FR2877039A1 - Regeneration of particle filter mounted in exhaust line of automobile engine comprises initiating process when level of contamination of filter exceeds predetermined value, with temperature of filter increased to burn off particles - Google Patents

Abstract

In the regeneration of a particle filter for an automobile, the process is initiated when the level of contamination of the filter exceeds a predetermined value, the temperature of the filter being increased to burn off the particles. Air is injected upstream of the filter.

Description

Method and system for regenerating a particulate filter

  The present invention relates generally to the regeneration of a particulate filter mounted on the exhaust line of an internal combustion engine of a motor vehicle.

  The heterogeneity of combustion processes in engines, especially in diesel engines, has the effect of generating polluting carbon particles which should be reduced in the atmosphere.

  The presence of a particulate filter in the exhaust line of the engine can significantly reduce the amount of particles, dust and other soot, emitted into the atmosphere, and meet pollution standards.

  Indeed, such a filter is designed to be able to retain the particles contained in the exhaust gas passing through the filter. However, as the engine is used, the particles accumulate in the filter and eventually result in significant backpressure to the engine exhaust, which significantly reduces its performance.

  Controlled regeneration devices make it possible to periodically burn the particles trapped in the filter and to avoid an excessive rise in the back pressure and clogging of the filter.

  This regeneration is carried out by raising the temperature within the particulate filter to a temperature of the order of 550 to 600 C, or 650 C, temperatures from which the carbon particles retained in the filter ignite instantly. To do this, it is generally carried out a delayed injection of fuel, or postinjection, in the combustion chambers of the engine. In particular, fuel can be injected after the top dead center during the expansion phase, which has the effect of increasing the temperature of the exhaust gas. It is also possible to provide one or more late injections, that is to say, clearly after the top dead center. The fuel thus injected does not burn in the combustion chamber of the engine, but, for example, in a catalytic device also provided in the exhaust line.

  When a delayed injection of fuel is applied after top dead center, during the expansion phase, increasing the flow rate of this injection requires a decrease in the flow rate of the main fuel injection. The lower efficiency of this delayed injection requires a higher total fuel flow to maintain the torque at a level identical to that obtained with a lower delayed injection rate. This causes an increase in the engine output temperature. When late injections are expected, high HC and CO emissions are generated at the engine output. These reducers react in the oxidation catalyst mounted on the exhaust line with the oxygen present in the exhaust gas. This reaction produces heat which contributes to increasing the temperature of the exhaust gas at the inlet of the particulate filter.

  It is also possible to delay the main fuel injection. The degradation of the combustion efficiency related to this injection requires an increase in the flow rate of the main injection to maintain the torque at a level identical to that obtained with an undelayed injection, which generates a higher output temperature of the engine.

  It is finally possible to increase the richness of the mixture. Indeed, the temperature of the exhaust gas increases with the richness since the charge in fresh air decreases.

  As is conceivable, regeneration techniques known to date have a number of disadvantages.

  Indeed, they cause a dilution of diesel in the lubricating oil of the engine. The result is a degradation of its physico-chemical properties that can lead to premature wear of the engine.

  The delayed injection or late injection, that is to say clearly after the top dead center, causes an increase in the temperature upstream of the engine turbocharger air, which is likely to cause a mechanical fatigue of the turbine. In addition, a very late injection causes an increase in the temperature of the oxidation catalyst, which is likely to cause wear of the oxidation function of the catalyst.

  Finally, the increase in the richness of the mixture, which requires the use of a valve to regulate the flow of fresh air at the intake, the delay of the main injection, and the increase of the post-injection flows cause a decrease in the oxygen content in the exhaust gas upstream of the particulate filter. In low and partial charge, the oxygen level may then be too low to regenerate properly.

  The object of the invention is therefore to overcome the drawbacks of the prior art and to propose a regeneration of a motor vehicle particle filter in order to reduce the duration of the regeneration or, where appropriate, to allow it when the composition of the exhaust gas does not make it possible to implement it.

  The subject of the invention is therefore a regeneration method of a motor vehicle particle filter, according to which filter regeneration means are used as soon as the value of the filter loading level exceeds a predetermined threshold value of in such a way as to cause a temperature rise capable of burning the particles in the filter, characterized in that an air injection is effected upstream of the particulate filter.

