FR2846370A1 - ASSISTANCE SYSTEM FOR THE REGENERATION OF A STORED / DETOCKED NOX TRAP FOR A DIESEL ENGINE - Google Patents

Abstract

This system for assisting the regeneration of a storage / retrieval NOx trap, integrated in an exhaust line (5) of a diesel engine (4) of a motor vehicle, is characterized in that it comprises means for admitting gas into the engine and means for injecting fuel (11) into the cylinders thereof in the form of at least pilot and main injections and means for controlling (12) these means of '' gas intake and / or fuel injection (11) to periodically switch the engine (4) from a standard lean-burn mode of operation, of NOx storage in the trap (6), to an operating mode for regeneration with a rich mixture, for a pilot injection and at least two main injections, for removing the NOx from the trap (6) and for regenerating the latter.

Description

I The present invention relates to an emission reduction system

  pollutants linked to the operation of a diesel engine of a motor vehicle and relates more particularly to a system for assisting the regeneration of a Nox trap for storage / release, integrated in an exhaust line of such an engine.

  It is known that on direct injection diesel engines for motor vehicles, the reduction of NOx emissions by DeNOx catalysis with storage / destocking is a technical solution envisaged to meet the standards relating to this type of discharge and in particular to the EURO IV standards.

  To this end, it is envisaged to use a NOx trap composed for example of barium sulphate intended to absorb NOx during operation

engine standard.

  When this trap is saturated, it is proposed to trigger a transient destocking phase by temporarily switching the engine from this standard lean mixture operating mode to a rich mixture regeneration operating mode to produce reducers, such as, for example, HC and CO, which reduces the NOx which is then desorbed from the trap,

  as in a traditional catalyst.

  However, this poses problems in controlling the operation of the engine under rich mixture, in a stable manner over the whole of its operating field, without impact on the driveability of the vehicle and the

combustion noise, etc.

  The object of the invention is therefore to solve these problems.

  To this end, the subject of the invention is a system for assisting the regeneration of a storage / destocking NOx trap, integrated into an exhaust line of a diesel engine of a motor vehicle, characterized in that '' it comprises means for admitting gas into the engine and means for injecting fuel into the cylinders thereof in the form of at least pilot and main injections and means for controlling these means of admission gas and / or fuel injection to periodically switch the engine from a standard lean mixture operating mode, NOx storage in the trap, to a rich mixture regeneration operating mode, to pilot injection and at least two main injections, to destock NOx from the trap

and regeneration thereof.

  According to other characteristics: - the control means are adapted to control the gas intake means in order to reduce the quantity of gas admitted into the engine when the latter is in its regeneration operating mode; - The control means are adapted to control the gas intake and / or fuel injection means according to these standard operating and regeneration modes for engine loads greater than a predetermined threshold value; - the predetermined load threshold value is defined by an effective average pressure of approximately 3 bars; - the pilot injection is triggered in a range between around 500 crankshaft and 50 crankshaft, before the top dead center of the cylinder concerned and in that the main injections are triggered in a range between around 200 crankshaft before the top point and 1200 crankshaft after top dead center; - The control means are adapted to control the gas intake and / or fuel injection means in order to operate the engine in lean mixture for approximately 60 seconds and in rich mixture for approximately 2 seconds; the engine being associated with means for recirculating the exhaust gases at the inlet thereof, the control means are adapted

  to regulate the operation of these recirculation means during operation of the rich mixture engine.

  The invention will be better understood on reading the description which will

  follow, given only by way of example and made with reference to the appended drawings 25, in which: FIGS. 1 and 2 illustrate the phases of storage and destocking of NOx in a trap forming part of the constitution of a system according to the invention; - Fig.3 illustrates the operation of fuel injection means used in an assistance system according to the invention; and - Fig.4 shows a block diagram illustrating the structure of a

system according to the invention.

  As indicated above, the invention relates to a

  aid system for the regeneration of a NOx trap for storage / destocking integrated into an exhaust line of a diesel engine of a motor vehicle.

  These storage and destocking phases are illustrated in Figures 1 and 2.

  As also indicated, the NOx trap absorbs the

  NOx during standard operation of the lean mixture engine, while in a rich mixture regeneration operating mode, these NOx are destocked and treated by the production of reducers such as HC and CO, which makes it possible to reduce the NOx which are then desorbed from the trap as in a traditional catalyst.

  However, and as indicated above, the problem arises of operating a diesel engine at such richness, in a stable manner over the whole of the engine field, without impact on the driving pleasure.

  and combustion noise among others.

  The operation of passage into a stoichiometric or rich mixture is necessary to purge the NOx trap but also to desulfate it, because the sulfur

  1 5 contained in the fuel causes poisoning of the trap.

  This operation is longer than the purge, which takes only a few seconds, and is therefore even more difficult to manage.

  Under these conditions, the aid for the regeneration of such a NOx trap to

  storage / destocking requires the development of a specific multiple injection strategy throughout the engine field, based on several engine adjustment parameters.

  In fact, this injection strategy must make it possible to: - operate at a richness close to I - produce a sufficient quantity of CO, which is the preferred reducing agent; 25 - limit the level of 02; - limit the level of HC; - respect the smoke level; - respect the exhaust gas temperature for reasons of mechanical strength; and finally - respect the services provided to customers, namely the approval of

  driving and engine noise.

