GB2512929A

GB2512929A - Method of controlling an adaptive desulphation process for an internal combustion engine

Info

Publication number: GB2512929A
Application number: GB1306679.0A
Authority: GB
Inventors: Roberto Argolini; Andrea Dutto
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2013-04-12
Filing date: 2013-04-12
Publication date: 2014-10-15
Also published as: GB201306679D0

Abstract

A method of controlling an adaptive desulphation process in an exhaust system of an internal combustion engine, the exhaust system comprising a lean NOx trap. The method comprises calculating S640 a desulphation index 640, whose value correlates to or is proportional to the need of desulphation of the lean NOx trap, estimating S65) a desulphation index threshold 650, as a function of a number of forced desulphation over vehicle lifetime 645, and requesting a desulphation process S660 if said desulphation index is larger than S655 said desulphation index threshold. The desulphation index may be based on a sulphur load 600, a soot load 610, a mission profile 620, ambient temperature 631 and ambient pressure 634. The desulphation index threshold may depend on a desulphation model error, which may be a counter of error-effected desulphation rich events.

Description

METHOD OF CONTROLL/NG AN ADAPTIVE DESULPHATION PROCESS FOR

AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of controlling an adaptive desulphation process for an internal combustion engine. In particular, the method is dedicated to the sulphur regeneration of a lean NOx trap located in the exhaust system of the internal combustion engine.

BACKGROUND

is It is known that the exhaust gas aftertreatment systems of a Diesel engine can be provided, among other devices, with a lean NO trap (hereafter, also LNT).

A LNT is provided for trapping nitrogen oxides NO contained in the exhaust gas and is located in the exhaust line.

A LNT is a catalytic device containing catalysts, such as rhodium, platinum and palladium, 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 are subjected to periodic regeneration processes, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NOr) from the LNT. :i

Due to the presence of supihur into the fuel, the LNT is exposed to the sulphur poisoning, which heavily reduces the NOx storage capacity of the catalyst. In order to re-enable the capability of the aftertreatment system, a desulphation (also called DeSOx s regeneration or simply DeSOx) is needed. The desulphation consists in a fast alternation of lean and rich atmosphere (hereafter, wobbling) at high temperature during engine The DeSOx regeneration is critical from the point of view of thermal degradation of the trap, because it requires high temperature. Moreover, it increases the fuel consumption, because of the additional injected fuel request, which is needed to provide a rich atmosphere at the inlet of the LNT.

Normally, aftertreatment systems also comprise a particulate filter (DPF), which traps particulates and also needs a periodical regeneration phase, to clean the filter. The DeSOx regeneration is linked to the DPF regeneration, because of similar physical conditions: high temperature and rich atmosphere inside both LNT and DPF to guarantee soot burning inside the DPF and sulphur removal inside the LNT, through rich spikes.

Coupling the two regeneration processes, also comparable ageing, performance and maintenance of the whole aftertreatment system is guaranteed.

The current DeSOx regeneration strategy faces the problem that during a certain number of DPF regenerations, the driving conditions are not optimal enough for an efficient desulphation, leading to a very high sulphur content inside the LNT and the consequent worsening of the NOx, HC and CO conversion performance. In fact, only the rich pulses during a desulphation contribute to the sulphur removal and the engine map region in which rich combustion is stable, is quite small. Moreover, the sulphur removed in a rich event is influenced by several parameters, among which there is also the sulphur content already inside the trap.

Therefore a need exists to for a method which is able to identify the conditions that would lead to an effective DeSOx regeneration process, without penalizing the components S ageing.

An object of an embodiment of the invention is to provide a method of controlling an adaptive desulphation strategy, able to evaluate the most appropriate conditions to execute a DeSOx regeneration.

An object of another embodiment of the invention is that the above method also evaluates the most appropriate conditions to force a DPF regeneration and execute a DeSOx regeneration during it.

With another embodiment the object is to provide an apparatus which allows to perform the above method.

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

The dependent claims delineate preferred andfor especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of controlling an adaptive desulphation process in an exhaust system of an internal combustion engine, the exhaust system comprising a lean NOx trap, the method comprising: -calculating a desulphation index, whose value correlates to or is proportional to the need of a desulphation. The desulphation index may be a function of a sulphur load, a soot load, a mission profile, an ambient temperature, an ambient pressure -estimating a desulphation index threshold, as a function of a number of forced desulphation cycles over vehicle lifetime, S -requesting a desulphation process if said desulphation index is larger than said desulphation index threshold.

