WO2006005866A1

WO2006005866A1 - System for assisting regeneration of pollution management means

Info

Publication number: WO2006005866A1
Application number: PCT/FR2005/050463
Authority: WO
Inventors: Christophe Colignon
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2004-06-23
Filing date: 2005-06-20
Publication date: 2006-01-19
Also published as: EP1766212A1; FR2872205B1; FR2872205A1

Abstract

The invention concerns a system for assisting regeneration of pollution management means (1) associated with oxidation catalyst forming means implementing an oxygen storage capacity (OSC) function and integrated in an exhaust line (2) of a motor vehicle diesel engine (3), wherein the engine (3) is associated with common ramp means (4) supplying fuel to the cylinders thereof. Said system further comprises means for monitoring (5) the pollution management means (1) to control the engine control means (4, 5, 6) based on operating sequences alternating rich mixture and lean mixture operating phases based on a first strategy of successive sequences of this type or a second strategy of sequences of this type separated by a lean mixture operating phase.

Description

The present invention relates to a system for assisting the regeneration of depollution means associated with oxidation catalyst means implementing an OSC function constituting an oxygen reserve, and integrated in an exhaust line of a diesel engine of a motor vehicle.

More particularly, the invention relates to such a system wherein the engine is associated with common cylinder fuel supply means thereof.

To ensure the regeneration of depollution means such as a particulate filter, the soot trapped in it is burned thanks to the thermal provided by the engine and the exotherm achieved by the conversion of HC and CO on the means. forming oxidation catalyst placed upstream of the particulate filter.

This combustion can be assisted by a catalyst element mixed with soot, resulting for example from a regeneration aid additive, mixed with the engine feed fuel or by a catalyst deposited directly on the walls of the particulate filter ( catalyzed particulate filter).

The higher the thermal levels in the exhaust line at the inlet of the particulate filter, the shorter the regeneration time of the filter. Such engines operating in sequences alternating operating phases rich mixture and lean mixture have already been proposed in the state of the art.

Indeed, in rich mode, the diesel engine emits a large amount of CO and unburned hydrocarbons in the exhaust gas. Moreover, the amount of oxygen present in these gases is greatly reduced (2 to 3% or even less than 1%). The passage of these gases in the oxidation catalyst means allows the combustion of CO and HC by the oxygen present in the gases.

In order to be able to convert a larger quantity of CO and HC, it is necessary to provide a greater quantity of oxygen.

For this purpose, the presence of an OSC (Oxygen Storage Capacity) type component such as cerium (which stores oxygen in the form of ceria C _e θ ₂ ) or a mixed oxide of cerium and zirconium, in the means oxidation catalyst, allows to release oxygen during the passages of the engine in rich mode. The combustion of CO and HC is an exothermic reaction and makes it possible to increase the thermal levels at the outlet of the oxidation catalyst, that is to say at the inlet of the particulate filter or within the particulate filter according to the configuration of the exhaust line. Compared to the poor mode of regeneration of the particulate filter, the rich mode produces a larger quantity of reducing agents and especially CO. Thus, despite a lower oxygen content, partially compensated by the OSC, the exotherm produced by the oxidation catalyst is greater in rich mode than in the poor mode of regeneration of FAP. The transition to rich mode thus allows to further heat the exhaust.

This speeds up the regeneration speed of the particulate filter. In the case of a particulate filter using a regeneration aid additive, the increase in the thermal levels makes it possible to reduce the dosage of additive and thus to increase the distance traveled before cleaning the filter.

The different strategies currently used implement the same set of parameters (injection and air loop), whatever the engagement rules used, that is to say that we seek to minimize overconsumption in fuel regeneration, maximize the chances of successful regeneration or protect the engine and / or particulate filter.

The aim of the invention is to propose a control of the engine which makes it possible to optimize the chances of success of regeneration attempts, especially in critical conditions. For this purpose, the subject of the invention is a system for assisting the regeneration of depollution means associated with means forming an oxidation catalyst implementing an OSC function and integrated into an exhaust line of a diesel engine. of a motor vehicle, in which the engine is associated with means with common rail for supplying cylinders with fuel, characterized in that it comprises means for monitoring the depollution means for controlling the control means of the engine. engine according to operating sequences alternating operating phases with rich mixture and lean mixture according to a first sequence strategy successive sequences of this type or a second strategy of sequences of this type separated by a lean operation phase. According to other characteristics:

the number of sequences and the duration of each phase during a sequence are calibrated;

