emission limit, -using the calculated ratios to determine a parameter representative of an Lean NO,, Trap status; -calculating a threshold of the parameter representative of the Lean NO,, Trap status ratio as a function of an age of the Lean NO,, Trap and of an engine operating point; -generating a DeNO,, request if the value of the parameter is greater than the threshold.

11⁄2n advantage of the invention is that it creates a logic to manage a DeNO,, request that takes into account all the physical parameters and external conditions that have an impact on the NQ emission at the LNT outlet.

By controlling the LNT working conditions from different aspects, the DeN request manager implemented according the above errUoodiment of the invention, is able to fulfill the needs coming from new requlation cycles and emission limits, exploiting the technical properties of the Lean NO Trap in an efficient way.

The DeNO,. request manager has a nodular structure that allows to exclude the impact of each parameter, in case a simplified approach is needed, for example during development activity, when the influence of a single parameter has to be analyzed, or for applications where it might be sufficient to use less inputs to request a DeNQ.

the NO,. mass flow downstream of the Lean N0 Trap anSuggerirei di inserire, qui come altrcve, la definizicne di "Reference NOx Mass Flow downstream of the LNT, here called Tail Pipe NOx E»=üssion Limit", per chiarire che si confrontano due misure della stessa quantitá.

According to a further eritodirnent of the invention, the NO,. quantity stored in the Lean NO,. Trap and the NO,. mass flow downstream of the Lean NO,. Trap are calculated by means of a physical model of the Lean NO,. Trap that receives as input a NO,. Mass flow measured or estimated upstream of the Lean NO, Trap and a correction factor depending on a desired DeNO,. regeneration frequency.

n advantage of this erribodiment is that it corrects the value of the NO,. Mass flow upstream of the Lean NO,. Trap in order to reduce in an optimized way the DeNO,. frequency taking into account that any DeN regeneration procedure has a cost in terms of fuel consumed.

According to another embodiment of the invention, the NO,. limit capacity is calculated as a function of a NO,. storage capacity of the Lean NO,. Trap multiplied by a limit factor, the limit factor being a function of a temperature and of a sulphur load of the Lean NO,. Trap.

An advantage of this embodiment is that it allows to take into account the fact that the efficiency of the Lean NO Trap depends on exhaust mass flow, sulphur load and ageing level of the LNT.

According to another embodiment of the invention, the tail pipe NO emission limit is calculated as a function of a combustion mode of the Internal Combustion Engine.

An advantage of this embodiment is that it allows to take into account the driving conditions and their variation over time, factors that can lead to a low DeNOX efficiency or even to a natural NO,< desorption.

According to still another embodiment of the invention, the parameter representative of a Lean NO, Trap status is determined by means of a map that receives as input the NO storage ratio and the tail pipe NO emission ratio.

Pn advantage of this embodiment is that it allows to evaluate the possibility of a DeNO regeneration considering the filling status of the catalyst and the emission outlet and weighting the two factors according to the needs.

According to a further embodiment of the invention, a check may be made before the generation of a DeNO request in order to determine if the Lean NQ Trap has a NO storage efficiency higher than a predefined threshold thereof and, if the check is positive, the DeNO request is not actuated.

An advantage of this embodiment is that it allows to avoid a DeNO regeneration in all cases in which the LNT has a high efficiency, avoiding therefore an unnecessary fuel consumption associated to a DeNQ1 regeneration event.

According to a further errbodimerit of the invention, a check may be made before the generation of a!DeNO request in order to determine if the Lean NQ Trap has a relative NO storage level lower than a predefined threshold thereof and, if the check is positive, the DeNQ< request is not actuated.

Pn advantage of this embodiment is that it allows to avoid a DeNO regeneration in all cases in which the LNT has a low relative NO storage level, avoiding therefore an unnecessary fuel consumption associated to a DeNQ< regeneration event.

According to still another embodiment of the invention, a DeNOX request is actuated if the parameter is greater than the threshold for a predetennined interval of time.

An advantage of this embodiment is that it allows to consider only the stable DeNO requests, namely to avoid initiating a DeNO,< regeneration procedure if the DeNO manager according to the various embodiments of the invention oscillates rapidly between an ON or OFF state of the request.