Consequently an apparatus is disclosed for implementing a method of controlling an adaptive desulphation process, the apparatus comprising: -means for calculating a desulphation index, whose value correlates to or is proportional to the need of a desulphation request, -means for estimating a desulphation index threshold as a function of a number of forced desulphation cycles over vehicle lifetime, -means for requesting a desulphation process if said desuiphation index is larger than said desulphation index threshold.

An advantage of this embodiment consists in the fact that a desulphation process is forced instead of waiting for a DPE natural request, based on a desulphation index which takes into account the most influencing parameters for an effective desuiphation to be actuated. Moreover, the use of a desulphation index threshold, as function of a number of forced desulphation processes over vehicle lifetime, guarantees that the desulphation is not forced in conditions in which it might damage the engine and the aftertreatment.

According to an aspect of the invention, said function between forced desulphation over vehicle lifetime and desulphation index threshold is a direct proportion.

Consequently the means for estimating a desulphation index threshold are configured to perform the estimation when said function between forced desulphation over vehicle lifetime and desulphation index threshold is a direct proportion.

An advantage of this aspect is that as soon as the number of the forced desulphation processes will be growing, the desulphation index threshold will grow as well. Since the function between the number of the forced DeSOx and the DeSOx index threshold is calibratable, it is therefore possible to let the threshold reaches values which can never be overcome by the desulphation index, thus avoiding further forced desulphation processes.

According to another embodiment, said desulphation index threshold depends on a desulphation model error.

Consequently the means for calculating a desulphation index are configured to take into account that said desulphation index threshold depends on a desulphation model error.

An advantage of this embodiment is to take into account the inaccuracy of a model, which estimates the sulphur loading and unloading.

According to an aspect said desulphation model error is a counter of error-affected desulphation rich events.

Consequently the means for calculating a desulphation index are configured to take into account that said desulphation model error is a counter of error-affected desulphation rich events.

Since the sulphur unloading phase happens during rich events, an advantage of this aspect is to consider the number of rich events which have not been performed properly, thus inducing, in the sulphur model, possible over estimations.

According to another aspect, said counter is increased if a desulphation rich time is larger than a predetermined desulphation minimum rich time and is reset if a modeled LNT sulphur quantity is smaller than a predetermined low sulphur quantity threshpld.

Consequently the means for calculating a desulphation index are configured to take into account that said counter is increased if a desulphation rich time is larger than a predetermined desulphation minimum rich time and is reset if a modeled LNT sulphur quantity is smaller than a predetermined low sulphur quantity threshold.

An advantage of this aspect is that the counter of error-affected desulphation rich events takes into account possible desulphation model errors, which have to be expected after a few seconds of a desulphation rich event have elapsed and when the quantity of sulphur inside the LNT is high enough.

According to a further embodiment the desuiphation index is a function of sulphur load, soot load, mission profile, ambient temperature and ambient pressure and is obtained by: -defining a normalized index in a scale 0-1 for each of said sulphur load, soot load, mission profile, ambient temperature and ambient pressure, -assuming a weight index for each of said sulphur load, soot load, mission profile, ambient temperature and ambient pressure, -multiplying each normalized index for the correspondent index weight, -adding the products of said multiplications to obtain the desuiphation index.

Consequently the apparatus for implementing a method of controlling an adaptive desulphation process, further comprises: -means for defining a normalized index in a scale 0-1 for each of said sulphur load, soot load, mission profile, ambient temperature and ambient pressure, -means for assuming a weight index for each of said sulphur load, soot load, mission profile, ambient temperature and ambient pressure, -means for multiplying each normalized index for the correspondent index weight, -means for adding the products of said multiplications to obtain the desulphation S index.

An advantage of this embodiment is to establish an easy criterion to establish the influence of each input parameter to the desuiphation process According to a still further embodiment, two further checks are required before requesting said desulphation process, a first one verifies if the DPF priority is lower than a DPF priority threshold and a second one verifies if no slow desulphation inhibitions are present.

Consequently the apparatus further comprises means for verifying if the DPF priority is lower than a DPF priority threshold and means for verifying if no slow desulphation inhibitions are present.

An advantage of this embodiment is to avoid forced desutphation when a DPF regeneration service is required or to avoid the waste of a DPF warm up phase without the actual possibility to perform a desulphation right after.

Internal combustion engine of an automotive system equipped with an exhaust system, comprising a lean NOx trap, at least an air/fuel ratio sensor and at least a temperature sensor, the automotive system comprising an electronic control unit configured for carrying out the method according to the one of the previous embodiments.

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 combustion 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.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a schematic view of the aftertreatment system according to the invention.

Figure 4 is a scheme of the DeSOx regeneration phases.

