FR2981983A1 - Device for controlling pollution of exhaust gas to exhaust line of diesel engine of vehicle, has recirculation pipe extending from inlet to output upstream to pollution control unit for heating exhaust gas passing via pollution control unit - Google Patents

Abstract

The device (10) has a particle filter (20) connected to a heating device (18) to regenerate the particle filter. A control device (48) controls the heating device for heating exhaust gas. A recirculation pipe (40) extends from an inlet (42) to an output (44) that is connected to an exhaust line (14) upstream to a pollution control unit (16) for heating the exhaust gas passing through the pollution control unit. An oxidation catalyst type pollution control unit (22) is arranged on the exhaust line for reducing carbon monoxide and unburned hydrocarbons of the exhaust gas.

Description

The invention relates to an exhaust gas recirculation depollution device 5 for an internal combustion engine. Internal combustion engines produce and emit toxic pollutants in the exhaust gases, in particular nitrogen oxides or NOx and soot particles. The anti-pollution standards applicable to motor vehicles 10 impose on manufacturers maximum amounts of pollutants released into the atmosphere, which must be lower and lower. This is the reason why the exhaust line of an internal combustion engine is generally equipped with depollution means. The depollution means comprise in particular a particulate filter for removing soot particles, a first catalyst allowing a selective catalytic reduction, also known under the acronym SCR for "Selective Catalytic Reduction" in English terminology, for eliminating or reducing oxides of carbon dioxide. nitrogen, and a second catalyst called diesel oxidation catalyst, also known under the acronym DOC for "Diesel Oxidation Catalyst" in English terminology, for removing carbon monoxide (CO) and unburned hydrocarbons (HC). Advantageously, the exhaust line comprises a heating means, such as a burner, for strongly heating the exhaust gases flowing in the particulate filter at a temperature of the order of 600 ° C. The heating of the exhaust gas regenerates the particulate filter by burning the captured soot particles. A disadvantage of such an arrangement is the activation time required for the first SCR-type catalyst before it is fully effective and fulfills its depollution function. The activation time corresponds here to the time required for the exhaust gas to reach an activation temperature of the catalyst, this activation temperature of the first catalyst is around 150 ° C. Thus, when the engine is cold and has just been started, the activation time of the catalyst lasts several seconds.

The document US-2008/083215-A1 describes and represents a device for recycling the thermal energy of an exhaust line of an internal combustion engine. The exhaust line comprises from upstream to downstream in the flow direction of the exhaust gas, a turbocharger, a fuel injector for heating the exhaust gas flowing in an oxidation catalyst of the type DOC and a particle filter. The device particularly for the purpose of heating the exhaust gas upstream of the oxidation catalyst and the particulate filter. For this purpose, the exhaust line comprises an exhaust duct extending from the outlet of the particulate filter to the outside of the vehicle, and a section of which is equipped with a heat exchanger. The heat exchanger, which is traversed by the exhaust gases from the particulate filter, extends across the exhaust line between the turbocharger and the fuel injector, to heat the exhaust gases. upstream of the catalyst and promote the activation of the oxidation catalyst. This device has the disadvantage of partially obstructing the exhaust line through the heat exchanger and causing a pressure drop in the exhaust line. Similarly, the heat exchanger requires a certain latency time to increase in temperature and to transmit its thermal energy to the exhaust gas upstream of the catalyst and the particulate filter. The invention proposes to overcome these disadvantages and more particularly to reduce the activation time of the SCR type catalyst. For this purpose, the invention proposes an exhaust gas depollution device for an exhaust line of an internal combustion engine, the device comprising, from upstream to downstream in the direction of flow of the exhaust gases. exhaust: at least one first depollution means, an exhaust gas heating device, a particulate filter which is connected to the heating device for regenerating the particulate filter, at least one control means. which is intended at least to control the heating device for heating the exhaust gas, characterized in that the pollution control device comprises a recirculation duct which extends from an inlet connected to the heating device, to a outlet connected to the exhaust line upstream of the first depollution means for heating the exhaust gas entering the first depollution means. The present invention makes it possible to increase the temperature of the first depollution means rapidly, thanks to which the latter is effective almost from the start of the engine. According to other features of the invention, the depollution device comprises a recirculation valve which is interposed between the heating device and the inlet of the recirculation duct and which is controlled by the control means, to derive all or part of exhaust gases heated by the heating device upstream of the first decontamination means, via the recirculation duct.

