GB2495750A - A Method for Operating a Lean NOx Trap of an Internal Combustion Engine - Google Patents

Abstract

A method for operating a lean nitrogen oxide (NOx) 281 trap located in an exhaust system 270 of a diesel internal combustion engine 110 equipped with an electronic control unit 450 . The method comprises the steps of monitoring a value of a quantity of sulphur oxides (SOx) accumulated in the lean NOx trap (LNT) 281, preferably by use of an estimation model, requesting a DeSOx regeneration phase of the lean NOx trap if the value of the accumulated sulphur oxides quantity exceeds a predetermined threshold value thereof, evaluating a condition of non-compliance of the DeS0x regeneration phase of the lean NOx trap, such as checking if a value of an engine operating parameter is outside a predetermined range, and inhibiting the DeS0x regeneration phase of the lean NOx trap, if the condition of non-compliance is met.

Description

METHOD FOR OPERATING A LEAN NO, TRAP OF AN INTERNAL COMBUSTION

ENGINE

TECHNICAL FIELD

Method for operating a Lean NO, Trap of an exhaust system of an internal combustion engine.

BACKGROUND

A diesel engine is normally provided with an exhaust gas after treatment system, for de- grading and/or removing the pollutants from the exhaust gas emitted by the Diesel en-gine before discharging it in the environment.

The after treatment system generally comprises an exhaust pipe for leading the exhaust gas from the Diesel engine to the environment; the exhaust pipe comprises a Lean NO, Trap (LNT) for trapping nitrogen oxides (NO,). The Lean NO, Trap 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 con-tained in the exhaust gas, in order to trap them within the device itself.

The Lean NO, Trap is subjected to periodic regeneration processes to release and re-duce the trapped nitrogen oxides (NO,).

Due to the sulphur contained in the diesel fuel and in the engine lubricating oil, the ex-haust gas produced by the diesel engines generally contains also sulphur oxides (SO,), which can be responsible for a progressive poisoning of the Lean NO, Trap. Conse-quently, in addition to the periodic NO, regeneration process or phase, the Lean NO, Trap must be subjected to a desulphurization process, also referred as DeSO, regenera-tion or desuiphurization process, so as to reduce the SO, accumulated and restore its original efficiency.

The DeSO, regeneration phase of the Lean NO, Trap is conventionally obtained by: -heating up the Lean NO Trap at a temperature, typically up to 600-650°, which is normally higher than the temperature needed for the regeneration of NO, and -operating the Diesel engine in a rich combustion mode i.e. operating the diesel engine with a combustion air fuel ratio lower than the stoichiornetric value (lambda < 1).

The OeSO regeneration phase requires high temperatures and a rich atmosphere.

Those conditions are very expensive from a fuel consumption point of view as they are normally achieved by injecting additional fuel in the combustion chambers. Furthermore because of the reduced amount of oxygen associated with a rich atmosphere, the pro-duction of sulphur Hydroxide, H2S, inside the Lean NO Trap would increase. This side effect is strongly unwelcome because of the bad smell of H2S. In order to facilitate SO2 production and avoid H2S production as much as possible the solution provided in the prior art is to alternate lean and rich stages during the DeSO regeneration phase until the process is completed, in particular: -a DeSO lean stage, i.e. a stage occurring in a lean combustion mode wherein very late injections burn in the Lean NO Trap and cause the temperature to in- crease; during this stage the quantity of oxygen in the Lean NO Trap is re-stored, the HC accumulated is burned off, the production of SO2 is facilitated, but only partial sulphate reduction can be obtained; -a DeSO rich stage, i.e. a phase occurring in a rich combustion mode, wherein additional fuel, i.e. after quantity injections, is injected to create the rich atmos-phere required for the effective desuiphuñzation process.

It has been noticed that in some working conditions the DeSO regeneration process does not occur efficiently. Those conditions vary depending on the stage of the process, i.e. rich or lean stage. Furthermore some of the components involved in the DeSO rege-neration process might be damaged by the extremely high temperatures needed.

It is therefore an object of an embodiment of the invention disclosed to identify the work- ing conditions and engine component constraints that might affect the DeSO regenera-tion process.

Another object of an embodiment of the invention disclosed is to define a method for op-erating a Lean NO Trap comprising a strategy to ensure that the DeSO regeneration process occurs only when optimal working conditions are satisfied.

In this way it is possible to increase the efficiency of the DeSO regeneration process, to optimize the fuel combustion and to limit potential damages to the engine components.

Another object is to provide a method for operating a Lean NO Trap in a rational way without using complex devices and by taking advantage of the computational capabilities of the Electronic Control Unit (ECU) of the vehicle.

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

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

SUMMARY

These and other objects are achieved by the embodiments of the invention having the features contained in the independent claims. The dependent claim relates to preferred or particularly advantageous aspects of the embodiments of the invention.

In particular, an embodiment of the invention provides a method for operating a Lean NO Trap located in an exhaust system of an internal combustion engine the method comprising the steps of: -monitoring, e.g. directly measuring or estimating, a value of a quantity of sulphur oxides accumulated in the Lean NO Trap, -requesting a DeSO regeneration phase of the Lean NO Trap, if the value of the accumulated sulphur oxides quantity exceeds a predetermined threshold value thereof, -checking if a condition of non-compliance of the DeSO regeneration phase of the Lean NO Trap, which is unrelated to the level of sulphur oxides accumu-lated in the Lean NO Trap, is met, -inhibiting the DeSO regeneration phase of the Lean NO Trap, if the condition of non-compliance is met.

Thanks to this solution the DeSO regeneration phase is carried on only with optimal op- erating conditions the efficiency of the regeneration process is improved, the fuel con-sumption is reduced and the operating components, which might be negatively affected by the physical conditions required by the regeneration process are protected.

According to an aspect of an embodiment of the present invention the quantity of sulphur oxides accumulated in the Lean NO Trap (281) is estimated using an estimation model.

Thanks to this solution it is possible to monitor the value of sulphur oxides accumulated in the Lean NO Trap without any additional components.

According to an aspect of an embodiment of the present invention the inhibition of the DeSO regeneration phase can comprise the steps of: -preventing a DeSO lean stage from starting, or -interrupting the DeSO lean stage if it has already started, or -preventing a DeSO rich stage from starting when the DeSO lean stage has al-ready started, or -interrupting the DeSO rich stage, if it has already started.

The non-compliance conditions are in fact tested before the beginning of the each stage, the DeSO lean stage and the DeSO rich stage, to avoid starting them when the operat-ing conditions are not optimal. Such conditions are also tested during the execution of the stages themselves so as to interrupt the regeneration phase when optimal working conditions are no more satisfied.

