GB2502797A

GB2502797A - Method of assessing the thermal ageing of a catalyst in an exhaust system

Info

Publication number: GB2502797A
Application number: GB1210028.5A
Authority: GB
Inventors: Andrea De Filippo; Salvatore Sannino
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-06-06
Filing date: 2012-06-06
Publication date: 2013-12-11
Also published as: GB201210028D0

Abstract

Disclosed is a method of assessing the thermal ageing of a catalyst in an exhaust system 270 of an internal combustion engine 110 of an automotive system 100. The exhaust system 270 comprises at least an after-treatment device 280 comprising a lean NOx trap 281. The method comprises the steps of activating a lean NOx trap regeneration event, terminating said regeneration event once the lean NOx trap is completely purged, activating a further lean NOx trap regeneration event once the lean NOx trap has reached a specific NOx storage capacity and terminating the further lean NOx trap regeneration event after a predetermined first time interval. The first time interval is compared with a time interval needed to reach a completely purged lean NOx trap and the difference in times is used to assess the thermal ageing of the catalyst. A system for carrying out the method including an electronic control unit loaded with a computer program for carrying out the method are also disclosed.

Description

METHOD OF ASSESSING THE THERMAL AGEING OFA CATALYST/N AN

EXHAUST SYSTEM OF AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of assessing the thermal ageing of a catalyst, particularly a Lean NOx Trap (LNT) catalyst, in an exhaust system of an internal combustion engine.

BACKGROUND

It is known that the exhaust gas after-treatment systems of a Diesel engine can be provided, among other devices, with a Lean NO Trap (LNT).

A Lean NO, Trap (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 (NOr) contained in the exhaust gas, in order to trap them within the device itself.

Lean NO Traps (LNT) 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.

The LNT are operated cyclically, for example by switching the engine from lean-burn operation to operation whereby an excess amount of fuel is available, referred also as rich operation or regeneration phase. During normal operation of the engine, the NO are stored on a catalytic surface. When the engine is switched to rich operation, the NO stored on the adsorbent site react with the reductants in the exhaust gas and are desorbed and converted to nitrogen and ammonia, thereby regenerating the adsorbent site of the catalyst.

The pollutant conversion efficiencies are highly dependent on the effective ageing status of the LNIT catalyst, For NOx, these conversion pollutant might change from about 80% with a new or "degreened' (i.e., in a range between 3,000 and 15,000 km1 the catalyst become stable in its behavior) catalyst to about 50% with a severely aged catalyst.

Therefore a need exists for a method that assesses the effective thermal ageing status of the LNT technology that has been chosen to reach future pollutant emission targets An object of this invention is to provide a method which assess the thermal ageing of a catalyst in order to let the owner of the vehicle to introduce countermeasures which allow to reach the emission targets, by refining the regeneration strategy of the lean NOx trap or even by substituting a severely aged component.

Another 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 computer program product, and by an electromagnetic signal having the features recited in the independent claims.

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

SUMMARY

An embodiment of the disclosure provides a method of assessing the thermal ageing of a catalyst in an exhaust system of an internal combustion engine of an automotive system, the exhaust system comprising at least an after-treatment device, said at least an after-treatment device being a lean WOx trap, the method comprising: -activating a lean NOx trap regeneration event, -terminating said regeneration event at a time (tO), in which the lean NOx trap is considered completely purged, -activating a further lean NOx trap regeneration event at a first time ti, in which the lean NOx trap has reached a specific NOx storage capacity, -terminating said further lean NOx trap regeneration event after a predetermined first time interval t2-tl, -comparing the first time interval t2-ti with a time interval tx-ti needed to reach a completely purged lean NOx trap.

Consequently, an apparatus is disclosed for assessing the thermal ageing of a catalyst in an exhaust system of an internal combustion engine of an automotive system, the apparatus comprising: -means for activating a lean NOx trap regeneration event, -means for terminating said regeneration event at a time (to), in which the lean NOx trap is considered completely purged, -means for activating a further lean NOx trap regeneration event at a first time ti, in which the lean NOx trap has reached a specific NOx storage capacity, -means for terminating said further lean NOx trap regeneration event after a predetermined first time interval t2-tl, -means for comparing the first time interval t2-tl with a time interval tx-ti needed to reach a completely purged lean NOx trap.

An advantage of this embodiment is that it provides a method of assessing the thermal ageing of the Jean NOx trap catalyst, thus allowing to use the [NT catalyst in the best proper way.

According to a further embodiment of the invention, the activation of the method depends on specific conditions ike a mileage interval from the last activation in the range of 10,000 -15,000 km, a recent and successful sulphur regeneration event and a stable steady state driving conditions.

An advantage of this embodiment is that it provides a periodic check of the lean NOx trap status.

According to a further embodiment said the exhaust system also comprises a lean NOx trap upstream air/fuel ratio sensor and a lean NOx trap downstream air/fuel ratio sensor and said Jean NOx trap is considered completely purged when the condition, that the upstream air/fuel ratio becomes equal to the downstream air/fuel ratio, has been reached.