Fig. 5 is a flowchart depicting the method for an adaptive desulphation strategy according to the invention.

Figure 6 is a flowchart detailing a first portion of the flowchart in Fig. 5.

S

Figure 7 is a flowchart of an alternative embodiment of a second portion of the flowchart in Fig. 5.

FigureS is a flowchart detailing a portion of the flowchart in Fig. 7.

Figure 9 is a flowchart of a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 2, that includes an internal combustion engine (ICE) 110 having an engine step 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 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 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 ambient 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 embodiments, 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 andfor 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 aftertreatment devices 280 include1 but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps 281, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems 282, particulate filters (DPF) or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate filter (SCRF) 283. 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.

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 and equipped with a data carrier 40. 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, 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, including1 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 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 embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

Turning back to exhaust system 270, the proposed invention is a method which evaluates the opportunity to force a DeSOx regeneration instead of waiting for a DPF regeneration natural request. Fig. 3 shows the scheme of the aftertreatment system 280, comprising a lean NOx trap (LNT) 281 and, advantageously, also comprising a particulate filter (DPF) 282 to trap particulate emitted in case of a Diesel engine.

Upstream and downstream the LNT, air/fuel ratio sensors 283, 284 and temperature sensors 285, 286 can be provided.

As mentioned, the DeSOx regeneration is defined as the process which leads to the S desuiphation of the lean NOx trap. It is critical from the point of view of thermal degradation of the trap, because of the requested high temperature, It is penalizing in terms of fuel consumption as well, because of the additional injected fuel needed to provide a rich atmosphere at the inlet of the trap. The desulphation is based on the "wobbling" concept, shown in Fig. 4, that is to say, an alternation of lean 510 and rich 520 phases at high temperature 500. The desulphation rich phase is needed to destabilize the chemical links between the sulphur and the barium and/or aluminium, causing the sulphur unloading and making the barium/aluminium sites free for the NOx and restoring the NOx trapping capability of the LNT. The desuiphation lean phase is used to maintain a stable and high temperature, to restore the oxygen content in the trap and to burn the HC cumulated in the trap during the rich phase.

The evaluation of the opportunity to force a desulphation instead of waiting for a DPF natural request needs the weighting of different parameters, in order to find an optimal condition in which the desulphation is efficient enough to restore an acceptable status of the LNT. Also, it is important to guarantee that the DeSOx is not forced in conditions in which it might damage the engine and the aftertreatment.

With reference to Figs. 5-6, the parameters that have been identified as the main drivers of the desuiphation need and efficiency are the following: sulphur load 600, which identifies the urgency of a desulphation and also is representative of the potential sulphur removal in known desuiphation conditions; soot load 610, since a desuiphation can be forced to anticipate a DPF regeneration, if the soot load is close to the conditions in which the DPF may request a regeneration and the driving conditions are optimized; mission profile 620, which represents the potential efficiency and effectiveness of the DeSOx, since gives an idea how stable rich combustion phases can be; ambient conditions, namely temperature 631 and pressure 634, which may reduce the permitted rich area, thus reducing the probability to perform effective desulphation rich events.

A logic has been set up to create a normalized index 603, 613, 623, 633, 636 and a weight index 602, 612, 622, 632, 635 for each of those parameters 600, 610, 620, 631, 634 to give them a different ranking. Then, each norftialized index is multiplied S604, S614, 8624, 8637, 8638 by the correspondent weight index and finally all these products are summed to calculate 8640 a desulphation index 640. The value of such desulphation index is therefore directly proportional to the need of a desulphation request, taking into account all those input parameters. Then, a desulphation index threshold 650 is estimated S650: if the desulphation index 640 is larger 5655 than said threshold, an active desulphation is requested 8660. The desulphation index threshold is set by is calibration, as a function of the number of desulphation already forced over the vehicle lifetime 645, By using this threshold, the method avoids to request 5660 a desulphation, when an increased ageing of the system can arise.

In Fig. 6 the details how the input parameters contributes to the calculation of the desulphation index is shown. As an example, let us consider the ambient pressure 634 (for the other parameters the procedure is exactly the same). An ambient pressure index 636 is defined, which normalizes in a scale 0-1 the whole ambient pressure possible range. For example, supposing the.ambient pressure ranging between 0.8 -0.95 kPa, the ambient pressure index 636 would correspondently range between 0.7 and 1. The normalized index is multiplied by a chosen ambient pressure index weight 635 which generally ranges between 0-100%. For the ambient pressure, the weight has been chosen equal to 10% (for the other parameters, a possible choice is: 70% sulphur load index weight 602, 10% mission profile index weight 622, 5% ambient temperature index weight 632, 5% soot load index weight 612). This product 8638 is entered in the calculation S640 of the desulphation index 640 and is added to the other products S604, S614, S624, 8637 of the other parameters. Ranging the normalized indexes between 0-1 and the indexes weight between 0-100% (with the indexes weight sum being 100%), the desulphation index 640 will also be ranging between 0-1.