According to another aspect of an embodiment of the present invention the step of pre-venting a DeSO lean stage, interrupting the DeSO lean stage, preventing a DeSO rich stage, preventing a DeSOK rich stage, interrupting the DeSO rich stage comprise the step of regulating, according to a predetermined combustion mode, the position of an engine actuator chosen among an EGR valve, a throttle body, a swirl valve, a VGT actu-ator, fuel injectors, a common rail high pressure fuel pump.

Thanks to this solution by controlling the position of the engine actuator the ECU pro-vides for the appropriate combustion mode.

According to another aspect of an embodiment of the present invention the step of checking if the non-compliance condition is met comprises the steps of: -assessing an actual value of at least an engine operating parameter, -establishing that the non-compliance condition is met, if the actual value of the engine operating parameter is outside a predetermined range of allowable val-ues thereof.

In this way an appropriate criteria and relative threshold, determined during a calibration phase, are associated to each engine operating parameter so as to improve the efficien- cy of the regeneration phase by maintain the engine operating parameter within prede-termined boundaries.

According to another aspect of an embodiment of the present invention the engine oper-ating parameter can be chosen among many engine operating parameters which could affect the efficiency either of the DeSO lean stage or of the DeSO rich stage In particu-Jar the engine operating parameters comprise an engine fuel temperature, an engine bulk temperature, an exhaust gas temperature, a temperature measured upstream the turbocharger turbine and a temperature measured downstream and upstream the Lean NO trap, an ambient temperature, an ambient pressure, a fuel level, an engine torque, an engine speed and an air to fuel ratio in the exhaust gas.

Thanks to this solution the efficiency of the regeneration process is increased by monitor- ing the ambient pressure and ambient temperature, the fuel temperature, then the struc- tural and thermal limitations of turbocharger turbine and of the Lean NO trap are res- pected by monitoring the temperature upstream the turbocharger turbine and the tem- perature upstream or downstream the Lean NO Trap, and the fuel consumption is opti-mized by monitoring the fuel level. Furthermore the efficiency of the regeneration process is guaranteed by allowing the regeneration process only when the engine is run-ning and the engine torque is not equal to zero and when the exhaust gas contains an appropriate air to fuel ratio.

According to another aspect of an embodiment of the present invention the step of checking if the non-compliance condition is met comprises the steps of: -detecting an engine component operating constraint which affects the DeSO regeneration phase -establishing that the non-compliance condition is met if the engine component operating constraint has been detected.

Thanks to this solution the regeneration process is executed when the engine compo-nents involved in the regeneration process are operating without any fault.

According to another aspect of an embodiment of the present invention the engine com-ponent is chosen among a fuel injector, an air fuel ratio (AFR) sensor and a turbocharger compressor.

By way of example a fuel injector operating constraint which affects the DeSO regenera-tion is an inhibition of the post injections, and a AFR sensor operating constraint which affects the DeSO regeneration is a fault of the AFR sensor and a turbocharger com-pressor operating constraint which affects the DeSO regeneration is an activation of an anti-surging compressor strategy.

Thanks to this solution the regeneration process is taken to completion only with optimal conditions of the relevant engine components.

According to another aspect of an embodiment of the present invention the step of checking if the non-compliance condition is met comprises the step of establishing that the non-compliance condition is met if the engine is not in a running state operating ac-cording to an engine torque control.

In particular, an engine running not according to torque control can occur when the en- gine is not running autonomously but is driven by an alternator or when the engine is op-erated according to an engine speed control. In this situation the regeneration process would not be executed in optimal conditions and the efficiency of the process would be reduced.

According to another aspect of an embodiment of the present invention the method com-prises the further steps of: -monitoring a time elapsed from a beginning of a DeSO lean stage; interrupting the DeSO regeneration phase if the monitored time exceeds a pre-determined threshold value thereof.

Thanks to this solution the fuel consumption is reduced by avoiding lingering in the De-SO. lean stage, which is expensive from a fuel consumption point of view and does not provide an actual reduction of SO,, if a predetermined time interval has been exceeded.

S According to another aspect of the present invention the step of requesting or inhibiting a DeSO regeneration phase comprises changing an engine combustion mode by regulat-ing the position of one or more engine actuators among an exhaust gas recirculation valve, a throttle body, a variable geometry turbocharger actuator a fuel injector, a corn-mon rail high pressure fuel pump.

The methods according to the invention can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the methods de-scribed above,.

The method can be also embodied as an electromagnetic signal, said signal being mod-ulated to carry a sequence of data bits which represent a computer program to carry out all steps of the method.

The present invention further provides an internal combustion engine equipped with a Lean NO Trap, an Electronic Control Unit, a memory system associated to the Electron- ic Control Unit, means for determining the level of SO, and a computer program accord-ing stored in the memory system.

According to an aspect of the invention the means for determining the level of SO corn-prise a SO level sensor located in the Lean NO Trap.

The present invention further provides an apparatus for operating a Lean NO Trap lo-cated in an exhaust system of an internal combustion engine the apparatus comprising: -means for monitoring a value of a quantity of sulphur oxides accumulated in the Lean NOTrap, -means for requestihg a DeSO regeneration phase of the Lean NO Trap, if the value of the accumulated sulphur oxides quantity exceeds a predetermined threshold value thereof, -means for checking whether a condition of non-compliance of the DeSO regen-eration phase of the Lean NO Trap is met, -means for inhibiting the DeSO regeneration phase of the Lean NO Trap, if the condition of non-compliance is met.

This embodiment of the invention has the same advantage of the method disclosed above, particularly that the DeSO regeneration phase is carried on only with optimal op- erating conditions, the efficiency of the regeneration process is improved, the fuel con-sumption is reduced and the operating components, which might be negatively affected by the physical conditions required by the regeneration process are protected.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 and 2 are schematic representations of an automotive system comprising an in-ternal combustion engine: Figure 3 is a schematic representation of the steps of an embodiment of the method dis-,I'joc Figure 4 to 7 are schematic representations of aspects of embodiments of the method disclosed.

DETAILED DESCR!PTION Preferred embodiments will now be described with reference to the enclosed drawings.