Another ertodiment of the invention provides an apparatus for operating *a Lean NOx Trap in an exhaust pipe of an Internal Combustion Engine, the apparatus comprising: -means fpr calculating a NO quantity stored in the Lean NO Trap, -means for calculating a NO mass flow downstream of the Lean NQ Trap, -means for calculating a NO,. storage ratio between the NO,. stored quantity and a NQ, limit capacity of the Lean NO,. Trap, -means for calculating a tail pipe NO,. emission ratio between the NO,. mass flow downstream of the Lean NO,. Trap and a tail pipe NO,.

emission limit, -means for using the calculated ratios to determine a parameter representative of an Lean NO,. Trap status, -means for calculating a threshold of the parameter representative of the Lean NO,. Trap status ratio as a function of an age of the Lean NO,. Trap and of an engine operating point, -means for generating a DeNC,. request if the parameter is greater than the threshold.

According to another aspect of the invention, the apparatus is provided with means for calculating the NO,. quantity stored in the Lean NO,. Trap and the NO,. mass flow downstream of the Lean NO,. Trap are using a physical model of the Lean NO,. Trap that receives as input a NO,. Mass flow measured or estimated upstream of the Lean NO,. Trap and a correction factor depending on a desired DeNO,. regeneration frequency.

An advantage of this aspect is that it corrects the value of the NO,.

Mass flow upstream of the Lean NO,. Trap in order to reduce in an optimized way the DeNO,. frequency taking into account that any DeNO,.

regeneration procedure has a cost in terms of fuel consumed.

According to another aspect of the invention, means are provided to calculate the NO,. limit capacity as a function of a N storage capacity of the Lean NO,. Trap multiplied by a limit factor, the limit factor being a function of a terrperature and of a sulphur load of the Lean NQ Trap.

An advantage of this aspect is that it allows to take into account the fact that the efficiency of the Lean NO,< Trap depends on exhaust mass flow, sulphur load and ageing level of the LNT.

According to another aspect of the invention, means are provided to calculate the tail pipe NO emission limit as a function of a combustion mode of the Internal Combustion Engine.

An advantage of this aspect is that it allows to take into account the driving conditions and their variation over time.

According to still another aspect, means are provided to determine the parameter representative of a Lean NO Trap status by means of a map that receives as input the NO,( storage ratio and the tail pipe NO emission ratio.

An advantage of this aspect is that it allows to evaluate the possibility of a DCNOX regeneration considering the filling status of the catalyst and the emission outlet and weighting the two factors according to the needs.

According to a further aspect, means are provided to perform a check before the generation of a DeNO,< request in order to determine if the Lean NO,{ Trap has a NO storage efficiency higher than a predefined threshold thereof and, if the check is positive, the DeNOX request is not actuated.

An advantage of this aspect is that it allows to avoid a DeNOX regeneration in all cases in which the LNT has a high efficiency, avoiding therefore an unnecessary fuel consumption associated to a DeNO,. regeneration event.

According to a further aspect of the invention, means are provided to perform a check before the generation of a DeNO request in order to determine if the Lean NO,. Trap has an absolute NO,. storage level lower than a predefined threshold thereof and, if the check is positive, the DeNO,. request is not actuated.

An advantage of this aspect is that it allows to avoid a DeNO,< regeneration in all cases in which the LNT has a low relative NO,.

storage level, avoiding therefore an unnecessary fuel consumption associated to a DeNOX regeneration event.

According to still another embodiment of the invention, means are provided to actuate a DeNOX request if the parameter is greater than the threshold for a predetermined interval of time.

An advantage of this aspect is that it allows to consider only the stable DeMO, requests, namely to avoid initiating a DeNO,. regeneration procedure if the DeNO,. manager according to the various embodiments of the invention oscillates rapidly between an ON or OFF state of the request.

Another embodiment of the invention provides an automotive system comprising an internal combustion engine managed by an engine Electronic Control Unit, the engine being connected to an air intake duct and to an exhaust pipe, the Electronic Control Unit being configured to: -monitor a NO,. quantity stored in the Lean MO, Trap, -monitor a N01< mass flow downstream of the Lean NO Trap, -calculate a NO,{ storage ratio between the NO,{ stored quantity and a NO& limit capacity of the Lean NO Trap, -calculate a tail pipe N emission ratio between the NQ mass flow downstream of the Lean NQ Trap and a tail pipe NO emission limit, -use the calculated ratios to determine a parameter representative of an Lean NO Trap status, -calculate a threshold of the parameter representative of the Lean NO, Trap status ratio as a function of an age of the Lean NO Trap and of an engine operating point, -generate a DeNQ< request if the parameter is greater than the threshold.

