EP0829622B1 - Process and apparatus for controlling a particulate filter - Google Patents

Abstract

Process for controlling a filter for catching particles placed in the exhaust from a diesel engine with the intention of post treating the particles, using a minimum amount of energy, by adapting the geometry of a filter (1) placed in the exhaust as a function of predetermined aims linked to the performance of the motor and by adapting the volume in which the exhaust gases are filtered to the volume flow of gas entering the filter. The process limits the mean back-pressure and therefore the degradation of the motor performance. Also claimed is a device for controlling the regeneration of particles deposited on a filter in a diesel exhaust comprising a filter divided into zones and valves connected to at least one zone allowing the gas flow to be directed into different zones; at least one pressure detector upstream of the filter; at least one means of measuring the gas volume flow through the filter, and means of controlling the valves.

Description

The present invention relates to the post-treatment of gases emitted at Diesel vehicle exhaust.

Particulate emission standards have recently emerged in Europe. These standards will become more stringent in the coming years. In this horizon, improvements related to engines and fuels can be insufficient, even in the presence of an oxidation catalytic converter.

A known technique for exhaust gas post-treatment is the particles. It is thus possible to obtain filtration efficiencies greater than 80%. Many filter technologies have been developed to date. As illustrative, may be cited the ceramic monolith marketed by the Company Corning, or the wound ceramic fiber cartridge as described in patent application WO-95 / 27,843.

The technical difficulty encountered for the development of such a system is that the filter must be periodically regenerated by combustion of the soot deposit. This combustion sometimes occurs naturally when the temperature of the gases by itself reaches the level required to initiate the oxidation of the particles. However, average operating conditions generally result in temperatures too low to spontaneously initiate combustion of the particles. This then leads to a clogging of the filter, which is detrimental for the good engine efficiency. It is then necessary to artificially ensure regeneration of the filter.

Many techniques have been developed in this direction. They can be essentially mechanical, based on changes in operation engine: intake valve, exhaust valve, advance delay injection, or local energy supply in the exhaust gases or at the level of the filter (electrical resistance, burner, microwave ...). It is then necessary to control these various devices by an external command supported by a computer. Most often, the criterion used to trigger the regeneration is the back pressure in the exhaust line.

To facilitate the regeneration of particulate filters, a different approach, chemical in nature consists in adding an additive, for example organometallic, to the fuel, which is found in the soot deposit which generally leads to a decrease in ignition temperature and therefore an increase in the frequency of regeneration.

Among the products most frequently used as additives, there may be mentioned copper, iron, cerium, sodium .... Studies show that in the presence of such additives, partial regenerations can occur spontaneously for relatively low exhaust gas temperatures (~ 200 ° C).

In addition, in known systems, problems related to back pressure and / or the energy consumed are often encountered.

Indeed, the accumulation of particles in the filter leads to a sometimes significant increase in back pressure and therefore a decrease in engine efficiency. By way of illustration, mention may be made of patent application WO-95 / 18,292.

When it comes to energy consumption, most systems known have an overall heating of the catalytic element. This results in a high energy consumption, more or less controlled. Patent EP-B1-0,485,179 illustrates a system based on this principle.

Furthermore and as is known from documents EP-A-0690210 and US 4502874, the conditions for regeneration can be highly dependent on the fouling condition of the filter. Known means do not allow to act on filter clogging. Advantageously, the present invention allows to adapt the filtration phase to all the operating conditions of the vehicle. It also makes it possible to overcome the problems of the prior art mentioned above.

In other words, the present invention has the overall effect of better controlling the medium exhaust back pressure and therefore limit degradation of the performance engine. In addition, the present invention makes it possible to minimize the contribution of energy necessary for the regeneration of said filter.

According to one of its aspects, the present invention relates to a method of control of a particulate filter placed at the exhaust of a Diesel engine for a post-treatment of particles, requiring a minimum of energy.