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 de-fining 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 combustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chamber 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 communication with a high pressure fuel pump 180 that increase the pressure of the fuel received 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 cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft S 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. In other embodiment, a swirl valve(s) (not shown in Fig.1) may be provided upstream the air intake port(s) 210. An air intake duct 205 may provide air from the ambient environ- ment to the intake manifold 200. In other embodiments, a throttle body 330 may be pro-vided to reguJate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a turbocharger compressor 240 rotation- ally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increas- es the pressure and temperature of the air in the duct 205 and manifold 200. An intercoo-er 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 (VOT) 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 after-treatment devices 280. The after-treatment devices may be any device configured to change the composition of the exhaust gases. Some examples of after-treatment de- vices 280 include, but are not limited to, catalytic converters (two and three way), oxida-tion catalysts, lean NOx Traps 281, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and a diesel particulate filters. Other embodiments may include an ex-haust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. Naturally after-treatment devices 280 the lean NOx Traps 281 and relative sensors can combined with different layouts compared to that of figure 1. An EGR system could also be coupled between exhaust pipes after turbine and intake pipes before compressor (Low Pressure EGR). 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.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication 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 ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coo-lant 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 or temperature sen- sors 430, air fuel ratio (AFR) sensors 431, an EGR temperature sensor 440, and an ac-celerator pedal position sensor 445. By way of example the AFR sensors can comprise a UEGO sensor, a NO, sensor or a lambda sensor. Furthermore, the ECU 450 may gen-erate 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 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is confi-gured to execute instructions stored as a program in the memory system, and send and receive signals tolfrom the interlace bus. The memory system may include various sto-rage types including optical storage, magnetic storage, solid state storage. and other non-volatile memory. The interface bus may be configured to send, receive, and mod-ulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

Going back to the exhaust system 280, the Lean NO, Trap 281 is a catalytic device suit-able for trapping nitrogen oxides (NOx) contained in the exhaust gas. The exhaust gas produced by the diesel engine and passing through the Lean NO, Trap generally con-tains sulphur oxides (SO,) which can be responsible for a progressive poisoning of Lean NO, Trap. Furthermore the sulphur contained in the fuel can easily oxidize as Barium and Aluminium Sulphates, causing a further reduction of the efficiency of the Lean NO, Trap 281 in terms of NO storage. A desulphurization process is therefore necessary to restore the efficiency of the Lean NO Trap 281.

In more details the Lean NO Trap 281 may be operated according to the following phases: -a loading phase, in which during normal mode of operation, the LNT 281 acts as trap for NO and for oxides such as HG and CO in the exhaust gas, -a DeNO, regeneration phase in which short periods of rich fuel mixture (with lambda < 1) are used to reduce to N2 the NO, in the Lean NO, Trap 281 in order to recover its storage capacity, -a DeSO regeneration phase in which a dedicated combustion with rich fuel mix-ture (lambda c 1) and high temperature, typically in a range that can extend from 600 to 700°, is used for recovering the Lean NO, Trap 281 from sulphur deposition. This phase becomes necessary when the level of SO in the Lean NO, Trap 281 exceeds a predetermined SO, threshold value, which is set during a preliminary calibration phase. The actual level of SO, in the Lean NO Trap 281 can be estimated for example using estimation models stored in the mem- ory system 451 based on, among other parameters, the current fuel consump-tion, oil consumption and driving style.

Of the three mentioned phases, the last one, i.e the DeSOx regeneration phase used to remove the sulphur, requires normally high temperatures and a rich atmosphere and is normally operated by alternating a DeSO, lean stage and a DeSO, rich stage until the process is completed.

The DeSO, lean stage is an ancillary phase to the DeSO, rich stage. It is used to limit some of the downsides of a prolonged rich phase, like production of H2S, while the actual desulphurization process occurs only during the DeSO, rich stage. During the DeSO, lean stage it is important to maintain high temperature to perform efficiently the IJeSO, regeneration process.

In particular a DeSO, lean stage is first started, i.e. the internal combustion engine 110 is operated in a lean combustion mode. After a certain time interval the DeSO, lean stage stops and a DeSO rich stage starts, i.e. the internal combustion engine 110 is operated in a rich combustion mode. The lambda value needed for the rich or lean combustion mode can be controlled by any suitable method, using for example, in specific conditions fuel after injections. In addition the ECU 450 operates the change of combustion mode by forcing the engine actuators to work in predetermining operating conditions. In particu-lar in order to execute or interrupt or preventing or inhibiting the DeSO lean stage or the DeSQ rich stage of the DeSOx regeneration phase the ECU 450 is configured for regu-lating the position of one or more engine actuators among, for example, the EGR valve 320, the throttle body 330, the swirl valve, the VGT actuator 290, the fuel injector 150, the common rail high pressure fuel pump 180. A predetermined combustion mode is as-sociated to predetermined position of the engine actuators consequently depending on the predetermined combustion mode required the ECU 450 regulates the position of the actuators. The alternation between DeSO rich and lean stages ends when the level of SOD, in the Lean NO Trap 281, as estimated by the ECU 450, reaches a value below a predetermined calibrated threshold value. Alternatively the process can be protracted for a fixed predetermined time interval, estimated using estimation models stored in the memory system 451 and corresponding to the minimum amount of time needed for the desulphurization process to reduce the SO, value in the Lean NO Trap 281 below a predetermined calibrated threshold value.

The method for operating the Lean NO Trap 281 according to an embodiment of the in-vention will now be described in more details with reference to Figures 3,3a.

During the operation of the internal combustion engine 110 the level of SO in the Lean NO Trap 281 is constantly monitored (block 1) by the ECU 450 using means for deter-mining the level of SQ. In particular, the level of SQ in Lean NO Trap 281 can be measured using a sensor 283, connected to the ECU 450, and located in the Lean NO Trap 281 or it can be estimated using estimation models stored in the memory system 451. Such estimation models estimate the level of SQ as a function of, among other pa-rameters1 the fuel consumption, the oil consumption, the driving styles.

When the monitored level of SQ is above (block 2) a predetermined threshold value Th1, determined in a calibration phase, a request for a DeSO regeneration phase is started.

The DeSO regeneration phase comprises the DeSO lean stage and the DeSO rich stage which are alternately executed until the level of SQ in the Lean NO Trap is below a second threshold Th2, also determined in a calibration phase.

As soon as a DeSO regeneration phase is requested the ECU 450 starts checking the non-compliance conditions in order to allow the start of the DeSO lean stage only in op-timal engine working conditions (block 3). If any of these nan-compliance conditions is met the DeSO regeneration process does not start while the internal combustion engine 110 operates as normal. In fact these conditions, which will be described in more details below, prevent the DeSO lean stage from starting and for clarity will be called from now on lean stage "preventing" conditions (block 3) since if any of them is met the DeSO lean stage is prevented from starting. If none of lean stage "preventing" conditions is met then the DeSO lean stage can start (block 4), the ECU 450 operates the engine in a lean combustion mode, with consequent increase of the quantity of oxygen in the Lean NO Trap 281.

Next additional non-compliance conditions are checked to verify that the working condi- tions continue to be appropriate for the DeSO lean stage (block 5). If any of these addi-tional non-compliance conditions is met the DeSO lean stage, and therefore the DeSO regeneration process, is interrupted (block 6). These conditions, which will be described in more details below, are called herein lean stage "interrupting" conditions (block 4) since if met they cause the interruption of the OeSO lean stage.

Next the ECU 450 checks the so called rich stage "preventing" conditions (block 7), which will be described in more details below, to verify if there is any reason preventing the start of the DeSO rich stage. If any of these rich stage preventing" conditions is met the DeSO rich stage does not start. On the other hand if none of these rich stage "pre-venting" conditions is met when the time estimated for the duration of the lean stage has elapsed (blockS) the DeSO rich stage is started (block 9).