According to another aspect of the invention, the Electronic Control Unit is configured to calculate the NQ quantity stored in the Lean NO Trap and the NO mass flow downstream of the Lean NOK Trap using a physical model of the Lean NO, Trap that receives as input a NO Mass flow measured or estimated upstream of the Lean NO Trap and a correction factor depending on a desired DeNOX regeneration frequency.

Pn advantage of this aspect is that it corrects the value of the NO Mass flow upstream of the Lean NO Trap in order to reduce in an optimized way the OeNQ frequency taking into account that any CeNQ< regeneration procedure has a cost in terms of fuel consumed.

According to another aspect of the invention, the ECU is configured to calculate the NO limit capacity as a function of a NO storage capacity of the Lean NO,. Trap multiplied by a limit factor, the Unit factor being a function of a temperature and of a sulphur load of the Lean NQ Trap.

Ni advantage of this aspect is that it allows to take into account the fact that the efficiency of the Lean NO, Trap depends on exhaust mass flow, sulphur load and ageing level of the LNT.

According to another aspect of the invention, the ECU is configured to calculate the tail pipe N0 emission limit as a function of a combustion mode of the Internal Combustion Engine.

An advantage of this aspect is that it allows to take into account the driving conditions and their variation over time.

According to still another aspect, the ECU is configured to determine the parameter representative of a Lean NO,< Trap status by means of a map that receives as input the N0 storage ratio and the tail pipe N0 emission ratio.

An advantage of this aspect is that it allows to evaluate the possibility of a DeN0 regeneration considering the filling status of the catalyst and the emission outlet and weighting the two factors according to the needs.

According to a further aspect, the ECU is configured to perform a check before the generation of a DeNQ request in order to determine if the Lean NO Trap has a NO storage efficiency higher than a predefined threshold thereof and, if the check is positive, the DeN0 request is not actuated.

An advantage of this aspect is that it allows to avoid a DeNQ regeneration in all cases in which the LNT has a high efficiency, avoiding therefore an unnecessary fuel consumption associated to a DeNO, regeneration event.

According to a further aspect of the invention, the ECU is configured to perform a check before the generation of a DeNQ request in order to determine if the Lean NO Trap has an absolute NQ storage level lower than a predefined threshold thereof and, if the check is positive, the DeNO request is not actuated.

I\xi advantage of this aspect is that it allows to avoid a DeNO regeneration in all cases in which the LNT has a low relative N storage level, avoiding therefore an unnecessary fuel consumption associated to a OeNO,{ regeneration event.

According to still another er±odixnent of the invention, the ECU is configured to actuate a DeNO request if the parameter is greater than the threshold for a predetermined interval of time.

Pu-i advantage of this aspect is that it allows to consider only the stable INQ requests, namely to avoid initiating a DeNOX regeneration procedure if the DeNQ manager according to the various ertodinients of the invention oscillates rapidly between an ON or OFF state of the request.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an internal corrbustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

BRIEF DESCRIPTICt'! OF THE DRAWINGS The various embodiments will now be described, by way of example, with reference to the accompanying drawings, wherein like numerals denote like elements, and in which: Figure 1 shows an automotive system; Figure 2 is a cross-section of an internal combustion engine belonging to the automotive system of figure 1; Figure 3 is a schematic representation of the main components of the automotive system employed in the various embodiment of the invention; Figure 4 is a graph representing NQ< storage efficiency as a function of NO relative storage in a LNT according to a prior art logic; Figure 5 is a graph representing various N0 storage efficiency curves as a function of NQ relative storage in a LNT according to different LNT conditions; Figure 6 is a schematic representation of the main logic involved in the various embodiments of the present invention; Figure 7 is a schematic representation of a logic for determining a corrected inputs for further calculations of the various embodiment of the present invention; Figure 8 is a schematic representation of a logic for determining a series of limits for the variables involved in the various ertodirnent of the present invention; Figure 9 represents a logic for calculating suitable ratios for indicating the status of the Lean NO Trap and of a map for determining a parameter correlated to a 0eN0, request; Figure 10 is a schematic representation of a logic for calculating a threshold above which a DeNQ request is generated; and Figure 11 is a schematic representation of a logic for limiting and debouncing a possible a DeN0, request.

DETAIlED DESCRIPTICV Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses.

Some embodiments may include an automotiye system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperateS with the piston 140 to define a conbustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chanter 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid conuunicatiOn with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cain phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the antient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other e1todiments, a forced air system such as a turbocharger 230, having a compressOr 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270.