According to the invention, said method consists in adapting the geometry a filter placed at the exhaust according to strategies predetermined conditions related to the operating conditions of said engine by adapting the volume of the filter in which the exhaust gases are filtered at the volume flow rate gases which enter the filtration means, so as to allow limitation the average exhaust back pressure and therefore the performance degradation engine.

According to another embodiment of the invention, the method consists in creating heterogeneities in the concentration of soot in different areas of the filtration.

Without departing from the scope of the invention, the method can consist in reserving certain areas of the filtration means to certain types of soot.

More particularly, a set of partitions is used intended to insulate the different zones constituting the filtration means.

Advantageously, the partitions can be provided with openings arranged so as to allow the propagation of combustion from one zone to another.

Furthermore, the method according to the invention can allow, when fouling of the filter exceeds a predetermined threshold causing heating gases necessary for regeneration. In other words, the method consists in limiting temporarily the exhaust gas passage section in the means of filtration when the fouling of said means exceeds a determined threshold, in order to initiate regeneration by raising the gas temperature.

• un moyen de filtration divisé en au moins deux zones de filtration,
• un moyen de vannage associé à l'une au moins desdites zones de filtration permettant de moduler la répartition de l'écoulement des gaz entre les différentes zones de filtration,

The invention further relates to a device for controlling the filtration and regeneration of a particulate filter comprising:

• a filtration means divided into at least two filtration zones,
• a valve means associated with at least one of said filtration zones making it possible to modulate the distribution of the gas flow between the different filtration zones,

• au moins un capteur de pression placé en amont du moyen de filtration,
• au moins un moyen d'évaluation du débit volumique des gaz passant dans le moyen de filtration,
• un moyen de commande du ou des moyens de vannage géré en fonction de stratégies prédéterminées liées aux conditions de fonctionnement du moteur et du débit volumique des gaz d'échappement qui entrent dans le moyen de filtration.

In particular, it also includes:

• at least one pressure sensor placed upstream of the filtration means,
• at least one means for evaluating the volume flow rate of the gases passing through the filtration means,
• control means of the valve control means managed according to predetermined strategies linked to the engine operating conditions and the volume flow rate of the exhaust gases entering the filtration means.

Optionally, the device according to the invention can comprise a set of partitions intended to isolate the various zones constituting the filtration means.

In addition, said partitions may be provided with openings arranged in so as to allow the propagation of combustion from one zone to another.

Furthermore, the control means reacts as a function of the pressure measured. upstream of the filtration means.

In particular, the device according to the invention comprises a sensor for temperature intended to evaluate the volume flow of gases from their flow Mass.

Advantageously, said control means makes it possible to determine the angle each winnowing means.

• La fig. 1 est un schéma de principe du dispositif selon l'invention,
• La fig. 2 montre des courbes illustrant l'asservissement des différentes vannes en fonction du débit volumique de gaz à l'échappement,
• La fig. 3 est un organigramme simplifié permettant la mise en oeuvre de l'un des modes de réalisation de l'invention,
• Les fig. 4A et 4B présentent des courbes illustrant l'asservissement des différentes vannes en fonction du débit volumique pour différents niveaux d'encrassement du filtre,
• La fig. 5 est un organigramme simplifié permettant la mise en oeuvre du mode de réalisation de l'invention selon les fig. 4A et 4B,
• Les fig. 6A, 6B, 6C sont des courbes montrant l'asservissement des différentes vannes en vue de créer une hétérogénéité en fonction de la nature des suies.