An advantage of this embodiment is that it does not require any additional costs: in fact, using the air/fuel ratio sensors (also indicated as X sensors) does not require additional features/components with respect to the current engine management configuration: for the L.NT management, the current/future sensor layout comprises at least a X sensor, placed upstream the LNT catalyst, and a second X sensor, placed downstream the LNT catalyst.

According to a still further embodiment, said predetermined time interval (t2-tl) is greater than lOs.

An advantage of this embodiment is that this method provides a quick strategy. Total duration for this monitoring strategy is no longer than 5 minutes at maximum.

According to a still further embodiment said comparison between time interval (t2-ti) and time (tx-ti) leads to the following lean NOx trap thermal ageing status: -if (tx-ti) > (t2-tl) then the lean NOx trap status is not aged", -if (t2-ti)/2 <(tx-ti) c (t2-tl) then the lean NOx trap status is moderately aged", -if(tx-tl) c(t2-tl)/2 then the lean NOx trap status is "severely aged".

An advantage of this embodiment is that the method provides a feedback on the current lean NOx trap regeneration strategy.

According to another embodiment, said lean NOx trap thermal ageing status is compared with a lean NOx trap ageing status by mileage, to determine if the catalyst is more or less aged than expected.

An advantage of this embodiment is that the method indicates countermeasure for the driver. In fact, if the catalyst is more aged than expected, it is necessary to change the regeneration strategy, otherwise there is the risk not to be compliant with emission legislation requirement; at the opposite, if the catalyst is less aged than expected, it is necessary to change the regeneration strategy as well, otherwise there is the risk to overstress the LNT catalyst.

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.

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

A still further aspect of 11th disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

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 after-treatment system according to the invention.

Figure 4 is a flowchart of a method of assessing the thermal ageing of a catalyst, according to an embodiment of the invention.

Figure 5 is a graph depicting the compèrison between the regeneration event duration and the duration of a regeneration event after which the catalyst can be considered completely purged.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system loot as shown in Figures land 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a 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 149. 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 50. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases thrOugh the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280 The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps 281, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems1 particulate filters (DPF) or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate filter (SCRF). 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 cpntrol 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 VOl 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 relies on a simple strategy to assess the thermal ageing of a LNT catalyst. The system comprises (Fig. 3) a LNT 281 with an air/fuel ratio sensor (X sensor) 284 placed upstream the LNT catalyst and a second A sensor 285 placed downstream the LNT catalyst. Therefore, the proposed strategy does not require any further component, since for the LNT management, the presence of the upstream and downstream ? sensors is already contemplated in current and future sensor layout.

Preferably, the LNT catalyst could be positioned as close as possible to the exit of the turbocharger to take advantage of the high temperature conditions which are beneficial for it.

The LNT reduces engine-out exhaust gas constituents (CO and HC) with high efficiency and stores NOx during lean operating conditions. During rich operating conditions (regeneration event), the N40x is released and converted. However, the pollutant conversion efficiencies are highly dependent on the effective ageing status of the LNT catalyst. For example, as far as NOx is concerned, this conversion pollutant might change from about 80% with a degreened catalyst to about 50% with a severely aged catalyst. Therefore, the purpose of this invention is to propose a simple strategy to assess the thermal ageing status of an LNT catalyst through A sensors measurements.

Looking at Fig.4, the method, as first step 20, detects if some specific conditions to activate the strategy are satisfied. This conditions are a mileage interval from the last activation in the range of 10,000 -15,000 km1 a recent sulphur regeneration event and stable steady state driving conditions. In fact, the activation of this monitoring strategy should be periodically applied after ranges of at least 10000 km, in consequence of a successful sulphur regeneration event that has been effectively completed the sulphur removal. Practically, a successful sulphur regeneration event means that the event has been performed for 1-2 mm under rich combustion mode and high temperature.

Furthermore, to be effective, the strategy needs that a desired driving condition is performed, This can be detected, for example, by the ECU 450 and should be represented by a stable steady state condition, like along the highway with an active cruise control.

Then, a first LNT regeneration event is activated 21 which should be terminated 22 only when the so called RX crossing" is reached, so that the catalyst can be considered S completely purged. This time value is defined as tO. For "X crossing" is to be intended that the upstream air/fuel ratio becomes equal to the downstream airffuel ratio and this means, in other words, the NOx conversion hasbeen completed.

From the so called time tO, the strategy should wait a time ti before triggering 23 a further regeneration event. This time ti is corresponding to the time needed to reach the specific NOx storage capacity (based on NOx engine out emissions) of the LNT catalyst, as indicated by the catalyst supplier or as calibrated for that specific driving condition.

This specific NOx storage capacity could be the maximum NOx storage capacity.

As the time ti is reached, the ECU should trigger the further regeneration event characterized, in this case, by a fixed duration (t2-tl, which can be preliminarily indicated at least higher than lOs). The need to have this time interval t2-tl > los is based on the experience with LNT catalysts, which generally are able to purge the trap within this time interval.

Based on the output response of the lambda crossing behavior, namely the time needed to reach the "X crossing" (tx-ti) between the X downstream and upstream the LNT catalyst, the strategy could recognize the thermal ageing status of the catalyst, by comparing 25 the time interval (t2-ti) with the time interval (tx-fl), either detected or extrapulated, needed to reach a completely purged lean NOx trap.