This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatrnent devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems.

Furthermore, in Figure 1. in the exhaust pipe 275 an aftertreatlfleflt device comprising a Lean NOx Trap 285 and a Diesel particulate Filter 295 is represented.

Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300. In other embodiments, a lQw pressure EGR may also be present.

The automotive system 100 may further include an electronic control unit (ECU) 450 in coinnunication with one or more sensors and/or devices associated with the ICE 110. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the [CE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature senscr 350, a combustion pressure senscr 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 45Q, this apparatus may include a digital central processing unit (CPU) in communication with a memory system, or data carrier 460, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may entody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

More specifically, Figure 3 shows a schematic representation of the main components of the automotive system 100 employed in the various entodiruent of the invention.

In Figure 3 the engine 110 is represented having the air intake duct 205 and the compressor 240 rotationally coupled to variable geometry turbine 250 having actuator 290.

In the exhaust pipe 275 an aftertreatment device is provided comprising a Lean N0 Trap 285 and a Diesel Particulate Filter 295.

Furthermore, a temperature sensor 520 and a NO,, concentration sensor 510 upstren of the Lean NQ Trap 285 are also provided, the mentioned sensors being connected to the ECU 450 to send signals therein.

Figure 4 is a graph representing NO,, storage efficiency as a function of NO,, relative storage in a LNT according to a prior art logic.

In this case the NO,, storage efficiency is represented by curve A and, in the prior art logic, is considered a function only of the relative quantity of NQstored in the LNT.

Therefore, if the LNT is progressively filled with NO,, until it reaches the exemplary value of 0.8 of NO,, relative storage, then NO,, storage efficiency decreases along curve A until it reaches a certain value B. However, in a real case and as considered in the various entodinents of the invention, the NOD. storage efficiency of a LNT depends also on tNT ageing, on sulphur storage and space velocity giving rise therefore to different efficiency curves depending on the particular conditions of the LNT, such as curves A' or A''.

For a given the exemplary value of 0.8 of NC relative storage, depending on which curve actually represents the status of the UJT, a different NQ storage efficiency value B' or B'' can be calculated, as represented in Figure 5.

Figure 5 represents also a predefined NQ storage efficiency threshold LNTeff that is useful, as explained in the following description, to set a limit over which a DeNOX regeneration request, even if generated by the logic of the various ervbodiments of the invention, is not actuated because the LNT still has a high efficiency and therefore does not need a costly DeNO regeneration.

In the same fashion, in Figure 5 it is also represented an absolute NQ storage level threshold LNTcp1 below which a DeNOX regeneration request is not actuated because the LNT does not yet have a significant amount of NQ stored therein.

Figure 6 is a schematic representation of the main logic involved in the various errodiments of the present invention.

In particular, this logic is excressed by different modules: in this way, each variable input is playing its role only in one module; this structure allows a LNT manager designer to be able to easily remove the impact of one input through calibration, when needed.

In Figure 6, a first block 600 represents the physical inputs that are used in known physical models of the Lean NO,. trap.

In particular, known physical models of the Lean NO,. trap may take into account variables such as LNT temperature, LNT mass flow, S sulphur load, NO,. mass flow upstream of the LNT, ageing of the LNT and eventually other parameters.

The value of these of these parameters may be measured by corresponding sensors and/or calculated by means of mathematical models.

The output of the Physical Inputs block 600 can be expressed in tern of modeled NO,. quantity stored and NO,. mass flow downstream of the LNT and of DeNO,. Manager correction factors.

In particular, the DeNQ Manager correction factors are applied to the physical model in order to alter these information according to DeNQ frequency reduction purposes, namely depending on a desired DeN regeneration frequency, as expressed by Corrected Inputs block 610.

A Reference Limits block 620 uses the modeled NO,. Capacity and defines capacity limits for NO,. quantity stored in the LNT as a function of LNT temperature and sulphur load.

The same block defines a tail pipe NO,. emission limit as a function of the various combustion modes provided by the engine.

The tail pipe NO,. emission limit may not exceed a target defined taking into account engine-out emission regulations.

A Ratios Calculation block 630 uses the outputs of Corrected Inputs block 610 and of the Reference Limits block 620, creating a ratio for each of the modeled variables considered, namely calculates a N0,{ storage ratio between the NQ quantity stored and the NQ< limit capacity of the Lean N0 Trap and calculates a tail pipe NOM emission ratio between the N0 mass flow downstream of the Lean NOK Trap and a tail pipe NO emission limit.