Other characteristics, advantages and details of the present invention will appear on reading the description which follows, given by way of illustration and in no way limiting in relation to the appended figures in which:

• Fig. 1 is a block diagram of the device according to the invention,
• Fig. 2 shows curves illustrating the slaving of the different valves as a function of the volume flow rate of exhaust gas,
• Fig. 3 is a simplified flowchart allowing the implementation of one of the embodiments of the invention,
• Figs. 4A and 4B present curves illustrating the slaving of the different valves as a function of the volume flow rate for different levels of fouling of the filter,
• Fig. 5 is a simplified flowchart allowing the implementation of the embodiment of the invention according to FIGS. 4A and 4B,
• Figs. 6A, 6B, 6C are curves showing the slaving of the different valves in order to create heterogeneity as a function of the nature of the soot.

Figure 1 is a diagram illustrating the means used according to the invention. These means essentially comprise a divided particle filter 1 in several zones 11, 12, 13. In each zone is arranged a filter element by example a filter cartridge 2.

A winnowing means 31, 32, 33 is associated with each sector. The means of winnowing 31, 32, 33 are controlled by one or more actuators (4), so independent of each other, and according to predefined strategies. To this end, a calculator 5 controls each actuator by calculating the position of each means of winnowing according to different parameters and according to different strategies.

The winnowing means 31, 32, 33 can be arranged upstream or in downstream of the filter relative to the direction of flow of the exhaust gases. They don't never close the entire filter passage section 1.

A set of partitions 6 as illustrated in FIG. 1 can be used for isolate the filtration zones 11, 12, 13 therebetween. Such a device here divides the filter with particles 1 in three equal angular sectors, in each of which is arranged a filter element 2. In addition, the partitions forming the assembly 6 can be provided openings to allow the spread of combustion inside the filter 1, when it has started locally in one of the filter elements 2.

It is assumed here that the filter 1 is divided into three substantially equal sectors having the characteristics set out above.

Of course, the number and the arrangement of the partitions 6 can vary according to the type and size of the filter used.

The acquisition of the input data of the computer 5 is carried out by several sensors and in particular by at least one pressure sensor and at least one sensor upstream of the filter.

Furthermore, according to the present embodiment of the invention two sensors pressure are arranged on either side of the filter 1; a means of assessing the Mass flow of gases through the filter is also required.

Fig. 2 illustrates one of the control methods of the winnowing means associated with the filter. This is to enslave the winnowing means 31, 32, 33 to the flow volume of gas passing through filter 1, the volume flow being deduced from both the temperature upstream of the filter, and the mass flow.

By thus modulating the speed of the gases in the filter 1, it is sought to improve the filtration (overall efficiency, deep deposition), as well as the acoustics of the system.

The fact of being able to thus adapt the volume of the filter to the volume of gas which cross member creates optimal filtration conditions and back pressure as limited as possible.

A possible strategy for opening / closing the different valves is illustrated in fig. 2.

The ordinate of the curves of fig. 2 gives (in%) the opening angle α of each of the three valves associated with each of the angular sectors described above.

The abscissa of the curves represents the volume flow rate Q, in m ³ / h, of the exhaust gases passing through the filter 1.

The behavior of one of the three valves is illustrated by curve A in line full; the second valve is actuated according to the dotted curve B while the third valve opens along curve C in phantom.

According to the strategy of fig. 2, valve A is always open regardless of the flow rate; valve B opens gradually for average volume flows (between 200 and 400 m ³ / h). Valve B remains open for high flow rates. The third valve C only opens for high flow rates, that is to say beyond 500 m ³ / h.

Thus the total filtration volume seen by the gases gradually adapts to the volume flow of gases.

The volume flow Q can be evaluated from the mass flow and a temperature measurement. Mass flow can be obtained by direct measurement, by example using a hot film flow meter, or it can be inferred from a engine mapping. The hot film flow meter can also be used to other specific engine control needs. Gas temperature measurement is preferably carried out upstream of the filter.

Fig. 3 is a simplified flowchart showing the main functions of the computer 5. The input data are the mass flow rate (in kg / h) and the temperature of the exhaust gases. From this data, the computer determines the volume flow rate in (m ³ / h) of the exhaust gases. Based on preset strategies stored in said computer 5, the latter defines the respective positions of the different valves. Then it triggers the commands of the various actuators associated with the valves, so that they respond according to the curves in FIG. 2.