Once the DeSO rich stage has started the ECU 450 checks the rich stage "interrupting" conditions (block 10), which will be described in more details below. If any of them is met the DeSC rich stage and therefore the entire DeSO regeneration phase is interrupted (block 11). On the other hand if none of them is met, once the time estimated for the du-ration of the rich stage has elapsed (block 12) the actual level of SO in the Lean NO Trap 281 is compared to a second threshold value Th2 (block 13), estimated in during a calibration phase, to decide whether to terminate the DeSO regeneration process.

lIthe actual level SQ in the Lean NO, Trap 261 is below the second threshold value Th2 the DeSC regeneration process ends otherwise the process starts again from the lean stage, so that lean and rich stages are alternated according to the method described herein until the desired level of SO in the Lean NO Trap 281 is reached, or until the es-timated time for reaching the desired level of SO, in the Lean NO Trap 281 has elapsed.

Non-compliance conditions, i.e. lean stage "preventing" conditions, lean stage interrupt-ing" conditions, rich stage "preventing" conditions, rich stage "interrupting" conditions, will now be described in more details with reference to figures 4 to 7. For each condition, an operating parameter and/or engine component operating constraint is defined and then it is checked versus a predefined criteria often comprising predetermined calibrated threshold value associated to the operating parameter and/or engine component operat-ing constraint. Threshold values are normally calibrated during a preliminary calibration phase.

In more details figures 4,4a are a schematic representation of block 3 of figure 3, and shows the lean stage "preventing" conditions. The order on which these conditions are tested is not important since each condition is independent from one other and it is suffi-cient that one of these conditions is met to prevent the DeSO, lean stage from starting.

First the DeSO lean stage is prevented from starting if the engine is not running. This condition is checked by monitoring (block 3001) a parameter indicative of the engine state, normally a signal provided by the ECU 450 assuming a predetermined value when the engine is running. in this way the DeSO lean stage is not allowed if the engine is not in a running mode (block 3002), i.e. if the engine is supported by the alternator and is not running autonomously, for example when the user has just started the engine.

Next condition is designed to identify one engine component constraint. In particular the AFR sensor located upstream the Lean NO trap 281 (block 3003), for example, a UEGO sensor or a NO sensor and connected to the ECU 450, is tested to ensure its proper functioning. If the sensor is not providing a lambda signal (block 3004), i.e. a signal pro-viding information on the oxygen concentration, the lean stage "preventing" condition is met. The regeneration process requires a predetermined lambda value to ensure an effi-cient desulphurization process, therefore it is not desirable to remain in the expensive (from a fuel consumption point of view) DeSO lean stage once it is clear that the sen-sors suitable for providing information on the oxygen concentration are faulty, damaged, not working correctly or simply not active.

Next, a parameter indicative of a level of fuel in the fuel source 190 (block 3005), for ex-ample a fuel level value, as measured by a fuel level sensor located in the fuel source 190 and connected to the ECU 450, is compared (block 3006) to a calibrated fuel level threshold value L1 and if the fuel level value is below the calibrated fuel level threshold value L1 the lean stage "preventing" condition is met. In this way the DeSO lean regen- eration phase, which requires an injected fuel quantity higher than the fuel quantity nor-mally injected in standard operation, does not take place if there is not enough fuel in the fuel source 190.

Next, a parameter indicative of an ambient temperature, for example an external air tem- perature value, as measured (block 3007) by a temperature sensor located on the vehi-cle rear mirrors and connected to the ECU 450 is compared (block 3008) to a calibrated first ambient temperature threshold value Tai and if the external air temperature value is below the calibrated first ambient temperature threshold value Tal, once a calibrated hys-teresis window has been taken in consideration, the lean stage "preventing" condition is met. The DeSO lean stage can be negatively affected not only by low external tempera-tures but also by high external temperature, therefore the external air temperature value is also compared (block 3008) to a calibrated second ambient temperature threshold value Ta2, greater than the first ambient temperature threshold value Ta1 If the external air temperature value is above the calibrated second ambient temperature threshold value I, once a calibrated hysteresis window has been taken in consideration, the lean stage "preventing" condition is met.

Next, a parameter indicative of an ambient pressure, for example an external pressure value, as measured (block 3009) by a pressure sensor located in ECU case is compared (block 3010) to a calibrated ambient pressure threshold value Pal and if the external pressure value is below the calibrated ambient pressure threshold value Pai, once a cali-brated hysteresis window has been taken in consideration, the lean stage "preventing" condition is met.

According to another aspect of an embodiment of the present invention parameters in- dicative of an engine temperature are then tested. Those parameters comprise a pa-rameter indicative of an engine bulk average temperature, a parameter indicative of a fuel temperature, a parameter indicative of an exhaust gas temperature upstream the turbocharger turbine 250 and a parameter indicative of an exhaust gas temperature downstream the Lean NO Trap 281.

In particular a parameter indicative of a bulk average temperature, for example an engine bulk temperature value, as measured (block 3005) for example by a metal temperature sensor located on the engine block 120 or by a coolant sensor located in the coolant tank or by a combination of the two sensors each of the sensors connected to the ECU 450, is compared (block 3005) to a calibrated lean stage engine bulk temperature threshold value Tbi and if the engine bulk temperature value is above the calibrated lean stage en-gine bulk temperature threshold value Tbl, once a calibrated hysteresis window has been taken in consideration, the lean stage "preventing" condition is met. The engine bulk temperature value affects the torque equivalence which is critical during the DeSQ re- generation phase to ensure a standard level of drivability. Bulk temperature values out-side a predetermined range, by affecting the drivability, reduce the efficiency of the DeSO regeneration process. In particular engine temperature values influence the en-gine friction. Since friction is normally estimated using known conditions for normal and DaSOx mode a problem couid arise in torque equivalence if the engine temperature val-ues used were not be properly calibrated.

Next, a parameter indicative of a fuel temperature, for example the fuel temperature value, as measured (block 3007) by a fuel temperature sensor located in the fuel source and connected to the ECU 450, is compared (block 3008) to a calibrated fuel tem-perature threshold value T11 and if the fuel temperature value is above the calibrated fuel temperature threshold value Tfl, once a calibrated hysteresis window has been taken in consideration, the lean stage "preventing" condition is met. An high fuel temperature value could in fact have a negative effect on the efficiency of the DeSO lean stage This is due to the fact the DeSO lean stage uses a closed loop control on temperature values measured downstream the Lean NO Trap 281 based on post injections and therefore depending on post injections fuel temperature value. Furthermore the fuel temperature affects the density of the fuel, and an abnormal fuel density value could interfere with the DeSO regeneration phase which is set to operate according to predetermined standard fuel density values.