This characteristic makes it possible to control all or part of the recirculation of the exhaust gases through the recirculation duct. According to a first embodiment, the depollution device comprises a temperature sensor which is arranged between a second depollution means and the outlet of the recirculation duct, and which cooperates with the control means so as to control the opening and closing the recirculation valve at least according to a temperature setpoint. The temperature sensor thus arranged makes it possible to evaluate the temperature of the exhaust gases flowing in the first depollution means, for example by means of a cartography. According to a second embodiment, the depollution device comprises a temperature sensor which is arranged between the outlet of the recirculation duct and the inlet of the first depollution means, and which cooperates with the control means so as to control the opening and closing of the recirculation valve at least according to a temperature setpoint. Thus arranged, the temperature sensor makes it possible to directly measure the temperature of the exhaust gases flowing in the first depollution means. Advantageously, the heating device is a burner which comprises at least one combustion chamber delimiting an air inlet orifice and a fuel supply orifice, said burner being equipped with a spark plug intended to ignite the air-fuel mixture injected into the combustion chamber to heat the exhaust gas passing through the burner. The burner makes it possible to raise the temperature of the exhaust gases rapidly. The first means of decontamination is a catalyst which is equipped with a reducing agent injector and which is designed for the reduction of nitrogen oxides. Also, the depollution device comprises a second means of decontamination of the oxidation catalyst type which is arranged on the exhaust line upstream of said first depollution means and upstream of the outlet of the recirculation duct, and which is designed to reduce at least carbon monoxide and unburnt hydrocarbons from the exhaust gases. The heating device is able to be controlled by the control means as soon as the vehicle electrical system is switched on, before the engine is switched on, to heat the exhaust gases entering the first depollution means via the recirculation duct. This characteristic has the advantage of allowing a very rapid rise in temperature of the exhaust gas, whereby the first 20 depollution means is effective from the first seconds of operation of the engine. The recirculation duct is equipped with a thermal protection means. This thermal protection means makes it possible to limit the heat losses by dissipation. Finally, the control means is an electronic control unit. Other features and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: FIG. 1 is a schematic view which illustrates a first embodiment of the depollution device according to the invention, in which a temperature probe is arranged upstream of the outlet of the recirculation duct; FIG. 2 is a schematic view similar to FIG. 1, which illustrates a second embodiment of the depollution device according to the invention, in which a temperature probe is arranged between the first depollution means and the outlet of the duct; recirculation. In the description and the claims, the terms "upstream" and "downstream", which are determined by the direction of flow of the exhaust gases in the exhaust line of the depollution device, will be used by way of nonlimiting reference. FIG. 1 shows a first embodiment of the exhaust gas depollution device 10 for an exhaust line 14 of an internal combustion engine 12, according to the invention. The depollution device 10 comprises, from upstream to downstream in the direction of flow of the exhaust gas, an upstream catalyst 22 of the "DOC" type constituting a second depollution means, a downstream catalyst 16 of the type known as " SCR "constituting a first depollution means, an exhaust gas heater 18 and a particulate filter 20. The upstream catalyst 22 is here an oxidation catalyst for a diesel engine, also known under the acronym DOC for" Diesel Oxidation Catalyst "in English terminology, which is designed to remove carbon monoxide and unburned hydrocarbons. For this purpose, the upstream catalyst 22 has an inlet which is connected to the engine 12 via a conduit 24, to treat the exhaust gas flowing from the engine 24. The downstream catalyst 16 is a so-called catalyst Selective catalytic reduction system, also known under the acronym SCR for "Selective Catalytic Reduction" in English terminology, which is designed to remove nitrogen oxides. As shown in FIG. 1, the upstream catalyst 22 and the downstream catalyst 16 are connected to one another via a conduit 26. The conduit 26 is equipped with a gearbox injector 28 which makes it possible to inject a reducing gear, here from the ammonia, in the downstream catalyst 16 via the conduit 26, to allow the reduction of nitrogen oxides in the exhaust gas. The downstream catalyst 16 is connected by its output to the heating device 18 via a conduit 30, to allow the flow of the exhaust gas through the heating device 18. By heating device is meant any device capable of generating heat energy for heating the exhaust gas, such as a heating resistor for example.

However, according to the embodiment described here, the heating device 18 is a burner 18 which comprises at least one combustion chamber 32 defining an air inlet port 34 and a fuel supply port 36.