The strategy described in relation to figs. 2 and 3 can also allow the creation of a heterogeneity of fouling within the filter, during prolonged operation at low or partial engine load. The study of spontaneous regeneration phenomena (especially in the presence of additives) shows that the creation of such heterogeneities can facilitate local lighting conditions which are dependent on the concentration of trapped material. Furthermore a stratification of the combustible material is favorable for good propagation of the combustion.

In addition, the control of the distribution of fouling inside the filter can provide lower back pressures for a total mass of particles given.

The valve opening strategy as set out above shows that if the engine operation continues at low load, cartridge A becomes clogged strongly while the other two B and C remain clean. In these conditions low speed and low torque (busy urban traffic), the stratification of fouling promotes regeneration if not difficult to reach due to low exhaust gas temperature. Even in the event of a heavy load (acceleration), the heterogeneity of fouling thus created results in more favorable regeneration conditions. The present invention therefore allows to organize the fouling, to control it and consequently, to organize the filter regeneration.

Figs. 4A and 4B correspond to strategies which take into account the filter clogging level.

In this case, the opening thresholds of the different valves as a function of the gas flow rate also change as a function of the pressure measured upstream of the filter. When the fouling is weak (case of fig. 4A), the openings of the valves B and C intervene for important volume flow rates for example beyond 400m ³ / h.

When the fouling becomes significant (fig. 4B), it is useful to open the valves B and C for lower gas flow rates, in order to avoid a too penalizing back pressure, for example as soon as the flow reaches 200m ³ / h.

Fig. 5 gives a simplified flowchart of the operation of the computer 5. The input data here are the mass flow, the temperature and the pressure measured at least upstream of filter 1.

From this data, the computer determines the gas volume flow exhaust. Then, taking into account the upstream pressure, the computer determines the level of fouling and calculates the position of the different flaps according to the curves of fig. 4A and 4B. It follows a command of the actuators associated with each of the components.

Note that as long as the filter clogging is low (back pressure weak) only one of the valves is open, the others remaining closed and not opening when approaching high flow rates: fig. 4A.

When the filter is dirty (fig. 4B) only one valve is open at low flow (low speeds) but from medium speeds, a second valve opens gradually then the third valve opens in turn, in order to have a maximum opening for high flows (high loads).

With regard to the strategy mentioned in relation to fig. 2, fouling represents the additional parameter which is taken into account here and which allows reach the curves according to fig. 4A and 4B.

Figs. 6A, 6B and 6C relate to another strategy for activating different flaps associated with the different zones forming the filter.

This is to reserve a filter area for a deposit of soot rich in hydrocarbons, said soot being generally produced at low load, and being (of by its nature) easier to burn. This area will be exclusively contaminated with idle neighborhood. The superposition of figs. 6A, 6B and 6C shows that for the idle (low flows) only one valve is open, the others being closed. So privileged way, only the zone of filter 1 associated with the open valve is clogged with idle neighborhood.

Partial load and regime, in order to keep the trapped soot in slow motion properties favorable to the initiation of combustion, the area in question is closed while the rest of the filter opens: valve 2 can open fully and instantly as shown in fig. 6B, and the third valve can open gradually as shown in fig. 6C.

For high speed and load (high volume flows), all valves are open; on the one hand, this limits the exhaust back pressure and on the other hand to trigger regeneration in the dirty cartridge at low load that is to say having soot rich in hydrocarbons. The triggering of the combustion in this specific area can also help initiate afterburning in the rest of the filter. This effect will be enhanced if the partitions of the filter holder 6 have suitable openings.

This strategy therefore makes it possible to deliberately create heterogeneity in the filter according to the nature of the soot. In connection with this, the filter adapts its geometry to the driving scenario. We note that the creation of an area rich in hydrocarbons is only operated during prolonged idling. In case of driving stabilized on motorways, the filter works completely normally.