Next, in order to avoid stressing the structural and thermal limitation of the turbocharger turbine 250 and of the Lean NOx Trap 281, an exhaust gas temperature value upstream the turbocharger turbine 250 and an exhaust gas temperature values downstream Lean NOx Trap 281 are measured and tested against predetermined threshold values.

In particular a parameter indicative of an exhaust gas temperature upstream the turbo-charger turbine 250, for example an exhaust gas upstream turbine temperature value, as measured (block 3009) by a temperature sensor located upstream the turbine 250, in the exhaust manifold, or estimated by the ECU 450 on the basis of the combustion parame-ters connected to the ECU 450 or alternatively as estimated by estimation models stored the memory system 451, is compared (block 301 0) to a calibrated exhaust gas upstream turbine temperature threshold value Tegi and if the exhaust gas upstream turbine tem- perature value is above the calibrated exhaust gas upstream turbine temperature thresh-old value Tegi, once a calibrated hysteresis window has been taken in consideration, the lean stage "preventing" condition is met. If the temperature value upstream the turbine 250 is modelled and used by the ECU 450, this condition has to be checked only if the temperature value upstream the turbine 250 is considered valid by the ECU 450. A too high exhaust gas temperature value upstream the tuibine 250 could damage the turbo-charger turbine 250 itseif with obvious negative consequences on the efficiency of the DeSO lean stage.

Then a parameter indicative of an exhaust gas temperature downstream the Lean NO trap 281, for example an exhaust gas downstream LNT temperature value, as measured (block 3011) by a temperature sensor located downstream the Lean NO Trap 281 for example positioned between the Lean NOx Trap 281 and the Diesel Particulate Filter 280 and connected to the ECU 450, is compared (block 3012) to a calibrated exhaust gas downstream LNT temperature threshold value T2 and if the exhaust gas down-stream LNT temperature value is above the calibrated exhaust gas downstream LNT temperature threshold value Te921 the lean stage "preventing" condition is met. The tem-perature threshold value 1eg21 is set during a calibration time and is equal for example to 800°C. The lean stage is immediately prevented and will not be authorized until the measured temperature drops below a temperature threshold value Teg2.3 set during a calibration phase.

Thanks to this test the DeSO lean stage is prevented from starting when the exhaust gas temperature downstream the LNT 281 is so high as to cause potential damages the Lean NO Trap 281 itself.

Next the exhaust gas downstream LNT temperature value is measured (block 3019) and compared (block 3020) to a calibrated exhaust gas downstream LNT temperature threshold value Teg22 and if the exhaust gas downstream LNT temperature value is above the calibrated exhaust gas downstream LNT temperature threshold value Te92.2 for a calibrated time interval, time interval set during a calibration phase, the lean stage preventing" condition is met. The temperature threshold value 1eg22 is set during a cali-bration time and is equal for example to 720°C. The lean stage is immediately prevented from starting if the threshold temperature is reached during and maintained for a cali- brated time interval. The lean stage will not be authorized until the measured tempera-ture drops below a temperature threshold value T0g2.3 set during a calibration phase.

As already mentioned above, the DeSO lean stage is prevented from staling (block 3021) if the any of the lean stage preventing" conditions is met. In this way the efficiency of the DeSO regeneration phase, which could be negatively affected by extreme work-ing conditions can be guaranteed. If none of the these conditions are met, then the DeSO lean stage is started (block 4).

Lean stage "interrupting" conditions will now be described in more details with reference to Figure 5,5a which are a schematic representation of block 5 of figure 3. The order on which these conditions are tested is not relevant since, as before, they are independent from one other and it is sufficient that one of these conditions is met to interrupt the DeSO lean stage.

The lean stage "interrupting" conditions comprise all conditions previously described and tested as lean stage "preventing" conditions wherein the threshold values are appropri-ately changed to new threshold values calibrated during a preliminary calibration phase.

In this way by continuing to monitor the engine operating parameters and or the engine component operating constraint the method according to an embodiment of the invention guarantees the compliance of the DeSO regeneration process only with optimal prede-fined working conditions.

In particular first the DeSO lean stage is interrupted if the engine is not running (block 5001, 5002).

Next, the AFR sensor located upstream the Lean NO Trap 281 is checked (block 5003) to ensure its proper functioning. Again if the sensor is not providing a lambda signal (block 5004) the lean stage "interrupting" condition is met.

Next, the fuel level value (block 5005) is compared (block 5006) to a calibrated fuel level threshold value L2, different from the fuel level threshold value L1 used in lean stage "preventing" conditions. If the fuel level value is below the calibrated fuel level threshold value L2 the lean stage "interrupting" condition is met.

Next, the external air temperature value (block 5007) is compared (block 5008) to a cali-brated first T33 and second Ta4 ambient temperature threshold values, different from the first Tai and second T ambient temperature threshold values used in lean stage "pre- venting" conditions. If the external air temperature value is outside this range of cali-brated values the lean stage "interrupting" condition is met.

Next, the external pressure value (block 5009) is compared (block 5010) to a calibrated ambient pressure threshold value Pa2, different from the ambient pressure threshold value Pai used in lean stage "preventing" conditions. lithe external pressure value is be-low the calibrated ambient pressure threshold value Pa2, once a calibrated hysteresis window has been taken in consideration, the lean stage "interrupting" condition is met.

Next, the engine bulk temperature value (block 5011) is compared (block 5012) to a cali- brated engine bulk temperature threshold value Tb2, different from the engine bulk tern-perature threshold value (11) used in lean stage "preventing" conditions. lithe engine bulk temperature value is above the calibrated engine bulk temperature threshold value 1b2 once a calibrated hysteresis window has been taken in consideration, the lean stage "interrupting" condition is met.

Next, the fuel temperature value (block 5013) is compared (block 5014) to a calibrated fuel temperature threshold value T, different from the fuel temperature threshold value Tfl used in lean stage "preventing" conditions. If the fuel temperature value is above the calibrated fuel temperature threshold value T12, once a calibrated hysteresis window has been taken in consideration, the lean stage "interrupting" condition is met.

Next, the exhaust gas upstream turbine temperature value (block 5015) is compared (block 5016) to a calibrated exhaust gas upstream turbine temperature threshold value Tegsi different from the exhaust gas upstream turbine temperature threshold value T91 used in lean stage preventing" conditions. If the exhaust gas upstream turbine tempera-ture value is above the calibrated exhaust gas upstream turbine temperature threshold value Tega, once a calibrated hysteresis window has been taken in consideration and the signal is valid, the lean stage interrupting" condition is met.