  In one embodiment, an air pump connected to the inlet of the particulate filter is used.

  According to another embodiment, the air is taken from a line supplying the engine of the motor vehicle with air. In this case, preferably, hot air is taken.

  For example, this hot air can be taken downstream of a supercharger engine air.

  The invention also relates to a regeneration system of a motor vehicle particle filter, comprising means for regenerating the filter comprising means for raising the temperature of the filter so as to burn the particles in the filter, characterized in that it comprises injection means for injecting air upstream of the filter.

  According to another characteristic of the invention, the system comprises an air pump.

  The pump can be associated with a non-return valve.

  In another embodiment, the injection means comprise a bypass of a supply line of the engine of the air vehicle which extends from said pipe to the exhaust line of the engine.

  In this case, the pipe is connected, for example, to the supply line downstream of a supercharger engine air, to collect hot air, which limits the cooling of the exhaust gas when the air is injected.

  The line can be equipped with a control valve to adjust the amount of air injected into the exhaust line.

  Other objects, features and advantages of the invention will become apparent on reading the following description, given solely by way of nonlimiting example and with reference to the appended drawings in which: FIG. 1 is a diagrammatic representation of a internal combustion engine for the propulsion of a motor vehicle equipped with a regeneration system of a particle filter according to the invention; FIG. 2 illustrates the variation of the regeneration time as a function of the temperature and the oxygen level at the inlet of the filter; and FIG. 3 is a diagram illustrating another embodiment of a regeneration system according to the invention.

  FIG. 1 shows a block diagram illustrating the general structure of an internal combustion engine of a motor vehicle, its means for supplying air and exhausting the combustion gases, as well as its control means.

  In this figure, the general numerical reference 1 designates very schematically the engine, which comprises a plurality of combustion chambers, such as 2, in the upper part of a cylinder 3 inside which a piston 4 moves. An intake valve 5 makes it possible to control the intake by opening or closing an intake duct 6 in communication with the combustion chamber 2. An exhaust valve 7 makes it possible, for its part, to close off or to open the exhaust passage from the combustion chamber 2 in the exhaust duct 8.

  Fresh air at atmospheric pressure, whose flow is symbolized by the arrow 9, enters a pipe 10 inside which is mounted a flowmeter 11 which measures the flow of air in the pipe 10. The air pressure is increased by a compressor 12 mounted in the pipe 10. The compressor is mounted on a shaft 13 common to a turbine 14, here variable geometry, mounted in the exhaust pipe 8. The exhaust gas passing through the turbine 14 and drive the compressor 12, so as to increase the pressure of the air admitted into the combustion chamber 2 through the intake duct 6.

  In the illustrated example, the engine further comprises an exhaust gas recirculation system (EGR). For this purpose, a bypass line 15 is stitched on the exhaust pipe 8 upstream of the turbine 14. A control valve 16, called EGR valve, controls the amount of exhaust gas that can be reinjected into the duct 6, after having been suitably mixed in a mixing chamber 18. An adjustable orientation flap 19 is further mounted in the compressed air intake duct 10 downstream of the compressor 12 and upstream of the combustion chamber. mixture 18.

  As regards the exhaust line 20, it connects the outlet of the turbine 14 to the atmosphere, the outlet of the exhaust gas being referenced 21. In the exhaust line, is mounted a catalyst device 22 directly downstream of the turbine 14, and a particulate filter 23 downstream of the catalytic device 22. The particulate filter is of conventional type and comprises means, for example electrostatic, for trapping soot and particles from the engine and carried by the exhaust gases in the exhaust line 20.

  An electronic control unit 24 ensures the operation of the engine 1 and receives for this purpose a certain amount of information on the operation of the engine. Various sensors are placed in the conduits and their signals are supplied to the electronic control unit 24.

  Thus, for example, a pressure sensor 25, connected to the central unit 24, can be provided upstream of the flap 19 and downstream of the turbine 14. A temperature sensor 27 can also be provided for measuring the temperature upstream. of the turbine 14.

  A sensor 28 for measuring the temperature in line 10 can also be used to provide the central unit 24 with a measurement of the temperature of fresh air admitted into the engine, and sensors 29 and 30 can be placed on each side. other of the filter 23 to measure the temperature on either side of the particulate filter and thus control the operation of the filter and, in particular, control the regeneration.