The burner 18 is equipped with a spark plug 38 intended to ignite the air-fuel mixture injected into the combustion chamber 32 to heat the exhaust gases which pass through the burner 18. The thermal energy supplied by the burner 18 allows in particular to regenerate the particulate filter 20 by burning the soot residues captured by the particulate filter 20. Advantageously, the burner 18 is here connected directly to the inlet of the particulate filter 20, thus limiting the energy losses. heat dissipation. The depollution device 10 comprises a recirculation duct 40 which extends from an inlet 42 connected to the burner 18, to an outlet 44 connected to the exhaust line 14, upstream of the downstream catalyst 16, for heating the exhaust gas entering the downstream catalyst 16. Advantageously, the recirculation duct 40 is equipped with a thermal protection means (not shown) to limit heat loss by heat dissipation. The outlet 44 of the recirculation duct 40 is stitched on the duct 26 which connects the upstream catalyst 22 and the downstream catalyst 16 between them, so that the exhaust gases are able to flow directly from the burner 18, until at the inlet of the downstream catalyst 16. The depollution device 10 comprises a recirculation valve 46 which is interposed between the burner 18 and the inlet 42 of the recirculation duct 40, to divert all or part of the heated exhaust gas. by the burner 18 upstream of the downstream catalyst 16, via the recirculation duct 40. For this purpose, the recirculation valve 46 is movably mounted between a rest position, in which the exhaust gas flows from the burner 18, up to the particulate filter 20, and a recirculation position, in which the exhaust gas flows from the burner 18 to the downstream catalyst 16 via the recirculation duct 40.

Similarly, the recirculation valve 46 can adopt an infinity of position between its rest position and its recirculation position, in each of which the exhaust gas flows from the burner 18, both to the particulate filter. 20 and the recirculation duct 40.

According to a first exemplary embodiment shown in FIG. 1, the control of the recirculation valve 46 is controlled by a control circuit 48, which is here a first electronic control unit 48, which also controls the burner 18. In addition, the depollution device 10 comprises a temperature probe 52 which is arranged between the upstream catalyst 22 and the downstream catalyst 16, upstream of the inlet 44 of the recirculation duct 40. The temperature probe 52 is connected to a second unit control electronics 50 which is here a unit that performs other control or calculation functions in the vehicle. Non-limitingly, the temperature sensor 52 may be directly connected to the first electronic control unit 48. Likewise, the temperature sensor 52 is a sensor whose measurements are used for other purposes by the electronic unit. 50. The temperature sensor 52 makes it possible to record an exhaust temperature T1 in the exhaust line 14. The downstream catalyst 16 must reach an activation temperature sufficient to effectively reduce the nitrogen oxides, this temperature activation is of the order of at least 150 ° C for example. Firstly, the second electronic control unit 50 compares the exhaust temperature T1 to a target temperature T2 which is equal to the activation temperature of the downstream catalyst 16. If the exhaust temperature T1 is lower than the set temperature T2, the second electronic control unit 50 transmits a command to the first electronic control unit 48 to activate the burner 18 during an activation period D1. The activation time D1 is calculated by the second electronic control unit 50 according to an operation map of the burner 18 so that the downstream catalyst 16 reaches at least its activation temperature.

In addition, the first electronic control unit 48 controls the driving of the recirculation valve 46 in its recirculation position, so that the heated exhaust gases flow from the burner 18 to the downstream catalyst 16, via the recirculation duct 40.

In a second step, at the end of the activation period D1, the first electronic control unit 48 controls the driving of the recirculation valve 46 in its rest position, and controls the stopping of the burner 18, so the exhaust gases flow from the burner 18 to the particulate filter 20.

According to a second embodiment shown in FIG. 2, the depollution device 10 comprises only one electronic control unit 48 which controls the control of the recirculation valve 46 and the burner 18. The depollution device comprises a probe temperature 56 which is arranged between the downstream catalyst 16 and the inlet 44 of the recirculation duct 40, and which cooperates with the electronic control unit 48. The temperature sensor 56 makes it possible to measure the exhaust temperature T3 of the Exhaust gas directly to the inlet of the downstream catalyst 16. At first, the electronic control unit 48 compares the exhaust temperature T3 to a setpoint temperature T2 which is equal to the activation temperature of the engine. Downstream catalyst 16. If the exhaust temperature T3 is lower than the set temperature T2, the electronic control unit 48 transmits an order to activate the burner 18 that the exhaust temperature T3 is equal to the set temperature T2. In addition, the first electronic control unit 48 controls the driving of the recirculation valve 46 into its recirculation position, so that the heated exhaust gases flow from the burner 18 to the downstream catalyst 16 via the recirculation duct 40. In a second step, when the exhaust temperature T3 is equal to the set temperature T2, the first electronic control unit 48 controls the driving of the recirculation valve 46 in its position of rest, and controls the stopping of the burner 18, so that the exhaust gas flows from the burner 18 to the particle filter 20.