A Ratios Combination block 640 combines the ratios calculated previously to determine a parameter LNTstatus representative of a Lean NQ Trap 285 status, namely a IJeNOX Request Ratio.

A Ratio Thresholds block 650 calculates a threshold LNTstatustnr of the parameter representative of the Lean N Trap 285 status as a function of an age of the Lean NQ Trap 285 and of an engine 110 operating point.

Finally, a DeNOX request is generated if the parameter LNTstatuS representing a OeNQ. Request Ratio is greater than the threshold LNTstatus.

As a consequence of the generation of a OeNQ request, a DeNQ regeneration event is initiated.

As it is known, IN0X regeneration event of the Lean N0 Trap 285 may be operated, for example, by switching the engine from a lean burn operation to a rich operation.

In order to avoid an excessive number of DeNOX regeneration events which may impact negatively on fuel consumption, a series of checks may be provided.

In particular, a Limit and Dthouncing Logic block 670 introduces calibratable delays for the edge rising and edge falling of the DeNOK Request, as well as boundary conditions on maximum NO storage efficiency and minimum relative NO storage level of the LNT suitable for generating a DeNQ regeneration request.

As it is known, with the expression "edge rising" it is intended a change of state of a Boolean variable from 0 to 1. The opposite change of state is designed as "edge falling". Therefore an edge rising of a DeNOX Request variable signals the request of a DeNO regeneration, while an edge falling of a DeNOX Request variable signals the interruption of a DeNO regeneration.

More in particular, according to the debouncing logic, a DeNQ< request is actuated if the parameter LNTstatus representing a DeNQ< Request Ratio is greater than the threshold LlvTstatus for a predetermined interval of time.

On the contrary, the actuation of a generated DeNOx request is delayed if a DeNO regeneration start inhibition procedure is activated for a predetermined interval of time.

Also, before the generation of a DeNQ request, a check may be made in order to determine if the Lean NQ Trap 285 has a NO,. storage efficiency LNTeff higher than a predefined threshold thereof LNTeff and, if the check is positive, the DeNOX request is not actuated.

Furthermore, a check may be made before the generation of a DeNQ{ request in order to determine if the Lean NOX Trap 285 has an absolute NO,. storage level LNTcap lower than a predefined threshold thereof LNTcap and, if the check is positive, the DeNO request is not actuated.

Figure 7 is a schematic representation of the logic of the Corrected Inputs block 610.

In this block the NO,, quantity stored in the Lean NQ, Trap 285 and the NQ( mass flow downstream of the Lean NQ Trap 285 are calculated (blocks 730,740) by means of a physical nodel (block 720) of the Lean NO,, Trap 285 that takes as input a NO,, Mass flow value (block 700) measured upstream of the Lean NO,, Trap 285 and a correction factor (block 710) dependent on a desired DeNO,, regeneration frequency.

The NO,, Mass flow value may be measured by means of the NO,, concentration sensor 510 upstream of the Lean NO,, Trap 285 or may be estimated by means of a mathematical or statistical model.

Figure 8 is a schematic representation of the logic of the Reference Limits block 620.

In the Reference Limits block 620, a Limit Capacity (block 810) for the LNT is calculated as the NO,, Storage Capacity (block 800) multiplied by a Limit Factor that is an output of a Limit Factor map function of LNT temperature (block 820) and of sulphur load (block 830).

At the same time, a Limit Tail Pipe Emission block 850 defines a tail pipe NO,, emission limit by means of a map that is a function of an engine combustion mode (block 840), since each normal combustion mode has a target in terms of emission reduction, the target being defined in order to comply with engine-rout emissions regulations.

Figure 9 represents a logic for calculating suitable ratios for representinq the status of the Lean NO Trap and of a map for determining a parameter correlated to a DeNO request.

In particular, the Ratios Calculation block 630 divides the outputs of Corrected Inputs block 610 with the outputs of Reference Limits block 620 generating a NO,. storage ratio (block 695) and a tail pipe NO,. emission ratio (block 697), both ratios being important to represent the status of the Lean NO Trap 285.

Therefore a NO storage ratio is calculated as the ratio between the NO quantity stored and a NO,. limit capacity of the Lean N0, Trap 285.

Also, a tail pipe NO,. emission ratio is calculated as a ratio between:the NO,. mass flow downstream of the Lean NO,. Trap 285 and a tail pipe NO,. emission limit.