the monitoring means comprise means for monitoring the state of charge of the depollution means in order to trigger the first strategy in the event of exceeding predetermined threshold values of overloaded and clogged charge states of the depollution means; the monitoring means comprise means for monitoring the number of successive incomplete regenerations of the depollution means in order to trigger the first strategy if a predetermined number is exceeded;

the monitoring means comprise means for monitoring the frequency of the last regenerations of the depollution means in order, in the case where this frequency crosses a predetermined threshold, to trigger the first strategy;

the frequency of the last regenerations is calculated over the last five regenerations of the filter; the monitoring means comprise means for measuring the temperature of the gases upstream of the depollution means and of comparing the latter with a temperature threshold in order to trigger the second strategy in the event of an overshoot and thus making it possible to maintain the temperature of the gas in an optimum window of regeneration; the depollution means comprise a particulate filter;

the particulate filter is catalyzed;

the depollution means comprise a NOx trap;

the fuel comprises an additive intended to be deposited with the particles to which it is mixed, on the depollution means, to facilitate their regeneration;

the depollution means are impregnated with a SCR formulation providing a CO / HC oxidation function;

the fuel comprises an additive forming a NOx trap; and

the engine is associated with a turbocharger. The invention will be better understood with the aid of the following description given solely by way of example and with reference to the appended drawings in which:

- Figure 1 shows a block diagram illustrating the structure and operation of pollution control means integrated in an exhaust line of a motor vehicle diesel engine;

FIGS. 2 and 3 respectively illustrate first and second strategies implemented in a regeneration assistance system according to the invention; and - Figure 4 illustrates the operation thereof.

FIG. 1 shows depollution means associated with oxidation catalyst means implementing an OSC function, generally designated by the general reference 1 and integrated in an exhaust line 2 of an engine. Diesel 3 of a motor vehicle. The oxidation catalyst means implement, for example, an OSC function constituting an oxygen reserve and the depollution means comprise, for example, a particulate filter.

Such oxidation catalyst means implementing an OSC function are already known in the state of the art. The engine is associated with common rail fuel supply means cylinders thereof, designated by the general reference 4, whose operation is controlled by a computer designated by the general reference 5, associated with means 6 of storage of control strategies to ensure the regeneration of the means of depollution. In the aid system according to the invention, there are provided means for monitoring the pollution control means for controlling the engine control means according to operating sequences alternating operating phases with rich mixture and lean mixture according to a first strategy of successive sequences of this type or a second strategy of sequences of this type separated by a lean operation phase.

These different means are implemented by the computer 5, and as can be seen in FIGS. 2 and 3, the first control strategy of the latter comprises successive sequences alternating phases of operation with rich mixture and lean mixture of the engine, for example in aid of the regeneration of level 2, and this loop until the end of the request for regeneration assistance.

FIG. 2 has in fact shown a first strategy of this type which comprises successive sequences of operation of the engine with rich mixture and lean mixture alternately.

On the other hand, in FIG. 3, a second control strategy is illustrated which comprises alternating operating sequences in rich mixture and in lean mixture, for example of level 2, separated by a lean operation phase, for example also of level 2. This allows then, as can be seen in FIG. 4, to drive the motor to obtain higher or lower thermal levels making it possible to optimize the regeneration of the filter depollution means. The number of rich / poor sequences is calibrated and the duration in each phase or mode (poor level 2 and rich) is also calibrable.

Two examples are given below.

1) triggering a series of X pulses (X is calibrated) R / P a) at the end of X pulses, if the temperature T upstream of the pollution control means is greater than a high threshold TH calibable (with a confirmation time ti), then the engine switches to level 2 lean mode only, b) as soon as T reverts below a calibrated low threshold TB (with a confirmation time t ₂ ) then we redo a sequence of X pulses R / P, c) looping of the strategy until the end of the request for GR support,

2) triggering of a series of X pulses (X is calibrated) R / P a) at the end of X pulses, if the temperature T upstream of the pollution control means is greater than a high threshold TH calibrated (with a confirmation time ti), then the engine switches to level 2 lean mode, b) new sequence of X pulses after Y seconds (calibrated) passed in level 2 lean mode.

Various means of monitoring the depollution means can be used. For example, these monitoring means may comprise means for monitoring the state of charge of the depollution means in order to trigger the first strategy if predetermined threshold values of overloaded and clogged charge states are exceeded. means of depollution.

Similarly, the monitoring means may also comprise means for monitoring the number of successive incomplete regenerations of the depollution means to engage the first strategy in case of exceeding a predetermined number. The monitoring means may also include means for monitoring the frequency of the last regeneration of the depollution means for, in the case where this frequency crosses a predetermined threshold, engage the first strategy.