Said comparison leads to the following lean NOx trap ageing status (see Fig. 4): -if (tx-ti) > (t2-tl) then the lean NOx trap status is not aged", -if (t2-tl)/2 c (tx-ti).< (t2-tl) then the lean NOx trap status is "moderately aged", S -if (tx-ti) <(t2-tl)/2 then the lean NOx trap status is "severely aged".

Furthermore, if said lean NOx trap ageing status is compared with a lean MOx trap ageing status by mileage, it is possible to determine if the catalyst is more or less aged than expected.

Based on the comparison between the ageing assessed with this lambda monitoring strategy and the accumulated vehicle mileage, the following actions might be taken: a) LNlageing status > LNT ageing status by mileage The catalyst is more aged than expected. Therefore, it is necessary to change the regeneration strategy (e.g., regeneration frequency andfor "X target"), considering the effective ageing of the catalyst, otherwise there is the risk not to be compliant with emission legislation requirements. In case the catalyst results in a aseverely aged" status it might be required the activation of a tamp which suggests the driver to change the component.

b) LNT ageing status = LNT ageing status by mileage The catalyst is aged as expected. Therefore, it is an indication that the current regeneration strategy is working properly.

c) LNT ageing status <INT ageirig status by mileage The catalyst is less aged than expected. Therefore, it is necessary to change the regeneration strategy, considering the effective ageing of the catalyst, otherwise there is the risk to overstress the LNT catalyst.

Summarizing, the advantages of this monitoring strategy are: -Use of the LNT catalyst in the best proper way -Feedback on the current regeneration strategy -Periodic check of LNT status -Zero additional costs because this monitoring strategy does not require additional features/sensors with respect to the current situation -It is a quick strategy. Total duration for this monitoring strategy is no Longer than 5 minutes at maximum.

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 desGription 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 block

21 block 22 block 23 block 24 block block 26 block data carrier 100 automotive system internal combustion engine engine block cylinder cylinder head 135 camshaft piston crankshaft combustion chamber cam phaser 160 fuel injector fuel rail fuel pump 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 284 upstream air/fuel ratio sensor (X sensor) 285 downstream air/fuel ratio sensor (X sensor) 290 VGT 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 tO, ti, t2, tx time constants t2-tl time interval of regeneration phase tx-ti time interval of a full regeneration phase (X crossing reached)

Claims

CLAIMS1. Method of assessing the thermal ageing of a catalyst in an exhaust system (270) of an internal combustion engine (110) of an automotive system (100), the exhaust system (270) comprising at east an after-treatment device (280), said at least an after-treatment device being a lean NOx trap (281), the method comprising: -activating (21) a lean NOx trap (281) regeneration event, -terminating (22) said regeneration event at a time (tO), in which the lean NOx trap is considered completely purged, -activating (23) a further lean NOx trap (281) regeneration event at a first time (ti), in which the lean NOx trap has reached a specific NOx storage capacity, -terminating (24) said further lean NOx trap (281) regeneration event after a predetermined first time interval (t2-tl), -comparing (25) the first time interval (t2-tl) with a time interval (tx-ti) needed to reach a completely purged lean NOx trap.
2. Method according to claim 1, wherein its activation depends on specific conditions like a mileage interval from the last activation in the range of 10,000-15,000 km a recent and successful sulphur regeneration event and a stable steady state driving conditions.
3. Method according to claim 1 or 2, wherein said the exhaust system (270) also comprises a lean NOx trap upstream airlfuel ratio sensor (284) and a lean NOx trap downstream air/fuel ratio sensor (285) and said lean NOx trap is considered completely purged when the condition, that the upstream airlfuel ratio becomes equal to the downstream air/fuel ratio, has been reached.
4. Method according to any of the previous claims, wherein said predetermined time interval (t2-tl) isgreaterthan los.S
5. Method according to any of the previous claims, wherein said comparison between time interval (t2-tl) and time interval (tx-ti) leads to a following lean NOx trap thermal ageing status: -if (tx-ti) (t2-tl) then the lean NOx trap status is "not aged", -if (t2-tl)12 c (tx-ti) c (t2-tl) then the lean NOx trap status is "moderately aged", -if (tx-ti) c (t2-tl)/2 then the lean NOx trap status is "severely aged.
6. Method according to claim 5, wherein said lean NOx trap ageing status is compared with a lean NOx trap thermal ageing status by mileage, to determine if the catalyst is more or less aged than expected.
7. Internal combustion engine (110) of an automotive system (100) equipped with an exhaust system (270), the exhaust system comprising at least an after-treatment device (280), said at least an after-treatment device being a lean NOx trap (281), and the exhaust system (270) also comprising a lean NOx trap upstream air/fuel ratio sensor (284) and a lean NOx trap downstream air/fuel ratio sensor (285), the automotive system (100) comprising an electronic control unit (450) configured for carrying out the method according to claims 1-6.
8. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-6.
9. Computer program product on which the computer program according to claim 8is stored.
10. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim B stored in the data carrier (40).
11. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 8.