According to an alternative embodiment of the invention not shown, which applies both to the first embodiment and to the second embodiment, the heating of the exhaust gases by the burner 18 begins at the start of the system. by the user, before the ignition of the engine 12. According to this variant, if the exhaust temperature T3, or T1, is lower than the set temperature T2, the electronic control unit 48 transmits an order for activate the burner 18 until the exhaust temperature T3, or T1, is equal to the set temperature T2. In addition, the first electronic control unit 48 controls the drive of the recirculation valve 46 in its recirculation position, so that the air injected into the burner 18 through its inlet 34 flows from the burner 18, to the downstream catalyst 16, via the recirculation duct 40. In a second step, when the exhaust temperature T3, or T1, is equal to the setpoint temperature T2, the first electronic control unit 48 controls the temperature. driving the recirculation valve 46 to its rest position, and controls stopping the burner 18.

Still according to this variant embodiment, the burner 18 cooperates with an additional blowing means (not shown) which is designed to generate a current of air and to promote the flow of heated air from the burner 18 to the catalyst 16. The depollution device 10 according to the invention allows the downstream catalyst 16 of the SCR type to reach its activation temperature quickly and thus to be effective rapidly, in particular after the engine 12 has been started. the burner 18 fulfills two functions, a first regeneration function of the particle filter 20 and a second fast activation function of the SCR type downstream catalyst 16. Non-limitingly, the burner 18 is able to be activated at any time to fulfill its function of regenerator of the particulate filter 20.

Claims (10)

REVENDICATIONS1. Exhaust gas cleaning device (10) for an exhaust line (14) of an internal combustion engine (12), the device (10) comprising, from upstream to downstream in the direction of flow exhaust gases: - at least a first depollution means (16), - an exhaust gas heating device (18), - a particulate filter (20) which is connected to the heating device (18). for regenerating the particulate filter (20), at least one control means (48) for at least controlling the heating device (18) for heating the exhaust gas, characterized in that the process (10) comprises a recirculation conduit (40) extending from an inlet (42) connected to the heater (18) to an outlet (44) connected to the exhaust line (14). ) upstream of the first depollution means (16), for heating the exhaust gas entering the first means of d pollution (16). 2. A depollution device (10) according to claim 1, characterized in that it comprises a recirculation valve (46) which is interposed between the heating device (18) and the inlet of the recirculation duct (40). and which is controlled by the control means (48) to divert all or part of the exhaust gas heated by the heater (18) to the upstream of the first depollution means (16) via the recirculation duct (40). 25 3. A pollution control device (10) according to any one of the preceding claims, characterized in that it comprises a temperature sensor (52) which is arranged between a second depollution means (22) upstream of the outlet (44). ) and the outlet (44) of the recirculation duct (40), and which cooperates with the control means (48) so as to control the opening and closing of the recirculation valve (46) at least as a function of a temperature setpoint. 4. A depollution device (10) according to any one of claims 1 or 2, characterized in that it comprises a temperature sensor (56) which is arranged between the outlet (44) of the recirculation duct 35 (40) and the inlet of the first depollution means (16), and which cooperates with the control means (48) so as to control the opening and closing of the recirculation valve (46) at least according to a set point of temperature. 5. A depollution device (10) according to any one of the preceding claims, characterized in that the heating device (18) is a burner (18) which comprises at least one combustion chamber (32) defining an orifice of an air inlet (34) and a fuel supply port (36), said burner (18) being equipped with a spark plug (38) for igniting the air-fuel mixture injected into the combustion chamber (32) for heating the exhaust gases passing through the burner (18). 6. depollution device (10) according to any one of the preceding claims, characterized in that the first depollution means (16) is a catalyst which is equipped with an injector (28) of a reducing agent and which is designed for the reduction of nitrogen oxides. 7. A depollution device (10) according to any one of the preceding claims, characterized in that it comprises a second means of pollution control (22) of the oxidation catalyst type which is arranged on the exhaust line (14). upstream of said first depollution means (16) and upstream of the outlet (44) of the recirculation conduit (40), and which is adapted to reduce at least carbon monoxide and unburnt hydrocarbons from the exhaust gas. 8. A depollution device (10) according to any one of the preceding claims, characterized in that the heating device (18) is adapted to be controlled by the control means (48) from the start of the electrical system of the vehicle, before the ignition of the engine (12), to heat the exhaust gas entering the first depollution means (16) via the recirculation duct (40). 9. A pollution control device (10) according to any one of the preceding claims, characterized in that the recirculation duct (40) is equipped with a thermal protection means. 10. Pollution control device (10) according to any one of the preceding claims, characterized in that the control means (48) is an electronic control unit (48).