More in particular, in the Ratios Corrbination block 640, the NO,.

storaqe ratio (block 695) and the tail pipe NO,. emission ratio (block 697) are inputted into a Ratio Cothination Map 760 that outputs a parameter LNTstatus representative of a Lean NO,. Trap status. (DeNOX Request Ratio block 770) In particular, in each cell of the Ratio Coitination Map 760, a value of the parameter LlVTstatus is contained, whereby such parameter expresses the need of a DeNO,. regeneration considering the filling status of the LNT catalyst and the engine-out emissions, weighting the two factors according to the needs.

Figure 10 is a schematic representation of a logic for calculating a threshold LNTstatus above which a DeNO,. request is generated.

The Ratio Thresholds block 650 calculates a value LNTstatustnr of the threshold above which a DeNO Request is generated: this threshold is expressed as the output of two maps, one map for a new (block 940) and one other map for an aged (block 950) Lean NO< Trap, whereby both maps are engine point dependent.

The engine point may be expressed as a function of engine speed (block 900) and engine torque (block 910) and of a Lean NO Trap temperature (block 920) The two maps are interpolated (block 960) according to a calibratable curve, function of the LNT Ageing (block 930).

Figure 11 is a schematic representation of a logic for limiting and debouncing a possible DeNQ request.

In the Limit and Debouncing Logic block, edge rising (block 1030) and edge falling (block 1040) of the DeNOX Request are delayed to avoid frequent switches between one condition and the other. A debouncing time ON (block 1040) is used to consider only the stable DeNO,. Requests, and debouncing time OFF (block 1060) is used to delay the DeNQ request removal in case an Inhibition is not allowing a DeNQ Start.

Moreover, as mentioned above, limitations to DeNOX request (block 1020) are set in order to avoid a DeNO,< regeneration in the conditions in which no benefit is granted after a regeneration, for example due to too high NO,< storage efficiency (block 1010) or too low relative NO storage level (block 1010) of the LNT.

The various entodiments of the invention create a logic to manage a DeNQ< request that takes into account all the physical parameters and external conditions that have an impact on the NQ emission at the LNT outlet.

Controlling the LNT working conditions from different aspects, the DeNQ. Manager is able to fulfill the needs corning from new regulation cycles and emission Units, exploiting the technical properties of the Lean NOx Trap in an efficient way.

The modular structure allows to exclude the impact of each parameter, in case a simplified approach is needed, during development activity (when the influence of a single parameter has to be analyzed) or for applications where it might be sufficient to use less inputs to request a DeNO.

In general, the impacts of the DeNQ< request method of the various eithodiment of the invention are the following.

First, even if the various errbodiments of the invention may increase the calibration effort, the whole structure has a modular quality in the sense that each additional functionality can be easily deactivated.

The various errtodirnents of the invention allow to optimize the DeNOX strategy and increase the potential of the LNT after treatment system (compared to the more expensive SCR system) also with incoming driving cycles (Worldwide harmonized Light vehicles Test Cycle (WLTC) or Real-world Driving Emissions (ROE)), considering that the driving conditions of the ROE cycle are not predictable, while driving conditions for the NEEC are predictable.

On the customer satisfaction standpoint, the described embodiments guarantee a more efficient usage of the DeNOx events, aiming to reduce the additional fuel consumption needed to ensure the storage and conversion of NQ< emitted by the engine, choosing the most effective conditions, from both the catalyst and the vehicle points of view, to perform a DeNOX regeneration.

While at least one exemplary embodiment has been presented in the foregoing surmtiary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing sunnary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents, REFEN NThERS automotive system internal corrffustion engine (ICE) engine block 125 cylinder cylinder head camshaft piston crankshaft 150 combustion chamber cam phaser fuel injector fuel rail fuel pump 190 fuel source intake manifold 205 air intake duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 290 exhaust aftertreatinent device 285 Lean NO,, Trap 290 VGT actuator 295 DEE' 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow sensor 350 manifold pressure and temperature sensor 360 corrbustion pressure sensor 390 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 460 data carrier 510 NO concentration sensor upstream 520 temperature sensor 600 block 610 block 620 block 630 block 640 block 650 block 660 block 670 block 680 block 695 block 697 block 700 block 710 block 720 block 730 block 740 block 750 block 760 map 800 block 810 block 820 block 830 block 840 block 850 block 900 block 910 block 920 block 930 block 940 block 950 block 960 block 1000 block 1010 block 1020 block 1030 block 1040 block 1050 block 1060 block aa