For example, the frequency of the last regenerations can be calculated over the last five regenerations of the filter.

Likewise, these monitoring means may comprise means for measuring the temperature of the gases upstream of the particulate filter and for comparing it with a temperature threshold in order to trigger the second strategy in case of overshoot and thus make it possible to maintain the temperature of the gases in an optimum regeneration window.

As indicated above, the transition to a rich operating mode therefore makes it possible to heat the exhaust gases further, which accelerates the regeneration speed of the particulate filter.

In the case of a particulate filter using a regeneration aid additive, the increase in the thermal levels makes it possible to reduce the dosage of additive and thus to increase the distance traveled by the vehicle before cleaning the filter.

It is known that such an additive can be mixed with the engine fuel supply to be deposited on the particulate filter with the particles to which it is mixed, in order to lower the combustion temperature of the soot trapped therein. .

In a conventional manner this additive is indeed present in the particles after combustion of the fuel additive in the engine.

Of course other embodiments can be envisaged. For example, the depollution means may comprise a particulate filter, catalyzed or not, a NOx trap, etc.

These depollution means may also be impregnated with a SCR formulation providing a CO / HC oxidation function in a conventional manner.

Moreover, the depollution means and the oxidation catalyst means may be integrated into one and the same element, in particular on the same substrate.

By way of example, a particulate filter incorporating the oxidation function can be envisaged.

Similarly a NOx trap integrating such an oxidation function can also be considered, whether it is additive or not.

This oxidation function and / or NOx trap can be filled for example by an additive mixed with the fuel. Finally, it should also be noted that the engine may or may not be associated with a turbocharger.

Claims

1. System for assisting the regeneration of depollution means (1) associated with oxidation catalyst means implementing an OSC function and integrated in an exhaust line (2) of a diesel engine (3) of a motor vehicle, in which the engine (3) is associated with means (4) with a common cylinder fuel supplying system thereof, characterized in that it comprises means for monitoring (5) means pollution control device (1) for controlling the engine control means (4, 5, 6) according to operating sequences alternating between rich and lean-mixture operating phases according to a first strategy (FIG. this type or a second strategy (FIG 3) of sequences of this type separated by a lean operation phase.

2. System for assisting the regeneration of depollution means according to claim 1, characterized in that the number of sequences and the duration of each phase during a sequence are calibrated.

3. System for assisting the regeneration of depollution means according to claim 1 or 2, characterized in that the monitoring means (5) comprise means for monitoring the state of charge of the depollution means (1) for engage the first strategy if predetermined threshold values of overloaded and clogged charge states of the depollution means are exceeded.

4. System for assisting the regeneration of depollution means according to claim 1 or 2, characterized in that the monitoring means (5) comprise means for monitoring the number of successive incomplete regenerations of the pollution control means (1) for activate the first strategy if a predetermined number is exceeded.

5. System for assisting the regeneration of depollution means according to claim 1 or 2, characterized in that the monitoring means (5) comprise means for monitoring the frequency of the last regenerations of the depollution means (1) for in the case where this frequency crosses a predetermined threshold, engage the first strategy.

6. System for assisting the regeneration of pollution control means according to claim 5, characterized in that the frequency of the last regenerations is calculated over the last five regenerations of the filter.

7. System for assisting the regeneration of depollution means according to claim 1 or 2, characterized in that the monitoring means (5) comprise means for measuring the temperature of the gases upstream of the depollution means (1). and comparing it to a temperature threshold to engage the second strategy in case of overshoot and thus to maintain the temperature of the gases in an optimum window of regeneration.

8. System for assisting the regeneration of pollution control means according to any one of the preceding claims, characterized in that the pollution control means (1) comprise a particulate filter.

9. System for assisting the regeneration of pollution control means according to claim 8, characterized in that the particulate filter is catalyzed.

10. System for assisting the regeneration of pollution control means according to any one of the preceding claims, characterized in that the pollution control means (1) comprise a NOx trap.

11. System for assisting the regeneration of pollution control means according to any one of the preceding claims, characterized in that the fuel comprises an additive intended to be deposited with the particles to which it is mixed, on the means of depollution, for facilitate their regeneration.

12. System for assisting the regeneration of depollution means according to any one of the preceding claims, characterized in that the pollution control means (1) are impregnated with a SCR formulation ensuring a CO / HC oxidation function.

13. Evaluation system according to any one of claims 1 to 10, characterized in that the fuel comprises a NOx trap additive.

14. System for assisting the regeneration of pollution control means according to any one of the preceding claims, characterized in that the engine is associated with a turbocharger.