Next, the exhaust gas downstream LNT temperature value (block 5017) is compared (block 5018) to a calibrated exhaust gas downstream LNT temperature threshold value Teg4-1 which could be set for example to 800°C or it could be different from the exhaust gas downstream LNT temperature threshold value T6921 used in lean stage "preventing" conditions. If the exhaust gas downstream LNT temperature value is above the cali- brated exhaust gas downstream LNT temperature threshold value T4 the lean stage "in-terrupting" condition is met.

The lean stage is immediately interrupted and will not be authorized until the measured temperature drops below a temperature threshold value Teg4.3 set during a calibration phase.

Next, the exhaust gas downstream LNT temperature value (block 5019) is compared (block 5020) to a calibrated exhaust gas downstream LNT temperature threshold value Tey4.2, which could be set for example to 720°C or it could be different from the exhaust gas downstream LNT temperature threshold value Te92.2 used in lean stage "preventing" conditions. If the exhaust gas downstream LNT temperature value is above the cali-brated exhaust gas downstream LNT temperature threshold value Teg4.2 for a calibrated time interval, time interval calibrated during a calibration phase, the lean stage "interrupt- ing" condition is met. The lean stage will not be authorized until the measured tempera-ture drops below a temperature threshold value Te92.3 set during a calibration phase.

Next a parameter indicative of an engine speed, for example the engine speed value as measured by a magnetic pick-up sensor that reads the information from the teeth of the crank wheel and connected to the ECU 450, is measured (block 5021) and compared (5022) to an engine speed threshold value (ES0), determined during a calibration phase.

If the engine speed value is below the calibrated engine speed threshold value ES0 for a calibrated time interval, time interval calibrated during a calibration phase, the lean stage "interrupting" condition is met. Two additional lean stage "interrupting" conditions are then tested to ensure optimal working conditions for DeSO lean stage.

In particular, a time elapsed from the beginning of the DeSOx lean stage is recorded (block 5023). The time measured includes all regeneration times, i.e. for example time spent in warm up phase, time spent on the steady state at high temperature, any rich spikes. If the recorded time exceeds a predetermined threshold time value t1 (block 5024), the lean stage "interrupting" condition is met. As explained above, the DeSO lean stage is only an auxiliary stage supporting and facilitating the actual process of sulphur removal occurring mainly during the DeSO rich stage. Therefore it becomes extremely expensive, from a fuel consumption point of view, to remain in the DeSO lean stage for too long without being able to alternate to the DeSOx rich stage.

Next, a parameter indicative of an authorisation of post injections (block 5025), for ex-ample a post injections authorisation signal provided by the ECU 450, is compared (block 5026) to a post injections authorisation flag to ensure that post injections are au-thorized, authorisation needs to be active for a predetermined calibrated time interval.

The ECU 450 may set post injections authorisation signal to a value different from the post injections authorisation flag if, for example, the fuel injection system management denies the authorisation.

Next, a zero torque flag, a flag set by the ECU 450 and indicating a zero engine torque value, is checked. The aim of this test (block 5027, 5028) is to interrupt the DeSO lean stage in case of long cut off period, i.e. protracted period of zero torque as indicated by an activated zero torque flag. In fact in those situations it would be expensive, from a fuel consumption point of view, to maintain the high temperatures required for the desulphuri- zation process. Because the torque value can change often during driving and in par-ticular the zero torque flag can be activated even in condition different from a real cut off, i.e. for example when the user is changing gears, it is important to monitor the zero torque flag during a predetermined calibrate time interval, generally a relatively small time interval in the range of 1-2 seconds. If the zero torque flag is active during such time interval then it can be assumed that the engine is in a cut off situation. Once the occur-rence of a cut off situation has been recognized, before deciding to interrupt the DeSO regeneration phase, the exhaust gas downstream LNT temperature value, as defined above, is also checked. The exhaust gas downstream LNT temperature value is com-pared (block 5028) to a calibrated exhaust gas downstream LNT temperature threshold value T5, different from the exhaust gas downstream LNT temperature threshold values Teg2, Te94 used in previous conditions, and this condition needs to be met for a second predetermined calibrated time interval. The second time interval is calibrated during a calibration time to ensure that the exhaust gas downstream LNT temperature value stays below the threshold value long enough to indicate stable temperature conditions. Finally a third predetermined time interval is considered and if the zero torque flag is active and the exhaust gas downstream LNT temperature value remains outside the threshold val-ues, the lean stage "interrupting" condition is met.

As already mentioned, it is enough to meet one of the lean stage interrupting" conditions for the ECU 450 to request an interruption of the DeSO lean stage (block 6). If none of the conditions is met the DeSO regeneration process continues and in particular the rich stage preventing" conditions are tested (block 7).

Rich stage "preventing" conditions will now be described in more details with reference to Figure 6 which is a schematic representation of block 7 of figure 3. The order on which these conditions are tested is not relevant since, as before, they are independent from one other and it is sufficient that one of these conditions is met to prevent the DeSO rich stage from starting.

First, the engine buik temperature value (block 7001), as defined above, is compared (block 7002) to a calibrated rich stage engine bulk temperature threshold value Tba, dif- ferent from the engine bulk temperature threshold values used in the lean stage condi-tions (Tbl and Ib2) and if the engine bulk temperature value is above the calibrated rich stage engine bulk temperature threshold value 1b3, once a calibrated hysteresis window has been taken in consideration, the rich stage "preventing" conditions condition is met.

This limit is set to guarantee the DeSO rich stage efficiency that could be negatively af-fected by engine temperature conditions not optimized.

Next the exhaust gas temperature as measured upstream and downstream the LNT 281 are checked to ensure efficiency while complying with the structural and thermal limits of the catalyst.

In particular a parameter indicative of an exhaust gas temperature upstream the Lean NO Trap 281, for example an exhaust gas upstream LNT temperature value, as meas- ured (block 7003) by a temperature sensor located upstream the Lean NO Trap 281 lo-cated in the pipe between the turbine 250 and the Lean NO Trap 281 and connected to the ECU 450, is compared (block 7004) to an upper limit calibrated exhaust gas up-stream LNT temperature threshold value Tegs and a lower limit calibrated exhaust gas upstream LNT temperature threshold value Tegy. If the exhaust gas upstream LNT tem-perature value is outside the range of allowable values defined by the upper Tege and lower Teg7 limit calibrated exhaust gas upstream LNT temperature threshold values, once a calibrated hysteresis window has been taken in consideration, the rich stage "prevent-ing" conditions condition is met.

Next the exhaust gas downstream LNT temperature value (block 7005) is compared (block 7006) to an upper limit calibrated exhaust gas downstream LNT temperature threshold value Tegs and a lower limit calibrated exhaust gas downstream LNT tempera- ture threshold value T099, both thresholds values different from the exhaust gas down-stream LNT threshold value used in the lean mode conditions Te94 If the exhaust gas downstream LNT temperature value is outside the range of allowable values defined by the upper T8 and lower Tegg limit calibrated exhaust gas downstream LNT temperature threshold value, once a calibrated hyst&esis window has been taken in consideration, the rich stage "preventing" conditions condition is met.