  Indeed, as is known per se, as soon as the quantity of soot particles in the filter 23 exceeds a predetermined threshold value, it is implemented a regeneration phase which consists of increasing the temperature in the filter up to about 600 C, to burn the particles. As is known, various conventional techniques can be used to implement this regeneration. For example, it is possible to post-inject fuel.

  As can be seen further in FIG. 1, in order to improve or facilitate the regeneration, the regeneration system is furthermore provided with an air pump 31 ensuring an injection of air into the exhaust gases. upstream of the particulate filter 23. This air pump is controlled by the central unit 24 so as to inject air during the regeneration regardless of the load conditions of the engine. A check valve 32 is mounted between the air pump and the exhaust line 20 to avoid sending hot gases into the pump when it is stopped.

  This injection of air into the exhaust gases has the effect of increasing the oxygen content and thus of reducing the duration of the regeneration or of allowing it in the case where the oxygen level is too low to allow the regeneration.

  As can be seen in FIG. 2, an increase in the oxygen content (% O 2) in the exhaust gases has the effect of considerably reducing the duration of the regeneration at constant particle filter temperature TEFAP. and this, in particular, when the temperature of the regeneration is close to about 600 C.

  According to another embodiment, represented in FIG. 3, the air injected into the particulate filter 23 during the regeneration is taken from the pipe 10, preferably downstream of the compressor 12, that is to say say where the air is hottest, which limits the cooling of the exhaust when the air is injected.

  It can be seen in FIG. 3 that, according to this embodiment, a bypass line 33 extends between the supply pipe 10 for supplying the engine with fresh air and the exhaust line, upstream of the filter 23. pipe 33 is equipped with an adjustment valve 34 controlled by the central unit 24, upstream of the filter 23. This pipe 33 is equipped with an adjustment valve 34 controlled by the central unit 24 to adjust the amount of air injected into the exhaust line.

  Note that this embodiment does not require an air pump of necessarily large dimensions to ensure a sufficient flow when the filter 23 is full, that is to say when the exhaust back pressure is important.

  In addition, when the filter 23 is partially loaded, the supercharging pressure of the engine air is greater than the counterpressure of the exhaust gas upstream of the filter 23. The air can then be easily injected into the exhaust line. This embodiment also makes it possible to take more energy from the turbine 14, which contributes to increasing the temperature of the exhaust gases without any harmful counterpart of the dilution type. Finally, note that the control of the control valve 34 may be proportional type to optimize the flow as a function of the operating conditions of the engine. It can also be all-or-nothing type control.

Claims (11)

  1. A method of regenerating a motor vehicle particle filter (23), according to which filter regeneration means are used as soon as the value of the filter loading level exceeds a predetermined threshold value so as to cause a temperature rise capable of burning the particles in the filter (23), characterized in that an air injection is applied upstream of the particulate filter.   2. Method according to claim 1, characterized in that it implements an air pump (31) connected to the input of the particulate filter (23).   3. Method according to claim 1, characterized in that the air is taken from a pipe (10) for supplying the engine of the motor vehicle with air.   4. Method according to claim 3, characterized in that the air taken is hot air.   5. Method according to claim 4, characterized in that the air is taken downstream of a compressor (12) supercharging the engine air.   6. Regeneration system for a particulate filter (23) of a motor vehicle, comprising means for raising the temperature in the particulate filter so as to burn the particles in the filter, characterized in that it comprises means ( 31, 33, 34) for injecting air upstream of the particle filter (23).   7. System according to claim 6, characterized in that it comprises an air pump (31).   8. System according to claim 7, characterized in that the pump (31) is associated with a valve (32) non-return.   9. System according to claim 6, characterized in that the injection means comprise a bypass (33) of a duct (10) for supplying the vehicle engine with air, which extends from said duct (10). at the exhaust line (20) of the engine.   10. System according to claim 9, characterized in that the bypass (33) is connected to the supply line (10) downstream of a compressor (12) supercharging the engine air.   11. System according to one of claims 9 and 10, characterized in that the bypass (33) is provided with a valve (34) for adjusting the amount of air injected into the exhaust line.