  To this end, the present invention proposes to improve the characteristics of combustion in terms of stability and noise, on points with predetermined loads.

  mined from the engine, applying an injection strategy to a pilot injection and

  at least two main injections, as illustrated in Figure 3.

  The application of these two main injections also makes it possible to maintain the temperature of the exhaust gases within limits acceptable by the architecture of the engine (cylinder head, valves, manifold, etc.).

  Furthermore, a recirculation of the burnt gases (EGR) may then be necessary or not to comply with the criteria for regenerating the NOx trap.

  On points with predetermined loads, such as for example for an effective average pressure (PME) also known in the state of the art under the English name "Brake mean effective pressure", greater than about 3 bars, the two-way strategy main injections therefore makes it possible to meet the criteria for regenerating the NOx trap, because it makes it possible to significantly reduce the combustion instabilities thanks to the phasing of the two main injections, to reduce the noise also thanks to this phasing of the two injections, to maintain the exhaust gas temperature to allowable values and finally generate an engine map for regenerating the trap

  at NOx based on a unique strategy.

  As noted earlier, this strategy can be

  applied to the points at predetermined engine operating loads, the EGR level then being appropriately controlled.

  This is illustrated in FIG. 3, where we recognize the pilot injection designated by the reference 1 and the two main injections designated by the general references 2 and 3.

  This pilot injection can be triggered in a range between approx. 25 ron 500 crankshaft and 50 crankshaft before the top dead center of the cylinder concerned, and the main injections can be triggered in a range between

  around 200 crankshaft before top dead center and 1200 after top dead center.

  We recognize in FIG. 4, a diesel engine of a motor vehicle

  designated by the general reference 4, the outlet of which is connected to an exhaust line 5 in which a NOx trap 6 is integrated.

  This engine is also associated with air intake means designated by the general reference 7 comprising means 8 for adjusting the

amount of air admitted.

  This engine can also be associated with means for recirculating exhaust gas at the inlet thereof, designated by the general reference 9, associated with means for controlling the circulation of gases designated by the

general reference 10.

  These recirculation means are therefore connected between the outlet and

  the engine inlet to ensure exhaust gas recirculation (EGR).

  The adjustment means 8 and control means 10 can conventionally comprise controllable valves.

  Furthermore, the engine is also associated with means 11 10 for injecting fuel into the cylinders thereof, in the form of injections.

  pilot and main, as noted, having any suitable structure.

  These various means, that is to say the gas recirculation means, the air intake means and the injection means are controlled by control means designated by the general reference 12, comprising all

  appropriate computer, receiving for example as input, engine rotation speed and pressure of the injection means, respectively of data acquisition means 13 and 14 corresponding.

  The standard operating modes with lean mixture of storing 20 NOx in the trap, and of operating with regeneration with rich mixture, of destocking of NOx from the trap and therefore of regeneration of the latter, can be switched periodically, by the means of control 12, the motor 4 operating for example in lean mixture for approximately 60 seconds, and in rich mixture for approximately 2 seconds. The control means 12 then act on the air intake means 7 in the engine 4 and the fuel injection means 11 in the cylinders thereof, for periodically switching the engine from the standard operating mode to poor mixture with

  rich mix regeneration operating mode.

  These control means 12 can in fact be adapted to pilot the gas intake means in order to reduce the quantity of gas admitted into the engine when the latter is in its regeneration operating mode.

  and to control the injection means in the manner indicated above.

  These control means can also be adapted to regulate the operation of the exhaust gas recirculation means 9

  during operation of the rich mixture engine.

  Of course, other embodiments can be envisaged.

Claims (7)

  1. System for assisting the regeneration of a NOx trap for storage / destocking, integrated in an exhaust line (5) of a diesel engine (4) of a motor vehicle, characterized in that it comprises means 5 for admitting gas into the engine and means for injecting fuel (11) into the cylinders thereof in the form of at least pilot and main injections and means for controlling (12) these means gas inlet and / or fuel injection (11) for periodically switching the engine (4) from a standard operating mode with lean mixture, storage of NOx in the trap, to an operating mode of rich mix regeneration, one pilot injection (1) and at least two main injections (2,3), destocking   NOx from the trap (6) and regeneration thereof.   2. System according to claim 1, characterized in that the control means (12) are adapted to control the gas intake means in order to reduce the quantity of gas admitted into the engine (4) when the latter is in   its mode of regeneration operation.   3. System according to claim 1 or 2, characterized in that the control means (12) are adapted to control the gas inlet and / or fuel injection means (11) according to these operating modes stan20 dard and regeneration for engine loads greater than a value of predetermined threshold.   4. System according to claim 3, characterized in that the predetermined load threshold value is defined by an effective average pressure (PME) of around 3 bars.   5. System according to any one of the preceding claims,   characterized in that the pilot injection is triggered in a range between about 500 crankshaft and 5 crankshaft, before the top dead center of the cylinder concerned and in that the main injections are triggered in a range between about 20 crankshaft before the top dead center and 1200 crankshaft after top dead center 30.   6. System according to any one of the preceding claims,   characterized in that the control means (12) are adapted to control the gas intake and / or fuel injection means (11) in order to operate the engine (4) in lean mixture for approximately 60 seconds and in   rich mixture for about 2 seconds.   7. System according to any one of claims 3 to 6, characterized in that the engine (4) being associated with means for recirculating the exhaust gases (9) at the inlet thereof, the control means (12) are   adapted to control the operation of these recirculation means (9) during   a rich mixture engine operation.