According to a preferred embodiment the function between the number of forced desulphation processes over vehicle lifetime and the desulphation index threshold is a direct proportion. The purpose of this function is to take into account the number of the forced desulphation processes between two consecutive DPF natural requests. In fact, the higher is this number, the higher will be the index threshold 650, which the desulphation index 640 has to overcome for a forced desulphation to be called. For instance, after the first forced desulphation, the index threshold could be 0.7. After the second one, would be 0.9 and after the third one, will be 2. In the latter case, being the index threshold higher than 1 (maximum possible value of the desuiphation index), the desuiphation index cannot be higher than the desuiphation index threshold and, consequently, a desulphation regeneration will never be called before the next natural DPF regeneration. This strategy has the advantage not to age so much the component, avoiding frequent forced DeSOx.

Advantageously, as can be seen in Fig. 7-8, the desuiphation index threshold 650 also depends S665 on a desulphation model error. The background for this embodiment is connected to the following considerations: it is assumed that a model, which estimates the sulphur loading and unloading is available and accurate enough over the whole vehicle lifetime. This accuracy can be easily accepted for the sulphur loading phase when all the sulphur contained in the consumed fuel and oil is cqnsidered as stored inside the LNT. On the contrary, it is plausible to consider that the sulphur unloading, which is influenced by many parameters, whose actions are much more concentrated in time respect to the sulphur loading phase, may be modeled with a over estimation of the desulphation efficiency introducing a significant error every time an unloading phase (desulphation rich event) occurs. To take into account the error that the model introduces, in the present invention, a desulphation model error is included in the S definition of the desulphation index threshold 650, allowing to lower the desulphation index threshold value at which a desulphation can be forced (through a map function of both the number of forced desuiphation and the model error indicator).

Said desulphation model error is a counter of error-affected desulphation rich events 760, which happen during a whole DeSOx regeneration process. The potential DeSOx model error is based on the following hypothesis: the mass flow, which is desulphated by the LNT is proportional to the sulphur mass stored inside the LNT in that instant; since the rich conditions are needed to favor the decomposition of the sulphur stored in the barium sites, it can be assumed that the impact of rich conditions is progressive.

Therefore, the first few seconds (depending on LNT technology) of a desulphation rich event have a desulphation efficiency equal to 0. The hypothesis lead to the assumption that the desulphation model error is meaningful (in term of potential over estimation of desulphation) after a few seconds of a desulphation rich event have elapsed and when the quantity of sulphur inside the LNT is high enough. Therefore, said counter is increased 5740 if a desulphation rich time 680 is larger than S685 a calibrated desulphation minimum rich time 690. On the other side, if the desulphated quantity always depends on the stored sulphur mass, the error propagation will be mitigated when the system goes towards small sulphur quantities (i.e., very low desulphated quantities per desulphation rich event). Therefore the counter can be reset 5750 every time the sulphur reaches a low threshold, since in that condition, the error can be brought to a minimum, in other words, if a modeled LNIT sulphur quantity 710 is smaller than S715 a calibrated low sulphur threshold 720. Of course, both conditions depend on how effective was the DeSOx process: was it possible to perform rich events over a certain time threshold? Was it possible to reach the end of the DeSOx process, thus obtaining low sulphur content in the trap or was the process aborted? The answers to these questions will determine the value of the counter and, consequently, the influence of the potential DeSOx model error in establishing the desulphation index threshold.

Fig. 9 shows a further flow chart showing two further checks, which can be performed together with the desulphation index logic. These two checks are performed to verify that the boundary conditions are suitable for a forced desulphation. A first check verifies that DPF priority 770 is lower than $775 a DPF priority threshold 780. on the contrary, if the DPF priority 770 is larger than a DPF priority threshold 780, this check indicates that critical conditions are present in the DPF (e.g. high soot load) and a service regeneration would be needed, Therefore, a desulphation on the road should be avoided.

Finally, a slow" desuiphation inhibition check S800 verifies if the desulphatiori is inhibited for reasons that are in general very slow to evolve: for example, low fuel level, adverse environmental conditions (high pressure, low temperature), not working sensors. In this case, a desulphation should not be forced to avoid the waste of a DPF warm up phase without the actual possibility to perform a desulphation right after. If the two checks S775, 8800, together with the desuiphation index check 8655 are satisfied S810, after a debouncing time 820, which is needed to consolidate such checks, a desulphation request 8660 and a DPF request 8830 will be performed.