The DeSO rich stage is prevented (block 7008) from starting if a Speed Control mode is activated. During operation the internal combustion engine 110 is normally controlled us- ing Torque Control mode wherein a specific torque value is required based on the cur-rent driving style and conditions and the engine is operated by the ECU 450 so as to achieve the required engine torque value. There are situations though, for example when the vehicle is not moving but the engine is running to supply auxiliaries components, like an air conditioning system, when the internal combustion engine 110 is instead con-trolled using Speed Control mode wherein a specific engine speed value is requested and the engine is operated by the ECU 450 so as to achieve the required engine speed value instead of a required engine torque value. In those situation it would less efficient to operate a rich combustion mode, naturally more instable than a typical lean combus-tion.

Next, a parameter indicative of an engine speed, for example the engine speed value as measured by a magnetic pick-up sensor that reads the information from the teeth of the crank wheel and connected to the ECU 450, and a parameter indicative of the engine torque, for example the engine torque value, as estimated by the ECU 450 on the basis of, among others, injected fuel, inlet air and engine friction, are checked (block 7009).

The combination of the engine speed value and the engine torque value defines an en-gine working point in the engine working plan formed by the engine speed values versus the engine toque values. A first working region is defined, comprising the region of the engine working plan delimited by calibrated lower and upper limit engine speed threshold values (ES1, ES2) and calibrated lower and upper engine torque threshold values (ET1, El2). This first working region varies depending on the engine gear, and is independently calibrated during a calibration phase for each engine gear. If the point determined by the measured engine speed value and the measured engine torque value is outside this first working region the rich stage "preventing" conditions condition is met. This test is de-signed to allow the rich stage to occur in engine speed and torque values considered to be optimal.

According to another aspect of an embodiment of the present invention the DeSO rich stage is prevented from starting if a turbocharger compressor anti-surging strategy is ac-tive (block 7011, 7012) or it has not been activated for a calibrated time interval since last activation. This limit is set to avoid the interruption of the anti-surging strategy by impos- ing a DeSOx rich stage. Surges occur when outlet pressure of the turbocharger com-pressor 240 is too high in relation to the flow through the turbocharger compressor 240.

The flow can change rapidly when there is a sudden change in the load that the turbo- charger compressor 240 is expected to deliver. If the surge is not controlled, the com-pressor can be destroyed. An anti-surge control strategy is implemented by the ECU 450 and designed to protect the turbocharger compressor 240 from these surges.

Last, the AFR sensor located upstream the Lean NOx trap 281 is checked (block 7013) to ensure its proper functioning. As for the lean mode conditions if the sensor upstream the Lean NOx trap 281 does not provide a lambda signal (block 7014) the rich stage "preventing" condition is met.

As already mentioned, the fulfilment of just one of the rich mode "preventing" conditions is enough for the ECU 450 to prevent the DeSO rich stage from starting. If none of the conditions is met the DeSO regeneration process continues and in particular the ECU 450 checks if the DeSO lean stage is completed, i.e. the predetermined calibrated time for the DeSO lean stage has elapsed (block 8).

Rich stage "interrupting" conditions will now be described in more details with reference to Figure 7 which is a schematic representation of block 10 of figure 3. The order on which these conditions are tested is not relevant since, as before, they are independent from one other and it is sufficient that one of these conditions is met to interrupt the DeSO rich stage.

JO

All rich stage preventing" conditions, whit the exclusion of the conditions on the anti-surging strategy, are adapted by appropriately changing the calibrated threshold values, and tested as rich stage "interrupting" conditions. In addition new interrupting* conditions are designed based on the signal provided by the AFR sensor.

In particular the engine bulk temperature value (block 10001) is compared (block 10002) to a calibrated rich stage engine bulk temperature threshold value T, different from the engrie buik temperature threshold values used in the lean stage conditions Tbi and Tb2 and the engine bulk temperature threshold value Tb3 used in the rich stage "preventing" conditions, lithe engine bulk temperature value is above the calibrated rich stage engine bulk temperature threshold value TM, once a calibrated hysteresis window has been taken in consideration, the rich stage "interrupting" condition is met. This limit is set to guarantee the DeSC rich stage efficiency that could be negatively affected by engine temperature conditions not optimized.

Next the exhaust gas upstream LNT temperature value (block 10003), is compared (block 10004) to an upper limit calibrated exhaust gas upstream LNT temperature threshold value Tegio and to a lower limit calibrated exhaust gas upstream LNT tempera-ture threshold value T0911, upper and lower exhaust gas upstream LNT temperature threshold values Tegio. Tegn different from upper and lower exhaust gas upstream LNT temperature threshold values Tega, Teg? used in the rich stage "preventing" conditions. If the exhaust gas upstream LNT temperature value is outside the range of allowable val-ues defined by the upper Tegia and lower Tegll limit calibrated exhaust gas upstream LNT temperature threshold values, once a calibrated hysteresis window has been taken in consideration, the rich stage "interrupting" condition is met.

Next the exhaust gas downstream LNT temperature value (block 10005) is compared (block 10006) to an upper limit calibrated exhaust gas downstream LNT temperature threshold value Tegi2 and to a lower limit calibrated exhaust gas downstream LNT tem-perature threshold value T13, both thresholds values different from the exhaust gas downstream LNT threshold value used in the lean stage conditions Teg4 and from the up-per and lower exhaust gas downstream LNT temperature threshold values T8, Tege used in the rich stage "preventing" conditions. If the exhaust gas downstream LNT tempera-ture value is outside the range of allowable values defined by the upper li2 and lower Tegl3 limit calibrated exhaust gas downstream LNT temperature threshold values, once a calibrated hysteresis window has been taken in consideration, the rich stage "interrupt-ing" condition is met.

Next, the DeSOx rich stage is interrupted (block 10007, 10008) if a Speed Control mode is activated.

A second working region in the engine working plan is defined, delimited by a calibrated lower and upper limit engine speed threshold values (ES3, ES4), different from the cali-brated lower and upper limit engine speed threshold values (ES1, ES2) used in the rich mode "preventing" conditions, and calibrated lower and upper engine torque threshold values (ET3, El4) different from the calibrated lower and upper limit engine torque threshold values (ET1, ET2) used in the rich mode "preventing" conditions. Even this sec-ond working region varies depending on the engine gear, and is independently calibrated during a calibration phase for each engine gear. If the point defined by the engine speed value and the engine torque value is outside this second working region the rich stage "interrupting" condition is met (block 10009, 10010).

Next, the AFR sensor located upstream the Lean NO trap 281 is checked (block 10011) to ensure its proper functioning. If the AFR sensor upstream the Lean NO trap 281 does not provide a lambda signal (block 10012) the rich stage "interrupting" condition is met.