Another strategy for controlling the regeneration of particles deposited on the filter 1 can consist in carrying out a temporary winnowing of the whole of the filter. This leads to heating of the exhaust gases which itself allows trigger regeneration.

More specifically, the strategy according to the invention consists in monitoring fouling of the filter via a measurement of the back pressure for example; then, when the latter reaches a certain threshold, to act on one or other of the valves 31, 32, 33, simultaneously or separately in order to limit the cross-section of the gas passage and thus causing their temperature to rise. The computer 5 makes it possible to precisely determine the opening angle of each valve 31, 32, 33.

Interestingly according to the invention, the winnowing strategy at a time given may be adapted to the level and distribution of fouling resulting from the application of the strategies described above, aimed in particular at maintaining the filter clogging conditions. A direct advantage lies in obtaining a lower exhaust back pressure, which helps increase engine performance. Furthermore, the present invention makes it possible to prepare a very efficient self-ignition.

Claims (13)

1. Method for controlling a particulate filter placed in the exhaust of a diesel engine with a view to post treatment of the particulates, necessitating a minimum of energy, said method consisting in adapting the geometry of a filtering means (1) placed in the exhaust as a function of predetermined strategies linked to the operating conditions of said engine by adapting the volume in which the exhaust gases are filtered to the volumetric flow of gases entering the filtering means (1) so as to allow limitation of the mean back pressure in the exhaust and hence the deterioration in the engine. performance.
2. Method according to claim 1, characterised in that it consists in creating heterogeneities in the concentration of the soots in different zones of the filtering means (1).
3. Method according to one of claims 1 or 2, characterised in that it consists in reserving certain zones of the filtering means (1) for certain types of soots.
4. Method according to any one of the preceding claims, characterised in that it consists in effecting partitioning of the filtering means (1) in order to isolate the different zones constituting said filtering means.
5. Method according to claim 4, characterised in that it consists in effecting partitioning with openings disposed so as to allow propagation of the combustion from one zone to the other.
6. Method according to any one of the preceding claims, characterised in that it consists in temporarily limiting the section for passage of the exhaust gases in the filtering means when the clogging of said means exceeds a predetermined threshold in order to trigger regeneration by raising the temperature of the gases.
7. Device for controlling the regeneration of particulates which may be deposited on a filtering means placed in the exhaust of a diesel engine, comprising:

   a filtering means divided into at least two filtering zones (11, 12, 13),

   a flow control means (31, 32, 33) associated with at least one of said filtering zones allowing modulation of the distribution of the flow of gases between the different filtering zones,

   characterised in that it additionally comprises:

   at least one pressure pickup placed upstream of the filtering means (1),

   at least one means for evaluating the volumetric flow of the gases passing into the filtering means (1),

   a control means (5) for the flow control means (31, 32, 33) operated as a function of predetermined strategies linked to the operating conditions of the engine and the volumetric flow of the exhaust gases entering the filtering means (1).
8. Control device according to claim 7, characterised in that it additionally comprises a set of partitions (6) designed to isolate the different zones (11, 12, 13) constituting the filtering means.
9. Control device according to claim 8, characterised in that said partitions (6) are provided with openings disposed so as to allow the propagation of the combustion from one zone to the other.
10. Device according to any one of claims 7 to 9, characterised in that said control means (5) additionally reacts as a function of the pressure measured upstream of said filtering means (1).
11. Device according to any one of claims 7 to 10, characterised in that it additionally comprises a temperature pickup designed to evaluate the volumetric flow of the gases from their mass flow.
12. Device according to any one of claims 7 to 11, characterised in that said control means (5) makes it possible to determine the opening angle of each flow control means (31, 32, 33).
13. Device according to claim 12, characterised in that one flow control means (31, 32, 33) is associated with each of said zones (11, 12, 13).

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