While at least one exemplary embodiment ha! been presented in the foregoing summary 25, 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.

REFERENCE NUMBERS

data carrier automotive system internal combustion engine 120 engine step cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phaser fuel injector fuel rail l8ofuelpump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 281 lean NOx trap (LNT) 282 diesel particulate filter (DPF) 283 LNT upstream air/fuel ratio sensor 284 LNT downstream air/fuel ratio sensor 285 LNT upstream temperature sensor 286 LNT downstream temperature sensor 290 VOT actuator 300 exhaust gas recirculation 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 temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 exhaust temperature 510 eombustion mode, lean phase 520 eombustion mode, rich phase 600 sulphur load 602 sulphur load weight index 603 sulphur load normalized index 610 soot load 612 soot load weight index 613 soot load normalized index 620 mission profile 622 mission profile weight index 623 mission profile normalized index 631 ambient temperature 632 ambient temperature weight index 633 ambient temperature normalized index 634 ambient pressure 635 ambient pressure weight index 636 ambient pressure normalized index 640 desulphation index 645 forced desulphation over vehicle lifetime 650 desulphation index threshold 680 desulphation rich time 690 calibrated desuiphation minimum rich time.

710 modeled LNT sulphur quantity 720 calibrated low sulphur threshold 760 counter of error-affected desulphation rich events 770 DPF priority 780 DPF priority threshold 820 debouncing time 3604 step 3614 step 8624 step S637 step 3638 step 8640 step 3650 step 8655 step S660 step 3665 step 3685 step 8715 step 3740 step 8750 step 8775 step 3800 step 3810 step S830 step

Claims

CLAIMS1. Method of controlling an adaptive desulphation process in an exhaust system (270) of an internal combustion engine (110), the exhaust system comprising a lean NOx trap (281), the method comprising: -calculating (S640) a desulphation index (640), whose value correlates.to or is proportional to the need of a desulphation of said lean NOx trap, -estimating (S650) a desulphation index threshold (650), as a function of a number of forced desulphation cycles over vehicle lifetime (645), -requesting a desulphation process (S660) if said desulphation index (640) is larger than (S655) said desulphation index threshold (650).
2. Method according to claim 1, wherein said function between forced desulphation over vehicle lifetime (645) and desulphation index threshold (650) is a direct proportion.
3. Method according to claim 1 or 2, wherein said desulphation index threshold (660) depends on a desulphation model error (655).
4. Method according to claim 3, wherein said desulphation model error (655) is a counter of error-affected desulphation rich events (760).
5. Method according to claim 4, wherein said counter (760) is increased (S740) if a desulphation rich time (680) is larger than (S685) a predetermined desulphation minimum rich time (690) and is reset (S750) if a modeled LNT sulphur quantity (710) is smaller than (S71 5) a predetermined low sulphur quantity threshold (720).
6. Method according to one of the previous claims, wherein the function between the desulphation index (640) and sulphur load (600), soot load (610), mission profile (620), ambient temperature (631) and ambient pressure (634) is obtained by: -defining a normalized index (603, 613, 623, 633, 636) in a scale 0-1 for each of S said sulphur load (600), soot load (610), mission profile (620), ambient temperature (631) and ambient pressure (634), -assuming a weight index (602, 612, 622, 632, 635) for each of said sulphur load (600), soot toad (610), mission profile (620), ambient temperature (631) and ambient pressure (634), -multiplying (S604, S614, S624, S637, S638) each normalized index for the correspondent index weight, -adding (S640) the products of said multiplications (S604, S614, S624, S637, S638) to obtain the desulphation index (640).
7. Method according to one of the previous claims, wherein two further checks are required before requesting said desulphation process, a first one verifies (S775) if the DPF priority (770) is lower than a DPF priority threshold (780) and a second one verifies (S800) if no slow desulphation inhibitions are present.
8. Internal combustion engine (110) of an automotive system (100) equipped with an exhaust system (270), comprising a lean NOx trap (281), at least an air/fuel ratio sensor (283, 284) and at least a temperature sensor (285, 286), the automotive system (100) comprising an electronic control unit (450) configured for carrying out the method according to claims 1-7.
9. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-7.
10. Computer program product on which the computer program according to claim 9 is stored.
11. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450) a data carrier (40) associated to the Electronic Control Unit (450) S and a computer program according to claim 9 stored in the data carrier (40).