Finally, a parameter indicative of the lambda value, for example a lambda signal (block 10017), as provided by sensor placed upstream the Lean NO Trap 281, connected to the ECU 450, is checked (block 10015 and 10016). The DeSO rich regeneration phase requires a predetermined lambda valueto ensure an efficient desuiphurization process.

First if the lambda signal, as provided by the AFR sensor upstream the LNT 261, doesn't reach a predetermined calibrated lambda signal threshold value (A1) after a predeter-mined calibrated time (block 10018) the condition is met. The aim of this condition is to interrupt the DeSO rich stage if the transition from the lean stage to the rich stage has not been performed successfully before a predetermined time limit.

Next the lambda signal, as provided by the AFR sensor upstream the LNT 261, is moni-tored (block 10017). Once the lambda signal is considered steady, i.e. the lambda signal value has been inside a first ranged of allowable values, defined by a first lower and up-per limit lambda value (A2, A3), for a predetermined time interval, if the lambda signal value falls outside a second range of allowable values, defined by a second lower and an upper limit lambda value (A4, A5), the rich stage "interrupting" condition is met. The test on the lambda signal value guarantees the stability of the rich combustion mode, maintain-in9 the lambda signal inside a calibrated predetermined range of values defining optimal conditions for the desulphurization process The fuifliment of just one of these rich mode "interrupting' conditions is enough for the ECU 450 to interrupt the DeSO rich stage (block 11).

While at least one exemplary embodiment has been presented in the foregoing summary 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 summary 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.

REFERENCES

100. Automotive System 110. Internal Combustion Engine 120. Engine Block 125. Cylinder 130. Cylinder head 135. Camshaft 140. Piston 145. Crankshaft 150. Combustion chamber 155. Cam phaser 160. Fuel injector 170. Fuel Rail 180. Fuel Pump 190. Fuel source 200. Intake Manifold 205. Intake duct n4n I4_.I -ii pulL 215. Valve 220. Exhaust Port 225. Exhaust manifold 230. Turbocharger 240. Compressor 250. Turbine 260. Intercooler 270. Exhaust system 275. Exhaust pipe 280-Exhaust after-treatment device 281. Lean NO, Trap 282. Diesel Particulate Filter 283. 50, level sensor 290. VGT actuator 300. EGR system 310. EGR cooler 320. EGR valve 330. Throttle Body 340. Mass airflow and temperature sensor 350. Manifold pressure and temperature sensor 360. Combustion pressure sensor 380. 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 sensors 431. AFR sensors 440. EGR temperature sensor 445. Accelerator pedal position sensor 450. Electronic Control Unit 451. Memory System

Claims (1)

1. <claim-text>CLAIMS1. A method for operating a Lean NO, Trap (281) located in an exhaust system (270) of an internal combustion engine (110) the method comprising the steps of: -monitoring a value of a quantity of sulphur oxides accumulated in the Lean NO Trap (281), -requesting a DeSO, regeneration phase of the Lean NO, Trap (281), if the value of the accumulated sulphur oxides quantity exceeds a predetermined threshold value thereof, -checking whether a condition of non-compliance of the DeSO, regeneration phase of the Lean NO, Trap (281) is met, -inhibiting the DeSO, regeneration phase of the Lean NO, Trap (281), if the condition of non-compliance is met.</claim-text> <claim-text>2. A method according to claim 1 wherein the quantity of sulphur oxides accumulated in the Lean NO, Trap (281) is estimated using an estimation model.</claim-text> <claim-text>3. A method according to claim 1, wherein the inhibiting of the DeSO, regeneration phase comprises the steps of: -preventing a DeSO, lean stage from starting, or -interrupting the DeSO lean stage if it has already started, or -preventing a DeSO, rich stage from starting when the DeSO, lean stage has already started, or -interrupting the DeSO, rich stage, if it has already started.</claim-text> <claim-text>4. A method according to claim 3 wherein the step of preventing a DeSO, lean stage, interrupting the DeSO, lean stage, preventing a DeSO, rich stage, preventing a DeSO rich stage, interrupting the DeSO, rich stage comprise the step of regulat- ing, according to a predetermined combustion mode, the position of one engine ac-tuator chosen among an EGR valve (320), a throttle body (330), a swirl valve, a VGT actuator (290), a fuel injector (160), a common rail high pressure fuel pump (180).</claim-text> <claim-text>5. A method according to claim 1, wherein the step of checking if the non-compliance condition is met comprises the steps of: -evaluating an actual value of an engine operating parameter, -establishing that the non-compliance condition is met, if the actual value of the engine operating parameter is outside a predetermined range of allowa-ble values thereof.</claim-text> <claim-text>6. A method according to claim 6, wherein the engine operating parameter is chosen among an engine bulk temperature, an engine fuel temperature, an exhaust gas temperature, an ambient temperature, an ambient pressure, a fuel level, an engine torque, an engine speed and an air to fuel ratio in the exhaust gas.</claim-text> <claim-text>7. A method according to claim 1, wherein the evaluation of the non-compliance con-dition comprises the steps of: -detecting an engine component operating constraint which affects the DeSO regeneration phase, -establishing that the non-compliance condition is met, if the operating con-straint has been detected.</claim-text> <claim-text>8. A method according to claim 8, wherein the engine component is chosen among a fuel injector (160), an air fuel ratio sensor (431) and a turbocharger compressor (240).</claim-text> <claim-text>9. A method according to claim 1, wherein the evaluation of the non-compliance con-dition comprises the step of establishing that the non-compliance condition is met if the engine is not in a running state operating according to an engine torque control.</claim-text> <claim-text>10. A method according to claim 1 comprising the further steps of: -monitoring a time elapsed from a beginning of the DeSO lean stage; -interrupting the DeSO regeneration phase if the monitored time exceeds a predetermined threshold value thereof.</claim-text> <claim-text>11. A method according to claim 1 wherein the step of requesting or inhibiting a DeSO regeneration phase comprises changing an engine combustion mode by regulating the position of one or more engine actuators among an exhaust gas recirculation valve (320), a throttle body (330), a variable geometry turbocharger actuator (250) a fuel injector (160), a common rail high pressure fuel pump (180).</claim-text> <claim-text>12. A computer program comprising a computer-code suitable for performing the method according to any of the claims from 1 to 11.</claim-text> <claim-text>13. An Internal combustion engine (110) equipped with a Lean NO Trap (281) an Electronic Control Unit (450), a memory system (451) associated to the Electronic Control Unit (450), means for determining the level of SO,, and a computer pro-gram according to claim 12 stored in the memory system (451).</claim-text> <claim-text>14. An Internal combustion engine (110) according to claim 13 wherein the means for determining the level of SQ comprise a SO, level sensor (283) located in the Lean NO Trap (281).</claim-text> <claim-text>15. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 12.</claim-text>